]. mar, biol. Ass. U.K. (1994), 74,211-223 211 Printed in Great Britain

GENETIC VARIATION, SYSTEMATICS AND DISTRIBUTION OF THE VENERID CLAM CHAMELEA GALLINA

THIERRY BACKELJAU, PHILIPPE BOUCHET*, SERGE GOFAS* AND LUC DE BRUYN+

Koninklijk Belgisch Instituut voor Natuurwetenschappen, Afdeling Malacologie, Vautierstraat 29, B-1040 Brussels, Belgium. ‘Muséum National d'Histoire Naturelle, Laboratoire de Biologie des Invertébrés Marins et Malacologie, 55 Rue de Buffon, F-75005 Paris, France. TJniversiteit Antwerpen, Departement Biologie, Groenenborgerlaan 172, B-2020 Antwerpen, Belgium

Two morphotypes of the venerid bivalve Chamelea gallina (L.), viz. C. gallina s.s. and C. striatula, were electrophoretically compared at seven polymorphic enzyme loci. In three populations from the Ría Formosa (southern Portugal), both morphotypes occurred sympatrically. Analyses of genotype frequencies in these mixed populations revealed departures from Hardy-Weinberg expectations at nearly all loci. These deviations were mainly attributable to a Wahlund effect, caused by mixing the two morphotypes. Nei's mean unbiased genetic distance between the two forms was D=1138, while the mean genetic distances between populations within morphotypes were D=0 083 in C.gallina s.s. and 0=0-229 in C.striatula. It is therefore concluded that C. gallina and C. striatula are reproductively isolated (biological) species, the geographical distribution of which is outlined.

INTRODUCTION

Chamelea gallina (Linnaeus, 1758) is an infaunal venerid bivalve, which is common in shallow water sand or mud habitats along the European coasts. Although the species is commercially exploited in the Mediterranean (e.g. Froglia, 1975), its taxonomy is still confused. There are three opinions about this issue. The first regards C. gallina as a single, widely distributed, polymorphic species (e.g. Dodge, 1952). The second assumes that C. gallina is a complex of two very similar, yet distinct, species, viz. the Mediterra­ nean C. gallina sensu stricto and the Atlantic C. striatula (Da Costa, 1778) (e.g. Spada & Maldonado Quiles, 1974). The third opinion relies on the apparent geographical separa­ tion of the two taxa to give them subspecific rank (e.g. Van Aartsen et al., 1984). In all cases the issue has been mostly a matter of opinion, the more recent papers quoting older ones without adding new evidence. The present study was prompted by the observation that C. gallina and C. striatula occur sympatrically in the Ría Formosa, southern Portugal. The two morphotypes differ by the outline of the shell (more pointed posteriorly in C. striatula), and by the shape and number of the concentric ridges (low, often bifurcated, 'fingerprint-like' ridges in C. gallina, versus acute, more numerous and rarely bifurcated ridges in C. 212 T. BACKELJAU, P. BOUCHET, S. GOFAS A N D L. DE BRUYN

Figure 1. Left valves of (A-C) Chamelea gallina and (D-F) Chamelea striatula from the Ría Formosa.

A Chamelea gallina

5 mm

r \ B Chamelea striatula Ci/iîM WWW)

Figure 2. Details of the siphons of (A) Chamelea gallina and (B)Chamelea striatula in the Ría Formosa. GENETIC VARIATION IN CHAMELEA GALLINA 213 striatula) (Figure 1). The lunula of C. gallina is heart-shaped and truncated towards the apex; that of C. striatula is more leaf-shaped. The two morphotypes can also be distinguished by their siphons. In C. gallina they are short, stout and mottled with yellow and violet dots, while the blunt tentacles are covered by orange spots which are lacking elsewhere (Figure 2). This type of siphon is similar to that figured by Amouroux (1980) for specimens from Banyuls, French Medi­ terranean. The siphons of C. striatula, on the contrary, are longer, more slender, and completely covered by yellow and orange spots. The tentacles are colourless. The palliai sinus reflects the differences in siphonal morphology for it is deeper in shells of C. striatula. We conducted an electrophoretic analysis of C. gallina sensu lato in the Ría Formosa to test whether the two morphotypes described above are reproductively isolated and may represent biological species sensu Mayr (1969).

