Shorter Larval Period Research Articles

Heritability Estimates for Growth Traits and Correlation Analysis between Weight and Metamorphosis Rate in the Bullfrog Rana (Aquarana) catesbeiana

Metamorphosis is a crucial process in the life cycle of Rana (Aquarana) catesbeiana. R. catesbeiana tadpoles, in their short larval period, possess a high survival rate and also a highly competitive ability in the amphibious stage. In actual seed production, the economic traits of larval period and metamorphosis rate are used as quantifiable indicators of quality for individuals and populations, respectively. However, studies of these economic traits in larval cultivation and production are still lacking. In this study, we constructed 40 full-sib families of R. catesbeiana and measured the weight and metamorphosis rate of tadpoles at different developmental stages. Subsequently, we calculated the phenotypic and genetic association between weight and metamorphosis rate in tadpoles and assessed the heritability of these two traits. The heritabilities of weight at three developmental stages were all higher than 0.40 and decreased with advancement of the developmental stage; the heritability of the metamorphosis rate was 0.18 ± 0.20, a moderate level. Correlation analysis of weight and metamorphosis rate at each developmental stage in each tadpole family showed that weight at stages 25-I, 25-II, and 25-III was significantly correlated at the phenotypic level but non-significantly at the genetic level. The metamorphosis rate was only moderately associated with stage 25-III weight (0.38, p < 0.05). The results of this study confirm the importance and transportability of tadpole weight in actual seed production and provide basic data and a potentially optimized direction for the selective breeding of high-metamorphosis-rate bullfrogs.

Life history of Copelatus kammuriensis Tamu and Tsukamoto, 1955 (Coleoptera: Dytiscidae: Copelatinae) and biological implications

The diversity of Japanese Dytiscidae has declined substantially in recent years, therefore, a better understanding of the biology and ecology of this insect family is essential to ensure its conservation. In this study, captive breeding experiments were conducted to elucidate the life history, and field surveys were performed to determine the reproductive habitats of the Japanese endemic species Copelatus kammuriensis Tamu and Tsukamoto, 1955. The reproductive habitats, egg-laying environments, immature periods, and unique ecology of the species were identified. The larval periods of five Copelatus species were compared, and that of C. kammuriensis was found to be the shortest; its reproductive habitats were unstable rain pools that easily dried up in the absence of rain over up to 10 days. These results suggest that a short larval period and rapid predatory behaviour are important for the survival of C. kammuriensis.

Naturally occurring variability in larval period length is associated with intraspecific differences in late tadpoles of a South American true toad

AbstractThe larval period in anurans is highly plastic. Even though larval period length and larval size have been the most studied characteristics showing intraspecific variability, other features such as morphology, behavior, food preferences and physiology have also been described as plastic. Metamorphic changes are triggered by thyroid and interrenal hormones, and environmental signals modulate the onset of metamorphosis via the hypothalamic–pituitary–interrenal axis. The South American bufonid toad Rhinella arenarum from nearby Buenos Aires City has a larval period of 30–120 days under the same environmental conditions. The goal of this study was to evaluate life‐history traits in tadpoles from different localities and potential morphological differences among tadpoles with different larval period length. For this purpose, we reared under natural conditions tadpoles from two different localities nearby Buenos Aires City and in three different years measured their size at the end of metamorphosis and recorded their larval period length. The external appearance, histo‐morphology and morphometry of the skin and kidney/interrenal complex were studied in metamorphs with short and long larval periods (SLP and LLP, respectively). We observed a larval period lasting 30–120 days in tadpoles from different localities or years. SLP metamorphs were smaller, darker, had less protruding eyes without eyelids, a thinner epidermis and fewer skin glands than LLP metamorphs. The secretion of skin glands from SLP tadpoles had acidic glycoconjugates. Kidney size was similar between LLP and SLP metamorphs, but the former had an adult‐like histomorphology. Interrenal gland in LLP early and late climax tadpoles had cells with a high nucleus/cell diameter ratio, a sign of highly active steroidogenic cells. Overall, these results show that intraspecific variability in size, skin and interrenal gland development is associated with differences in larval period length. Distinct skin gland number and secretion, along with distinct interrenal histology at late climax, could have physiological consequences in the post‐metamorphic life.

