Academic journal article Genetics

Natural Selection and Genetic Diversity in the Butterfly Heliconius Melpomene

Academic journal article Genetics

Natural Selection and Genetic Diversity in the Butterfly Heliconius Melpomene

Article excerpt

GENETIC variation within and between populations is shaped by numerous factors. In particular, genetic driftis stronger in smaller populations, such that organisms with larger population sizes should be more diverse under neutral evolution. However, it has long been known that the amount of genetic variation does not always scale as expected with population size, with a deficit of genetic variability in larger populations as compared to the neutral expectation (Lewontin 1974). This has become known as "Lewontin's paradox." It is likely that this paradox can be explained by considering the influence of natural selection (Ohta and Gillespie 1996; Leffler et al. 2012; Cutter and Payseur 2013; Corbett-Detig et al. 2015). Since driftcan act to retard selection, natural selection tends to be more efficient in organisms with larger population sizes. Consistent with this, estimated rates of adaptive evolution are often greater for smaller organisms with larger population sizes. For example, it has been estimated that .50% of amino acid substitutions between fruit fly species are driven by positive selection (Sella et al. 2009; Messer and Petrov 2013), but in humans, ,15% of recent amino acid substitutions appear to have been driven by selection (Eyre- Walker 2006; Messer and Petrov 2013). Considering the relative importance of natural selection and genetic driftin maintaining genetic diversity has important implications for explaining current patterns of biodiversity and predicting future adaptive potential (Gillespie 2001; Leffler et al. 2012).

The solution to Lewontin's paradox appears to lie in the influence of natural selection on linked sites. Selection acting on one locus can cause the removal of genetic variation at physically linked, neutral loci. This can occur either through fixation of beneficial alleles ("hitchhiking") (Maynard Smith and Haigh 1974) or by purging of deleterious alleles ("background selection") (Charlesworth et al. 1993). Both of these processes have more pronounced effects in genomic regions of lower recombination rate. The importance of linked selection is supported by a positive correlation between recombination rate and neutral genetic diversity, first and most thoroughly studied in Drosophila melanogaster (Begun and Aquadro 1992; Langley et al. 2012; Mackay et al. 2012; McGaugh et al. 2012; Campos et al. 2014), and subsequently observed in other taxa, including humans (Nachman et al. 1998; Payseur and Nachman 2002; McVicker et al. 2009; Lohmueller et al. 2011), yeast (Cutter andMoses 2011),mice, rabbits (Nachman and Payseur 2012), and chickens (Mugal et al. 2013). A major recent advance has come from a population genomic analysis of 40 species, which showed not only that this phenomenon is widespread in plants and animals, but importantly, that the effectiveness of selection at removing variation at linked sites is correlated with population size (Corbett-Detig et al. 2015). The increased effectiveness of natural selection in larger populations reduces genetic diversity to a much greater extent than in smaller populations, countering to some degree the reduced influence of genetic drift.

However, this correlative evidence fails to capture the complexities of how natural selection acts in different species. A range of factors will affect the efficiency of natural selection and how strongly it influences linked sites, including the recombinational landscape across the genome, the frequency of adaptive change, and historical population demography (Cutter and Payseur 2013). These factors vary enormously between species, and in-depth analyses of an increasing number of taxa have revealed that not all conform to the same general trends. For example, certain plant species do not show a correlation between recombination and neutral polymorphism (see Cutter and Payseur 2013 for a thorough review). In the insects, most of what we have learned about the action of selection and driftin natural populations comes from studies of the genus Drosophila (Andolfatto 2007; Sella et al. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.