Sunday, March 23, 2014

Lab-meeting on intraspecific assortative mating, disruptive selection and sympatric speciation

Posted by Erik Svensson on behalf of John Waller

This week's lab-meeting will continue on the theme of assorative mating and how it can possibly work together with disruptive selection to cause sympatric speciation. We will discuss two papers by Daniel Bolnick at University of Texas (Austin): one review paper in American Naturalist and one modelling paper in American Zoologist. Abstracts are found below.

Date: Tuesday March 25, 10.30
Place: "Argumentet", 2nd floor, Ecology Building

Assortative mating occurs when there is a correlation (positive or negative) between male and female phenotypes or genotypes across mated pairs. To determine the typical strength and direction of assortative mating in animals, we carried out a meta-analysis of published measures of assortative mating for a variety of phenotypic and genotypic traits in a diverse set of animal taxa. We focused on the strength of assortment within populations, excluding reproductively isolated populations and species. We collected 1,116 published correlations between mated pairs from 254 species (360 unique species-trait combinations) in five phyla. The mean correlation between mates was 0.28, showing an overall tendency toward positive assortative mating within populations. Although 19% of the correlations were negative, simulations suggest that these could represent type I error and that negative assortative mating may be rare. We also find significant differences in the strength of assortment among major taxonomic groups and among trait categories. We discuss various possible reasons for the evolution of assortative mating and its implications for speciation.

Current Zoology    2012, 58(3): 484 - 492

The term 'assortative mating' has been applied to describe two very different phenomena: (1) the tendency for individuals to choose phenotypically similar mates from among conspecifics; or (2) the tendency to prefer conspecific over hete- rospecific mates (behavioral reproductive isolation). Both forms of assortative mating are widespread in nature, but the relationship between these behaviors remains unclear. Namely, it is plausible that a preference for phenotypically similar conspecifics incidentally reduces the probability of mating with phenotypically divergent heterospecifics. We present a model to calculate how the level of reproductive isolation depends on intraspecific assortative mating and the phenotypic divergence between species. For empirically reasonable levels of intraspecific assortment on a single trait axis, we show that strong reproductive isolation requires very substantial phenotypic divergence. We illustrate this point by applying our model to empirical data from threespine stickleback Gasterosteus aculeatus and Darwin’s Finches (Geospiza spp). We conclude that typical levels of intraspecific assortment cannot generally be extrapolated to explain levels of interspecific reproductive isolation. Instead, reproductive isolation between species likely arises from different mate choice behaviors, or multivariate assortative mating  

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