GENETIC DIFFERENTIATION AND SPECIATION IN STOMION (COLEOPTERA, TENEBRIONIDAE) - FLIGHTLESS BEETLES OF THE GALAPAGOS-ISLANDS, ECUADOR

Stomion is a swarm of 13 tenebrionid beetle tara endemic to the Galapa gos Islands. The taxa show marked morphological variation, and all are flightless. They can be divided into three divergent morphological gr oups based on external sculpturing of the elytra. Eleven taxa were exa mined electrophoretically at 20 enzyme loci to measure the extent of g enetic differentiation which accompanied morphological differentiation and speciation. Stomion are shown to be ideal candidates for allopatr ic and founder event speciation, with their limited dispersal ability narrow distributions, and incidence of single-island endemics. Accordi ngly, individual heterozygosities were low in most taxa, and gene pool divergence was apparent among populations of single taxa occupying di fferent islands. Both interspecific and intraspecific genetic identiti es were high, with an average I = 0.88 and I = 0.96, respectively. The relatively young age of the genus and the allopatric mode of speciati on may account for high genetic relatedness. No clear relationship was found between allozyme phenotypes and the three morphological groups, thus, the evolution of these traits may have been facilitated by simi lar selection among islands of similar age and geography. The geograph ical distributions of the morphological groups can be used to suggest a general pattern of speciation for the group. (C) 1997 The Linnean So ciety of London.