Cohort effects in red squirrels: the influence of density, food abundance and temperature on future survival and reproductive success

1. Environmental conditions experienced early in life may have long-lasting effects on individual performance, thereby creating 'silver-spoon effects'. 2. We used 15 years of data from a North American red squirrel (Tamiasciurus hudsonicus Erxleben) population to investigate influences of food availability, density and spring temperature experienced early in life on reproduction and survival of female squirrels during adulthood. 3. We found that spring temperature and food availability did not affect female survival after 1 year of age, whereas higher squirrel densities led to lower survival, thereby affecting longevity and lifetime fitness. 4. In addition, both food availability experienced between birth and weaning, and spring temperature in the year of birth, had long-lasting positive effects on female reproductive success. These results emphasize the critical effect environmental conditions during the early life stages can have on the lifetime performance of small mammals. 5. These long-term effects of early food and temperature were apparent only once we controlled for conditions experienced during adulthood. This suggests that silver-spoon effects can be masked when conditions experienced early in life are correlated to some environmental conditions experienced later in life. 6. The general importance of silver-spoon effects for adult demographic performance might therefore be underestimated, and taking adult environment into account appears to be necessary when studying long-term cohort effects.     

Lifespan, lifetime reproductive performance and paternity loss of within-pair and extra-pair offspring in the coal tit Periparus ater

The hypothesis that females of socially monogamous species obtain indirect benefits (good or compatible genes) from extra-pair mating behaviour has received enormous attention but much less generally accepted support. Here we ask whether selection for adult survival and fecundity or sexual selection contribute to indirect selection of the extra-pair mating behaviour in socially monogamous coal tits (Periparus ater). We tracked locally recruited individuals with known paternity status through their lives predicting that the extra-pair offspring (EPO) would outperform the within-pair offspring (WPO). No differences between the WPO and EPO recruits were detected in lifespan or age of first reproduction. However, the male WPO had a higher lifetime number of broods and higher lifetime number of social offspring compared with male EPO recruits, while no such differences were evident for female recruits. Male EPO recruits did not compensate for their lower social reproductive success by higher fertilization success within their social pair bonds. Thus, our results do not support the idea that enhanced adult survival, fecundity or within-pair fertilization success are manifestations of the genetic benefits of extra-pair matings. But we emphasize that a crucial fitness component, the extra-pair fertilization success of male recruits, has yet     

Offspring diet supersedes the transgenerational effects of parental diet in a specialist herbivore Neolema abbreviata under manipulated foliar nitrogen variability

Diet quality influences organismal fitness within and across generations.For herbivorous insects,the transgenerational effecets of diet remain relatively underexplored.Usinga3×3×2 factorial experiment,we evaluated how N enrichment in parental diets of Neolemd abbreviata(Larcordaire)(C oleoptera:Chrysomelidae),a biological control agent for Tradescantia fluminensis Vell.(Commelinaceae),may influence life history and performance of Fi and F2 offspring under reciprocal experiments.We found limited transgenerational effects of foliar nitrogen variability among life-history traits in both larvae and adults.Larval weight gain and mortality were responsive to parental diet contrary to feeding damage,pupal weight and duration taken to pupate.There were significant parental diet x test interactions in larval feeding damage,weight gain,pupal weight and time to pupation.Generally,offspring from parents under high N plants performed better even under low N test plants.Adult traits including oviposition selection,feeding weight and longevity did not respond to the efects of parental diet nor its interaction with test diet as was the case in the larval stage.However,the main efects of test diet were more important in determining adult performance in both generations suggesting limited sensitivity to parental diet in the adult stage.Our results show conflicting responses to parental diet between larvae and adults ofthe same generation among an insec species with both actively feeding larual and adult life stagee These tranegeneratinonal efferte,or lack thereof,may have implications on the field performance of N.abbrevita under heterogencous nutritional landscapes.     

