How fitness consequences of early-life conditions vary with age in a long-lived seabird: A Bayesian multivariate analysis of age-specific reproductive values

Evolutionary theory suggests that individuals can benefit from deferring the fitness cost of developing under poor conditions to later in life. Although empirical evidence for delayed fitness costs of poor developmental conditions is abundant, individuals that die prematurely have not often been incorporated when estimating fitness, such that age-specific fitness costs, and therefore the relative importance of delayed fitness costs are actually unknown. We developed a Bayesian statistical framework to estimate age-specific reproductive values in relation to developmental conditions. We applied it to data obtained from a long-term longitudinal study of common terns Sterna hirundo, using sibling rank to describe variation in developmental conditions. Common terns have a maximum of three chicks, and later hatching chicks acquire less food, grow more slowly and have a lower fledging probability than their earlier hatched siblings. We estimated fitness costs in adulthood to constitute c. 45% and 70% of the total fitness costs of hatching third and second, respectively, compared to hatching first. This was due to third-ranked hatchlings experiencing especially high pre-fledging mortality, while second-ranked hatchlings had lower reproductive success in adulthood. Both groups had slightly lower adult survival. There was, however, no evidence for sibling rank-specific rates of senescence. We additionally found years with low fledgling production to be associated with particularly strong pre-fledging selection on sibling rank, and with increased adult survival to the next breeding season. This suggests that adults reduce parental allocation to reproduction in poor years, which disproportionately impacts low-ranked offspring. Interpreting these results, we suggest that selection at the level of the individual offspring for delaying fitness costs is counteracted by selection for parental reduction in brood size when resources are limiting.

Competition-induced transgenerational plasticity influences competitive interactions and leaf decomposition of offspring

Phenotypic plasticity, within and across generations (transgenerational plasticity), allows organisms and their progeny to adapt to the environment without modification of the underlying DNA. Recent findings suggest that epigenetic modifications are important mediators of such plasticity. However, empirical studies have, so far, mainly focused on plasticity in response to abiotic factors, overlooking the response to competition. We tested for within-generation and transgenerational phenotypic plasticity triggered by plant-plant competition intensity, and we tested whether it was mediated via DNA methylation, using the perennial, apomictic herb Taraxacum brevicorniculatum in four coordinated experiments. We then tested the consequences of transgenerational plasticity affecting competitive interactions of the offspring and ecosystem processes, such as decomposition. We found that, by promoting differences in DNA methylation, offspring of plants under stronger competition developed faster and presented more resource-conservative phenotypes. Further, these adjustments associated with less degradable leaves, which have the potential to reduce nutrient turnover and might, in turn, favour plants with more conservative traits. Greater parental competition enhanced competitive abilities of the offspring, by triggering adaptive phenotypic plasticity, and decreased offspring leaf decomposability. Our results suggest that competition-induced transgenerational effects could promote rapid adaptations and species coexistence and feed back on biodiversity assembly and nutrient cycling.

Do the ages of parents or helpers affect offspring fitness in a cooperatively breeding bird?

Age-related changes in parental phenotypes or genotypes can impact offspring fitness, but separating germline from nongermline transgenerational effects of ageing is difficult for wild populations. Further, in cooperatively breeding species, in addition to parental ages, the age of 'helpers' attending offspring may also affect juvenile performance. Using a 30-year study of a cooperative breeder with very high rates of extra-pair paternity, the superb fairy-wren (Malurus cyaneus), we investigated the effects of maternal, paternal and helper ages on three measures of offspring performance: nestling weight, juvenile survival to independence and recruitment to the breeding population. Mothers with a longer lifespan had offspring with higher juvenile survival, indicating selective disappearance, but the effect of maternal age on juvenile survival was of similar magnitude but negative. For extra-pair offspring, there was no evidence of any effect of the ages of either the genetic sire or the cuckolded 'social' father. However, for within-pair offspring, there was a positive effect of paternal age on juvenile survival, which we suggest may be driven by sexual selection. There were positive associations between the average age of helpers attending a nest and two of the three aspects of offspring performance; these effects were stronger than any of the effects of parental age. In general, the multiple associations between offspring fitness and the ages of adults around them appeared to be driven more by age-related changes in environmental effects than by age-related changes in the germline.