MATERIAL AND METHODS

Live Chamelea gallina s.Z. were collected by hand-picking and diving in the Parque Natural da Ría Formosa, southern Portugal (Figure 3) in May-June 1988 (mission ALGARVE 88). Locality data and morphotype composition of the populations are provided in Table 1. Each sampling site covered only a few m2. Morphotypes were identified using the shell and siphon characteristics outlined above. Specimens were transported in liquid nitrogen and stored at -80°C. Total body homogenates of 154 clams were prepared by homogenizing each animal in a 20% (w/v) aqueous sucrose solution (5 pi mg'1 tissue). Crude homogenates were centrifuged during 45 min at -27000# (15000 rpm) and at ~4°C. Vertical Polyacrylamide Gel Electrophoresis (PAGE) was performed as described by Backeljau (1989), using two buffer systems: a discontinuous one with tris/glycine (pH 9-0) in the tray and tris/HCl (pH 9-0) in the gels, and a continuous one with tris/citric acid (pH 8-0) in both tray and gels. Seven polymorphic enzymes were surveyed. The discontinuous buffer system was employed to resolve superoxide dismutase (SOD, E.C. 1.15.1.1). The tris/citric acid buffer was used to resolve glucose-6-phosphate isomerase (GPI, E.C. 5.3.1.9), glycerol-3-phosphate dehydrogenase (GPD, E.C. 1.1.1.8), malate dehydrogenase (MDH, E.C. 1.1.1.37), malic enzyme (ME, E.C. 1.1.1.40), 6- phosphogluconate dehydrogenase (PGD, E.C. 1.1.1.44) and xanthine dehydrogenase (XDH, E.C. 1.2.3.2). All enzymes were stained according to Harris & Hopkinson (1976). Alleles were designated alphabetically according to decreasing electrophoretic mobilities (A=fastest allele or most anodal position). Previously typed specimens were included with each run in order to compare different gels. Data were analysed with the BIOSYS-1 computer package (Swofford & Selander, 1981). For each population we determined allele frequencies, mean observed heterozy­ gosities (H0), mean Nei's (1978) unbiased expected heterozygosities (He) and heterozy­ gote deviations [DH=(H0-He)/H J. Genotype frequencies were tested for departures from Hardy-Weinberg (HW) equi­ librium expectations with the exact probability test implemented by BIOSYS-1. For loci 214 T. BACKELJAU, P. BOUCHET, S. GOFAS A N D L. DE BRUYN

FARO

J V ILHA /DA CULATRA

tLHA D A ^ -~ BARRETA 10 km

Figure 3. Map of the Iberian Peninsula showing the sampling localities ofChamelea gallina s.l. Figures refer to the population numbers in Table 1.

Table 1. Locality data of the Chamelea gallina s.l. populations sampled in the Ría Formosa.

Stn Date Locality Nt n g N s Habitat 1 30-05-1988 Canai de Olhâo 34 23 11 Sand, depth: 5m 2 02-06-1988 Ilha da Barreta 31 31 - Sand, at low tide 3 06-06-1988 Canai de Olhâo, Culatra 28 19 9 Muddy sand, depth: 7m 4 09-06-1988 Canai de Olhâo, Hangares 61 19 42 Fine sand, depth: 5m Nt/ total numbers of individuals; NG, numbers ofChamelea gallina;

with more than two alleles, data were pooled in three genotype classes: (1) homozygotes for the most common allele, (2) all heterozygotes involving the most common allele, and (3) all other genotypes. Finally, Nei's (1978) unbiased genetic identities (I) and distances (D) between popula­ tions were calculated. The I values were used to construct a UPGMA dendrogram. The shells of the specimens studied are deposited in the collections of the Koninklijk Belgisch Instituut voor Natuurwetenschappen (I.G. no. 27353), Brussels. GENETIC VARIATION IN CHAMELEA GALLINA 215

RESULTS

The seven enzymes surveyed were assumed to be coded by single loci. Allele frequencies at these loci are presented in Table 2.

