Exposure to exogenous egg cortisol does not rescue juvenile Chinook salmon body size,condition, or survival from the effects of elevated water temperatures

Climate change is leading to altered temperature regimes which are impacting aquatic life, particularly for ectothermic fish. The impacts of environmental stress can be translated across generations through maternally derived glucocorticoids, leading to altered offspring phenotypes. Although these maternal stress effects are often considered negative, recent studies suggest this maternal stress signal may prepare offspring for a similarly stressful environment (environmental match). We applied the environmental match hypothesis to examine whether a prenatal stress signal can dampen the effects of elevated water temperatures on body size, condition, and survival during early development in Chinook salmon Oncorhynchus tshawytscha from Lake Ontario, Canada. We exposed fertilized eggs to prenatal exogenous egg cortisol (1,000 ng/ml cortisol or 0 ng/ml control) and then reared these dosed groups at temperatures indicative of current (+0°C) and future (+3°C) temperature conditions. Offspring reared in elevated temperatures were smaller and had a lower survival at the hatchling developmental stage. Overall, we found that our exogenous cortisol dose did not dampen effects of elevated rearing temperatures (environmental match) on body size or early survival. Instead, our eyed stage survival indicates that our prenatal cortisol dose may be detrimental, as cortisol‐dosed offspring raised in elevated temperatures had lower survival than cortisol‐dosed and control reared in current temperatures. Our results suggest that a maternal stress signal may not be able to ameliorate the effects of thermal stress during early development. However, we highlight the importance of interpreting the fitness impacts of maternal stress within an environmentally relevant context.     

Countergradient vs. cogradient variation in growth and diapause in a lichen‐feeding moth,Eilema depressum (Lepidoptera: Arctiidae)

Separating genetic and environmental causes of the latitudinal differences among populations is crucial when evaluating the potential for microevolutionary responses to the changing environment. We studied among‐population and environmental components of variation in several life‐history traits of a lichen‐feeding moth Eilema depressum when offspring of replicate Swiss and Finnish females were reared in a common‐garden factorial experiment. A partial second generation was produced only among Swiss larvae, more likely so at higher temperature regime and higher host quality, and more frequently among the offspring of particular females. Growth rates of larvae that chose the diapause development were higher in northern individuals. Our results thus reveal adaptive differences between latitudinal populations in studied life‐history traits, allowing to expect rapid adaptation of the species to further environmental changes. In contrast, invariable responses of the growth rates of the larvae to temperature and host quality support the idea that some basic parameters of insect growth show a high degree of evolutionary conservatism.     

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.     

The effect of prey availability on offspring survival depends on maternal food resources

Maternal nutrition can strongly influence embryo development and offspring fitness. The environmental matching hypothesis posits that developmental conditions affect offspring in ways that enable them to appropriately deal with similar post‐developmental conditions, although mismatches between developmental and post‐developmental environments will reduce fitness. To test this hypothesis, reproductive lizards (Anolis sagrei) were reared in environments with high versus low prey availability. The resultant offspring were then reared reciprocally under the same two prey conditions that their mothers experienced. High levels of prey available to mothers increased egg production, although the survival of eggs was low compared to those produced by mothers in the low‐prey treatment. Low prey availability to offspring reduced growth, regardless of the amount of prey available to their mothers. Low prey availability also compromised offspring survival, although this negative effect was only present when mothers experienced high‐prey conditions, whereas matching of low‐prey conditions in maternal and offspring stages resulted in high survival. However, because the mismatch of low maternal and high offspring prey availability resulted in similar offspring survival to the matched treatments, our results do not fully support the environmental matching hypothesis. Nevertheless, the present study highlights the interactive role of maternal and post‐hatching environments in generating variation in offspring fitness. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 437–447.     

When and how can <Emphasis Type="Italic">Daphnia</Emphasis> prepare their offspring for the threat of predation?

The life history of Daphnia exposed to fish kairomone at different developmental stages was examined in a laboratory experiment. The strongest life history response to the applied predation threat was observed in females exposed during the 4th instar. Compared to Daphnia experiencing the presence of fish at earlier or later instars, these individuals reached maturity at a smaller size and released fewer neonates. Moreover, their offspring also demonstrated the strongest reaction to predation threat, exhibiting the broadest phenotypic plasticity in the life history response to predation. The breadth of their reaction norm was, on average, two times larger comparing with individuals from other treatments. Broader phenotypic plasticity may offer clear selective advantages under the unpredictable predation regime. This finding highlights the adaptive role of maternal effect in shaping life history of cladocerans.     

