Responses on morphology and development in tadpoles of Physalaemus santafecinus exposed to chemical cues of predators.

GÓMEZ, VALERIA I.; KEHR, ARTURO I.

Curitiba

Congreso; IX Congreso Latinoamericano de Herpetología y V Congreso Brasilero de Herpetología.; 2011

Asociación Brasilera de Herpetología

Many prey species, especially in aquatic environments, use chemical cues produced during predation events to estimate predation risk, therefore several antipredator responses are mediated or induced by the prey’s capacity to identify chemical cues from predators. The presence of chemicals from predators maybe provide reliable information concerning its presence to tadpoles, thus, a higher response to alarm cues or predator presence may increase prey survival possibilities. Although many predators can decrease prey abundance, predator consequence on prey survival can be adjusted through a very ample kind of tactics employed by prey. Such strategies include morphological change, modification of behavioral responses and alteration on time of life-history and these adjustments can have very influences on juvenile performance, through size-dependent consequences. In this study we examined responses in morphology (body length, tail length, body depth, tail depth, and muscle tail depth), growth and development rate of Physalaemus santafecinus tadpoles raised in presence of chemical cues from predators: water beetles (Hydrophillidae) and fish (Characidae). Our main goal was determine is tadpoles of P. santafecinus, can use chemical cues from predators, fish and water beetles, to adjust their morphology and growth rate in response to the perceived predation risk. Also we registered the time to tadpoles taken to reach metamorphosis, and the weight of metamorphic individuals to determine if exist shifts in the timing of life-history events, like acceleration of larval stages. The experiment was performed under microcosm conditions. The experimental design consisted of three treatments: chemical cues from fish, from water beetles and a control group. Each treatment was replicated thirty times. Each container held a single larva in order to obtain independent data from different variables. Main results were: 1) tadpoles morphology was significantly affected by predator presence, there were significant differences for all morphological variables between either predator treatment and a control group (MANCOVA Wilks’s Lambda = 0.560; F10, 150 = 5.051; p < 0.001) 2) there were not significant differences in growth rate for any treatment (ANOVA F2, 80 = 0.349; p = 0.707) 3) there were not significant differences in development rate for any treatment (Kruskal Wallis = 5.991; df = 2; p = 0.163) and 4) there were not significant differences in time to metamorphosis and weight of metamorphic individuals (MANOVA Wilk`s Lambda = 0.950; F2, 34 = 0.886; p = 0.422) Our results suggest that tadpoles are able to perceive predators by chemical cues released in the water, and P. santafecinus tadpoles alter their morphology to chemical cues that indicate predation. In this study we observed that, although the tadpoles exposed to chemical cues of predators presented a mean value lower than control treatments, they reach the same weigh and development stage at the same time. Furthermore, they were not either significant difference in time to metamorphosis or mass on metamorphic individuals. Maybe, this can be result of a selective increase in development rate which produce that all tadpoles do not have the same development rate, therefore there is no difference in mean values between treatments.