The influence of food supplementation on a coastal dune rodent community

Studies of the rodent community in regenerating coastal dune forest areas north of Richards Bay, South Africa, have indicated that a number of species occupy newly rehabilitating areas. Unstable environmental conditions result in habitat changes, rather than competitive interactions, being the major determinant of rodent community development. This led to the present study, which investigated the effects of supplementary food on rodent assemblages. We attempted to stabilize food availability in order to elucidate some of the mechanisms responsible for the development of the rodent community. By only increasing an existing portion of the resource spectrum, we reduced species diversity, probably through dominance by competitive superior exploiters of the augmented resource. Thus, species diversity decreased with food supplementation, as a result of an increase in the abundance of Mastomys natalensis rather than because of a change in the number of species or the abundance of other species.     

Selection on personality in a songbird affects maternal hormone levels tuned to its effect on timing of reproduction

The increase or decrease in yolk androgens over the laying sequence of a clutch in birds may mitigate or enhance, respectively, the disadvantage of the last-hatched chicks, providing a potentially adaptive tool to adjust brood size to food conditions. This variation may involve a genetic component on which Darwinian selection can act. We found that two lines of a wild bird species selected for bold and shy personalities show, respectively, increased and decreased androgen concentrations over the laying sequence. The line showing the increase laid earlier in the season, when food conditions are normally sufficient to raise the whole brood. The line showing the decrease laid later, when food is normally scarce, which may facilitate brood reduction. The results indicate a correlated response in maternal hormone transfer to genetic selection on personality, which relates to ecological conditions.     

Happily together forever: temporal variation in spatial patterns and complete lack of territoriality in a promiscuous rodent

The availability of resources, their effect on population density and territoriality, and the ways in which these factors are interwoven with mating systems are important determinants of small mammal space use. It is often difficult to study these patterns in an integrated way, however, especially because long-term data are needed but not readily available. In this paper, we investigate effects of population density, season and breeding status on home range patterns of the promiscuous rodent Mastomys natalensis using monthly capture-mark-recapture data collected over 17 years in a 3-ha grid. Home ranges were estimated using minimum convex polygons bounded by trap locations, and home range overlap and visitation rates were calculated as a measure of territoriality. As higher population densities coincide with increased resource availability, we predicted that home range sizes would correlate negatively with density. Furthermore, as M. natalensis is promiscuous and population densities are generally high, we predicted that territoriality would be low, and home range overlap would therefore be high. Contrary to expectations the home ranges of female adults increased with population density, although those of male adults and subadults followed the expected decrease. Home range overlap and visitation rates were generally high, and increased significantly with population density. More importantly, they were never lower than those of simulated datasets consisting of randomly moved home ranges. These results therefore suggest that M. natalensis displays a complete lack of territoriality that is rarely seen in small mammals but still meets predictions based on knowledge of density and mating system.     

Intergenerational effects of maternal birth season on offspring size in rural Gambia

Environmental conditions experienced in early life can influence an individual's growth and long-term health, and potentially also that of their offspring. However, such developmental effects on intergenerational outcomes have rarely been studied. Here we investigate intergenerational effects of early environment in humans using survey- and clinic-based data from rural Gambia, a population experiencing substantial seasonal stress that influences foetal growth and has long-term effects on first-generation survival. Using Fourier regression to model seasonality, we test whether (i) parental birth season has intergenerational consequences for offspring in utero growth (1982 neonates, born 1976-2009) and (ii) whether such effects have been reduced by improvements to population health in recent decades. Contrary to our predictions, we show effects of maternal birth season on offspring birth weight and head circumference only in recent maternal cohorts born after 1975. Offspring birth weight varied according to maternal birth season from 2.85 to 3.03 kg among women born during 1975-1984 and from 2.84 to 3.41 kg among those born after 1984, but the seasonality effect reversed between these cohorts. These results were not mediated by differences in maternal age or parity. Equivalent patterns were observed for offspring head circumference (statistically significant) and length (not significant), but not for ponderal index. No relationships were found between paternal birth season and offspring neonatal anthropometrics. Our results indicate that even in rural populations living under conditions of relative affluence, brief variation in environmental conditions during maternal early life may exert long-term intergenerational effects on offspring.     