Table 2. Allele frequencies in the two morphotypes of Chamelea gallina s.l. in the Ría Formosa.

Locus 1G ÍS 2G 3G 3S 4G 4S MDH (N) 18 11 31 19 9 19 42 A 0.028 0.000 0.000 0.026 0.000 0.000 0.000 B 0.000 1.000 0.000 0.000 1.000 0.000 0.988 C 0.972 0.000 1.000 0.948 0.000 1.000 0.012 D 0.000 0.000 0.000 0.026 0.000 0.000 0.000 ME (N) 11 10 30 19 9 17 42 A 0.000 0.000 0.000 0.000 0.111 0.000 0.000 B 0.000 0.000 0.000 0.000 0.444 0.000 0.500 C 0.091 0.900 0.033 0.105 0.222 0.000 0.214 D 0.909 0.100 0.467 0.368 0.000 0.235 0.262 E 0.000 0.000 0.100 0.053 0.000 0.000 0.000 F 0.000 0.000 0.400 0.474 0.222 0.706 0.024 G 0.000 0.000 0.000 0.000 0.000 0.059 0.000 XDH (N) 18 10 29 19 9 19 42 A 0.000 0.100 0.000 0.000 0.278 0.000 0.155 B 0.167 0.900 0.000 0.000 0.111 0.000 0.250 C 0.777 0.000 0.414 0.474 0.555 0.053 0.571 D 0.056 0.000 0.552 0.526 0.056 0.894 0.024 E 0.000 0.000 0.034 0.000 0.000 0.053 0.000 PGD (N) 23 11 26 19 9 19 42 A 0.000 0.000 0.000 0.000 0.000 0.000 0.012 B 0.000 0.000 0.000 0.000 0.000 0.026 0.012 C 0.000 0.000 0.019 0.000 0.000 0.000 0.000 D 0.044 0.182 0.096 0.132 0.333 0.053 0.202 E 0.000 0.000 0.000 0.000 0.000 0.000 0.012 F 0.891 0.773 0.846 0.868 0.556 0.921 0.702 G 0.065 0.045 0.039 0.000 0.111 0.000 0.060 GPI (N) 18 11 31 19 9 19 39 A 0.000 0.000 0.000 0.026 0.000 0.000 0.038 B 0.043 0.000 0.000 0.026 0.000 0.053 0.026 C 0.043 0.000 0.161 0.184 0.056 0.158 0.077 D 0.065 0.228 0.177 0.133 0.056 0.053 0.090 E 0.174 0.228 0.097 0.105 0.222 0.235 0.231 F 0.261 0.045 0.145 0.158 0.277 0.079 0.064 G 0.239 0.136 0.242 0.263 0.111 0.211 0.256 H 0.022 0.182 0.048 0.000 0.111 0.132 0.064 I 0.131 0.045 0.113 0.079 0.167 0.053 0.090 I 0.022 0.091 0.017 0.026 0.000 0.026 0.038 K 0.000 0.045 0.000 0.000 0.000 0.000 0.026 SOD (N) 19 9 31 18 1 19 28 A 0.132 0.000 0.113 0.167 0.000 0.079 0.018 B 0.842 0.444 0.839 0.805 0.000 0.895 0.268 C 0.000 0.232 0.000 0.000 0.000 0.000 0.143 D 0.026 0.222 0.048 0.028 1.000 0.026 0.285 E 0.000 0.000 0.000 0.000 0.000 0.000 0.143 F 0.000 0.112 0.000 0.000 0.000 0.000 0.107 G 0.000 0.000 0.000 0.000 0.000 0.000 0.036 216 T. BACKELJAU, P. BOUCHET, S. GOFAS a n d L. d e BRUYN

