Agrestis Populations Research Articles

Insights into the differentiation and adaptation within Circaeasteraceae from Circaeaster agrestis genome sequencing and resequencing

Circaeaster agrestis and Kingdonia uniflora are sister species that reproduce sexually and mainly asexually respectively, providing a good system for comparative genome evolution between taxa with different reproductive models. Comparative genome analyses revealed the two species have similar genome size, but C.agrestis encodes many more genes. The gene families specific to C.agrestis show significant enrichment of genes associated with defense response, while those gene families specific to K.uniflora are enriched in genes regulating root system development. Collinearity analyses revealed C.agrestis experienced two rounds of whole-genome duplication. Fst outlier test across 25C.agrestis populations uncovered a close inter-relationship between abiotic stress and genetic variability. Genetic feature comparisons showed K.uniflora presents much higher genome heterozygosity, transposable element load, linkage disequilibrium degree, and πN/πS ratio. This study provides new insights into understanding the genetic differentiation and adaptation within ancient lineages characterized by multiple reproductive models.

Identifying Past Remains of Morphologically Similar Vole Species Using Molar Shapes

Accurate species identification in fossil remains is a complex task but is a key component for developing good inferences on many, if not all, fundamental questions in macroecology and macroevolution. In the Quaternary, arvicolines are very abundant remains in archeological and paleontological sites in Western Europe and their identification is often based on the first lower molar. The common vole Microtus arvalis (Pallas, 1778) and the field vole Microtus agrestis (Linnaeus, 1761) are commonly found in those deposits. These two species are genetically and ecologically divergent. Nonetheless, their lower molars, on which species identification is done, exhibit a large morphological variation that can potentially lead to some confusion and misinterpretation. Moreover, molecular data suggest that present-day M. agrestis populations are a complex of divergent lineages, some of them being recognized nowadays as valid species. On the basis of extant populations representing a large part of the present-day geographical distribution of these two species, we developed a classification model based on geometric morphometrics of the first lower molar. Our statistical model was then applied on four fossil sites selected to evaluate the relevance of taxonomic determination found in species lists. The model using landmarks describing the overall shape of the first lower molar classifies the two species with the smallest prediction error together with very high individual posterior probabilities. The obtained classification is much better than those arising from shapes of any specific molar part such as the anterior loop, asymmetry or peculiar triangle shape. Discrepancies with expert classification on fossils suggest that existing faunal lists should always be considered cautiously for these two species. Our morphometric model provides a first step towards a rationalized way of revising past collections and expertise for future small mammal assemblages. It will thus help us better understand the paleobiogeographical expansion of these two key species in Quaternary faunas.

Patterns of variation in Microtus arvalis and Microtus agrestis populations from Middle to Late Pleistocene in southwestern Europe

Fifteen paired fossil populations of Microtus arvalis and Microtus agrestis from southwestern Europe have been analysed from a morphological and morphometric point of view. The sites under consideration are located in the northern Iberian Peninsula and southern France, from the Middle Pleistocene to the end of the Late Pleistocene. The aim of this study is to stress once again the importance of keeping these two species separated in the fossil record in order to recognize specific trends of evolution and divergence and to obtain more precise information on palaeoclimatic and palaeoenvironmental conditions. It was possible to observe remarkable intraspecific differences between Middle and Late Pleistocene populations of both species. Furthermore, in synchronic co-specific populations from the Late Pleistocene, climatic and geographic conditions seem to exert a major influence in shaping intraspecific changes in dental pattern.

The cascading impacts of livestock grazing in upland ecosystems: a 10‐year experiment

Livestock grazing is a major driver of land‐use change, causing significant biodiversity loss globally. Although the short‐term effects of livestock grazing on individual species are well studied, a mechanistic understanding of the long‐term, cascading impacts is lacking. We manipulated livestock densities using a unique, replicated upland experiment over a 10‐year period and found significant effects of grazing treatment on plant and arthropod biomass; the number of Anthus pratensis breeding bird territories; the amplitude of Microtus agrestis population cycles and the activity of a top predator, Vulpes vulpes. Lower plant biomass as a result of higher stocking densities led to cascades across trophic levels, with fewer arthropods and small mammals, the latter affecting predator activity. Breeding bird territories were a function of arthropod abundance and vegetation structure heterogeneity. Our results provide a novel food‐web analysis in a grazing experiment to provide a mechanistic understanding of how food‐webs in upland ecosystems respond to long‐term livestock grazing pressure, with consequences for management.

