Timing Of Metamorphosis Research Articles

Living in a multi-stressor world: nitrate pollution and thermal stress interact to affect amphibian larvae.

The interaction of widespread stressors such as nitrate pollution and increasing temperatures associated with climate change are likely to affect aquatic ectotherms such as amphibians. The metamorphic and physiological traits of amphibian larvae during the critical onset of metamorphosis are particularly susceptible to these stressors. We used a crossed experimental design subjecting Rana temporaria larvae to four constant rearing temperatures (18, 22, 26, 28 °C) crossed with three environmentally relevant nitrate concentrations (0, 50, 100 mg×L-1) to investigate the interactive and individual effects of these stressors on metamorphic (i.e., growth and development) and physiological traits (i.e., metabolism and heat tolerance) at the onset of metamorphosis. Larvae exposed to elevated nitrate concentrations and thermal stress displayed increased metabolic rates but decreased developmental rate, highlighting interactive effects of these stressors. However, nitrate pollution alone had no effect on either metamorphic or physiological traits, suggesting that detoxification processes were sufficient to maintain homeostasis but not in combination with increased rearing temperatures. Furthermore, larvae exposed to nitrate displayed diminished abilities to exhibit temperature-induced plasticity in metamorphosis timing and heat tolerance, as well as reduced acclimation capacity in heat tolerance and an increased thermal sensitivity of metabolic rate to higher temperatures. These results highlight the importance of considering the exposure to multiple stressors when investigating how natural populations respond to global change.

Geographic variation in developmental plasticity among populations of the canyon treefrog in response to temperature and pond‐drying

AbstractUnderstanding how species respond to environmental changes, particularly in the context of climate change, is crucial for biodiversity conservation. This study focuses on the plastic responses of canyon tree frog (Dryophytes arenicolor) larvae to variations in temperature and pond‐drying, examining potential consequences of climate change. Frog larvae serve as an excellent model due to their high responsiveness to environmental cues during development. We analysed the impact of temperature and pond‐drying on morphological and life‐history traits, via a common garden experiment with individuals from three distinct populations with different ecological conditions. The experiments revealed significant differences in responses among populations, indicating geographic variation in plasticity. Pond‐drying treatments led to reduced survival and reduction of morphological traits and growth, challenging the assumption that tadpoles have adaptive responses to drying conditions. In contrast, temperature treatments showed variable effects, with elevated temperatures generally favouring growth rates, reducing metamorphosis time, and having population‐specific morphological shifts. We emphasize the importance of considering both morphological and life‐history traits, as well as geographic variation, in assessing species' vulnerability to climate change. Furthermore, the integration of environmental standardized plasticity index (ESPI) and relative distances plasticity index (RDPI) in amphibian developmental plasticity will allow to quantify and compare plastic responses among populations and even other amphibian species in which these metrics are obtained in the future. Our results underscore the complexity of phenotypic plasticity, revealing genotype–environment interactions. These findings contribute valuable insights into the potential adaptability of D. arenicolor populations to ongoing climate changes, highlighting the need for comprehensive inter‐population studies for a more nuanced understanding of species' responses to environmental change, and suggest that certain populations may be more vulnerable to extinction or better equipped to handle climate change based on their ability to adapt to environmental change.

Optimal outbreeding is shaped during larval life-history in the splash pool copepod Tigriopus californicus.

