Introgressive hybridization in Heteroptera: the example of Limnoporus Stål (Gerridae) species in western Canada

Abstract

Populations of the pondskaters, Limnoporous dissortis and Limnoporous notabilis, hybridize extensively in the Cordilleran region of western Canada. In laboratory crosses using L. dissortis from central Alberta and L. notabilis from southwestern British Columbia, most eggs are fertilized and begin development, but only ca. 50% of the eggs hatch and nearly all F1 hybrid adults are males. F1 hybrid males are fertile in backcrosses to females of both species, although egg hatch is reduced and mainly male progeny result from crosses to females of the paternal species. These species both have an XO sex chromosome system, and the foregoing results suggest that either products of genes on X chromosomes of the two species are incompatible or that they are incompatible with heterospecific cytoplasmic elements. Males of L. dissortis are more successful at interspecific copulations than are those of L. notabilis, perhaps because they more frequently adopt aggressive mating behaviour that circumvents premating barriers. Although gene pools of these two species are partially isolated by both pre- and post-mating barriers, there has been large-scale exchange of genes at autosomal loci, and significant introgression occurs over a large geographic area. Introgression is asymmetric, with genes of L. dissortis tending to flow disproportionately into L. notabilis populations, reflecting differences between the species in mating behaviour and dispersal tendencies. Because these two species are not closest relatives, I conclude that reticulations can be important considerations in the evolution of semiaquatic bugs. A literature survey shows that interspecific hybridization occurs in a number of heteropteran families, although partial barriers to gene flow are common.