Geographically differentiating morphology of genetically similar dogroses: consequences of canina meiosis

Despite their genetic homogeneity, many taxonomic species are described as European dogroses (Rosa L. section Caninae (DC.) Ser.) with consistent morphological variability. Here we report a morphometric study of 27 hip and leaf characters of proximate dogrose populations that include Rosa agrestis, a member of the subsection Rubigineae, in Flanders. In principal components analysis one R. agrestis population in Kanne had intermediate morphology between R. canina and R. corymbifera, on the one hand, and three other R. agrestis populations, on the other, suggesting hybridogenic origin. Half-sib R. agrestis seedlings were grown under controlled conditions and their leaf characters were studied. A tendency toward deviating morphology in seedlings from the Kanne population, analogous to the mother plants in the field, and a correlation for specific leaf characters between mother plants and their corresponding seedlings reinforce a genetic basis for the observed divergence in the Kanne population. The assumed hybridogenic mother plants did not produce fewer seeds per hip than the others of the pure populations. In addition, for all sampled dogroses, which included six species, the diameter of the discus was correlated with the number of seeds per hip, whereas the diameter of the orifice was not correlated with this character. This implies that only the diameter of the orifice and not the diameter of the discus might be decisive for species identification among European dogroses.

Cowpox virus infection in natural field vole Microtus agrestis populations: delayed density dependence and individual risk

1. Little is known about the dynamics of pathogen (microparasite) infection in wildlife populations, and less still about sources of variation in the risk of infection. Here we present the first detailed analysis of such variation. 2. Cowpox virus is an endemic sublethal pathogen circulating in populations of wild rodents. Cowpox prevalence was monitored longitudinally for 2 years, in populations of field voles exhibiting multiannual cycles of density in Kielder Forest, UK. 3. The probability that available susceptible animals seroconverted in a given trap session was significantly positively related to host density with a 3-month time lag. 4. Males were significantly more likely to seroconvert than females. 5. Despite most infection being found in young animals (because transmission rates were generally high) mature individuals were more likely to seroconvert than immature ones, suggesting that behavioural or physiological changes associated with maturity contribute to variation in infection risk. 6. Hence, these analyses confirm that there is a delayed numerical response of cowpox infection to vole density, supporting the hypothesis that endemic pathogens may play some part in shaping vole cycles.

Life History Adaptation to Changeable Agricultural Habitats: Developmental Plasticity Leads to Cohort Splitting in an Agrobiont Wolf Spider

The wolf spider, Pardosa agrestis Westring (Araneae: Lycosidae), is a dominant arthropod predator in central European agricultural areas. Recent studies have indicated that this spider has a unique phenology among Pardosa species. Three years of systematic field monitoring of a P. agrestis population in Hungary confirmed that an early summer peak (P1) of adults typical of the Pardosa genus is followed by a second late summer peak (P2) that does not occur among congenerics. Rearing experiments conducted outdoors revealed that offspring from P1 can reach maturity in ≈2 mo time, well before the end of summer. Thus, P2 adults represent a second generation of the species, with a chance for a potentially successful reproduction. However, the speed of development was variable among P1 offspring; individuals, which proved to be slower developers, did not mature during P2; rather they overwintered as juveniles and matured during the following year P1 period. Thus, members of the P1 cohort followed different developmental pathways; this corresponds to a cohort-splitting strategy. Splitting occurred even among spiderlings originating from the same clutch (cocoon) at the beginning of P1. In contrast, spiderlings born at the end of P1 uniformly matured by next spring. Splitting among offspring spreads the mother’s reproductive success between risk averse slow-developing and risk prone fast-developing offspring. The facultative bivoltine life cycle arising through cohort splitting may allow P. agrestis to adapt to predictably ephemeral agricultural habitats by flexibly producing the most dispersive juvenile stages in synchrony with the appearance of vacated habitats.

