Source–sink dynamics: how sinks affect demography of sources

Models of source–sink population dynamics have to make assumptions about whether, and eventually how, demographic parameters in source habitats are dependent on the demography in sink habitats. However, the empirical basis for making such assumptions has been weak. Here we report a study on experimental root vole populations, where estimates of demographic parameters were contrasted between source patches in source–sink (treatment) and source–source systems (control). In the presence of a sink patch (simulated by a pulsed removal of immigrants), source‐patch populations failed to increase over the breeding season, mainly due to a high spatially density‐dependent dispersal rate from source to sink patches. The per capita recruitment rate was almost two times higher in source–sink than in the source–source systems, but this did not compensate for the loss rate due to dispersal from source to sink patches. Sex ratio in the source–sink systems became less female biased, probably as a result of an enhanced frequency of dispersal movements in females. Good knowledge of the degree of density‐and habitat‐dependent dispersal is critical for predicting the dynamics of source–sink populations.     

Spatial explicit demography: The effects habitat patch isolation have on vole matrilines

Populations of many species are spatially structured in matrilines, and their dynamics may be determined by matriline specific demographic processes. We examined whether the isolation of habitat patches (i.e. interpatch distance) affected the demography of matrilines in 14 experimentally fragmented populations of the root vole. Matrilines inhabiting the most isolated patches decreased in size over the breeding season, while matrilines in less isolated patches increased. The survival rate of adult females was the main factor underlying the variation in growth rates among matrilines. Low survival when patches were isolated seemed to be due to long-distance interpatch movements exposing females to increased predation rate.
The differential success of matrilines in patchy populations with variable interpatch distances acted to decrease the matrilineal diversity at the population level. Furthermore, isolated patches may function as sinks. Thus spatially explicit landscape features may affect both population demography and genetics.     

Did the Quaternary climatic fluctuations really influence the tempo and mode of diversification in European rodents?

The objective of this study was to establish whether the Quaternary climatic fluctuations influenced the tempo and mode of diversification in European rodents. Our case study is the subgenus Microtus (Terricola) distributed from western Europe to the Caucasus. Mitochondrial cytochrome b gene sequences from several representatives of all the species were used to generate maximum‐likelihood and Bayesian phylogenetic trees, to estimate divergence times, to identify biogeographic ancestral areas and to study the rate of diversification. Results showed that phylogenetic tree topologies were similar to previous published studies but with a better resolution at some nodes. The origin of Microtus (Terricola) is dated back to approximately 4.05 Myr in the Early Pliocene, and molecular dating for most Terricola species corresponds to several glacial periods of the Pleistocene. Results of the biogeographic ancestral area reconstruction suggest that Microtus (Terricola) diversified from the Caucasus/Turkey/Iran area through western Europe. Several periods of diversity variation were highlighted as follows: two period of diversity increase, between 3 and 2 Myr, and after 1 Myr; two periods of diversity decrease, before 3 Myr, and between 2 and 1 Myr. The diversification rate of Microtus (Terricola) was 0.353 ± 0.004 event/Myr, a rate similar to that of the Muridae family. To conclude, although the Pleistocene glacial conditions had an impact on the speciation events, the Quaternary does not appear however as a period with an exceptional rate of diversification for European rodents.     

幼体生长发育特征可导致橙腹田鼠的单配体制吗?

橙腹田鼠(Microtus ochrogaster)和草原田鼠(M. pennsylvanicus)是两种亲缘关系很近,但有着完全不同交配体制的田鼠。本文试图通过他们头骨的形态学比较来验证幼体生长发育(paedomorphosis)可以印证单配制交配体制进化的假说。通过几种头骨的测量,我们发现草原田鼠头骨的长与宽比例大于橙腹田鼠,说明前者具有相对狭长的头骨。进一步的测量发现,这种不同是由于草原田鼠具有相对较长的鼻骨造成的。最后,我们对同种内成年和幼年的头骨进行了比较,发现单配制的橙腹田鼠相对于多配制的草原田鼠,其成年的头骨与幼年的头骨更相似。这些测量结果说明与多配制的田鼠相比,单配制的田鼠在形态及行为上保留更多的幼年状态,而这种行为很可能与其交配体制有关。     

农田周围生态保留带中普通田鼠的种群生态学：种群数量动态及结构

于2003年5月~2004年11月,采用标志重捕法对栖息在生态保留带的普通田鼠种群结构和数量动态进行了跟踪研究。结果表明,两年中种群密度夏季最大分别达到410个体/hm2和641个体/hm2,春季最少分别达到166个体/hm2和153个体/hm2,种群数量从7月份开始增长,8月份种群密度减少并于11月份开始重新增长。种群中雌性个体数量比较多,雌性在种群中的居留时间较长,同时存活率比雄性高,这导致种群数量的季节变化。种群周转率比较高,在两个捕鼠期间种群中的80%个体被更新,这表明普通田鼠在生态保留带中的活动非常频繁,不断与周围的其他种群进行交流,提高了种群对环境的适应能力。种群中雌雄个体的巢区之间没有年间变化,活动巢区比较小,巢区长度2003年平均为11 m,最长为37.5 m,2004年平均为13 m,最长为52 m。Pearson相关指数表明种群数量和生态保留带年龄、覆盖率和高度之间没有相关性。     

