Maternal effects and their consequences for offspring fitness in the Yellow Dung Fly

1. Maternal adult diet and body size influence the fecundity of a female and possibly the quality and the performance of her offspring via egg size or egg quality. In laboratory experiments, negative effects in the offspring generation have often been obscured by optimal rearing conditions.
2. To estimate these effects in the Yellow Dung Fly, Scathophaga stercoraria , how maternal body size and adult nutritional status affected her fecundity, longevity and egg size were first investigated.
3. Second, it was investigated how female age and adult nutritional experience, mediated through the effects of egg size or egg quality, influenced the performance of offspring at different larval densities.
4. Maternal size was less important than maternal adult feeding in increasing reproductive output. Without food restriction, large females had larger clutch sizes and higher oviposition rates, whereas under food restriction this advantage was reversed in favour of small females.
5. Offspring from mothers reared under nutritional stress experienced reduced fitness in terms of egg mortality and survival to adult emergence. If the offspring from low-quality eggs survived, the transmitted maternal food deficiency only affected adult male body size under stressful larval environments.
6. Smaller egg sizes due to maternal age only slightly affected the performance of the offspring under all larval conditions.     

Senescence and costs of reproduction in the life history of a small precocial species

Species following a fast life history are expected to express fitness costs mainly as increased mortality, while slow‐lived species should suffer fertility costs. Because observational studies have limited power to disentangle intrinsic and extrinsic factors influencing senescence, we manipulated reproductive effort experimentally in the cavy (Cavia aperea) which produces extremely precocial young. We created two experimental groups: One was allowed continuous reproduction (CR) and the other intermittent reproduction (IR) by removing males at regular intervals. We predicted that the CR females should senesce (and die) earlier and produce either fewer and/or smaller, slower growing offspring per litter than those of the IR group. CR females had 16% more litters during three years than IR females. CR females increased mass and body condition more steeply and both remained higher until the experiment ended. Female survival showed no group difference. Reproductive senescence in litter size, litter mass, and reproductive effort (litter mass/maternal mass) began after about 600 days and was slightly stronger in CR than IR females. Litter size, litter mass, and offspring survival declined with maternal age and were influenced by seasonality. IR females decreased reproductive effort less during cold seasons and only at higher age than CR females. Nevertheless, offspring winter mortality was higher in IR females. Our results show small costs of reproduction despite high reproductive effort, suggesting that under ad libitum food conditions costs depend largely on internal regulation of allocation decisions.     

Effects of Increased Flight on the Energetics and Life History of the Butterfly Speyeria mormonia

Movement uses resources that may otherwise be allocated to somatic maintenance or reproduction. How does increased energy expenditure affect resource allocation? Using the butterfly Speyeria mormonia, we tested whether experimentally increased flight affects fecundity, lifespan or flight capacity. We measured body mass (storage), resting metabolic rate and lifespan (repair and maintenance), flight metabolic rate (flight capacity), egg number and composition (reproduction), and food intake across the adult lifespan. The flight treatment did not affect body mass or lifespan. Food intake increased sufficiently to offset the increased energy expenditure. Total egg number did not change, but flown females had higher early-life fecundity and higher egg dry mass than control females. Egg dry mass decreased with age in both treatments. Egg protein, triglyceride or glycogen content did not change with flight or age, but some components tracked egg dry mass. Flight elevated resting metabolic rate, indicating increased maintenance costs. Flight metabolism decreased with age, with a steeper slope for flown females. This may reflect accelerated metabolic senescence from detrimental effects of flight. These effects of a drawdown of nutrients via flight contrast with studies restricting adult nutrient input. There, fecundity was reduced, but flight capacity and lifespan were unchanged. The current study showed that when food resources were abundant, wing-monomorphic butterflies living in a continuous meadow landscape resisted flight-induced stress, exhibiting no evidence of a flight-fecundity or flight-longevity trade-off. Instead, flight changed the dynamics of energy use and reproduction as butterflies adopted a faster lifestyle in early life. High investment in early reproduction may have positive fitness effects in the wild, as long as food is available. Our results help to predict the effect of stressful conditions on the life history of insects living in a changing world.     