Decoupling the effects of food and density on life-history plasticity of wild animals using field experiments: Insights from the steward who sits in the shadow of its tail, the North American red squirrel

Long-term studies of wild animals provide the opportunity to investigate how phenotypic plasticity is used to cope with environmental fluctuations and how the relationships between phenotypes and fitness can be dependent upon the ecological context. Many previous studies have only investigated life-history plasticity in response to changes in temperature, yet wild animals often experience multiple environmental fluctuations simultaneously. This requires field experiments to decouple which ecological factor induces plasticity in fitness-relevant traits to better understand their population-level responses to those environmental fluctuations. For the past 32 years, we have conducted a long-term integrative study of individually marked North American red squirrels Tamiasciurus hudsonicus Erxleben in the Yukon, Canada. We have used multi-year field experiments to examine the physiological and life-history responses of individual red squirrels to fluctuations in food abundance and conspecific density. Our long-term observational study and field experiments show that squirrels can anticipate increases in food availability and density, thereby decoupling the usual pattern where animals respond to, rather than anticipate, an ecological change. As in many other study systems, ecological factors that can induce plasticity (such as food and density) covary. However, our field experiments that manipulate food availability and social cues of density (frequency of territorial vocalizations) indicate that increases in social (acoustic) cues of density in the absence of additional food can induce similar life-history plasticity, as does experimental food supplementation. Changes in the levels of metabolic hormones (glucocorticoids) in response to variation in food and density are one mechanism that seems to induce this adaptive life-history plasticity. Although we have not yet investigated the energetic response of squirrels to elevated density or its association with life-history plasticity, energetics research in red squirrels has overturned several standard pillars of knowledge in physiological ecology. We show how a tractable model species combined with integrative studies can reveal how animals cope with resource fluctuations through life-history plasticity.

The jury is still out regarding the generality of adaptive 'transgenerational' effects

A recent meta-analysis concluded, 'transgenerational effects are widespread, strong and persistent'. We identify biases in the literature search, data and analyses, questioning that conclusion. Re-analyses indicate few studies actually tested transgenerational effects - making it challenging to disentangle condition-transfer from anticipatory parental effects, and providing little insight into the underlying mechanisms.

Measuring the Costs of Limb Regeneration and Their Transgenerational Consequences in Two Nearctic Lady Beetles (Coleoptera: Coccinellidae)

We examined the ability of Coleomegilla maculata DeGeer and Hippodamia convergens Guerin-Meneville to regenerate, during pupation, a foreleg amputated in the fourth instar. Leg regeneration was complete for 80.7% of amputated H. convergens larvae, with 12.5% regenerating partially, and 6.8% showing no regeneration. Regeneration in C. maculata was 72.2% complete, 20.5% partial, and 7.2% none, but mortality following ablation was slightly higher than for H. convergens (7.4 vs. 0.6%). Ablation/regeneration caused a slight delay in pupation, but pupation time, fresh mass at emergence, and reproductive performance remained unaffected in either species. Reciprocal crosses were made between regenerated and unoperated beetles, and 12 progeny reared from the second clutch of each female in all treatments. Mating treatment affected eclosion time in H. convergens, whereas in C. maculata, larval development and pupation time were also affected. Considering all treatments, larval mortality was higher in H. convergens than in C. maculata, but lower when both H. convergens parents regenerated. Parental mating treatment did not affect adult weight in either species, but development of C. maculata progeny was faster when only the sire regenerated, and slower when the only the dame regenerated, whereas progeny of regenerated sires completed pupated faster than those sired by controls. We infer that genes activated during regeneration have pleiotropic effects with subtle, gender-specific, epigenetic consequences. If these pleiotropic effects are genetically linked to important traits, regenerative genetic elements could be conserved in coccinellids via natural selection acting on these traits, rather than on regenerative ability per se.

Illustrating the importance of meta-analysing variances alongside means in ecology and evolution

Meta-analysis is increasingly used in biology to both quantitatively summarize available evidence for specific questions and generate new hypotheses. Although this powerful tool has mostly been deployed to study mean effects, there is untapped potential to study effects on (trait) variance. Here, we use a recently published data set as a case study to demonstrate how meta-analysis of variance can be used to provide insights into biological processes. This data set included 704 effect sizes from 89 studies, covering 56 animal species, and was originally used to test developmental stress effects on a range of traits. We found that developmental stress not only negatively affects mean trait values, but also increases trait variance, mostly in reproduction, showcasing how meta-analysis of variance can reveal previously overlooked effects. Furthermore, we show how meta-analysis of variance can be used as a tool to help meta-analysts make informed methodological decisions, even when the primary focus is on mean effects. We provide all data and comprehensive R scripts with detailed explanations to make it easier for researchers to conduct this type of analysis. We encourage meta-analysts in all disciplines to move beyond the world of means and start unravelling secrets of the world of variance.

