On members of the Gammarus pulex-group (Crustacea-

Amphipoda) from western Europe

by

Sjouk Pinkster

Institute of Taxonomic Zoology, University of Amsterdam, The Netherlands

Résumé kraba, 1958), or an independant species (Koch,

variabilité des Gammares du Wautier & Roux, La morphologique groupe 1835; Schellenberg 1934; 1959; pulex et la confusion concernant la position systématique Straskraba, 1962). The subsequent description of

des différentes formes de ce groupe, déjà démontrées par the same species, G. fossarum, under other names l’auteur en 1970, l’ont conduit à donner des descriptions (e.g. G. delebecquei Chevreux & de Guerne, 1892; de différentes formes du leur varia- groupe et à discuter G. rambouseki S. G. bilité. Des expériences d’hybridation ont été faites entre pulex Karaman, 1931; pulex

des populations morphologiquement différentes, étroite- danubialis S. Karaman, 1931) made the whole sit- ment liées ou bien intermédiaires entre G. pulex et of à, uation still more confusing. The introduction G. wautieri provenant de différentes localités d’Europe the generic name Rivulogammarus by Karaman, occidentale. Les résultats de ces expériences clarifient la 1931 and the description of supposed intermediate position systématique de ces populations. Les données forms between Gammarus and G. disponibles concernant l’écologie et la distribution des pulex fossarum

sont fournies. différentes espèces (e.g. Dusaugey, 1955) contributed to the confu-

sion.

Abstract Roux, 1967 aided to clear the situation to some

The morphological diversity within the Gammarus pulex- extent in proving that the so-called intermediate

the confusion the group and concerning systematic po- forms between G. pulex and G. fossarum of Du- sition of the various forms belonging to this al- group, between saugey, 1955, were certainly no hybrids ready noticed by the author in 1970, formed the reason these two species but members of a good species, to give detailed descriptions of the different forms in

this and discuss the within these that could be both on mor- group to variability clearly distinguished

forms. have been between Hybridization experiments run phological and on physiological and ecological various morphologically different populations, closely grounds. However, at the other hand, Roux did related to, or intermediate between G. pulex and G. of this not give a complete description new spe- wautieri from different localities in Western Europe. cies, which he called G. wautieri. The results of these experiments, have an implication to

the systematic position of these different populations. This situation instigated Stock, 1969 and Pink-

When information is the and available, given on ecology ster, 1970 to attack the problem at the bottom, distribution of the various species. the first by clearing the generic position of G.

pulex, the second by giving a redescription of the INTRODUCTION species and by stabilizing the nomenclature

Gammarus the species, belonging to pulex- group through indication of a neotype.

have been a source of confusion for quite a long At the same time systematic sampling was

time, both amongst taxonomists as physiologists. started in certain areas where members of this the The causes of this confusion can be found in species-group occur. During the sampling, it be-

of different very poor original descriptions the came clear that, apart from the classical species,

species within the group, as well as in differences G. pulex (Linne, 1758), G. fossarum Koch, 1835,

of opinion concerning the systematic position of G. wautieri A. L. Roux, 1967, and G. lacustris

certain forms. G. O. Sars, 1863, several populations could be

found, that showed distinct morphological de-

viations So, Gammarus fossarum Koch, 1835, was alter- from these typical forms.

At the there of nately considered a subspecies of Gammarus pulex one hand, was a group popu-

(Linne, 1758), (e.g. Schellenberg, 1937, 1942; lations, all very close to, but clearly distinguishable

Carausu, Dobreanu & Manolache, 1955; Stras- from G. fossarum, at the other hand there was a BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 165

Without these the work could cluster of populations all very close to, or inter- (Z.W.O.). grants, present have been done. mediate between, G. pulex and G. wautieri. It is never Special thanks are due to Mr. H. H. Mittelberg, of the worth noting that most of these aberrant forms I.T.Z., Amsterdam, for technical assistance during the found in rather are some few, restricted, areas, experiments.

viz. the French Alps (in the departements Isere, Prof. Dr. J. H. Stock has been of great help, because of his assistance both in the field and in the laboratory, Var and Alpes-Maritimes) and in the region and his critical remarks during the preparation of this around Montpellier (dept. Herault). The present for which manuscript, I am very grateful. series of author started a large hybridization ex-

to clear the of these periments, systematic position THE CHARACTERS OF THE GAMMARUS

different forms. In these experiments seven pop- PULEX-GROUP

ulations were used, showing morphological affin- Within the genus Gammarus, the Gammarus pulex- ity to G. pulex and G. wautieri. One of the pop- group is characterized by the following characters: ulations, a typical G. pulex, came from the Neth- (1) small, kidney-shaped or rounded (al- other eyes, erlands; the six, including a population of less twice the ways than as long as wide), upper typical G. wautieri, came from southern France. margin of which is widely separated from the In addition, other members of the research team mid-dorsal line; (2) hands of gnathopods almost of the Institute of Taxonomic Zoology (ITZ), Am- equal in size, though different in shape: the first sterdam, started other series of hybridization ex-

one is always pyriform, the second one has an periments (e.g. with populations morphologically almost transverse palm; (3) both gnathopods are close to G. fossarum, see Goedmakers, 1972). provided with a medial palmar spine in males; Where the results of these necessary experiments (4) P5 through P7 armed with spines only; (5) will be referred to. inner ramus of third uropod always at least half This article will be an attempt to bring more as long as the outer ramus; (6) first segment of clarity in the taxonomic status of the various exopod of third uropod armed with setae and "forms" within the Gammarus pulex-group and to spines along the outer margin. understand the importance of the certain slight Although some of these characters occur in morphological differences, which make this group other groups within the genus Gammarus as well, so difficult. Descriptions and illustrations are given this combination of features is quite characteris- of the western European species within the group. tic. So, the Gammarus balcanicus-group differs Variability will be discussed while figures are from the pulex-group in character (6) having the various given of those characters in which the pop- outer-margin of Ur 3 armed with spines only. ulations differ from each other. Where available, Gammarus roeseli Gervais could also be consid- the and information will be given on ecology ered as a member of the pulex-group, considering distribution of the various species. all the characters mentioned above, but never-

ACKNOWLEDGEMENTS theless it is left because of the charact- out, very

The author is indebted to Dr. Roy Olerod of the Natur- eristic teethlike projections on the metasome seg-

historiska Riksmuseum of Dr. J. Forest Stockholm; to ments.

of the Museum National d'Histoire Naturelle, Paris; to

Dr. K. Jazdzewski of the University of Lodz, Poland; VARIABILITY to Dr. A. Skalski of the University of Czestochowa, Po-

land; to Dr. W. Besch of the Landesstelle fur Gewasser- Within the Gammarus pulex-group, like in all other Dr. R. of the kunde, Karlsruhe, G.F.R.; to Margalef certain characters groups of gammarids, are very Instituto de Investigaciones Pesqueras, Barcelona, Spain; stable, while others can show an enormous and to for material. To many others, sending me prof.

Dr. A. L. Roux for his help in collecting the right variability. after material for the hybridization experiments and for his As far as we could ascertain, studying ma- advice and interest in the to the enthu- personal work; terial of the various species, the following char- siastic team of B.Sc. students, working for their degree stable: acters within this group are more or less at the I.T.Z. for collecting materials and assistance with 1) The of the (always less than twice the fieldwork, especially to Miss A. M. C. Goedmakers, shape eye

as Miss M. J. van Maren, Mr. R. Robelus and Mr. F. v. d. as long wide).

Beld for their in and the help catching transporting 2) The structure of the mandible palp (which al- animals for the hybridization experiments. of the ways has a regular row spines on ven- wish for the Furthermore, I to acknowledge grants tral margin of the third segment). fieldwork from the University of Amsterdam, and of the The setation of the of A2 Netherlands' Organisation for Pure Scientific Research 3) flagellum (although 166 S. PINKSTER - GAMMARUS PULEX-GROUP

in there be general stable, can exceptions, e.g. an effect that is intensified by the relative short

in G. fossarum). antennae. The colour of live specimens is rather

The hand of the from 4) shape of the gnathopods variable, greyish to red-brown or greenish,

(the first one is always pyriform, the second depending on the composition of the bottom and

one has an almost transverse in the in which found. The is always palm vegetation they are eye this group. Both gnathopods are provided rather small (fig. IB).

with a medial palmar spine in males). The first antenna is relatively short (fig. 1C),

5) The ratio between the endopod and the first about 1/3 of the total body length of the animal.

to 25 exopodal segment of the third uropod (al- The main and accessory flagellum have 18

and though this ratio changes during the develop- 3 to 4 segments, respectively.

it is The second is shorter ment, nevertheless stable, within a certain antenna (fig. ID) even

than range, and can often be used as a discriminat- the first. Its fourth and fifth peduncle seg-

ing character). ments are almost equal in length, both armed

of the basal with few tufts of in 3 lon- 6) The shape segment of legs 5 to 7 some setae, implanted

(although this character is age-dependant and gitudinal rows. The short (10- to 14-segmented)

the ratio increases with neither has flattened in length/width age, a flagellum segments as wide basal in segment never changes into a nar- G.p.pulex, nor setae implanted transverse rows.

row one). Calceoli are nearly always present in the 6 to 7

7) The type of armature of legs 5 through 7 proximal flagellar segments.