Long-term shifts in the cyclicity of outbreaks of a forest-defoliating insect

Optimisation of reproductive investment is crucial for Darwinian fitness, and detailed long-term studies are especially suited to unravel reproductive allocation strategies. Allocation strategies depend on the timing of resource acquisition, the timing of resource allocation, and trade-offs between different life-history traits. A distinction can be made between capital breeders that fuel reproduction with stored resources and income breeders that use recently acquired resources. In capital breeders, but not in income breeders, energy allocation may be decoupled from energy acquisition. Here, we tested the influence of extrinsic (weather conditions) and intrinsic (female characteristics) factors during energy storage, vitellogenesis and early gestation on reproductive investment, including litter mass, litter size, offspring mass and the litter size and offspring mass trade-off. We used data from a long-term study of the viviparous lizard, Lacerta (Zootoca) vivipara. In terms of extrinsic factors, rainfall during vitellogenesis was positively correlated with litter size and mass, but temperature did not affect reproductive investment. With respect to intrinsic factors, litter size and mass were positively correlated with current body size and postpartum body condition of the previous year, but negatively with parturition date of the previous year. Offspring mass was negatively correlated with litter size, and the strength of this trade-off decreased with the degree of individual variation in resource acquisition, which confirms theoretical predictions. The combined effects of past intrinsic factors and current weather conditions suggest that common lizards combine both recently acquired and stored resources to fuel reproduction. The effect of past energy store points out a trade-off between current and future reproduction.     

Relative contributions of offspring quality and environmental quality to adult field performance

Determinants of adult performance, such as growth and survival, are influenced by extrinsic, environmental and intrinsic, phenotypic factors. The relative importance of extrinsic and intrinsic factors, while ecologically relevant, is rarely estimated simultaneously. We estimate the relative contributions of offspring size (intrinsic) and various environmental factors (extrinsic) on adult performance in the marine colonial bryozoan Watersipora subtorquata. We used a variance partitioning approach for both new and previously published data, enabling us to examine the performance of over 1000 individuals in the field. We found offspring size to explain relatively little variation in adult performance. Of the environmental factors taken to account, temporal variation and an environmental gradient had the strongest influences.     

Shifting body weight-fecundity relationship in a capital breeder: maternal effects on egg numbers of the autumnal moth under field conditions

In the literature, various environmental factors are described as being capable of influencing the reproductive output of insect females irrespective of their body size. Still, female body size or weight is widely used as a proxy for fecundity. In the present study, a seven-year data set on the autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae), was used to analyze whether the body weight-fecundity relationship in this capital breeding, cyclic forest defoliating lepidopteran is constant across years. Ambient temperature conditions and density of conspecifics during larval development, the length of the pupal period, as well as moth densities in the parent generation were examined as factors capable of modifying the body weight-fecundity relationship. While the regression slope of potential fecundity (total egg numbers per female) on pupal mass was constant across years, the mean total egg number per given body weight (the regression intercept) was significantly different between years. This residual variance in egg numbers after controlling for the effect of pupal mass was best explained by the pooled geometrid density (autumnal and winter moths) in the parent generation. The total egg number per given body weight decreased with increasing density of geometrid moths in the parent generation. Thus, maternal density effects on offspring fecundity were found in this system. Their rather weak nature suggests, however, that this maternal effect alone does not have the potential of causing cyclic population dynamics in the autumnal moth.     

Maternal influences on brood sex ratios: an experimental study in tree swallows

When the reproductive value of sons and daughters differ, parents are expected to adjust the sex ratio of their offspring to produce more of the sex that provides greater fitness returns. The body condition of females or environmental factors, such as food abundance and mate quality, may influence these expected fitness returns. In a previous study of tree swallows (Tachycineta bicolor), we found that females produced more sons in their broods when they were in better body condition (mass corrected for size). We tested this relationship by experimentally clipping some flight feathers to reduce female body condition. As predicted, we found that females with clipped feathers had a lower proportion of sons in their broods and poorer body condition. However, female body condition alone was not a significant predictor of brood sex ratio in our experiment. We suggest that brood sex ratio is causally related to some other factor that covaries with body condition, most likely the foraging ability of females. The hypothesis that brood sex ratios are influenced by individual differences in female foraging ability is supported by a high repeatability of brood sex ratio for individual females. Thus, maternal effects may have a strong influence on the sex ratios of offspring.     