The effects of larval nutrition on reproductive performance in a food-limited adult environment

It is often assumed that larval food stress reduces lifetime fitness regardless of the conditions subsequently faced by adults. However, according to the environment-matching hypothesis, a plastic developmental response to poor nutrition results in an adult phenotype that is better adapted to restricted food conditions than one having developed in high food conditions. Such a strategy might evolve when current conditions are a reliable predictor of future conditions. To test this hypothesis, we assessed the effects of larval food conditions (low, improving and high food) on reproductive fitness in both low and high food adults environments. Contrary to this hypothesis, we found no evidence that food restriction in larval ladybird beetles produced adults that were better suited to continuing food stress. In fact, reproductive rate was invariably lower in females that were reared at low food, regardless of whether adults were well fed or food stressed. Juveniles that encountered improving conditions during the larval stage compensated for delayed growth by accelerating subsequent growth, and thus showed no evidence of a reduced reproductive rate. However, these same individuals lost more mass during the period of starvation in adults, which indicates that accelerated growth results in an increased risk of starvation during subsequent periods of food stress.     

Development time mediates the effect of larval diet on ageing and mating success of male antler flies in the wild

High-quality developmental environments often improve individual performance into adulthood, but allocating toward early life traits, such as growth, development rate and reproduction, may lead to trade-offs with late-life performance. It is, therefore, uncertain how a rich developmental environment will affect the ageing process (senescence), particularly in wild insects. To investigate the effects of early life environmental quality on insect life-history traits, including senescence, we reared larval antler flies (Protopiophila litigata) on four diets of varying nutrient concentration, then recorded survival and mating success of adult males released in the wild. Declining diet quality was associated with slower development, but had no effect on other life-history traits once development time was accounted for. Fast-developing males were larger and lived longer, but experienced more rapid senescence in survival and lower average mating rate compared to slow developers. Ultimately, larval diet, development time and body size did not predict lifetime mating success. Thus, a rich environment led to a mixture of apparent benefits and costs, mediated by development time. Our results indicate that ‘silver spoon'' effects can be complex and that development time mediates the response of adult life-history traits to early life environmental quality.     

Thermal and nutritional environments during development exert different effects on adult reproductive success in Drosophila melanogaster

Environments experienced during development have long‐lasting consequences for adult performance and fitness. The “environmental matching” hypothesis predicts that individuals perform best when adult and developmental environments match whereas the “silver spoon” hypothesis expects that fitness is higher in individuals developed under favorable environments regardless of adult environments. Temperature and nutrition are the two most influential determinants of environmental quality, but it remains to be elucidated which of these hypotheses better explains the long‐term effects of thermal and nutritional histories on adult fitness traits. Here we compared how the temperature and nutrition of larval environment would affect adult survivorship and reproductive success in the fruit fly, Drosophila melanogaster. The aspect of nutrition focused on in this study was the dietary protein‐to‐carbohydrate (P:C) ratio. The impact of low developmental and adult temperature was to improve adult survivorship. High P:C diet had a negative effect on adult survivorship when ingested during the adult stage, but had a positive effect when ingested during development. No matter whether adult and developmental environments matched or not, females raised in warm and protein‐enriched environments produced more eggs than those raised in cool and protein‐limiting environments, suggesting the presence of a significant silver spoon effect of larval temperature and nutrition. The effect of larval temperature on adult egg production was weak but persisted across the early adult stage whereas that of larval nutrition was initially strong but diminished rapidly after day 5 posteclosion. Egg production after day 5 was strongly influenced by the P:C ratio of the adult diet, indicating that the diet contributing mainly to reproduction had shifted from larval to adult diet. Our results highlight the importance of thermal and nutritional histories in shaping organismal performance and fitness and also demonstrate how the silver spoon effects of these aspects of environmental histories differ fundamentally in their nature, strength, and persistence.     

Male age, dominance, and mating success among rhesus macaques

Some previous primate studies have found a positive correlation between male dominance and mating success when data from subadult males were included in the analyses. The information in this paper suggests that an unconscious bias may have been introduced when data on subadult males were included because of the lower dominance rank of these animals. Data from a study of rhesus monkeys on Cayo Santiago showed that subadult males mated significantly less than adults. Because these monkeys are not fully mature, data on them should not be used in any test for correlation between adult male dominance and mating success. The only significant correlation found for adult male mating success was an inverse one with relation to age. Based on behavioral data young, fully adult males have the best chance of fathering offspring regardless of their dominance rank.     