The Nidobiome: A Framework for Understanding Microbiome Assembly in Neonates

The importance of microbial associations to animals' development, physiology, and fitness is widely recognized. In most animals, these microbial associations must be developed anew with every generation, making microbiome assembly a critical ecological and evolutionary process. To fully understand neonate microbial colonization, we need to study the interacting effects of neonate, parents, nest, and external environment. We propose an integrative approach based on the concept of the 'nidobiome', a new unit of microbiome-host interactions, which brings together these key elements. We discuss the contribution of each element on microbial colonization at different stages of host development, and we provide a framework based on key developmental events to compare microbiome assembly across animal species.

Environmental enrichment induces intergenerational behavioural and epigenetic effects on fish

Parental effects influence offspring phenotypes through pre- and post-natal routes but little is known about their molecular basis, and therefore their adaptive significance. Epigenetic modifications, which control gene expression without changes in the DNA sequence and are influenced by the environment, may contribute to parental effects. We investigated the effects of environmental enrichment on the behaviour, metabolic rate and brain DNA methylation patterns of parents and offspring of the highly inbreed mangrove killifish (Kryptolebias marmoratus). Parental fish reared in enriched environments had lower cortisol levels, lower metabolic rates and were more active and neophobic than those reared in barren environments. They also differed in 1,854 methylated cytosines (DMCs). Offspring activity and neophobia were determined by the parental environment. Among the DMCs of the parents, 98 followed the same methylation patterns in the offspring, three of which were significantly influenced by parental environments irrespective of their own rearing environment. Our results suggest that parental environment influences the behaviour and, to some extent, the brain DNA methylation patterns of the offspring.

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 effects of diet remain relatively underexplored. Using a 3 × 3 × 2 factorial experiment, we evaluated how N enrichment in parental diets of Neolema abbreviata (Larcordaire) (Coleoptera: Chrysomelidae), a biological control agent for Tradescantia fluminensis Vell. (Commelinaceae), may influence life history and performance of F₁ 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 × 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 effects of parental diet nor its interaction with test diet as was the case in the larval stage. However, the main effects 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 of the same generation among an insect species with both actively feeding larval and adult life stages. These transgenerational effects, or lack thereof, may have implications on the field performance of N. abbrevita under heterogeneous nutritional landscapes.

Relish as a Candidate Marker for Transgenerational Immune Priming in a Dampwood Termite (Blattodae: Archeotermopsidae)

Natural selection should favor the transfer of immune competence from one generation to the next in a context-dependent manner. Transgenerational immune priming (TGIP) is expected to evolve when species exploit pathogen-rich environments and exhibit extended overlap of parent-offspring generations. Dampwood termites are hemimetabolous, eusocial insects (Blattodea: Archeotermopsidae) that possess both of these traits. We predict that offspring of pathogen-exposed queens of Zootermopsis angusticollis will show evidence of a primed immune system relative to the offspring of unexposed controls. We found that Relish transcripts, one of two immune marker loci tested, were enhanced in two-day-old embryos when laid by Serratia-injected queens. These data implicate the immune deficiency (IMD) signaling pathway in TGIP. Although an independent antibacterial assay revealed that embryos do express antibacterial properties, these do not vary as a function of parental treatment. Taken together, Z. angusticollis shows transcriptional but not translational evidence for TGIP. This apparent incongruence between the transcriptional and antimicrobial response from termites suggests that effectors are either absent in two-day-old embryos or their activity is too subtle to detect with our antibacterial assay. In total, we provide the first suggestive evidence of transgenerational immune priming in a termite.