An analysis of pre- and post-hatching maternal effects mediated by carotenoids in the blue tit

Maternal effects increase phenotypic plasticity in offspring traits and may therefore facilitate adaptation to environmental variability. Carotenoids have been hypothesized to mediate costs of reproduction in females as well as maternal effects. However, assessing potential transgenerational and population consequences of environmental availability of carotenoids requires a better understanding of mechanisms of maternal effects mediated by these antioxidant pigments. Manipulating dietary availability of carotenoids to egg-laying female blue tits and subsequently cross-fostering nestlings between female treatments allowed us to specifically investigate the relative importance of maternal effects through egg carotenoids and through post-hatching care mediated by antioxidants in females. Nestling body size and mass and plasma antioxidants were not significantly affected by pre- or post-hatching maternal effects mediated by antioxidants, although both types of maternal effects in interaction explained the variation in growth, as measured by wing length. Development of the ability to mount a cell-mediated immune response as well as its temporal dynamics was influenced by both pre- and post-hatching maternal effects, with an advantage to nestlings originating from, or reared by, carotenoid-supplemented females. In addition, nestlings reared by carotenoid-fed females had a lower blood sedimentation rate, indicating that they may have been less infected than nestlings from controls. Finally, prehatching maternal effects in interaction with nestling plasma carotenoid levels affected the development of carotenoid-based plumage. Maternal effects mediated by carotenoids may thus act as a proximate factor in development and phenotypic plasticity in traits associated with nestling fitness, such as immune response and ability to metabolize and use antioxidants, and ultimately participate in the evolution of phenotypic traits.     

Intrinsic post‐ejaculation sperm ageing does not affect offspring fitness in Atlantic salmon

Post‐meiotic sperm ageing, both before ejaculation and after ejaculation, has been shown to negatively affect offspring fitness by lowering the rate of embryonic development, reducing embryonic viability and decreasing offspring condition. These negative effects are thought to be caused by intrinsic factors such as oxidative stress and ATP depletion or extrinsic factors such as temperature and osmosis. Effects of post‐ejaculation sperm ageing on offspring fitness have so far almost exclusively been tested in internal fertilizers. Here, we tested whether intrinsic post‐ejaculation sperm ageing affects offspring performance in an external fertilizer, the Atlantic salmon Salmo salar. We performed in vitro fertilizations with a split‐clutch design where sperm were subjected to four post‐ejaculation ageing treatments. We varied the duration between sperm activation and fertilization while minimizing extrinsic stress factors and tested how this affected offspring fitness. We found no evidence for an effect of our treatments on embryo survival, hatching time, larval standard length, early larval survival or larval growth rate, indicating that intrinsic post‐ejaculation sperm ageing may not occur in Atlantic salmon. One reason may be the short life span of salmon sperm after ejaculation. Whether our findings are true in other external fertilizers with extended sperm activity remains to be tested.     

Evolutionary ecology of egg size and number in a seed beetle: genetic trade-off differs between environments

Abstract In many organisms, large offspring have improved fitness over small offspring, and thus their size is under strong selection. However, due to a trade-off between offspring size and number, females producing larger offspring necessarily must produce fewer unless the total amount of reproductive effort is unlimited. Because differential gene expression among environments may affect genetic covariances among traits, it is important to consider environmental effects on the genetic relationships among traits. We compared the genetic relationships among egg size, lifetime fecundity, and female adult body mass (a trait linked to reproductive effort) in the seed beetle, Stator limbatus , between two environments (host-plant species Acacia greggii and Cercidium floridum ). Genetic correlations among these traits were estimated through half-sib analysis, followed with artificial selection on egg size to observe the correlated responses of lifetime fecundity and female body mass. We found that the magnitude of the genetic trade-off between egg size and lifetime fecundity differed between environments–a strong trade-off was estimated when females laid eggs on C. floridum seeds, yet this trade-off was weak when females laid eggs on A. greggii seeds. Also differing between environments was the genetic correlation between egg size and female body mass–these traits were positively genetically correlated for egg size on A. greggii seeds, yet uncorrelated on C. floridum seeds. On A. greggii seeds, the evolution of egg size and traits linked to reproductive effort (such as female body mass) are not independent from each other as commonly assumed in life-history theory.     

