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Notice: ©1980 Taylor & Francis Group. This is an electronic version of an article which may be cited as: Nelson, W. G. (1980). Reproductive patterns of gammaridean amphipods. Sarsia, 65(2), 61-71. doi:10.1080/00364827.1980.10431474. Sarsia is available online at: http://www.tandfonline.com/openurl?genre=article&issn=0036- 4827&date=1980&volume=65&issue=2&spage=61

REPRODUCTIVE PATTERNS OF GAMMARIDEAN AMPHIPODS

W ALTER G. N E LSONl NELSON, WALTER G. 198005 31. Reproductive patterns of gammari dean amphi­ SARSIA pods. - Sarsia 65 :61-71. Bergen. ISSN 0036-4827. Patterns of reproductive parameters found among the gam mari dean amphipod crustaceans were examined qu an titatively. Highly significant positive correlations were found in pairwise comparisons of brood size, egg size, minimum size of repro­ ducti ve females, and mean size of reproductive females. Significantly higher values of minimum and mean size of reproductive females and brood size were found for comparisons of: I) winter versus summer populations of the same amphipod spe­ cies, 2) brackish-water versus freshwater and marine species, 3) species of the family Gammaridae versus the families Ampeliscidae and Haustoriidae, 4) single-brooded versus multiple-brooded species (brood size only), and 5) infaun al versus epifaunal species. Reproductive patt erns app ear to be more specific within amphipod family groupings than is tru e for some other organisms, potentiall y because of the habit at specificity of the gammaridean families examined.

W.G. Nelson, Harbor Branch Institution, Inc., RR 1, Box 196-A , Ft. Pierce, FL. 33450, USA . - Present address, Institute of Marine Biology, N-5065 Blomsterdalen, Norway .

INTRODUCTION group of infaunal and epifau nal am phipod Conside rable recent theoreti cal attention has crustaceans. This is a n attractive group to study been focu sed on factors affecting th e evolu tion because relatively abundant reproducti ve d ata of individual reproductive parameters and com­ are availa ble in th e literature, presu mably be­ posite life history stra teg ies (CHARNOV & SCHAF­ cause th ere is no la rval phase and egg size a nd FER 197 3 ; PRICE 1974; WILBUR & a l. 1974; number are easily m easured (VAN DOLAH & SMITH & FRETWELL 1974 ; TH OM PSON 197;); BIRD 1980). Gammaridean amphipods are also HIRSHFIELD & TI NKLE 1975 ; STEARNS 1976; of in terest because th ey are often major con­ SNELL 197 8). Within th e marine enviro nmen t, stitutents of a variety of mar ine (MILLS 1967 ; consid erations of re prod uctive patterns have CRO KER & al. 1975; BRENNER & al. 1976 ; NEL­ largely d ealt with the eco logical significance of SON 1979a , b) and freshwater comm u nities various types of larval d evelopment (THORSON (COOPER 196 5 ; MATHIAS 1971 ). 1950 ; MI LEIKOVSKY 1971; VANCE 1973a , b,1974; Amphipods exploit a wide variety of micro­ STRATHMAN 1974 ; U NDERWOOD 1974) a nd have habitats and include species which are epifaunal been m ostly th eoretical or qualitative in nature. free living, epifau nal tube dwellers, infaunal For the m arine crustac eans in particular, stud ies free burrowers, infaunal tube dweller s, as well are available which examine certain quantita­ as pelagic and commensal forms. A correspo nd ­ tive relationship s among reproductive para­ ingly wide variation in reproducti ve parameter s meter s, e.g. bo dy size and egg number (JENSEN is al so found within this group. Brood size may 1958 ) or egg size and embryonic development vary from I egg per brood (e.g. Seborgia minima, time (STEELE & STEELE 1973a , 1975d). H ow ever, BOUSFIELD 1970b) to nearly 500 (Gammaracan­ relatively few attem p ts have be en made to use thus loricatus, STEELE & STEELE 1976), and othe r quantitative d ata to exam ine in d etail th e re ­ parameters are equally as variable. The possi­ productive patterns of any group of m arine bilit y th erefore exists th at certain sets of envi­ crustaceans in th e sta tistical m anner used by ronmental cond itio ns may be correla ted with TINKLE & al. (1970) for th eir study of evo lu tio­ certain sets of reproductive parameters. nary strategies of reproduction among th e lizards. The presen t paper a ttem p ts to exam ine in a R ecently, VAN DOLAH & BIRD (1980) have quantitative manner th e ge neral rep roductive made a valuable con trib u tion in this d irection patterns found among th e gam maridean am ­ by com paring egg size and number in a selected phipods. Specifically, th e relationship s a mong the rep roductive pa ramet ers of brood size, egg

