Objective 1. Quantify the differences in life history between the two species.

Locomotor activity

A primary goal of ecology is to understand the processes governing species coexistence and how species are assembled into communities. Stable coexistence requires competitors to differ in their niches, and species that are too ecologically similar cannot coexist (limiting similarity). The spadefoot toads from Dobrudja provide a very interesting study-case: the ranges of two species of the genus overlap at the limit of their distribution ranges - southern limit for P. fuscus and northern limit for P. syriacus. Both spadefoot toad species are nocturnal, fossorial, and exploit a similar ecological niche. They both have similar size at metamorphosis, reach sexual maturity at a similar age but P. syriacus becomes significantly larger than P. fuscus.

Any movement carries potential costs for amphibians, including energetic costs, exposure to predation and exposure to drought or other unfavorable climatic conditions. On the other hand, increased locomotor activity may be the only way to maximize access to food. Considering these aspects, we examined the adaptive value of interspecific variation in behavioural patterns, such as level of activity (locomotor behaviour).

The nocturnal activity of adult P. fuscus and P. syriacus individuals is monitored in a laboratory setting. By using webcams we are able to capture time-lapse photographs of the toads' movement, which then is used to obtain tracks for each individual. A measure of overall locomotor activity is derived by summing the magnitude of the displacements between pairs of consecutive images for each individual on each night of recording. These individual sums are subsequently expressed as the average distance moved in cm per minute.

Our  preliminary results suggests that P. syriacus is significantly more active than P. fuscus with almost 2.5 overall distance covered and more than twice the speed achieved, but with approximately the same time spent outside burrows. This seems to indicate that the closely related Pelobates species from Dobrudja differ in patterns of foraging behaviour, P. fuscus being relatively sedentary (‘sit-and-wait’) whereas P. syriacus is more an active (‘widely-foraging’) predator.

Acoustic communication

We aim to identify and characterize patterns and differences in the acoustic repertoire of the two species of spadefoot toads (genus Pelobates) in order to understand the role of calling pattern in their evolution. At least three types of calls have been described: release, mating and distress. We are looking for (i) interpopulation variation, (ii) interspecific differences, and (iii) general patterns that might be explained based on the phylogenetic relationships and evolution of this lineage. The detailed characterization of calls and compared analyses may offer interesting insights over the ethology of these species and reveal some of the evolutionary implications of communication mechanisms within this genus.

Recordings are made with a Marantz PMD660 portable solid state recorder equipped with a Sennheiser microphone. Water and air temperature, humidity and recording distance are also measured. Sound processing (e.g. background noise removal) and analysis are performed using Raven Pro 1.4 software (The Cornell Lab of Ornithology; http://www.birds.cornell.edu/raven).

Copyright 2011-2018. Facultatea de Științe ale Naturii și Științe Agricole - Universitatea Ovidius Constanța.

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