Depauperate major histocompatibility complex variation in the endangered reticulated flatwoods salamander (Ambystoma bishopi)

The Amphibian Major Histocompatibility Complex-A Review and Future Outlook

The major histocompatibility complex (MHC) is a cluster of functionally related genes encoding proteins which, among other functions, mediate immune system activation. While the MHC of many vertebrates has been extensively studied, less is known about the amphibian MHC. This represents an important knowledge gap because amphibians mark the evolutionary transition from an aquatic to a terrestrial lifestyle and often maintain a biphasic lifestyle. Hence, they tend to be exposed to both aquatic and terrestrial pathogen communities, providing opportunities to gain fundamental insights into how the immune system responds to different environmental challenges. Moreover, amphibians are globally threatened by invasive pathogens and the MHC may play a role in combating population decline. In this review, we summarize the current state of knowledge regarding the amphibian MHC and identify the major differences with other vertebrates. We also review how the number of MHC gene copies varies across amphibian groups and how MHC-based variation relates to amphibian ontogeny, behaviour, disease, and phylogeography. We conclude by identifying knowledge gaps and proposing priorities for future research.

Genetic Diversity and Differentiation of MHC Class I Genes in Red-Crowned Crane Populations

The red-crowned crane (Grus japonensis) has been demoted to “vulnerable species” because its populations have apparently stabilized in Japan and Korea. Low variation and genetic drift may cause damage to the nascent recovery of the G. japonensis population. The major histocompatibility complex (MHC) is one of the most polymorphic gene families in the vertebrate genome and can reflect information on the adaptive evolution of endangered species. In this study, variations in MHC I exon 3 of captive G. japonensis in China were assessed and compared with those in cranes from Japan. Forty MHC alleles of 274 base pairs were isolated from 32 individuals from two captive populations in China. There was high variability in the nucleotide and amino acid composition, showing the proportion of polymorphic sites of 18.98 and 32.97%, respectively. Comparative analyses of the Chinese and Japanese populations based on 222 base pair sequences revealed more alleles and higher variation in the Chinese population. The lack of significant geographical differentiation of G. japonensis was supported by the genetic differentiation coefficient (0.04506) between the Chinese and Japanese populations. Positive selection of antigen-binding sites was observed, which contributed to maintaining the diversity of MHC class I genes. Phylogenetic analysis suggested the persistence of trans-species polymorphisms among MHC class I genes in Gruidae species. Our results may contribute to optimizing the management of G. japonensis populations and population recovery of this threatened species.

Population structure, gene flow, and sex-biased dispersal in the reticulated flatwoods salamander (Ambystoma bishopi): Implications for translocations

Understanding patterns of gene flow and population structure is vital for managing threatened and endangered species. The reticulated flatwoods salamander (Ambystoma bishopi) is an endangered species with a fragmented range; therefore, assessing connectivity and genetic population structure can inform future conservation. Samples collected from breeding sites (n = 5) were used to calculate structure and gene flow using three marker types: single nucleotide polymorphisms isolated from potential immune genes (SNPs), nuclear data from the major histocompatibility complex (MHC), and the mitochondrial control region. At a broad geographical scale, nuclear data (SNP and MHC) supported gene flow and little structure (F ST = 0.00-0.09) while mitochondrial structure was high (ΦST = 0.15-0.36) and gene flow was low. Mitochondrial markers also exhibited isolation by distance (IBD) between sites (p = 0.01) and within one site (p = 0.04) while nuclear markers did not show IBD between or within sites (p = 0.17 and p = 0.66). Due to the discordant results between nuclear and mitochondrial markers, our results suggest male-biased dispersal. Overall, salamander populations showed little genetic differentiation and structure with some gene flow, at least historically, among sampling sites. Given historic gene flow and a lack of population structure, carefully considered reintroductions could begin to expand the limited range of this salamander to ensure its long-term resilience.