Douglas B. Meikle

Female choice based on male spatial ability and aggressiveness among meadow voles

The way in which female mate choice, scramble competition and contest competition for mates interact to influence the evolution of male traits is poorly understood. We tested female preferences for males that varied in spatial ability and aggressiveness, traits likely to be selected by scramble and contest competition, respectively. Male meadow voles, Microtus pennsylvanicus, were tested for their spatial ability using a series of water maze tests, and their aggressiveness was determined using paired arena trials. Females were given a choice between two tethered males, and their preferences were scored based on relative frequency and duration of visits. Females preferred males with low aggressiveness and good spatial ability to males with high aggressiveness and poor spatial ability. Females showed no preference between males with high aggressiveness and good spatial ability and males with low aggressiveness and poor spatial ability. These results suggest that female choice and scramble competition will favour males with better spatial ability. In contrast, female choice does not seem to favour more aggressive males.

Reproduction, foraging and the negative density–area relationship of a generalist rodent

While many species show positive relationships between population density and habitat patch area, some species consistently show higher densities in smaller patches. Few studies have examined mechanisms that may cause species to have negative density–area relationships. We tested the hypothesis that greater reproduction in edge versus interior habitats and small versus large fragments contributes to higher densities of white-footed mice (Peromyscus leucopus) in small versus large forest fragments. We also examined vegetation structure and foraging tray utilization to evaluate if greater reproduction was a result of higher food availability. There were greater number of litters and proportion of females producing litters in the edge versus interior of forest fragments, which may have contributed to greater population growth rates and higher densities in edge versus interior and small versus large fragments. Data on vegetation structure and giving-up densities of seeds in artificial patches suggest that food availability may be higher in edge versus interior habitats and small versus large fragments. These results, in an area with few or no long-tailed weasels, provide a distinct contrast to the findings of Morris and Davidson (Ecology 81:2061, 2000) who observed lower reproduction in forest edge habitat as a result of high weasel predation, suggesting that specialist predators may be important in affecting the quality of edge habitat. While we cannot exclude the potential contributions of immigration, emigration, and mortality, our data suggest that greater reproduction in edge versus interior habitat is an important factor contributing to higher densities of P. leucopus in small fragments.

The relationship between dominance rank and spatial ability among male meadow voles (Microtus pennsylvanicus).

Males of many mammalian species exhibit contest competition and scramble competition for mates, but the relationship between these 2 forms of competition remains poorly understood. The authors measured dominance rank and spatial ability as traits likely to be selected by contest and scramble competition, respectively, among male meadow voles (Microtus pennsylvanicus). The spatial ability of males was assessed using water maze tests, and dominance rank was determined using paired trials in a neutral arena. Dominant males had better spatial-learning ability and tended to have quicker learning speed but did not have better spatial memory than less aggressive subordinates. Therefore, the authors found no evidence that contest and scramble competition have favored alternative reproductive phenotypes among male meadow voles.

Social dominance rank and accessory sex glands in wild adult male house mice born to food-deprived mothers.

Food deprivation after weaning often has greater effects on the reproduction of females than males. However, if animals are deprived prenatally (i.e., through deprivation of the mother during gestation), the reproduction of males may be more negatively impacted because it may decrease their ability to compete with other males and their attractiveness to females. We tested the predictions that adult sons of females that are food-deprived during gestation would tend to lose agonistic encounters with sons of well-nourished (control) females and would have smaller accessory sex glands as well. Sons of control mothers were more frequently dominant to sons of deprived mothers. They also had heavier vesicular-coagulating gland complexes and tended to have heavier preputial glands. However, among males that had not been tested for social dominance rank, there were no such differences in accessory gland weights. These data indicate that maternal food deprivation affects sons only if they engage in agonistic encounters. These effects may be due to a disruption of the organizational effects of testosterone that occur in neonatal male mice and they are likely to have a strong negative impact on the reproduction of the sons of deprived mothers.

PREVALENCE OF DEER TICKS (IXODES SCAPULARIS) ON WHITE-FOOTED MICE (PEROMYSCUS LEUCOPUS) IN FOREST FRAGMENTS

Abstract Effects of fragmentation on distribution of ectoparasites of mammals are not well understood. A previous study reported higher nymphal tick (Ixodes scapularis) densities in smaller than in larger fragments. We tested whether there was a higher prevalence of ticks on white-footed mice (Peromyscus leucopus) in small forest fragments in an agricultural landscape. We observed a lower prevalence of ticks on mice in smaller than in larger fragments. Differences in infection rates between fragments, use of fragments by white-tailed deer, and agricultural history of landscapes could contribute to the apparent differences in tick abundance between this study and that reported previously. Resolution of the apparently contradictory data will require that the abundance of host-seeking ticks and prevalence on mice be measured in both landscapes.

