Revista Chilena de Historia Natural 76 (3): 501-507, 2003
RESEARCH ARTICLE
Allozymic variation in the clam genus Eurhomalea (Bivalvia: Veneriidae) along
southern South American coast
The correspondence between allozymic variation and specific differentiation was studied
in four populations corresponding to the three nominal, allopatric species of clam genus Eurhomalea (E. rufa,
E. lenticularis, E. exalbida) described for southern South America. Allozyme variation scored in 12 loci was
high as indicated by heterozygosity levels (15.8 20.7 %) and by the presence of only three monomorphic loci (Hk-2,
Icd-2, and Xdh-1). These high estimates of allelic variability were influenced by the low levels of interspecific
genetic similarity (I = 0.64) and for the high conspecific values of genetic identity observed. The high estimates of substructuring found
at the species level (F<sub>ST</sub> = 0.39) contrasted with the low differentiation (F<sub>ST</sub> = 0.027) and
high migration rate (Nm = 9) existing among conspecific samples. Diagnostic allele fixation coinciding with specific
recognition was recorded at locus Hk-1 whereas nearly-fixed differences at loci (Adh, α-Gpd,
Icd-1, Ldh, Odh, Pgm-3) differed sharply in frequency among species. The Wagner
procedure and the neighbor-joining algorithm produced a similar tree topology highly related to the geographic distance and to their
taxonomic recognition. The lack of coincidence between patterns of allozymic variation and the two distinctive shell morphs (flat and
globoid) occurring in E. exalbida from Ushuaia bay do not support their taxonomic recognition.
Key words:
allozymic variation,
Eurhomalea, genetic structure, taxonomic status
