Ammonium effects on oxidative stress, telomere length, and locomotion across life stages of an anuran from habitats with contrasting land-use histories

Effects of larval foam-making and prolonged terrestriality on morphology, nitrogen excretion and development to metamorphosis in a Leptodactylid frog

At ontogenetic transitions, animals often exhibit plastic variation in development, behavior and physiology in response to environmental conditions. Most terrestrial-breeding frogs have aquatic larval periods. Some species can extend their initial terrestrial period, as either a plastic embryonic response to balance trade-offs across environments or an enforced wait for rain that allows larvae to access aquatic habitats. Terrestrial larvae of the foam-nesting frog, Leptodactylus fragilis, can arrest development, make their own nest foam to prevent dehydration, and synthesize urea to avoid ammonia toxicity. These plastic responses enable survival during unpredictably long periods in underground nest chambers, waiting for floods to enable exit and continued development in water. However, such physiological and behavioral responses may have immediate and long-term carry-over effects across subsequent ecological and developmental transitions. We examined effects of prolonged terrestriality and larval foam-making activity on larval physiology, development, and metamorphosis in L. fragilis. We tested for changes in foam-making ability by measuring the nests larvae produced following complete removal of parental foam at different ages. We measured ammonia and urea levels in larval foam nests to assess nitrogen excretion patterns, testing for effects of larval age, soil hydration around parental nests, and repeated nest construction. We also assessed immediate and long-term effects of larval foam-making and prolonged terrestriality on larval morphology at water entry and development to metamorphosis. We found that larvae arrested development during prolonged time on land and even young larvae were able to effectively produce multiple foam nests. We found high ammonia concentrations in larval nests, very high urea excretion by developmentally arrested older larvae, and faster growth of larvae in water than while constructing nests. Nonetheless, sibling larvae had a similar aquatic larval period and size at metamorphosis, regardless of their nest-making activity and timing of water entry. Sibship size increased the size of larval foam nests, but reduced per-capita foam production and increased size at metamorphosis, suggesting maternal effects in cooperative groups. Metamorph size also decreased with aquatic larval period. Our results highlight the extent of larval ability to maintain and construct a suitable developmental environment and excrete N-waste as urea, which are both crucial for survival during enforced extensions of terrestriality. Our results suggest that the energetic reserves in large eggs are sufficient to meet metabolic costs of urea synthesis and foam production during developmental arrest over an extended period on land, with no apparent carry-over effects on fitness-relevant traits at metamorphosis.

Telomere dynamics in maturing frogs vary among organs

It is important to know whether organs age at the same rate and are equally affected by developmental conditions as this provides insights into causes of ageing. However, data on organ-specific telomere dynamics remain scant. In a previous study of the early life of the amphibian Xenopus laevis, we detected changes in telomere lengths in gut cells, while liver, heart and muscle telomeres were unchanged; larval rearing temperature had minimal effects. Here, we extend that study to examine telomere dynamics in the same four organs and larval temperature treatments from 70-day post-metamorphic juvenile Xenopus through to sexually mature (2-year-old) adults. Telomeres shortened from juvenile to adult in the gut, heart and hindlimb muscle. In contrast, liver telomere lengths did not change with age but were shorter if the early life temperature was warm. Organ telomere lengths were influenced by sex only in adults. Warmer larval temperatures were also associated with longer gut telomeres in juveniles. Hence, pre-metamorphic conditions can influence post-metamorphic telomere dynamics, and telomere loss between juvenile and adult life stages occurs in different organs from those affected earlier in life. These findings indicate the existence of organ-dependent ageing rates across lifetimes, potentially related to developmental and environmental history.

The impact of chemical pollution across major life transitions: a meta-analysis on oxidative stress in amphibians

Among human actions threatening biodiversity, the release of anthropogenic chemical pollutants which have become ubiquitous in the environment, is a major concern. Chemical pollution can induce damage to macromolecules by causing the overproduction of reactive oxygen species, affecting the redox balance of animals. In species undergoing metamorphosis (i.e. the vast majority of the extant animal species), antioxidant responses to chemical pollution may differ between pre- and post-metamorphic stages. Here, we meta-analysed (N = 104 studies, k = 2283 estimates) the impact of chemical pollution on redox balance across the three major amphibian life stages (embryo, tadpole, adult). Before metamorphosis, embryos did not experience any redox change while tadpoles activate their antioxidant pathways and do not show increased oxidative damage from pollutants. Tadpoles may have evolved stronger defences against pollutants to reach post-metamorphic life stages. In contrast, post-metamorphic individuals show only weak antioxidant responses and marked oxidative damage in lipids. The type of pollutant (i.e. organic versus inorganic) has contrasting effects across amphibian life stages. Our findings show a divergent evolution of the redox balance in response to pollutants across life transitions of metamorphosing amphibians, most probably a consequence of differences in the ecological and developmental processes of each life stage.

Carbon nitride dots do not impair the growth, development, and telomere length of tadpoles

Carbon nanoparticles, or carbon dots, can have many beneficial uses. However, we must consider whether they may have any potential negative side effects on wildlife or the ecosystem when these particles end up in wastewater. Early development stages of amphibians are particularly sensitive to contaminants, and exposure to carbon dots could disrupt their development and cause morbidity or death. Past studies have investigated short-term exposure to certain types of nanoparticles, but if these particles get into wastewater exposure may not be short term. Therefore, we tested whether chronic exposure to different concentrations of carbon dots affects the growth, metamorphosis, and telomere length of Cuban tree frog (Osteopilus septentrionalis) tadpoles. We exposed 12 groups of five tadpoles each to different concentrations of carbon dots and a control for three months and tracked survival, growth and metamorphosis. We used carbon nitride dots approximately 2 nm in size at concentrations of 0.01 mg/ml and 0.02 mg/ml, known to interrupt development in zebrafish embryos. After three months, we measured telomere length from tissue samples. We found no difference in tadpole survivorship, growth, development rate, or telomere length among any of the groups, suggesting that carbon dots at these concentrations do not disrupt tadpole development.

Telomere DNA length regulation is influenced by seasonal temperature differences in short-lived but not in long-lived reef-building corals

Telomeres are environment-sensitive regulators of health and aging. Here,we present telomere DNA length analysis of two reef-building coral genera revealing that the long- and short-term water thermal regime is a key driver of between-colony variation across the Pacific Ocean. Notably, there are differences between the two studied genera. The telomere DNA lengths of the short-lived, more stress-sensitive Pocillopora spp. colonies were largely determined by seasonal temperature variation, whereas those of the long-lived, more stress-resistant Porites spp. colonies were insensitive to seasonal patterns, but rather influenced by past thermal anomalies. These results reveal marked differences in telomere DNA length regulation between two evolutionary distant coral genera exhibiting specific life-history traits. We propose that environmentally regulated mechanisms of telomere maintenance are linked to organismal performances, a matter of paramount importance considering the effects of climate change on health.