Developmental environment has lasting effects on amphibian post-metamorphic behavior and thermal physiology.

Environmental challenges early in development can result in complex phenotypic trade-offs and long-term effects on individual physiology, performance and behavior, with implications for disease and predation risk. We examined the effects of simulated pond drying and elevated water temperatures on development, growth, thermal physiology and behavior in a North American amphibian, Rana sphenocephala. Tadpoles were raised in outdoor mesocosms under warming and drying regimes based on projected climatic conditions in 2070. We predicted that amphibians experiencing the rapid pond drying and elevated pond temperatures associated with climate change would accelerate development, be smaller at metamorphosis and demonstrate long-term differences in physiology and exploratory behavior post-metamorphosis. Although both drying and warming accelerated development and reduced survival to metamorphosis, only drying resulted in smaller animals at metamorphosis. Around 1month post-metamorphosis, animals from the control treatment jumped relatively farther at high temperatures in jumping trials. In addition, across all treatments, frogs with shorter larval periods had lower critical thermal minima and maxima. We also found that developing under warming and drying resulted in a less exploratory behavioral phenotype, and that drying resulted in higher selected temperatures in a thermal gradient. Furthermore, behavior predicted thermal preference, with less exploratory animals selecting higher temperatures. Our results underscore the multi-faceted effects of early developmental environments on behavioral and physiological phenotypes later in life. Thermal preference can influence disease risk through behavioral thermoregulation, and exploratory behavior may increase risk of predation or pathogen encounter. Thus, climatic stressors during development may mediate amphibian exposure and susceptibility to predators and pathogens into later life stages.

Artificial rearing of Actinopyga lecanora (Holothuroidea: Holothuriida) with spawning induction using relaxin: Lecithotrophic short larval period

Artificial rearing techniques of larvae and juveniles of the tropical sea cucumber, Actinopyga lecanora were developed for the first time. Broodstock individuals were collected in Yaeyama Islands, Okinawa, subtropical Japan and sorted by the gonad maturity which was determined by biopsy. An artificially-synthesized relaxin peptide, originated from Holothuria (Metriatyla) scabra, was injected into the coelomic fluid of mature A. lecanora at amounts of 3 × 10−9 to 10 × 10−9 mol kg−1 body weight, which successfully induced spawning in 10 of 14 females and 3 of 3 males after 26–70 min. The number of eggs spawned per one female individual ranged 2.2–9.5 × 105. The mean diameter of oocytes of A. lecanora individuals which spawned by the induction was 324 ± 13 μm, much larger than those of sea cucumber species having a planktotrophic larval stage. The embryo hatched during gastrula, and the larva metamorphosed to planktonic auricularia followed by doliolaria and finally settled into the benthic stage as pentactula. Time after fertilization to settlement was 4–8 days when larvae were reared in 5–500 L tanks at 26–28 °C, which is one of the shortest development periods among sea cucumbers. Although larvae were supplied with Chaetoceros gracilis cells in most rearing batches, the larvae were later confirmed as lecithotrophic (non-feeding) as (1) larvae were successfully reared until settlement without feeding, and (2) chlorophyll a fluorescence of C. gracilis was not incorporated into the larval intestine as observed under fluorescence microscopy. Auricularia larvae showed poor development of lateral arm protrusion and did not form hyaline spheres. Initial rearing densities under 0.4 larva mL−1 resulted in relatively good survival. Settling larvae were retrieved using polycarbonate corrugated sheets on which periphytic diatoms had been grown beforehand. Survival from hatching to 2 months after settlement was 1.0–1.8%, comparable with values reported for other sea cucumbers. Postsettled juveniles became orange-colored with black dorsal papillae in 50 days after settlement and subsequently gradually obtained a dark green-brown dorsal pigment. Juveniles having anal teeth and adult-like color pattern appeared from 4 months after settlement. Growth of the settled juveniles was 91.8 ± 1.5 μm day−1 from Jun to Dec, reaching 15.11 ± 5.63 mm long in 170 days, while the juveniles negatively grew during winter from Dec to Feb. The lecithotrophic short larval period of A. lecanora has potential for low-cost seed production, which is advantageous for development of aquaculture and restocking.

