Microsatellite markers for the common vole ( Microtus arvalis ) and their cross-species utility

Fragmentation of natural habitats of the common vole (Microtus arvalis) provides an excellent model system to study the consequences of restricted gene flow and small population sizes for isolated populations. Here we describe the isolation and characteristics of 10 autosomal and one X-linked microsatellite marker. These new markers were tested in 24 voles from a natural population in eastern Germany. Loci were highly polymorphic with numbers of alleles per locus ranging from three to 26 and expected heterozygosities from 0.51 to 0.97. All loci except for the X-linked locus Mar105 followed Hardy-Weinberg expectations. Cross-species amplifications revealed that most loci were polymorphic as well in M.agrestis, M.thomasi, and M.pennsylvanicu

High variability and non-neutral evolution of the mammalian avpr1a gene

<p>Abstract</p> <p>Background</p> <p>The arginine-vasopressin 1a receptor has been identified as a key determinant for social behaviour in <it>Microtus </it>voles, humans and other mammals. Nevertheless, the genetic bases of complex phenotypic traits like differences in social and mating behaviour among species and individuals remain largely unknown. Contrary to previous studies focusing on differences in the promotor region of the gene, we investigate here the level of functional variation in the coding region (exon 1) of this locus.</p> <p>Results</p> <p>We detected high sequence diversity between higher mammalian taxa as well as between species of the genus <it>Microtus</it>. This includes length variation and radical amino acid changes, as well as the presence of distinct protein variants within individuals. Additionally, negative selection prevails on most parts of the first exon of the <it>arginine-vasopressin receptor 1a (avpr1a) </it>gene but it contains regions with higher rates of change that harbour positively selected sites. Synonymous and non-synonymous substitution rates in the <it>avpr1a </it>gene are not exceptional compared to other genes, but they exceed those found in related hormone receptors with similar functions.</p> <p>Discussion</p> <p>These results stress the importance of considering variation in the coding sequence of <it>avpr1a </it>in regards to associations with life history traits (e.g. social behaviour, mating system, habitat requirements) of voles, other mammals and humans in particular.</p

Demographic history and genomic consequences of 10,000 generations of isolation in a wild mammal.

Increased human activities caused the isolation of populations in many species-often associated with genetic depletion and negative fitness effects. The effects of isolation are predicted by theory, but long-term data from natural populations are scarce. We show, with full genome sequences, that common voles (Microtus arvalis) in the Orkney archipelago have remained genetically isolated from conspecifics in continental Europe since their introduction by humans over 5,000 years ago. Modern Orkney vole populations are genetically highly differentiated from continental conspecifics as a result of genetic drift processes. Colonization likely started on the biggest Orkney island and vole populations on smaller islands were gradually split off, without signs of secondary admixture. Despite having large modern population sizes, Orkney voles are genetically depauperate and successive introductions to smaller islands resulted in further reduction of genetic diversity. We detected high levels of fixation of predicted deleterious variation compared with continental populations, particularly on smaller islands, yet the fitness effects realized in nature are unknown. Simulations showed that predominantly mildly deleterious mutations were fixed in populations, while highly deleterious mutations were purged early in the history of the Orkney population. Relaxation of selection overall due to benign environmental conditions on the islands and the effects of soft selection may have contributed to the repeated, successful establishment of Orkney voles despite potential fitness loss. Furthermore, the specific life history of these small mammals, resulting in relatively large population sizes, has probably been important for their long-term persistence in full isolation

Life-stage specific environments in a cichlid fish: implications for inducible maternal effects

Through environmentally induced maternal effects females may fine-tune their offspring's phenotype to the conditions offspring will encounter after birth. If juvenile and adult ecologies differ, the conditions mothers experienced as juveniles may better predict their offspring's environment than the adult females' conditions. Maternal effects induced by the environment experienced by females during their early ontogeny should evolve when three ecological conditions are met: (1) Adult ecology does not predict the postnatal environmental conditions of offspring; (2) Environmental conditions for juveniles are correlated across successive generations; and (3) Juveniles occasionally settle in conditions that differ from the juvenile habitat of their mothers. By combining size-structured population counts, ecological surveys and a genetic analysis of population structure we provide evidence that all three conditions hold for Simochromis pleurospilus, a cichlid fish in which mothers adjust offspring quality to their own juvenile ecology. In particular we show (1) that the spatial niches and the habitat quality differ between juveniles and adults, and we provide genetic evidence (2) that usually fish of successive generations grow up in similar habitats, and (3) that occasional dispersal in populations with a different habitat quality is likely to occur. As adults of many species cannot predict their offspring's environment from ambient cues, life-stage specific maternal effects are likely to be common in animals. It will therefore be necessary to incorporate parental ontogeny in the study of parental effects when juveniles and adults inhabit different environment