Inbreeding and outbreeding depression are dynamic forms of selection critical to mating system evolution and the efficacy of conservation biology. Most evidence on how the relative severity and timing of these forces are shaped is confined to self-fertilization, distant outcrossing, and intermediate 'optimal outcrossing' in hermaphrodites. We tested the notion that closed population demographics may reduce and delay the costs of inbreeding relative to distant outbreeding in an intertidal copepod with separate sexes and a biphasic larval / post-metamorphic life-history (Tigriopus californicus). At three lifecycle stages (fecundity, metamorphosis, and post-metamorphosis), we quantified the effects of inbreeding and outbreeding in crosses with varying degrees of recent common ancestry. Although inbreeding and outbreeding depression have distinct genetic mechanisms, both manifested the same stage-specific consequences for fitness. Inbreeding and outbreeding depression were not apparent for fecundity, post-metamorphic survival, sex ratio, or the ability to acquire mates, but inbreeding between full siblings and outbreeding between interpopulation hybrids reduced the fraction of offspring that completed metamorphosis by 32% and 47%, respectively. On average, the effects of inbreeding on metamorphic rate were weaker and nearly twice as variable among families than those of outbreeding, suggesting genetic load was less pervasive than the incompatibilities accrued between divergent populations. Overall, our results indicate the transition from larval to juvenile life stages is markedly susceptible to both inbreeding and outbreeding depression in T. californicus. We suggest stage-specific selection acting concurrently with the timing of metamorphosis may be an instrumental factor shaping reproductive optima in species with complex life-histories.

Integrated biomarker-based ecological risks assessment of tadpole responses to tris(2-chloroethyl) phosphate, tris(1-chloro-2-propyl) phosphate, and their combined environmental exposure

Tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCPP) are common chlorinated organophosphorus flame retardants (OPFRs) used in industry. They have been frequently detected together in aquatic environments and associated with various hazardous effects. However, the ecological risks of prolonged exposure to these OPFRs at environmentally relevant concentrations in non-model aquatic organisms remain unexplored. This study investigated the effects of long-term exposure (up to 25 days) to TCEP and TCPP on metamorphosis, hepatic antioxidants, and endocrine function in Polypedates megacephalus tadpoles. Exposure concentrations were set at 3, 30, and 90 μg/L for each substance, conducted independently and in equal-concentration combinations, with a control group included for comparison. The integrated biomarker response (IBR) method developed an optimal linear model for predicting the overall ecological risks of TCEP and TCPP to tadpoles in potential distribution areas of Polypedates species. Results showed that: (1) Exposure to environmentally relevant concentrations of TCEP and TCPP elicited variable adverse effects on tadpole metamorphosis time, hepatic antioxidant enzyme activity and related gene expression, and endocrine-related gene expression, with their combined exposure exacerbating these effects. (2) The IBR value of TCEP was consistently greater than that of TCPP at each concentration, with an additive effect observed under their combined exposure. (3) The ecological risk of tadpoles exposed to the combined presence of TCEP and TCPP was highest in China's Taihu Lake and Vietnam's Hanoi than in other distribution locations. In summary, prolonged exposure to environmentally relevant concentrations of TCEP and TCPP presents potential ecological risks to amphibian tadpoles, offering insights for the development of policies and strategies to control TCEP and TCPP pollution in aquatic ecosystems. Furthermore, the methodology employed in establishing the IBR prediction model provides a methodological framework for assessing the overall ecological risks of multiple OPFRs.

Effects of growing season and individual growth rates on the occurrence of larval overwintering in Otton frog tadpoles

AbstractThe timing and size of metamorphosis are crucial for the future fitness of organisms with complex life cycles, such as amphibians. In some amphibian species, a portion of tadpoles will metamorphose in their natal year whereas others from the same cohort overwinter as tadpoles. Low temperature and food availability were previously assumed to be the underlying reasons; however, the factors influencing the decision to overwinter as tadpoles or metamorphose in the natal year have not been extensively studied. This study investigated these factors by conducting laboratory‐rearing experiments on Babina subaspera tadpoles. The tadpoles were individually reared under controlled temperature and light conditions that simulated five different growing seasons (i.e., the start month) observed in the field. Four different food quantity levels were set to induce different growth rates, which were measured individually. The results revealed that 33 tadpoles metamorphosed within their natal year, whereas 52 tadpoles were overwintered as tadpoles and metamorphosed the following spring. The size at metamorphosis was larger in tadpoles that metamorphosed after winter than in those that metamorphosed before winter. Whether tadpoles metamorphosed before or after winter was influenced by the individual growth rate and growing season. Tadpoles with slower growth rates were more likely to metamorphose after winter, possibly because slower growth prevented them from reaching the critical size threshold required for metamorphosis before winter. The threshold for the occurrence of larval overwintering varied with the growing season; tadpoles that spawned later in the year were more likely to overwinter, even with a high growth rate. The results suggested that slow‐growing B. subaspera tadpoles with insufficient time until the onset of winter would gain a higher fitness by metamorphosing after winter. This would be advantageous due to the tadpoles' potentially high survival rate during dormancy as well as their larger size at metamorphosis in the following year.