Climate change can be seen through a disaster medicine lens.

Climate change can be seen through a disaster medicine lens.

Evaluation of Castor (Ricinus communis L.) Genotypes and Their Feeding Values on Rearing Performance of Eri Silkworm (Samia cynthia ricini Boisduval) (Lepidoptera: Saturniidae) in Southwest Ethiopia

The quality of feed plays an important role in the growth and development of silkworms and eventually in the economic traits of cocoons. This study was conducted to evaluate ten castors (Ricinus communis L.) genotypes and their feeding values on the rearing performance of Eri Silkworm (Samia cynthia ricini Boisduval) (Lepidoptera: Saturniidae) at Tepi, southwest Ethiopia. A total of ten castor genotypes were evaluated in a randomized complete block design (RCBD), and the suitability of castor genotypes as feed for a mixed strain of Eri-silkworm was also evaluated in a completely randomized design (CRD) under laboratory conditions. A hundred worms were used in each replication. Castor genotypes showed significant differences in fresh leaf yield. Among the castor genotypes tested, genotype 219645 recorded 439 g of ten fresh leaf yields. Results of Eri-silkworm rearing performance depict that a shorter larval period (22 days), a higher effective rate of rearing (94.54%), and a shorter life cycle (58 days) were observed in Eri-silkworm fed on leaves of the 200390 genotype, while a higher larval weight (6.16 g) was recorded in the Abaro genotype. However, higher cocoon weight (3.26 g), pupal weight (2.46 g), shell weight (0.45 g), and silk ratio (13.80%) were found in Eri-silkworms fed on leaves of genotype 219645. Hence, based on silkworm rearing performance, genotype 219645 showed relatively superior results and is recommended for future development work. Further studies should continue giving more emphasis to the multilocation study of genotype 219645 to understand its performance in the diverse growing environment.

Barriers in European spiny lobster (Palinurus elephas) aquaculture: What we know so far?

AbstractPalinurids, also known as spiny lobsters, are high‐value seafood, which is economically important for many European and Asian seafood trades. However, the reduction of wild European spiny lobster populations produces a need for developing alternative renewable strategies to meet current and future demands. Aquaculture of spiny lobsters has the potential to become of major economic importance in the coming years with growing markets in Asia, Europe, and America, with Palinurus elephas being a promising candidate species for use in the commercial culture and stock enhancement of natural fisheries. This is due to its shorter larval periods and rapid growth to the critical puerulus stage compared with other spiny lobster species. While we have a basic understanding of the lifecycle and biology of P. elephas, much of this is based on work undertaken on similar species globally. There are many gaps in our knowledge that need to be addressed to make its aquaculture viable with appropriate feeds being an immediate issue as well as many other husbandry‐related factors. Previous studies act as a platform providing a baseline for further research and highlighting constraints. Developments in the use of P. elephas are promising due to realistically bridgeable knowledge gaps, the likelihood of producing sustainable food and the high commercial value of spiny lobsters. This review identifies our present state of knowledge and outlines the scope for further research and necessary technological developments to make it a viable contribution towards crustacean aquaculture in Europe.