取食重金属铜对棕尾别麻蝇亲代及子代生长发育与繁殖的影响

为了评估取食含重金属铜饲料对棕尾别麻蝇Boettcherisca peregrine亲代及子代的生长发育与繁殖的影响,在室内给棕尾别麻蝇初产幼虫饲喂含不同浓度（200, 400,800和1 600 µg/g）Cu²⁺的饲料直至化蛹,并对亲代和子代的生长发育和繁殖有关指标进行了观察和分析。结果表明：低浓度的Cu²⁺（200 µg/g）对其体重和体长起促进作用,但对幼虫历期、化蛹率、蛹历期、羽化率、性比、交配率和产仔量无显著作用;较高浓度的Cu²⁺ 则有抑制作用,且Cu²⁺处理浓度越高,亲代幼虫、蛹和雌雄成虫的体重越轻,幼虫和蛹的体长越短,化蛹率、羽化率、交配率和产仔量越低,幼虫历期和蛹期越长,成虫寿命越短。但Cu²⁺处理对成虫性比则无显著的影响。相比之下,经Cu²⁺处理后雌虫所产的子代若不再经Cu²⁺处理,其子代生存、生长发育与繁殖则基本不受影响,说明Cu²⁺对亲代的影响不能遗传至子代。此外,还探讨了该蝇亲代与子代体内Cu²⁺含量在其变态过程中的变化。     

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. II. Variance in male mating success and effective population size

Variance in reproductive success is a primary determinant of genetically effective population size (Ne), and thus has important implications for the role of genetic drift in the evolutionary dynamics of animal taxa characterized by polygynous mating systems. Here we report the results of a study designed to test the hypothesis that polygynous mating results in significantly reduced Ne in an age-structured population. This hypothesis was tested in a natural population of a harem-forming fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The influence of the mating system on the ratio of variance Ne to adult census number (N) was assessed using a mathematical model designed for age-structured populations that incorporated demographic and genetic data. Male mating success was assessed by means of direct and indirect paternity analysis using 10-locus microsatellite genotypes of adults and progeny from two consecutive breeding periods (n = 431 individually marked bats). Combined results from both analyses were used to infer the effective number of male parents in each breeding period. The relative proportion of successfully reproducing males and the size distribution of paternal sibships comprising each offspring cohort revealed an extremely high within-season variance in male mating success (up to 9.2 times higher than Poisson expectation). The resultant estimate of Ne/N for the C. sphinx study population was 0.42. As a result of polygynous mating, the predicted rate of drift (1/2Ne per generation) was 17.6% higher than expected from a Poisson distribution of male mating success. However, the estimated Ne/N was well within the 0.25-0.75 range expected for age-structured populations under normal demographic conditions. The life-history schedule of C. sphinx is characterized by a disproportionately short sexual maturation period scaled to adult life span. Consequently, the influence of polygynous mating on Ne/N is mitigated by the extensive overlap of generations. In C. sphinx, turnover of breeding males between seasons ensures a broader sampling of the adult male gamete pool than expected from the variance in mating success within a single breeding period.     

Influence of environmental variability on breeding effort in a long-lived seabird, the yellow-nosed albatross

The provisioning parameters, breeding success, adult mass, andsurvival of yellow-nosed albatrosses were studied over 7 successiveyears at Amsterdam Island, southern Indian Ocean. We examinedthe ability of this long-lived seabird to adjust its breedingeffort under different environmental conditions and the fitnessconsequences in terms of survival and quality of offspring produced. Provisioning rate and adult mass varied extensivelybetween years, and the lowest and highest values were associatedwith sea surface temperature anomalies. When waters aroundthe island were colder, adults were in good condition and broughtlarge meals at short intervals, whereas warmer waters resultedin lower provisioning rates, lower adult mass, and lighter chicksat fledging. Adult survival and fledging success were not affectedby sea surface temperature anomalies. Yellow-nosed albatrossesappear to be unable to adjust their breeding effort every season,and their differential breeding investment probably primarilyreflects different levels of food availability. Yellow-nosedalbatrosses are able to regulate their provisioning behavior according to the nutritional status of their chick only whenconditions are favorable. Birds appear to invest primarilyin their own future maintenance rather than in provisioning.They have a wide safety margin in body mass that limits mortalityrisks during good years as well as during poor years. However,during unfavorable seasons adults continue to provision chicksthat have a poor prospect of survival to breeding, withoutadditional survival costs for the parents. Favorable seasonstherefore have a high value in terms of fitness because ofthe high quality of the chick produced. We suggest that understandinghow long-lived animals optimize their provisioning behaviorand lifetime reproduction can only be achieved through studiesencompassing several contrasted seasons.     

