Biomedical subjects

Loeske E B Kruuk

Publications and source records attributed to Loeske E B Kruuk.

16 recordsLinked to original sources

PubMed2006

Responding to environmental change: plastic responses vary little in a synchronous breeder.

The impact of environmental change on animal populations is strongly influenced by the ability of individuals to plastically adjust key life-history events. There is therefore considerable interest in establishing the degree of plasticity in traits and how selection acts on plasticity in natural populations. Breeding time is a key life-history trait that affects fitness and recent studies have found that females vary significantly in their breeding time-environment relationships, with selection often favouring individuals exhibiting stronger plastic responses. In contrast, here, we show that although breeding time in the common guillemot, Uria aalge, is highly plastic at the population level in response to a large-scale environmental cue (the North Atlantic Oscillation, NAO), there is very little between-individual variation-most individuals respond to this climate cue very similarly. We demonstrate strong stabilizing selection against individuals who deviate from the average population-level response to NAO. This species differs significantly from those previously studied in being a colonial breeder, in which reproductive synchrony has a substantial impact on fitness; we suggest that counter selection imposed by a need for synchrony could limit individuals in their response and potential for directional selection to act. This demonstrates the importance of considering the relative costs and benefits of highly plastic responses in assessing the likely response of a population to the environmental change.

Adaptation, Physiological↗

PubMed2006

Comparative evidence for a link between Peyer's patch development and susceptibility to transmissible spongiform encephalopathies.

BACKGROUND: Epidemiological analyses indicate that the age distribution of natural cases of transmissible spongiform encephalopathies (TSEs) reflect age-related risk of infection, however, the underlying mechanisms remain poorly understood. Using a comparative approach, we tested the hypothesis that, there is a significant correlation between risk of infection for scrapie, bovine spongiform encephalopathy (BSE) and variant CJD (vCJD), and the development of lymphoid tissue in the gut. METHODS: Using anatomical data and estimates of risk of infection in mathematical models (which included results from previously published studies) for sheep, cattle and humans, we calculated the Spearman's rank correlation coefficient, rs, between available measures of Peyer's patch (PP) development and the estimated risk of infection for an individual of the corresponding age. RESULTS: There was a significant correlation between the measures of PP development and the estimated risk of TSE infection; the two age-related distributions peaked in the same age groups. This result was obtained for each of the three host species: for sheep, surface area of ileal PP tissue vs risk of infection, rs = 0.913 (n = 19, P < 0.001), and lymphoid follicle density vs risk of infection, rs = 0.933 (n = 19, P < 0.001); for cattle, weight of PP tissue vs risk of infection, rs = 0.693 (n = 94, P < 0.001); and for humans, number of PPs vs risk of infection, rs = 0.384 (n = 46, P = 0.008). In addition, when changes in exposure associated with BSE-contaminated meat were accounted for, the two age-related patterns for humans remained concordant: rs = 0.360 (n = 46, P = 0.014). CONCLUSION: Our findings suggest that, for sheep, cattle and humans alike there is an association between PP development (or a correlate of PP development) and susceptibility to natural TSE infection. This association may explain changes in susceptibility with host age, and differences in the age-susceptibility relationship between host species.

Age Distribution↗

PubMed2006

The rate of senescence in maternal performance increases with early-life fecundity in red deer.

Tradeoffs between reproduction and somatic maintenance are a frequently cited explanation for reproductive senescence in long-lived vertebrates. Between-individual variation in quality makes such tradeoffs difficult to detect and evidence for their presence from wild populations remains scarce. Here, we examine the factors affecting rates of senescence in maternal breeding performance in a natural population of red deer (Cervus elaphus), using a mixed model framework to control for between-individual variance. Senescence began at 9 years of age in two maternal performance traits. In both traits, females that produced more offspring in early life had faster rates of senescence. This tradeoff is evident alongside significant effects of individual quality on late life breeding performance. These results present rare evidence in support of the disposable soma and antagonistic pleiotropy theories of senescence from a wild vertebrate population and highlight the utility of mixed models for testing theories of ageing.

Aging↗

PubMed2006

Live fast, die young: trade-offs between fitness components and sexually antagonistic selection on weaponry in Soay sheep.