(usually consisting of spines only). The mandible palp (fig. IE) has an unarmed

first segment. The setae along the inferior margin Variable characters are: of the third segment are equal in length, The number forming 1) of the segments in the flagellum a regular comb. of both the first and second antenna. General- The first and second gnathopods (figs. IF, 1G) this number increases with but it also ly age, do not show important differences in comparison shows geographical and ecological variation. to those of Gammarus pulex. In both hands, a 2) The shape of the epimeral plates. strong medial palmar spine is present. 3) The density of the setation along the outer The setation of the third and fourth legs is margin of the exopod in uropod 3 and the less dense and slightly longer, than normally found number of plumose setae participating in it. in G. pulex (figs. 2A, 2B). 4) The armature and shape of the telson.

6, and 7 show no obvious differences number of and Legs 5, 5) The spines setae on the uro- from those in other within this species group some, and on the anterior legs. 2C, 2D, A (figs. 2E). similar pattern of variability can be found The the this inner ramus of third uropod attains throughout species group, and will not be almost of the of the first of discussed for 3/4 length segment every single species. Only if the var- the outer ramus. The second segment ofthe exopod iability pattern is different in one or more traits, is rather well developed. The setae along the in- this will be emphasized. ner and outer margins of both endo- and exopod DESCRIPTIVE PART are practically always plumose.

The descriptions are comparative in relation to the The urosome (fig. 1A) has no elevations or redescription by Pinkster (1970) of Gammarus excavations. The armature is usually very poor. pulex The (Linnaeus, 1758). telson lobes (fig. 2G) are scarcely armed.

Rarely a subbasal spine, often present in G. pulex, Gammarus lacustris G. O. Sars, 1863 can be found.

references. — Principal Schellenberg, 1942 : 32—33; Reid, The of 1944 18 structure the epimeral plates (fig. 1H) : —19; Fryer, 1953 : 155—156; Segerstrale. 1954 :

1 —91; Micherdzinski, 1959:571—573; Menon, 1969: is one of the discriminating characters of this spe-

14—32; Pljakic, 1963 15—22; : Bagge, 1964 : 292—294; cies. The posteroinferior corner of the first one 1969 0kland, : 11—152; Roux, 1972 : 287—296. is somewhat rounded, that of the second and

Material examined. — More than 80 samples from third are always sharply pointed. Although this Scandinavia, Poland, Russia, Scotland, Eire and Canada. character is variable in other species, and sharp

A the male large species: largest out of 30 samples epimeral plates can occur in some of them, they is about 20 mm. never show the constant, pointed corner encoun-

Adult male. — Habitus (fig. 1A) rather robust, tered in the present species. BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 167

Fig. 1. Gammarus lacustris G. O. Sars, 1863, ￿, from E, mandible palp (2); F, hand of first leg (2); G, hand

Loch Loyal (Sutherland), Scotland. A, habitus (scale 3); of second leg (2); H, epimeral plates (1). B, head (1); C, first antenna (1); D, second antenna (1); 168 S. PINKSTER - GAMMARUS PULEX-GROUP

Fig. 2. Gammarus lacustris G. O. Sars, 1863, ￿, from fourth leg (1); C, fifth leg (1); D, sixth leg (1); E, seventh

Loch Loyal (Sutherland), Scotland. A, third leg (1); B, leg (1); F, third uropod (2); G, telson (2). BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 169

Female. — Smaller than the male, most char- planted on these segments in three longitudinal

acters less pronounced, as in all other members rows. On segment 5 a maximum of five groups is of this Females still rather group. are readily recognisable, found. The flagellum is short, 10- to 13-

because of the sharp 2nd and 3rd epimeral plates. segmented. The segments are never swollen and

less compressed than in G. pulex. A transverse Ecology and distribution. — The species usually row of at most 5 setae is implanted on each inhabits mountain and glacier lakes, but in some flagellar segment, never forming a brush as in areas (e.g. Denmark, northern Germany and Po- G. pulex. Calceoli are nearly always present on land), it can also be found in lowland lakes and the 2nd to 8th segments. relic ponds as a of glacial periods. It has been The mandible palp (fig. 3B) does not show found in Finland, Norway, Sweden, Scotland, differences in to other striking comparison spe- Ireland, Denmark, Germany, northern Poland, cies in the group. Czechoslowakia, France, Switzerland, Italy, Aus- The first and second gnathopods are identical to tria, and the entire Balkan region, U.S.S.R. in- those in G. pulex. The third leg is armed with cluding Siberia, Turkey, Canada, and the north- many rather long setae, often curled in older males. of ern parts the U.S.A. (see Bagge, 1964; Fryer, The fourth the is leg on contrary sparingly armed 1953; Kaiser, 1958; Segerstrale, 1954, 1966; Mi- with rather short setae. cherdziriski, 1959; Hynes, 1955; Reid, 1940; Du- Legs 5, 6, and 7 are of the normal type within saugey, 1955; Pljakic, 1952, 1963; Ruffo, 1951; the Gammarus pulex-group (see figs. 2C, D, E). Menon, 1969; 0kland, 1969). Only occasionally The basal of the fifth segment leg always forms a (in Norway, 0kland, 1969; Eire and Poland, own backward protruding lobe. In the seventh leg, the exploration) the species has been found in riv- basal segment is always set with a small spine (fig. downstream of ers, a lake, but this can be due 3C). drift to passive (0kland, 1969). In such rare cases In general, the endopod of the third uropod is only, there is a narrow zone of overlap with G. little shorter than % of the total length of In other pulex. countries, e.g. France (Dusaugey, the exopod. Its setation is usually less dense than 1955), Italy (Ruffo, 1951) or Central Europe in G. pulex. Plumose setae are found on inner and (Pljakic, 1952), the species has never been found outer margins of both endo- and exopod (fig. 3D). together with other of the G. species pulex- group. The telson lobes (fig. 31) do not show striking It prefers stagnant waters with a relatively high differences from those in G. pulex, and have the of sediment amount organic (Fryer, 1953). It can same variable armature. survive at low temperatures for a long time, but The first has urosome segment no dorsal exca- is rather susceptible for temperatures higher than vation or elevation; the last two uro- 20°C. ("saddle")

some segments however, have a small dorsal

Gammarus wautieri A. L. Roux, 1967 hump. The dorsal armature has the normal mid-

— dorsal of elements and lateral References. Dusaugey, 1955 : 9—18; Roux, 1967 group a group at

1—172. either side.

Material examined. — More than 250 samples from The epimeral plates have variably shaped pos- the french Hautes departements Isere, Vaucluse, Drome, teroinferior these corners. Usually corners are Alpes, Basses Alpes and Jura. rounded in the first, almost rectangular in the

Male. — Medium large, the largest male out of second, and slightly pointed in the third plate. few thousands of a specimens is about 16 mm

In this resembles long. general appearance species Female. — As in the other species, females of

G. pulex. The colour of live specimens is usually G. wautieri lack most of the discriminating featur- brown. greyish to es present in the males. In mixed populations of

The of the head and is of the G. and G. of shape eyes same pulex wautieri, or G. wautieri and

as we find in other within this type species group. G. fossarum, the females can still be distinguished The first is antenna not very characteristic, hav- because of slight differences in both the second main and of ing a an accessory flagellum 30 to antenna and third uropod (Roux, 1967), but this

36 and 4 to 5 segments, respectively. The fifth does not hold true for populations from different

of the second localities. segment antenna (figs. 3A, 3A') is In that case intraspecific, interpopula- little than the longer fourth segment. A variable tional variability completely overlaps that found number of setae, usually forming groups, is im- in allopatric populations of other species. 170 S. PINKSTER - GAMMARUS PULEX-GROUP

from Fig. 3. A—D and I, Gammarus wautieri A. L. Roux, E and H, Gammarus fossarum Koch, 1835, ￿, a Pas-de- 1967, ￿, from the river Vence near le Sappey-en-Char- small brook near Ambleteuse, France, dépt.