Limited contribution of photoenzymatic DNA repair in mitigating carry-over effects from larval UVB exposure: Implications for frog recruitment

Solar ultraviolet-B (UVB) radiation has increased due to stratospheric ozone depletion, climate and ecosystem changes and is a driver of amphibian population declines. Photoenzymatic repair (PER) is a critical mechanism for limiting UVB lethality in amphibian larvae. However, the link between PER and the UVB-induced effects remains understudied through long-term investigations in vivo. Here, we assessed how larval PER determines the lethal and sublethal effects induced by environmentally relevant acute UVB exposure until the juvenile phase in the Neotropical frog Odontophrynus americanus. We conducted laboratory-based controlled experiments in which tadpoles were or were not exposed to UVB and subsequently were exposed to light (for PER activation) or dark treatments. Results showed that the rates of mortality and apoptosis observed in post-UVB dark treatment are effectively limited in post-UVB light treatment, indicating PER (and not dark repair, i.e. nucleotide excision repair) is critical to limit the immediate genotoxic impact of UVB-induced pyrimidine dimers. Nonetheless, even tadpoles that survived UVB exposure using PER showed sublethal complications that extended to the juvenile phase. Tadpole responses included alterations in morphology, chromosomal instability, increased skin susceptibility to fungal proliferation, as well as increased generation of reactive oxygen species. The short-term effects were carried over to later stages of life because metamorphosis time increased and juveniles were smaller. No body abnormalities were visualized in tadpoles, metamorphs, and juveniles, suggesting that O. americanus is UVB-resistant concerning these responses. This study reveals that even frog species equipped with an effective PER are not immune to carry-over effects from early UVB exposure, which are of great ecological relevance as late metamorphosis and smaller juveniles may impact individual performance and adult recruitment to breeding. Future ecological risk assessments and conservation and management efforts for amphibian species should exercise caution when linking PER effectiveness to UVB resistance.

Dynamic energy budget model for the complete life cycle of chub mackerel in the Northwest Pacific

Chub mackerel (Scomber japonicus) in the Northwest Pacific is an important pelagic fishery resource and a significant target species in purse seine fisheries. However, the catch of chub mackerel fluctuates greatly from year to year, and recent studies have shown that the Tsushima stock may be overfished. Therefore, research on the biology and population dynamics of this species is required to provide sufficient scientific support for the development of reasonable management and recovery plans and for the increased sustainable use of resource fisheries. In this study, a dynamic energy budget (DEB) model was constructed based on DEB theory for the complete life cycle of chub mackerel in the Northwest Pacific by using biological data to simulate processes, including growth, reproduction, and death. The key results were as follows. 1) The DEB model accurately simulated the complete life cycle of chub mackerel, with a good fit for the relationships between age and length as well as length and weight, while accurately estimating annual absolute fecundity, aging, and death and predicting the metamorphosis time of larval fish. 2) The DEB model can incorporate the effects of temperature and food to describe the effects of marine environmental conditions on chub mackerel growth. 3) The DEB model involved multiple interrelated parameters; however, owing to a lack of observational data, there was a certain degree of uncertainty in estimated parameter values. The DEB model provides a basis for establishing correlations and intrinsically unifying biological processes, including growth, sexual maturation, reproduction, aging, and death, thereby guiding studies of growth, reproduction, and population dynamics of chub mackerel in the Northwest Pacific.