Offspring fitness and the optimal propagule size in a fluctuating environment

Propagule size is an important maternal effect on offspring fitness and phenotype in birds and other oviparous animals. The performance of propagules often increases with size, but a fluctuating environment may introduce temporal variation in the optimal phenotype. Understanding these mechanisms will provide novel insights into the eco‐evolutionary dynamics of life history strategies in parental reproductive investment. We investigated the interaction between propagule size (measured as egg volume) and environmental conditions on offspring mortality and phenotype in a Norwegian house sparrow population. Increased propagule size reduced offspring mortality in early life, with more pronounced effects under heavy precipitation. However, the optimal propagule size for low offspring mortality until recruitment shifted from large to small as temperature increased. Propagule size had no significant effect on fledgling body mass and tarsus length. These results reveal a potential for eco‐evolutionary dynamics in propagule size, as populations adapt to fluctuating environmental conditions. The ultimate outcome of this dynamic process will also depend on variation in parental fitness and tradeoffs with other life‐history traits, particularly clutch size.     

Habitat quality ranking depends on habitat-independent environmental factors: a model and results from Callosobruchus maculatus

1. Survival and reproduction in different habitats of a heterogeneous environment are affected by intrinsic habitat properties as well as by habitat-independent extrinsic factors. It is argued that the ranking of habitats according to quality may depend on extrinsic environmental factors that act with the same intensity in all habitats. This can happen if, across habitats, high reproductive success in the absence of extrinsic mortality is coupled with late reproduction.
2. In a model of a semelparous organism with overlapping generations that uses two habitats, the effect of different patterns of extrinsic mortality on habitat quality are analysed, as measured by the reproductive value of an egg, which estimates its expected contribution to the future gene pool.
3. Measurements of fitness components in Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) on four host species demonstrate that, across hosts, long development can be associated with high reproductive success in the absence of extrinsic mortality. As a result, the quality ranking of three out of the four hosts would be different in a stable population regulated by intraspecific competition and egg parasitoids than in a growing population or a stable population regulated by age-independent larval mortality.
4. It is suggested that habitat-independent mortality may play a role in the evolution of ecological niches.     

升温对北草蜥雌体繁殖、卵孵化及幼体特征的影响

在围栏条件下,比较升温和对照处理北草蜥(Takydromus septentrionalis)繁殖、卵孵化及幼体特征的差异,以揭示升温对其繁殖生活史特征的作用。升温处理对北草蜥母体体温有显著影响,但并不影响其繁殖输出。升温显著影响卵孵化期和幼体的运动能力,但不影响幼体大小等形态特征。升温条件下孵出的幼体运动能力较弱。结果表明,北草蜥母体能耐受短期的环境增温,维持相对恒定的繁殖输出;升温能影响幼体的功能表现,进而可能改变后代适合度。     

Grandparental effects in marine sticklebacks: transgenerational plasticity across multiple generations

Nongenetic inheritance mechanisms such as transgenerational plasticity (TGP) can buffer populations against rapid environmental change such as ocean warming. Yet, little is known about how long these effects persist and whether they are cumulative over generations. Here, we tested for adaptive TGP in response to simulated ocean warming across parental and grandparental generations of marine sticklebacks. Grandparents were acclimated for two months during reproductive conditioning, whereas parents experienced developmental acclimation, allowing us to compare the fitness consequences of short‐term vs. prolonged exposure to elevated temperature across multiple generations. We found that reproductive output of F1 adults was primarily determined by maternal developmental temperature, but carry‐over effects from grandparental acclimation environments resulted in cumulative negative effects of elevated temperature on hatching success. In very early stages of growth, F2 offspring reached larger sizes in their respective paternal and grandparental environment down the paternal line, suggesting that other factors than just the paternal genome may be transferred between generations. In later growth stages, maternal and maternal granddam environments strongly influenced offspring body size, but in opposing directions, indicating that the mechanism(s) underlying the transfer of environmental information may have differed between acute and developmental acclimation experienced by the two generations. Taken together, our results suggest that the fitness consequences of parental and grandparental TGP are highly context dependent, but will play an important role in mediating some of the impacts of rapid climate change in this system.     