Isère. second second antenna H, third treuse, France, dépt. A, antenna (1); A’, Calais. E, (1); uropod (2). the detail of second antenna (2); B, mandible palp (2); C, F and G, Gammarus fossarum Koch, 1835, ￿, from second seventh leg (1); D, third uropod (1); I, telson (2). river Amby, near Optevoz, France, dépt. Isère. F, antenna (1); G, third uropod (2). BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 171

Distribution and ecology. — As far as we know Gammarus fossarum Koch, 1835 rather at this the is limited to a moment, species Syn.: see Goedmakers, 1972. the small area in the French Alps, in departements Material examined. — About 600 samples from Germa- Isere and Rhone. the has been Recently species ny, France, Yugoslavia, Austria, Switzerland, Belgium, found in the french Jura. Jazdzewski, 1970, also Luxembourg, the Netherlands, Roumania, Poland and

Czechoslovakia. mentions this species from certain localities in

of this material and this Poland. However, a study A redescription of species was recently given systematic sampling of the area concerned by one by Goedmakers, 1972. Therefore only the most

that these of the members of our team, learned important characters will be summarized here.

similar to the Polish forms, although very typical Gammarus fossarum is a relatively small spe-

G. wautieri in some characters, certainly show cies within the Gammarus pulex-group. The maxi-

differences from G. wautieri as observed is 14 The colour morphological mum length ( S ) mm.

which well. Maybe hybridization experiments, of live specimens usually is a lighter or darker

started in the were spring 1972, can provide an an- shade of brown. The peduncle segments of

this It is that bear the usual of swer to new question. remarkable, second antenna groups setae, is throughout its range the species practically implanted in three different rows. The length of

almost with never found alone, but nearly together these setae, although variable, is at least as long other of this G. G. fos- but than the diameter of the species group, viz., pulex, as, usually longer and sarum, or both of them (Dusaugey, 1955; own segments on which they are implanted. The seg-

the characters of results). Since morphological ments of the flagellum are set with some short

this somewhat intermediate between their distal species are setae near end, never forming a flag-

G. pulex and G. fossarum, Dusaugey (1955) sup- like brush as in G. pulex. In some populations

of these in- calceoli absent. posed that hybrids two species were are found, in others they are

volved. Wautier & Roux (1959) and Roux (1967) Goedmakers already explained that considerable

that clearly proved that this is not the case, and variation can be encountered in the setation of the

G. wautieri is a good species, having a complete 2nd antenna, especially in different populations

set of isolating mechanisms, a result that is com- (see also figs. 3E and 3F). The first and second

pletely confirmed by the present experiments. gnathopods closely resemble those of the other

the dif- Moreover, Roux showed that species was species within this group. The length of the setae

ferent in both its physiology and its ecology. It in P3 and P4 is somewhat variable (Goedmakers,

appeared to be intermediate between the two 1972); these legs do not show fundamental dif-

species in its oxygen consumption-rate (meta- ferences from those of G. pulex. The other ap-

bolism), its sensibility for high temperatures, as pendages, except the third uropod, are similar to

well its resistance water-currents. This those of other members of this as against group.

is reflected in the distribution in the One of the most salient characters of this pattern alpine spe- which these be found. In streams in species can cies is the ratio length endopod versus first seg-

the G. is ment of the in 3 which upper reaches, only fossarum represent- exopod Ur is about Vi.

ed; in the mid-course G. wautieri is coming on Although the setation of the 3rd uropod is extreme-

~ G. variable the scene (although fossarum almost never ly throughout its distribution area

disappears). In the lower parts it is replaced by (see figs. 3G, H, and Goedmakers, 1972), this

G. pulex. In localities where wautieri coexists with ratio stays rather constant. other fast The smaller species of the group, the stony, run- female shows the same sexual di-

ning central axis of the streams, where vegetation morphism as in other species. is nearly absent, is inhabited by G. fossarum, Distribution and ecology. — See Goedmakers, while G. pulex is predominantly found in the near- 1972. shore where less zone, water currents are severe

— of the and a rich vegetation can be found. G. wautieri Remarks. Goedmakers gives a survey

usually is the dominant species in between these variability of certain characters within one popu-

microhabitats. of the lation and She two extreme In none zones between populations. points out

of the other that there is correlationbetween the however, one species disappears com- no geographi-

the lives in and the absence pletely (Roux, 1967; own results). cal region population

or presence of certain characters. She proved,

through hybridization experiments, that all mor- 172 S. PINKSTER - GAMMARUS PULEX-GROUP

phologically different populations belong to the started simultaneously by both Roux and

same species, G. fossarum. Meijering, 1972, point- Goedmakers, failed to give any positive results that certain considered ed out characters, to be up to this moment.

discriminative between this species and G. pulex, Distribution and ecology. — This species is known the of plumose setae on the outer e.g. presence from northern Africa from and many, more or margin of the exopod in Ur 3 in the latter, also less isolated localities in Spain (Pinkster, 1971). show in old males of G. up very fossarum. raised calcium It seems to prefer waters with a

ion content. Its localized occurrence in wells and Gammarus gauthieri (Karaman, 1935) upper reaches of rivers in Spain, as well as the Rivulogammarus gauthieri Karaman, 1935 : 47. extreme variability within some populations, are Gammarus pulex subsp. gauthieri; Margalef 1951 : 267. an indication that these populations are relics of Gammarus gauthieri; Pinkster, 1971 : 45—49. a formerly greater, probably more continuous, Material. — See Pinkster, 1971. distribution in the Iberian peninsula. of Pinkster, 1971, recently gave a redescription Gammarus ibericus Margalef, 1951 this medium large species (maximum length ob-

served 17 mm). Gammarus pulex ibericus Margalef, 1951 : 263; 1953 : 198. The first antenna head, eyes, and mouthparts Gammarus ibericus; Pinkster 1971 : 51 —52 are identical to those in other members of this

Material. — See Pinkster, 1971 species-group. The strongly developed fourth ped-

attention this uncle segment of the second antenna is almost Pinkster, 1971, already payed to

in the fifth small within the equal length to one (fig. 4A). They relatively species pulex- group.

are armed with few groups of setae only. The only Maximum length observed 11 mm. The species

striking feature of the flagellum is the absence of has many characters in common with G. gauthieri,

the special characters. Calceoli are always present in but can be easily distinguished by morphology

males. of the fifth to seventh legs (figs. 4E, 4 F and 4G);

The morphology of the first four legs never the basal segments of these legs are rather slen-

shows salient differences in comparison to other der, tapering towards the distal end, always form-

within this less lobe. The species group. ing a more or protruding armature

The distal end of the basal of consists of in- segments legs 5 of the distal four segments spines,

to 7 (figs. 4B, C) is always wider than the proxim- termixed with setae, the latter being much longer

al end of the ischium, thus forming a protruding than these spines. Such well-developed setation

sometimes is other described members of lobe, set with a small setule, but never not found in the

having the small spine that is always found in the pulex-group except for G. acalceolatus from

homologous position in P7 of G. wautieri. In northern Africa. The setation of the third uropod

adult specimens, the ratio endopod/exopod of is less dense than in G. gauthieri.