Biological notes on immature stages of Hydaticus pacificus conspersus (Coleoptera: Dytiscidae)

Abstract Hydaticus pacificus conspersus Régimbart, 1899 (Coleoptera: Dytiscidae), is currently considered “endangered,” according to the national Red List of Japan. Herein, the developmental period of the immature stages of H. pacificus conspersus during laboratory rearing is described in detail for the first time. We found that this species deposits eggs not only on aquatic plants but also on the surface of driftwood. The observed durations of developmental stages were as follows: egg period – 3 days; first instar – 1–2 days (1.7 ± 0.5); second instar – 1–4 days (2.4 ± 0.6); third instar – 4–7 days (5.0 ± 0.7 days); and construction of a pupal chamber to emergence: 8–13 days (9.6 ± 0.8). Based on these observed results, H. pacificus conspersus has one of the shortest larval developmental periods among the Dytiscidae species. The short larval period and the ability to lay eggs on substrates other than plants may be an adaption of the species to increase reproductive success in unstable environments.

Habitat ephemerality affects the evolution of contrasting growth strategies and cannibalism in anuran larvae.

Ephemeral streams are challenging environments for tadpoles; thus, adaptive features that increase the survival of these larvae should be favored by natural selection. In this study, we compared the adaptive growth strategies of Bombina orientalis (the oriental fire-bellied toad) tadpoles from ephemeral streams with those of such tadpoles from non-ephemeral streams. Using a common garden experiment, we tested the interactive effects of location (ephemeral vs. non-ephemeral), food availability, and growing density on larval period, weight at metamorphosis, and cannibalism. We found that tadpoles from ephemeral streams underwent a shorter larval period compared with those from non-ephemeral streams but that this difference was contingent on food availability. The observed faster growth is likely to be an adaptive response because tadpoles in ephemeral streams experience more biotic/abiotic stressors, such as desiccation risk and limited resources, compared with those in non-ephemeral streams, with their earlier metamorphosis potentially resulting in survival benefits. As a trade-off for their faster growth, tadpoles from ephemeral streams generally had a lower body weight at metamorphosis compared with those from non-ephemeral streams. We also found lower cannibalism rates among tadpoles from ephemeral streams, which can be attributed to the indirect fitness costs of cannibalizing their kin. Our study demonstrates how ephemeral habitats have affected the evolutionary change in cannibalistic behaviors in anurans and provides additional evidence that natural selection has mediated the evolution of growth strategies of tadpoles in ephemeral streams.

Long lasting effects of early temperature exposure on the swimming performance and skeleton development of metamorphosing Gilthead seabream (Sparus aurata L.) larvae

Temperatures experienced during early ontogeny significantly influence fish phenotypes, with clear consequences for the wild and reared stocks. We examined the effect of temperature (17, 20, or 23 °C) during the short embryonic and yolk-sac larval period, on the swimming performance and skeleton of metamorphosing Gilthead seabream larvae. In the following ontogenetic period, all fish were subjected to common temperature (20 °C). The critical swimming speed of metamorphosing larvae was significantly decreased from 9.7 ± 0.6 TL/s (total length per second) at 17 °C developmental temperature (DT) to 8.7 ± 0.6 and 8.8 ± 0.7 TL/s at 20 and 23 °C DT respectively (p < 0.05). Swimming performance was significantly correlated with fish body shape (p < 0.05). Compared with the rest groups, fish of 17 °C DT presented a slender body shape, longer caudal peduncle, terminal mouth and ventrally transposed pectoral fins. Moreover, DT significantly affected the relative depth of heart ventricle (VD/TL,p < 0.05), which was comparatively increased at 17 °C DT. Finally, the incidence of caudal-fin abnormalities significantly decreased (p < 0.05) with the increase of DT. To our knowledge, this is the first evidence for the significant effect of DT during the short embryonic and yolk-sac larval period on the swimming performance of the later stages.

Ecological adaptation drives wood frog population divergence in life history traits.

