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ABSTRACT: The major histocompatibility complex (MHC) genes code for proteins that play a critical role in the immune system response. The MHC genes are among the most polymorphic genes in vertebrates, presumably due to balancing selection. The two MHC classes appear to differ in the rate of evolution, but the reasons for this variation are not well understood. Here, we investigate the level of polymorphism and the evolution of sequences that code for the peptide-binding regions of MHC class I and class II DRB genes in the Alpine marmot (Marmota marmota). We found evidence for four expressed MHC class I loci and two expressed MHC class II loci. MHC genes in marmots were characterized by low polymorphism, as one to eight alleles per putative locus were detected in 38 individuals from three French Alps populations. The generally limited degree of polymorphism, which was more pronounced in class I genes, is likely due to bottleneck the populations undergone. Additionally, gene duplication within each class might have compensated for the loss of polymorphism at particular loci. The two gene classes showed different patterns of evolution. The most polymorphic of the putative loci, Mama-DRB1, showed clear evidence of historical positive selection for amino acid replacements. However, no signal of positive selection was evident in the MHC class I genes. These contrasting patterns of sequence evolution may reflect differences in selection pressures acting on class I and class II genes.
Journal of Evolutionary Biology 05/2012; 25(8):1686-93. · 3.28 Impact Factor
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ABSTRACT: Assuming that a male’s genetic characteristics affect those of his offspring, extra-pair copulation has been hypothesized
to increase heterozygosity of the progeny—the “genetic compatibility” hypothesis—and the genetic diversity within litters—the
“genetic diversity” hypothesis. We tested these two hypotheses in the alpine marmot (Marmota marmota), a socially monogamous mammal showing a high rate of extra-pair paternity (EPP). In a first step, we tested the assumption
that a male’s genetic characteristics (heterozygosity and genetic similarity to the female) affect those of his offspring.
Genetic similarity between parents influenced offspring heterozygosity, offspring genetic similarity to their mother, and
litter genetic diversity. The father’s heterozygosity also influenced litter genetic diversity but did not affect offspring
heterozygosity. Hence, heterozygosity seems not to be heritable in the alpine marmot. In a second step, we compared genetic
characteristics of extra-pair young (EPY) and within-pair young (WPY). EPY were less genetically similar to their mother but
not more heterozygous than WPY. EPY siblings were also less genetically similar than their WPY half siblings. Finally, the
presence of EPY promoted genetic diversity within the litter. Thus, our data support both the “genetic compatibility” and
the “genetic diversity” hypotheses. We discuss further investigations needed to determine the primary causes of EPP in this
species.
Behavioral Ecology and Sociobiology 04/2012; 61(7):1081-1092. · 3.18 Impact Factor
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ABSTRACT: Extra-pair paternity (EPP) can be influenced by both social setting and female mate choice. If evidence suggests that females
try to obtain extra-pair copulations (EPCs) in order to gain genetic benefits when mated to a homozygous and/or to a related
male, females may not be able to choose freely among extra-pair mates (EPMs) as the social mate may constrain female access
to EPMs. In this study, we investigated, first, how EPP depended on social setting and specifically on the number of subordinate
males in the family group in a highly social and monogamous mammal, the alpine marmot. Second, we investigated how EPP depended
on female mate choice for genetic benefits measured as male mate-heterozygosity and within-pair relatedness. Our results reveal,
first, that EPP depended on the social setting, increasing with the number of subordinate males. Second, EPPs were related
to relatedness between mates. Third, EPMs were found to be more heterozygous than within-pair males. Thus, social setting
may constrain female choice by limiting opportunities for EPC. However, after accounting for social confounding factors, female
choice for genetic benefits may be a mechanism driving EPP in monogamous species.
Behavioral Ecology and Sociobiology 04/2012; 59(5):597-605. · 3.18 Impact Factor
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ABSTRACT: The relationship between individual genetic diversity and fitness-related traits are poorly understood in the wild. The availability
of highly polymorphic molecular markers, such as microsatellites, has made research on this subject more feasible. We used
three microsatellite-based measures of genetic diversity, individual heterozygosity H, mean d
2 and mean d
2
outbreeding to test for a relationship between individual genetic diversity and important fitness trait, juvenile survival, in a population
of alpine marmots (Marmota marmota), after controlling for the effects of ecological, social and physiological parameters that potentially influence juvenile
survival in marmots. Analyses were conducted on 158 juveniles, and revealed a positive association between juvenile survival
and genetic diversity measured by mean H. No association was found with mean d
2 and with mean d
2
outbreeding. This suggests a fitness disadvantage to less heterozygous juveniles. The genetic diversity-fitness correlation (GDFC) was
somewhat stronger during years with poor environmental conditions (i.e. wet summers). The stressful environmental conditions
of this high mountain population might enhance inbreeding depression and make this association between genetic diversity and
fitness detectable. Moreover the mating system, allowing extra pair copulation by occasional immigrants, as well as close
inbreeding, favours a wide range of individual genetic diversity (mean H ranges from 0.125 to 1), which also may have facilitated the detection of the GDFC. The results further suggest that the
observed GDFC is likely to be explained by the “local effect” hypothesis rather than by the “general effect” hypothesis.
Conservation Genetics 05/2006; 7(3):371-382. · 1.61 Impact Factor
