Patterns of postmating reproductive isolation in a newly discovered species pair, Aquarius remigis and A. remigoides (Hemiptera;Gerridae).
Aquarius remigoides Gallant and Fairbairn has recently been described as specifically distinct from A. remigis (Say) based upon genetic and morphological data. Both species are common, semiaquatic bugs (Hemiptera; Gerridae) found on the surface of streams and small rivers. Allozyme studies have shown them to be more distantly related than most other congeneric species in the Gerridae, with significant barriers to gene flow where their ranges abut. We assess postmating reproductive isolation between A. remigoides and A. remigis, using a bracket cross design with five sampling sites along a north-south cline traversing the hybrid zone. We also report the results of long-distance conspecific crosses of A. remigis, using populations from California and Quebec. Neither these nor the intraspecific bracket crosses reveal any evidence of isolation by distance within species. However, heterospecific crosses show significantly reduced fertility, hatching success, survival of both sexes to eclosion (final moult) and percentage of males. Egg production is not influenced by cross type, and we found no evidence of hybrid sterility in either sex. Analyses of genotypic frequencies at three isozyme loci in eight hybrid and 22 pure populations reveal significant deficiencies of heterozygotes in hybrid populations. The proportion of males is also significantly lower in hybrid populations than in pure populations. The laboratory and field results indicate that postmating isolation between these two species occurs in the form of severe reductions in both the fertility of heterospecific crosses and the viability of hybrids, particularly hybrid males. Genetic mechanisms for Haldane's rule and asymmetries in the reciprocal heterospecific crosses are discussed.
Gallant
S L
SL
Department of Biology, Concordia University, Montreal, Quebac, Canada.
Fairbairn
D J
DJ
D000818:Animals; D003433:Crosses, Genetic; D005260:Female; D005298:Fertility / Q000235:genetics; D014644:Genetic Variation; D005828:Genetics, Population; D006430:Hemiptera / Q000235:genetics*; D006579:Heterozygote; D008297:Male; D010063:Ovum / Q000502:physiology; D012098:Reproduction / Q000235:genetics*; D012494:Sampling Studies; D012744:Sex Ratio