Evidence of environmental niche differentiation in the striped mouse (Rhabdomyssp.): inference from its current distribution in southern Africa

Abstract

The aim of this study was to characterize environmental differentiation of lineages within Rhabdomys and provide hypotheses regarding potential areas of contact between them in the Southern African subregion, including the Republic of South Africa, Lesotho, and Namibia. Records of Rhabdomys taxa across the study region were compiled and georeferenced from the literature, museum records, and field expeditions. Presence records were summarized within a 10 × 10 km grid covering the study area. Environmental information regarding climate, topography, land use, and vegetation productivity was gathered at the same resolution. Multivariate statistics were used to characterize the current environmental niche and distribution of the whole genus as well as of three mitochondrial lineages known to occur in southern Africa. Distribution modeling was carried out using MAXENT in order to generate hypotheses regarding current distribution of each taxa and their potential contact zones. Results indicate that the two species within Rhabdomys appear to have differentiated across the precipitation/temperature gradient present in the region from east to west. R. dilectus occupies the wettest areas in eastern southern Africa, while R. pumilio occupies the warmer and drier regions in the west, but also penetrates in the more mesic central part of the region. We provide further evidence of environmental differentiation within two lineages of R. dilectus. Contact zones between lineages appear to occur in areas of strong environmental gradients and topographic complexity, such as the transition zones between major biomes and the escarpment area where a sharp altitudinal gradient separates coastal and plateau areas, but also within more homogeneous areas such as within grassland and savannah biomes. Our results indicate that Rhabdomys may be more specialized than previously thought when considering current knowledge regarding mitochondrial lineages. The genus appears to have differentiated along two major environmental axes in the study region, but results also suggest dispersal limitations and biological interactions having a role in limiting current distribution boundaries. Furthermore, the projection of the potential geographic distribution of the different lineages suggests several contact zones that may be interesting study fields for understanding the interplay between ecological and evolutionary processes during speciation.

Extinction or Survival? Behavioral Flexibility in Response to Environmental Change in the African Striped Mouse Rhabdomys

“…Its adaptation to arid habitats, together with its bolder personality type, lower levels of anxiety [93] and the socially flexible phenotype [70] could result in R. pumilio displacing both R. dilectus sister taxa, forcing them either into extinction or displacing them into the more northern and eastern parts of South Africa (Figure 3). Finally, since R. d. dilectus occupies the warmer, more stable grasslands, while R. d. chakae occupies more humid, cooler environments [83], we suggest that R. d. dilectus is more likely to persist and displace its sister subspecies, as the general drying trend will limit the niches available for R. d. chakae.…”

“…In addition, the eastern regions are less likely to experience as intense aridification as the western regions [123]. Since Rhabdomys apparently originated in the historical arid western open shrubland vegetation of southern Africa, and from there colonized the moist eastern regions secondarily [83], we suggest that R. pumilio may also respond by shifting its range further east, occupying habitats that will likely become similar to what they currently experience (Figure 3). The various Rhabdomys species are associated with specific vegetation types [82,95], and general aridification in an easterly direction will have a corresponding impact on the vegetation of the different biomes.…”

“…Our long-term studies on striped mice from the arid Succulent Karoo of South Africa correspond with the currently recognized R. pumilio (proposed to remain as R. pumilio; Figure 1), while our studies on striped mice from the grasslands in Gauteng correspond with the currently recognized R. d. chakae and R. d. dilectus. R. d. dilectus occurs primarily in warm, stable grassland/savanna environments, while R. d. chakae occurs in colder, more humid environments [83] (Figure 1). Our field site for studies on R. pumilio is located in Goegap Nature Reserve (Northern Cape Province), in the arid Succulent Karoo.…”

“…Since the grasslands of South Africa are comparatively stable environments [83], it is possible that selection has favored relatively similar genotypes across a wide range of habitats.…”

“…Whether the taxon can exploit this potential for flexibility under rapidly changing conditions, however, is unknown. Assuming that R. dilectus survives through displaying behavioral flexibility and R. pumilio shifts eastwards, the two species could coexist in the mid northern parts of South Africa (Figure 3) because of niche separation/specialization [83].…”