Reproductive resilience to food shortage in a small heterothermic primate

The massive energetic costs entailed by reproduction in most mammalian females may increase the vulnerability of reproductive success to food shortage. Unexpected events of unfavorable climatic conditions are expected to rise in frequency and intensity as climate changes. The extent to which physiological flexibility allows organisms to maintain reproductive output constant despite energetic bottlenecks has been poorly investigated. In mammals, reproductive resilience is predicted to be maximal during early stages of reproduction, due to the moderate energetic costs of ovulation and gestation relative to lactation. We experimentally tested the consequences of chronic-moderate and short-acute food shortages on the reproductive output of a small seasonally breeding primate, the grey mouse lemur (Microcebus murinus) under thermo-neutral conditions. These two food treatments were respectively designed to simulate the energetic constraints imposed by a lean year (40% caloric restriction over eight months) or by a sudden, severe climatic event occurring shortly before reproduction (80% caloric restriction over a month). Grey mouse lemurs evolved under the harsh, unpredictable climate of the dry forest of Madagascar and should thus display great potential for physiological adjustments to energetic bottlenecks. We assessed the resilience of the early stages of reproduction (mating success, fertility, and gestation) to these contrasted food treatments, and on the later stages (lactation and offspring growth) in response to the chronic food shortage only. Food deprived mouse lemurs managed to maintain constant most reproductive parameters, including oestrus timing, estrogenization level at oestrus, mating success, litter size, and litter mass as well as their overall number of surviving offspring at weaning. However, offspring growth was delayed in food restricted mothers. These results suggest that heterothermic, fattening-prone mammals display important reproductive resilience to energetic bottlenecks. More generally, species living in variable and unpredictable habitats may have evolved a flexible reproductive physiology that helps buffer environmental fluctuations.     

The influence of juvenile and adult environments on life-history trajectories

There is increasing evidence that the environment experienced early in life can strongly influence adult life histories. It is largely unknown, however, how past and present conditions influence suites of life-history traits regarding major life-history trade-offs. Especially in animals with indeterminate growth, we may expect that environmental conditions of juveniles and adults independently or interactively influence the life-history trade-off between growth and reproduction after maturation. Juvenile growth conditions may initiate a feedback loop determining adult allocation patterns, triggered by size-dependent mortality risk. I tested this possibility in a long-term growth experiment with mouthbrooding cichlids. Females were raised either on a high-food or low-food diet. After maturation half of them were switched to the opposite treatment, while the other half remained unchanged. Adult growth was determined by current resource availability, but key reproductive traits like reproductive rate and offspring size were only influenced by juvenile growth conditions, irrespective of the ration received as adults. Moreover, the allocation of resources to growth versus reproduction and to offspring number versus size were shaped by juvenile rather than adult ecology. These results indicate that early individual history must be considered when analysing causes of life-history variation in natural populations.     

Maternal Investment in the Swordtail Fish Xiphophorus multilineatus: Support for the Differential Allocation Hypothesis

The differential allocation hypothesis predicts that reproductive investment will be influenced by mate attractiveness, given a cost to reproduction and a tradeoff between current and future reproduction. We tested the differential allocation hypothesis in the swordtail fish Xiphophorus multilineatus, where males have genetically influenced (patroclinous inheritance) alternative mating tactics (ARTs) maintained by a tradeoff between being more attractive to females (mature later as larger courting males) and a higher probability of reaching sexual maturity (mature earlier as smaller sneaker males). Males in X. multilineatus do not provide parental care or other resources to the offspring. Allelic variation and copy number of the Mc4R gene on the Y-chromosome influences the size differences between males, however there is no variation in this gene on the X-chromosome. Therefore, to determine if mothers invested more in offspring of the larger courter males, we examined age to sexual maturity for daughters. We confirmed a tradeoff between number of offspring and female offspring’s age to sexual maturity, corroborating that there is a cost to reproduction. In addition, the ART of their fathers significantly influenced the age at which daughters reached sexual maturity, suggesting increased maternal investment to daughters of courter males. The differential allocation we detected was influenced by how long the wild-caught mother had been in the laboratory, as there was a brood order by father genotype (ART) interaction. These results suggest that females can adjust their reproductive investment strategy, and that differential allocation is context specific. We hypothesize that one of two aspects of laboratory conditions produced this shift: increased female condition due to higher quality diet, and/or assessment of future mating opportunities due to isolation from males.     