Transgenerational effects of parental light environment on progeny competitive performance and lifetime fitness

Plant and animal parents may respond to environmental conditions such as resource stress by altering traits of their offspring via heritable non-genetic effects. While such transgenerational plasticity can result in progeny phenotypes that are functionally pre-adapted to the inducing environment, it is unclear whether such parental effects measurably enhance the adult competitive success and lifetime reproductive output of progeny, and whether they may also adversely affect fitness if offspring encounter contrasting conditions. In glasshouse experiments with inbred genotypes of the annual plant Polygonum persicaria, we tested the effects of parental shade versus sun on (a) competitive performance of progeny in shade, and (b) lifetime reproductive fitness of progeny in three contrasting treatments. Shaded parents produced offspring with increased fitness in shade despite competition, as well as greater competitive impact on plant neighbours. Inherited effects of parental light conditions also significantly altered lifetime fitness: parental shade increased reproductive output for progeny in neighbour and understorey shade, but decreased fitness for progeny in sunny, dry conditions. Along with these substantial adaptive and maladaptive transgenerational effects, results show complex interactions between genotypes, parent environment and progeny conditions that underscore the role of environmental variability and change in shaping future adaptive potential. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Transgenerational Plasticity in Human-Altered Environments

Our ability to predict how species will respond to human-induced rapid environmental change (HIREC) may depend upon our understanding of transgenerational plasticity (TGP), which occurs when environments experienced by previous generations influence phenotypes of subsequent generations. TGP evolved to help organisms cope with environmental stressors when parental environments are highly predictive of offspring environments. HIREC can alter conditions that favored TGP in historical environments by reducing parents' ability to detect environmental conditions, disrupting previous correlations between parental and offspring environments, and interfering with the transmission of parental cues to offspring. Because of the propensity to produce errors in these processes, TGP will likely generate negative fitness outcomes in response to HIREC, though beneficial fitness outcomes may occur in some cases.

Spider mite mothers adjust reproduction and sons' alternative reproductive tactics to immigrating alien conspecifics

Maternal effects on environmentally induced alternative reproductive tactics (ARTs) are poorly understood but likely to be selected for if mothers can reliably predict offspring environments. We assessed maternal effects in two populations (Y and G) of herbivorous arrhenotokous spider mites Tetranychus urticae, where males conditionally express fighting and sneaking tactics in male-male combat and pre-copulatory guarding behaviour. We hypothesized that resident mothers should adjust their reproduction and sons' ARTs to immigrating alien conspecifics in dependence of alien conspecifics posing a fitness threat or advantage. To induce maternal effects, females were exposed to own or alien socio-environments and mated to own or alien males. Across maternal and sons' reproductive traits, the maternal socio-environment induced stronger effects than the maternal mate, and G-mothers responded more strongly to Y-influence than vice versa. G-socio-environments and Y-mates enhanced maternal egg production in both populations. Maternal exposure to G-socio-environments demoted, yet maternal Y-mates promoted, guarding occurrence and timing by sons. Sneakers guarded earlier than fighters in Y-environments, whereas the opposite happened in G-environments. The endosymbiont Cardinium, present in G, did not exert any classical effect but may have played a role via the shared plant. Our study highlights interpopulation variation in immediate and anticipatory maternal responses to immigrants.

Parent and offspring genotypes influence gene expression in early life

Parents can have profound effects on offspring fitness. Little, however, is known about the mechanisms through which parental genetic variation influences offspring physiology in natural systems. White-throated sparrows (Zonotrichia albicollis, WTSP) exist in two genetic morphs, tan and white, controlled by a large polymorphic supergene. Morphs mate disassortatively, resulting in two pair types: tan male × white female (T × W) pairs, which provide biparental care and white male × tan female (W × T) pairs, which provide female-biased care. To investigate how parental composition impacts offspring, we performed RNA-seq on whole blood of WTSP nestlings sampled from nests of both pair types. Parental pair type had a large effect on nestling gene expression, with 881 genes differentially expressed (DE) and seven correlated gene coexpression modules. The DE genes and modules expressed at higher levels in W × T nests with female-biased parental care function in metabolism and stress-related pathways resulting from the overrepresentation of proteolysis and stress-response genes (e.g., SOD2, NR3C1). These results show that parental genotypes and/or associated behaviours influence nestling physiology, and highlight avenues of further research investigating the ultimate implications for the maintenance of this polymorphism. Nestlings also exhibited morph-specific gene expression, with 92 differentially expressed genes, comprising immunity genes and genes encompassed by the supergene. Remarkably, we identified the same regulatory hub genes in these blood-derived expression networks as were previously identified in adult WTSP brains (EPM2A, BPNT1, TAF5L). These hub genes were located within the supergene, highlighting the importance of this gene complex in structuring regulatory networks across diverse tissues.