Intraspecific interference retards growth and development of cane toad tadpoles, but those effects disappear by the time of metamorphosis.

Competition among larval anurans can occur via interference as well as via a reduction in per-capita food supply. Previous research on intraspecific interference competition in cane toad (Rhinella marina) tadpoles found conflicting results, with one study detecting strong effects on tadpoles and another detecting no effects on metamorphs. A capacity to recover from competitive suppression by the time of metamorphosis might explain those contrasting impacts. In a laboratory experiment, we found that nine days of exposure to intraspecific interference competition strongly reduced tadpole growth and development, especially when the competing tadpoles were young (early-stage) individuals. Those competitive effects disappeared by the time of metamorphosis, with no significant effect of competition on metamorph body condition, size, larval period or survival. Temporal changes in the impact of competition were not related to tadpole density or to variation in water quality. The ability of larval cane toads to recover from intraspecific interference competition may enhance the invasive success of this species, because size at metamorphosis is a significant predictor of future fitness. Our study also demonstrates a cautionary tale: conclusions about the existence and strength of competitive interactions among anuran larvae may depend on which developmental stages are measured.

Warmer temperature overrides the effects of antidepressants on amphibian metamorphosis and behavior.

Climate change can exacerbate the effects of environmental pollutants on aquatic organisms. Pollutants such as human antidepressants released from wastewater treatment plants have been shown to impact life-history traits of amphibians. We exposed tadpoles of the wood frog Lithobates sylvaticus to two temperatures (20°C and 25°C) and two antidepressants (fluoxetine and venlafaxine), and measured timing of metamorphosis, mass at metamorphosis, and two behaviors (startle response and percent motionless). Antidepressants significantly shortened time to metamorphosis at 20°C, but not at 25°C. At 25°C, tadpoles metamorphosed significantly faster than those at 20°C independent of antidepressant exposure. Venlafaxine reduced body mass at 25°C, but not at 20°C. Temperature and antidepressant exposure affected the percent of tadpoles showing a startle response. Tadpoles at 20°C displayed significantly more responses than at 25°C. Exposure to fluoxetine also increased the percent of tadpoles showing a startle response. Venlafaxine reduced the percent of motionless tadpoles at 25°C but not at 20°C. While our results showed that antidepressants can affect the timing of metamorphosis in tadpoles, warmer temperatures overrode these effects and caused a reduction in an important reaction behavior (startle response). Future studies should address how warmer global temperatures may exacerbate or negate the effects of environmental pollutants.

Development and sexual dimorphism of branchiae in Streblospio benedicti

AbstractThe Spionidae is one of the largest and most studied annelid families, but to date, the development and differentiation of post‐metamorphic anatomy have not been documented. This study used scanning electron microscopy to examine the development of the branchiae, presumed respiratory organs, in Streblospio benedicti. Branchiae in this species are prominent, paired head structures and first appear around the time of metamorphosis, but do not complete their development until the worm reaches the older juvenile or adult stages. We observed that as the branchiae grew, their overall morphology changed through four different shapes: small bud, tubular, tapered, and, finally, bilimbate. In addition, the abfrontal and frontal surfaces each possessed a unique set of cilia patterns, which we named, and these arose in a particular sequence between the 8‐ and 35‐chaetiger stages. This detailed examination of every stage of branchial development led us to discover that branchia in Streblospio benedicti was a sexually dimorphic organ. Streblospio benedicti is one of approximately eight Spionidae in which there is any type of structural sexual dimorphism, and it is the only species in which sexually dimorphic branchiae are found. The male's frontal surface had four unique cilia patterns, and we hypothesize that those located around the medial protrusion capture and control the release of the spermatophores. This first documentation of a spionid's branchial developmental sequence revealed that not only is this respiratory organ involved in reproduction, but it significantly differentiates after metamorphosis through adulthood.

