Abstract
Hookworms are intestinal blood-feeding nematodes that parasitize and cause high levels of mortality in a wide range of mammals, including otariid pinnipeds. Recently, an empirical study showed that inbreeding (assessed by individual measures of multi-locus heterozygosity) is associated with hookworm-related mortality of California sea lions. If inbreeding increases susceptibility to hookworms, effects would expectedly be stronger in small, fragmented populations. We tested this assumption in the New Zealand sea lion, a threatened otariid that has low levels of genetic variability and high hookworm infection rates. Using a panel of 22 microsatellites, we found that average allelic diversity (5.9) and mean heterozygosity (0.72) were higher than expected for a small population with restricted breeding, and we found no evidence of an association between genetic variability and hookworm resistance. However, similar to what was observed for the California sea lion, homozygosity at a single locus explained the occurrence of anaemia and thrombocytopenia in hookworm-infected pups (generalized linear model, F = 11.81, p < 0.001) and the effect was apparently driven by a particular allele (odds ratio = 34.95%; CI: 7.12–162.41; p < 0.00001). Our study offers further evidence that these haematophagus parasites exert selective pressure on otariid blood-clotting processes.
Highlights
Natural populations commonly harbour substantial variation in their ability to resist infection
Similar to what was observed for the California sea lion, homozygosity at a single locus explained the occurrence of anaemia and thrombocytopenia in hookworm-infected pups and the effect was apparently driven by a particular allele
Considering the parasite’s wide host range and pathogenesis, it is possible that hookworms drive selection on platelet (PLT) function or blood-clotting across different host species. We tested these assumptions in NZSL pups by examining whether (i) relatively less heterozygous individuals are more susceptible to hookworm infection and (ii) occurrence of hookworm-related anaemia is explained by associative overdominance, as observed for California sea lions (Acevedo-Whitehouse et al 2006)
Summary
Natural populations commonly harbour substantial variation in their ability to resist infection. An empirical study showed that inbreeding (assessed by individual measures of multi-locus heterozygosity) is associated with hookworm-related mortality of California sea lions.
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More From: Proceedings of the Royal Society B: Biological Sciences
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