Divergent gut microbiota in two closely related house mouse subspecies under common garden conditions.

The gastrointestinal microbiota (GM) is considered an important component of the vertebrate holobiont. GM-host interactions influence the fitness of holobionts and are, therefore, an integral part of evolution. The house mouse is a prominent model for GM-host interactions, and evidence suggests a role for GM in mouse speciation. However, previous studies based on short 16S rRNA GM profiles of wild house mouse subspecies failed to detect GM divergence, which is a prerequisite for the inclusion of GM in Dobzhansky-Muller incompatibilities. Here, we used standard 16S rRNA GM profiling in two mouse subspecies, Mus musculus musculus and M. m. domesticus, including the intestinal mucosa and content of three gut sections (ileum, caecum, and colon). We reduced environmental variability by sampling GM in the offspring of wild mice bred under seminatural conditions. Although the breeding conditions allowed a contact between the subspecies, we found a clear differentiation of GM between them, in all three gut sections. Differentiation was mainly driven by several Helicobacters and two H. ganmani variants showed a signal of codivergence with their hosts. Helicobacters represent promising candidates for studying GM-host coadaptations and the fitness effects of their interactions.

House mouse subspecies do differ in their social structure.

It is widely acknowledged that population structure can have a substantial impact on evolutionary trajectories. In social animals, this structure is strongly influenced by relationships among the population members, so studies of differences in social structure between diverging populations or nascent species are of prime interest. Ideal models for such a study are two house mouse subspecies, Mus musculus musculus and M. m. domesticus, meeting in Europe along a secondary contact zone. Though the latter subspecies has usually been supposed to form tighter and more isolated social units than the former, the evidence is still inconclusive. Here, we carried out a series of radiofrequency identification experiments in semi-natural enclosures to gather large longitudinal data sets on individual mouse movements. The data were summarized in the form of uni- and multi-layer social networks. Within them, we could delimit and describe the social units ("modules"). While the number of estimated units was similar in both subspecies, domesticus revealed a more "modular" structure. This subspecies also showed more intramodular social interactions, higher spatial module separation, higher intramodular persistence of parent-offspring contacts, and lower multiple paternity, suggesting more effective control of dominant males over reproduction. We also demonstrate that long-lasting modules can be identified with basic reproductive units or demes. We thus provide the first robust evidence that the two subspecies differ in their social structure and dynamics of the structure formation.

Ontogeny of social hierarchy in two European house mouse subspecies and difference in the social rank of dispersing males.

In social species such as house mouse, being dominant is vital. Determination of dominance may start early in life and vary during ontogeny. We asked whether pre-pubertal and adolescent behaviour predicts the rank a male mouse finally obtains. Moreover, we asked how dominant vs. subordinate adults differ in exploration and propensity to emigrate. We studied fraternal pairs as the simple social units, from weaning to full-grown adulthood. By utilizing two mouse subspecies known to differ in many behavioural traits, we take into account any potential subspecific idiosyncrasies. We did not find any significant effect of future social status on any behavioural type displayed before adulthood, but the subspecies themselves differ in behaviours prevailing in particular ontogeny phases. While musculus males start as more pro-social, they later became significantly more passive. Conversely, domesticus are slightly less passive at the beginning but significantly more proactive close to adulthood and rapidly establishing hierarchy through overt conflicts. We found no difference in exploration between ranks, however, domesticus males were significantly more active in an unknown area than musculus. Most importantly, while dominant domesticus males seem to be more prone to emigration, in musculus it was the subordinate males who left base significantly more often. This is consistent with extended contests of musculus males over dominance found in this study as well as with differences in endocrinological changes we have reported previously.