Population cycles of small rodents are caused by specialist predators: or are they?

Predation by specialist mammalian predators has been hypothesized to be the primary cause of multi-annual density fluctuations (‘population cycles’) in voles. Using a series of replicated field experiments, Isla Graham and Xavier Lambin have now shown that specialist mammalian predators are neither necessary nor sufficient to drive field vole Microtus agrestis population cycles. These findings conclusively contradict the specialist predator hypothesis. The search for the mechanisms underlying the spectacular dynamics of cyclic vole populations must, therefore, continue.

Genetic evidence for tula virus in Microtus arvalis and Microtus agrestis populations in Croatia.

To determine the threat of hantavirus infection to U.S. Forces, small mammals were sampled from training areas within Croatia. Of the 152 samples, 20 were positive for Tula virus (TUL), 12 common voles (Microtus arvalis) and eight field voles (Microtus agrestis). Sequences from M. agrestis were found in five and sequences from M. arvalis were found in six of seven sequence groups. The high percentage of the same TUL sequences in M. agrestis and M. arvalis suggests the co-occurrence of this virus in both Microtus species is not an accident. If M. agrestis field voles were accidentally infected with TUL, the percentage of polymerase chain reaction-positive animals should be lower than that of M. arvalis. Because the infection rate in M. arvalis (11.8%) was less than half of that found in M. agrestis (27.6%), it is unlikely that the predominance of positive M. agrestis could be due to accidental exposure. It is much more likely that the Croatian virus is circulating between both rodent species.

Use of coupled oscillator models to understand synchrony and travelling waves in populations of the field vole Microtus agrestis in northern England

1. Earlier studies have reported that field vole Microtus agrestis populations in Kielder Forest, UK, exhibit typical 3–4‐year cyclical dynamics, and that the observed spatiotemporal patterns are consistent with a travelling wave in vole abundance moving along an axis south‐west–north‐east at approximately 19 km year–1. One property of this wave is that nearby populations fluctuate more synchronously than distant ones, with correlations falling lower than the average for the sampling area beyond approximately 13 km. 2. In this paper we present a series of models that investigate the possibility that both the observed degree of synchrony and the travelling wave can be explained as a simple consequence of linking a series of otherwise independently oscillating populations. Our ‘coupled oscillator’ models consider a series of populations, distributed either in a linear array or in a two‐dimensional regular matrix. Local population fluctuations, each with a 3–4‐year period, were generated using either a Ricker equation or a set of discrete‐time Lotka–Volterra equations. Movement among populations was simulated either by a fixed proportion of each population moving locally to their nearest neighbour populations, or the same proportion being distributed via a continuous geometric function (more distant populations receiving less). 3. For a variety of different ways of generating cycles and a number of different movement rules, local exchange between oscillating populations tended to generate synchrony domains that extended over a large number of populations. When the rates of exchange between local populations were relatively low, then permanent travelling waves emerged, especially after an initial invasion phase. There was a non‐linear relationship between the amount of dispersal and the domain of synchrony that this movement generated. Furthermore, the observed spatiotemporal patterns that emerged following an initial invasion phase were found to be highly dependent on the extreme distances reached by rare dispersers. 4. As populations of voles are predominantly distributed in grassland patches created by clear‐cutting of forest stands, we estimated the mean patch diameter and mean interpatch distance using a geographical information system (GIS) of the forest. Our simplified models suggest that if as much as 5–10% of each vole population dispersed a mean of 178 m between clear‐cuts per generation, then this would generate a synchrony domain and speed of wave in the region of 6–24 km (per year), which is reasonably consistent with the observed synchrony domain and speed. Much less dispersal would be capable of generating this scale of domain if some individuals occasionally moved beyond the nearest‐neighbour patch. 5. While we still do not know what causes the local oscillations, our models question the need to invoke additional factors to explain large‐scale synchrony and travelling waves beyond small‐scale dispersal and local density‐dependent feedback. Our work also suggests that the higher degrees of synchrony observed in Fennoscandian habitats compared with Kielder may be due in part to the relative ease of movement of voles in these former habitats. As our work confirms that the rates of exchange among local populations will have a strong influence on synchrony, then we anticipate that the spatiotemporal distribution of clear‐cuts will also have an important influence on the dynamics of predators of voles.