Maternal warming affects early life stages of an invasive thistle

Maternal environment can influence plant offspring performance. Understanding maternal environmental effects will help to bridge a key gap in the knowledge of plant life cycles, and provide important insights for species’ responses under climate change. Here we show that maternal warming significantly affected the early life stages of an invasive thistle, Carduus nutans. Seeds produced by plants grown in warmed conditions had higher germination percentages and shorter mean germination times than those produced by plants under ambient conditions; this difference was most evident at suboptimal germination temperatures. Subsequent seedling emergence was also faster with maternal warming, with no cost to seedling emergence percentage and seedling growth. Our results suggest that maternal warming may accelerate the life cycle of this species via enhanced early life‐history stages. These maternal effects on offspring performance, together with the positive responses of the maternal generation, may exacerbate invasions of this species under climate change.     

Transgenerational effects of nutrition are different for sons and daughters

Food shortage is an important selective factor shaping animal life‐history trajectories. Yet, despite its role, many aspects of the interaction between parental and offspring food environments remain unclear. In this study, we measured developmental plasticity in response to food availability over two generations and tested the relative contribution of paternal and maternal food availability to the performance of offspring reared under matched and mismatched food environments. We applied a cross‐generational split‐brood design using the springtail Orchesella cincta, which is found in the litter layer of temperate forests. The results show adverse effects of food limitation on several life‐history traits and reproductive performance of both parental sexes. Food conditions of both parents contributed to the offspring phenotypic variation, providing evidence for transgenerational effects of diet. Parental diet influenced sons’ age at maturity and daughters’ weight at maturity. Specifically, being born to food‐restricted parents allowed offspring to alleviate the adverse effects of food limitation, without reducing their performance under well‐fed conditions. Thus, parents raised on a poor diet primed their offspring for a more efficient resource use. However, a mismatch between maternal and offspring food environments generated sex‐specific adverse effects: female offspring born to well‐fed mothers showed a decreased flexibility to deal with low‐food conditions. Notably, these maternal effects of food availability were not observed in the sons. Finally, we found that the relationship between age and size at maturity differed between males and females and showed that offspring life‐history strategies in O. cincta are primed differently by the parents.     

Maternal Effects of Photoperiod and Food Level on Life History Characteristics of the Cladoceran Daphnia Pulicaria Forbes

The response of various life-history characteristics of Daphnia pulicaria to photoperiod and food concentration was measured in 16 combinations of maternal and offspring environments (long vs. short day, high vs. low food) in flow-through experiments. Response variables in offspring were time and survival to release of first offspring, clutch size and neonate mass in the first brood, mass of adult females after 30days and somatic growth rate during the course of the experiment. Most of these parameters were directly controlled by food concentration in the offspring environment, but maternal effects frequently modified the response. A long day length in the maternal environment resulted in a prolongation of the time to first clutch release in offspring similar to the direct effect of low food. Likewise, survival to maturation and female mass were affected by maternal photoperiod. Somatic growth rate and clutch size responded to combined effects of maternal food conditions and photoperiod. The laboratory results were used to predict the seasonal change of fecundity of Daphnia in the field. When data on clutch size are ordered in a sequence as the different combinations of maternal and offspring environment occur during the seasonal succession in a temperate lake, they show a bimodal distribution with a high peak in spring and a lower peak in fall. This pattern is consistent with field observations. We conclude that photoperiod and maternal effects are important factors influencing life history and population dynamics of Daphnia.     

Bigger is better: changes in body size explain a maternal effect of food on offspring disease resistance

Maternal effects triggered by changes in the environment (e.g., nutrition or crowding) can influence the outcome of offspring–parasite interactions, with fitness consequences for the host and parasite. Outside of the classic example of antibody transfer in vertebrates, proximate mechanisms have been little studied, and thus, the adaptive significance of maternal effects on infection is not well resolved. We sought to determine why food‐stressed mothers give birth to offspring that show a low rate of infection when the crustacean Daphnia magna is exposed to an orally infective bacterial pathogen. These more‐resistant offspring are also larger at birth and feed at a lower rate. Thus, reduced disease resistance could result from slow‐feeding offspring ingesting fewer bacterial spores or because their larger size allows for greater immune investment. To distinguish between these theories, we performed an experiment in which we measured body size, feeding rate, and susceptibility, and were able to show that body size is the primary mechanism causing altered susceptibility: Larger Daphnia were less likely to become infected. Contrary to our predictions, there was also a trend that fast‐feeding Daphnia were less likely to become infected. Thus, our results explain how a maternal environmental effect can alter offspring disease resistance (though body size), and highlight the potential complexity of relationship between feeding rate and susceptibility in a host that encounters a parasite whilst feeding.     

