Determinants of mating success in the golden hamster (Mesocricetus auratus) IV. Sperm competition

Summary This study was designed to clarify several aspects of sperm competition in the golden hamster (Mesocricetus auratus). By mating females homozygous for a recessive coat color gene with two males, one homozygous for the dominat gene (agouti) and one homozygous for the recessive (cream), paternity of the resulting young could be determined by day 2 postpartum. When females received 5 consecutive ejaculations from a male of one strain followed by 5 ejaculations from a male of the other strain, there was a significant advantage with respect to litter composition for the male ejaculating first. A mechanism for the first male mating advantage was suggested by the results of an experiment in which the time interval between first and second males was varied. Delays of 30 min between first and second males significantly increased the proportion of young sired by the first male. With a delay of 8 h, the first male sired all of the young. Delays between matings by males of the two strains had greater effects when mating tests began around the time of ovulation, rather than several hours before. Ejaculations in excess of those required for pregnancy initiation were shown to have a two-fold effect. They afforded the first male a measure of protection against displacement by a subsequent male. Conversely, prolonged copulation by the second male resulted in significant displacement of the sperm of a predecessor. The protective effects of multiple ejaculations by the first male were mediated by two mechanisms: the delay in introduction of competing sperm and an increase in the relative concentration of the first male's sperm. Prolonged copulation by the second male also appeared to function through its effect on relative sperm concentrations. Males of these genotypes differed with respect to the relative fertilizing capacity of their cjaculates. When ejaculations from males of the two strains were alternated (thus minimizing mating order effects), agouti males sired over 90% of the young. The time during which mating tests were conducted (relative to the occurrence of ovulation) had no effect on the relative performance of the strains. The effects of prolonged copulation and first male mating advantage demonstrated in this study are consistent with observations of mating behavior under semi-natural conditions. Thus, it appears that patterns of sperm allocation and manipulation, male and female mating strategies, and mating systems have coevolved.     

Frequency, not relative abundance, of temperate tree species varies along climate gradients in eastern North America

There have been many attempts to model the impacts of climate change on the distributions of temperate tree species, but empirical analyses of the effects of climate on the distribution and abundance of tree species have lagged far behind the models. Here, we used forest inventory data to characterize variation in adult tree abundance along climate gradients for the 24 most common tree species in the northeastern United States. The two components of our measure of species abundance--local frequency vs. relative abundance--showed dramatically different patterns of variation along gradients of mean annual temperature and precipitation. Local frequency (i.e., the percentage of plots in a given climate in which a species occurred) varied strongly for all 24 species, particularly as a function of temperature. Relative abundance when present in a plot, on the other hand, was effectively constant for most species right up to their estimated climatic range limits. Although the range limits for both temperature and precipitation were quite broad for all of the species, the range of climates within which a species was common (i.e., high frequency) was much narrower. Because frequency in sites within a given climate shows a strong sensitivity to temperature, at least, this suggests that the processes determining canopy tree recruitment on new sites also vary strongly with climate.     

The functional response of a hoarding seed predator to mast seeding

Mast seeding involves the episodic and synchronous production of large seed crops by perennial plants. The predator satiation hypothesis proposes that mast seeding maximizes seed escape because seed predators consume a decreasing proportion of available seeds with increasing seed production. However, the seed escape benefits of masting depend not only on whether predators are satiated at high levels of seed production, but also on the shape of their functional response (type II vs. type III), and the actual proportion of available seeds that they consume at different levels of seed production. North American red squirrels (Tamiasciurus hudsonicus) are the primary vertebrate predator of white spruce (Picea glauca) mast seed crops in many boreal regions because they hoard unopened cones in underground locations, preempting the normal sequence of cone opening, seed dispersal, and seed germination. We document the functional response of cone-hoarding by red squirrels across three non-mast years and one mast year by estimating the number of cones present in the territories of individual red squirrels and the proportion of these cones that they hoarded each autumn. Even though red squirrels are not constrained by the ingestive and on-body (fat reserves) energy reserve limitations experienced by animals that consume seeds directly, most squirrels hoarded < 10% of the cones present on their territories under mast conditions. Cone availability during non-mast years also reached levels that satiated the hoarding activity of red squirrels; however, this occurred only on the highest-quality territories. Squirrels switched to mushroom-hoarding when cone production was low and mushrooms were abundant. This resulted in type III functional response whereby the proportional harvest of cones was highest at levels of cone availability that were intermediate within non-mast years. Overall, more cones escaped squirrel cone-hoarding during a mast event than when cone production was low in non-mast years, which supports the predator satiation hypothesis. However, the highly variable seed escape in non-mast years may help to explain why all spruce cone production is not concentrated into fewer, larger, mast years.     

