Patterns of Genetic Diversity and Gene Flow Associated With an Aridity Gradient in Populations of Common Mole-rats, Cryptomys hottentotus hottentotus

Genetic adaptation is the change of a population toward a phenotype that best fits the present ecological conditions of the environment it inhabits. As environmental conditions change, allele frequencies shift, resulting in different populations of the same species possessing genetic variation and divergent phenotypes. Cooperatively breeding common mole-rats (Cryptomys hottentotus hottentotus) inhabit environments along an aridity gradient in South Africa, which provides an opportunity for local genetic adaptations to occur. Using one mitochondrial gene (cytochrome b) and 3,540 SNP loci across the whole genome, we determined the phylogenetic relationship, population structure and genetic diversity of five populations of C. h. hottentotus located along an aridity gradient. Mitochondrial data identified population-specific clades that were less distinct in the two mesic populations, potentially indicating historical or recent gene flow, or the retention of ancestral haplotypes. Arid and semi-arid populations formed a distinct cluster from the non-arid populations. Genetic diversity and gene flow were higher in arid-dwelling individuals, suggesting greater connectivity and interactions between colonies in arid regions in comparison to mesic ones. Using an Aridity Index, we determined that isolation by environment, rather than isolation by geographical distance, best explains the genetic distance between the populations. Further analyses using target loci may determine if there are differing underlying genetic adaptations among populations of C. h. hottentotus. These analyses could help unravel population differences in response to environmental factors within a subspecies of bathyergid mole-rat and determine the adaptive capacity of this small nonmigratory subterranean rodent species in response to aridification in the face of climate change.

The Evolution and Ecology of Oxidative and Antioxidant Status: A Comparative Approach in African Mole-Rats

The naked mole-rat of the family Bathyergidae has been the showpiece for ageing research as they contradict the traditional understanding of the oxidative stress theory of ageing. Some other bathyergids also possess increased lifespans, but there has been a remarkable lack of comparison between species within the family Bathyergidae. This study set out to investigate how plasma oxidative markers (total oxidant status (TOS), total antioxidant capacity (TAC), and the oxidative stress index (OSI)) differ between five species and three subspecies of bathyergids, differing in their maximum lifespan potential (MLSP), resting metabolic rate, aridity index (AI), and sociality. We also investigated how oxidative markers may differ between captive and wild-caught mole-rats. Our results reveal that increased TOS, TAC, and OSI are associated with increased MLSP. This pattern is more prevalent in the social-living species than the solitary-living species. We also found that oxidative variables decreased with an increasing AI and that wild-caught individuals typically have higher antioxidants. We speculate that the correlation between higher oxidative markers and MLSP is due to the hypoxia-tolerance of the mole-rats investigated. Hormesis (the biphasic response to oxidative stress promoting protection) is a likely mechanism behind the increased oxidative markers observed and promotes longevity in some members of the Bathyergidae family.

Historical demography and climatic niches of the Natal multimammate mouse (Mastomys natalensis) in the Zambezian region

The Natal multimammate mouse (Mastomys natalensis) is the most widespread rodent species in sub-Saharan Africa, often studied as an agricultural pest and reservoir of viruses. Its mitochondrial (Mt) phylogeny revealed six major lineages parapatrically distributed across open habitats of sub-Saharan Africa. In this study we used 1949 sequences of the mitochondrial cytochrome b gene to elaborate on distribution and evolutionary history of three Mt lineages inhabiting the open habitats of the Zambezian region (corresponding roughly to the African savannas south of the Equator). We describe in more detail contact zones between the lineages—their location and extent of co-occurrence within localities—and infer past population trends. The estimates are interpreted in the light of climatic niche models. The lineages underwent reduction in effective population size during the last glacial, but they spread widely after that: two of them after the last glacial maximum and the last one in mid-Holocene. The centers of expansion, i.e., possible long-term savanna refugia, were estimated to lie close to the Eastern Arc Mountains and lakes of the Great African Rift, geomorphological structures likely to have had long-term influence on geographical distribution of the lineages. Environmental niche modeling shows climate could also affect the broad scale distribution of the lineages but is unlikely to explain the narrow width of the contact zones. The intraspecific Mt differentiation of M. natalensis echoes phylogeographic patterns observed in multiple co-distributed mammal species, which suggests the mammal communities in the region are shaped by the same long-term processes.

Population genetics of the naked mole-rat Heterocephalus glaber: The role of rivers in shaping genetic structure

We used nested clade phylogeographic analysis (NCPA) of mitochondrial DNA sequence data to examine the processes contributing to population structure in naked mole-rats. We examined sequence variation in the (1097 bp) control region D-loop of the mitochondrial genome in 303 individuals from 174 colonies of naked mole-rats (Heterocephalus glaber) located mainly within an 870 km2 area in Meru National Park, Kenya. Four rivers were found to be correlated to a significant fragmentation inference in the NCPA. The largest pairwise divergence between haplotypes from populations separated by rivers was 2.74%, which was well over half of the divergence reported between the extremes of the distribution from southern Ethiopia to southern Kenya (4.6%). However, the size of the river (measured in current discharge) was not a good predictor of the amount of sequence divergence between populations separated by a river. It appears that a large-scale historical fragmentation event may have conflated fragmentation patterns on a smaller scale, when recent colonization and range expansion brought two old lineages together at a location with a relatively small river separating them.