Early life of fathers affects offspring fitness in a wild rodent

Intergenerational fitness effects on offspring due to the early life of the parent are well studied from the standpoint of the maternal environment, but intergenerational effects owing to the paternal early life environment are often overlooked. Nonetheless, recent laboratory studies in mammals and ecologically relevant studies in invertebrates predict that paternal effects can have a major impact on the offspring's phenotype. These nongenetic, environment‐dependent paternal effects provide a mechanism for fathers to transmit environmental information to their offspring and could allow rapid adaptation. We used the bank vole Myodes glareolus, a wild rodent species with no paternal care, to test the hypothesis that a high population density environment in the early life of fathers can affect traits associated with offspring fitness. We show that the protein content in the diet and/or social environment experienced during the father's early life (prenatal and weaning) influence the phenotype and survival of his offspring and may indicate adaptation to density‐dependent costs. Furthermore, we show that experiencing multiple environmental factors during the paternal early life can lead to a different outcome on the offspring phenotype than stimulated by experience of a single environmental factor, highlighting the need to study developmental experiences in tandem rather than independent of each other.     

Environmental and genetic effects shape the development of personality traits in the mangrove killifish Kryptolebias marmoratus

Consistent individual differences in behaviour are well documented, for example, individuals can be defined as consistently bold or consistently shy. To date our understanding of the mechanisms underpinning consistent individual differences in behaviour (also termed behavioural types (BTs)) remains limited. Theoretical work suggests life‐history tradeoffs drive BT variation, however, empirical support is scarce. Moreover, whilst life‐history is known to be phenotypically plastic in response to environmental conditions during ontogeny, the extent to which such plasticity drives plasticity in behavioural traits and personality remains poorly understood. Using a natural clonal vertebrate, Kryptolebias marmoratus, we control for genetic variation and investigate developmental plasticity in life‐history and three commonly studied behavioural traits (exploration, boldness, aggression) in response to three ecologically relevant environments; conspecific presence, low food and perceived risk. Simulated predation risk was the only treatment that generated repeatable behaviour i.e. personality during ontogeny. Treatments differed in their effects on mean life‐history and behavioural scores. Specifically, low food fish exhibited reduced growth rate and exploration but did not differ from control fish in their boldness or aggression scores. Conspecific presence resulted in a strong negative effect on mean aggression, boldness and exploration during ontogeny but had minimal effect on life‐history traits. Simulated predation risk resulted in increased reproductive output but had minimal effect upon average behavioural scores. Together these results suggest that life‐history plasticity/variation may be insufficient in driving variation in personality during development. Finally, using offspring derived from each rearing environment we investigate maternal effects and find strong maternal influence upon offspring size, but not behaviour. These results highlight and support the current understanding that risk perception is important in shaping personality, and that social experience during ontogeny is a major influence upon behavioural expression.     

Effects of experimental warming on survival,phenology, and morphology of an aquatic insect (Odonata)

1. Organisms can respond to changing climatic conditions in multiple ways including changes in phenology, body size or morphology, and range shifts. Understanding how developmental temperatures affect insect life‐history timing and morphology is crucial because body size and morphology affect multiple aspects of life history, including dispersal ability, whereas phenology can shape population performance and community interactions. 2. It was experimentally assessed how developmental temperatures experienced by aquatic larvae affected survival, phenology, and adult morphology of dragonflies [Pachydiplax longipennis (Burmeister)]. Larvae were reared under three environmental temperatures: ambient, +2.5, and +5 °C, corresponding to temperature projections for our study area 50 and 100 years in the future, respectively. Experimental temperature treatments tracked naturally‐occurring variation. 3. Clear effects of temperature were found in the rearing environment on survival and phenology: dragonflies reared at the highest temperatures had the lowest survival rates and emerged from the larval stage approximately 3 weeks earlier than animals reared at ambient temperatures. There was no effect of rearing temperature on overall body size. Although neither the relative wing nor thorax size was affected by warming, a non‐significant trend towards an interaction between sex and warming in relative thorax size suggests that males may be more sensitive to warming than females, a pattern that should be investigated further. 4. Warming strongly affected survival in the larval stage and the phenology of adult emergence. Understanding how warming in the developmental environment affects later life‐history stages is critical to interpreting the consequences of warming for organismal performance.     

