Can MHC‐assortative partner choice promote offspring diversity? A new combination of MHC‐dependent behaviours among sexes in a highly successful invasive mammal

Abstract

Sexual selection involving genetically disassortative mate choice is one of several evolutionary processes that can maintain or enhance population genetic variability. Examples of reproductive systems in which choosers (generally females) select mates depending on their major histocompatibility complex (MHC) genes have been reported for several vertebrate species. Notably, the role of MHC-dependent choice not in mating contexts, but in other kinds of social interactions such as in the establishment of complex social systems, has not yet drawn significant scientific interest and is virtually absent from the literature. We have investigated male and female MHC-dependent choice in an invasive population of North American raccoons (Procyon lotor) in Germany. Both male and female raccoons rely on olfaction for individual recognition. Males have an unusually complex social system in which older individuals choose unrelated younger ones to form stable male coalitions that defend territories and a monopoly over females. We have confirmed that females perform MHC-disassortative mate choice and that this behaviour fosters genetic diversity of offspring. We have also observed that males build coalitions by choosing male partners depending on their MHC, but in an assortative manner. This is the first observation of antagonistic MHC-dependent behaviours among sexes. We show that this is the only combination of MHC-dependent partner choice that leads to outbreeding. In the case of introduced raccoons, such behaviours can act together to promote the invasive potential of the species by increasing its adaptive genetic divergence.

The best smellers make the best choosers: mate choice is affected by female chemosensory receptor gene diversity in a mammal

“…Library preparation followed a two-step PCR approach, with the first PCR (26 cycles) being dedicated to product amplification and a second PCR (10 cycles) to index (or barcode) incorporation. After initial optimization of the annealing temperatures, all PCRs for initial amplification with CS primers (Fluidigm reference) were set to a final volume of 10 ml, with 3 ml PCR buffer containing MgCl 2 , 0.5 ml of each primer [ We employed a recently developed bioinformatic workflow [5,38] to filter, interpret and call alleles out of the raw sequences. Raw reads were initially quality-checked by removing royalsocietypublishing.org/journal/rspb Proc.…”

“…originated from independent PCRs). All other steps on the bioinformatic pipeline were performed as described elsewhere [5].…”

“…We tested whether females chose their mating partners depending on the male MHC class I alleles. Parentage and relatedness indices of all individuals had previously been established in our earlier study, and detailed methods are described therein [5]. In general terms, all individuals were genotyped for 10 microsatellite loci that were used for parentage inference and relatedness estimation.…”

“…Females of many vertebrate species are believed to use their sense of smell to assess the genetic quality of potential reproductive partners [1,2]. The genes of the major histocompatibility complex (MHC) are now widely accepted to play a central role in sexual selection, as they are targeted by females who aim at boosting the genetic variability of their offspring by preferring to mate with males that are particularly diverse (or dissimilar to the female) in their MHC [3][4][5][6]. Although examples of MHC-dependent mate choice have been reported for almost all major vertebrate taxa [7][8][9][10], and although females are probably able to smell the odours that reveal the MHC composition of males [4,5,[11][12][13], the odorants involved in this type of communication and their corresponding chemosensory receptors remain mysterious.…”

Assigning alleles to different loci in amplifications of duplicated loci

“…Several studies have used the number of alleles that individuals possess to estimate variation of MHC loci within individuals, as well as the proportion of shared alleles to estimate pairwise similarity between individuals when alleles cannot be assigned to a particular locus (e.g., Gaigher et al, 2018;Huchard, Knapp, Wang, Raymond, & Cowlishaw, 2010;Miller, Moore, Nelson, & Daugherty, 2009;Santos, Michler, & Sommer, 2017;Strandh et al, 2012). However, these methods are generally inaccurate and are largely influenced by the polymorphism of loci or genetic diversity within a population.…”