Subspecies-specific response to ACTH challenge test in the house mouse (Mus musculus).

Long term changes in hormonal levels of small and rare animal species can be effectively monitored by non-invasive methods such as immunoenzymatic analysis. These methods generally analyze metabolites instead of the hormone itself and thus do not invade the organism. However, they can be influenced by many factors, so before they are used, they need to be validated. For this purpose we used the "ACTH challenge" test based on stimulating the animal's adrenocortical activity and measuring the consequent increase of the level of its glucocorticoid ("stress") hormones. Specifically, we measured concentrations of fecal glucocorticoid metabolites of two house mouse subspecies, Mus musculus musculus and M. m. domesticus. Using polyclonal antibody we investigated the mice's naturally occurring circadian fluctuation and their reaction to the adrenal stimulation. This study confirmed that the selected method is suitable for analysis of fecal corticosterone metabolites in the wild house mouse. More importantly, we revealed a subspecies-specific stress response at the level of corticosterone production: while the significant effect of ACTH was proved in both subspecies, a notable adrenocortical reaction was also elicited by injecting the saline solution in M. m. domesticus. Our results thus highlight the importance of considering potential cryptic variation within the species under study when designing projects on adrenal stress hormone assessments.

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 group's 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.

Signalling components of the house mouse mate recognition system.

Subspecies-specific mate recognition may represent significant barrier to gene flow between diverged genomes potentially leading to speciation. In the house mouse, assortative mating involves the coevolution of several signals and receptors. We compared signalling ability of bedding material, faeces, urine, saliva, salivary androgen binding proteins (ABP) and combinations of urine with saliva and urine with ABP in mate choice in two wild-derived inbred strains (one of Mus musculus musculus and one of Mus musculus domesticus origin). We observed high levels of variation in assortative preferences between the two strains and sexes. The strongest preferences were observed in M. m. musculus-derived individuals in tests where urine was present either alone or as part of a composite signal target. M. m. domesticus-derived mice displayed strain-specific preferences for faeces. Saliva was the least preferred stimulus in both strains and sexes. No effect of two-compound cues was detected. We conclude that there is divergence across both the stimulus and preference parts of the recognition system for both house mouse strains. Of the tested stimuli, those that have the capacity to carry a signal for extended periods under natural conditions (such as urine and faeces) seem to be the most important substances in strain-specific recognition.

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.

Genetic variation and phylogeography of free-living mouse species (genus Mus) in the Balkans and the Middle East.

This work presents a study of the distribution and pattern of variation throughout the ranges of three free-living mouse species of the genus Mus-M. macedonicus, M. spicilegus, and a M. cypriacus - based on sequencing of two segments of the mitochondrial DNA (mtDNA) control region. The study shows a similar level of variability in the three species and suggests their recent population expansion. The highest proportion of variation is found within populations indicating low genetic structuring. Phylogenetic analysis confirms the significant divergence of a mitochondrial lineage of M. macedonicus from Israel, recently described as a new subspecies, M. macedonicus spretoides. Conversely, no genetic hiatus is revealed between European and Asian populations of M. macedonicus macedonicus. Although phylogenetic relationships among M. spicilegus populations could not be unravelled precisely, the results suggest a recent westward expansion of the species. The mtDNA divergence between M. macedonicus and M. spicilegus is 7.3%, suggesting their split between c. 700,000 and 1 million years ago. These dates correspond with a coalescent estimate about 720,000 years ago. On the other hand, M. cypriacus appeared almost twice as divergent from the former species (4.5%) as from the latter (8.8%) suggesting a divergence of c. 430,000-610,000 years ago (coalescent approximately 490,000 years ago) and 830,000-1.2 million years ago (coalescent approximately 780,000 years ago), respectively. Approximate times of population expansion have also been estimated for all taxa and groups of populations. Existence of several glacial refuges and various colonization scenarios are discussed; since all estimated divergence times fall within interglacial periods it seems that climatic oscillations did not play a crucial role in the evolution of the three species.

The mammalian model for population studies of B chromosomes: the wood mouse (Apodemus).

The presence of B chromosomes was reported in six species of the genus Apodemus (A. peninsulae, A. agrarius, A. sylvaticus, A. flavicollis, A. mystacinus, A. argenteus). High frequencies of Bs were recorded particularly in A. peninsulae and A. flavicollis. The origin of Bs in Apodemus seems to be rather ancient, and it is possible that the supernumerary elements, and/or a tendency for their appearance, were inherited from the common ancestor of the extant species. We have not found any correlated changes between frequencies of Bs and the level of protein polymorphism and/or heterozygosity assessed in electrophoretic studies. No measurable effect of Bs on overall genetic variability was thus revealed in studied populations. The pattern of evolutionary dynamics of Bs can be distinctly different between geographical populations, and both the parasitic and the heterotic models can be applied to explain the maintenance of Bs in different populations. Further studies are desirable to improve our understanding of the complicated evolutionary dynamics of Bs in the Apodemus species. An essential condition for success in this respect is much more detailed information on inheritance and the molecular structure of Bs.

Phylogeny of the genus Apodemus with a special emphasis on the subgenus Sylvaemus using the nuclear IRBP gene and two mitochondrial markers: cytochrome b and 12S rRNA.

Phylogenetic relationships among 17 extant species of Murinae, with special reference to the genus Apodemus, were investigated using sequence data from the nuclear protein-coding gene IRBP (15 species) and the two mitochondrial genes cytochrome b and 12S rRNA (17 species). The analysis of the three genes does not resolve the relationships between Mus, Apodemus, and Rattus but separates Micromys from these three genera. The analysis of the two mitochondrial regions supported an association between Apodemus and Tokudaia and indicated that these two genera are more closely related to Mus than to Rattus or Micromys. Within Apodemus, the mitochondrial data sets indicated that 8 of the 9 species analyzed can be sorted into two main groups: an Apodemus group, with A. agrarius, semotus, and peninsulae, and a Sylvaemus group, with uralensis, flavicollis, alpicola, sylvaticus, and hermonensis. The position of Apodemus mystacinus is ambiguous and might be either included in Sylvaemus or considered a distinct subgenus, Karstomys, more closely related to Sylvaemus than to Apodemus. Estimation of the divergence time for these taxa suggests a separation between 7 and 8 My ago for the three groups (mystacinus and the two subgenera Apodemus and Sylvaemus). Within each subgenus, divergence times are between 5.4 and 6 My for Apodemus and between 2.2 and 3.5 My for Sylvaemus and mystacinus.

Karyotype of the giant mole-rat, Cryptomys mechowi (Rodentia, Bathyergidae).

The karyotype of the giant mole-rat, Cryptomys mechowi (Rodentia, Bathyergidae), from Zambia was investigated in one male and one female by means of G-, C-, and AgNOR-banding techniques. The diploid chromosomal set consisted of 40 biarmed chromosomes (2n = 40, NF = 80). A pair of autosomes in the male and the X chromosomes in the female were heteromorphic. The sex chromosomes were unusually large.

Sex chromosome abnormalities in natural populations of the common vole (Microtus arvalis).

Four specimens with an aberrant sex chromosome constitution were found in natural populations of the common vole (Microtus arvalis). Two females had an X0 sex chromosome constitution and single males were 2n = 47, XXY and 2n = 47, XYY, respectively. No apparent phenotypical anomalies were recorded in the sex chromosome aneuploids, but their fertility may have been impaired. The incidence of sex chromosome aneuploidy seems to be unusually high in natural populations of the common vole (1.5% of animals examined). Possible explanations for this are discussed.