Transgenerational effects decrease larval resilience to ocean acidification and warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic

The aim of this study was to investigate the effect of ocean acidification (OA) and warming (OW) as well as the transgenerational effect of OA on larval and juvenile growth and metabolism of a large economically important fish species with a long generation time. Therefore we incubated European sea bass from Brittany (France) for two generations (>5 years in total) under current and predicted OA conditions (PCO2: 650 and 1700 μatm). In the F1 generation both OA condition were crossed with OW (temperature: 15-18 °C and 20-23 °C). We found that OA alone did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine metabolic rate (RMR) and juvenile standard metabolic rate (SMR) were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA on RMR or SMR. Juvenile PO2crit was not affected by OA, OW or OAW in both generations. We discuss the potential underlying mechanisms resulting in beneficial effects of OW on F1 larval growth and RMR and in resilience of F0 and F1 larvae and juveniles to OA, but on the other hand resulting in vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

Competition Between The Tadpoles of Toads Versus Frogs: A Study of Four Japanese Anuran Taxa

Competition within and among species can play a key role in structuring the assemblages of anuran tadpoles. Previous studies have reported that tadpoles of the invasive cane toad (Rhinella marina) are more strongly disadvantaged by the presence of native frog tadpoles than by the same number of conspecific toad tadpoles. That effect might arise from a lack of coevolution of the invasive toad with its competitors; and/or from a generalized superiority of frog tadpoles over toad tadpoles. To clarify those possibilities, we conducted experimental trials using the larvae of a native rather than invasive toad (Bufo japonicus formosus in Japan) exposed to larvae of native anurans (the sympatric frogs Rana japonica and Rana ornativentris and the parapatric toad Bufo japonicus japonicus). In intraspecific competition trials, higher densities of B. j. formosus prolonged the larval period and reduced size at metamorphosis, but did not affect survival. In interspecific competition trials, the effects of the other anuran species on B. j. formosus were similar to the effects of the same number of conspecific larvae. This similarity in impact of interspecific versus intraspecific competition argues against any overall competitive superiority of frog larvae over toad larvae. Instead, the vulnerability of larval cane toads to frog tadpoles may result from a lack of coevolutionary history.

Plasticity and flexibility in the anti-predator responses of treefrog tadpoles

Tadpoles can respond to perceived predation risk by adjusting their life history, morphology, and behavior in an adaptive way. Adaptive phenotypic plasticity can evolve by natural selection only if there is variation in reaction norms and if this variation is, at least in part, heritable. To provide insights into the evolution of adaptive phenotypic plasticity, we analyzed the environmental and parental components of variation in predator-induced life history (age and size at metamorphosis), morphology (tail depth), and behavior of Italian treefrog tadpoles (Hyla intermedia). Using an incomplete factorial design, we raised tadpoles either with or without caged predators (dragonfly larvae, gen. Aeshna) and, successively, we tested them in experimental arenas either with or without caged predators. Results provided strong evidence for an environmental effect on all three sets of characters. Tadpoles raised with caged predators (dragonfly larvae, gen. Aeshna) metamorphosed earlier (but at a similar body size) and developed deeper tails than their fullsib siblings raised without predators. In the experimental arenas, all tadpoles, independent of their experience, flexibly changed their activity and position, depending on whether the cage was empty or contained the predator. Tadpoles of the two experimental groups, however, showed different responses: those raised with predators were always less active than their predator-naive siblings and differences slightly increased in the presence of predators. Besides this strong environmental component of phenotypic variation, results provided evidence also for parental and parental-by-environment effects, which were strong on life-history, but weak on morphology and behavior. Interestingly, additive parental effects were explained mainly by dams. This supports the hypothesis that phenotypic plasticity might mainly depend on maternal effects and that it might be the expression of condition-dependent mechanisms. Significance statement Animals, by plastically adjusting their phenotypes to the local environments, can often sensibly improve their chances of survival, suggesting the hypothesis that phenotypic plasticity evolved by natural selection. We test this hypothesis in the Italian treefrog tadpoles, by investigating the heritable variation in the plastic response to predators (dragonfly larvae). Using an incomplete factorial common-garden experiment, we showed that tadpoles raised with predators metamorphosed earlier (but at similar body size), developed deeper tails, and were less active than their siblings raised without predators. The plastic response varied among families, but variation showed a stronger maternal than paternal component. This suggests that plasticity might largely depend on epigenetic factors and be the expression of condition-dependent mechanisms.