Quantifying and comparing size selectivity among Alaskan sockeye salmon fisheries

Quantifying long-term size-selective harvest patterns is necessary for understanding the potential evolutionary effects on exploited species. The comparison of fishery selection patterns on the same species subject to different gear types, in different areas, and over multi-decadal periods can reveal the factors influencing selection. In this study we quantified and compared size-selective harvest by nine Alaskan sockeye salmon (Oncorhynchus nerka) fisheries to understand overall patterns. We calculated length-specific linear selection differentials (the difference in average length of fish before vs. after fishing), which are produced by different combinations of exploitation rates and length-selectivity values, and nonlinear standardized differentials, describing disruptive selection, across all years for each fishery. Selection differentials varied among years, but larger fish were caught in 73% of years for males and 84% of years for females, leaving smaller fish to spawn. Disruptive selection was observed on female and male fish in 84% and 92% of years, respectively. Linear selection was stronger on females than males in 77% of years examined, and disruptive selection was stronger on males in 71% of years. Selection pressure was influenced by a combination of factors under and beyond management control; analyses using mixed-effects models indicated that fisheries were less size selective in years when fish were larger than average and had lower exploitation rates. The observed harvest of larger than average sockeye salmon is consistent with the hypothesis that size-selective fishing contributes to decreasing age and length at maturation trends over time, but temporal variability in selection and strong disruptive selection suggests that the overall directional pressure is weaker than is often assumed in evolutionary models.     

Personality and parasites: sex-dependent associations between avian malaria infection and multiple behavioural traits

The evolution and ecology of consistent behavioural variation, or personality, is currently the focus of much attention in natural populations. Associations between personality traits and parasite infections are increasingly being reported, but the extent to which multiple behavioural traits might be associated with parasitism at the same time is largely unknown. Here, we use a population of great tits, Parus major, to examine whether infection by avian malaria (Plasmodium and Leucocytozoon) is associated with three behavioural traits assayed under standardized conditions. All of these traits are of broad ecological significance and two of them are repeatable or heritable in our population. Here, we show weak correlations between some but not all of these behavioural traits, and sex-dependent associations between all three behavioural traits and parasite infection. Infected males showed increased problem-solving performance whereas infected females showed reduced performance; furthermore, uninfected females were four times more likely to solve problems than uninfected males. Infected females were more exploratory than uninfected females, but infection had no effect on males. Finally, infected males were more risk-averse than uninfected males but females were unaffected. Our results demonstrate the potential for complex interactions between consistent personality variation and parasite infection, though we discuss the difficulty of attributing causality in these associations. Accounting for complex parasite-behaviour associations may prove essential in understanding the evolutionary ecology of behavioural variation and the dynamics of host–parasite interactions.     

Heterogeneity in social network connections is density-dependent: implications for disease dynamics in a gregarious ungulate

Behavioral Ecology and Sociobiology - Individual animals across all taxa differ consistently in behaviour, i.e. they show personality traits. This inter-individual variability has significant...     

Safety margins for lead in the general population

The results of monitoring blood lead concentrations, the accepted biological indicator for lead in man, are examined against the three trigger values put forward in the UK, first as justifying environmental investigation (25 g 100 ml^-1), second as justifying health checks (35 g 100 ml^-1) and third as likely to give rise to obvious symptoms in a few individuals (50 g 100 ml^-1). Arguments for using the proportion or the number of individuals above a trigger value rather than the ratio of the mean blood lead concentration to the trigger value, the conventional safety margin, are presented. The numbers of individuals or proportions in the total population who are likely to be above the trigger values have been estimated and shown to be relatively small for all three. Factors likely to affect blood lead concentrations are examined against the possible effects of the changes, current and proposed, in the controls imposed on lead usage and on pathways. The qualitative changes expected are considered by groups-eg. smokers and drinkers, by regions, eg., those with lead-free drinking water as against those still with lead in their supplies, and for the general population eg. from the elimination of the soldered can for food and the reduction, and eventual elimination, of lead in petrol.Because the relationship between intake and blood concentration is non-linear in the UK, those with the highest existing blood lead concentrations in the general population must be expected to show the smallest relative reductions in blood lead for any small reduction in exposure. The analysis also concludes that those at highest risk will have to depend on their being identified individually and action taken on them and their immediate specific environment.     

Visitor perceptions of rural landscapes: a case study in the Peak District National Park, England

Maintaining national parks is an integral policy tool to conserve rare habitats. However, because national parks are funded by taxpayers, they must also serve the needs of the general public. Increasingly, and thanks to today's diverse society, there is evidence that this creates challenges for park managers who are pulled in two opposing directions: to conserve nature on the one hand and to meet different visitor expectations on the other. This tension was explored in the Peak District National Park, a rural landscape dominated by heather moorland and sheep farming in Northern England where research was conducted to determine how social class and ethnicity shaped perceptions of the park. Results uncovered that social class played a very strong role in shaping perceptions of this region with 'middle class' respondents reacting far more favourably to the park than people from more working class backgrounds. We observed ethnicity playing a similar role, though our results are less significantly different.