Extraordinary multilocus genetic organization in mole crickets, Gryllotalpidae

Allozymic diversity at 21 loci was analyzed in 370 individuals of three spe cies of mole cricket superspecies, Gryllotalpa gryllotalpa (two new chromos omal species, G. tall and G. marismortui) and G. africana in Israel, which are distributed along a southward transect of increasing aridity. Two outst anding findings emerged in G. tali and G. marismortui: (1) genetic polymorp hism was high but heterozygosity very low, indicating significant deviation s from Hardy-Weinberg expectations; and (2) significant linkage disequilibr ia at an unprecedented level for outbreeders and remarkable intersite diffe rences. The results may characterize subterranean gryllotalpids worldwide b ecause a single sample of Neocurtilla hexadactyla from Tefe, Amazonia, show s the same features. Significant variation of heterozygote paucity among lo ci, combined with the biology of the species, rejects the simple explanatio n of inbreeding or any other single explanatory model. Likewise, direct sel ection against heterozygotes or specific multilocus associations can explai n, but is not necessary nor likely to explain, the observed results in mole crickets. To explain these results, we developed a multiple-factor mathema tical model combining niche viability selection, niche choice, and positive assortative mating. This model involves a special case of Wahlund effect a nd inbreeding. Simulations based on this model showed that a combination of these three mechanisms may produce the observed distribution of alleles, v ia selection on a few loci, to affect the entire genome organization.