1 Contribu tion No. 164 of the Harbor Branch Foun­ size, m inim um size of reproductive fem ales, and dation. m ean size of rep roductive females are deter- 62 WALTER G. NE LSON SARS IA 65 (2) 1980 m ined. I n a d dition, these fa ctors are exa m ined egg , wh er eas th e numerous publications of STEELE & w ith r esp ect to w h ether sys tem a tic d ifferences STEELE ( 1969, and others) utilized len gth-l-width/Z. In order to conver t th e values given by length-l-width /Z exist between amphip ods due to d iffer en ces in to length , an em pirical for mul a (length = width + th eir h abita t sa lin ity , taxonom ic grou p, n u m ber 0.09 mm) for th e relation ship of egg length and wid th of broods per seas o n, ep ifa u n a l versu s in fa u nal was estima ted using seven species of a mphipods (A mpithoe longimana, Cymadusa compta, E lasmopus levis, lifest yl e, and seas on of the yea r. M elita appendiculata, Corophium acherusicum, Ampelisca abdita, and Lembos websteri) for wh ich extensive m ea­ MATERIAL ANDM ETHODS surements of egg length and width were avail able Data for thi s stud y were drawn from th e litera tu re. (NELSON 1978). In one report in which egg volume W here possibl e, th e following da ta were obtained for was used (STRONG 1972) length was estima ted by each sp.ecies : minimum. size of reproducti ve fem ales, utilizing th e for mula for the volu me of a sphere . mean size of reproductive fem ales, mean brood size In all cases , the data were analyzed using no n­ bro od size/body size ratio, number of broods pe; parametric sta tistics (following met hods given in So­ fem ale li.fetime, mean egg size, the salinity range of KAL & R OHLF 1969) because no a priori con clusion th e spe cies, and th e ecological habit of th e species con cerning th e normality of the data could be made. (Table I). Also, med ian va lues of reproductive paramet ers were Although no attempt was made to restrict the da ta mo re readily estim ated th an means from th e extensive base to any subset of gamm aride an amphipods most publications of STEELE & STEELE (refer to Refer ences) are shallow-water marine species from the 'north and th e non-parametri c sta tistics used only required temper ate zon e. Fou rteen families (65 species 89 a relative ranki ng of data. Pairwise correlations of re­ populat!on.s) are re p re s e n~ed in th is stud y, a l t h~ugh prod uctive parameters were calcula ted using K endalls' th e m ajority of the spe cies belongs to the fam ilies tau. Co mparisons of reproductive parameters between Gan;tm a r i ~a e and H austoriidae, T he on ly criterion groups of species found in different sali nities and for inclu sion of a species was th at information be taxonomic groupings were performed using paired available on a t least two of th e variables listed above. Wilcoxon two-sample tests. R eproductive parameters VY~e r e refer enc e.is m ade in thi s paper to th e wer e compared for sing le- versus m ul tiple-brooded fam ilies of gammandean a mphipods, only a sma ll species and for infaunal vers us epifaunal species using percentage of genera are represent ed. O nly six of th e th e Wilcoxon two-sample test. Finally, th e sign test 196 genera in . the family Gammaridae (BOUSFIELD was used for th e comparison of summer versus winter 1977), one of five genera of th e family Ampeliscid ae, reproductive parameters. and eight of nmeteen gen era of the fami ly Haustori­ idae are represented. BOUSFIELD (1978) has recently RESULTS suggested th at th e subfamily Pon toporeiinae of th e J:I au st orii~ a e . ~e ra ise ~ to fam i li ~ 1 status. I n this study, L a rger mean b rood size was sig n ific a n tly co rre­ sm ce no significant differen ces m rep roducti ve para ­ lated with I ) larger m ean size of reprodu c ti ve m eters w er~ found bet~e en th e Pontop oreiinae and femal es, 2) larger m ean egg size, a n d 3) la rger th e .subfamtly H austoriinae, th e Pontoporeiinae are ret amed as part of the H austoriidae. m in im u m size of reproductive fem ales (T a b le Rep roductive sta tus of amphipod fem ales may be 2) .L arger m ea n size of reprodu ctive females readily determined from th e presen ce of seta e on th e w a s also sig n ifican tly co rrela te d with I ) larger oostegites or brood plates which form th e brood pouch. m inim u m size of reproduc ti ve fem ales, a n d 2) Fo r th e sake of simplicity, the sm allest size recorded egg size, w hile la rger minimum size of repro­ for a fe m ~l ~ with s~ t ae on th e oostegites was designat­ ed t~ e minimum SIze of reproduc tive fem ales for th a t ducti ve females was sig n ifican tly cor rela te d species ra ther th an using th e size a t which 50 % of with m ean egg size (T a b le 2) . all fem ales are found to be m at ure as utilized by R eprodu ctive fem ales had a larger minimum STEELE & STEELE ( 1969). M ean brood size pe r size , a larger m ean size, a nd a larger m ean b rood fem ale was defined as th e mean number of eggs per fem ale for all fem ale sizes. In cases where monthly size in winter versus su m mer po pulati ons of the or seasonal values of mea n size of mature females or sa me sp ec ie s (T a b le 3). No systematic tren d was mean brood size per female were given , grand means observed for those few species w h ich possessed over all month s or seasons were ca lculated . H owever larger values of these p arameters in su m mer than for the calculati ons of pairwise correla tions of vari­ abies (T able 2), indi vidual va lues were used thus w in te r . resulting in sample sizes greater than the 89 entries Significan tly la rger r eprod uctiv e females (bo th of T able I. m in im u m a n d m ean size) w ere found in bra ck­ Because of general difficulties in determining the ish-water « 20 %0) sp ec ies than fo r amp h ipod e.xact number of broods produced per female per life­ time, number of brood s was considered to be either on e species found in eit her fully marine or fresh w a ter or more than one and was based on origin al papers environ ments (T a b le 4). H ow ever , n o sig n ifica n t ra the; ~ han com!,Jendia such as BOUSFIELD (1973) . In differences occur in either pa rameter b etween descnbmg egg SIze, several d ifferent meth ods have m arin e and fr eshwater species . Brood size is been used ~n t~ e litera tu re, requiring som e m easure of s ta nda rd I~a tIO n for th e present comparison. M any sig n ifican tly g rea ter in bra ckish-w a ter a m ph ipod authors provide onl y th e length of the long axis of th e species than m arine specie s which in turn have SARSIA 65 (2) 1980 REPRODUCTIVE PATTER NS OF GAMMARIDEAN AMPHIPODS 63

Table I. R eproductive and habitat dat a for gammaridean arn ph ipods. N- multiple-brooded, S - single­ brooded, F - freshwater, B- brackish water, M- marine, E - ep ifaunal, I - infa unal, P - pelagic.

