BackgroundWithin-generational plasticity (WGP) and transgenerational plasticity (TGP) are mechanisms allowing rapid adaptive responses to fluctuating environments without genetic change. These forms of plasticity have often been viewed as independent processes. Recent evidence suggests that WGP is altered by the environmental conditions experienced by previous generations (i.e., TGP). In the context of inducible defenses, one of the most studied cases of plasticity, the WGP x TGP interaction has been poorly investigated.ResultsWe provide evidence that TGP can alter the reaction norms of inducible defenses in a freshwater snail. The WGP x TGP interaction patterns are trait-specific and lead to decreased slope of reaction norms (behaviour and shell thickness). Offspring from induced parents showed a higher predator avoidance behaviour and a thicker shell than snails from non-induced parents in no predator-cue environment while they reached similar defenses in predator-cue environment. The WGP x TGP interaction further lead to a switch from a plastic towards a constitutive expression of defenses for shell dimensions (flat reaction norm).ConclusionsWGP-alteration by TGP may shape the adaptive responses to environmental change and then has a substantial importance to understand the evolution of plasticity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0795-9) contains supplementary material, which is available to authorized users.

Almost all animal species are engaged in predator-prey interactions. These interactions, variable in time and space, favor the emergence and evolution of phenotypic plasticity, which allows prey to fine-tune their phenotype to the current risk of predation. A famous example is the induction of defensive neck-teeth, spines or helmets in some water fleas when they detect cues of predator presence. In general, the response may involve different types of traits (behavioral, morphological, physiological, and life-history traits), alone or in combination. The induced traits may be adaptive anti-predator defenses or reflect more general stress-based responses. Recently, it has been found that predator-induced plasticity occurs not only within but also across generations (transgenerational plasticity), i.e., the phenotype of a generation is influenced by the detection of predator-cues in previous generation(s), even if the current generation is not itself exposed to these cues. In this paper, we aim to review this accumulating literature and propose a current state of key aspects of predator-induced transgenerational plasticity in metazoans. In particular, we review whether patterns of predator-induced transgenerational plasticity depend on the type of traits. We analyze the adaptive value of predator-induced transgenerational plasticity and explore the evidence for its evolution and underlying mechanisms. We also consider its temporal dynamics: what are the time windows during which predator-cues must be detected to be transmitted across generations? Are transgenerational responses in offspring stage-dependent? How many generations does transgenerational plasticity persist? Finally, we discuss other factors highlighted in the literature that influence predator-induced transgenerational plasticity: what are the relative contributions of maternal and paternal exposure to predator-cues in generating transgenerational plasticity? Do transgenerational responses depend on offspring sex? Do they scale with the perceived level of predation risk? This review shows that we are only at the beginning of understanding the processes of predatorinduced transgenerational plasticity, and it encourages future research to fill the lack of knowledge highlighted here.

Phenotypic plasticity can occur across generations (transgenerational plasticity) when environments experienced by the previous generations influenced offspring phenotype. The evolutionary importance of transgenerational plasticity, especially regarding within‐generational plasticity, is a currently hot topic in the plasticity framework. How long an environmental effect can persist across generations and whether multigenerational effects are cumulative are primordial—for the evolutionary significance of transgenerational plasticity—but still unresolved questions. In this study, we investigated how the grand‐parental, parental and offspring exposures to predation cues shape the predator‐induced defences of offspring in the Physa acuta snail. We expected that the offspring phenotypes result from a three‐way interaction among grand‐parental, parental and offspring environments. We exposed three generations of snails without and with predator cues according to a full factorial design and measured offspring inducible defences. We found that both grand‐parental and parental exposures to predator cues impacted offspring antipredator defences, but their effects were not cumulative and depended on the defences considered. We also highlighted that the grand‐parental environment did alter reaction norms of offspring shell thickness, demonstrating an interaction between the grand‐parental transgenerational plasticity and the within‐generational plasticity. We concluded that the effects of multigenerational exposure to predator cues resulted on complex offspring phenotypic patterns which are difficult to relate to adaptive antipredator advantages.

While an increasing number of studies highlights that parental environment shapes offspring phenotype (transgenerational plasticity TGP), TGP beyond the parental generation has received less attention.Studies suggest that TGP impacts population dynamics and evolution of phenotype, but these impacts will depend on how long an environmental effect can persist across generations and whether multigenerational effects are cumulative. Here we tested the impact of both grand-parental and parental environments on offspring reaction norm in a prey-predator system. We exposed three generations of Physa acuta snails without and with predator-cues according to a full factorial design and measured offspring inducible defenses. We found that both grand-parental and parental exposure to predator cues impacted offspring anti-predator defenses, but their effects were not cumulative and depended on the defenses considered. We also highlighted that grand-parental environment could alter reaction norm of offspring shell thickness, demonstrating a grand-parental TGP and WGP interaction. We called for more studies covering the combine effects of multigenerational environments.

