Abstract
Condition-dependent expression of alternative male morphologies (AMMs) exists in many arthropods. Understanding their coexistence requires answering (at least) two questions: (i) what are the ecological selection pressures that maintain condition-dependent plasticity of AMM expression, and (ii) what maintains the associated genetic variation? Focusing on acarid mites, we show that the questions should not be conflated. We argue how, instead, answers should be sought by testing phenotype-level (question 1) or genotype-level (question 2) hypotheses. We illustrate that energy allocation restrictions and physiological trade-offs are likely to play a crucial role in AMM expression in acarid mites. We thus conclude that these aspects require specific attention in identifying selection pressures maintaining condition-dependent plasticity, and evolutionary processes that maintain genetic variation in condition-dependent phenotypic plasticity.
Highlights
Male secondary sexual traits are often differently expressed depending on nutrition during development [1]
Condition-dependent expression of alternative male morphologies (AMMs) exists in many arthropods. Understanding their coexistence requires answering two questions: (i) what are the ecological selection pressures that maintain condition-dependent plasticity of AMM expression, and (ii) what maintains the associated genetic variation? Focusing on acarid mites, we show that the questions should not be conflated
In many arthropods, such condition-dependent plasticity leads to male dimorphism [2,3,4], with ensuing within-population male morph coexistence having evolved multiple times
Summary
Male secondary sexual traits are often differently expressed depending on nutrition during development [1]. Critical resource or body size thresholds underlying alternative male morph (AMM) expression can evolve rapidly in response to artificial selection (acarid mites [11,12,13]) or after introduction to novel environments (dung beetles [14]; earwigs [15]; acarid mites [11]). (b) The first question — what are the ecological selection pressures that maintain condition-dependent plasticity and that set the threshold for AMM expression — can be tested using two, non-mutually exclusive hypotheses.
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