Specie s

Gamma ridae 1) Chaelogammarus stoermsis• . •• • . 27. 1 M E W ales Ch eng (1942 ) 2) Chaelogammarus stoermsis . 6.0 6.0 13.0 2.17 N 0.49 F E New Brunswick Steele & Steele (1975a) 3) Crangonyx gracilis• ... . • •. . . .. 5.0 7.3 33.3 3.15 N F E Eng land Hynes (1955) 4 ) Crangonyx richmondensis 11.0 13.8 43.0 3.10 S 0.54 F E Ca nada Sprules ( 1967) 5 ) Eulimnogammarus obtwatus . 12.0 12.0 1.00 M E W ales Cheng (1942) 6) Eulimnogammarus obtusatus . 8.0 12.6 9.0 0.71 N 0.67 M E England Sheader & Chia (1970) 7) Eulimnogammarus obtusatus . 7.5 10.5 7.0 0.66 N 0.68 M E New found la nd Steele & Steele (1970a) 8) Gammarellus angulosus . 8.8 13.0 30.0 2.30 N 0.7 M E Newfoundland Steele & Steele (1972h) 9) Gammarel/us homari 17.0 S 1.22 M E N ewfoundl and Steele (1972 ) 10) Gammaracanthus loricafus . 30.0 40.3 407.0 10.10 S 0.9 M E Arctic, Canada Steele & Steele (1976) I I) Gammarus crinicornis . 7.8 9.1 32.5 3.60 0.57 M E Provence, France Dumay (1973) 12) Gammarus duebmi . 8.0 10.5 17.9 1.70 N 0.68 B E England H ynes (1954 ) 13) Gammarus duebeni . 8.0 10.9 19.7 1.80 N 0.72 F E England H ynes (1954) 14) Gammarus duebeni . 11.0 18.1 1.64 M E Wales Ch eng (1942 ) 15) Gammarus duebeni . 11.0 14.0 29.0 2.07 N 0.60 B E Newfoundland Steele & Steele (1969 ) 16) Garnmarus duebeni . 10.5 13.3 36.7 2.76 N B E Polan d ] azdzewski (1973) 17) Gammarus[asciatus . 6.2 8.0 16.7 2.09 N F E Ohio Clemens (1950 ) 18) Gammarusfasciatus . 5.0 9.3 29.3 3.15 N F E En gland H ynes (1955 ) 19) Gammarus inaequicauda . . • •. .. 5.0 8.6 29.3 3.40 B E Poland ] azdzewski (19 73) 20 ) Gammarus lacustris . 9.0 11.8 21.8 1.84 N F E En gland H ynes (1955 ) 2 1) Gammarus lacustris . 7.0 19.5 N F E Ont ario H ynes & Harper (1972) 22) Gammarus Iaumnciamu . 5.3 7.5 25.0 3.33 N 0.45 M E Newfoundland Steele & Steele (l 970b) 23 ) Gammaru s locus/a . 6.0 9.4 40.2 4.30 B E Poland ] azdzewski ( 1973) 24 ) Gammarus palustris . 4.0 5.8 6.4 1.10 N M E M aryland V an Dolah et al. (1975) 25 ) Gammarus pseudolimnaeus 8.0 44.3 N F E Ont ario Hynes & Harper (1972) 26 ) Gammarus pul ex pulex .• . . . . .• 6.0 8.8 15.5 1.76 N F E En gland Hvnes (1955) 27 ) Gammarus subtypicus . 9.3 11.3 21.5 1.90 0.48 M E Proven ce, France Dum ay ( 1973) 2R) Gammarus tigrinus . 6.1 10.0 35.0 3.50 N 0.50 B E New Brunswick Steele & Steel e (1972a) 29 ) Gamma rus z addechi . 7.0 42.0 B E Germany Kinne (1961) 30) Gam marus za ddechi . 6.0 9.1 33.7 3.70 B E Poland ] azdzewski (1973) 3 1) Lagunogammarus oceanicus •. • . . 12.7 16.0 60.0 3.75 N 0.60 M E Newfoundland Steele, V.]. & Steele ( 1972) 32 ) Lagunogammorus oceanicus . 130 B E Polan d ] azdzewski (1973) 33) Lagunogammarus salinus . 7.5 B E Poland ] azdzewski (1973) 34) l. agunogammarus setosus 13.5 16.8 45.0 2.68 S 0.74 M E Newfoundland Steel e, V.] . & Stee le (1970) 35 ) Lagunogammarus unlkitzkii . . .. 20.0 26.0 150.0 5.77 S 0.78 M E Newfoundla nd Steele &Steele (1975a ) 36 ) M arinogammarus [inmarchicus . . 