MHC class I diversity predicts non-random mating in Chinese alligators (Alligator sinensis)

Abstract

The major histocompatibility complex (MHC) has several important roles in kin recognition, pathogen resistance and mate selection. Research in fish, birds and mammals has suggested that individuals optimise MHC diversity, and therefore offspring fitness, when choosing mates. In reptiles, however, it is unclear whether female mate choice is based on genome-wide genetic characteristics such as microsatellite DNA loci, particular functional-trait loci (e.g., MHC) or both, and MHC's effects on mate choice remain relatively understudied. Herein, we used 13 microsatellite loci and two MHC class I loci to investigate female mate choice of Chinese alligators (Alligator sinensis) in the semi-natural condition. We also determined correlations between the MHC genotype of breeding males and male reproductive success. We found that MHC-heterozygous males harbour a greater reproductive success, which probably is the reason that these males are more preferred by the females than MHC-homozygous males. Furthermore, the MHC class I amino-acid distance and functional distance of true mating pairs were higher compared with those of randomly sampled pairs. Analysis of microsatellites revealed that, despite mate choice, females did not completely avoid inbreeding. These findings are the first evidence of MHC-associated mate choice in Chinese alligators, suggesting that females may adopt different mating strategies after assessing the MHC characteristics of potential mates.

Patterns of MHC‐dependent sexual selection in a free‐living population of sheep

“…Second, some studies have reported that individuals with higher diversity or heterozygosity at the MHC were favoured as partners (Cutrera et al, 2012; Landry et al, 2001; Richardson et al, 2005; Winternitz et al, 2015). Third, in terms of MHC compatibility, MHC‐dependent disassortative mating has been reported, which could maximise the MHC diversity of offspring (Han et al, 2019; Hoover et al, 2018; Schwensow et al, 2008; Setchell et al, 2010). Several studies have also demonstrated that MHC genes could be a cue for kin recognition enabling avoidance of mating with relatives through MHC‐associated odours (Grob et al, 1998; Milinski, 2006; Penn, 2002).…”

“…Second, some studies have reported that individuals with higher diversity or heterozygosity at the MHC were favoured as partners (Cutrera et al, 2012;Landry et al, 2001;Richardson et al, 2005;Winternitz et al, 2015). Third, in terms of MHC compatibility, MHC-dependent disassortative mating has been reported, which could maximise the MHC diversity of offspring (Han et al, 2019;Hoover et al, 2018;Schwensow et al, 2008;Setchell et al, 2010).…”

Major histocompatibility complex genomic investigation of endangered Chinese alligator provides insights into the evolution of tetrapod major histocompatibility complex and survival of critically bottlenecked species

“…We took a population survey for MHC-I and MHC-IIB genes in previous studies (Zhai et al, 2017;Han et al, 2019). Unlike the various high alleles found in MHC-IIB in Chinese alligator, only I1327 (Alsi-I7), I20 (Alsi-Iψ-BAC32), and Beta1085 (Alsi-IIB11) were found all dimorphic: two alleles at each locus (Zhai et al, 2017).…”

“…In our previous study, the BAC library was constructed (He et al, 2012), the genome was sequenced (Wan et al, 2013), and the differential mRNA expression of several tissues of the Chinese alligator was investigated (Lin et al, 2018) to understand the immune system and genetic basis of sex determination and longdiving behavior. Furthermore, MHC genes were investigated to study MHC-associated mate choice in Chinese alligators (Han et al, 2019). Together, all these studies make it possible to tackle the unanswered questions about the MHC architecture in Crocodylia.…”

Patterns of MHC-dependent sexual selection in a free-living population of sheep

“…In addition, some studies have reported that individuals with higher diversity or heterozygosity at the MHC were favoured as partners (Landry, Garant et al 2001, Richardson, Komdeur et al 2005, Cutrera, Fanjul et al 2012, Winternitz, Promerova et al 2015). In terms of MHC compatibility, MHC-dependent disassortative mating has been reported, which could maximise the MHC diversity of offspring (Schwensow, Eberle et al 2008, Setchell, Charpentier et al 2010, Hoover, Alcaide et al 2018, Han, Sun et al 2019). However, as excessive expression of MHC molecules could lead to depletion of the mature T-cell repertoire and elevated risk of autoimmune disease, it has also been suggested that individuals may optimise rather than maximise MHC diversity (Reusch, Haberli et al 2001, Griggio, Biard et al 2011, Rekdal, Anmarkrud et al 2019).…”