Home range size and overlap in female root voles: effects of season and density

In small mammals living in highly seasonal environments, observationalstudies show that female home range size and exclusiveness aresmaller in the nonbreeding winter season than in the breedingsummer season. This has led to the notion that nonbreeding femalesare more social and decrease territorial behavior during winter.However, because territoriality decreases with increasing populationdensity, and density normally increases during the breedingseason, the effects of density and season on social structureare usually confounded. To find out which of the 2 factors explainsspace use, we experimentally established 3 high-density and3 low-density root vole (Microtus oeconomus) populations inlate spring and monitored the populations into the nonbreedingwinter season. Population sizes were controlled throughout thebreeding period to minimize seasonal variation in density. Homerange sizes were larger in founder females than in field-bornfemales but did not change with season or density. Area exclusivelyused by individual females was lower in winter than summer,and founder females decreased exclusiveness as density increased.We argue that this seasonal pattern of space use might be causedby variation in benefits of group living, whereas founder femalesalso responded to density-dependent competition by reducingarea exclusively used.     

Field tests of cis-regulatory variation at the prairie vole avpr1a locus: association with V1aR abundance but not sexual or social fidelity

The neuropeptide vasopressin and its receptor V1aR are broadly implicated in social behavior and play a central role in several key aspects of male mating tactics in voles. In the prairie vole, a microsatellite in the cis-regulatory region of the gene encoding V1aR (avpr1a) provides a potential genetic basis for individual variation in neural phenotype and behavior; recent studies found that allele length predicts V1aR expression and male social attachment in the laboratory. Here, we explore the relationship between avpr1a microsatellite length, V1aR neural phenotype, and field measures of monogamy and fitness in male prairie voles. We found significant effects of allele length on V1aR expression in structures integral to pairbond formation. These effects did not, however, translate to differences in mating tactics or reproductive success. Together, these data suggest that, while length polymorphism in the avpr1a microsatellite influences neuronal phenotype, this variation does not contribute significantly to male reproductive success and field behavior. We propose that previously reported behavioral effects may be mediated primarily by sequence variation at this locus, for which allele length is an imperfect proxy. By combining genetic, neuronal and ecological approaches, these data provide novel insights into the contribution of genotype to natural diversity in brain and behavior.     

The dynamics of health in wild field vole populations: a haematological perspective

1. Pathogens have been proposed as potentially important drivers of population dynamics, but while a few studies have investigated the impact of specific pathogens, the wealth of information provided by general indices of health has hardly been exploited. By evaluating haematological parameters in wild populations, our knowledge of the dynamics of health and infection may be better understood. 2. Here, haematological dynamics in natural populations of field voles are investigated to determine environmental and host factors associated with indicators of inflammatory response (counts of monocytes and neutrophils) and of condition: measures of immunological investment (lymphocyte counts) and aerobic capacity (red blood cell counts). 3. Individuals from three field vole populations were sampled monthly for 2 years. Comparisons with individuals kept under controlled conditions facilitated interpretation of field data. Mixed effects models were developed for each cell type to evaluate separately the effects of various factors on post-juvenile voles and mature breeding females. 4. There were three well-characterized 'physiological' seasons. The immunological investment appeared lowest in winter (lowest lymphocyte counts), but red blood cells were at their highest levels and indices of inflammatory response at their lowest. Spring was characterized by a fall in red blood cell counts and peaks in indicators of inflammatory response. During the course of summer-autumn, red blood cell counts recovered, the immunological investment increased and the indicators of inflammatory response decreased. 5. Poor body condition appeared to affect the inflammatory response (lower neutrophil and monocyte peaks) and the immunological investment (lower lymphocyte counts), providing evidence that the capacity to fight infection is dependent upon host condition. 6. Breeding early in the year was most likely in females in better condition (high lymphocyte and red blood cell counts). 7. All the haematological parameters were affected adversely by high population densities.     

Egorov’s narrow-skulled vole (Rodentia,Arvicolinae) from the Late Pleistocene of Eastern Siberia,a North American immigrant

A comparative study of the Late Pleistocene Egorov’s narrow-skulled vole from the Indigirka River basin is performed. The taxon was previously regarded as a subspecies of Microtus (Stenocranius) gregalis (Pallas, 1779). Based on a number of morphological characters, it is shown that this vole is closer to the American species Mynomes (Vocalomys) miurus (Osgood, 1901). It is proposed that Mynomes (V.) miurus egorovi (Fejgin in Baranova et Fejgin, 1980) penetrated into northeastern Siberia during the Zyryanian glacial.     

雌性根田鼠对血液气味的行为识别

大量研究表明尿液在动物的嗅觉通讯中具有重要作用,血液是尿液的根本来源,但对其嗅觉通讯功能的研究较少.因此以雌性根田鼠Microtus oeconomus为研究对象,在行为选择箱中观察其对4种气味源的行为响应模式以判断能否识别不同血液气味.气味源分别为雌性根田鼠血液、雄性根田鼠血液、雄性Wistar大鼠血液和蒸馏水对照.结果表明:雌性根田鼠能够识别血液气味,且通过血液气味进行种间识别,但不能进行性别识别.