Metapopulation structure and genetic differentiation among subpopulations will be tightly related to patterns andprocesses of local adaptation and microevolution. Understanding the mechanisms behind genetic substructuringwill aid in the interpretation of species’ ecological performances and strategies. The marine gastropodLittorinafabalisoccurs in two size morphs - a small and a large - found in microhabitats of different wave exposure, butoverlapping in distribution where wave exposure is intermediate. Earlier studies have found substantial genetic differentiationlinked to morph in one allozyme locus (arginine kinase), while 29 other allozyme loci reveal no orminute differences between morphs. Here we add new results showing DNA variation in a RAPD marker beingtightly linked to the allozyme variation. Indeed, 97% of the snails homozygotic for one of theArkalleles had aunique DNA band, while 89% of the snails homozygotic for the otherArkallele lacked the marker. We discuss alternativehypotheses explaining the genetic substructure and suggest that the linkage of size, allozyme and DNA traitsmight be due to a paracentric chromosomal inversion involving loci coding for these traits. A genetic linkage of traitsmight promote microhabitat specialization of this species, and such a chromosomal transformation may therefore beadaptive. |
