SIGNIFICANT ROLE FOR HISTORICAL EFFECTS IN THE EVOLUTION OF REPRODUCTIVE ISOLATION: EVIDENCE FROM PATTERNS OF INTROGRESSION BETWEEN THE CYPRINID FISHES,LUXILUS CORNUTUSANDLUXILUS CHRYSOCEPHALUS

Abstract

Abstract.-Samples of Luxilus cornutus, Luxilus chrysocephalus, and their hybrids were collected along hypothesized routes of dispersal from Pleistocene refugia to examine the significance of geographic variation in patterns of introgression between these species. Patterns of allozyme and mitochondrial DNA (mtDNA) variation were generally consistent with those from previous studies. Tests of Hardy-Weinberg equilibrium revealed significant deficiencies of heterozygotes in all samples, indicating some form of reproductive isolation, Mitochondrial DNAs of each species were not equally represented in F) hybrids; however, this bias was eliminated when the two largest samples were excluded from the analysis. Backcross hybrids exhibited biased mtDNA introgression, as samples from Lake Erie (eastern) and Lake Michigan (western) drainages showed significant excesses of mtDNAs from L. chrysocephalus and L. cornutus, respectively, relative to frequencies of diagnostic allozyme markers. The extent and direction of allozyme and mtDNA introgression was quantifiedby calculating isolation index values from morphologically "pure" individuals of each species from each locality. Analysis of variance of these measures identified limited introgression of allozyme variants with no geographic pattern, but significant differences in direction of mtDNA introgression between drainages (i.e., postglacial dispersal route). Association between patterns of mtDNA introgression and dispersal route across the latitudinal width of the contact zone is best explained by genetic divergence during past isolation of ancestral populations from these drainages. These results identify a significant role for historical effects in the evolution of reproductive isolation and the process of speciation.

Novelties in Hybrid Zones: Crossroads between Population Genomic and Ecological Approaches

“…There was therefore no hybrid gradient based on the ecological preferences of the species, as would have been expected based on the route followed by C. n. nasus during the colonization process. These findings conflict with those for two other well known cyprinid models: a gradient hybrid zone has been reported between Barbus barbus and Barbus meridionalis in the Lergue (Europe) [11] and asymmetric introgression in two Luxilus species (America) [12] has been accounted for by historic effects (refuge populations and dispersal route).…”

Single Nucleotide Polymorphisms Reveal Genetic Structuring of the Carpathian Newt and Provide Evidence of Interspecific Gene Flow in the Nuclear Genome

“…Examination of several transects through hybrid zones in the context of local environmental conditions and relative species abundance could be informative as demonstrated in multiple systems [87], [91]–[93]. Another important way forward would be to use multilocus sequence data [94] to construct and test multipopulation models of gene flow between Lm and Lv .…”

Introgressive hybridization between two Iberian endemic cyprinid fish: a comparison between two independent hybrid zones

“…Moreover, this study shows that intra‐specific population structure between river basins exists in these fishes, particularly for A. oligolepis . Genetic differences between populations as a result of historical processes are also known to influence introgressive hybridization (Dowling et al. , 1997) and can be especially important in the case of multiple, independent areas of hybridization, like in different river basins, each not only with its own distinctive environmental features but also with their unique evolutionary history (Nolte et al.…”