The effect of flight on reproduction in an outbreaking forest lepidopteran

Post‐flight reproductive investment by female insects may be limited as a result of a trade‐off in resource allocation between flight and reproduction. Outbreaking forest pests reduce their habitat quality as a result of severe defoliation when population densities are high. Female relocation to better‐quality habitats can increase offspring survival but reduce their reproductive fitness through flight. In the present study, the effect of flight on the capacity of female Choristoneura conflictana (Walker) (Lepidoptera: Tortricidae) to mate and produce eggs is examined. Females are flown on flight mills, and the subsequent reproductive capacity of each moth is assessed through measures of mating success and egg production. There is no effect of flight on commencement or the duration of mating. Although flight does not affect egg production directly, energy expenditure as a result of flight (as measured by weight loss) shows a negative correlation to potential fecundity, possibly indicating the resorption of eggs in some females. The effect of female size on fecundity is dependent on mating status, suggesting that energy allocated to reproduction is not dependent on flight treatment. Female moth longevity also has a significant effect on egg production but is dependent on flight and mating treatments. There is a relationship between energy expenditure to flight and reproduction in C. conflictana. Females that fly away from dense populations may produce fewer offspring, although this cost may be mitigated by improved offspring survivorship in less defoliated habitats.     

Sexual conflict and cooperation in butterfly reproduction: a comparative study of polyandry and female fitness

Most butterfly species can be characterized as capital breeders, meaning that reproductive output is strongly coupled to the amount of resources they have procured during the larval stage. Accordingly, female fecundity is generally correlated with female mass, both within and across species. However, the females of some species can be partly characterized as income breeders, in the sense that their reproductive output is dependent not only on larval-derived capital but also on resources acquired during the adult stage. These adult resources can be derived from female feeding or from male-transferred nuptial gifts. Recent studies on the within-species effects of multiple matings on female fitness show that females generally gain directly from multiple matings in terms of increased lifetime offspring production. Here, we test whether the positive effects of multiple mating on female fitness also hold at a comparative level, by conducting a laboratory study of female reproductive output in eight pierid species that differ in life-time female mating frequency. Female reproductive output, measured as cumulative egg mass divided by female mass, increased significantly with polyandry (r = 0.942, p < 0.001), demonstrating that the positive effect of mating rate on female reproductive fitness also holds between species. The positive effect of male nutrient contribution is substantial, and the per capita reproductive output is more than twice as high in the most polyandrous species as in the most monandrous ones. Hence, the positive net effect of the ejaculates is highly substantial, although males and females can have sexual interests that run counter to each other, setting the stage for sexually antagonistic coevolution, so that the various component parts of the male ejaculate-sperm, nutrients, anti-aphrodisiacs, and gonadotrophic hormones-may each correspond to a separate conflict-cooperation balance between the sexes. Two scenarios for the evolution of nuptial gifts in butterflies are discussed, one arguing that variation in larval food is the underlying factor and the other arguing that sexually antagonistic coevolution is the driving force. The two views are complementary rather than mutually exclusive, although the former hypothesis predicts that variation in female mating rate depends on variation in larval food availability, whereas the latter suggests that variation in female mating rate between species results from species-specific idiosyncrasies.     