An Integrative Framework for Understanding the Mechanisms and Multigenerational Consequences of Transgenerational Plasticity

Transgenerational plasticity (TGP) occurs when the environment experienced by a parent influences the development of their offspring. In this article, we develop a framework for understanding the mechanisms and multi-generational consequences of TGP. First, we conceptualize the mechanisms of TGP in the context of communication between parents (senders) and offspring (receivers) by dissecting the steps between an environmental cue received by a parent and its resulting effects on the phenotype of one or more future generations. Breaking down the problem in this way highlights the diversity of mechanisms likely to be involved in the process. Second, we review the literature on multigenerational effects and find that the documented patterns across generations are diverse. We categorize different multigenerational patterns and explore the proximate and ultimate mechanisms that can generate them. Throughout, we highlight opportunities for future work in this dynamic and integrative area of study.

Limited Support for Thyroid Hormone or Corticosterone Related Gene Expression as a Proximate Mechanism of Incubation Temperature-Dependent Phenotypes in Birds

The conditions that animals experience during early development can have profound consequences for health and fitness. In birds, one of the most important aspects of development is egg incubation temperature. A small decrease in average temperature leads to various impacts on offspring phenotype, such as smaller body sizes, slower growth rates, and less efficient metabolic activity. Little is known, however, about the proximate mechanisms underlying these incubation temperature-induced phenotypic changes. Two important hormones which could play a proximate role are thyroid hormone and corticosterone, which mobilize stored energy reserves and coordinate the normal growth of tissues, particularly in the brain. Previous research shows that circulating blood concentrations of both hormones are influenced by incubation temperature, but the mechanism by which incubation temperature may lead to these changes is unknown. We hypothesized that incubation temperature induces changes in thyroid hormone and corticosterone regulation, leading to changes in expression of hormone-sensitive genes in the brain. To test this, we incubated wood duck (Aix sponsa) eggs at three different temperatures within the natural range (35.0, 35.8, and 37.0°C). We measured mRNA expression of thyroid hormone-related neuroendocrine endpoints (deiodinase 2/3, thyroid hormone receptor α/β, neural regeneration related protein, and Krueppel-like factor 9) in newly hatched ducklings and corticosterone-related neuroendocrine endpoints (mineralocorticoid receptor, glucocorticoid receptor, cholecystokinin, and brain-derived neurotrophic factor) in 15 day-old ducklings using qPCR on brain tissue from the hippocampus and hypothalamus. Contrary to our predictions, we found that mRNA expression of thyroid hormone-related endpoints in both brain areas were largely unaffected by incubation temperature, although there was a trend for an inverse relationship between mRNA expression and incubation temperature for several genes in the hypothalamus. We also found that mineralocorticoid receptor mRNA expression in the hypothalamus was lower in ducklings incubated at the low relative to the high temperatures. This study is the first to evaluate the effects of incubation temperature on mRNA expression of neuroendocrine endpoints in the developing avian brain and suggests that these particular endpoints may be largely resistant to changes in incubation temperature. Thus, further research into the proximate mechanisms for incubation temperature-induced developmental plasticity is needed.

Water influences how seed production responds to conspecific and heterospecific pollen

PREMISE

Outcrossing species depend on pollen from conspecific individuals that may not be exposed to the same abiotic conditions as maternal plants. Additionally, many flowers receive heterospecific pollen, which can also influence seed production. Studies aimed to understand how abiotic conditions influence seed production tend to focus on maternal conditions and leave unexplored the effect of abiotic conditions experienced by pollen donors. We tested how water availability to pollen donors, both conspecific and heterospecific, influenced the seed production of recipient plants exposed to different water availability regimes.

METHODS

In a greenhouse setting we manipulated the water availability (low- or high-water treatment) to potted recipient plants (Phacelia parryi), to conspecific pollen donors, and to heterospecific pollen donors (Brassica nigra). We hand pollinated recipient plants with different pollen mixes that represented all combinations of conspecific pollen mixed with heterospecific pollen. From these hand pollinations we determined the amount of pollen that was transferred, pollen volume, pollen shape, and seed production.

RESULTS

Higher water availability to conspecific pollen donors led to higher seed production. Under low water availability to heterospecific pollen donors, seed production was unaffected by recipient or conspecific pollen donor treatment. Under high water availability to heterospecific pollen donors, seed production was highest when conspecific pollen donors and pollen recipients also received the high-water treatment.