Males are predicted to compete for reproductive opportunities, with sexual selection driving the evolution of large body size and weaponry through the advantage they confer for access to females. Few studies have explored potential trade-offs of investment in secondary sexual traits between different components of fitness or tested for sexually antagonistic selection pressures. These factors may provide explanations for observed polymorphisms in both form and quality of secondary sexual traits. We report here an analysis of selection on horn phenotype in a feral population of Soay sheep (Ovis aries) on the island of Hirta, St. Kilda, Scotland. Soay sheep display a phenotypic polymorphism for horn type with males growing either normal or reduced (scurred) horns, and females growing either normal, scurred, or no (polled) horns; further variation in size exists within horn morphs. We show that horn phenotype and the size of the trait displayed is subject to different selection pressures in males and females, generating sexually antagonistic selection. Furthermore, there was evidence of a trade-off between breeding success and longevity in normal-horned males, with both the normal horn type and larger horn size being associated with greater annual breeding success but reduced longevity. Therefore, selection through lifetime breeding success was not found to act upon horn phenotype in males. In females, a negative association of annual breeding success within the normal-horned phenotype did not result in a significant difference in lifetime fitness when compared to scurred individuals, as no significant difference in longevity was found. However, increased horn size within this group was negatively associated with breeding success and longevity. Females without horns (polled) suffered reduced longevity and thus reduced lifetime breeding success relative the other horn morphs. Our results therefore suggest that trade-offs between different components of fitness and antagonistic selection between the sexes may maintain genetic variation for secondary sexual traits within a population.

Animals↗

PubMed2005

Constraints on plastic responses to climate variation in red deer.

Influences of climate on life history traits in natural populations are well documented. However, the implications of between-individual variation in phenotypic plasticity underlying observed trait-environment relationships are rarely considered due to the large, long-term datasets required for such analysis. Studies typically present correlations of annual trait means with climate or assume that individual phenotypic responses are constant. Here, we examine this additional level of variation and show that, in a red deer population on the Isle of Rum, Scotland, changes in climate generate changes in phenotype only amongst individuals who have experienced favourable ecological conditions. Examination of relationships between offspring birth weight and spring temperature within the lifetimes of individual females revealed that the tendency to respond to climate declined as the population density experienced early in life increased. The presence of such systematic variation in individual plasticity is rarely documented in the wild, and has important implications for our understanding of the environmental dependencies of traits under varying ecological conditions.

Acclimatization↗

PubMed2005

Ontogenetic patterns in heritable variation for body size: using random regression models in a wild ungulate population.

Body size is an important determinant of fitness in many organisms. While size will typically change over the lifetime of an individual, heritable components of phenotypic variance may also show ontogenetic variation. We estimated genetic (additive and maternal) and environmental covariance structures for a size trait (June weight) measured over the first 5 years of life in a natural population of bighorn sheep Ovis canadensis. We also assessed the utility of random regression models for estimating these structures. Additive genetic variance was found for June weight, with heritability increasing over ontogeny because of declining environmental variance. This pattern, mirrored at the phenotypic level, likely reflects viability selection acting on early size traits. Maternal genetic effects were significant at ages 0 and 1, having important evolutionary implications for early weight, but declined with age being negligible by age 2. Strong positive genetic correlations between age-specific traits suggest that selection on June weight at any age will likely induce positively correlated responses across ontogeny. Random regression modeling yielded similar results to traditional methods. However, by facilitating more efficient data use where phenotypic sampling is incomplete, random regression should allow better estimation of genetic (co)variances for size and growth traits in natural populations.

Aging↗

PubMed2005

Heritability and genetic constraints of life-history trait evolution in preindustrial humans.

An increasing number of studies have documented phenotypic selection on life-history traits in human populations, but less is known of the heritability and genetic constraints that mediate the response to selection on life-history traits in humans. We collected pedigree data for four generations of preindustrial (1745-1900) Finns who lived in premodern fertility and mortality conditions, and by using a restricted maximum-likelihood animal-model framework, we estimated the heritability of and genetic correlations between a suite of life-history traits and two alternative measures of fitness. First, we demonstrate high heritability of key life-history traits (fecundity, interbirth interval, age at last reproduction, and adult longevity) and measures of fitness (individual lambda and lifetime reproductive success) for females but not for males. This sex difference may have arisen because most of the measured traits are under physiological control of the female, such that a male's fitness in monogamous societies may depend mainly on the reproductive quality of his spouse. We found strong positive genetic correlations between female age at first reproduction and longevity, and between interbirth intervals and longevity, suggesting reduced life spans in females who either started to breed relatively early or who then bred frequently. Our results suggest that key female life-history traits in this premodern human population had high heritability and may have responded to natural selection. However genetic constraints between longevity and reproductive life-history traits may have constrained the evolution of life history and facilitated the maintenance of additive genetic variance in key life-history traits.

Animals↗

PubMed2005

Evolution driven by differential dispersal within a wild bird population.

