Ondřej Mikula

Pan-African phylogeny of Mus (subgenus Nannomys) reveals one of the most successful mammal radiations in Africa

BackgroundRodents of the genus Mus represent one of the most valuable biological models for biomedical and evolutionary research. Out of the four currently recognized subgenera, Nannomys (African pygmy mice, including the smallest rodents in the world) comprises the only original African lineage. Species of this subgenus became important models for the study of sex determination in mammals and they are also hosts of potentially dangerous pathogens. Nannomys ancestors colonized Africa from Asia at the end of Miocene and Eastern Africa should be considered as the place of their first radiation. In sharp contrast with this fact and despite the biological importance of Nannomys, the specimens from Eastern Africa were obviously under-represented in previous studies and the phylogenetic and distributional patterns were thus incomplete.ResultsWe performed comprehensive genetic analysis of 657 individuals of Nannomys collected at approximately 300 localities across the whole sub-Saharan Africa. Phylogenetic reconstructions based on mitochondrial (CYTB) and nuclear (IRBP) genes identified five species groups and three monotypic ancestral lineages. We provide evidence for important cryptic diversity and we defined and mapped the distribution of 27 molecular operational taxonomic units (MOTUs) that may correspond to presumable species. Biogeographical reconstructions based on data spanning all of Africa modified the previous evolutionary scenarios. First divergences occurred in Eastern African mountains soon after the colonization of the continent and the remnants of these old divergences still occur there, represented by long basal branches of M. (previously Muriculus) imberbis and two undescribed species from Ethiopia and Malawi. The radiation in drier lowland habitats associated with the decrease of body size is much younger, occurred mainly in a single lineage (called the minutoides group, and especially within the species M. minutoides), and was probably linked to aridification and climatic fluctuations in middle Pliocene/Pleistocene.ConclusionsWe discovered very high cryptic diversity in African pygmy mice making the genus Mus one of the richest genera of African mammals. Our taxon sampling allowed reliable phylogenetic and biogeographic reconstructions that (together with detailed distributional data of individual MOTUs) provide a solid basis for further evolutionary, ecological and epidemiological studies of this important group of rodents.

Shaking the myth: Body mass, aggression, steroid hormones, and social dominance in wild house mouse.

In social mammals, the position of a male in the groups hierarchy strongly affects his reproductive success. Since a high social rank is often gained through competition with other males, selection should favour bigger males over smaller ones. We may therefore predict faster growth and/or delayed sexual maturity in dominant males. Likewise, dominants should have higher levels of testosterone, hormone important in many aspects of male dominance. Less obvious is the relationship between dominance and levels of corticosterone but generally higher concentrations are expected in subordinate individuals. We studied body growth, sexual maturation and endocrinal changes in males of two house mouse subspecies, raised in fraternal pairs. Since Mus musculus domesticus is the subspecies which dominates mutual encounters with Mus musculus musculus we predicted higher growth rate, delayed puberty and aggression, and higher testosterone and corticosterone levels in domesticus males compared to musculus. In all comparisons, no differences were found between dominant and subordinate musculus brothers. On the other hand, in M. m. domesticus, dominant males revealed a different growth trajectory and lower corticosterone levels than subordinate males but not delayed puberty and higher testosterone concentrations, thus contradicting our predictions. In inter-subspecific comparisons, musculus males matured earlier but became aggressive at the same time as domesticus males. The musculus testosterone ontogeny suggests that social positions in this subspecies remain unfixed for an extended period and that the increasing levels probably reflect prolonged hierarchy contests. It appears that the ontogeny of behaviour and physiological traits diverge cryptically between the two subspecies.

There is no heterotic effect upon developmental stability in the ventral side of the skull within the house mouse hybrid zone

Fluctuating asymmetry (FA) of a body is expected to be related to an organism’s developmental instability. We studied patterns of FA in the ventral side of the skull along a transect across the central‐European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. We found that FA was not significantly different between introgression classes relative to differences between localities within those classes and that the within‐class differences were much larger than differences between individual‐signed asymmetries within localities. However, if year was added to the same analysis as another factor, FA was not significantly different among localities within the same introgression class. When individual asymmetries were plotted against individual hybrid indices, hybrids appeared more asymmetric than individuals from outside of the zone. Thus contrary to previous studies, we did not find lower FA indicating heterotic effect in hybrids for the traits studied. It is suggested that the impact of hybridization on FA in the ventral side of the mouse skull is negligible or overwhelmed by other factors.