3 Ur3 is almost A. Plumose setae are found on The other characters differ from G. gauthieri in

both inner and outer margins of the exopod. The minor details only.

telson has a variable number of elements near its

— to Distribution and ecology. Up now the spe- top (fig. 4D). A subbasal spine, or group of spines, cies is known from the type locality only. Ecolo- has never been found. The armature of me- gical data are not available. and well the of tasome urosome, as as shape the

resemble those in epimeral plates closely G. pulex Gammarus pulex pulex (Linnaeus, 1758) pulex. Principle references. — Stebbing, 1906 : 474; Chevreux

& 1925 1931 Female. — Shows the normal sexual dimorphism Fage, : 253—254; Karaman, : 101—102; Schellenberg, 1942 : 24—31; Reid, 1944 : 17—18; Carau- similar to females of other members of this group. Dobreanu & 1955 82 1967 su, Manolache, : —85; Roux, :

Remarks. — This species shows considerable 1—172; Stock, 1969 : 106—107; Pinkster, 1970 : 177—186;

Vincent, 1971 : 1—132; Meijering, 1972: 313—325. intraspecific variation (Pinkster, 1971). Due to

this, it is possible to find specimens that are mor- Material examined. — More than 1000 samples from all

over its distribution area. phologically almost completely identical to Gam- marus wautieri A. L. Roux, 1967. Hybridization A redescription of the nominal subspecies of this experiments, however, between populations of G. species has already been given by Pinkster, 1970.

gauthieri from Spain and G. wautieri from France, Since it is moreover the nominal form of the en- 42 - 1972 BIJDRAGEN TOT DE DIERKUNDE, (2) 173

Fig. 4. A—D, Gammarus gauthieri Karaman, 1935, ￿, E—G, Gammarus ibericus Margalef, 1951, ￿, paratype from Ifrane, Morocco. A, second antenna fifth from the Fuentes de la „El Tobar”, (1); B, Laguna Spain, prov. leg (1); C, seventh leg (1); D, telson (2). Cuenca. E, fifth leg (1); F, sixth leg (1); G, seventh leg (1). 174 S. PINKSTER - GAMMARUS PULEX-GROUP

Fig. 5. A—C, Gammarus pulex pulex (Linnaeus, 1758), D— E, Gammarus pulex gallicus Karaman, 1931, ￿, from

from the the small brook ￿, Hierdense Beek, Netherlands, prov. a near Balaruc-les-Vieux, France, dépt.

Gelderland. A, second antenna (1); A’, detail of second Hérault. D, second antenna (1); D’, detail of second antenna (2); B. third uropod(2); C, meta- and urosome (1). antenna (2); E, meta- and urosome (1). - 175 BIJDRAGEN TOT DE DIERKUNDE, 42 (2) 1972

3 of the first tire species-group, its characters will be summa- attains about A of the length exopod the the in- rized here. segment. The greater part of setae on

ner and outer margins of both endo- and exopod

— the Male. Large, maximum length observed 23 are plumose, except for those implanted near

a second The mm, rather robust in general appearance with top of the exopod segment. density and the outer greyish to brown or green colour, depending on of the setation spinulation along the biotope in which it is found. margin of the exopod is largely variable through-

of the The third peduncle segment of A1 is about out the distribution area species (the same other the 24-to shown for G. half as long as each of the two; was by Goedmakers, 1972, fossa-

35-segmented flagellum has no particularities; rum).

the is 4- The which overreaches the accessory flagellum to 6-segmented. telson, peduncle seg- of the third is variable in its The second antenna (figs. 5A, A') shows some ment uropod, very

of the discriminating characters of the species. Its armature (see Pinkster, 1970). has peduncle segments 4 to 5 bear some groups of The first urosome segment a distinct, though the shallow excavation The other short setae, whose lengths are less than dis- rather ("saddle").

between the in three do neither show elevations tances groups, implanted segments nor excava- consists of longitudinal rows. The flagellum, probably the tions. The dorsal armature generally

of and most characteristic part of the animal, has 12 to a middorsal group spines a lateral group

16 each side. with these small wide, compressed segments making a swollen on Intermixed spines,

impression, each of them provided with a trans- setae can be found. The posteroinferior corners

rather verse row of 12 or more setae on the inner sur- of the epimeral plates (fig. 5C) are variable; and face, together forming a flag-like brush. Calceoli generally the first one is rounded, the second

are nearly always present on the outer margin of third ones rectangular or slighthly pointed, res-

the second to tenth segment. pectively.

The mandible palp bears a regular comb-like Female. — Less characteristic than the male; row of spinules along the inferior margin of the of the brush-like aspect of the flagellum A2, very third segment. The first gnathopod has a strong is absent here. distinctive in the other sex, usually hand with pyriform set a strong medial palmar the of In general, the setae on peduncle segments spine. A strong palmar angle spine together with the first and second antennae are longer than in several smaller spines (the so-called "Stiftsta- less the males. All other features are pronounced, cheln") can be found along the posterior margin be in all other a situation that can met species and the inner surface of the hand. within this group. The hand of the second gnathopod has about

the same size as the first but is completely differ- Distribution and ecology. — As far as we know,

ent in because of its almost transverse G. is known from southern Fin- shape, p. pulex Sweden, The Russia palm. strong medial palmar spine is separated land, Denmark, and (Segerstrale, 1954, from the Poland palmar angle group by a wide gap. 1955a, 1955b), (Micherdzinski 1959),

The number of spines in the palmar angle group Great Britain, including Scotland and Ulster (Hy- is rather variable. In specimens from the type nes, 1955; Hamond, 1967; Macan & Mackereth,

locality, 1 strong and 4 smaller spines could be 1957; Reid, 1951), the Netherlands (den Hartog, found, in populations from the Hierdense Beek, 1964; Holthuis, 1956; Nijssen & Stock, 1966), Bel-

brook in France a the Netherlands, 3 strong and 3 small gium (Stephensen & Hynes, 1953), (Pa- spines were present. caud, 1952; Dusaugey, 1955; Roux, 1967; Vin-

The third and fourth bear Ger- legs a number of, cent, 1971), Luxembourg (Hoffmann, 1963), often Schellen- curved, setae on the distal three segments. In many (Besch, 1968; Meijering, 1971;

P3 these the lower of Switzerland setae are generally longer than in P4. berg, 1942), parts (own

The coxal have rounded inferior and Roumania Do- plates corners. material), Bulgaria (Carausu,

The shape of the basal segments of legs 5, 6, breanu & Manolache, 1955), Jugoslavia (Kara- and 7 Lake Baikal gradually changes from wide in the fifth to man, 1931), Siberia, including (Sars, elongate in the seventh leg. The armature of the 1901; Bazikalova, 1945), Turkey and Greece

distal consists of In of segments usually a varying num- (own material). spite an intensive research, ber of found in spines exclusively. the species has never been Norway

The inner ramus of the third uropod (fig. 5B) (0kland, 1969), Eire (Sutcliffe, 1967), Italy and 176 S. PINKSTER - GAMMARUS PULEX-GROUP

Spain (own data), Czechoslovakia and Hungary top of the cliff, but reached the beach, when large

(Straskraba, 1962, 1967). portions of the cliff came down during gales in

In western Europe, G. p. pulex is the common winter. The population that reached the beach this

freshwater species in the plains, where stream ve- way, looked very healthy 18 months after the

this of it of locities are rather low. In type biotope brusque change habitat. is often found together with Echinogammarus be- The reproduction period of this species is large- rilloni (Catta, 1878). There are no indications ly variable throughout its distribution area and

exists be- that a strong interspecific competition seems to be a function of both climatical and light

tween these two species (Pinkster et al., 1970; factors.

Gras & Maassen, 1971). In mountainous areas, Gammarus from les Landes however, e.g. in the French Alps, or in certain pulex pulex,

of western Germany the species meets with parts Material examined. — About 100 samples from the

of other in this french Landes also strong competition species group, departement (see map III).

viz. G. fossarum and G. wautieri, or G. fossarum Populations from this part of France differ from and G. roeseli, respectively (Roux, 1967; Mete- "normal" G. p. pulex in the flagellum of their results in ring, 1971). This competition usually a second the antenna only (figs. 6F, 6F'), segments distribution with G. fossarum in the upper pattern of which never give the compressed and swollen reaches of the stream, where water currents are impression that is so characteristic for the typical

strong and G. p. pulex in the lower reaches of the G. p. pulex. Moreover, the number of setae, partic- the French third river In Alps a species, systems. ipating in the flag-like brush along the inferior G. wautieri, can be found in a somewhat interme- margin of the flagellum is somewhat reduced, in diate ecological position (Roux, 1967). Meijering, comparison with "normal" G. p. pulex. Notwith- 1971, pointed out that G. pulex is more sensi- p. standing this difference in the flagellum of the tive for lower temperatures and high stream second antenna, this form must be considered a velocities than G. fossarum and he makes clear mere variety of G. p. pulex, as will be shown in that the combination of these two factors an plays the sequel. important role in the competition between the two

