avpr1a length polymorphism is not associated with either social or genetic monogamy in free-living prairie voles

Recent discoveries of single-gene influences on social behaviour have generated a great deal of interest in the proximate mechanisms underlying the expression of complex behaviours. Length polymorphism in a microsatellite in the regulatory region of the gene encoding the vasopressin 1a receptor (avpr1a) has been associated with both inter- and intra-specific variation in socially monogamous behaviour in voles (genus Microtus) under laboratory conditions. Here, we evaluate the relationship between avpr1a length polymorphism and social associations, genetic monogamy, and reproductive success in free-living prairie vole (M. ochrogaster) populations. We found no evidence of a relationship between avpr1a microsatellite length and any of our correlates of either social or genetic monogamy in the field. Our results, especially when taken in conjunction with those of recent experimental studies in semi-natural enclosures, suggest that avpr1a polymorphism is unlikely to have been a major influence in the evolution or maintenance of social monogamy in prairie voles under natural conditions.     

A demographic analysis of vole population responses to fragmentation and destruction of habitat

 Fragmentation and destruction of natural habitats is currently considered to be the major threat to wildlife populations. We here perform a comprehensive analysis of the demographic effects of habitat fragmentation and destruction on 14 populations of the root vole. The experiment was divided into two consecutive periods. During the first period, we contrasted populations with the same initial size and structure in continuous and fragmented habitat. During the second period, we fragmented the continuous habitat into the same configuration as the permanently fragmented habitat so that the effect of habitat destruction could be evaluated. We estimated survival and fecundity parameters and combined them into population projection matrices to evaluate their relative impact on population growth. In the first period of the experiment there was no difference in population growth rate between fragmented and continuous populations, although litter size was significantly higher in the continuous populations. In the second period, we found higher population growth rates in populations that had experienced habitat destruction. By applying the transition matrix model to empirical estimates of demographic parameters, we demonstrate that the difference in population growth rate in the second period of the experiment was the result of a nonsignificant difference in adult survival. Movements out of the habitat patches were significantly lower in populations that had experienced habitat destruction. We conclude that predator-caused mortality of animals moving out of the habitat patches was the main determinant of demographic variation in this system. Received: January 31, 2002 / Accepted: March 25, 2003     

Population dynamics of Microtus arvalis in a weed strip

A population of Microtus arvalis Pallas, 1779, living in a weed strip was studied by capture–recapture method over a 2-year period. Weed strips are characterized by their linear shape and high vegetation cover, and are not comparable to the habitats examined in most previous studies on M. arvalis.Abundance of voles was found to be high in the strip with a maximum of 410 voles/ha known to be alive in the first year and 641 voles/ha in the successive year. Abundance was minimal in spring and increased until July. A decrease in population size at the beginning of August was followed by a new increase in both years. One difference between the 2 years was a pronounced peak abundance at the end of June in the second year. The peak may be related to a shift in sex ratio in favour of females in this year (ratio of males:females of 1:8). Also the time of residency of females was significantly longer in the second year than in the year before, and the survival rate of females was greater than in males.The turnover was generally very high and reached maximum values of 80% renewal of population every 2 weeks.     

An extension of the Cormack-Jolly-Seber model for continuous covariates with application to Microtus pennsylvanicus

Recent developments in the Cormack-Jolly-Seber (CJS) model for analyzing capture-recapture data have focused on allowing the capture and survival rates to vary between individuals. Several methods have been developed in which capture and survival are functions of auxiliary variables that may be discrete, constant over time, or apply to the population as a whole, but the problem has not been solved for continuous covariates that vary with both time and individual. This article proposes a new method to handle such covariates by modeling changes over time via a diffusion process and using logistic functions to link the variable to the CJS capture and survival rates. Bayesian methods are used to estimate the model parameters. The method is applied to study the effect of body mass on the survival of the North American meadow vole, Microtus pennsylvanicus.     

Vole population cycles in northern and southern Europe: is there a need for different explanations for single pattern?

1. Students of population cycles in small rodents in Fennoscandia have accumulated support for the predation hypothesis, which states that the gradient in cycle length and amplitude running from southern to northern Fennoscandia reflects the relative influence of specialist and generalist predators on vole dynamics, itself modulated by the presence of snow cover. The hypothesized role of snow cover is to isolate linked specialist predators, primarily the least weasel, Mustela n. nivalis L. and their prey, primarily field voles Microtus agrestis L., from the stabilizing influence of generalist predators. 2. The predation hypothesis does not readily account for the high amplitude and regular 3-year cycles of common voles documented in agricultural areas of western, central and eastern Europe. Such cycles are rarely mentioned in the literature pertaining to Fennoscandian cycles. 3. We consider new data on population cycles and demographic patterns of common voles Microtus arvalis Pallas in south-west France. We show that the patterns are wholly consistent with five of six patterns that characterize rodent cycles in Fennoscandia and that are satisfactorily explained by the predation hypothesis. They include the: (a) existence of cycle; (b) the occurrence of long-term changes in relative abundance and type of dynamics; (c) geographical synchrony over large areas; (d) interspecific synchrony; and (e) voles are large in the increase and peak phase and small in decline and low phase, namely. There is a striking similarity between the patterns shown by common vole populations in south-west France and those from Fennoscandian cyclic rodent populations, although the former are not consistent with a geographical extension of the latitudinal gradient south of Fennoscandia. 4. It is possible that the dominant interaction leading to multiannual rodent oscillations is different in different regions. We argue, however, that advocates of the predation hypothesis should embrace the challenge of developing a widely applicable explanation to population cycles, including justifying any limits to its applicability on ecological and not geographical grounds.     