Simulation analysis to test the influence of model adequacy and data structure on the estimation of genetic parameters for traits with direct and maternal effects

Simulations were used to study the influence of model adequacy and data structure on the estimation of genetic parameters for traits governed by direct and maternal effects. To test model adequacy, several data sets were simulated according to different underlying genetic assumptions and analysed by comparing the correct and incorrect models. Results showed that omission of one of the random effects leads to an incorrect decomposition of the other components. If maternal genetic effects exist but are neglected, direct heritability is overestimated, and sometimes more than double. The bias depends on the value of the genetic correlation between direct and maternal effects. To study the influence of data structure on the estimation of genetic parameters, several populations were simulated, with different degrees of known paternity and different levels of genetic connectedness between flocks. Results showed that the lack of connectedness affects estimates when flocks have different genetic means because no distinction can be made between genetic and environmental differences between flocks. In this case, direct and maternal heritabilities are under-estimated, whereas maternal environmental effects are overestimated. The insufficiency of pedigree leads to biased estimates of genetic parameters.     

Testing hypotheses for maternal effects in Daphnia magna

Maternal effects are widely observed, but their adaptive nature remains difficult to describe and interpret. We investigated adaptive maternal effects in a clone of the crustacean Daphnia magna, experimentally varying both maternal age and maternal food and subsequently varying food available to offspring. We had two main predictions: that offspring in a food environment matched to their mothers should fare better than offspring in unmatched environments, and that offspring of older mothers would fare better in low food environments. We detected numerous maternal effects, for example offspring of poorly fed mothers were large, whereas offspring of older mothers were both large and showed an earlier age at first reproduction. However, these maternal effects did not clearly translate into the predicted differences in reproduction. Thus, our predictions about adaptive maternal effects in response to food variation were not met in this genotype of Daphnia magna.     

Evidence for inbreeding depression in a species with limited opportunity for maternal effects

It is often assumed that mating with close relatives reduces offspring fitness. In such cases, reduced offspring fitness may arise from inbreeding depression (i.e., genetic effects of elevated homozygosity) or from post‐mating maternal investment. This can be due to a reduction in female investment after mating with genetically incompatible males (“differential allocation”) or compensation for incompatibility (“reproductive compensation”). Here, we looked at the effects of mating with relatives on offspring fitness in mosquitofish, Gambusia holbrooki. In this species, females are assumed to be nonplacental and to allocate resources to eggs before fertilization, limiting differential allocation. We looked at the effects of mating with a brother or with an unrelated male on brood size, offspring size, gestation period, and early offspring growth. Mating with a relative reduced the number of offspring at birth, but there was no difference in the likelihood of breeding, gestation time, nor in the size or growth of these offspring. We suggest that due to limited potential for maternal effects to influence these traits that any reduction in offspring fitness, or lack thereof, can be explained by inbreeding depression rather than by maternal effects. We highlight the importance of considering the potential role of maternal effects when studying inbreeding depression and encourage further studies in other Poeciliid species with different degrees of placentation to test whether maternal effects mask or amplify any genetic effects of mating with relatives.     

Low heritabilities, but genetic and maternal correlations between red squirrel behaviours

Consistent individual differences in behaviour, and behavioural correlations within and across contexts, are referred to as animal personalities. These patterns of variation have been identified in many animal taxa and are likely to have important ecological and evolutionary consequences. Despite their importance, genetic and environmental sources of variation in personalities have rarely been characterized in wild populations. We used a Bayesian animal model approach to estimate genetic parameters for aggression, activity and docility in North American red squirrels (Tamiasciurus hudsonicus). We found support for low heritabilities (0.08-0.12), and cohort effects (0.07-0.09), as well as low to moderate maternal effects (0.07-0.15) and permanent environmental effects (0.08-0.16). Finally, we found evidence of a substantial positive genetic correlation (0.68) and maternal effects correlation (0.58) between activity and aggression providing evidence of genetically based behavioural correlations in red squirrels. These results provide evidence for the presence of heritable variation in red squirrel behaviour, but also emphasize the role of other sources of variation, including maternal effects, in shaping patterns of variation and covariation in behavioural traits.     

Density dependence in a fluctuating wild reindeer herd; maternal vs. offspring effects

Summary The Hardangervidda wild reindeer herd in Norway is the largest in Western Europe. It has fluctuated between 7000 and 32000 animals during the last 35 years. Four density-dependent effects were found: 1. A food limitation effect due to a shift in diet after overgrazing lichen on the winter range. This led to increased tooth wear and lowered body size and fat reserves. 2. A significant correlation between population density and juvenile winter survival rate. No effect on adult female survival rate was found. 3. A cohort effect. After population increase and overgrazing, recruitment was reduced by 30% and remained so after population reduction. Birth weights had increased by 30% 5 years after population reduction and the mean calving time was earlier. As a result, after population reduction weights of newborns were 40% greater at a comparable date. Neonatal survival rate was related to maternal condition during the last part of gestation which coincides with the peak winter snow accumulation. The slow increase in adult dressed body weights (DBW) after population reduction is due to the combined effects of increased tooth wear when winter range was limiting and to the cohort-generation time, so that an improvement in neonatal survival and size was first expressed in subsequent offspring cohorts. 4. An inter-generation effect. During 30 years of resource limitation, DBW decreased by 23%, birth rate was unchanged after the first peak, while fecundity increased by 15%, suggesting increased reproductive effort per unit body weight. Natural selection for increased reproductive effort by smaller females when food was limiting was suggested. Some size-effect due to hunters selecting the largest adult phenotypes was possible but not the main cause. These results do not support some earlier hypotheses about the effects of population density on size at maturity in ungulates.     