CONCLUSIONS

Environmental conditions of pollen donors can influence the seed production of maternal plants. These results illustrate potential impacts of environmental heterogeneity on post-pollination events that lead to seed production and thus impact a pollinator's contribution to plant fitness.

Revisiting mechanisms and functions of prenatal hormone-mediated maternal effects using avian species as a model

Maternal effects can adaptively modulate offspring developmental trajectories in variable but predictable environments. Hormone synthesis is sensitive to environmental factors, and maternal hormones are thus a powerful mechanism to transfer environmental cues to the next generation. Birds have become a key model for the study of hormone-mediated maternal effects because the embryo develops outside the mother's body, facilitating the measurement and manipulation of prenatal hormone exposure. At the same time, birds are excellent models for the integration of both proximate and ultimate approaches, which is key to a better understanding of the evolution of hormone-mediated maternal effects. Over the past two decades, a surge of studies on hormone-mediated maternal effects has revealed an increasing number of discrepancies. In this review, we discuss the role of the environment, genetic factors and social interactions in causing these discrepancies and provide a framework to resolve them. We also explore the largely neglected role of the embryo in modulating the maternal signal, as well as costs and benefits of hormone transfer and expression for the different family members. We conclude by highlighting fruitful avenues for future research that have opened up thanks to new theoretical insights and technical advances in the field. This article is part of the theme issue 'Developing differences: early-life effects and evolutionary medicine'.

Experimentally reduced insulin/IGF-1 signaling in adulthood extends lifespan of parents and improves Darwinian fitness of their offspring

Classical theory maintains that ageing evolves via energy trade-offs between reproduction and survival leading to accumulation of unrepaired cellular damage with age. In contrast, the emerging new theory postulates that ageing evolves because of deleterious late-life hyper-function of reproduction-promoting genes leading to excessive biosynthesis in late-life. The hyper-function theory uniquely predicts that optimizing nutrient-sensing molecular signaling in adulthood can simultaneously postpone ageing and increase Darwinian fitness. Here, we show that reducing evolutionarily conserved insulin/IGF-1 nutrient-sensing signaling via daf-2 RNA interference (RNAi) fulfils this prediction in Caenorhabditis elegans nematodes. Long-lived daf-2 RNAi parents showed normal fecundity as self-fertilizing hermaphrodites and improved late-life reproduction when mated to males. Remarkably, the offspring of daf-2 RNAi parents had higher Darwinian fitness across three different genotypes. Thus, reduced nutrient-sensing signaling in adulthood improves both parental longevity and offspring fitness supporting the emerging view that suboptimal gene expression in late-life lies at the heart of ageing.

Diel CO2 cycles and parental effects have similar benefits to growth of a coral reef fish under ocean acidification

Parental effects have been shown to buffer the negative effects of within-generation exposure to ocean acidification (OA) conditions on the offspring of shallow water marine organisms. However, it remains unknown if parental effects will be impacted by the presence of diel CO2 cycles that are prevalent in many shallow water marine habitats. Here, we examined the effects that parental exposure to stable elevated (1000 µatm) and diel-cycling elevated (1000 ± 300 µatm) CO2 had on the survival and growth of juvenile coral reef anemonefish, Amphiprion melanopus. Juvenile survival was unaffected by within-generation exposure to either elevated CO2 treatment but was significantly increased (8%) by parental exposure to diel-cycling elevated CO2. Within-generation exposure to stable elevated CO2 caused a significant reduction in juvenile growth (10.7-18.5%); however, there was no effect of elevated CO2 on growth when diel CO2 cycles were present. Parental exposure to stable elevated CO2 also ameliorated the negative effects of elevated CO2 on juvenile growth, and parental exposure to diel CO2 cycles did not alter the effects of diel CO2 cycles on juveniles. Our results demonstrate that within-generation exposure to diel-cycling elevated CO2 and parental exposure to stable elevated CO2 had similar outcomes on juvenile condition. This study illustrates the importance of considering natural CO2 cycles when predicting the long-term impacts of OA on marine ecosystems.