Impacts of isolated or mixed Roundup® Original DI and Boral® 500 SC herbicides on the survival and metamorphosis of Melanophryniscus admirabilis tadpoles

The bufonid species Melanophryniscus admirabilis is restricted to a single location in the southern Atlantic Forest, Brazil. Although the site of occurrence of M. admirabilis is covered with native forest and it is not directly exposed to pesticides application, the area is surrounded by agricultural activity. Our objectives were to evaluate possible alterations in morphological parameters (body mass, snout-vent length, and body index), metamorphosis (time to reach Gosner stages 42, 46 and to complete metamorphosis), and survival of M. admirabilis exposed to isolated Roundup® Original DI (R1: 234 and R2: 2340 µg.L−1 of glyphosate) and Boral® 500 SC, (B1: 130 and B2: 980 µg.L−1 of sulfentrazone) or mixed (R1+B1, R2+B1, R1+B2, R2+B2). Spawns of M. admirabilis were collected in natural lakes in the municipality of Arvorezinha and taken to laboratory cultivation. After the tadpoles acquired free swimming, the animals were acclimated for five days and fed ad libitum. The aquariums were contaminated with herbicides on the sixth day of cultivation, and the animals stayed in these aquariums for four days. Afterwards, the tadpoles were transferred to aquariums with clean water and monitored until metamorphosis (Gosner stage 46), when they were weighed, measured (snout-cloacal length) and cryoeuthanized. We observed no alterations in morphological parameters; however, survival was reduced in exposed groups (mortality index: 71 % in R2 and 29–64 % in mixed groups), suggesting energy allocation for metamorphosis at the expense of survival. Boral did not alter metamorphosis time. Roundup isolated and mixed with Boral altered the timing of Gosner stages 42 and 46 and reduced metamorphosis time, suggesting endocrine disruption. Thus, monitoring the presence and limiting the use of these pesticides in the area where M. admirabilis occurs can be crucial for conservation strategies.

Are juveniles full-scale replicas of adults? Evaluation of anuran special locomotion and digging adaptations during and after metamorphosis

Many species of anurans display special mechanical abilities, such as excavation and climbing. The aim of this study is to investigate the development of traits that are associated with these special mechanical abilities, under the hypothesis that these structures attain their configuration during the juvenile stages of development. We examined specimens from four different species of Leptodactylidae and six species of Hylidae. For the digging behavior, we evaluated the progress of calcification in the anterior region of the skulls, as well as the development of the snout-ridge. To assess climbing ability, we examined the ossification rate, the variation in the shape of the phalanx, the progress of the offset angle, and the distance between the terminal phalanx and the penultimate phalange of finger IV. The ossification of the skull and phalanges, along with the development of the snout-ridge, progresses and reaches completion during the juvenile phase of ontogeny, suggesting that at the time of metamorphosis, individuals are not yet full-scale replicas of the adults. The shape and the mechanical characteristics of terminal phalanges are already established by the conclusion of metamorphosis, revealing intriguing distinctions among arboreal species with walking and jumping locomotion.

Marsh frog response to urea fertilizer during the embryonic, larval, and metamorphosis stages: a new perspective into urea toxicity on amphibians.

Amphibian populations are declining worldwide. These declines are caused by a variety of factors, one of which is the use of fertilizers in agriculture. This is especially true for tadpoles, which may develop in fertilizer-polluted agricultural water bodies. Nevertheless, there is little data on the toxicological consequences of fertilizers on amphibians. The goal of this study was to determine the acute and chronic toxicity of urea fertilizer on marsh frogs' (Pelophylax sp.) embryonic, larval, and metamorphic stages. For this purpose, in a static-renewal test, individuals were exposed to twelve nominal concentrations (0 to 15000mg/L) of urea for 122days to determine hatching success, survival, growth, development, and metamorphic traits, as well as histological consequences. Based on the results, at concentrations greater than 500mg/L, no hatching occurred. Survivorship was unaffected for the first 72hours, but it reached 0% on day 26 at concentrations greater than 150mg/L. Survival and development rates decreased significantly in 100 and 150mg/L treatments after a longer duration (day 86). Growth was reduced as well, but it was only significant at 150mg/L. Metamorphosis time and percentage were significantly impacted, but not metamorphosis size. Increased urea fertilizer concentrations had significant histopathological consequences for the skin, gills, liver, kidneys, and striated muscles. Our results suggest that urea fertilizer, at concentrations commonly found in agroecosystems, may pose a serious threat to temperate anuran species inhabiting these conditions.