Predators can influence the host‐parasite dynamics of their prey via nonconsumptive effects

Ecological communities are partly structured by indirect interactions, where one species can indirectly affect another by altering its interactions with a third species. In the absence of direct predation, nonconsumptive effects of predators on prey have important implications for subsequent community interactions. To better understand these interactions, we used a Daphnia‐parasite‐predator cue system to evaluate if predation risk affects Daphnia responses to a parasite. We investigated the effects of predator cues on two aspects of host–parasite interactions (susceptibility to infection and infection intensity), and whether or not these effects differed between sexes. Our results show that changes in response to predator cues caused an increase in the prevalence and intensity of parasite infections in female predator‐exposed Daphnia. Importantly, the magnitude of infection risk depended on how long Daphnia were exposed to the cues. Additionally, heavily infected Daphnia that were constantly exposed to cues produced relatively more offspring. While males were ~5× less likely to become infected compared to females, we were unable to detect effects of predator cues on male Daphnia–parasite interactions. In sum, predators, prey, and their parasites can form complex subnetworks in food webs, necessitating a nuanced understanding of how nonconsumptive effects may mediate these interactions.     

Maternal care of heterozygous dopamine receptor D4 knockout mice: Differential susceptibility to early‐life rearing conditions

The differential susceptibility hypothesis proposes that individuals who are more susceptible to the negative effects of adverse rearing conditions may also benefit more from enriched environments. Evidence derived from human experiments suggests the lower efficacy dopamine receptor D4 (DRD4) 7‐repeat as a main factor in exhibiting these for better and for worse characteristics. However, human studies lack the genetic and environmental control offered by animal experiments, complicating assessment of causal relations. To study differential susceptibility in an animal model, we exposed Drd4^+/? mice and control litter mates to a limited nesting/bedding (LN), standard nesting (SN) or communal nesting (CN) rearing environment from postnatal day (P) 2‐14. Puberty onset was examined from P24 to P36 and adult females were assessed on maternal care towards their own offspring. In both males and females, LN reared mice showed a delay in puberty onset that was partly mediated by a reduction in body weight at weaning, irrespective of Drd4 genotype. During adulthood, LN reared females exhibited characteristics of poor maternal care, whereas dams reared in CN environments showed lower rates of unpredictability towards their own offspring. Differential susceptibility was observed only for licking/grooming levels of female offspring towards their litter; LN reared Drd4^+/? mice exhibited the lowest and CN reared Drd4^+/? mice the highest levels of licking/grooming. These results indicate that both genetic and early‐environmental factors play an important role in shaping maternal care of the offspring for better and for worse.     

Evolutionary history of Daphnia drives divergence in grazing selectivity and alters temporal community dynamics of producers

Consumers with different seasonal life histories encounter different communities of producers during specific seasonal phases. If consumers evolve to prefer the producers that they encounter, then consumers may reciprocally influence the temporal composition of producer communities. Here, we study the keystone consumer Daphnia ambigua, whose seasonal life history has diverged due to intraspecific predator divergence across lakes of New England. We ask whether grazing preferences of Daphnia have diverged also and test whether any grazing differences influence temporal composition patterns of producers. We reared clonal populations of Daphnia from natural populations representing the two diverged life history types for multiple generations. We conducted short‐term (24 hr) and long‐term (27 days) grazing experiments in equal polycultures consisting of three diatom and two green algae species, treated with no consumer, Daphnia from lakes with anadromous alewife, or from lakes with landlocked alewife. After 24 hr, life history and grazing preference divergence in Daphnia ambigua drove significant differences in producer composition. However, those differences disappeared at the end of the 27‐day experiment. Our results illustrate that, despite potentially more complex long‐term dynamics, a multitrophic cascade of evolutionary divergence from a predator can influence temporal community dynamics at the producer level.     

Cross‐generational effects of temperature on flight performance,and associated life‐history traits in an insect

Nongenetic parental effects may affect offspring phenotype, and in species with multiple generations per year, these effects may cause life‐history traits to vary over the season. We investigated the effects of parental, offspring developmental and offspring adult temperatures on a suite of life‐history traits in the globally invasive agricultural pest Grapholita molesta. A low parental temperature resulted in female offspring that developed faster at low developmental temperature compared with females whose parents were reared at high temperature. Furthermore, females whose parents were reared at low temperature were heavier and more fecund and had better flight abilities than females whose parents were reared at high temperature. In addition to these cross‐generational effects, females developed at low temperature had similar flight abilities at low and high ambient temperatures, whereas females developed at high temperature had poorer flight abilities at low than at high ambient temperature. Our findings demonstrate a pronounced benefit of low parental temperature on offspring performance, as well as between‐ and within‐generation effects of acclimation to low temperature. In cooler environments, the offspring generation is expected to develop more rapidly than the parental generation and to comprise more fecund and more dispersive females. By producing phenotypes that are adaptive to the conditions inducing them as well as heritable, cross‐generational plasticity can influence the evolutionary trajectory of populations. The potential for short‐term acclimation to low temperature may allow expanding insect populations to better cope with novel environments and may help to explain the spread and establishment of invasive species.     