Parental habituation to human disturbance over time reduces fear of humans in coyote offspring

A fundamental tenet of maternal effects assumes that maternal variance over time should have discordant consequences for offspring traits across litters. Yet, seldom are parents observed across multiple reproductive bouts, with few studies considering anthropogenic disturbances as an ecological driver of maternal effects. We observed captive coyote (Canis latrans) pairs over two successive litters to determine whether among‐litter differences in behavior (i.e., risk‐taking) and hormones (i.e., cortisol and testosterone) corresponded with parental plasticity in habituation. Thus, we explicitly test the hypothesis that accumulating experiences of anthropogenic disturbance reduces parental fear across reproductive bouts, which should have disparate phenotypic consequences for first‐ and second‐litter offspring. To quantify risk‐taking behavior, we used foraging assays from 5–15 weeks of age with a human observer present as a proxy for human disturbance. At 5, 10, and 15 weeks of age, we collected shaved hair to quantify pup hormone levels. We then used a quantitative genetic approach to estimate heritability, repeatability, and between‐trait correlations. We found that parents were riskier (i.e., foraged more frequently) with their second versus first litters, supporting our prediction that parents become increasingly habituated over time. Second‐litter pups were also less risk‐averse than their first‐litter siblings. Heritability for all traits did not differ from zero (0.001–0.018); however, we found moderate support for repeatability in all observed traits (r = 0.085–0.421). Lastly, we found evidence of positive phenotypic and cohort correlations among pup traits, implying that cohort identity (i.e., common environment) contributes to the development of phenotypic syndromes in coyote pups. Our results suggest that parental habituation may be an ecological cue for offspring to reduce their fear response, thus emphasizing the role of parental plasticity in shaping their pups’ behavioral and hormonal responses toward humans.

Parental effect of diapause in relation to photoperiod and temperature in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Increasing evidence has demonstrated that the environmental conditions experienced by parents can shape offspring phenotypes. Here, we examined the effects of the photoperiod and temperature experienced by parents on the incidence of diapause in their progeny in the cabbage beetle, Colaphellus bowringi, using three experiments. The first experiment examined parental diapause incidence under different photoperiods at 25°C and the incidence of diapause in progeny from both non-diapausing and diapausing parents under the same rearing conditions. The results revealed that the incidence of diapause among progeny was exactly opposite to that of their parents, i.e., higher parental diapause incidence led to lower progeny diapause incidence, showing a negative relationship in diapause incidence between the parental generation and the progeny generation. The incidence of diapause among progeny produced by diapausing parents was higher than that in progeny produced by non-diapausing parents. The second experiment examined parental diapause incidence at different temperatures under LD 12:12 and the incidence of diapause in progeny from both non-diapausing and diapausing parents under the same rearing conditions. Similarly, the incidence of diapause in progeny was also opposite to that of their parents. However, the incidence of diapause in progeny produced by non-diapausing parents was different from that in progeny produced by diapausing parents. In the third experiment, naturally diapausing adults were maintained at a constant temperature of 9, 28°C or the mean daily summer temperature of 27.84°C under continuous darkness for 3 months of dormancy. After dormancy, the progeny of these post-diapause parents were reared under different photoperiods at 25°C. The results showed that the incidence of diapause among progeny was higher when their parents experienced high temperatures than when they experienced low temperatures. All results demonstrate that the photoperiod and temperature experienced by parents may significantly affect the diapause incidence among progeny.

Timing of maternal exposure to toxic cyanobacteria and offspring fitness in Daphnia magna: Implications for the evolution of anticipatory maternal effects

Organisms that regularly encounter stressful environments are expected to use cues to develop an appropriate phenotype. Water fleas (Daphnia spp.) are exposed to toxic cyanobacteria during seasonal algal blooms, which reduce growth and reproductive investment. Because generation time is typically shorter than the exposure to cyanobacteria, maternal effects provide information about the local conditions subsequent generations will experience. Here, we evaluate if maternal effects in response to microcystin, a toxin produced by cyanobacteria, represent an inheritance system evolved to transmit information in Daphnia magna. We exposed mothers as juveniles and/or as adults, and tested the offspring's fitness in toxic and non-toxic environments. Maternal exposure until reproduction reduced offspring fitness, both in the presence and in the absence of toxic cyanobacteria. However, this effect was accompanied by a small positive fitness effect, relative to offspring from unexposed mothers, in the presence of toxic cyanobacteria. This effect was mainly elicited in response to maternal exposure to toxic cyanobacteria early in life and less so during reproduction. None of these effects were explained by changes in egg size. A meta-analysis using our and others' experiments suggests that the adaptive value of maternal effects to cyanobacteria exposure is weak at best. We suggest that the beneficial maternal effect in our study is an example of phenotypic accommodation spanning generations, rather than a mechanism evolved to transmit information about cyanobacteria presence between generations.