Evolutionary pathways in shorebird breeding systems: sexual conflict, parental care, and chick development

Sexual selection, mating opportunities, and parental behavior are interrelated, although the specific nature of these relationships is controversial. Two major hypotheses have been suggested. The parental investment hypothesis states that the relative parental investment of the sexes drives the operation of sexual selection. Thus, the sex that invests less in offspring care competes more intensely and monopolizes access to mates. The sexual conflict hypothesis proposes that sexual selection (the competition among both males and females for mates), mating opportunities, and parental behavior are interrelated and predicts a feedback loop between mating systems and parental care. Here we test both hypotheses using a comprehensive dataset of shorebirds, a maximum-likelihood statistical technique, and a recent supertree of extant shorebirds and allies. Shorebirds are an excellent group for these analyses because they display unique variation in parental care and social mating system. First, we show that chick development constrains the evolution of both parental care and mate competition, because transitions toward more precocial offspring preceded transitions toward reduced parental care and social polygamy. Second, changes in care and mating systems respond to one another, most likely because both influenced and are influenced by mating opportunities. Taken together, our results are more consistent with the sexual conflict hypothesis than the parental investment hypothesis.     

亲本体色及环境因子对长绿飞虱成虫体色、寿命与繁殖的影响

【目的】明确亲本体色和环境因素对长绿飞虱Saccharosydne procerus F1代成虫体色的影响及不同体色成虫个体在不同环境中产卵量、交配率、成虫寿命的变化。【方法】长绿飞虱不同体色(黑化与非黑化)亲本所产若虫在室内经不同温度(30℃和22℃)和光周期(20L∶4D和16L∶8D)组合处理,观察成虫黑化率;将不同体色的成虫同样经历这些温度和光周期组合处理,记录成虫寿命、产卵量和交配率变化,分析不同因素对其的贡献率。【结果】长绿飞虱不同体色亲本所产若虫在实验室内经过上述温度和光周期组合处理后,成虫黑化率变化范围为18.6%~60.8%。若虫期高温、长光照以及黑化亲本均显著增加子代中黑化个体的比例。低温短光照条件下非黑化个体寿命显著长于黑化个体,高温长光照则相反;黑化个体交配率与产卵量随着温度和光照时间的下降而下降,非黑化个体的交配率与产卵量则主要受到光周期影响。统计分析表明,在几种因子中,温度对长绿飞虱的交配率变化贡献率最高,为39.1%;光周期对长绿飞虱体色及产卵量变化贡献率最高,分别达到42.5%和47.4%。体色与温度交互作用对长绿飞虱雌、雄成虫寿命的贡献率最高,分别可达50.3%和60.6%。【结论】本研究表明,若虫期光周期对长绿飞虱成虫体色变化影响最显著,且该虫体色变化在一定程度上改变了其成虫生物学特性,提高了该虫对环境的适应性。     

Links between parental life histories of wild salmon and the telomere lengths of their offspring

The importance of parental contributions to offspring development and subsequent performance is self‐evident at a genomic level; however, parents can also affect offspring fitness by indirect genetic and environmental routes. The life history strategy that an individual adopts will be influenced by both genes and environment; and this may have important consequences for offspring. Recent research has linked telomere dynamics (i.e., telomere length and loss) in early life to future viability and longevity. Moreover, a number of studies have reported a heritable component to telomere length across a range of vertebrates, although the effects of other parental contribution pathways have been far less studied. Using wild Atlantic salmon with different parental life histories in an experimental split‐brood in vitro fertilization mating design and rearing the resulting families under standardized conditions, we show that there can be significant links between parental life history and offspring telomere length (studied at the embryo and fry stage). Maternal life history traits, in particular egg size, were most strongly related to offspring telomere length at the embryonic stage, but then became weaker through development. In contrast, paternal life history traits, such as the father's growth rate in early life, had a greater association in the later stages of offspring development. However, offspring telomere length was not significantly related to either maternal or paternal age at reproduction, nor to paternal sperm telomere length. This study demonstrates both the complexity and the importance of parental factors that can influence telomere length in early life.     