Developmental Plasticity in Anurans: Meta-analysis Reveals Effects of Larval Environments on Size at Metamorphosis And Timing of Metamorphosis.

Many anuran amphibians (frogs and toads) rely on aquatic habitats during their larval stage. The quality of this environment can significantly impact the overall lifetime fitness and dynamics of the population. Over 450 studies have been published on the impact of the environment on anuran developmental plasticity, yet we lack a synthesis of these effects across different environments. We conducted a meta-analysis and used a comparative approach to understand whether developmental plasticity in response to different larval environments produces predictable changes in metamorphic phenotypes. We analyzed data from 124 studies spanning 80 anuran species and six larval environments and showed that interspecific variation in mass at metamorphosis and the duration of the larval period are partly explained by the type of environment experienced during the larval period. Phylogenetic relationships among species were not associated with variation in mass at metamorphosis plasticity or duration of the larval period plasticity. Larval environments tended to reduce mass at metamorphosis relative to control conditions, with the degree of change depending on the identity and severity of environmental change. Higher temperatures and lower water levels shortened the duration of the larval period, whereas less food and higher densities increased the duration of the larval period. Our results provide a foundation for future studies on developmental plasticity, especially in response to global changes. This study provides motivation for additional work that links developmental plasticity with fitness consequences within and across life stages, as well as how the outcomes described here are altered in compounding environments.

Determining spatiotemporal trends in hatch and metamorphosis timing of young-of-year southern flounder Paralichthys lethostigma) in Texas bays

It is important to monitor spatiotemporal shifts in the timing of key life history events (i.e., hatch and metamorphosis) since these can influence larval survival and juvenile recruitment success. We use otolith microstructure analysis to examine spatiotemporal trends in hatch and metamorphosis timing of a widespread and economically-valuable finfish, southern flounder Paralichthys lethostigma, in Texas. We use linear regressions that predict otolith-based age from length for young-of-year (YOY) individuals caught coastwide from 2019 to 2021 to calculate hatch and metamorphosis dates of YOY individuals caught coastwide across a 39-yr time series from 1980 to 2018. Also, we use YOY hatchery-reared individuals to indirectly validate the association between otolith accessory growth centers and larval metamorphosis. Our analysis reveals that on the middle coast average hatch timing is shifting toward earlier in the year across the 39-yr time series. In contrast, we find that coastwide, and especially on the middle coast, average metamorphosis timing is shifting toward later in the year across the 39-yr time series. On average, YOY individuals show similar hatch and metamorphosis timing coastwide. We find that on the middle coast and across the 39-yr time series, higher maximum water temperature correlates with earlier average hatch timing. In contrast, we find that coastwide, and especially on the lower and middle coast, higher average water temperature (later years in time series) correlates with later average metamorphosis timing across the 39-yr time series. Fishery-independent monitoring shows no concurrent evidence of individuals emigrating earlier in the fall to spawn offshore. We interpret the spatiotemporal trends in average hatch and metamorphosis timing as evidence of a narrowing survival window where (1) individuals caught on the middle coast that hatch earlier experience higher survival during years with higher maximum water temperature and (2) individuals caught coastwide that metamorphose later experience higher survival during years with higher average water temperature (later years in time series). We highlight the ecological and management implications of the impact of water temperature on hatch and metamorphosis timing and in turn, larval survival and juvenile recruitment success.

