Abstract
BackgroundA multitude of correlations between heterozygosity and fitness proxies associated with disease have been reported from wild populations, but the genetic basis of these associations is unresolved. We used a longitudinal dataset on wild Galapagos sea lions (Zalophus wollebaeki) to develop a relatively new perspective on this problem, by testing for associations between heterozygosity and immune variation across age classes and between ecological contexts.ResultsHomozygosity by locus was negatively correlated with serum immunoglobulin G production in pups (0–3 months of age), suggesting that reduced genetic diversity has a detrimental influence on the early development of immune defence in the Galapagos sea lion. In addition, homozygosity by locus was positively correlated with total circulating leukocyte concentration in juveniles (6–24 months of age), but only in a colony subject to the anthropogenic environmental impacts of development, pollution and introduced species, which suggests that reduced genetic diversity influences mature immune system activity in circumstances of high antigen exposure.ConclusionsThese findings demonstrate the environmental context-dependency of the phenotypic expression of immune variation, which is implicit in the theory of ecoimmunology, but which has been rarely demonstrated in the wild. They also indicate that heterozygosity may be linked to the maintenance of heterogeneity in mammalian immune system development and response to infection, adding to the body of evidence on the nature of the mechanistic link between heterozygosity and fitness.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0519-6) contains supplementary material, which is available to authorized users.
Highlights
A multitude of correlations between heterozygosity and fitness proxies associated with disease have been reported from wild populations, but the genetic basis of these associations is unresolved
Heterozygosity is of interest because it quantifies within individual genetic diversity, and is likely to be related to inbreeding in some way – in exactly which way is contentious
Change in pup body length was greater in the human-impacted colony than in the control colony (GLM: n = 40, estimate = −3.93, Standard error (SE) = 1.54, p = 0.014), but there was no significant difference between sexes (GLM: n = 40, estimate = 3.14, SE = 1.59, p = 0.056)
Summary
A multitude of correlations between heterozygosity and fitness proxies associated with disease have been reported from wild populations, but the genetic basis of these associations is unresolved. An alternative to calculation from pedigrees is to use data from neutral genetic markers to either summarise genetic diversity as multi-locus heterozygosity (MLH), or to estimate inbreeding coefficients directly using relatedness algorithms, as a proxy for inbreeding value. These latter methods have the advantage of being calculable for individuals sampled from a single cohort, and are feasible in many study systems, especially given recent advances in sequencing technology and the availability of resources for the study of genetics
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