Table 2. (continued.) (N) 8 6 26 19 9 18 39 A 0.000 0.000 0.000 0.000 0.000 0.000 0.013 B 0.000 0.000 0.000 0.000 0.000 0.056 0.013 C 1.000 0.084 1.000 0.974 0.000 0.888 0.051 D 0.000 0.583 0.000 0.000 0.667 0.028 0.602 E 0.000 0.333 0.000 0.000 0.333 0.000 0.308 F 0.000 0.000 0.000 0.026 0.000 0.028 0.013 G, Chamelea gallina; S, Chamelea striatula.

Although none of the loci studied is 100% diagnostic, the MDH locus allows a fairly good separation of the two morphotypes. Only five out of the 154 specimens surveyed (<3-5%) would be misclassified using this locus. At the other loci the differences between the morphotypes are much less obvious, particularly at highly variable loci such as GPI and SOD. Mean H0 values in the four populations before (T), and after subdividing them into morphotypes (G or S), differ only slightly. The He values, however, are substantially higher in the mixed than in the subdivided populations. Hence, the difference between H0 and He in the subdivided populations is smaller than in the mixed populations (Table 3). The results of the HW tests and the coefficients of heterozygote deviation are summa­ rized in Table 3, which shows that in mixed populations genotype frequencies at most loci depart significantly (P<0-05) from the expected values. This picture changes in part after subdividing the populations into morphotypes. For example, the genotype fre-

Table 3. Heterozygote deviations (D,,) and exact probability tests (Pexact) of departures from H W expectations in mixed (T) and subdivided populations of Chamelea gallina in the Ría Formosa.

Locus 1T 1G ÍS 2G 3T 3G 3S 4T 4G 4S

MDH pexact 0.000* 1.000 M M 0.000* 1.000 M 0.000* M 1.000 Dh -0.931 0.000 -0.855 +0.014 -0.963 0.000 ME pexact 0.000* 0.048* 0.053 0.000* 0.000* 0.000* 0.005* 0.000* 0.000* 0.000* Dh -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 -1.000 XDH pexact 0.000* 0.000* 0.053 0.000* 0.000* 0.000* 0.168 0.000* 0.002* 0.000* Dh -1.000 -1.000 -1.000 -1.000 -0.883 -1.000 -0.649 -0.954 -1.000 -0.920 PGD Pexact 0.011* 0.008* 0.401 0.077 0.604 1.000 1.000 0.001* 1.000 0.002* Dh -0.445 -0.573 -0.292 -0.171 +0.041 +0.121 +0.109 -0.358 +0.037 -0.389 GPI Pexact 0.019* 0.649 0.825 0.349 0.669 0.615 1.000 0.282 0.369 0.231 Dh -0.251 -0.169 -0.373 -0.053 -0.215 -0.202 -0.227 -0.014 -0.026 -0.013 SOD pexact 0.157 1.000 0.170 0.568 1.000 1.000 M 0.000* 1.000 0.000* Dh -0.400 +0.127 -0.696 +0.128 -0.072 +0.172 -0.844 +0.065 -0.956 GPD Pexact 0.002* M 1.000 M 0.000* 1.000 0.163 0.000* 1.000 0.000* Dh -0.623 -0.154 -0.792 0.000 -0.528 -0.718 +0.053 -0.671 Mean He 0.537 0.275 0.422 0.367 0.573 0.391 0.472 0.642 0.297 0.563 Mean H0 0.190 0.165 0.220 0.194 0.241 0.213 0.254 0.206 0.205 0.203 G, Chamelea gallina; S, Chamelea striatula. *, significant HW departures (a=0.05). M, monomorphic loci. expected and Hn, observed heterozygosity per population. GENETIC VARIATION IN CHAMELEA GALLINA 217 quencies at MDH, GPI and GPD in population IT show significant HW deviations, which disappear in populations 1G and IS. Both mixed and subdivided populations reveal considerable degrees of heterozygote deficiencies (Table 3). Yet mixed populations are more heterozygote deficient than subdivided ones. This is obvious for MDH and partly for PGD, SOD and GPD. At ME and XDH, on the contrary, all populations show extreme homozygote excesses.

