Microplastics (MPs) are nowadays abundant, persistent, and ubiquitous in the environment, representing a new threat for terrestrial, marine, and freshwater ecosystems. Although anuran populations and ...species are globally declining, the effect of MP exposure on this taxon has been poorly investigated. With the aim of assessing the effects of microplastic exposure on the defensive responses of Italian agile frog (
Rana latastei
) tadpoles, we exposed them to three different concentrations (1, 7, and 50 mg L
−1
) of a mixture of plastic polymers (HPDE, PVC, PS, and PES) for 2 weeks. Then, we measured the total distance covered by individual tadpoles before and after exposure to tadpole-fed dragonfly larvae (
Aeshna cyanea
) cues. As expected, predation risk sharply lowered the total distance travelled by tadpoles; however, MP concentration did not affect their defensive performances. We also collected data on tadpole development, activity, and mortality. In contrast with previous experiments, neither tadpole growth nor mortality varied with MP concentration. Our results indicate that the intensity of MP effects on growth and development may depend on tadpole size, with large tadpoles being less susceptible to the negative effects of MP exposure.
Prey species must constantly acquire information on predator identity, abundance and dangerousness from the environment. In aquatic habitats, this information is mainly propagated by water‐borne ...chemical signals, either predator‐specific odours or prey alarm cues. Anuran larvae innately respond to conspecific alarm cues and are able to associate them to predator cues during their lifetime. In this study, we investigated the anti‐predatory responses of endemic Italian agile frog (Rana latastei) tadpoles exposed to either conspecific or heterospecific alarm cues and a native predator's (Anax imperator larvae) odour. Pre‐and post‐stimulus behaviours of each tadpole were recorded by a digital camera and analysed by a source executable software for image‐based tracking. We found that Italian agile frog tadpoles responded to fasted dragonfly odour by strongly reducing their activity, both in terms of the amount of time they spent active and path length covered in comparison to control groups. Contrary to previous studies, predators' diet had a negligible effect on tadpole response and our experiment did not bring any evidence of the phylogenetic‐relatedness hypothesis. The innate or early‐in‐development recognition of dragonfly larvae is clearly adaptive and may increase tadpole survival with relatively low costs, but, at the same time, may increase the risk of ignoring novel potential threats.
Trajectory of a single tadpole from control (below, grey patch) and Italian agile frog fed predator (IAF, yellow patch above) groups. Plots represent the schedule used in the experiment: 5 min of pre‐stimulus video recording, injection of olfactory cues and 5 min post‐stimulus video recording. Trajectories were obtained using R package trajr (McLean & Volponi, 2018).
We monitored egg clutch numbers of a population of the endemic Italian agile frog Rana latastei in a Site of Community Interest in northern Italy (SCI IT 209000) during 1997–2017 with the aim of ...assessing the long-term variation in its abundance. We walked along the banks of canals and small ponds (n = 22) 1–3 times per week between early February and mid-April each year to detect egg clutches. The relationships between the start of the breeding season, yearly egg mass counts, rate of yearly change in the number of recorded egg masses and 15 climatic and environmental variables were assessed by multiple regression. The first deposition of eggs occurred progressively later in the year throughout the study period and mean air temperature during the breeding season decreased over this period. Agile frogs showed high deposition site-fidelity. Despite large variations in the number of egg clutches detected from year to year, the population size remained stable in the long term. Peaks in the number of egg clutches occurred 2 years after the dredging of canals, carried out every 4–6 years to improve water availability, starting in 2004 as part of a LIFE Nature Project. This was the only predictor of the number of egg clutches deposited, suggesting that periodical management is needed to support the agile frog population. Our results reinforce the need for multi-year monitoring to determine both the long-term success of habitat restoration projects and the status of residual populations.
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