Questions Is there selection for an intermediate level of population genomic variation in populations? Is heterozygosity the best measure of genomic variation? Do breeding individuals exhibit mate choice to produce individuals that are intermediate in genomic variation?

Is too little and too much genetic variation a problem in populations? Inbreeding Depression: Reduced fitness caused by inbreeding. e.g. deleterious recessive alleles. Outbreeding Depression: Reduced fitness caused by out breeding. e.g. disruption of coadapted gene complexes. Perhaps an intermediate level is optimal?

1) Inbreeding decreases heterozygosity. 2) Inbreeding results in inbreeding depression. measures of heterozygosity should by definition be good metrics for inbreeding depression. 3) However, notice that the relationship isn’t exactly linear the deeper the inbreeding.

4) At the other end of the spectrum, too much genomic divergence might be a bad thing. It might break up combinations of alleles that allow for local adaptation. (Outbreeding depression). Heterozygosity as a metric might not perform as well here. Maybe a better metric than heterozygosity: mean d2 : it estimates the average divergence time between an individual’s parents. Presumably is better when Ne x m > 1 thus, best suited for microsatellite markers 5) Maybe there is an optimum level of population genetic variation that is selected (stabilizing selection).

Lakes and rivers. Large population sizes. Nesting parentals court and spawn with females and provide care. Cuckolder males mature quickly and sneak fertilizations. Lepomis macrochirus: Blue gill Collected all breeding adults and larvae from nests in L. Opinicon. Genotypes were determined for each adult and a sample of kids. Reproductive success was calculated by weighting each nest by brood size, which was estimated based on larval dry weight. 4)

Table 1. Summary of the measures for genomic divergence. Genomic divergence and heterozygosity do not differ among parental males, cuckolder males, females. 2. Heterozygosity and mean d2 are correlated measures.

Intermediate values of mean d2 were associated Cuckolder males Parental males A quadratic model provided the best fit to the data. females Intermediate values of mean d2 were associated with higher reproductive success and less fluctuating assymetry.

mean d2 based upon 10 loci still yields a dataset that is best explained by a quadratic model

Mate Choice 1). Offspring of parental had lower values of mean d2 than expected under random mating. They were closer to the optimum. 2). Offspring of cuckolders had higher values of mean d2 than expected under random mating. They were larger than the parental offspring values and farther from the optimum. 3) Across all offspring, mean d2 values were not significantly different, thus indicating constancy or stability of mean d2 .

Conclusions Stabilizing selection may be operating to maintain genomic divergence in bluegill. mean d2 maybe a better metric for detecting both high and low levels of divergence (especially for deeper cases of inbreeding). 2) Parental males and females appear to select mates such that their offspring have intermediate levels of genomic divergence. 3) Cuckolder’s take what they can get. Their offspring were further from the optimum than was expected. This would presumably contribute to the maintenance of genetic variation.

What genetically is happening in hybrid populations of tiger salamander in California? Ambystoma californiense Ambystoma tigrinum

Tiger salamanders occur in three different habitats in CA. The vernal pool habitat is the natural habitat of the CA tiger sal. A. tigrinum is found in all three types of habitat in the midwest

The different pond types are found in close geographical proximity

Markers used in the Study: Both Nuclear and mtDNA

A greater proportion of A. tigrinum alleles

There is considerable variation in allele frequencies at all levels of analysis.

Conclusions (without going into all of the stats tests) There is considerable genetic heterogeneity in these hybrid populations. There does appear to be an association between perennial ponds and A. tigrinum alleles. Paedomorphosis may be important. 2) This may reflect a number of things: endogenous selection: maintenance of different alleles in different genetic backgrounds due to within-genome interactions such as heterozygote advantage, disadvantage, or epistasis. exogenous selection: maintenance of different alleles in different environments due to trade-offs in local adaptation. stochasticity of genetics and demography.