Reassessment of the environmental model of developmental polyphenism in spadefoot toad tadpoles

Abstract

Polyphenism is the expression of multiple, discrete phenotypes from one genotype, and understanding the environmental factors that trigger development of alternative phenotypes is a critical step toward understanding the evolution of polyphenism and its developmental control. While much is known about the ecology of the well-known carnivore/omnivore polyphenism in spadefoot toad tadpoles, the environmental cues for the development of the specialized carnivore phenotype are not completely clear. We examined 27 different experimental treatments in two spadefoot toad species and used over 1,000 tadpoles in an attempt to elucidate those cues. While only 44 carnivores developed in these treatments, they were concentrated at cooler water temperatures and a diet that included fairy shrimp. However, while a diet of fairy shrimp promoted carnivore development, it was not necessary for inducing carnivore development at lower and intermediate water temperatures. Evidence also suggested a role for social inhibition that limited the proportion of interacting tadpoles that become carnivores. Tadpoles of Spea multiplicata grew larger at cooler temperatures and larger when their diets included fairy shrimp, whereas tadpoles of S. bombifrons grew larger at warmer temperatures and when their diets did not include fairy shrimp. These results indicate that carnivore induction can occur through different cues and that our current model for carnivore development is too limited. Finally, we argue that the carnivore/omnivore spadefoot system is neither a polyphenism nor a polymorphism but is a continuously distributed plasticity.

An inducible offense: carnivore morph tadpoles induced by tadpole carnivory

“…The carnivore morph is environmentally triggered (Pomeroy 1981). Although numerous extrinsic and intrinsic factors contribute to the production of this morph (Pomeroy 1981;Pfennig 1992;Pfennig and Murphy 2000;Storz 2004;Pfennig and Martin 2009;Storz et al 2011), theory predicts the most reliable trigger should be correlated with morph functionality. Consistent with this prediction, previous studies have shown that ingestion of fairy shrimp or conspecificscommon food sources of this morphreliably predicts the carnivore phenotype (Pomeroy 1981;Pfennig 1990).…”

Entomopathogenic fungi stimulate transgenerational wing induction in pea aphids, Acyrthosiphon pisum (Hemiptera: Aphididae)

“…It allows a given genotype to explore multiple habitats and/or at different seasons, and to develop new features whilst preserving the established ones (West‐Eberhard, 1989; Nijhout, 1999). In order to better understand the population dynamics of organisms, it is crucial to observe the environmental cues that trigger phenotypic plasticity (Storz et al , 2011).…”

Predatory cannibalism in Drosophila melanogaster larvae

“…For example, in some anuran tadpoles cannibalism is mediated by morphological plasticity 21,22 and chemical cues 13 , and has an adaptive value in terms of nutrition and reduction of future competition 2 . In highly gregarious locusts and crickets cannibalism is an important source of protein and salts, which allows the cannibals to survive longer and migrate farther; cannibalism avoidance is an important factor driving their mass migrations 5,7 .…”