Field variations in mass at metamorphosis in a stream frog, Odorrana splendida, and their relationship with the stream environment

Animals with complex life cycles, such as amphibians, shift their habitats when they metamorphose. Metamorphosing traits (e.g., size at, and timing of, metamorphosis) at an early stage can affect the growth, reproduction, and survival in the adult stage. Thus, metamorphosing traits are important factors that affect the fitness of the individuals. Although size at metamorphosis in the field has been investigated in amphibians, its relationship with environmental factors has been scarce. We aimed to quantify variations in the mass at metamorphosis of a stream frog, Odorrana splendida, among multiple streams, and show the relationship of these variations with environmental conditions. We searched for metamorphs in 11 field streams and measured their body size. We then examined the relationship between environmental conditions of each stream and the mass at metamorphosis to reveal the factors determining the mass. We found 229 metamorphs over three years. The estimated mass at metamorphosis ranged from 0.17 g to 1.44 g, with a coefficient of variation among streams of 0.38. The size at metamorphosis significantly differed among streams, and was found to be positively affected by water temperature and chlorophyll a concentration, and negatively affected by altitude, slope gradient, and the number of adult calls. We showed that O. splendida has a large variation in mass at metamorphosis within and among natural streams. A lower mass at metamorphosis may correlate with scarce food resources in the stream and higher competition during the larval stages, resulting from a higher number of mating adults.

Life-history traits and the first demographic data of Iranian population of the West Asian Lemon-Yellow Tree Frog, Hyla savignyi (Audouin, 1827)

The life-history of an organism consists of its lifetime pattern of growth, development, storage, age, and reproduction. In this study, some life-history traits of Hyla savignyi were studied in populations from different parts of Iran. The microscopic and macroscopic analysis showed that testicular activity in H. savignyi is potentially continuous, reaching its peak level in April. Metamorphosis was completed in approximately 102 days after egg deposition, and body size at metamorphosis was 10 mm. Significant sexual size dimorphism was present in all populations, and a larger female asymptotic body size was observed (43.07 mm for females vs 41.16 mm for males). The adult survival rate (S) and life expectancy (ESP) were the same for both sexes (S = 0.73 and ESP = 4.2 years). Age and body size were positively correlated with each other for both females and males. Maximum longevity was recorded to be six years in both females and males, and ages of sexual maturity were estimated to be two or three years in breeding individuals. The adult sample age ranged from two to six years (mean age of females: 4.40±0.68 years; males: 3.63±0.13 years). Our data confirm the general patterns of body size variation and mean age in anurans and show that females are larger than males and live longer.

Larval development and survival of pond-breeding anurans in an agricultural landscape impacted more by phytoplankton than surrounding habitat

The destruction of freshwater habitat is a major contributor to biodiversity loss in aquatic ecosystems. However, created or restored wetlands could partially mitigate aquatic biodiversity loss by increasing the amount of available habitat across a landscape. We investigated the impact of surrounding terrestrial habitat and water quality variables on suitability for two species of pond-breeding amphibians (bullfrogs [Lithobates catesbeianus] and Blanchard’s cricket frogs [Acris blanchardi]) in created permanent wetlands located on an agricultural landscape. We examined tadpole growth and survival in field enclosures placed in ponds surrounded by agricultural, forested, or grassland habitats. We also evaluated the potential for carryover effects of the aquatic environment on terrestrial growth and overwinter survival of cricket frog metamorphs. We found that habitat adjacent to ponds did not predict tadpole growth or survival. Rather, phytoplankton abundance, which showed high variability among ponds within habitat type, was the only predictor of tadpole growth. Cricket frogs emerged larger and earlier from ponds with higher phytoplankton abundance; bullfrogs were also larger and at a more advanced developmental stage in ponds with higher levels of phytoplankton. Overwinter survival of cricket frogs was explained by size at metamorphosis and there were no apparent carryover effects of land use or pond-of-origin on overwinter growth and survival. Our results demonstrate that created ponds in human-dominated landscapes can provide suitable habitat for some anurans, independent of the adjacent terrestrial habitat.