Larval Life History of Coastal Tailed Frogs (Ascaphus truei) Across an Elevational Gradient in Northern California: Implications for a Changing Climate

Coastal Tailed Frogs (Ascaphus truei) range across the Pacific Northwest from northern California, USA, into British Columbia, Canada, and from sea level to >2,131 m. Previous work has shown a variable larval period but has not clearly separated elevational from latitudinal effects. Therefore, we examined size at beginning of metamorphosis, larval period, individual growth rates, and timing of metamorphosis of A. truei populations along an elevational gradient from 152 to 2,131 m across a small latitudinal range (29 km) to reduce potential latitudinal effects, all within the Klamath Mountains of northern California. We sampled larvae at 15 study sites, of which we used 6 sites as intensive capture–mark–recapture (CMR) locations, and the other 9 for supplemental data on larval period and size at metamorphosis. In CMR sites, we individually marked tadpoles to determine within-season growth rates. We found that the A. truei larval period in these populations ranges from 2 yr in low and middle elevations to ‡3 yr in high-elevation populations. We also found decreased size at beginning of metamorphosis and increased growth rates of tadpoles with increasing elevation. Our high-elevation populations had the longest larval period documented in California. The associations of growth and timing of metamorphosis to elevation in A. truei populations suggest that responses to changing climate may differ across elevations.

Phenotypic Plasticity in Juvenile Frogs That Experienced Predation Pressure as Tadpoles Does Not Alter Their Locomotory Performance

Anuran species can respond to environmental changes via phenotypic plasticity, which can also result in ecological impacts across the life history of such species. We investigated the effects of predation pressure (i.e., the non-consumption effect) from the dragonfly larva (Anax parthenope) on the phenotypical change of tadpoles into juvenile frogs (specifically the black-spotted pond frog, Pelophylax nigromaculatus), and also analyzed the impact of morphological changes on locomotory performance after metamorphosis. The experiments on predator impact were conducted in the laboratory. Body length, weight, development timing, and metamorphosis timing in the presence of dragonfly nymphs were measured in both tadpoles and juvenile frogs. The body and tail shapes of the tadpoles, as well as the skeletal shape of the juvenile frogs, were analyzed using landmark-based geometric morphometrics. Furthermore, the locomotory performance of the juvenile frogs was tested by measuring their jumping and swimming speeds. Tadpoles that had grown with predators possessed smaller bodies, deeper tail fins, and slower development rates, and they waited longer periods of time before commencing metamorphosis. Having said this, however, the effect of predator cues on the body length and weight of juvenile frogs was not found to be significant. These juvenile frogs possessed longer limbs and narrower skulls, with subtle morphological changes in the pelvis and ilium, but there was no subsequent difference in their swimming and jumping speeds. Our results showed that the changes in anatomical traits that can affect locomotor performance are so subtle that they do not affect the jumping or swimming speeds. Therefore, we support the view that these morphological changes are thus by-products of an altered tadpole period, rather than an adaptive response to predator-escape ability or to post-metamorphosis life history. On the other hand, delayed metamorphosis, without an increase in body size, may still be disadvantageous to the reproduction, growth, and survival of frogs in their life history following metamorphosis.

ANOVA of Cerium Chloride on Morphology and Metamorphosis Development in Tadpoles of C. melanogaster

In this experiment, the effects of 0.004 mg·L-1, 0.02 mg·L-1, 0.1 mg·L-1, and 0.5 mg·L-1 cerium chloride solutions on the growth and metamorphosis development of the tadpoles of the black spotted frog were investigated. The experimental results showed that cerium chloride solution at 0.5 mg·L-1significantly reduced the survival rate of tadpoles, which was 6.67% at 168h (7d) in the 0.5 mg·L-1 treatment compared with 93.3% in the blank control (lake water). The growth condition (body weight) at 168h (7d) (0.56 g) was different from that of the blank control (lake water) tadpoles (The growth (mass) of tadpoles at 0.5 mg·L-1 slowed down significantly in early development compared to the blank control (lake water) tadpoles (0.67g ± 0.05g); at the same time, we noticed that the tadpoles at 0.5 mg·L-1 concentration were in a dormant state of growth, and the mass was not significantly different compared to the beginning of the experiment. The metamorphosis time of tadpoles in the high concentration of cerium chloride salt solution (31 ± 5 days) was greater than that of the blank control tadpoles (26 ± 3 days). Tadpoles at concentrations of 0.02 mg·L-1, 0.1 mg·L-1, and 0.5 mg·L-1 were significantly heavier than the blank control tadpoles at metamorphosis. The results of this experiment indicated that moderate concentration levels of cerium chloride (0.004 mg·L-1, 0.02 mg·L-1) could significantly accelerate the growth and promote the metamorphosis development of the tadpoles of C. melanogaster.