Sex-specific maternal effects in a viviparous fish

Mothers vary in their effects on their offspring, but studies of variation in maternal effects rarely ask whether differences between mothers are consistent for sons and daughters. Here, we analysed maternal effects in the mosquitofish Gambusia holbrooki for development time and adult size of sons and daughters, and a primary male sexual character (gonopodium length). We found substantial maternal effects on all traits, most notably for gonopodium length. There were significant correlations within each sex for maternal effects on different traits, indicative of trade-offs between development rate and adult size. By contrast, there was no evidence of any consistency in maternal effects on sons and daughters. This suggests that the evolution of maternal effects will follow independent trajectories dependent on sex-specific selection on offspring. Importantly, failure to recognize the sex-specific nature of maternal effects in this population would have substantially underestimated the extent of their variation between mothers.     

Context-dependent sex allocation: constraints on the expression and evolution of maternal effects

Despite decades of research, whether vertebrates can and do adaptively adjust the sex ratio of their offspring is still highly debated. However, this may have resulted from the failure of empirical tests to identify large and predictable fitness returns to females from strategic adjustment. Here, we test the effect of diet quality and maternal condition on facultative sex ratio adjustment in the color polymorphic Gouldian finch (Erythrura gouldiae), a species that exhibits extreme maternal allocation in response to severe and predictable (genetically-determined) fitness costs. On high-quality diets, females produced a relatively equal sex ratio, but over-produced sons in poor dietary conditions. Despite the lack of sexual size dimorphism, nutritionally stressed foster sons were healthier, grew faster, and were more likely to survive than daughters. Although these findings are in line with predictions from sex allocation theory, the extent of adjustment is considerably lower than previously reported for this species. Females therefore have strong facultative control over sex allocation, but the extent of adjustment is likely determined by the relative magnitude of fitness gains and the ability to reliably predict sex-specific benefits from environmental (vs. genetic) variables. These findings may help explain the often inconsistent, weak, or inconclusive empirical evidence for adaptive sex ratio adjustment in vertebrates.     

Multigenerational maternal effect on diapause induction in Trichogramma species (Hymenoptera: Trichogrammatidae)

Maternal photoperiodic response is known to influence the percentage of diapausing prepupae in Trichogramma species. However, the influence of several preceding generations has not yet been studied. We have investigated the stability of photoperiod-induced changes in multiple generations of Trichogramma buesi Voegele and Trichogramma principium Sug. et Sor. Short-day conditions during preimaginal development induced an increase in the percentage of diapausing progeny and grand progeny of both Trichogramma species. A similar trend was also detected in the fourth and fifth generations, but the response was weak although statistically significant. This grand-grandmaternal photoperiodic effect (which has not been demonstrated before for Trichogramma or for any other insect parasitoid) is most probably based on the transgenerational transmission of variations in DNA expression. We conclude that in mass rearing, to facilitate diapause induction before cold storage, it is advisable to rear both maternal and grandmaternal generations under the short-day conditions. In scientific studies, several generations preceding the experiment should be kept under equal conditions to exclude multigenerational maternal effects.     

Variation among populations of Diodia teres (Rubiaceae) in environmental maternal effects

Previous studies have quantified variation in environmental maternal effects (EME) within populations, but these effects could differ among populations as well. In this study we grew clonal replicates of individuals from three populations of the annual plant Diodia teres in their native and non-native environments. Our goal was to estimate the effects of maternal environment and maternal population on seed and seedling traits. Seeds that were produced in this field study were then planted in two soil types to quantify effects of the offspring environment on seedling traits. There was substantial variation among populations for seed weight. We found population variation for EME, and maternal environment by offspring environment interactions. We conclude that variation among populations in EME may be an unrecognized component of local adaptation, and that attempts to control maternal effects by statistically accounting for variation in seed weight may be ineffective.     