Distribution and ecology. — This form is known In where in species. source areas, changes tem- from the French departement Landes only perature both during the year, as well as during (see map III), a region that is covered with ex- the day-night cycle are relatively limited and the tensive and dense pineries. Consequently the wa- stream velocities are rather low, the species can in in ters this region are rather acid. So, the spring successfully compete with G. fossarum. In those of 1970 pH values of 4.5 or lower have been areas where G. fossarum is absent, G. p. pulex measured in more than 100 localities in which often inhabits the entire stream system, on con- this form was found. Moreover, these waters are dition that winter temperatures are moderate. in other such chloride very poor important ions, as Although the species is usually found in fresh and calcium. these waters In summer, can partly waters, it can thrive successfully at higher salini- dry up, because of evaporation and low precipi- ties. So, Schmidt (1913) and Von Alten (1915) tation. the report species from mineral springs with sa- linities In up to 25370 mg/1. 1968, when some of Gammarus pulex gallicus (Karaman, 1931) these springs were revisited by some members of our team, this situation was still unchanged. Vin- References. — Karaman, 1931 : 102; Roux, 1967 : 1—

172. G.cent, 1966, 1971, showed experimentally that

could live in normal in 40% Material examined. — More than 100 samples from the p. pulex a way sea- french departements Bouches-du-Rhone, Herault, Gard, water. Schmitz, 1959, and Schmitz, Besch & Var, Vaucluse and Basses Alpes. Kneissl, 1967, also record the adaptibility of this amphipod to higher salinities. Male. — This subspecies is much smaller than

On the French Channel Coast, N. of Wimereux G. pulex pulex. The largest male observed

few thousands of animals 14 (France, dept. Pas-de-Calais) healthy populations amongst a was mm. can be found on the open exposed beach, just Its general appearance, however, is very much above High-Water-Spring, in waters with a chlo- like that of the other subspecies. rinity that is often more than 1000 mg/1 (own The main differences from G. pulex pulex are observation). These populations originally lived on found in the second antenna of the male (figs. 5D, BUDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 177

St-Martin-de- DO. The peduncle segments 4 and 5 resemble l-VIII-1970, in the river Lamalou, near Lamalou, France, dept. Herault, have been designated those of G. p. pulex, but the segments of the 9 the as types: the 6 holotype, allotype and paratypes flagellum are different since they are less swollen have been deposited in the Zoologisch Museum Amster- than in G. p. pulex and moreover, the setae im- dam under cat. no. ZMA Amph. 103.345.

planted on these segments are shorter and reduc-

Male. — Rather 20 in large, up to mm length ed in thus brush number, never forming a flag-like and resembling closely Gammarus p. pulex in al- as its larger relative. most every character except in the second anten- The fifth through seventh legs generally are na, the peduncle segments of which possess more less slender than in most other taxa within the groups of setae than in p. pulex, usually 3 to 4 group. on the fourth and 5 to 7 on the fifth segment, A slight excavation is visible on the ("saddle") The implanted in 3 longitudinal rows. segments first of the the the segment urosome. On contrary, of the flagellum, however, are never flattened as other form low two urosome segments dorsally a in the nominal form. The setae, implanted near but distinct hump (fig. 5E). the top of each segment are as long as in p. pulex, Although smaller in absolute size, the other but reduced in number (7 to 8) in comparison to of this animal appendages are similar to those in G. p. pulex (12 to 15) (figs. 6E, 6E'). G. p. pulex. The segments of the urosome never bear a dor-

Female. — Of small in adult sal size, even stages hump as in G. monspeliensis or in G. p. gal- often than This no longer 7 mm. sex has no spe- licus.

cial characters and be confused with can easily This form, which was originally found in the

of G. G. wautieri. of the river Herault juveniles p. pulex or drainage system (Van Maren, which river the 1972) (to proposed name G. Distribution and ecology. — This species is known p. araurensis must be considered sub- from rather limited in the southern alludes), a new a area part species as will be shown in the sequel. of France only (see map I). It usually inhabits the

lower — stretches of the river systems, where stream Ecology and distribution. This form has been velocities low. in the french are usually Often, e.g. found in the upper regions of the rivers Lez, He-

Var and Bouches-du-Rhone departements (own rault, and Vidourle, or their tributaries. Within

observation), it has been found together with G. these river systems, it inhabits the fast and mod-

The distribution in those river fast is fossarum. pattern erately running stretches, a biotope that

in which both G. and G. systems fossarum p. gallicus sometimes shared with Gammarus fossarum, or found are resembles that in other parts of Europe with another still unidentifiedform, that resembles

where G. and G. somewhat the ibericus. fossarum p. pulex occur together, Spanish G. It never

and it that in this of France G. seems part galli- occurs with G. p. jointly p. gallicus (see map II). the cus occupies same ecological niche as is

G. in other of Gammarus monspeliensis nov. usually occupied by p. pulex parts spec.

western Europe, and shows a similar competition

Material examined. — pattern with G. fossarum.

— France, dept. Herault: Source du Lez, N. of Mont- Margalef, 1944, mentions this subspecies from about 100 of them in pellier, specimens, many pre- the Serrania de la Cerdana on the Spanish side of copulation, 8-1-1968. The 3 holotype, 9 allotype and the eastern to retrace this form have been in the Pyrenees. Attempts many paratypes deposited Zoologisch

failed however, so some doubts remain about its Museum Amsterdam under cat.no. ZMA Amph.

103.344. real identity. — Same locality, l-V-1968. 7 specimens (ZMA). StraSkraba, 1967, footnote 36, suggests that G. — Same locality, 11 specimens, 13-X-1965 (ZMA). gallicus should be identical to G. caucasicus p. — Same l-VIII-1970 locality, many specimens, (ZMA).

1932. of — Same of them in Martynow, However, comparison our locality, many specimens, many pre- 15-XI-1970 (ZMA). material with the descriptions and illustrations of copulation,

— Same of them in locality, many specimens, many pre- Martynow does not support this suggestion. copulation, 26-111-1970 (ZMA).

— France, dept. Hdrault: le Lez, W. of Prades-le-Lez, Gammarus araurensis nov. of in pulex subspec. many specimens, many them precopulation, 1- VIII-1970 (ZMA).

Material examined. — 22 samples from the drainage Populations from the course of the river systems of the rivers Herault and Lez (France, dept. upper

About are different from G. or Herault) (see map II). 100 specimens, collected Lez, clearly p. pulex any 178 S. PINKSTER - GAMMARUS PULEX-GROUP

A Fig. 6. —D, Gammarus monspeliensis nov. spec., ￿, E and E’, Gammarus pulex araurensis nov. subspec., ￿, from the Sources du Lez, France, dépt. Hérault. A, first from the river Lamalou, France, dépt. Hérault. E, second

antenna (1); B, second antenna (1); B’, detail of second antenna (1); E’, detail of second antenna (2).

antenna (2); C, hand of second leg (2); D, meta- and F and F’, Gammarus pulex pulex (Linnaeus, 1758), ￿, urosome (1). from a small brook near Arès, France, dépt. Landes.

F, second antenna (1); F’, detail of second antenna (2). - 1972 BIJDRAGEN TOT DE DIERKUNDE, 42 (2) 179

other member of the in the rest of HYBRIDIZATION EXPERIMENTS WITH pulex-group in WITHIN THE Europe a few characters. VARIOUS POPULATIONS

GAMMARUS PULEX-GROUP.