Table 4. Nei's (1978) unbiased genetic identities (above diagonal) and distances (below diagonal) between subdivided sympatric populations of Chamelea gallina s.l. in the Ría Formosa.

Pop 1G IS 2G 3G 3S 4G 4S 1G - 0.352 0.924 0.918 0.273 0.778 0.463 IS 1.043 - 0.315 0.331 0.689 0.306 0.809 2G 0.079 1.155 - 1.000 0.258 0.959 0.392 3G 0.086 1.105 0.000 - 0.278 0.962 0.408 3S 1.297 0.373 1.356 1.282 - 0.221 0.902 4G 0.251 1.184 0.042 0.038 1.509 - 0.324 4S 0.771 0.212 0.936 0.895 0.103 1.127 - G, Chamelea gallina; S, Chamelea striatula

0.20 0.60 1.00 r

------I C- v jl — P 3 G L-4G ------1S 3S 4S

Figure 4. UPGMA dendrogram derived from Nei's (1978) unbiased genetic identities between subdivided populations of Chamelea gallina s.l. in the Ría Formosa. Population numbers refer to Table 1. G, Chamelea gallina; S, Chamelea striatula.

Nei's (1978) unbiased genetic identities and distances between populations are pre­ sented in Table 4. The corresponding UPGMA dendrogram shows that each morphotype forms a well-defined group (Figure 4). The mean genetic identity between these groups (7=0-327, D=l-138) is remarkably low in comparison to the mean I values within groups (7=0-924, D=0-083 between the four C. gallina s.s. populations, and 7=0-800, D=0-229 between the three C. striatula populations).

DISCUSSION

Systematics Thorpe (1983) calculated that in about 97% of interspecific comparisons between 'good' animal species Nei's mean genetic identity is 7<0-850, whereas in 98% of intraspe- 218 T. BACKELJAU, P. BOUCHET, S. GOFAS A N D L. DE BRUYN cific comparisons it is />0-850. Hence the I value between Chamelea gallina and C. striatula (1=0-327) is typical of a specific difference, especially since the I values between populations within morphotypes are much higher and fall reasonably well within the range of conspecific populations. This is confirmed by Table 5, which shows that the genetic distance between C. gallina and C. striatula is consistent with interspecific D values observed among several marine bivalves. Similarly the D values within the two morphotypes are comparable to the intraspecific genetic distances reported for other bivalves (Table 5).

Table 5. Selected literature data on intra- and interspecific genetic distances in some marine bivalves.

Species D value Reference Intraspecific Crassostrea gigas <0.453 Buroker et al. (1979a) <0.012 Moragaet al. (1989) Saccostrea commercialis <0.087 Buroker et al. (1979a) Ostrea edulis <0.017 Johannessonet al. (1989) Mytilus edulis <0.002 Fevolden & Gamer (1986) <0.042 Yamanaka & Fujio (1984) Tridacna maxima =0.032 Ayala (1975) Ruditapes philippinarum <0.096 Oniwaet al. (1988) Teredo navalis =0.290 Hoagland (1986) Teredo bartschi =0.096 Hoagland (1986) Interspecific 6 Crassostrea spp. 0.325-2.293 Buroker et al. (1979b) 3 Saccostrea spp. 0.171-0.454 Buroker et al. (1979b) 3 Ostrea spp. 1.243-1.905 Buroker (1982) 3 lucinid spp. 1.406-2.262 Dwiono et al. (1989) 3 Ruditapes spp. 1.050-1.840 Borsa & Thiriot-Quiévreux (1990) 2 Teredo spp. 0.756 Hoagland (1986) 2 Lyrodus spp. 0.840 Hoagland (1986) 2 Bankia spp. 0.480 Hoagland (1986)