Evolutionary theory predicts that local population divergence will depend on the balance between the diversifying effect of selection and the homogenizing effect of gene flow. However, spatial variation in the expression of genetic variation will also generate differential evolutionary responses. Furthermore, if dispersal is non-random it may actually reinforce, rather than counteract, evolutionary differentiation. Here we document the evolution of differences in body mass within a population of great tits, Parus major, inhabiting a single continuous woodland, over a 36-year period. We show that genetic variance for nestling body mass is spatially variable, that this generates different potential responses to selection, and that this diversifying effect is reinforced by non-random dispersal. Matching the patterns of variation, selection and evolution with population ecological data, we argue that the small-scale differentiation is driven by density-related differences in habitat quality affecting settlement decisions. Our data show that when gene flow is not homogeneous, evolutionary differentiation can be rapid and can occur over surprisingly small spatial scales. Our findings have important implications for questions of the scale of adaptation and speciation, and challenge the usual treatment of dispersal as a force opposing evolutionary differentiation.

Aging↗

PubMed2005

Quantitative genetics of larval life-history traits in Rana temporaria in different environmental conditions.

The degree to which genetic variation in a given trait varies among different populations of the same species and across different environments has seldom been quantified in wild vertebrate species. We investigated the expression of genetic variability and maternal effects in three larval life-history traits of the amphibian Rana temporaria. In a factorial laboratory experiment, five widely separated populations (max. 1600 km) were subjected to two different environmental treatments. Animal model analyses revealed that all traits were heritable (h(2) approximately 0.20) in all populations and under most treatment combinations. Although the cross-food treatment genetic correlations were close to unity, heritabilities under a restricted food regime tended to be lower than those under an ad libitum food regime. Likewise, maternal effects (m(2) approximately 0.05) were detected in most traits, and they tended to be most pronounced under restricted food conditions. We detected several cross-temperature genetic and maternal effects correlations that were lower than unity, suggesting that genotype-environment interactions and maternal effect-environment interactions are a significant source of phenotypic variation. The results reinforce the perspective that although the expression of genetic and maternal effects may be relatively homogeneous across different populations of the same species, local variation in environmental conditions can lead to significant variation in phenotypic expression of quantitative traits through genotype-environment and maternal effect-environment interactions.

Animals↗

PubMed2005

Genotype-level variation in lifetime breeding success, litter size and survival of sheep in scrapie-affected flocks.

Five different sheep flocks with natural outbreaks of scrapie were examined to determine associations between individual performance (lifetime breeding success, litter size and survival) and scrapie infection or PrP genotype. Despite different breed composition and forces of infection, consistent patterns were found among the flocks. Regardless of the flock, scrapie-infected sheep produced on average 34 % fewer offspring than non-scrapie-infected sheep. The effect of scrapie on lifetime breeding success appears to be a function of lifespan as opposed to fecundity. Analysis of litter size revealed no overall or genotype differences among the five sheep flocks. Survival, however, depends on the individual's scrapie status (infected or not) and its PrP genotype. Susceptible genotypes appear to perform less well in lifetime breeding success and life expectancy even if they are never affected with clinical scrapie. One possible explanation for these results is the effect of pre-clinical scrapie. Additional evidence supporting this hypothesis is discussed.

Animals↗

PubMed2005

How to use molecular marker data to measure evolutionary parameters in wild populations.

Estimating the genetic basis of phenotypic traits and the selection pressures acting on them are central to our understanding of the evolution and conservation of wild populations. However, obtaining such evolutionary-related parameters is not an easy task as it requires accurate information on both relatedness among individuals and their breeding success. Polymorphic molecular markers are very useful in estimating relatedness between individuals and parentage analyses are now extensively used in most taxa. The next step in the application of molecular data to wild populations is to use them to derive estimates of evolutionary-related parameters for quantitative traits, such as quantitative genetic parameters (e.g. heritability, genetic correlations) and measures of selection (e.g. selection gradients). Despite their great appeal and potential, the optimal use of molecular tools is still debated and it remains unclear how they should best be used to obtain reliable estimates of evolutionary parameters in the wild. Here, we review the methods available for estimating quantitative genetic and selection parameters and discuss their merits and shortcomings, to provide a tool that summarizes the potential uses of molecular data to obtain such parameters in wild populations.

Biological Evolution↗

PubMed2005

Selection on mothers and offspring: whose phenotype is it and does it matter?