10.5 15.0 28.0 2.07 N 0.55 M E Newfoundland Steele & Steele (1975a) 37 ) Marinogammarus marinus . 21.7 M E W ales Ch eng (1942) 38) M arinogammarus marinu s . 10.0 15.0 19.0 1.27 N M E Neth erlands Vasbloom (1969 ) 39) Mucrogammarus mucronatus . . • . 3.5 5.5 12.0 2.18 0.4 8 M E New Brunswick Stee le & Steele (1975a) 40) N iphargus aquilex aquilex . .. . . 4.0 5.0 2.9 0.57 F E Eng land Gledhill & Ladle (1969) Haustor iidae 41) Acanthohaustorius millsi . 3.5 4.5 6.3 1.40 S M I Massachusetts Sam eoto (l 969b) 42 ) Acan/hohaustorius sp . 3.2 5.2 M I Georgia Croker ( 1967) 43) B a/hyp oreia elegans . 2.9 3.5 3.5 1.00 M I En gland Fincha m (197 1) 44 ) Bathyporeia guilliamsonia . 7.2 22.0 3.06 M I France Salvat (196 7) 45 ) B athyporeia nana • ...... 2.0 2.4 2.4 1.00 M I England Fincham (1971) 46) B athyporeia pelagica 4.8 5.6 7.5 1.33 N M I France Salvat (1967) 4 7 ) B a/hyporeia pelagi ca . 3.4 4. 1 3.7 0.90 M I En gland Finch am (197 1) 48) Bathyporeia pelagica . 5.2 6.4 1.23 N 0.59 M I En gland Fish ( 1975) 49) B a/hyp oreia pilosa ..• ...... 4.0 5. 1 5.0 0.98 M I France Salvat (1967 ) 50 ) Bathyporeia pilosa . 4.4 4.7 1.06 N 0.61 M I Wales Fish (1975) 5 1) Ba /hyporeia pilosa . 4.4 5.2 1.18 N M I Englan d Fish (1975) 52 ) Bathyporeia pilosa . 5.3 7.3 1.37 N M I Englan d Fish (1975 ) 53) Bathyporeia sarsi ...... • ...... 4.0 5.1 5.0 0.98 M I France Sa lva t (196 7) 54) Ba thyporeia sarsi . 3.5 5.2 7.2 1.38 M I Englan d Ladl e (1975) 55 ) H austorius arenarius . . •...... 5.0 7.2 15.0 2.08 S M I Wissant, France Sa lvat ( 1967) 56) H austorius arenarius . 6.0 M I Ar ach on , France Salvar (1967 ) 57 ) Haustorius canadensis . 1\,\ S M I Massachusetts Sameoto (1969a) 58) Haustorius sp , . . 5.7 5.9 S M I Georgia Croker (1967) 59 ) Lepidaa ylus dysticus . 3.3 4.4 N M I Georgia Croker (1967 ) 60) N eohaustorius biarticulatus . 4.5 7.0 N M I Massachusetts Sam eoto (l 969a) 61 ) N eohauslorius schmitzi . 2.6 3.0 S M I Georgia Croker (1967) 6 2) N eohaustorius schmitzi . 3.0 3.7 5.8 1.56 S M I North Carolina Dexter (1971) 63) Parahaustorius longimerus . 4.4 6.5 5.3 0.81 S M I Massachusetts Sa meoto (l969b) 64) Parahaunorius Iongimerus . .. .• 5.7 8.9 M I Georgia C roker (1967) 65 ) P rotohaustorius deichmanae .. . • • 3.0 3.8 3.2 0.84 N M I Massachusetts Sameoto (l969b) 66 ) Urot hoe breuicom is . 4.3 6.2 18.8 3.03 N M I France Sa1vat (1967 ) Ampeliscidae 67 ) Ampelisca abdit o . .. . • ...... 4.8 5.4 26.0 4.80 S 0.4 3 M I Massachusetts M ills (1967) 68 ) Ampelisca abdit a . 2. 1 5.3 13.7 2.68 S 0.43 M I North Carolina Nelson (1978 ) 69) Ampelisca breoicomis . 7.9 10.0 12.9 1.29 M I France K aim-M alka (1969) 70) Ampelisca hrevicornis . 12.0 13.5 23.0 1.70 S M I Germa ny K lein e t a1. (1975) 71) Ampelisca macrocephala . 17.0 60.0 3.52 S M I Denmark Kannew orlf (1965 ) 72 ) Ampelisca vadorum . 6.8 8.1 32.0 3.95 S 0.56 M I Massachusetts Mills (1967 ) 64 WA LTER G. NE LSON SARSIA 65 (2) 1980