Male. — Maximum length 21 mm. Colour

greenish, very often vertically striated with bright- Introduction. —

er bands. In order to form an idea about the significance

The first antenna (fig. 6A) is remarkable be- of the morphological differences in populations

of the of in the cause extreme length the main flagel- from different localities, as described syste-

lum, that often consists of 45 to 50 segments matic part, the necessity of hybridization experi-

(against 24 to 35 in G. p. pulex). ments came up. Other authors, e.g. Wautier &

The of the Roux, 1959, Roux 1967, and Meijering, 1972, peduncle segments second antenna

already tried to cross-breed Gammarus pulex (figs. 6B, B') resemble those in G. p. pulex. The pu- lex and Gammarus with the flagellum is slightly different, since its segments fossarum, always results. are never compressed or swollen, while the 11 to same, negative Although precopulations

13 these can often be obtained between setae, implanted on segments are even heterogeneous

under and even longer than in normal pulex, together forming a couples laboratory conditions,

flag-like brush. ovoposition takes place in many cases (Meijering,

1972), an offspring has never been obtained. The Compared with other members within this of the after few development eggs always stops a group, the number of spines near the palmar angle cleavage and the are removed by the of P2 has increased (fig. 6C). stages eggs females within a few days. Moreover, we must The other appendages, including the third uro- realize that the of forms presence eggs no proof pod and the telson, do not show noteworthy dif- that fertilization has taken place, since sponta- ferences from G. p. pulex. neous ovoposition of unfertilized eggs has often A striking difference in comparison to the other been observed in females kept solitary (e.g. by members within this species-group, however, is Goedmakers, 1972). Anyhow, all these experi- the presence of well-developed dorsal humps on ments leave no doubt that Gammarus pulex pulex the of the almost segments urosome, resembling and G. fossarum are intersterile. With these re- the situation found in Echinogammarus thoni, a sults in mind, and to reduce the number of pos- species that likewise occurs in the source area of sible the decision crosses, was made to leave G. the river Lez and some adjacent river systems. fossarum out of our experiments. Seven popula- These dorsal humps are not restricted to the adult tions of the G. pulex-group, including G. pulex stage, but occur already in just hatched juveniles, pulex and G. wautieri, where chosen to start hy- found in the female marsupium. bridization experiments with. These populations The special morphological characters and the all show morphological differences, described in result of the hybridization experiments (vide infra) the systematic part, but have in common that the consider form were grounds to this a good species. endopod of their third uropod is about 3 A of the

Female. — the normal sexual Shows dimorphism, length of the exopod. Other characters, like the known for this group. The dorsal elevations of structure of the second antenna and the contour

the so in the urosome, typical male, do also of the urosome show differences in the various

characterize the female series quite clearly. populations. Almost at the same time, of

Ecology and distribution. — This form exclu- cross-breeding experiments were carried out with

sively inhabits the upper reaches of the river Lez, some morphologically different populations of North of Montpellier, France, dept. Herault (hence Gammarus fossarum (see Goedmakers, 1972) and

the with of G. wautieri side and G. specific name proposed, monspeliensis). This populations at one

river is fed rheocrene at the series that is still by an enormous well, pro- gauthieri other, a going on. of the have been carried ducing water with a high amount of electrolites, Most experiments out in

collaboration with Mr. F. d. especially Ca-ions. The species is found under v. Beld, B.Sc., to

stones and between plants, always together with whom I am greatly indebted.

Echinogammarus thoni, a species that, although

Material. — another is belonging to genus, provided with the same of dorsal as the in have carried out with type humps species ques- The experiments been 1500 tion. to 2000 individuals from each of the following 180 S. PINKSTER - GAMMARUS PULEX-GROUP

localities (the names in italics have been used to different types of thermostates, one for cooling

indicate the populations in the tables and in the and one for heating. Most experiments have been

A diagrammatic model of the results): done at a temperature of 15± 1°C. problem,

which Gammarus from small of in the first series of p. pulex, a brook, N. Ares, especially experiments, started in November the France, dept. Landes, on road D 106; collected 13 No- 1970, was that repro-

vember 1970; 11.3°C, 4.5, chloride 34 temperature pH ductive cycles of the various populations were not mg/1. calcium 7.6 mg/1. reduce synchronous. Therefore, to introduce or

Gammarus p. pulex from the Hierdense beek, about 2 sexual activity, temperatures in some basins had km. E. of Hierden, the Netherlands, prov. Gelderland; be raised lowered. The animals occasionally to or collected 15 December 1970 and 30 March 1971; tem- terrestrial were fed with Stellaria media VIII., a perature 7.4° (10.2)°C, pH 6.5, chloride 39 mg/1, calcium This 31 mg/1. weed, that can be found in all seasons. plant

is to other of since it is Gammarus p. pulex from a tributary of la Laye, near a preferable types food,

chapel called Notre-Dame-des-Anges, N.W. of Forcal- eaten completely by the animals leaving neither quier, France, dept. Basses-Alpes; collected 21 Novem- skeleton, nor slimy bacterial growth. As soon as ber 1970; temperature 9.8°C, pH 5.5, chloride 8 mg/1, in the precopulations were found storage basins, calcium 84 mg/1. the couples were separated. Females were always Gammarus araurensis from the p. river Lamalou, France, checked to see if ovoposition had not tak- dept. Herault, N.E. of St. Martin-de-Londres, 1 km W. already males of Pont de Januc; collected 14 November 1970 and 26 en place. Next, precopulated were put

March 1971; temperature 12.8 (13.2)°C, pH 6.0 (6.5), together with precopulated females from other chloride 7 (5) mg/1, calcium 70 (50) mg/1. populations, etc. So, some 10 to 50 heterogeneous

Gammarus from the "Sources du Lez", N. monspeliensis couples were brought together in the same plastic of Montpellier, France, dept. Herault; collected 15 No- storage basins mentioned above, in a mixture of vember 1970 and 26 March 1971; temp. 13.5°C, pH 6.5- from which each of the water two sexes originated. 7.0, chloride 16 mg/1, calcium 103 mg/1. Gradually this water was replaced by Amsterdam Gammarus p. gallicus from a small brook near Balaruc-

water. In most cases were les-Vieux, N. of Sete, France, dept. Herault; collected 14 tap precopulations

November 1970 and 25 March 1971; temperature 13.8 formed very soon again. As soon as females from

(12.8)°C, pH 6.5, chloride 122 mg/1, calcium 161 mg/1. such heterogeneous couples produced eggs, they

isolated in smaller 7 7 10 Gammarus wautieri from the river Amby, near Optevoz, were plastic basins, x x

E. of Lyon, France, dept. Isere; collected 21 November cm, again in 5 to 7 cm of water. Every two days 1970; temperature 10.2°C, chloride 13 mg/1, calcium 86 these females were checked as to the presence or mg/1. absence of As of the eggs. soon as hatching ju- Gammarus wautieri from the river Vence, upstream of le veniles took place, the "empty" females were put Sappey-en-Chartreuse, France, dept. Isere; collected 28 back in the basins, in order to save the March 1971, temp. 5.6°C, pH 5.5, chloride 7 mg/1, cal- storage from cium 88 mg/I. juveniles being devoured by their own moth-

first weeks the of er. The two offspring one

Methods. — female was kept apart in the smaller type of stor-

All experiments were carried out in the Institute age basin, but after that period it was put together of Taxonomic Zoology of the University of Am- with juveniles from identical crosses, to grow up. sterdam (I.T.Z.), in an air-conditioned room, in rather Mortality was usually high among these which the day/night period could be controlled. juveniles, mainly due to lack of place and time the series of During a present experiments light to attend properly to them. Nevertheless adults

period of 16 hours was alternated with a dark could be obtained from most of the fertile crosses.

of 8 hours. The period various populations were Because of of it shortage space, was not always in kept plastic storage basins of 25 x 25 x 10 cm, possible to run a control series with the same

in 5 to 7 cm of water, with a constant circulation number of homogeneous couples. A proof, how- of air. Some pebbles were added to basin every ever, that the populations used did thrive under

as a hiding place for the animals. About 200 ani- laboratory conditions, can be found in the fact, mals were in basin. In the kept every beginning, that new precopulations were formed in the stor- the water in these basins corresponded with the age basins, and that ovigerous females from the water from which the animals originated, but couples thus formed produced an offspring. gradually they were adapted to normal Amster-

dam tap water. Temperature in the different ba- Results. — sins could be controlled by a combination of two Two series of crosses have been done: a first one BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 181

Fig. 7. Diagrammatic model of the hybridization experiments. 182 S. PINKSTER - GAMMARUS PULEX-CROUP

with material from les Landes, Balaruc, le Lez, le with G. wautieri. Therefore, in a second series of

Lamalou, Notre-Dame-des-Anges, Amby, and experiments, started in March 1971, this popu-

Hierden. time homo- The results of this series, started in Oc- lation was replaced by another, this

tober 1970, together with the number of animals geneous, population of G. wautieri from the river involved, the number of ovigerous females, and Vence. Since the results with the population from

the that idea about number of females produced an offspring les Landes had already given a good

table I. these are summarized in the isolating mechanisms of animals, parents

I this left out of the second Table from origin were se-

ries, to reduce the number of possible crosses.

