Selection outweighs drift at a fine scale: Lack of MHC differentiation within a family living lizard across geographically close but disconnected rocky outcrops

Abstract

The highly polymorphic genes of the major histocompatibility complex (MHC) are involved in disease resistance, mate choice and kin recognition. Therefore, they are widely used markers for investigating adaptive variation. Although selection is the key driver, gene flow and genetic drift also influence adaptive genetic variation, sometimes in opposing ways and with consequences for adaptive potential. To further understand the processes that generate MHC variation, it is helpful to compare variation at the MHC with that at neutral genetic loci. Differences in MHC and neutral genetic variation are useful for inferring the relative influence of selection, gene flow and drift on MHC variation. To date, such investigations have usually been undertaken at a broad spatial scale. Yet, evolutionary and ecological processes can occur at a fine spatial scale, particularly in small or fragmented populations. We investigated spatial patterns of MHC variation among three geographically close, naturally discrete, sampling sites of Egernia stokesii, an Australian lizard. The MHC of E. stokesii has recently been characterized, and there is evidence for historical selection on the MHC. We found E. stokesii MHC weakly differentiated among sites compared to microsatellites, suggesting selection, acting similarly at each site, has outweighed any effects of low gene flow or of genetic drift on E. stokesii MHC variation. Our findings demonstrate the strength of selection in shaping patterns of MHC variation or consistency at a fine spatial scale.

Too much of a good thing? Finding the most informative genetic data set to answer conservation questions

“…Looking at this another way, in Maria Island devils at least, inbreeding appears to be a sufficiently powerful process to drive the diversity of loci that are probably also experiencing selection. With the growing availability of various data sets in molecular ecology, we are increasingly able to ask questions about the extent to which neutral vs. adaptive processes shape patterns of diversity in natural populations (Grueber et al, 2013;Pearson, Bull, & Gardner, 2018;Sutton, Nakagawa, Robertson, & Jamieson, 2011). This is particularly relevant in small populations, which experience significant genetic drift and are under threat from novel environmental and ecological pressures (Gilroy, Phillips, Richardson, & van Oosterhout, 2017).…”

Fine‐scale genetic structuring in a group‐living lizard, the gidgee skink (Egernia stokesii)

“…We found evidence for a consistent pattern of significant fine‐scale genetic structure within seven close but disconnected E. stokesii sampling sites. Our results extend that of an earlier study that found significant genetic structure among three of the sites we sampled (Pearson et al ) and suggest similar ecological and evolutionary processes may have occurred across the seven sites. The significant genetic differentiation we observed is likely to be due to the family group social structure and limited dispersal exhibited in this species.…”

“…We would expect a much sharper break between the clusters if assortative mating is invoked. In addition, previous work on MHC in this species from these locations did not uncover any differentiation at MHC (Pearson et al ).…”

“…In order to better understand the genetic consequences of group living, we aimed to identify if E. stokesii exhibit a consistent pattern of fine‐scale genetic structure across the same seven outcrops. We extend the work of Pearson et al (), which identified significant neutral (based on microsatellite data) genetic structuring of lizards among three of the seven outcrops we studied. For E. stokesii , limited dispersal, habitat constraints, and formation of long‐term pair bonds and stable family groups, are likely to constrain gene flow and generate genetic structure at a fine scale.…”

Genetic diversity of major histocompatibility complex class I genes in Zootoca vivipara

“…The researchers successfully obtained sequence information and analyzed their genetic structure and population dynamics [4][5][6][7]. Later, when analyzing the MHC of some endangered or newly discovered species [8,9], people further studied from the aspects of species relationship, survival and reproduction, and disease resistance [10][11][12][13][14][15][16][17].…”