Table I (contd)

Species

Ampi tho ida e 73 ) Ampithoe longimana ...... • .. 2.4 5.8 9.4 1.62 N 0.42 M E North Carolina Nelson (1978) 74 ) Cymadusa compta . 3.5 5.8 13.5 1.6 N 0.41 M E No rth Carolina Nelson (1978) Ao ridae 75 ) Lembos ux bsteri . 2.5 4. 7 8.0 1.7 N 0.43 M E Nor th Carolina Nelson (1978) Calliopiid ae 76 ) Calliopius laevisculus. . 5.6 11.5 65.0 5.65 N 0.48 M E Newf oundland Steele & Steele (1973b) Corophiidae 77) Corophium acherusicum . 1.9 3.0 7.9 2.63 N 0.34 M E Nor th Carolina Nelso n (1978) H yall eli dae 78 ) Hyallela azuca . 4.8 6.7 17.0 2.53 N 0.38 F E Or egon Strong (1972) 79 ) Hyallcla azteca •...•• ...... 4.9 5.9 18.0 3.05 N 0.32 F E O regon Strong (1972) 80 ) Hyalicla aeuca . 3.3 4.3 8.0 1.86 N 0.30 F E Oregon Strong (1972) 8 1) Porhyallcla pielschmoni 5.5 8.0 1.45 N 0.44 M E Mad agascar Steele (1973) Ischyroceridae 82 ) J assa faleala . 3.6 4.6 25.6 5.56 N 0.32 M E No rth Ca rolina McGovern (U npubl.) lIIelitidae 83 ) Elasmopus levis . 2.8 4.3 4. 7 1.09 N 0.44 M E Nor th Carolina Nelson (1978) 84 ) M elita appendiculala . 2.9 3.8 5. 1 f. 34 N 0.41 M E Nor th Carolina Nelso n (1978) Oedicerotidae 85) Poniocrates altamirinus ...... 3.4 4.0 4.8 1.20 M England Fin cham (1971 ) 86 ) Pontccrates arenarius .•...... 2.5 3.2 3.1 0.96 M Eng land Fin cham (1971) Phoxo cephalidae 87 ) T richophoxus epistomus 2. 1 3.4 M No rth Car olina Nelson (1978) P on togen eidae 88) Bovallia gigantica 40.0 45.1 108.0 2.39 S 1.53 M E Ant arctic Thurston (1968) Stegocephal idae 89) Stegocephalus inf lalus ...... • . 23.0 28.0 28.0 1.0 N 1.75 ME(P) Arctic Steele (1967)

T able 2.Results of pairwi se comparisons of repro­ Table 3. R esults of comparisons of th e magni tudes of ductive parameters for all available data on gam­ reproductive variables between summer and winter maridean amphipods. populations of the same amphipod species.

V N Prob­ .;;; Variable Winter > SaI?ple summe r size ability Variable level

Minimum size of reproductive females 23 25 0.0 1 M ean size of reproductive females 0.40 94 0.00 1 Mean size of Mean brood size reproductive females 22 30 0.05 M ean size of reproductive females 0.42 41 0.001 Mean brood size 22 25 0.01 M ean egg size M ean size of reproductive females 0.47 83 0.001 Minimum size of reproductive females significantly larger broods than freshwater spe­ cies (T able 4). Minimum size of reproductive females 0.68 40 0.00 I M ean egg size Examination of reproductive parameters among the three families of amphipods for which Minimum size of reproductive females 0.40 102 0.00 I sufficient information is available indicates that M ean brood size significant differences between families do exist. M ean brood size 0.31 41 0.0 1 M inimum size of reproductive females is signifi­ M ean egg size cantly greater for species of the fami ly Gamma- SAR SIA 65 (2) 1980 REPRODU CTIVEPATTERNS OF GAM MAR IDEAN AMPH I PO DS 65

T able 4. R esults of comparisons of mean va lues (± I standard deviation ) of reproductive variables between species found in habitats of differing salinity. Numbers beside vertical bars indicate th e significance level a t whi ch the two varia bles being compared a re significantly different. n.s. - not- significant. Sample M ean Probability Varia ble Salini ty size (± I s.d.) level

M inimum size of reproductive females (mm) Freshwater 13 6.3 ( 2.1) ...... ] n.s. Marine 53 7.3 ( 7.2) ] 0.05 Brackish 10 8.0 ( 2.6) ] 0.05

M ean size of reproductive females (mm) ...... Freshwater 12 8.2 ( 2.8) ] n. s. Marine 53 9.4 ( 8.5) ] 0.05 Brackish 8 10.7 ( 2.1) ] 0.05

M ean brood size ...... Freshwater 13 21.6 (12.0) ] 0.05 Marine 6 1 25.4 (55.2) ] 0.05 Brackish 9 33.0 ( 7.6) ] 0.0 1

Table 5. R esults of th e comparison of m ean values (± 1 standard deviation) of reproductive va riables between amphipod families. Numbers beside vertical bars indicate significance levels at which th e two families are significan tly differ ent. n.s . - no t-significant. Amphipod M ean Probability Variable Sa,?ple family size (± 1 s.d.) level

Minimum size of reproductive fem ales (m m) ...... Haustoriidae 20 4.5 ( 2.0) ] n.s. Ampeliscidae 25 6. 7 ( 3.7) ] 0.05 Gammaridae 35 9. 1 ( 5.2) ] n .s. M ean size of reproductive fem ales (mm) ...... H austo riidae 18 1. 3 ~ 5.0 ( ] 0.01 Ampeliscidae 6 9.9 ~ 4.6 ] 0.05 Gammaridae 31 12.2 6.6) ] 0.01

M ean brood size ...... H austoriid ae 25 8.7 ( 7.6) ] 0.001 Ampeliscidae 6 27.9 (17.3) ] 0.001 Gamm arid ae 37 40.3 (66.4) ] 0.001

Brood size/body size ratio ...... H austo riidae 18 1.43 ( 0.7) ] 0.005 Ampeliscidae 6 2.97 ( 1.4) ] 0.001 Gam marid ae 3 1 2.76 ( 1.8) ] n.s,

Table 6. Comparison of reproductive variables between singl e- and multiple-brooded amphipod species. n. s. - not significant. Number V ariable of broods Sample Mean Probability per female size (± 1 s.d .) level

Minimum size of reproductive females (m m) 1 18 10.4 ( 10.6) n.a] > 1 36 6.6 ~ 3.9 ) M ean size of reproductive females (m m) ...... 1 15 14.5 13.0) n.s. > 1 39 8.5 ( 4.9) M ean brood size ...... 1 17 56.5 (98.7) 0.001 > 1 43 18.5 ( 14.3) M ean egg size (mm) ...... 1 9 0.79 (0 . 3 7 ~ 0.001 > 1 24 0.55 (0.28 66 WALTER G. NELSON SARS IA 65 (2) 1980

Table 7. Comparison of reproductive variables between infaunal and epifaunal species.