Results of the first series of hybridization experiments The results of the second series are summarized

in table II, along with other data. Number of Number of Number of Code Locality Locality ovlg. Offspring

? after cross produced Finally, the combined results of both series of

A 21 Lez 21 Balaruc 7 - x model experiments are illustrated in a diagrammatic B Balaruc X 20 11 M Um -

27 Undes 20 C 20 Lei X H (fig. 7). With the aid of this model and with the

D 3 Undes X 2 Lez 2 -

E 114 Bala 111 Hierden 69 12 rue X zoogeographical data we have at our disposition, 35 17 F 69 Hierden X 50 Balaruc

K 49 Bala rue 40 Undes 20 7 understand status X one can easily the systematic L 61 Undes 50 Balaruc 39 12 X

M 40 Umalou 57 Hierden 33 - of the various used in these series of X populations

N 20 Hierden 20 Umalou 1 X 1

Lamalou 50 Balaruc 36 7 O 50 X experiments.

P 23 Bala rue X 31 Umalou 12 1 These results will be discussed for T 46 Lamalou 74 Undes 30 5 separately X

V 27 La tides 25 Umalou 9 X - every population. V 130 La tides X 130 Hierden 58 6

w 52 Hierden X 64 Undes 30 5

IS 14 5 Y Notre Dame X Umalou - Gammarus wautieri from the rivers Vence and

Z 20 lamalou * 25 Notre Dame 13 " Amby (France, dept. Isere).

The AA 2 Lamalou X 2 Uz I . results of the hybridization experiments

A8 2 Uz 5 Umalou 4 X - make it that a well-established n - clear, reproductive AI 39 Laurie s X NotreDame 8

AJ 14 Notre Dame X 19 Undes 14 9 barrier exists between this species and all other AK 10 Bala rue X 17 Notre 11 Dame -

21 AL Notre Dame X 28 Balaruc 43 12 populations used in these experiments (see fig. 7 AM 40 Hierden 39 Noire Dame 24 5 X

AN 60 Notre 70 35 7 Dame X Hierden This is in with the (5)). complete agreement re- G 35 50 Undes 11 Amby X -

H 25 .a 25 19 I tides X Amby ■ sults obtained by Roux, 1967, and the fact that 26 Notre Dame 13 AE X 26 Amby -

AD 30 >: 34 Notre Dame 20 this is often found with Amby species very sympatric

other members of the G. pulex-group, viz., G. 1 after 24 hour« T and G. G. pulex pulex fossarum. Moreover, wau-

The of the crosses in which G. greater part tieri is differentfrom these species, in its morpho- wautieri from Amby were involved, have been left logy, as well as in its ecology and physiology.

out of this table, since a second inspection, after Gammarus from the river the end of the learned, that the monspeliensis nov. spec, experiments pop- Lez (France, dept. Herault). ulation was not homogeneous, and that some- The tables and 7 show, that this times G. fossarum or G. pulex pulex were mixed fig. (6) clearly

population never produced an offspring when

Table II crossed with specimens belonging to other popu-

lations. took in Results of the second series of hybridizationexperiments Although ovoposition place many the of the cases, development eggs usualy stopped

Code Number of Number of Number of Locality Locality ovig. after 5 to 15 o used some In one case in J used s after cross tt J* days. only,

crossing a male from the Lez, with a female from BA 70 Lez 91 Lamalou 26

BB 45 Lamalou 45 Lez 6 X . les Landes one juvenile was found, after 24 77 days, BC Lez X 85 Vence 29 .

BD 60 Vence X 57 Lez 14 but this juvenile died within one day. Females BE 40 Balarue X 43 Lez 31 .

BF 88 Lez 120 Bala 65 X rue . from the river this Lez, during series of crosses, BG 47 Let 65 Hierden 20 X .

BH SI Hierden X 50 males from Lez 33 never produced any offspring with

BI 70 Lamalou X 85 Vence 15

BJ 85 Vence 96 Lamalou 39 other In the basins normal X populations. storage

BK 70 Hierden X 95 Lamalou 43 6 reproduction took place. Consider- BL 54 Lamalou 65 Hierden 27 8 homogeneous X

BM 49 Vence 65 X Hierden 18 ing these results, we must come to the conclusion BN 75 Hierden X 80 Vence 15

BO 95 Bala 95 Lamalou 29 rue X that this population is not only different from the BP 92 Lamalou X 120 Balarue 30 3

BQ 75 Vence X 120 Balarue 43 other forms and from Gammarus pulex pulex in

BR 70 Balarue X 80 Vence 22 its morphology, but also has established an effec- BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 183

tive reproductive barrier with other populations Roux, 1967, showed that juveniles, resulting within the pw/ex-group. A geographical barrier from hybridization between G. pulex pulex and G.

identical is not always clear, since in the system of the pulex gallicus were morphologically to river Lez, where this form is exclusively found, G. pulex pulex, and therefore we must assume,

there might be a zone of contact with its relatives, that the genotype of the latter form is dominant

G. pulex gallicus and G. p. araurensis. In conclu- over that of G. pulex gallicus. G. pulex gallicus

differences first has been found in rather restricted in the sion, the morphological in the a area and second second and South of France in which antenna, the gnathopod only, an area no "typi- the urosome, together with the effective repro- cal" G. pulex pulex is found. It is almost sure,

that in this fac- ductive isolation from other populations within the case geographical isolation is the species-group, leave no doubt that this character- tor through which an aberrant morphology was

of istic form must be considered a good, distinct developed without simultaneous development species. a genetical isolating mechanism. Such a geogra- phical isolation mechanism is easily demonstrable Gammarus pulex pulex from the Hierdense Beek, in most of the waters in which G. gallicus can the Netherlands. p.

be found, because of the mere absence of closely The results of the hybridization experiments related forms. In some river in the french with this systems population (tables I and II, fig. 7 (2) are d6partement Herault, however, e.g. in the drainage completely different from those discussed before. systems of the rivers Herault and Lez, the situa- Offspring could be obtained in all crosses, ex- tion is little these a more complicated. In systems cept in those with G. wautieri from the river another very close relative, G. p. araurensis, can Vence, and with Gammarus monspeliensis from be found, a form which has been successfully the river Lez. This is not astonishing since these crossed, not with G. but likewise only p. pulex, two populations proved to be good species them- with G. In these G. p. gallicus. situations, p. araur- selves. These results also mean, that the other ensis usually inhabits the fast running or moder- populations must belong to the same species, G. fast ately running parts, while G. p. gallicus is pulex, as the Dutch material (of course they may found farther downstreams in the more slowly belong to other subspecies). running parts of the river system.

Gammarus from small near pulex gallicus a stream Although these two forms have never been

Balaruc-les-Vieux, France. found there be dept. Herault, together, might a possibility for This form be from can easily distinguished them to get into contact with each other. Never- Gammarus because of the still believe pulex pulex, morpholo- theless, we that an effective isolation

of its second gy antenna. Hybridization experi- mechanism is working here, since there is always showed ments, however, clearly (Roux, 1967; pre- a zone in between the two populations in which no

sent tables I and 7 that paper, II, fig. (7)) crosses gammarids do occur at all, or a zone that dries between this and other subspecies many morpho- up completely from the early spring to the be- logically different populations within the species ginning of the rainy season, a period that roughly G. succesful pulex are possible. So, a offspring corresponds with the reproductive period of the could be obtained in experiments in cross-breeding populations question (see map II). between this form and animals from the Hierdense In the river Lez, where a third member of the Beek from les (The Netherlands), Landes (Fran- Gammarus pulex-group is found (Gammarus from ce), the river Lamalou (France, dept. He- monspeliensis) and where the geographic barrier from rault), and a small brook near Notre-Dame- is well effective not always so established, an re- In des-Anges (France, d6pt. Isere). the last case barrier has between G. productive developed pu-

the crosses were successful in one and G. however, way lex gallicus monspeliensis. This is in com- only: males from females Ba- Notre-DameX from plete agreement with the theory, that reproductive laruc produce an but the cros- offspring reciprocal barriers between two closely related forms are al-

did work out. This is due size ses not probably to ways better developed in sympatric than in allo- differences; males of G. pulex gallicus are usually patric populations. much smaller than females of G. pulex pulex,

in and there Gammarus araurensis the especially this case, occur enormous pulex nov. subspec. from

"mechanical" difficulties in forming precopula- river Lamalou (France, dept. Herault). tions. Regarding the results of the hybridization ex- 184 S. PINKSTER - GAMMARUS PULEX-GROUP

periments with animals from this population (ta- nature, viz., the change in water composition,

bles I and II, fig. 7 (1)) we see that combinations caused by the pineries. Indeed, the pH rapidly successful in both with G. pulex gallicus were drops to very low values (4 to 4.5) as soon as

directions. The combination with G. pulex pulex a stream enters the woods. Probably, in this case,

from failed N.-Dame-des-Anges, however, to give we have to do with some kind of morphological

any success. This can be due to the rather small reaction, or with a special physiological race,

