Exploring Antipredator Mechanisms: New Findings in Ceratophryid Tadpoles

Recovery of Ceratophrys ornata tadpoles exposed to environmental concentrations of chlorpyrifos: evaluation of biomarkers of exposure

Chlorpyrifos (CPF) is one of the most widely used insecticides worldwide despite the fact that many authors have warned about its effects in non-target biota. The effects of CPF on anurans are well known, but the process of recovery from these effects after exposure is less explored. The aim of this study was to evaluate the duration of sublethal effects induced by environmental concentrations of CPF on Ceratophrys ornata tadpoles after exposure. The experimental design consisted of an exposure phase (96 h) in which tadpoles were individually exposed to three concentrations of CPF (0, 0.01 and 0.02 mg CPF/L) and a post-exposure phase (72 h) in which exposed tadpoles were transferred to CPF-free media. Individuals that survived the exposure phase to CPF showed neither long-term lethal effects nor long-term swimming alterations and altered prey consumption after being transferred to CPF-free media. No morphological abnormalities were observed either. However, at the end of both phases, tadpoles emitted shorter sounds with a higher dominant frequency than the tadpoles in the control group, i.e., the tadpoles did not recover their normal sounds. Thus, for the first time in this species, we have shown that effects on sounds should be prioritized as biomarkers of exposure, as they not only provide longer detection times after cessation of exposure, but also involve non-destructive methods. The following order of priority could be established for the selection of biomarkers that diagnose the health status of individuals and precede irreversible responses such as mortality: alterations in sounds > swimming alterations > prey consumption.

Disruptive effects of chlorpyrifos on predator-prey interactions of Ceratophrys ornata tadpoles: Consequences at the population level using computational modeling

Large-scale ecotoxicological studies have technical and ethical limitations, both related to the need to expose large numbers of individuals to potentially harmful compounds. The computational modeling is a complementary useful and predictive tool that overcomes these limitations. Considering the increasing interest in the effects of pesticides on behavioral traits, the aim of this study was to evaluate the effects of chlorpyrifos (CPF) on intra- and inter-specific interactions of anuran tadpoles, complementing traditional ecotoxicological tools with a theoretical analysis verified by computational simulations. Experiments were developed under two consecutive phases: a first phase of exposure (treated and control group), and a second phase of interactions. The second phase consisted of evaluating the effects of CPF on intra- and inter-specific interactions of exposed C. ornata (Co) tadpoles acting as predators and unexposed Rhinella fernandezae (Rf) tadpoles acting as prey (Experiment I), under different predator-prey proportions (0/10 = 0Co-10Rf, 2/8, 4/6, 6/4, 8/2, 10/0). Also, intraspecific interactions of three Co tadpoles under different conditions of exposure were evaluated (Experiment II: 3 exposed Co, 2 exposed Co/1 non-exposed, 1 exposed Co/2 non-exposed). During the exposure phase, chlorpyrifos induced significant mortality from 48 h (48 h: p < 0.05, 72 h-96 h: p < 0.001), irregular swimming, tail flexure, and the presence of subcutaneous air. Also, it induced effects on the sounds emitted after 96 h of exposure, registering a smaller number of pulses and higher dominant frequencies, and altered intra- and inter-specific interactions. During the interaction phase, the larvae continued to show sound effects, however, the antipredator mechanism continued to be operating and efficient. Finally, it was possible to model the behavior of the larvae under the effects of chlorpyrifos. We conclude that experimental data and computational modeling matched. Therefore, computational simulation is a valuable ecotoxicological tool that provides new information and allows prediction of natural processes.

Amphibian Assisted Reproductive Technologies: Moving from Technology to Application

Amphibians have experienced a catastrophic decline since the 1980s driven by disease, habitat loss, and impacts of invasive species and face ongoing threats from climate change. About 40% of extant amphibians are under threat of extinction and about 200 species have disappeared completely. Reproductive technologies and biobanking of cryopreserved materials offer technologies that could increase the efficiency and effectiveness of conservation programs involving management of captive breeding and wild populations through reduced costs, better genetic management and reduced risk of species extinctions. However, there are relatively few examples of applications of these technologies in practice in on-the-ground conservation programs, and no example that we know of where genetic diversity has been restored to a threatened amphibian species in captive breeding or in wild populations using cryopreserved genetic material. This gap in the application of technology to conservation programs needs to be addressed if assisted reproductive technologies (ARTs) and biobanking are to realise their potential in amphibian conservation. We review successful technologies including non-invasive gamete collection, IVF and sperm cryopreservation that work well enough to be applied to many current conservation programs. We consider new advances in technology (vitrification and laser warming) of cryopreservation of aquatic embryos of fish and some marine invertebrates that may help us to overcome factors limiting amphibian oocyte and embryo cryopreservation. Finally, we address two case studies that illustrate the urgent need and the opportunity to implement immediately ARTs, cryopreservation and biobanking to amphibian conservation. These are (1) managing the biosecurity (disease risk) of the frogs of New Guinea which are currently free of chytridiomycosis, but are at high risk (2) the Sehuencas water frog of Bolivia, which until recently had only one known surviving male.

Differential success in obtaining gametes between male and female Australian temperate frogs by hormonal induction: A review

Most Australian frogs fall into two deeply split lineages, conveniently referred to as ground frogs (Myobatrachidae and Limnodynastidae) and tree frogs (Pelodryadidae). Species of both lineages are endangered because of the global chytrid pandemic, and there is increasing interest and research on the endocrine manipulation of reproduction to support the use of assisted reproductive technologies in conservation. Hormonal induction of gamete release in males and females is one such manipulation of the reproductive process. This paper reviews progress in temperate ground and tree frogs towards developing simple and efficient hormonal protocols for induction of spermiation and ovulation, and presents some new data, that together build towards an understanding of advances and obstacles towards progress in this area. We report that protocols for the non-invasive induction of sperm release, relying on single doses of gonadotropin-releasing hormone (GnRH) or human chorionic gonadotropin are very effective in both ground and tree frog species investigated to date. However, we find that, while protocols based on GnRH, and GnRH and dopamine antagonists, are moderately efficient in inducing ovulation in ground frogs, the same cannot be said for the use of such protocols in tree frogs. Although induced ovulation in the pelodryadid tree frogs has not been successfully implemented, and is difficult to explain in terms of the underlying endocrinology, we propose future avenues of investigation to address this problem, particularly the need for a source of purified or recombinant follicle-stimulating hormone and luteinising hormone for species from this group.

Tadpoles of the horned frog Ceratophrys ornata exhibit high sensitivity to chlorpyrifos for conventional ecotoxicological and novel bioacoustic variables

Previous studies reported that some species of the family Ceratophryidae are able to produce sounds during premetamorphic tadpole stages. We have now determined the effects of the cholinesterase-inhibiting insecticide chlorpyrifos (CPF) on sounds emitted by tadpoles of Ceratophrys ornata. Tadpoles were exposed individually in order to evaluate the progression of effects. Effects on sound production were complemented with common ecotoxicological endpoints (mortality, behavior, abnormalities and growth inhibition). C. ornata was found to be more sensitive than other native (= 67%, 50%) and non-native species (= 75%, 100%) considering lethal and sublethal endpoints, respectively. Effects on sounds appear along with alterations in swimming, followed by the presence of mild, then severe abnormalities and finally death. Therefore, sound production may be a good biomarker since it anticipates other endpoints that are also affected by CPF. Ceratophrys ornata is a promising new model species in ecotoxicology.