Trans‐generational effects of maternal rearing density on offspring development time in a parasitoid wasp

Maternal pre‐reproductive experience can impose phenotypic changes on offspring traits. These modifications may result from physiological constraints, although they can also increase the adaptation of offspring to their anticipated environment. Distinguishing between the two interpretations is often difficult. The effects of virgin female rearing density on their longevity and the characteristics of their male offspring are explored in the polyembryonic parasitoid wasp Copidosoma koehleri (Blanchard) (Encyrtidae: Hymenoptera). High rearing density may adversely affect maternal physiology or, alternatively, act as a cue for anticipated competition during the lives of the mothers and their offspring. Male offspring of group‐reared females reach pupation significantly sooner than male offspring of females reared alone. This accelerated development may provide an advantage when competition from superparasitising individuals is expected. The lifespan of high‐density females is longer than that of singly‐reared females, and their male offspring survive longer, suggesting that crowded rearing does not reduce the fitness of females or offspring. The shortened development time of male offspring may reflect an adaptive epigenetic response to predicted competitive conditions.     

Paternal effects associated with melanism in Harmonia axyridis (Coleoptera: Coccinellidae): mating sequence asymmetries and interactions with age‐specific maternal effects

1. For this study a cohort of melanic Harmonia axyridis males homozygous for the spectabilis allele was produced. These were used to produce four kinds of twice‐mated females, comprising all four permutations of melanic and non‐melanic (succinic) males. A series of 12 larvae were then reared from the first and 10th clutches of each female to compare progeny developmental phenotypes. 2. There were no effects of mating treatment on overall female reproductive performance (preoviposition period, 20‐day fecundity, or egg fertility). 3. Age‐specific maternal effects were evident in progeny developmental phenotypes; larvae of 10th clutches developed more slowly, pupation was shorter, and adults emerged at heavier weights. 4. Paternal effects were superimposed on maternal effects and affected progeny independent of their paternity; melanic males induced slower larval development and slower pupation, but only in 10th clutches and only when they mated second. 5. There was a significant three‐way interaction between male mating treatment, clutch number and progeny phenotype, indicating that progeny developmental responses to (mixed) paternal effects varied depending on their own phenotype and the time elapsed since their mother's last mating. 6. Melanic males mating second obtained a P2 advantage over succinic males, which increased from first to 10th clutch, but the reverse was not true when succinic males mated second. Thus, polyandry in H. axyridis facilitates both genetic and epigenetic competition among males while simultaneously enabling the sharing of predominant paternal effects among the progeny of different fathers.     

Environmental and not maternal effects determine variation in offspring phenotypes in a passerine bird

Maternal and environmental effects can profoundly influence offspring phenotypes, independent of genetic effects. Within avian broods, both the asymmetric post‐hatching environment created by hatching asynchrony and the differential maternal investment through the laying sequence have important consequences for individual nestlings in terms of the allocation of resources to body structures with different contributions to fitness. The purpose of this study was to evaluate the relative importance of post‐hatching environmental and maternal effects in generating variation in offspring phenotypes. First, an observational study showed that within blue tit, Cyanistes caeruleus, broods, late‐hatched nestlings allocated resources to tarsus development, maintained mass gain and head‐bill growth and directed resources away from the development of fourth primary feathers. Second, a hatching order manipulation experiment resulted in nestlings from first‐laid eggs hatching last, thereby allowing comparison with both late and early‐hatched nestlings. Experimental nestlings had growth patterns which were closer to late‐hatched nestlings, suggesting that within‐brood growth patterns are determined by post‐hatching environmental effects. Therefore, we conclude that post‐hatching environmental effects play an important role in generating variation in offspring phenotypes.     

Nest-site preference and maternal effects on offspring growth

Maternal preferences for oviposition sites are assumed to beadaptive, but offspring fitness is not always higher at preferredsites and, thus, further study of the selection pressures thatinfluence oviposition behavior is warranted. Among birds, predationis regarded as the primary agent of selection on nest-site microhabitatpreferences, but alternatives are rarely considered. We testedthe hypothesis that avian nest-site preferences are an adaptiveresponse to fitness costs imposed by variation in nest-sitemicroclimate. We documented that Chestnut-collared Longspurs(Calcarius ornatus) strongly preferred to orient nests towardsthe southeast and showed that this preference influenced microclimate:nests facing southeast had the highest midday temperatures.Yet, preferences were not adaptive because nestlings in nestswith the preferred orientation gained mass at a slower rate,had retarded skeletal growth, and reached a smaller final size.We experimentally tested this result by altering orientationof nests and confirmed, for the first time, that variation innestling growth was causally linked to variation in nest microclimatearising from nest-orientation preferences. Adults respondedto the high temperatures at preferred southeast-facing nestsby spending more time shading young from the sun, apparentlyattempting to ameliorate heat costs. This response, however,resulted in parents spending less time feeding young, potentiallyexplaining slower growth in these nests. Direct effects of highertemperatures may also play a role in slower growth. Althoughwe lack an explanation for this apparently maladaptive preference,these results demonstrate that nest-site choices of birds canyield fitness costs imposed by variation in nest microclimate.