M ean Variable H abitat SaI?ple Probability size (± I s.d .) level

Minimum size of reproductive females (mm) . . . .. Infaunal 25 4.5 ( 2.I) 0.0005 Epifaunal 45 8.6 ( 6.9) M ean size of reproductive females (mm) ...... Infaunal 26 5.9 ( 3.2) 0.0005 Epifaunal 42 II.2 ( 8.4) M ean brood size ...... Infaunal 33 10.8 (I1.5) 0.0005 Epifaunal 47 36.5 (61.0) Brood size/b ody size ratio ...... Infaunal 28 1.76 (1.0) 0.01 Epifaunal 38 2.72 (I. 72) ridae than for th e H austoriidae, while th ere are vidual spec ies or groups of species (e.g. SAMEOTO no significant differen ces between th e Ampelis­ 1969a, b ; DEXTER 1971 ; FISH 1975 ; STEELE & cidae and either th e Haustoriidae or Gammar­ STEELE 1975c). Both lin ear (STEELE & STEELE idae (T able 5). Mean size of reproducti ve 1969, 1973b , 1975b) and curvilinear (SPRULES females and brood size are both significantly 1967; VAN D OLAH & al. 1975) regression s have gr eater for species of th e Gammaridae than for been used to describe this particul ar relationship. species of th e families Am peliscidae and Hau­ J ENSEN (1958) also described linear relationships storiidae. These two parameters are also signifi­ between brood size and bod y size in a variety of cantly greater for th e Ampeliscidae than for the Decapoda, Isopoda, M ysidacea , and Cumacea . Haustoriidae. H owever, although brood size/ Therefore, it is probable th at th e pattern of in­ body size ratios for the Ampeliscidae and Gam­ creased brood size with body size is general maridae are significantly gr eater than this ratio through ou t the Amphipod a as well as th e M ala­ for the Haustoriidae, th ey are not significan tly costracan Crustacea. different from one ano the r. The pattern of correlation between body size Minimum size of reproducti ve females and and brood size across a variety of spec ies in th e mean size of reproductive fem ales do not differ ga mmaridean amphipods differs markedl y from significa ntly between single- versus multiple­ th at found for birds and liza rds, in which th ere brooded species, although sing le-brooded spec ies is no apparent correlation between th ese factors tended to be larger th an multiple-b rood ed species either intraspecifically or between species (TINK­ (T able 6). Both mean brood size and egg size LE & al. 1970) ; altho ugh a significant positive are significantly greater in single-broo de d versus relationship does exist between minimum size of multiple-brooded species (T able 6). females at maturity and clutch size for lizards. For all comparisons of reproductive para­ The increased importance of body size as a meters, epifaunal spec ies possessed significantly correla te of brood size for crustacean groups may grea ter values than did infaunal spec ies (T able arise from limits placed on brood volume by th e 7). In most cases, values for epifaunal species are presence of an exoskeleton. In the polych aete s, more than 2 times grea ter than for infaunal spe ­ which lack suc h an exoskeleton, th e across spe­ cies. Mean brood size for epifaunal species is cies relationship of brood size and body size is nearly 3 tim es greater th an for infaunal spec ies not as important (K . Fauch ald pers. comm n). (T able 7). The brood size/bo dy size ratio is also The positive relationship between brood size significantly greater for epifaunal amphipod spe­ and egg size indicates that larger broods also cies than for infaunal amphipod spec ies. have larger eggs, altho ugh for a constant female size th ere must gene rally be an inverse rela­ tionship between egg size and brood size (STEE­ DISCUSSION LE & STEELE 1975 ; VAN D OLAH & BIRD 1980). The ob served correlation s amo ng measures of The positive relationship presumably arise from body size (minimum and mean size of repro­ th e observed tendency of larg er amphipod spe­ ductive females) and measures of reproductive cies to have both larger broods and larger eggs outpu t (mean brood and egg size) for th e diverse than smaller spec ies, regardless of other factors. assemblage of amhipod species conside red are A decrease in minimum or mean size of re­ similar to th ose reported for a number of indi- productive females or of brood size in summe r SARSIA 65 (2) 1980 REPRODUCTIVE PATTERNSOF GAMMARIDEAN AMPHIPODS 67