Environmental cues influence parental brood structure decisions in the burying beetle <Emphasis Type="Italic">Nicrophorus marginatus</Emphasis>

Parents evaluate multiple extrinsic and intrinsic cues when making decisions associated with reproduction. These decisions often reflect classic trade-offs between the cost of a strategy and its perceived fitness payoff. Life history theory predicts that when parents experience austere conditions, reproductive success is increased by producing fewer but larger offspring with a competitive advantage in this environment. Conversely, parents experiencing favorable conditions are expected to increase current reproductive success by favoring quantity over quality of offspring. We tested the predictions of life history theory using Nicrophorus marginatus (Coleoptera: Silphidae), a burying beetle species that exhibits infanticide during biparental care and hypervariable adult size across populations, by employing a factorial design that manipulated density and nutritional quality of food. We measured (1) the average number of offspring produced, (2) the average individual size of offspring, and (3) the sex ratio of the offspring. We found no effect of density or food quality on offspring sex ratio, but mean offspring size and number differed between low and high-density treatments. Nutritional environment interacted with density effects such that parents with access to high quality diets were able to modulate offspring size and number to match the perceived competitive environment, whereas those in poor nutritional condition appeared to exhibit physiological constraints to producing optimal brood structures.     

Maternal effects are long‐lasting and influence female offspring's reproductive strategy in the swordtail fish Xiphophorus multilineatus

The adaptive benefits of maternal investment into individual offspring (inherited environmental effects) will be shaped by selection on mothers as well as their offspring, often across variable environments. We examined how a mother's nutritional environment interacted with her offspring's nutritional and social environment in Xiphophorus multilineatus, a live‐bearing fish. Fry from mothers reared on two different nutritional diets (HQ = high quality and LQ = low quality) were all reared on a LQ diet in addition to being split between two social treatments: exposed to a large adult male during development and not exposed. Mothers raised on a HQ diet produce offspring that were not only initially larger (at 14 days of age), but grew faster, and were larger at sexual maturity. Male offspring from mothers raised on both diets responded to the exposure to courter males by growing faster; however, the response of their sisters varied with mother's diet; females from HQ diet mothers reduced growth if exposed to a courter male, whereas females from LQ diet mothers increased growth. Therefore, we detected variation in maternal investment depending on female size and diet, and the effects of this variation on offspring were long‐lasting and sex specific. Our results support the maternal stress hypothesis, with selection on mothers to reduce investment in low‐quality environments. In addition, the interaction we detected between the mother's nutritional environment and the female offspring's social environment suggests that female offspring adopted different reproductive strategies depending on maternal investment.     

COMPLEX INTERACTIONS BETWEEN PATERNAL AND MATERNAL EFFECTS: PARENTAL EXPERIENCE AND AGE AT REPRODUCTION AFFECT FECUNDITY AND OFFSPRING PERFORMANCE IN A BUTTERFLY

Parental effects can greatly affect offspring performance and are thus expected to impact population dynamics and evolutionary trajectories. Most studies have focused on maternal effects, whereas fathers are also likely to influence offspring phenotype, for instance when males transfer nutrients to females during mating. Moreover, although the separate effects of maternal age and the environment have been documented as a source of parental effects in many species, their combined effects have not been investigated. In the present study, we analyzed the combined effects of maternal and paternal age at reproduction and a mobility treatment in stressful conditions on offspring performance in the butterfly Pieris brassicae. Both paternal and maternal effects affected progeny traits but always via interactions between age and mobility treatment. Moreover, parental effects shifted from male effects expressed at the larval stage to maternal effects at the adult stage. Indeed, egg survival until adult emergence significantly decreased with father age at mating only for fathers having experienced the mobility treatment, whereas offspring adult life span decreased with increasing mother age at laying only for females that did not experience the mobility treatment. Overall, our results demonstrate that both parents’ phenotypes influence offspring performance through nongenetic effects, their relative contribution varying over the course of progeny's life.