Phenotypic variation among populations is thought to be generated from spatial heterogeneity in environments that exert selection pressures that overcome the effects of gene flow and genetic drift. Here, we tested for evidence of isolation by distance or by ecology (i.e., ecological adaptation) to generate variation in early life history traits and phenotypic plasticity among 13 wood frog populations spanning 1200 km and 7° latitude. We conducted a common garden experiment and related trait variation to an ecological gradient derived from an ecological niche model (ENM) validated to account for population density variation. Shorter larval periods, smaller body weight, and relative leg lengths were exhibited by populations with colder mean annual temperatures, greater precipitation, and less seasonality in precipitation and higher population density (high-suitability ENM values). After accounting for neutral genetic variation, the QST-FST analysis supported ecological selection as the key process generating population divergence. Further, the relationship between ecology and traits was dependent upon larval density. Specifically, high-suitability/high-density populations in the northern part of the range were better at coping with greater conspecific competition, evidenced by greater postmetamorphic survival and no difference in body weight when reared under stressful conditions of high larval density. Our results support that both climate and competition selection pressures drive clinal variation in larval and metamorphic traits in this species. Range-wide studies like this one are essential for accurate predictions of population's responses to ongoing ecological change.

Life-History Traits and Flight Capacity of Grapholita molesta (Lepidoptera: Tortricidae) Using Artificial Diets With Varying Sugar Content.

Successful application of the sterile insect technique (SIT), an environmentally friendly control technology, mainly depends on mass-rearing of high-quality and high-performance insects. For mass-rearing of insects, the development of artificial diets is a key component. For optimal insect growth and development, sugar is an essential nutrient as it provides energy for flight. To date, few studies have analyzed the effects of different sugar contents on the biological parameters, including the flight capacity of Grapholita molesta, a globally important economic pest. Artificial diets with different sucrose contents (0, 15, and 30 g) were evaluated in two consecutive generations. The insect flight mill was used to study the G. molesta flight capacity. The larval and pupal periods, adult longevity and pupal weight of the first-generation of G. molesta reared on artificial diets with different sucrose contents were significantly different. Insects of the second-generation had a shorter larval period, greater adult longevity, and heavier larvae and pupae in the treatment with 30 g of sucrose than using 15 g. Among the males, strong, medium, and weak flight capacities were recorded and the weakest one was observed in the diet without sucrose. Results showed that the proportion of insects with highest flight capacity increased with increasing sucrose content in insects of the second generation. It can be concluded that sucrose content is a key determinant in the biological traits, including flight capacity of G. molesta, and should be taken into consideration during the mass-rearing of the pest for SIT.

Performance of Sesamia nonagrioides on cultivated and wild host plants: Implications for Bt maize resistance management.

BACKGROUND Sesamia nonagrioides is an important maize pest in the Mediterranean basin that is effectively controlled by Cry1Ab‐expressing maize (Bt maize). The continued cultivation of Bt maize in Spain exerts high selection pressure on the target pests, which could lead to the development of resistance. Provision of refuges of non‐Bt plants is an essential component in the high‐dose/refuge (HDR) strategy to delay resistance evolution. Here we analyze the suitability of cultivated (rice and sorghum) and wild (Johnsongrass, cattail, common reed and giant reed) plants, reported as hosts of S. nonagrioides, for larval development and oviposition of this pest compared to maize, and we evaluate their potential role in delaying resistance development to Bt maize.RESULTSBioassays conducted with plant pieces or whole plants showed that the larval cycle could only be completed in the three cultivated plants and in Johnsongrass. Females showed a strong preference for ovipositing on maize in comparison with sorghum or rice. Although young larvae consumed more sorghum than maize in two‐choice bioassays, both larvae and adults had a better performance (shorter larval period and higher pupal weight, fecundity and fertility) when larvae fed on maize throughout their larval stage than when they fed on sorghum or rice.CONCLUSIONNone of the alternative hosts of S. nonagrioides tested here should be considered as natural unstructured refuges within the HDR strategy for Bt maize and this pest in Spain, as some of the necessary requirements to fulfill this strategy would not be met. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Developmental life history is associated with variation in rates of climatic niche evolution in a salamander adaptive radiation.