The specific status of C. gallina and C. striatula is also supported by the fact that D values of 0-190-0-410 between geographical morphotypes of the tellinid bivalve Macoma balthica have been used to suggest (semi) specific differences (Väinölä & Varvio, 1989). Similarly D values of 0-170-0-280 have been relied on to differentiate species in the Mytilus edulis complex (e.g. Skibinski et al., 1980), while Sarver et al. (1992) treated the ribbed mussels Geukensia demissa demissa and G. d. granosissima as separate species because they were separated by a D value of 0-550. As interbreeding between 'species' in both Macoma sp. and M ytilu s sp. regularly occurs, these taxa are currently regarded as complexes of semispecies or incipient species (e.g. Väinölä & Varvio, 1989). The breeding biology and population genetics of C. gallina s.l., on the contrary, suggest that introgression between the two morphotypes may be limited. According to Salvatorelli (1967), Froglia (1975) and Corni et al. (1980) the reproductive season of C. gallina in the Adriatic lasts from the end of spring until the GENETIC VARIATION IN CHAMELEA GALLINA 219

end of August, while Vives & Suau (1962) observed that in populations from north-east Spain the gonads reached maturity at the beginning of summer and regressed after August. Nevertheless Poggiani et al. (1973) and Guérin (1973) reported more complex breeding patterns. For C. striatula Jagnow & Gosselck (1987) noted that in the German Bight larvae are mainly found in summer, while in Brittany the species reproduces the whole year round (Lucas, 1965). So, despite the probable overlap in breeding season between the two morphotypes, they maintain a large genetic distance in sympatric conditions. Because of this apparent reproductive isolation, and considering the mor­ phological differentiation outlined above, we interpret C. gallina and C. striatula as two biological species. A subspecific status seems not appropriate here, for this requires by definition allopatric distributions (Mayr, 1969). Concepts such as semispecies or incipi­ ent species do not seem applicable to C. gallina and C. striatula as the genetic distance between the two species is comparatively large, even though it may be somewhat inflated by the small number of loci surveyed. The oldest available names for the complex are Venus gallina Linnaeus, 1758 (type locality: 'in Mediterráneo'; type specimens in the collection of the Linnean Society, London) and Pectunculus striatula Da Costa, 1778 (described from the British Isles). For reasons outlined by Hanley (1855,1856) we restrict the former name to the Mediterra­ nean species, while the latter name should be used for the Atlantic species. Many more nominal taxa have been described in the C. gallina complex, but it is beyond the scope of this paper to revise them.

