The following article is adapted from a talk presented by Jaime Heiniger at SICB 2012, along with coauthors Billy Van Uitregt and Robbie Wilson. The original talk was called: "Fine tuning anti-predator responses: are the costs of inducible predator defences proportional to the magnitude of the responses?"
***
For amphibians, it's a mad, mad world. And - importantly - an unpredictable one. Natal pools might contain predators, or not; competitors, or not; food, or not; and conditions can change every day. As a result of all this unpredictability, many amphibians can alter their appearance and behaviour in ways that increase their likelihood of survival. But these defensive strategies usually come at a cost - slower growth, higher metabolic requirements, and smaller size at maturation are just a few common outcomes.
To maximise the benefits and minimise the costs associated with predator defense, it's predicted that the magnitude of the defensive response should reflect the magnitude of the threat. Thus, more threat = more phenotypic change; and less threat = less phenotypic change. This is known as the threat-sensitive predator avoidance hypothesis (TSPAH), and although it's known that prey can fine-tune their responses to the degree of predation risk, it's unclear if the magnitude of threat-sensitive defensive responses relate to their associated costs.
{Jaime} tested this idea by examining the effects of increases in perceived predation risk on the expression of defences and their associated costs in larvae of the toad, Bufo marinus. She reared tadpoles in varying concentrations of predation cue* and quantified their growth, morphology and development, as well as metamorphic size, locomotor performance and oxygen consumption.
*for those curious, predation cue is actually water from around deceased tadpoles. Tadpoles are sensitive to the smell of their dead mates. (Aren't we all?)
{Jaime} found that tadpoles responded to increases in perceived predation risk by gradually decreasing their activity.
As a consequence of their more-sedentary lifestyle, individuals metamorphosed later, smaller and with reduced endurance. Toads that emerged from the different treatments didn't vary in maximum jumping distance but those from 'high predation' treatments metamorphosed with longer relative hind limbs - meaning they could jump farther for their body size.
These are interesting results, because they show that
a) toads produce defenses that are proportional to the perceived threat
b) defensive behaviour is costly
c) the costs are in proportion to the amount of defense
d) but phenotypes produced in response to predation threat may aid the individual.
Cool stuff, Jaime!
***
For amphibians, it's a mad, mad world. And - importantly - an unpredictable one. Natal pools might contain predators, or not; competitors, or not; food, or not; and conditions can change every day. As a result of all this unpredictability, many amphibians can alter their appearance and behaviour in ways that increase their likelihood of survival. But these defensive strategies usually come at a cost - slower growth, higher metabolic requirements, and smaller size at maturation are just a few common outcomes.
 |
| toadlets in the lab |
To maximise the benefits and minimise the costs associated with predator defense, it's predicted that the magnitude of the defensive response should reflect the magnitude of the threat. Thus, more threat = more phenotypic change; and less threat = less phenotypic change. This is known as the threat-sensitive predator avoidance hypothesis (TSPAH), and although it's known that prey can fine-tune their responses to the degree of predation risk, it's unclear if the magnitude of threat-sensitive defensive responses relate to their associated costs.
{Jaime} tested this idea by examining the effects of increases in perceived predation risk on the expression of defences and their associated costs in larvae of the toad, Bufo marinus. She reared tadpoles in varying concentrations of predation cue* and quantified their growth, morphology and development, as well as metamorphic size, locomotor performance and oxygen consumption.
*for those curious, predation cue is actually water from around deceased tadpoles. Tadpoles are sensitive to the smell of their dead mates. (Aren't we all?)
 |
| taddies in the lab |
{Jaime} found that tadpoles responded to increases in perceived predation risk by gradually decreasing their activity.
As a consequence of their more-sedentary lifestyle, individuals metamorphosed later, smaller and with reduced endurance. Toads that emerged from the different treatments didn't vary in maximum jumping distance but those from 'high predation' treatments metamorphosed with longer relative hind limbs - meaning they could jump farther for their body size.
 |
| jaime's metamorph habitats |
These are interesting results, because they show that
a) toads produce defenses that are proportional to the perceived threat
b) defensive behaviour is costly
c) the costs are in proportion to the amount of defense
d) but phenotypes produced in response to predation threat may aid the individual.
Cool stuff, Jaime!