Breeding suppression between two unrelated and initially unfamiliar females occurs with or without social tolerance in common voles (<Emphasis Type="Italic">Microtus arvalis</Emphasis>)

Female common voles can breed in small groups or in isolation. Given the option, will isolated females opt for communal breeding with unrelated females and a probable low reproductive bias, or will they remain isolated, forgoing the advantages of group living? This laboratory work examined the response of two unrelated females to a foreign male in order to determine their social and breeding strategies. Before encountering a male, 70% of the females lived communally and 30% were solitary with a dominance hierarchy. In the presence of the male, only 33% of the females were still associated and lived with the male in a communal nest. In the other triads, only the oldest female lived with the male and she dominated the younger female. Although all animals were then experimentally separated to avoid late abortion due to social stress or infanticide, in 89% of the dyads only one female littered. This breeding suppression happened in hierarchic dyads but also in tolerant ones. This laboratory study on the social influence on reproduction showed that breeding suppression can occur in unrelated female common voles even when they are not closely grouped. It suggests that cooperative breeding between unrelated females should remain rare.     

不同生存条件下东方田鼠肝脏基因表达谱分析

目的比较实验室条件下饲养的东方田鼠和野外捕捉东方田鼠肝脏的基因表达差异,寻找可能参与肝脏病变的关键基因。方法以实验室条件饲养的东方田鼠和野外捕捉东方田鼠为研究对象,分别抽提RNA,逆转录成cDNA,体外转录为cRNA并进行片段化;利用表达谱芯片分别进行杂交,扫描后筛选差异基因,并应用real-time PCR方法对部分基因的表达水平进行进一步测定,验证芯片数据的结果。结果实验室饲养东方田鼠肝组织与野外捕捉东方田鼠相比,共有99个基因和41个EST差异表达。其中参与机体代谢的基因占主导,约占35.4%;其次为参与信号通路的基因,约占24.2%;参与细胞周期和免疫的基因分别占6.1%和3.0%。结论利用基因表达谱芯片初步筛选了可能参与东方田鼠脂肪肝形成过程的基因,发现机体代谢通路的基因占主导,肝脏中细胞色素家族基因表达差异明显。     

Holarctic phylogeography of the root vole (Microtus oeconomus): implications for late Quaternary biogeography of high latitudes

A species-wide phylogeographical study of the root vole (Microtus oeconomus) was performed using the whole 1140 base pair mitochondrial (mt) cytochrome b gene. We examined 83 specimens from 52 localities resulting in 65 unique haplotypes. Our results demonstrate that the root vole is divided into four main mtDNA phylogenetic lineages that seem to have largely allopatric distributions. Net divergence estimates (2.0-3.5%) between phylogroups, as well as relatively high nucleotide diversity estimates within phylogroups, indicate that the distinct phylogeographical structure was initiated by historical events that predated the latest glaciation. European root voles are divided into a Northern and a Central mtDNA phylogroup. The mtDNA data in concert with fossil records imply that root voles remained north of the classical refugial areas in southern Europe during the last glacial period. The currently fragmented populations in central Europe belong to a single mtDNA phylogroup. The Central Asian and the North European lineages are separated by the Ural Mountains, a phylogeographical split also found in collared lemmings (Dicrostonyx) and the common vole (M. arvalis). The Beringian lineage occurs from eastern Russia through Alaska to northwestern Canada. This distribution is congruent with the traditional boundaries of the Beringian refugium and with phylogeographical work on other organisms. In conclusion, similarities between the phylogeographical patterns in the root vole and other rodents, such as Arctic and subarctic lemmings, as well as more temperate vole species, indicate that late Quaternary geological and climatic events played a strong role in structuring northern biotic communities.     

青春期雌性根田鼠初次择偶行为与雄性优势等级

在实验室条件下，研究了性刚成熟的雌性根田鼠对一对互为同胎同胞的以体重划分为优势和从势的雄性个体的择偶行为，目的在于检验雄性社会等级是否影响其配偶选择。结果发现：(1)根田鼠存在显著的偏雄性二型，而雄性动物优势度与体重大小成正比；(2)在Y字型迷宫中，初次发情雌鼠对优势雄鼠的访问时间、社会探究频次和友好频次等显著大于从属雄鼠；(3)在随后24h的一雌二雄共居中，优势雄优先交配；从属雄的干扰不能中断优势雄鼠的交配。这些结果说明，体重差异可以作为划分雄性优势的指标，社会等级可以作为择偶行为的一个依据。优势雄鼠与处于从属地位的同胞相比，能获得优先交配机会。同胎同胞虽具有遗传相似性，但雄性竞争的结果表现在体重和社会等级上具有显著差异，表明配偶选择在发挥着作用。根田鼠是一雄多雌制，而且具有较大的偏雄性二型，提示社会等级、雌性选择和婚配制度有密切关联[动物学报49(3)：303—309，2003]。