Rates of climatic niche evolution vary widely across the tree of life and are strongly associated with rates of diversification among clades. However, why the climatic niche evolves more rapidly in some clades than others remains unclear. Variation in life history traits often plays a key role in determining the environmental conditions under which species can survive, and therefore, could impact the rate at which lineages can expand in available climatic niche space. Here, we explore the relationships among life-history variation, climatic niche breadth, and rates of climatic niche evolution. We reconstruct a phylogeny for the genus Desmognathus, an adaptive radiation of salamanders distributed across eastern North America, based on nuclear and mitochondrial genes. Using this phylogeny, we estimate rates of climatic niche evolution for species with long, short, and no aquatic larval stage. Rates of climatic niche evolution are unrelated to the mean climatic niche breadth of species with different life histories. Instead, we find that the evolution of a short larval period promotes greater exploration of climatic space, leading to increased rates of climatic niche evolution across species having this trait. We propose that morphological and physiological differences associated with variation in larval stage length underlie the heterogeneous ability of lineages to explore climatic niche space. Rapid rates of climatic niche evolution among species with short larval periods were an important dimension of the clade's adaptive radiation and likely contributed to the rapid rate of lineage accumulation following the evolution of an aquatic life history in this clade. Our results show how variation in a key life-history trait can constrain or promote divergence of the climatic niche, leading to variation in rates of climatic niche evolution among species.

The effects of hydroperiod and predator density on growth, development, and morphology of wood frogs (Rana sylvatica)

Accelerated development and metamorphosis allow tadpoles to escape death by leaving the aquatic habitat before it dries. Phenotypic plasticity in response to predators typically includes development of physical and behavioral traits, including changes in tail coloration, activity rate, and tail shape and body size. Responding to predators increases the probability of survival, but lowers growth rate. Responses to two common stressors in ephemeral aquatic habitats appear to be in direct opposition to one another. In this study, we examined the individual and interactive effects of hydroperiod and predator density on the life history, morphology, and metamorphosis of wood frog (Rana sylvatica) tadpoles in an outdoor mesocosm study. Tadpoles were exposed to three hydroperiods (constant, intermediate, and short) and three predator densities (zero, four, and eight Anax junius naiads) using a complete block design. The threat of habitat desiccation resulted in increased developmental rate and shorter larval periods. Increased predator densities resulted in increased size at metamorphosis and development of the induced morphology. Although the threat of predation precluded growth and developmental responses to shortened hydroperiod in tadpoles, it did not negate the metamorphic responses to hydroperiod. It appears that, at least at the treatment levels imposed in this experiment, the interaction between these multiple stressors is complex, with the stressors acting both individually and together on different aspects of tadpole ecology.

Histology and microscopic anatomy of the thyroid gland during the larval development of Pseudis platensis (Anura, Hylidae).

Several hormones regulate anuran larval development, most notably thyroid hormones (THs). In anurans, metamorphosis fails when the thyroid gland is absent or inactivated, resulting in giant tadpoles. Larval gigantism occurs naturally in neotropical frogs of the genus Pseudis as a result of a prolonged larval period. Its thyroid function is poorly investigated and the focus of this study. We describe qualitative and quantitative variations in larval development for field-captured specimens of Pseudis platensis and compare those to the development of two sympatric species, Phyllomedusa sauvagii and Pithecopus azureus, which have small tadpoles and a shorter larval period. We describe morphological changes in the thyroid glands of larval and adult specimens. In contrast to other species with similar ecological requirements, P. platensis exhibits distinct glandular activity. During premetamorphosis, there was little or no thyroid activity, a period in which the tadpole reached 70% of its maximum size. Development and degree of activity of the thyroid gland determine the duration of the early stages of the larval period. Thyroid gland histology in tadpoles appears to correlate with the TH activity, and in turn with the diversity in anuran life history transitions.