Variation in Effects of Fragmentation on the White-Footed Mouse (Peromyscus leucopus) during the Breeding Season

Abstract The effects of fragmentation may be variable for species that have seasonal patterns of density and reproduction. We tested whether the effects of fragment size and habitat on reproduction and density varied over the course of the breeding season for the white-footed mouse (Peromyscus leucopus). The relative density of mice changed; in small fragments densities were lower in spring, similar during the midsummer lull, and higher in autumn than in large fragments. Large fragments displayed the bimodal pattern of litter production previously reported for P. leucopus, but small fragments showed a relatively constant number of litters among spring, lull, and autumn reproductive periods. Although no differences were found between edge and interior habitats in density, litter production, and reproductive effort during spring and lull periods, all were higher in edge than interior habitats during autumn. Changes in effects of fragment size and habitat may be mediated by the influence of fragmentation on seasonally important abiotic and biotic factors.

The Effects of Forest Fragmentation on Densities of White-footed Mice (Peromyscus leucopus) During the Winter

Abstract Forest fragmentation can influence abiotic and biotic factors important for the reproduction and survival of animals. Previous investigations suggest that, in the fall, more food is available for white-footed mice (Peromyscus leucopus) in edge than interior habitats and in small than large forest fragments. However, in the winter, individuals in small fragments and edge habitat may be more exposed to harsh weather extremes, which can result in higher mortality. We examined the effects of fragment size (small and large) and habitat (edge and interior) on populations of white-footed mice during nest box censuses in the winter (January–April) of 2003 in southwestern Ohio. While population density was initially higher in small than large fragments and edge than interior habitats, by the end of the winter there were no significant differences in population size. Populations in small fragments and edge habitat had larger decreases and greater rates of decline in density than those in large fragments and interior habitats over the course of the winter. These results suggest that while small fragments and edge habitat may be high quality habitat in the fall, animals in these areas may suffer higher mortality rates during the winter, compared with animals in large fragments and interior habitat.

Annual changes in structural complexity of understory vegetation and relative abundance ofPeromyscus leucopus in fragmented habitats

Greater structural complexity of understory vegetation may be one factor that contributes to the negative relation ship between density of generalist rodents (eg,Peromyscus leucopus Rafinesque, 1818) and forest patch area; however, this hypothesis is difficult to test. We removed the problem of multicollinearity among variables by analyzing changes in structural complexity and relative abundance ofP. leucopus in 15 forest patches (1.3–200 ha) over a 3-yr period. We found that an in crease in the relative abundance ofP. leucopus was associated with an increase in structural complexity of understory vegetation in the same patches between years. Structural complexity of the understory was greater in smaller forest patches which we speculate may be influenced by moisture. It is possible that understory vegetation provides greater food availability and/or cover from some predators in small patches, but the specific mechanism(s) remains unclear. Multiple factors can potentially influence populations ofP. leucopus, but our results provide strong evidence that structural complexity of understory vegetation positively in fluences relative abundance ofP. leucopus in fragmented habitats.

Effects of male kinship and agonistic behaviour on reproduction and odour preferences of female house mice, Mus domesticus

In gregarious species, males may wound or kill females during intermale contest competition, which directly affects females fitness. However, male–male agonistic encounters may also have more subtle effects on females by creating a stressful social environment in which females live. We examined whether male–male aggression affects female fitness and odour preference in house mice. We tested (1) whether pairs of brothers would be less likely to fight than pairs of nonbrothers; (2) whether females housed with two males that were brothers would have higher reproductive success than females housed with two males that were not brothers and (3) whether females would show a preference for the odours of brother or nonbrother pairs. Males that were brothers were less aggressive towards each other than were nonbrothers, and females housed with males that were brothers produced significantly more litters than those housed with males that were not brothers. Females did not show a preference for the odours of brothers or nonbrothers, but they did prefer odours of less aggressive pairs of males. These findings suggest that while contest competition favours fighting among males, female choice and kin selection favour tolerance.

Do male house mice (Mus musculus) discriminate between females that differ in nutritional status

Most studies of mate choice have focused on female preference for male traits because it is generally assumed that since males provide less parental investment they are not choosy. However, if males suffer missed opportunity costs by mating with lower quality females, selection should favor males with the ability to discriminate among females. We tested the hypothesis that male house mice (Mus musculus) discriminate between females that differ in nutritional status (non-food-deprived versus food-deprived). We recorded the time males spent investigating either type of female and used that to determine preference (spending > or = 55% of their total investigation time with one female). We also examined the effects of female nutritional status and female preference status (preferred versus non-preferred) on the reproductive success of males. Males did not display a preference for non-food-deprived females nor did their reproductive success vary with nutritional status or preference status of females. Interestingly, males spent more time investigating females that were closest to the males own weight. In addition, pairs that were closer in weight were more likely to produce a litter. These results suggest that male house mice are capable of discriminating among females and that such discrimination may influence their reproductive success.