vers us winter populations of amphipods has been in relation to salinity changes are some what previously no ted (STEELE & STEELE 1969, 1973b ; ambiguous (DORGELO 1973 ; DENNERT 1974), DEXTER 1971 ; FISH 1975 ; NELSON 1978). The and do not offer a clear mechanism for producing significant differences observed here indicate that the observed patterns . It is likely, however, that suc h decreases are fairly general among amphi­ brackish environme n ts are more uncertain than pod s, although by no means universal. Three freshwater or marine ones and it is often ad­ factors have been proposed as possibly genera­ vantageous to maximize reproduction in un­ ting decreases in amphipod female size and certain envi ronments (STEARNS 1976). fecundity in summer populations : 1) tempera­ An important finding of the present analysis ture, 2) decreases in food supply, and 3) pred a­ is that significant differen ces in reproduc tive tion. KI NNE (1959 ) dem onstrated that above parameters occur between the three ga mmari­ water temperatures of 18° C, egg number of dean amphipod families compared . The Gam­ Gammarus duebeni sharply decreased . H igher maridae, a family of ep ifaunal spec ies, possess summe r wa ter temperatures may result in in­ significantly larger females and larger broods creased metabo lic maintenance costs which only than the Ampeliscidae, a tube-dwelling infauna1 allow a decreased expenditure of energy for egg family. In tu rn, th e Ampeliscidae have signi­ product ion. This mechanism was suggested by ficantly larg er fem ales and broods th an th e SAWCHYN & H AMMER (1968) to explain signifi­ H austoriidae, a family of infaunal burrowers ca nt negative correlations between temperature in sand. Comparisons of the brood size/body and brood size among copepods, and is support­ size ratios for th ese species indicate th at the ed by the seasonal energy budget of the amphi­ smaller brood size of ampeliscids relative to pod Hy alella azteca constructed by MATHIAS gammarids is largely due to the smaller female (1971). VAN D OLAH & BIRD (1980 ) present size of ampeliscids, while th e significantly smaller evide nce that egg size decreases within seven broo d size of the haustoriids is not totally due amphipo d species from high to low latitu des, to differences in female body size. which may also be a reflection of tem perature­ The results of the present broadly base d com­ related metabolic considerations. FISH & PREECE parison between infaunal and ep ifaunalamphi­ (1970) suggested th a t differences in food levels pods largely ag ree with the concl usions of VAN may resul t in fecundity differen ces for th e haus­ D OLAH & BIRD (1980) in th at epifaunal species toriids Baihyporeia pilosa and B. pelagica. H ow­ possess significantly larger broods than infaunal ever, a precise examination of the interactions species (T able 7) . Epifaunal amphipod species between food levels and amphipod fecundity has have been shown to be generally more subject not yet been carried out. Pred ation possibly pl ays to morta lity due to predation th an infa unal a more direct role on minimum size and mean species in at least one ha bitat examined (NELSON size of reproductive females th an on fecundity. 1979a, b), and the re are suggestions that thi s STRONG (1972) demonstrated that minimum size may be true of soft-bottom habitats in general of mature females is lower in amphipod popu­ (RICHARDS 1963). Such a mo rtality regime lations permanen tly subjected to predation as suggests that reproductive effort for epifaunal compared with predator-free populations. H ow­ spec ies sho uld be proportionally greater th an ever, it has not yet been shown that predation for infaunal spec ies (H IRSCHFIELD & T INKLE can affect minimum size of reproductive females 1975). Greater rep roductive effor t is indeed within a single season, although decreases in indicated by the sign ifica ntly greater brood size mean size of reproductive females within a sea­ per unit body length of epi fau nal versus infaunal son due to predation have been shown by COOPER species.H owever, VAN DOLAH & BIRD (1980) (1965) an d NELSON (1978) . Therefore, although analysed clutch volume for the two types of spe­ temperature differences may be of primary im­ cies for females of the same body size and found portance in generating differences between sum­ no significant differen ces. T he differences in mer and winter populations, othe r factors may results of the two methods may be due to dif­ be locall y important. ferences in egg size in the two groups of species T he significantly larger val ues of reproductive (demonstrated by VAN D OLAH & BIRD 1980), parameters for brackish-water spec ies as com­ as well as the fact that they compared clutch pared to both marine and freshwater species volume for th e larger size classes of infaunal were unanticip ated . Comparisons of metabolic spec ies and th e smaller size classes of epifaunal costs for amphipods from these th ree habitats species. If rep roductive effort increases with age 68 WALTER G. NELSON SARSIA 65 (2) 1980