Integrating morphology and physiology of the key endocrine organ during tadpole development: The interrenal gland

Indirect development is widespread in anurans and is considered an ancestral condition. The metamorphosis of larvae into juveniles involves highly coordinated morphological, physiological, biochemical, and behavioral changes, promoted by the thyroid hormone and interrenal corticosteroids. Stress response to environmental changes is also mediated by corticosteroids, affecting the timing and rate of metamorphosis and leading to great developmental plasticity in tadpoles. Given the potential effect of interrenal gland ontogeny alterations on metamorphosis and the lack of studies addressing both the morphology and endocrinology of this gland in tadpoles, we present corticosterone (CORT) production and histological changes through the ontogeny of interrenal gland in the generalized pond-type tadpole of Rhinella arenarum (Anura, Bufonidae). This species shows the highest concentration of whole-body CORT by the early climax when drastic metamorphic changes begin. This is coincident with the morphological differentiation of steroidogenic cells and the formation of interrenal cords. By this stage, steroidogenic cells have a shrunken cytoplasm, with a significantly higher nucleus-to-cell diameter ratio. The lowest CORT concentration during premetamorphosis and late climax is associated with small undifferentiated cells with lipid inclusions surrounding large blood vessels between kidneys, and with cords of differentiated steroidogenic cells with a significantly lower nucleus-to-cell diameter ratio, respectively. Our study characterizes the morphological and physiological pattern of interrenal gland development, showing an association between certain histological and morphometric characteristics and CORT levels. Variations in this morpho-physiological pattern should be considered when studying the phenotypic plasticity or variable growth rates of tadpoles.

Comprehensive assessment of the ecological risk of exposure to triphenyl phosphate in a bioindicator tadpole

The toxicity of triphenyl phosphate (TPhP) to aquatic organisms in surface waters has been demonstrated; However, an understanding of toxicity profiles of TPhP in amphibians is limited. Therefore, the adverse effects and threshold concentrations of TPhP on metamorphosis, growth, locomotion, and hepatic antioxidants of Gosner stage 25 Polypedates megacephalus tadpoles under long-term (35 d) exposure to six TPhP concentrations until complete metamorphosis were assessed. Additionally, the overall effect of using integrated multiple biomarkers were determined to demonstrate the potential ecological risks of waterborne TPhP at environmentally relevant concentrations in amphibian tadpoles. With increasing TPhP concentrations, physical parameters (snout-vent length, body mass, condition factor, and hepatic somatic index), jumping distance, hepatic catalase, and superoxide dismutase activities decreased, whereas metamorphosis time and malondialdehyde content increased. The threshold concentration of TPhP that affected the tadpole biomarker, except for metamorphosis rate and jumping distance, was 50–400 μg/L. Furthermore, the standardized scores of the examined integrated biomarkers in the six TPhP concentrations were visualized using radar plots and calculated as the integrated biomarker responses (IBRs). The varying TPhP concentrations had different scores in the radar plots, and the threshold for affecting the IBR value was 10 μg/L, which was close to the TPhP concentration in surface waters. Additionally, IBR values were strongly positively correlated with the TPhP concentrations. These findings indicate that environmentally relevant exposure to waterborne TPhP can pose an ecological risk to amphibian tadpoles. This study can serve as a reference and assist in the formulation of relevant policies and strategies to control TPhP pollution in water bodies.