a b s t r a c tIn this study we estimated the timing of speciation events in a group of angelfishes using 1186 RADseq markers corresponding to 94,880 base pairs. The genus Holacanthus comprises seven species, including two clades of Panama trans-Isthmian geminates, which diverged approximately 3-3.5 Mya. These clades diversified within the Tropical Eastern Pacific (TEP, three species) and Tropical Western Atlantic (TWA, two species) which our data suggest to have occurred within the past 1.5 My in both ocean basins, but may have proceeded via different mechanisms. In the TEP, speciation is likely to have followed a peripatric pathway, while in the TWA, sister species are currently partially sympatric, thus raising the possibility of sympatric speciation. This study highlights the use of RADseq markers for estimating both divergence times and modes of speciation at a 1-3 My timescale.

Estimating population sizes and genetic diversity are key factors to understand and predict population dynamics. Marine species have been a difficult challenge in that respect, due to the difficulty in assessing population sizes and the open nature of such populations. Small, isolated islands with endemic species offer an opportunity to groundtruth population size estimates with empirical data and investigate the genetic consequences of such small populations. Here we focus on two endemic species of reef fish, the Clipperton damselfish, Stegastes baldwini, and the Clipperton angelfish, Holacanthus limbaughi, on Clipperton Atoll, tropical eastern Pacific. Visual surveys, performed over almost two decades and four expeditions, and genetic surveys based on genomic RAD sequences, allowed us to estimate kinship and genetic diversity, as well as to compare population size estimates based on visual surveys with effective population sizes based on genetics. We found that genetic and visual estimates of population numbers were remarkably similar. S. baldwini and H. limbaughi had population sizes of approximately 800,000 and 60,000, respectively. Relatively small population sizes resulted in low genetic diversity and the presence of apparent kinship. This study emphasizes the importance of small isolated islands as models to study population dynamics of marine organisms.

The evolution of parental care opens the door for the evolution of brood parasitic strategies that allow individuals to gain the benefits of parental care without paying the costs. Here we provide the first documentation for alloparental care in coral reef fish and we discuss why these patterns may reflect conspecific and interspecific brood parasitism. Species‐specific barcodes revealed the existence of low levels (3.5% of all offspring) of mixed interspecific broods, mostly juvenile Amblyglyphidodon batunai and Pomacentrus smithi damselfish in Altrichthys broods. A separate analysis of conspecific parentage based on microsatellite markers revealed that mixed parentage broods are common in both species, and the genetic patterns are consistent with two different modes of conspecific brood parasitism, although further studies are required to determine the specific mechanisms responsible for these mixed parentage broods. While many broods had offspring from multiple parasites, in many cases a given brood contained only a single foreign offspring, perhaps a consequence of the movement of lone juveniles between nests. In other cases, broods contained large numbers of putative parasitic offspring from the same parents and we propose that these are more likely to be cases where parasitic adults laid a large number of eggs in the host nest than the result of movements of large numbers of offspring from a single brood after hatching. The evidence that these genetic patterns reflect adaptive brood parasitism, as well as possible costs and benefits of parasitism to hosts and parasites, are discussed.

Transgenerational plasticity, which occurs when the environment experienced by parents changes the phenotype of offspring, is widespread in animal and plant species. Both maternal and paternal environments can underlie transgenerational plasticity, but experimental studies unraveling how their effects interact together and with the personal (both developmental and immediate) environments are still rare. Yet unraveling these interactions is fundamental to understanding how offspring integrate past and present environmental cues to produce adaptive phenotype. Using the hermaphroditic and freshwater snail Physa acuta, we tested how predator cues experienced by offspring, mothers and fathers interact to shape offspring anti-predator behavior. We raised a first generation of snails in the laboratory with or without chemical predator cues and realized full-factorial crosses to disentangle maternal and paternal cues. We then raised the second generation of snails with or without predator cues and assessed, when adults, their escape behavior in two immediate environments (with or without predator cues) and activity in the immediate environment without predator cues. We found that personal, maternal, and paternal predator cues interacted to shape offspring escape behavior and activity. Firstly, for escape behavior, snails integrated the cues from developmental and parental environments only when exposed to predator cues in their immediate environment, suggesting that personal immediate experience must corroborate the risky parental environment to reveal transgenerational plasticity. For activity, this same hypothesis helps explain why no clear pattern of transgenerational plasticity was revealed, as activity was only measured without predator cues in the immediate environment. Secondly, a single maternal exposure to predator cues decreased offspring escape behavior while a single paternal exposure had no effect, surprisingly demonstrating sex-specific transgenerational plasticity for a simultaneous hermaphroditic species. Thirdly, when both mother and father were exposed, paternal cues were integrated by offspring according to their own developmental environment. The paternal exposure then mitigated the reduction in escape behavior due to the maternal exposure only when offspring developed in control condition. Overall, our study highlighted complex patterns of sex-specific transgenerational plasticity resulting from non-additive interactions between parental, developmental and immediate experiences.