Intraspecific Variation in Dynamics: Small Rodents between Food and Predation in Changing Landscapes

Population densities, food and predators were examined for bank voles, Clethrionomys glareolu and field voles, Microtus agrestis, during the period 1971-1998 in one northern (Stromsund) and one south-central (Uppsala) region in Sweden to see if trophic relationships persisted in the presence of large changes in landscape composition, and rodent dynamics, in the northern region. The main work was done on early reforestations. Whereas the limited forest areas at Uppsala were consistently situated on poor soil, forests were extensively clearcut at Stromsund in the 1960-1980s, continuously leaving poorer and fragmented old forests and extensive young thicket forests that were of little use to small rodents. Population densities and amplitudes were larger at Stromsund in the 1970-1980s than in the 1990s and densities at Stromsund reached higher peaks than at Uppsala. The proportion of M. agrestis in the rodent communities was consistently larger at Stromsund. Densities of C. glareolus were higher in forests than on reforestations but there was a continuous exchange of individuals between the two habitats. M. agrestis on abandoned fields, a main habitat for this species, did not show any temporal or regional variation and were more common than on reforestations, except at Stromsund in the 1970-1980s. Consumption of artificial seed supplies did not differ annually at Uppsala but did so at Stromsund in 1994-96; almost all supplies were there consumed at a vole peak year, particularly inside forests. Consumption of an artificial bark supply on reforestations was much larger in the 1980s than in the 1990s at Stromsund; it was consistently low at Uppsala. There was not any difference between regions in such bark consumption on abandoned fields. Vole damage to forestry seedlings was important in the 1960-1970s, of less importance in the 1980s, and did not occur at all in the surveyed years of the 1990s. Mustelid numbers (particularly Mustela erminea) were high at Stromsund after vole peaks in the 1980s but were generally low in the 1990s; they were consistently low at Uppsala. Fox tracks did not vary in any consistent way. Following interpretation emerged: Sheltering snow cover generated cycles. Peak C. glareolus numbers were generally limited by winter food, particularly by pendulous lichens that decreased during the study period. Abundant seed or fruit supply in increase autumns can irregularly cause particularly high C. glareolus peaks. Massive invasion of northern reforestations by C. glareolus from forests appears to have buffered predation on M. agrestis, permitting extensive cycles of the latter species on reforestations in the 1960-1980s. Limited numbers of C. glareolus on reforestations permitted only small M. agrestis populations there and generalist predators as foxes or raptors may then have terminated minor increases already in summer. Trophic interactions are intensified and spatially extended at pronounced peak numbers. More generally, regional changes in fluctuation patterns of small rodents can be related to varying use of managed landscapes, where habitat quality changes both in time and space.

Density-Related Home-Range Size and Overlap in Adult Field Voles (Microtus agrestis) in Southern Sweden

Home-range dynamics and the relation between population density, home-range size, and spacing pattern in a Microtus agrestis population were examined in a 2-year-long mark-recapture study. Home-range size varied with vole density. At high densities during the nonbreeding season, ranges were half the size of those measured at low densities. Home ranges during the breeding season were considerably larger than those established during the nonbreeding season with high densities, but did not differ in size from those in the nonbreeding season with low densities. Ranges of males generally were larger than those of females. Established voles generally stayed in the same restricted area throughout winter. At low densities, males showed a tendency to change home ranges. With onset of breeding in spring, overwintered individuals usually settled in areas adjacent to their winter ranges. Adult females became distributed according to a territorial pattern in spring, whereas ranges of males still overlapped extensively during the early part of the breeding season. During the nonbreeding season, vole ranges overlapped extensively, especially at high densities. There was, however, no evidence of group structure with aggregation behavior in any of the sexes.