Genomic Scans Support Repetitive Continental Colonization Events during the Rapid Radiation of Voles (Rodentia: Microtus): the Utility of AFLPs versus Mitochondrial and Nuclear Sequence Markers

Single locus studies might not resolve phylogenetic relationships and the evolutionary history of taxa. The analysis of multiple markers promises higher resolution, and congruence among loci may indicate that the phylogenies represent the underlying species history. Here, we examine the utility of a genome-wide approach based on amplified fragment length polymorphisms (AFLP) and several DNA sequence markers in resolving phylogenetic signals in the rapidly radiating rodent genus Microtus which produced about 70 vole species within the last 1.2-2 myr. The current Holarctic distribution of Microtus is assumed to have resulted from three independent colonization events out of Asia to North America, Europe, and northern Asia without subsequent colonization, which would have led to deep splits between species from different continents. We investigated this hypothesis of three single colonization events by reconstructing the phylogenetic relationships among species from all three continents based on data from the first exon of the nuclear arginine vasopressin receptor 1a gene (EXON1), an adjacent noncoding region and the mitochondrial cytochrome b gene. The phylogenetic patterns obtained from these sequence markers are contrasted to genome-wide data on more than 1800 amplified fragment length polymorphisms (AFLP) analyzed for the same samples. Our results show that the single sequence markers partially resolve the phylogenetic relationships within Microtus, but with some incongruence mostly between EXON1 and the other loci. However, deeper nodes of the radiation are only weakly supported and neither the combination of the markers nor additional nuclear sequences improved the resolution significantly. AFLPs provided much stronger support for major continent-specific clades, and show also that reciprocal monophyly of American and European voles is incomplete. Our results demonstrate that Microtus voles colonized the American and European continents each repeatedly in several independent events on similar colonization routes during their radiation. More generally, this study supports the suitability of AFLPs as an alternative to sequence markers to resolve the evolutionary history of rapidly radiating tax

Host genetic factors associated with the range limit of a European hantavirus

The natural host ranges of many viruses are restricted to very specific taxa. Little is known about the molecular barriers between species that lead to the establishment of this restriction or generally prevent virus emergence in new hosts. Here, we identify genomic polymorphisms in a natural rodent host associated with a strong genetic barrier to the transmission of European Tula orthohantavirus (TULV). We analysed the very abrupt spatial transition between two major phylogenetic clades in TULV across the comparatively much wider natural hybrid zone between evolutionary lineages of their reservoir host, the common vole (Microtus arvalis). Genomic scans of 79,225 single nucleotide polymorphisms (SNPs) in 323 TULV-infected host individuals detected 30 SNPs that were consistently associated with the TULV clades CEN.S or EST.S in two replicate sampling transects. Focusing the analysis on 199 voles with evidence of genomic admixture at the individual level (0.1–0.9) supported statistical significance for all 30 loci. Host genomic variation at these SNPs explained up to 37.6% of clade-specific TULV infections. Genes in the vicinity of associated SNPs include SAHH, ITCH and two members of the Syngr gene family, which are involved in functions related to immune response or membrane transport. This study demonstrates the relevance of natural hybrid zones as systems not only for studying processes of evolutionary divergence and speciation, but also for the detection of evolving genetic barriers for specialized parasites

Gene flow in admixed populations and implications for the conservation of the Western honeybee, Apis mellifera

Anthropogenic activity, especially modern apiculture, has considerable impact on the natural distribution of the Western honeybee, Apismellifera, leading to the spread, replacement and fragmentation of many subspecies. This creates demand for the conservation of some subspecies, in particular, Apismelliferamellifera, which once was widely distributed in Western Europe and nowadays is endangered through habitat loss and fragmentation. Moreover, A.m.mellifera may be further endangered by hybridisation in populations that now occur in artificial sympatry with other subspecies. Here, we quantify and compare individual hybridisation between sympatric and allopatric honeybee populations of A.m.mellifera and A.m.carnica using microsatellite markers and a Bayesian model-based approach. We had a special focus on pure breeding populations, which are a major tool in honeybee conservation. Our results demonstrate that subspecies are still highly differentiated, but gene flow is not prevented by the current management strategies, creating urgent demand for an improved conservation management of A.m.mellifera. However, the occurrence of a high number of pure individuals might suggest that some sort of hybrid barrier acts against the complete admixture of the two subspecie

A Bocage Landscape Restricts the Gene Flow of Pest Vole Populations.