Evolutionary history and species diversity of African pouched mice (Rodentia: Nesomyidae: Saccostomus)

We explore diversity of African pouched mice, genus Saccostomus (Rodentia, Nesomyidae), by sampling molecular and morphological variation across their continental‐scale distribution in southern and eastern African savannahs and woodlands. Both mitochondrial (cytochrome b) and nuclear DNA (IRBP, RAG1) as well as skull morphology confirm the distinction between two recognized species, S. campestris and S. mearnsi, with disjunct distribution in the Zambezian and Somali–Maasai bioregions, respectively. Molecular dating suggests the divergence of these taxa occurred in the Early Pliocene, 3.9 Ma before present, whereas the deepest divergences within each of them are only as old as 2.0 Ma for S. mearnsi and 1.4 Ma for S. campestris. Based on cytochrome b phylogeny, we defined five clades (three within S. campestris, two in S. mearnsi) whose species status was considered in the light of nuclear DNA markers and morphology. We conclude that S. campestris group consists of two subspecies S. campestris campestris (Peters, 1846; comprising two cytochrome b clades) and S. campestris mashonae (de Winton, 1897) that are moderately differentiated, albeit distinct in IRBP and skull form. They likely hybridize to a limited extent along the Kafue–Zambezi Rivers. Saccostomus mearnsi group consists of two species, S. mearnsi (Heller, 1910) and S. umbriventer (Miller, 1910), that are markedly differentiated in both nuclear markers and skull form and may possibly co‐occur in south‐western Kenya and north‐eastern Tanzania. Analysis of historical demography suggests both subspecies of S. campestris experienced population expansion dated to the Last Glacial. In the present range of S. campestris group, the distribution modelling suggests a moderate fragmentation of suitable habitats during the last glacial cycle, whereas in the range of S. mearnsi group it predicts substantial shifts of its occurrence in the same period.

Phylogeography of a widespread sub-Saharan murid rodent Aethomys chrysophilus: the role of geographic barriers and paleoclimate in the Zambezian bioregion

Abstract Murid rodents of the genus Aethomys are one of the most common rodents in drier habitats in sub-Saharan Africa. Among them, the red veld rat Aethomys chrysophilus is the most widespread species with the core distribution located in the Zambezian bioregion. In this study, we describe phylogeographic structure of the species and estimate its age from a time-calibrated phylogeny of the genus. Seven parapatric clades were identified in the mitochondrial cytochrome b phylogeny, where some of the distributions of these clades have been separated by previously described biogeographical divides (Zambezi-Kafue river system, Rukwa Rift and the Eastern Arc Mountains). One internal clade corresponded to populations previously described as a distinct species, Aethomys ineptus. The whole A. chrysophilus complex was estimated to be 1.3 (0.5–2.4) Mya old, with A. ineptus originating 0.7 (0.1–1.4) Mya before present. The internal position of A. ineptus was also recovered in phylogenetic reconstruction based on two nuclear genes and thus it is not a consequence of mitochondrial introgression. In addition, we analyzed skull form variation across the species’ distributional range and found no significant difference between A. ineptus and the rest of A. chrysophilus complex.

Evolution of the Grey-bellied pygmy mouse group: Highly structured molecular diversity with predictable geographic ranges but morphological crypsis

The grey-bellied pygmy mouse (Mus triton) from the endemic African subgenus Nannomys is a widespread rodent species inhabiting the highlands of eastern and central Africa. Although it has long been considered as a single species, recent data has suggested the existence of a species complex. In order to evaluate the geographical structure and current taxonomy of M. triton, we analysed one mitochondrial and six nuclear genes from individuals covering most of its distribution range. Our analysis revealed the existence of at least five distinct genetic lineages with only marginal overlaps among their distributional ranges. Morphological comparisons, however, showed large overlaps in external body measurements and only a weak differentiation in skull form. Therefore, we suggest maintaining M. triton as a single taxon with pronounced intraspecific genetic structure. Divergence dating analysis placed the most recent common ancestor of the extant lineages of M. triton to the early Pleistocene (about 2.0 Ma). The phylogeographic structure of the species was likely shaped by Pleistocene climatic oscillations and the highly diverse topography of eastern Africa.