Effects of hydroperiod on growth, development, survival and immune defences in a temperate amphibian

Abstract The many and varied effects of human‐induced environmental change have the potential to threaten animal biodiversity and species abundance. Importantly, human land use and global climate change are predicted to reduce water availability, which might have negative consequences for freshwater organisms. In this study, we tested for an effect of a shortened hydroperiod on larval growth and development, and post‐metamorphic survival and immune function in a temperate frog, Rana pipiens. Animals developing under pond drying conditions metamorphosed at a smaller size and had lower survival after metamorphosis. We found sex‐specific differences in larval period in our fastest drying treatment, with males metamorphosing more quickly than females. Individuals that developed under drying conditions also showed reduced skin swelling after phytohaemagglutinin injection, indicating a compromised immune response. We found support for trade‐offs between growth, development and post‐metamorphic immune function across hydroperiod treatments. Whole blood from animals with shorter larval periods had lower bacterial killing ability, and small‐bodied juveniles had lower antibody titres. Overall, our results indicate that a shortened hydroperiod can affect the rate of larval amphibian growth and development, and might negatively impact the condition of species that rely on freshwater for development. Our work improves understanding of the complex impacts that environmental stressors might have on the health of animal populations. A free Plain Language Summary can be found within the Supporting Information of this article.

Potential fecundity, larval development, and survival of two invasive species of &lt;i&gt;Arhopalus&lt;/i&gt; (Coleoptera: Cerambycidae) coexisting in southern South America

Biological invasions are one of the main threats to forest health. Although Arhopalus rusticus and Arhopalus syriacus (Cerambycidae) are alien species in South America, the ecology of these invasive species is not well studied. Here, we examined the effect of the female size on potential fecundity, size and number of mature eggs in ovaries, in both insect species. We also compared egg morphometric characteristics, larval measurements, larval development and survival between these two species. We found a positive relationship between the female size and the number of eggs in their ovaries but no relationship between the female size and egg morphometric characteristics in each of these two species. The females of A. rusticus were significantly larger and had bigger eggs than those of A. syriacus, but no significant difference was observed in the number of eggs between them. Larval body length and head capsule exuviae width were larger in A. rusticus than in A. syriacus. Arhopalus rusticus had the highest larval survival rate, but A. syriacus had the shortest larval period. Thus, female and egg size, as well as larval size and survivorship are competitive advantages to A. rusticus. However, A. syriacus has a similar number of eggs to A. rusticus and faster larval development; these could be key features to explain the coexistence of these two species.

Effects of the invasive crayfish Procambarus clarkii on growth and development of Pelophylax perezi tadpoles in field conditions

Introduced predatory aquatic invertebrates may contribute to the global decline of amphibians as their larval are extremely vulnerable to predators. The objective of this study was to examine the effects of the predatory invasive crayfish Procambarus clarkii on the growth and development of native Iberian green frog tadpoles, Pelophylax perezi, in field conditions. We hypothesized that P. clarkii might affect P. perezi development by (a) inducing a delay in its metamorphosis and (b) reducing survival and mass of metamorphs. The experiment was developed in two ponds (with and without P. clarkii’s presence) in the Natural Park of Aiguamolls de l’Empordà (NE of the Iberian Peninsula). For each pond, groups of 10 tadpoles were randomly assigned to 15 cylindrical field enclosures. These enclosures avoided direct contact (i.e. predation) between both species. Our results suggest that, in field conditions, the presence of P. clarkii accelerates metamorphosis of P. perezi tadpoles. The higher growth rate of P. perezi through shorter larval periods could be the result of behavioural plasticity in response to the strong pressure imposed by P. clarkii. This conclusion would be in accordance with the hypothesis that phenotypic plasticity plays an important role in the conservation of P. perezi in front of biological invasions.