Low heterozygosity is associated with vector‐borne disease in crows

Abstract

Infectious diseases can have devastating impacts on wildlife populations and are of particular concern for small, inbred populations. Identifying specific pathogens that are linked to morbidity and mortality in inbred individuals is a priority for the conservation of small populations, but opportunities to examine them in the wild are rare. Here, we examined the relationship between heterozygosity and infectious disease in American crows (Corvus brachyrhynchos), a species that engages in close inbreeding, focusing on three pathogens common in Davis, California, USA: West Nile virus (WNV), Plasmodium spp. (avian malaria), and Campylobacter jejuni. We found that low heterozygosity at a panel of 33 microsatellite loci was associated with two vector-borne infectious diseases (WNV and avian malaria), but not with infection by the bacterial gut pathogen C. jejuni. Reasons for this association with vector-borne pathogens are unclear, but might include behavioral factors and immunological differences associated with inbreeding. Overall, these data are consistent with the idea that inbred individuals may be more susceptible to both novel and endemic vector-borne pathogens, underscoring the importance of protecting genetic diversity within populations and buffering small populations against infectious diseases.

Apparent inbreeding preference despite inbreeding depression in the American crow

“…In general, however, our estimates of b were probably conservative, as they were based solely on fledging failure associated with inbreeding. Inbreeding is associated with many additional costs in crows (e.g., poor body condition, lower long‐term survival probability, elevated disease probability, and suppressed immune response; Townsend, Clark, McGowan, Buckles et al., ; this study; Townsend, Clark, McGowan, Miller et al., ; Townsend et al., ), and their accumulated costs are likely higher than those that we specified in this model.…”

“…We scored all birds at a minimum of 30 loci, and most were scored at all loci (mean proportion of loci typed >0.99). PCR conditions are given in elsewhere (Townsend et al., ). Locus characteristics (e.g., alleles/ locus, tests of Hardy–Weinberg equilibrium and null allele frequencies) are given in the supplementary materials (Supporting Information Table ).…”

Towards a more healthy conservation paradigm: integrating disease and molecular ecology to aid biological conservation†

“…Whitehorn et al 2011), birds (e.g. Ortego et al 2007a;Townsend et al 2018), mammals (e.g. Mitchell et al 2017;Rijks et al 2008) and fish (e.g.…”

Heterozygosity and fitness in a threatened songbird: blood parasite infection is explained by single-locus but not genome-wide effects

“…In American Crows (Corvus brachyrhynchos), lower heterozygosity was associated with infection of offspring, but not adults, by Plasmodium spp. (Townsend et al 2018a). However, other avian studies failed to find any relationship (Ortego et al 2007;Vallender et al 2012).…”

“…One of the traits with a potential effect on infection occurrence is the genetic diversity of the host Frankham 2005). However, the link between genetic diversity and blood parasitism in birds is not well understood, because studies that addressed it have been scarce and yielded mixed results (MacDougall-Shackleton et al 2005;Vallender et al 2012;Boerner et al 2013;Ferrer et al 2014;Townsend et al 2018a). In addition, only one study focused on a species with a small population (Ortego et al 2007).…”