The population dynamics of most animal species inhabiting agro-ecosystems may be determined by landscape characteristics, with agricultural intensification and the reduction of natural habitats influencing dispersal and hence limiting gene flow. Increasing landscape complexity would thus benefit many endangered species by providing different ecological niches, but it could also lead to undesired effects in species that can act as crop pests and disease reservoirs. We tested the hypothesis that a highly variegated landscape influences patterns of genetic structure in agricultural pest voles. Ten populations of fossorial water vole, Arvicola scherman, located in a bocage landscape in Atlantic NW Spain were studied using DNA microsatellite markers and a graph-based model. The results showed a strong isolation-by-distance pattern with a significant genetic correlation at smaller geographic scales, while genetic differentiation at larger geographic scales indicated a hierarchical pattern of up to eight genetic clusters. A metapopulation-type structure was observed, immersed in a landscape with a low proportion of suitable habitats. Matrix scale rather than matrix heterogeneity per se may have an important effect upon gene flow, acting as a demographic sink. The identification of sub-populations, considered to be independent management units, allows the establishment of feasible population control efforts in this area. These insights support the use of agro-ecological tools aimed at recreating enclosed field systems when planning integrated managements for controlling patch-dependent species such as grassland voles

Territorial songs indicate male quality in the sac-winged bat Saccopteryx bilineata (Chiroptera, Emballonuridae)

Defense of territories in many animal species involves the advertisement of territory holder quality by acoustic signaling. In the sac-winged bat Saccopteryx bilineata, males engage in territorial countersinging when reoccupying their day-roost territories in the morning and in the evening before abandoning the roost for the night. Females roost mainly in male territories, and territory holders are reproductively more successful than nonterritorial males. In territorial songs of male S. bilineata, we distinguished 6 syllable types and parameterized their acoustic properties. The analysis of 11 microsatellite loci allowed assignments of juveniles to their parents. Males had a higher reproductive success both when they uttered more territorial songs per day and when their long buzz syllables had a lower end frequency of the fundamental harmonic. Long buzzes had a harsh quality due to a pulsation of the fundamental frequency at the syllable onset and also had the highest sound pressure level of all syllable types in most territorial songs. Territorial songs and especially long buzz syllables are thus likely to advertise territory holder quality and competitive abilit

Cichlids do not adjust reproductive skew to the availability of independent breeding options

Helpers in cooperatively breeding species forego all or part of their reproduction when remaining at home and assisting breeders to raise offspring. Different models of reproductive skew generate alternative predictions about the share of reproduction unrelated subordinates will get depending on the degree of ecological constraints. Concession models predict a larger share when independent breeding options are good, whereas restraint and tug-of-war models predict no effects on reproductive skew. We tested these predictions by determining the share of reproduction by unrelated male and female helpers in the Lake Tanganyika cichlid Neolamprologus pulcher depending on experimentally manipulated possibilities for helper dispersal and independent breeding and depending on helper size and sex. We created 32 breeding groups in the laboratory, consisting of two breeders and two helpers each, where only the helpers had access to a nearby dispersal compartment with (treatment) or without (control) breeding substrate, using a repeated measures design. We determined the paternity and maternity of 1185 offspring from 47 broods using five to nine DNA microsatellite loci and found that: (1) helpers participated in reproduction equally across the treatments, (2) large male helpers were significantly more likely to reproduce than small helpers, and (3) male helpers engaged in significantly more reproduction than female helpers. Interestingly, in four broods, extragroup helper males had fertilized part of the brood. No helper evictions from the group after helper reproduction were observed. Our results suggest that tug-of-war models based on competition over reproduction within groups describe best the reproductive skew observed in our study system. Female breeders produced larger clutches in the treatment compared to the control situation when the large helpers were males. This suggests that male breeder-male helper reproductive conflicts may be alleviated by females producing larger clutches with helpers aroun