Search

Individuals colonizing new areas at expanding ranges encounter numerous and unpredictable stressors. Exposure to unfamiliar environments suggests that colonists would differ in stress levels from residents living in familiar conditions. Few empirical studies tested this hypothesis and produced mixed results, and the role of stress regulation in colonization remains unclear. Studies relating stress levels to colonization mainly use a geographical analysis comparing established colonist populations with source populations. We used faecal glucocorticoid metabolites (FGMs) to assess both spatial and temporal dynamics of stress levels in an expanding population of midday gerbils (Meriones meridianus). We demonstrated that adult males and females had higher FGM levels in newly emerged colonies, compared with the source population, but differed in the pattern of FGM dynamics post-foundation. In males, FGM levels sharply decreased in the second year after colony establishment. In females, FGM levels did not change with time and remained high despite the decreasing environmental unpredictability, exhibiting among-individual variation. Increased stress levels of colonist males damping with time post-colonization suggest they are flexible in responding to immediate changes in environmental uncertainty. On the contrary, high and stable over generations stress levels uncoupled from the changes in the environmental uncertainty in female colonists imply that they carry a relatively constant phenotype associated with the reactive coping strategy favouring colonization. We link sex differences in consistency and plasticity in stress regulation during colonization to the sex-specific life-history strategies. [ABSTRACT FROM AUTHOR]

Analysis of Cladocera (Crustacea: Branchiopoda) subfossil remains in lake sediments features prominently in paleolimnological studies. It is well known, however, that species composition in a taphocoenosis (assemblage of subfossil remains in sediments) does not represent perfectly that of the original living community (biocoenosis) from which it came. We analyzed the representation of different Cladocera skeletal components in sediments of 27 Russian water bodies to compare two methods of enumerating relative abundances of cladoceran remains: (1) recording the number of most abundant fragments of each taxon to represent the number of individuals, and (2) recording each fragment of a taxon as belonging to an individual specimen. Overall, for all cladoceran taxa and all water bodies sampled, proportions of different skeletal components differed from what would be expected based on those in live individuals. Carapaces were the most abundant component in 23 of 27 water bodies. Head shields were common, but predominated in only four samples, whereas postabdomens were rare, accounting for < 10% of the whole sample set. Several hypotheses are proposed to explain the different proportions of cladoceran skeletal remains in sediment samples. Both methods for counting remains yielded similar relative abundance estimates for different taxa, which can be regarded as evidence that both methods are adequate, with some exceptions. For example, Alona affinis was represented by a relatively high portion of postabdomens, a component that for other taxa was usually poorly represented. In general, recording of the total number of skeletal components, as compared to using the most abundant fragment method (MAF), slightly overestimates the significance of some taxa in the community. Disproportionate preservation of different skeletal components among cladoceran taxa does not compromise the results of cladoceran-based paleoecological analyses using either counting method, but should be considered when interpreting results. [ABSTRACT FROM AUTHOR]

Inbreeding depression is commonly considered an evolutionary influence on pre-copulatory mechanisms of inbreeding avoidance. Inbreeding may be minimized by: (1) delayed maturation and reproduction, (2) sex-biased dispersal, (3) behavioural avoidance of mating with relatives, and/or (4) mating by females with multiple males (polyandry). Time constraints on reproduction and limited opportunities for outbred matings may limit mate choice, forcing females to mate with relatives and favouring multiple paternity to reduce the costs of inbred matings. Using parentage, relatedness, and spatial genetic analyses, we studied genetic mating system, dispersal and inbreeding patterns in a wild partially isolated colony of the yellow ground squirrels (Spermophilus fulvus), fast-living hibernators. Females were phylopatric, while males dispersed within the colony. Nevertheless, male-biased dispersal could not completely separate closely related males and females, and the potential risk of inbreeding was high, in particular due to early maturation of males — some of them matured before dispersal. Females did not mate assortatively with respect to relatedness of males, mating both with close kin and non-kin, and 38% of sire-mother pairs were closely related (coefficient of relatedness > 0.125). Multiple paternity was common (56% of all litters), and multiply sired litters combined offspring from inbred and outbred matings. Parents of singly sired litters were mostly unrelated. The overall level of inbreeding was low. We conclude that, under strong time constraints on reproduction and mate choice, females do not mate selectively with unrelated males. However, multiple paternity dilutes inbred matings effectively enough to maintain the overall low level of inbreeding. Significance statement: Models predict that inbreeding should be more common in nature than is observed. Time constraints on reproduction and low availability of mates should make females tolerant of inbreeding, while multiple mating partners of females can help them reduce its costs. Based on observations in a free-living colony of the yellow ground squirrel, Spermophilus fulvus, a hibernator with a fast pace of life, we report high rates of inbred matings in females who have limited mate choice and face severe time constraints on reproduction. However, multiple paternity observed in more than half of females reduced the average relatedness between partners and, therefore, among their offspring, resulting in the overall low inbreeding within the colony. This is a new evidence for inbreeding tolerance under limited mate choice and female polyandry as a bet-hedging strategy against inbreeding. [ABSTRACT FROM AUTHOR]

Fitness consequences of early-life conditions remain unclear and poorly studied in mammals. Based on long-term observations of yellow ground squirrels (Spermophilus fulvus), we identified early determinants of female fitness by analyzing the effects of early-life individual and environmental characteristics (weaning weight, weight gain rate, date of natal emergence, natal litter size, location of the natal burrow, local density of juveniles, population density and precipitation in the post-weaning period) on lifetime reproductive success (LRS). We found high variation and right-skewed distribution in all five LRS components (survival to adulthood, adult lifespan, and lifetime numbers of weaned litters, weanlings, and yearling offspring). Numbers of litters, weanlings, and adult offspring were correlated with each other and increased with lifespan, confirming that longevity is a better predictor of LRS than fecundity. Survival to adulthood was the most sensitive fitness component to early conditions and was higher in females (a) with greater weaning weight, (b) born further from human settlement and (c) born at lower population density. Population density at birth was the best early predictor of all LRS components and negatively influenced adult lifespan and numbers of weanlings and yearling offspring. Early growth rate positively affected the probability of reproducing after the first hibernation and the number of offspring weaned. Such syndrome of high-quality (heavy and fast-growing) young born in a favourable environment ("a silver spoon effect") with downstream damping fitness consequences has been observed so far in only a few mammalian species. [ABSTRACT FROM AUTHOR]