As be in the number of couples used, of course. could sense of Vincent, 1971, particularly adapted

expected, the combinationwith G. wautieri and G. for life in these acid waters. However, the fact

monspeliensis gave negative results. With the that populations from those very acid waters do

population from les Landes, the crosses were on- normally reproduce in Amsterdam tap water with

fertile. value of about does this ly partly a pH 7 not support sup-

position. One should keep in mind that the pine- When studying the results of the experiments, it ries, which cause the extremely low pH values, looks rather strange that two morphologically dif-

ferent were only a hundred years ago, so much forms (in absolute size, in the second an- planted available too short a period was to develop a new tenna, and in the dorsal contour of the urosome)

species or even a subspecies. Consequently, we from the same river system, which do successfully must come to the conclusion that these crossbreed, can still maintain their own character- populations

from les Landes are mere variations of G. pulex istic morphological features. Intensive sampling pulex. in the area in question in various seasons showed,

however, that an effective isolation mechanism Gammarus pulex pulex from Notre-Dame-des- (desiccation during the reproductive period) is Anges. working here (see under G. pulex gallicus). In reviewing the results with this population we Since the reproductive barriers are still incom- must bear in mind that they are possibly influenc-

plete, the morphologically aberrant and executed. present ed by the small number of crosses

isolated form must be considered geographically The results with this population are somewhat distinct a subspecies of Gammarus pulex. Since it confusing. Morphologically, the animals are com- was found in the french exclusively departement pletely identical to those from the Hierdense Beek the G. Herault, name p. araurensis is proposed. and between these (the Netherlands) crosses pop-

ulations are rather succesful. However, with the

Gammarus pulex pulex from les Landes. other two G. and G. subspecies, p. gallicus p. Most the of crosses proved to be successful, araurensis the results are less convincing and we except those with Gammarus wautieri from the must conclude that reproductive barriers have river and with Gam- be- Amby (France, dept. Isere) already been formed or are being formed,

marus monspeliensis from the river Lez. (Once tween these subspecies and the populations in

male from the river Lez female a x from les question. The same holds true for the crosses be-

Landes produced a juvenile, but this died within tween this population and that from les Landes.

24 the male from les hours). Only combination However, since no morphological differences be-

Landes X female from Notre-Dame-des-Anges tween this form and the typical G. pulex pulex

be appeared to less succesful. However, we could be found, and since no strong genetical bar- must conclude that an effective reproductive bar- rier exists, we must consider this population as rier has not yet been formed between this form another (maybe physiologically different) form of and the other populations of G. pulex used in G. pulex pulex. our experiments. Taking the geographical position DISCUSSION of this form into consideration, we must come

the to conclusion, that no sharp geographical When we consider the morphological diversity barrier between this form and the normal pulex within the Gammarus pulex-group, and the results be found. This can form can be found in those of hybridization experiments that have been run regions of les Landes, where large pineries occur. during the last few years (Roux, 1967; Goedma- that However, once outside these woods, to the North, kers, 1972; present paper) it will be clear

South rather or East, the typical G. pulex pulex, with speciation within this species-group is a the and swollen there is compressed antenna is reappearing. complicated process. At the one hand, a

The only possible barrier would be of ecological number of good species like G. pulex, G. fossa- BIJDRAGEN TOT DE DIERKUNDE, 42 (2) - 1972 185

rum and G. wautieri, all having successfully devel- absence of reproductive isolation can easily be

iso- oped mutual reproductive barriers. These species, explained, since we know that the geographic

be often coexisting in the same localities, can be lation between the different populations must

and which after the clearly distinguished both on morphological a rather recent one, developed ecophysiological grounds. Their fairly large distri- melting of the glaciers that covered Europe during

that these bution areas seem to be an indication the glacial periods.

time the the is species developed quite a long ago. At Within G. pulex same process going on, other hand, however, evolution did not stop after and all different steps on this way towards spe- this first speciation step. It is still going on, as is ciation can be found. shown the aberrant which is by many morphologically So in the french departement Landes, forms of G. fossarum and G. pulex. One of the almost completely covered with large pineries and

low most important factors playing a role in this proc- where the waters are characterized by pH-

of is the of that differ from ess speciation degree (geographic) values, populations are found, isolation. continuous normal in feature Isolation, preventing a gene- pulex one only. These popula- flow between the various populations, creates a tions can maintain their own morphological char- possibility to develop special morphological char- acter, although considerable gene-flow, between acters within the isolates. this form and typical pulex is probable (they both

form Morphological variability, which can be consid- inhabit the same stream systems, and the

in ered the first step towards speciation, is encoun- from les Landes can successfully thrive waters tered in G. fossarum (see Goedmakers, 1972), a with normal pH-values). Probably, in this case, species subdivided into a considerable number of selection pressures corresponding to environ- morphologically different populations. These pop- mental factors are interfering with the regular ulations inhabit isolated reach- of material. time usually the upper exchange gene However, seems es of stream systems, especially in mountainous to have been too short to develop a new species

areas, while the less isolated lower reaches are or even a subspecies.

In of southern in inhabited by other members of the pulex- group, some parts France, especially e.g. G. pulex pulex and G. wautieri. Because of the departement H6rault, the situation is even more but this distribution pattern, gene-flow will be reduced complicated since not only one, even three and could its aberrant forms be all every population develop own spe- morphologically can found, cial characters. Goedmakers, 1972, proved that a occuring in the same river system. As we explain-

number of populations tested still are conspecific, ed in the previous chapters, two of these forms,

cross-breed. The viz., G. and G. araurensis should be since they all did successfully p. gallicus p.

Table III

" Species G. p. pulex G. p. gallicus G. p. araurensis G. p. pulex (Landes) G. monspeliensis

Character

Maximal length 23 mm 14 mm 20 mm 21 mm 21 mm

Number of segments 24-35 24-32 31-37 26-34 45-50 in flagellum of A 1

Flagellum ofA 2 swollen slightly not swollen not swollen not swollen

swollen

Number of setae on 12-15 7-8 4-6 8-10 11-13 proximal flagellar segments ofA 2

Lengths of these relatively relatively relatively relatively very long setae (see fig.) long short long long forming brush no brush no brush forming brush "M ////.,? -Jl!i # m \MM/ .. w' UM' Mj M f W M

H 1 '

Dorsal contour of

urosome

™ A 1 1 TirS 186 S. PINKSTER - GAMMARUS PULEX-GROUP

considered as subspecies of G. pulex, while the snecies of fish, Cottus petiti Bacescu & Bacescu-

third one, G. monspeliensis must be considered a Mester, 1964, in the Sources du Lez. (Bacescu &

Goed- In full species. Very recently Miss A. M. C. Bacescu-Mester, 1964). the same region, we

makers discovered another aberrant form within find a member of the Echinogammarus pungens-

the drainage system of the river Herault. Since group, viz. E.thoni, likewise a species whose dis- the this continuous distribution identity of form, whose morphology re- area is restricted to, geolog-

sembles somewhat the G. is not old viz. Dalmatia Spanish ibericus, ically spoken, very regions and

yet solved, it has been left out of this discussion. Herzogovina (Yugoslavia) and the french depar-

The development of these three forms, two of tements Herault and Gard (Stock, 1968).

them endemic to this departement, is not so sur- S'nce several different forms of the G. pulex-

since know that this of France found in such limited and since prising, we part is, group are a area,

a old one. Its old the differences geologically spoken, very geolog- morphological are usually very

ical age is reflected in the presence of many small, the salient differences between the various

endemic insects and other forms aquatic aquatic organ- of G. pulex and G. monspeliensis are reca-

isms (Harant & Jarry, 1963), and of an endemic pitulated in table 111.

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Received: 29 May 1972. 42 - 1972 BIJDRAGEN TOT DE DIERKUNDE, (2) 189

based than 100 Map I. Distribution area of Gammarus pulex gallicus Karaman, 1931, upon more samples. 190 S. PINKSTER - GAMMARUS PULEX-CROUP

Map II. The microgeographic distribution of the various members of the Gammarus pulex-group in the

stream systems of the Herault and Lez. 42 - 1972 BIJDRAGEN TOT DE DIERKUNDE, (2) 191

aberrant form of in the Landes. Map III. Distribution area of the Gammarus pulex pulex french département