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- Teplitsky, Celine, et al.
(author)
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Adaptive plasticity in stressful environments : Acidity constrains inducible defences in Rana arvalis
- 2007
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In: Evolutionary Ecology Research. - 1522-0613 .- 1937-3791. ; 9:3, s. 447-458
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Journal article (peer-reviewed)abstract
- Questions: How do environmental stressors affect the expression of adaptive phenotypicplasticity? Is there inter-population variation in these effects? Hypothesis: Acid stress constrains the expression of inducible defences by decreasinginvestment in defences or by increasing the costs of investment. Organisms originating fromneutral environments suffer more from acid stress than organisms originating from acidenvironments. Organism: Tadpoles of Rana arvalis, originating from two different populations (acid andneutral). This species displays inducible defences in response to insect predators (here dragonflylarvae). Methods: A laboratory experiment with a factorial design crossing two factors: predatorpresence (present vs. absent) and acidity (neutral vs. acid). We tested the effects of experimentaltreatment on tadpole morphology as well as age and size at metamorphosis. Results: Tadpoles from the neutral origin population invested less in inducible defences (tailfin depth) in the acid than in the neutral treatment. In contrast, tadpoles from the acid originpopulation were able to respond equally well to predators in both pH treatments. pH-relatedcosts differed between populations: while tadpoles from the neutral origin population sufferedfrom acid stress in terms of reduced developmental rate, those from the acid origin populationseemed to suffer from neutral stress in terms of reduced size at metamorphosis.
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- Teplitsky, Céline, et al.
(author)
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Flexible defense strategies : competition modifies investment in behavioral vs. morphological defenses
- 2007
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In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 88:7, s. 1641-1646
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Journal article (peer-reviewed)abstract
- Competition is predicted to affect the expression of inducible defenses, but because costs of behavioral and morphological antipredator defenses differ along resource gradients, its effects on defenses may depend on the traits considered. We tested the predictions from different defense models in tadpoles of the common frog Rana temporaria, which exhibit both types of defenses. In an outdoor experiment, we exposed the tadpoles to nonlethal predators (Aeshna dragonfly larvae) and to a gradient of intraspecific competition. Morphological responses did not follow any of the expected patterns, since investment in defense was not affected by resource level. Instead, tail depth decreased in the absence of predators. Behavioral defenses followed a state-dependent model. Overall, the defense strategy of the tadpoles revealed a shift from morphological and behavioral defenses at low tadpole density to morphological defense only at high density. This difference probably reflects the different efficiency of the defenses. Hiding is an effective means of defense, but it is unsustainable when resources are scarce. Morphological responses become more important with increasing density to compensate for the increase in behavioral risk-taking. Our results indicate that competition can strongly affect reaction norms of inducible defenses and highlight the importance of integrating ecological parameters that affect the cost–benefit balance of phenotypic plasticity.
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