Hybridization patterns and the evolution of reproductive isolation in ducks

Abstract

Much of our knowledge of the evolution of reproductive isolation comes from studies of Drosophila . This body of work has revealed the following patterns: (1) reproductive isolation increases with phylogenetic distance between hybridizing species; (2) reproductive isolation is greater between sympatric than allopatric species with the same level of divergence; and (3) hybrid crosses conform to Haldane's rule. We tested for the existence of these patterns in ducks (subfamily Anatinae, sensu Livezey, 1997b) based on 1037 hybrids of known parentage. Our analyses of the number of interspecific crosses in relation to phylogenetic distance found a significant deviation between the observed and expected distribution of crosses controlling for the topology of the Anatinae phylogeny. In particular, we found both an excess of hybrid crosses among closely related species and a scarcity among distantly related species. The number of hybrid males also decreased with increasing phylogenetic distance between parental species, although the number of hybrid females remained low and constant. Sympatric species produced higher numbers of hybrid males than allopatric ones, despite no difference in phylogenetic distance among parental species in compared groups. The number of hybrid males exceeded the number of hybrid females, consistent with Haldane's rule. This was evident even though the analysis was restricted to a reduced set of phylogenetically independent crosses. However, the pattern was no longer significant after correction for the number of hybrid males by the male-biased sex ratio of adult ducks.

Mutation rate is linked to diversification in birds

“…The two isolated subpopulations will gradually diverge, and eventually may become so different that they are unable to reproduce, either through the acquisition of phenotypic differences that create prezygotic reproductive isolation, or through the acquisition of genomic differences which create postzygotic reproductive isolation (or both). Previous studies in birds have shown that hybrid fitness is inversely proportional to the genetic distance between the hybrid's parents (19,40,41), and similar results have been reported in flies (42, 43), butterflies and moths (44), and frogs (45). Whatever the underlying cause of reproductive isolation, a higher rate of mutation would provide a greater amount of raw material for both drift and selection, and so could accelerate the development of separate species from two diverging populations (18).…”

Haldane's rule in the 21st century

“…Laurie (1997) provided a list of all taxa examined thus far. More recent authors have focused in more detail on taxa with female heterogamety, viz Aves (Price and Bouvier, 2002;Tubaro and Lijtmaer, 2002;Lijtmaer et al, 2003), Lepidoptera (Presgraves, 2002) and certain Teleostei (Russell, 2003). The most recent update is by Coyne and Orr (2004) who provide a summary table of the number of species that support HR.…”

Gene Regulatory Evolution During Speciation in a Songbird

“…Second, the evolution of reproductive isolation is protracted in birds relative to other taxa (Prager and Wilson 1975;Fitzpatrick 2004;Price 2008). Astoundingly, fully fertile hybrids have been documented from bird species that have diverged for up to 10 million years (Tubaro and Lijtmaer 2002;Lijtmaer et al 2003;Price 2008;Arrieta et al 2013). In many other taxa, studies of gene expression have pointed to frequent misexpression in F1 hybrids (Landry et al 2005;McManus et al 2010;Malone and Michalak 2008;Renaut et al 2009;Bell et al 2013;Coolon et al 2014).…”

“…Although there is extensive information about fertility and viability loss in hybrid birds (Tubaro and Lijtmaer 2002;Lijtmaer et al 2003;Price 2008;Arrieta et al 2013), to date there have been no studies of regulatory divergence in bird species and their hybrids. While zebra finches (Taeniopygia guttata) are an established model system for the neurobiology of song learning (Clayton et al 2009), they also have great potential for mechanistic studies of speciation.…”