Nutrient-dependent allometric plasticity in a male-diphenic mite

Male secondary sexual traits often scale allometrically with body size. These allometries can be variable within species, and may shift depending on environmental conditions such as food quality. Such allometric plasticity has been hypothesized to initiate local adaptation and evolutionary diversification of scaling relationships, but is under-recorded, and its eco-evolutionary effects are not well understood. Here, we test for allometric plasticity in the bulb mite (Rhizoglyphus robini) in which large males tend to develop as armed adult fighters with thickened third legs, while small males become adult scramblers without thickened legs. We first examined the ontogenetic timing for size- and growth-dependent male morph determination, using experimentally amplified fluctuations in growth rate throughout juvenile development. Having established that somatic growth and body size determine male morph expression immediately before metamorphosis, we examined whether the relationship between adult male morph and size at metamorphosis shifts with food quality. We found that the threshold body size for male morph expression shifts towards lower values with deteriorating food quality, confirming food-dependent allometric plasticity. Such allometric plasticity may allow populations to track prevailing nutritional conditions, potentially facilitating rapid evolution of allometric scaling relationships.

Shifts in the developmental rate of spadefoot toad larvae cause decreased complexity of post-metamorphic pigmentation patterns

Amphibian larvae are plastic organisms that can adjust their growth and developmental rates to local environmental conditions. The consequences of such developmental alterations have been studied in detail, both at the phenotypic and physiological levels. While largely unknown, it is of great importance to assess how developmental alterations affect the pigmentation pattern of the resulting metamorphs, because pigmentation is relevant for communication, mate choice, and camouflage and hence influences the overall fitness of the toads. Here we quantify the variation in several aspects of the pigmentation pattern of juvenile spadefoot toads experimentally induced to accelerate their larval development in response to decreased water level. It is known that induced developmental acceleration comes at the cost of reduced size at metamorphosis, higher metabolic rate, and increased oxidative stress. In this study, we show that spadefoot toads undergoing developmental acceleration metamorphosed with a less complex, more homogeneous, darker dorsal pattern consisting of continuous blotches, compared to the more contrasted pattern with segregated blotches and higher fractal dimension in normally developing individuals, and at a smaller size. We also observed a marked effect of population of origin in the complexity of the pigmentation pattern. Complexity of the post-metamorphic dorsal pigmentation could therefore be linked to pre-metamorphic larval growth and development.

Facultative feeding in a marine copepod: effects of larval food and temperature on performance

Most marine invertebrate larvae either feed or rely on reserves provisioned by parents to fuel development, but facultative feeders can do both. Food availability and temperature are key environmental drivers of larval performance, but the effects of larval experience on performance later in life are poorly understood in facultative feeders. In particular, the functional relevance of facultative feeding is unclear. One feature to be tested is whether starved larvae can survive to adulthood and reproduce. We evaluated effects of larval temperature and food abundance on performance in a marine harpacticoid copepod, Tisbe sp. In doing so, we report the first example of facultative feeding across the entire larval stage for a copepod. In a series of experiments, larvae were reared with ad libitum food or with no food, and at 2 different temperatures (20 vs. 24°C). We found that higher temperatures shortened development time, and larvae reared at higher temperature tended to be smaller. Larval food consistently improved early performance (survival, development rate and size) in larvae, while starvation consistently decreased survival, increased development time and decreased size at metamorphosis. Nonetheless, a small proportion (3-9.5%, or 30-42.7% with antibiotics) of larvae survived to metamorphosis, could recover from a foodless larval environment, reach maturity and successfully reproduce. We recommend that future studies of facultative feeding consider the impact of larval environments on adult performance and ability to reproduce.

Carryover effects and the evolution of polyphenism

An individual’s early-life environment and phenotype often influence its traits and performance as an adult. We investigated whether such ‘carryover effects’ are associated with alternative, environmentally-induced phenotypes (‘polyphenism’), and, if so, whether they influence the evolution of polyphenism. To do so, we studied Mexican spadefoot toads, Spea multiplicata, which have evolved a polyphenism consisting of two, dramatically different forms: a carnivore morph and an omnivore morph. We sampled both morphs from a fast-drying and a slow-drying pond and reared them to sexual maturity. Larval environment (pond) strongly influenced survival as well as age and size at metamorphosis and sexual maturity; i.e. environment-dependent carryover effects were present. By contrast, larval phenotype (morph) did not affect life-history traits at sexual maturity; i.e. phenotype-dependent carryover effects were absent. These results are consistent with theory, which suggests that by amplifying selective trade-offs in heterogenous environments, environment-dependent carryover effects might foster the evolution of polyphenism. At the same time, by freeing selection to refine a novel phenotype without altering the existing form, the absence of phenotype-dependent carryover effects might enable polyphenism to evolve in the first place. Generally, carryover effects might play an underappreciated role in the evolution of polyphenism.