A Zone of Overlap and Hybridization Between <I>Allonemobius socius</I> and a New <I>Allonemobius</I> sp.

Abstract

This study investigates the zone of overlap and hybridization between a new species in the Allonemobius species complex and Allonemobius socius (Scudder 1877). The new species, Allonemobius sp. nov. Tex was previously misidentified as Allonemobius fasciatus (De Geer 1773). Our survey of genetic variation at 13 allozyme loci shows that the new species differs from A. fasciatus in at least two allozyme loci. A. sp. nov. Tex is distributed mainly in Texas, and it is sympatric with A. socius in some parts of its distribution where the two species hybridize. In addition to the two fixed allelic differences between the two species, there is also a unique allele at a third locus in A. sp. nov. Tex. The proportion of hybrids in the mixed populations where the two species co-occur is always low, resulting in bimodal hybrid index scores. The bimodal distribution suggests that there is reproductive isolation between the new species and A. socius. This reproductive isolation is maintained, at least in part, through conspecific sperm precedence, which also serves as the major barrier to gene flow between A. socius and A. fasciatus.