Optimal size and number of propagules: allowance for discrete stages and effects of maternal size on reproductive output and offspring fitness

Existing optimality models of propagule size and number are not appropriate for many organisms. First, existing models assume a monotonically increasing offspring fitness/propagule size relationship. However, offspring survival during certain stages may decrease with increasing propagule size, generating a peaked offspring fitness/propagule size function (e.g., egg size in oxygen-limited aquatic environments). Second, existing models typically do not consider maternal effects on total reproductive output and the expression of offspring survival/propagule size relationships. However, larger females often have greater total egg production and may provide better habitats for their offspring. We develop a specific optimality model that incorporates these effects and test its predictions using data from salmonid fishes. We then outline a general model without assuming specific functional forms and test its predictions using data from freshwater fishes. Our theoretical and empirical results illustrate that, when offspring survival is negatively correlated with propagule size, optimal propagule size is larger in better habitats. When larger females provide better habitats, their optimal propagule size is larger. Nevertheless, propagule number should increase more rapidly than propagule size for a given increase in maternal size. In the absence of density dependence, females with greater relative reproductive output (i.e., for a given body size) should produce more but not larger propagules.     

Maternal influences on offspring phenotypes and sex ratios in a multi‐clutching lizard with environmental sex determination

Maternal and environmental factors are important sources of phenotypic variation because both factors influence offspring traits in ways that impact offspring and maternal fitness. The present study explored the effects of maternal factors (maternal body size, egg size, yolk‐steroid allocation, and oviposition‐site choice) and seasonally‐variable environmental factors on offspring phenotypes and sex ratios in a multi‐clutching lizard with environmental sex determination (Amphibolurus muricatus). Maternal identity had strong effects on offspring morphology, but the nature of maternal effects differed among successive clutches produced by females throughout the reproductive season (i.e. maternal identity by environment interactions). The among‐female and among‐clutch variation in offspring traits (including sex ratios) was not mediated through maternal body size, egg size, or variation in yolk steroid hormones. This lack of nongenetic maternal effects suggests that phenotypic variation may be generated by gene by environment interactions. These results demonstrate a significant genetic component to variation in offspring phenotypes, including sex ratios, even in species with environmental sex determination. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 256–266.     

Life-History Characteristics and Fitness in Descendents of Parthenogenetic and Ex-Ephippio Females of Daphnia Magna

Daphnids of ex-ephippial and parthenogenetic origin differ substantially in life-history. Possible maternally transmitted ex-diapause effects of differing female origin on the fitness of their offspring were studied across multiple clones in Daphnia magna. Ex-ephippial daphnids responded in egg size to different constant food concentrations with the same pattern as parthenogenetic females. Significant differences in egg characteristics between females of different origin were only found for the first clutch produced under high food. The smaller size of eggs in ex-ephippial females, however, did not translate into size differences of first-clutch neonates. A trend for lower mass density per body volume was detected in offspring from ex-ephippial females in comparison with parthenogenetic daphnids. Hence, an ex-diapause effect transmitted by ex-ephippial mothers to their parthenogenetic offspring is likely. However, there was no difference in life-histories and fitness between offspring produced by females of ex-ephippial and parthenogenetic origin at both, high and low food concentrations across multiple clones. Thus, a significant ex-diapause effect on fitness in successive parthenogenetic generations may not be expected in D. magna at the population level.     

Maternal and environmental influences on reproductive success of a viviparous grassland lizard

Understanding the factors that drive population persistence and growth is fundamental to both conservation management and evolutionary biology. Internal (maternal) and external (environmental) factors can affect female reproductive output, and in oviparous reptiles both may strongly influence offspring phenotype and quality. However, the link between these effects, their importance for reproductive output and offspring characteristics of live-bearing lizards, and whether population declines are linked to these factors in modified versus native habitats are unknown. We used a common New Zealand skink species, Oligosoma maccanni (McCann?s skink), found in grazed native and exotic grassland to test whether differences in environmental or maternal characteristics influenced birth date, pregnancy success and offspring phenotype. In both grassland types the date of birth was c. 8 days earlier at lower altitudes (altitudinal range = 564?719 m a.s.l), and small females were less likely to have successful pregnancies. However, larger females had more weak or deformed offspring, suggesting that reproductive senescence may exist in this species. While other research shows that exotic grasslands do not support as many skinks as native tussock grassland, reproductive success of pregnant skinks (viable litter size) was not affected by habitat modification. However, neonates had greater body condition (mass for length) when from females with higher post-partum body condition, and these females were from the native tussock grasslands. In conjunction with previously published data on McCann?s skink, our data suggest that reduced offspring quality may contribute to the lower population numbers in the exotic habitats.