Population genetics

The strongly negative heterozygote deviations at most loci in the mixed populations are in part the result of the Wahlund effect (pooling subpopulations with different allele frequencies). Yet even in C. gallina and C. striatula separately there remain considerable heterozygote deficiencies. This is a common phenomenon among marine bivalves having been observed in more than 50 species (e.g. Gaffney et al., 1990). Next to the Wahlund effect, several other factors may cause heterozygote deficiencies, including mis-scoring of gels, inbreeding, null alleles, aneuploidy, molecular imprinting and selection (e.g. Zouros & Foltz, 1984; Gaffney et al., 1990). Our analyses do not permit an assessment as to which of these factors is responsible for the residual heterozygote deficiencies (as in ME and XDH). The mean heterozygosity values we observed in C. gallina (Ho=0-194, He=0-332) and C. striatula (Ho=0-226, He=0-486) are comparable to those of C. gallina from the Adriatic Sea, for which Stella & Rodinó (1986) reported Ho=0-403 and He=0-442. Hence Adriatic C. gallina shows a closer agreement between H0 and He than in our study. This is probably due to the larger number of specimens and loci surveyed by Stella & Rodinó (1986), for heterozygosity estimates strongly depend on the numbers of both loci and individuals sampled (e.g. Nei, 1978). In this context we should stress that our study involved only polymorphic loci. Stella & Rodinó (1986) observed one locus (MPI), out of 22, at which genotype frequencies deviated from HW conditions. These authors therefore probably dealt with 220 T. BACKELJAU, P. BOUCHET, S. GOFAS A N D L. DE BRUYN a single species {i.e. C. gallina s.s.), since in their study MDH-1 and XDH were fixed for single alleles, while there were fewer alleles at PGD, GPI, SOD and MDH-2 (=our ME?) than we found in the mixed populations. Moreover the number of alleles at GPI (9) in the Adriatic population matches the number we observed in C. gallina from the Ría Formosa.

Distribution

The Chamelea gallina complex is distributed from Finnmark (Höisaeter, 1986), through­ out the British Isles and the North Sea (Seaward, 1990) to southern Morocco (Pasteur- Humbert, 1962), the Mediterranean (Angelo & Gargiullo, 1978) and the Black Sea (Grossu, 1962). Records from the Canary Islands (Tebble, 1966), Iceland (Parenzan, 1976) and the Caspian Sea (Grossu, 1962) are probably erroneous for they are not supported by Odhner (1931), Madsen (1949) and Logvinenko & Starobogatov (1968), respectively. Using the morphological criteria outlined above, we checked all the material (mostly empty shells) of C. gallina and C. striatula in the Muséum National d'Histoire Naturelle, Paris and the Koninklijk Belgisch Instituut voor Natuurwetenschappen, Brussels. These records are plotted in Figure 5, which shows that C. striatula occurs in the Atlantic from Finnmark to Agadir (Morocco) and in the western Mediterranean. Valves of C. striatula have also been collected at depths of 80-100 m off Banyuls, French Mediterranean (indicated by 'F?' in Figure 5). These probably belong to submerged Pleistocene cold- water thanatocoenoses known from that region (e.g. Mars, 1958).

zn

Figure 5. European distribution of (■)Chamelea gallina and ( • )Chamelea striatula based on material in the collections of the Muséum National d'Histoire Naturelle and the Koninklijk Belgisch Instituut voor Natuurwetenschappen. *, mixed populations; F?, supposed fossil records. GENETIC VARIATION IN CHAMELEA GALLINA 221

Chamelea gallina is distributed throughout the Mediterranean and the Black Sea (Figure 5). There are a few localities in the Atlantic, along the southern coast of the Iberian Peninsula as far west as Faro, Algarve. The species is absent from Atlantic Morocco. Two lots of C. gallina in the Muséum National d'Histoire Naturelle, Paris dated from the 19th century and labelled from the French Atlantic coast (Le Pouliguen and Ile de Ré), led Fischer-Piette & Vukadinovic (1977) to the conclusion that C. gallina and C. striatula are synonyms. Since subsequent collecting efforts failed to confirm these records, we consider them as temporary accidental introductions, or mislabelled Medi­ terranean specimens. In conclusion, the distributional overlap between C. gallina and C. striatula is re­ stricted to the coast of Algarve, the Gulf of Cadiz, the Strait of Gibraltar and the Alboran Sea.

J.L. Van Goethem and two anonymous referees provided valuable comments on the manu­ script and H. Van Paesschen prepared several figures. T.B. and L.D.B. were supported by the Belgian National Fund for Scientific Research. Travel grants were provided by the Centre National de la Recherche Scientifique (France) and the Muséum National d'Histoire Naturelle, Paris.

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Submitted 22 June 1993. Accepted 23 August 1993.