Reproductive and early life-history traits can be considered aspects of either offspring or maternal phenotype, and their evolution will therefore depend on selection operating through offspring and maternal components of fitness. Furthermore, selection at these levels may be antagonistic, with optimal offspring and maternal fitness occurring at different phenotypic values. We examined selection regimes on the correlated traits of birth weight, birth date, and litter size in Soay sheep (Ovis aries) using data from a long-term study of a free-living population on the archipelago of St. Kilda, Scotland. We tested the hypothesis that selective constraints on the evolution of the multivariate phenotype arise through antagonistic selection, either acting at offspring and maternal levels, or on correlated aspects of phenotype. All three traits were found to be under selection through variance in short-term and lifetime measures of fitness. Analysis of lifetime fitness revealed strong positive directional selection on birth weight and weaker selection for increased birth date at both levels. However, there was also evidence for stabilizing selection on these traits at the maternal level, with reduced fitness at high phenotypic values indicating lower phenotypic optima for mothers than for offspring. Additionally, antagonistic selection was found on litter size. From the offspring's point of view it is better to be born a singleton, whereas maternal fitness increases with average litter size. The decreased fitness of twins is caused by their reduced birth weight; therefore, this antagonistic selection likely results from trade-offs between litter size and birth weight that have different optimal resolutions with respect to offspring and maternal fitness. Our results highlight how selection regimes may vary depending on the assignment of reproductive and early life-history traits to either offspring or maternal phenotype.

Animals↗

PubMed2004

Evolution in a changing environment: a case study with great tit fledging mass.

Heritable phenotypic traits under significant and consistent directional selection often fail to show the expected evolutionary response. A potential explanation for this contradiction is that because environmental conditions change constantly, environmental change can mask an evolutionary response to selection. We combined an "animal model" analysis with 36 years of data from a long-term study of great tits (Parus major) to explore selection on and evolution of a morphological trait: body mass at fledging. We found significant heritability of this trait, but despite consistent positive directional selection on both the phenotypic and the additive genetic component of body mass, the population mean phenotypic value declined rather than increased over time. However, the mean breeding value for body mass at fledging increased over time, presumably in response to selection. We show that the divergence between the response to selection observed at the levels of genotype and phenotype can be explained by a change in environmental conditions over time, that is, related both to increased spring temperature before breeding and elevated population density. Our results support the suggestion that measuring phenotypes may not always give a reliable impression of evolutionary trajectories and that understanding patterns of phenotypic evolution in nature requires an understanding of how the environment has itself changed.

Animals↗

PubMed2004

Estimating genetic parameters in natural populations using the "animal model".

Estimating the genetic basis of quantitative traits can be tricky for wild populations in natural environments, as environmental variation frequently obscures the underlying evolutionary patterns. I review the recent application of restricted maximum-likelihood "animal models" to multigenerational data from natural populations, and show how the estimation of variance components and prediction of breeding values using these methods offer a powerful means of tackling the potentially confounding effects of environmental variation, as well as generating a wealth of new areas of investigation.

Analysis of Variance↗

PubMed2004

Parasitism reduces the potential for evolution in a wild bird population.

We tested the effect of detrimental environmental conditions during growth on the heritability of chick body size in a wild population of blue tits (Parus caeruleus) highly parasitized by blowfly larvae. During nine years, we experimentally induced deparasitized broods, whereas unmanipulated control broods remained heavily infested by two species of Protocalliphora ectoparasites. The heritability of tarsus length was significantly higher in deparasitized broods than control broods, due in part to a very low common brood environment effect in deparasitized broods. We also found evidence for significant genotype-by-environment interactions, which further reflected the effect of the ecological conditions on the expression of additive genetic effects and could represent an additional constraint on the evolution of tarsus length. To our knowledge, this experiment provides the first evidence of host quantitative genetics being influenced by parasitism, and illustrates the potential for parasitism to constrain an evolutionary response to selection.

Analysis of Variance↗

PubMed2002

Severe inbreeding depression in collared flycatchers (Ficedula albicollis).

The causes and magnitude of inbreeding depression are of considerable importance for a wide range of issues in evolutionary and conservation biology, but we have only a limited understanding of inbreeding depression in natural populations. Here, we present a study of inbreeding in a large wild population of collared flycatchers (Ficedula albicollis). Inbreeding was rare, to the extent that we detected only 1.04% of 2139 matings over 18 years that resulted in offspring with a non-zero inbreeding coefficient, f > 0. When it did occur, inbreeding caused a significant reduction in the egg-hatching rate, in fledgling skeletal size and in post-fledging juvenile survival, with the number of offspring being recruited to the breeding population from a nest of f = 0.25 being reduced by 94% relative to a non-inbred nest. A maximum-likelihood estimate of the number of lethal equivalents per gamete was very high at B = 7.47, indicating a substantial genetic load in this population. There was also a non-significant tendency for inbreeding depression to increase with the strength of selection on a trait. The probability of mating between close relatives (f = 0.25) increased throughout the breeding season, possibly reflecting increased costs of inbreeding avoidance. Our results illustrate how severe inbreeding depression and considerable genetic load may exist in natural populations, but detecting them may require extensive long-term datasets.

Animals↗