Functional mechanisms of an inducible defence in tadpoles: morphology and behaviour influence mortality risk from predation

Abstract

In many amphibian larvae a suite of morphological and behavioural characters varies together in an induced defence against predators, but it remains unclear which features are functionally related to defence. We independently manipulated behaviour and morphology in tadpoles of Hyla versicolor and assessed their consequences for swimming performance and predator escape. Data on burst swimming showed that tadpoles which accelerated rapidly were elongate, with shallow bodies and tails. Predator escape was measured by exposing tadpoles to predators (larval Anax dragonflies or larval Ambystoma salamanders) and recording time until death. Tadpoles were first reared for 30 days in ponds containing either caged Anax or no predators; individuals responded to predators by developing large brightly coloured tails and short bodies. We placed tadpoles of both morphological phenotypes into plastic tubs, and manipulated their behaviour using food and chemical cues from predators. Mortality risk experienced by the predator‐induced phenotype was about half that of the no‐predator phenotype, and risk increased with time spent swimming. An interaction between morphology and behaviour arose because increasing activity caused higher risk for tadpoles with deep tail fins but not shallow tail fins.

Ecological consequences of phenotypic plasticity

“…Phenotypic plasticity in frog larvae Frog tadpoles are an effective system for exploring the ecology of phenotypic plasticity. Frequently, predators induce tadpoles to reduce their foraging activity, which reduces detection by predators [62]. Predators also induce relatively larger tails and smaller bodies in tadpoles ( Figure I) [62], which reduce capture by predators [63] owing to faster swimming abilities and because a large tail lures predator strikes away from the vulnerable body [64].…”

“…Frequently, predators induce tadpoles to reduce their foraging activity, which reduces detection by predators [62]. Predators also induce relatively larger tails and smaller bodies in tadpoles ( Figure I) [62], which reduce capture by predators [63] owing to faster swimming abilities and because a large tail lures predator strikes away from the vulnerable body [64]. However, both defenses come at the cost of slower growth [65], because predatorinduced tadpoles have smaller mouthparts [66] and shorter, less efficient intestines, and spend less time foraging [67].…”

Locomotion and survival of two sympatric larval anurans, Bufo gargarizans (Anura: Bufonidae) and Rana zhenhaiensis (Anura: Ranidae), after partial tail loss

“…However, other studies have shown that tadpoles usually do not have a chance to generate defensive responses (ZOTTOLI et al 2001) or increase their swimming speed before being attacked by an aquatic predator ( VAN BUSKIRK & MCCOLLUM 2000a, LUQUET et al 2011. Experimental manipulations of tadpoles with tail damage have revealed that swimming performance is affected only after large tail segments are removed (HOFF & WASSERSUG 2000, VAN BUSKIRK & MCCOLLUM 2000b).…”

“…A high level of tail damage was found by BLAIR & WASSERSUG (2000) in a wild population of tadpoles. Tail damage in tadpoles can be caused by vertebrates, such as fish, turtles and salamanders, and by invertebrates, such as crayfish and dragonfly larvae (WILBUR & COLLINS 1973, CALDWELL et al 1980, VAN BUSKIRK & MCCOLLUM 2000a, VAN BUSKIRK et al 2003, WILSON et al 2005.…”

“…According to some studies, larger tails not only improve the swimming performance of tadpoles, but they also help tadpoles to escape from aquatic predators by allowing them to turn suddenly and burst their speed (SMITH & VAN BUSKIRK 1995, VAN BUSKIRK & MCCOLLUM 2000b, TEPLITSKY et al 2005, ARENDT 2010. However, other studies have shown that tadpoles usually do not have a chance to generate defensive responses (ZOTTOLI et al 2001) or increase their swimming speed before being attacked by an aquatic predator ( VAN BUSKIRK & MCCOLLUM 2000a, LUQUET et al 2011.…”