Offspring size–number tradeoffs and food quality feedbacks impact population dynamics in a Daphnia–algae system

Population fluctuations can be affected by both extrinsic (e.g. weather patterns, food availability) and intrinsic (e.g. life‐history) factors. A key life‐history tradeoff is the production of offspring size versus number, ranging from many small offspring to few large offspring. Models show that this life‐history tradeoff in offspring size and number, through maturation time, can have significant impacts on population dynamics. However, few manipulative experiments have been conducted that can isolate life‐history effects from impacts of extrinsic factors in consumer–resource systems. We experimentally tested the effect of an offspring size–number tradeoff on population stability and food availability in a consumer–resource system. Using Daphnia pulex, we created a shift from many, small offspring being produced to fewer, larger offspring. Two sets of experiments were performed to examine the interaction of an extrinsic factor (light levels) and intrinsic population structure on dynamics, and we controlled for the ingestion pressure on algal prey at the time of the manipulation. We predicted that the tradeoff would impact internal consumer population characteristics, including biasing the stage structure towards adults, increasing adult size, and increasing average population‐level reproduction. This adult‐dominated stage structure was predicted to then lead to instability and a low quantity–high quality food state. Under all light levels, the manipulated populations became dominated by large adults. Contrary to predictions, the amplitudes of fluctuations in Daphnia biomass were lower in populations shifted to few–large offspring, representing higher stability in these populations. Furthermore, in high light conditions, a stable low Daphnia – high algae biomass (low food quality) state was observed in few–large offspring treatments but not in control (many–small offspring) treatments. Our results show a strong link between light levels as an extrinsic factor and the life‐history tradeoff of consumer offspring size versus number that impacts consumer–resource population dynamics through feedbacks with resource quality.     

Depth selection and life history strategies as mutually exclusive responses to risk of fish predation in <Emphasis Type="Italic">Daphnia</Emphasis>

We tested if pelagic crustaceans of the genus Daphnia use different anti-predator defences in environmental conditions that do or do not offer deep refuge from planktivorous fish. We kept Daphnia catawba in two series of 9-m deep enclosures with and without caged cyprinid fish Phoxinus eos. In one series of enclosures, Daphnia could select its depth of residence and hide in deep dark water layers to avoid anticipated fish predation, while in another series of enclosures, a plankton net barrier fixed at 2-m depth forced them to stay in subsurface zone exposed to fish kairomones. We compared depth residence and migratory behaviour strategies with life history strategies (body size and size at first reproduction, diapause induction) in Daphnia exposed or not to fish kairomones with or without deep refuge. In deep enclosures with fish, Daphnia spent daytime hours in deep dark layers while at night, they resided closer to the water surface. Yet, no change in life history parameters of migrating individuals was observed compared to the fish-free conditions. In enclosures with fish, where the net barrier forced Daphnia to reside in subsurface zone, they produced smaller offspring, matured at smaller size and achieved lower maximum body length compared to the fish-free conditions. However, they did not produce diapausing eggs. Our experimental study supports the hypothesis that diel vertical migration behaviour with daytime residence in deep, dark water are the preferred antipredator strategy chosen by Daphnia facing anticipated fish predation over life history changes such as reduced size and low growth rate which are used when dark deep refuge is not present or accessible.     

Transgenerational plasticity in the eye size of Daphnia

It is well established that environmental signals can induce phenotypic responses that persist for multiple generations. The induction of such ‘transgenerational plasticity’ (TGP) depends upon the ability of organisms to accurately receive and process information from environmental signals. Thus, sensory systems are likely intertwined with TGP. Here we tested the link between an environmental stressor and transgenerational responses in a component of the sensory system (eye size) that is linked to enhanced vision and ecologically relevant behaviours. We reared 45 clones of Daphnia pulicaria in the presence and absence of a low-quality resource (cyanobacteria) and evaluated shifts in relative eye size in offspring. Our results revealed divergent shifts in relative eye size within- and across-generations. Parental Daphnia that were fed cyanobacteria produced a smaller eye than Daphnia fed high-quality algae. Such differences were then reversed in the offspring generation; Daphnia whose mothers were fed cyanobacteria produced larger eyes than Daphnia that were continually fed green algae. We discuss the extent to which this maternal effect on eye size is an adaptive response linked to improved foraging.     

Maternal consumption of non‐toxic Microcystis by Daphnia magna induces tolerance to toxic Microcystis in offspring

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