(= size) in amphipods, as sho uld be generally dance of eight haustoriid spec ies over a 10 year true (WILLIAMS 1966) and is suggested by th e period. During planktonic periods, ampeliscids curvilinear relationships between body size and may be exposed to predation by fishes, a situa­ brood size found by some authors (SPRULES tion more allied to that of epifaunal species. 1967 ; VAN DOLAH & al. 1975), th en an estimate This may explain th e lack of any significant of th e mean reproductive effort over all body difference in the brood size of Ampeliscidae and sizes (such as mean brood size/mean body size Gammaridae (T able 5). ratios) may be more appropriate. That mean brood size is significan tly greater The fact that epifaunal amphipods have sig­ in single-broo de d versus multiple-brooded spe­ nificantly larger minimum and m ean sizes of cies agrees with th e prediction of gr eater repro­ reproductive females than infaunal species in­ ductive effort for single-brooded spec ies made by dicates that selective factors in th e two habitats th e th eory of 'r and K selection' (summarized by may be operating directly on bod y size. The STEARNS 1976). H owever, th e concurrent greater differences in body size ob served among th e egg sizes of single-brooded versus mul tiple­ three amphipod families examined also appear brooded spec ies differs from the usual 'large to correlate with th e epifaunal versus infaunal clutch-small eggs' predi ctions of thi s model. habits of th ese families. In addition to the few One factor to account for thi s is that many families considered here, th e body size of in ­ singl e-brooded species are infaunal and it has faunal amphipod families tends to be generall y been suggested that larger eggs (and hence smaller than for epifaunal families (BOUSFIELD larger juveniles) are a necessity for the surv ial 1973). Reduced infaunal bod y size may be a of some infaunal species in coarse-grained sand result of adaptations for sand burrowing and environments (VAN DOLAH & BIRD 1980 ). feeding on interstitial microflora and micro­ Several general reproductive patterns appear fauna with a concommitant decreased need for to be presen t amo ng th e amphipod spec ies ex­ mobility. amined. One gr oup, consisting of high -latitude The presence of th e exoske leton in th e Amphi­ species (Gammarus wilkitzkii , Bovallia gigantica, poda may tend to lock together a suite of struc­ Gammaracanthus loricatus), tends to have delayed tures which are then constrained to change maturity, single broods, and large clutch es of together in th e transition from one typ e of large eggs. Delayed maturity, un like th e case organizational plan to another (V ERMEIJ 1973) ­ for birds and lizards (T INKLE & al. 1970), is i.e, from epifaunal to infaunal. Thus, th e rela­ almost certainly a result of low gr owth rates tionship of brood size and egg size with bod y caused by cold water temperatures, and may size may be con strained by such considerations. allow better timing for th e release of- a single Within th e general constraints imposed by large brood wh en food conditions are optimal habitat on body size, differences in mortality (STEELE & STEELE 1975c). Other patterns tend regimes (NELSON 1979a, b) may still offer a to closely follow taxonomi c groupings. The haus­ possible mechanism for th e observed differences toriids ten d to have singl e broods, mature at in brood size (this paper; VAN DOLAH & BIRD small sizes, and produce small brood s of rela­ 1980) and egg size (VAN DOLAH & BIRD 1980) tively large eggs (for egg size see BOUSFIELD between epifaunal and infaunal species. Of 1970a ; V AN DOLAH & BIRD 1980). Gammarids interest in this respect are infaunal tube-dwelling tend to have multiple broods and produce larger ampeliscids which occupy an intermediate posi­ broods of smaller eggs (for egg size see VAN Do­ tion in terms of bod y size and brood size between LAH & BIRD 1980). The ampeliscids hav e an th e burrowing haustoriids and epifaunal gam­ intermediate pattern with single broods, and marids. Ampeliscids retain a greater need for relatively large clutch es of intermediate-sized mobility than haustoriids since th ey enter the eggs (for egg size see VAN D OLAH & BIRD 1980 ). plankton in order to mate (M ILLS 1967), whereas The degree to which rep roductive patterns in the haustoriids apparently do not (BOUSFIELD amphipods follow taxonomic lin es is much 1970a). These differences in relative epifaunal gr eater than for birds and lizards wh ere strategies exposure are partially documented by th e re­ cu t across taxonomic divisions (TINKLE & al. lative frequency of th e two families in long­ 1970), and m ay be due to gr eater habitatfidelity term plankton samples (WILLIAMS & BYNUM of amphipod families. 1972) where the abundance of two Ampelisca Several important aspects of reproductive spec ies was 3 times greater than th e total abun- patterns in amphipods cannot ye t be treated SAR SI A 65 (2) 1980 REPRODUCTIVE PATT ER NS O FGAMMARIDEAN AMPH IPODS 69

because of lack of data. Despite increased taxo­ CHENG, C. 1942. On th e fecundity of some gammarids. nomic information, almost no life history data - J. mar. bioI. Ass. U.K. 25 :467--475. CLEMENS, H.P. 1950. Life cycle and ecology of Gammar­ are available for tropical amphipod species. us fasciatus Sa y. - Ohio State Univ., Contr. Franz j I ndication s of intraspecific variation in repro­ Theodore Stone Inst, Hydrobiol. 12: 1-61 . ductive parameters with latitude are available COOPER, W.E. 1965. Dynamics and production of a (FISH 1975; STEELE & STEELE 1970a, b; VAN natural population of a freshw at er amphipod, Hyalella azteca. - Ecol. Monogr. 35 :377- 394. DOLAH & BIRD 1980), but no detailed intra­ CROKER, R .A 1967. Niche diversity in five sympatric specific study, either with many local popula­ species of intertidal amphipods (Crus tacea: tions or geographically, has yet been conducted . Haustoriidae) - Ecol. Mon ogr. 37 :173-200. Standardization of the reproductive parameters CROKER, R .A, R .P. HAGER & KJ. SCOTT 1975. Macroinfauna of northern New England ma­ measured in amphipod life-history studies to rine sand. II. Amphipod dominated commu­ include size at onset of reproduction (WENNER nities. - Can. ]. Z ool. 53 :42-5 1. & al. 1974), mean size of reproductive females, DEN NERT, H .G . 1974. Tolerance differences and in­ mean brood size, and mean egg size would also terspecific competition in three members of th e amphipod genus Gammarus. - B ijdr. D ierk. be an improvem ent. 44 :83-99. The information presented here provides cor­ DEXTER, D.M. 1971. Life history of th e sandy-b each relations between environmental factors and amphipod Neohaustorius schmitzi (Cru stacea : reproductive patterns which should be useful Haustoriidae). - Mar. Bioi. 8:232-237. DORGELO, J . 1973. Comparative ecophysiology of in identifying trends of potential in terest. 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