Abstract
Although comprehending the significance of phenotypic plasticity for evolution is of major interest in biology, the pre-requirement for that, the understanding of variance in plasticity, is still in its infancy. Most researchers assess plastic traits at single developmental stages and pool results between sexes. Here, we study variation among sexes and developmental stages in inducible morphological defences, a well-known instance of plasticity. We raised fathead minnows, Pimephales promelas, under different levels of background predation risk (conspecific alarm cues or distilled water) in a split-clutch design and studied morphology in both juveniles and adults. In accordance with the theory that plasticity varies across ontogeny and sexes, geometric morphometry analyses revealed significant shape differences between treatments that varied across developmental stages and sexes. Alarm cue-exposed juveniles and adult males developed deeper heads, deeper bodies, longer dorsal fin bases, shorter caudal peduncles and shorter caudal fins. Adult alarm cue-exposed males additionally developed a larger relative eye size. These responses represent putative adaptive plasticity as they are linked to reduced predation risk. Perhaps most surprisingly, we found no evidence for inducible morphological defences in females. Understanding whether similar variation occurs in other taxa and their environments is crucial for modelling evolution.
Highlights
Traits are highly variable due to phenotypic plasticity, the ability of genotypes to express different phenotypes dependent on the environment[1]
Www.nature.com/scientificreports without further verification across taxa is likely to misinterpret the degree of plasticity present in nature, which distorts our view of the ability of organisms to cope with fluctuating levels of predation risk[2]
We aim to study the ontogeny-specificity and sex-specificity of inducible defences in a classical model system that is phylogenetically similar to the crucian carp, the fathead minnow Pimephales promelas[35], a small-bodied cyprinid common to lakes and rivers across North America[36]
Summary
Traits are highly variable due to phenotypic plasticity, the ability of genotypes to express different phenotypes dependent on the environment[1]. Well-known examples of phenotypic plasticity are inducible defences[13,14] These predator-induced morphological defences in prey organisms such as the helmets and defensive spines in predator-exposed Daphnia[15,16,17] and the body depth response of predator-exposed crucian carp Carassius carassius[18] increase fitness through reduced levels of predation[19,20]. As Meuthen et al.[30], following the theory of Fischer et al.[7], suggest that morphological changes are present only during early development and at the onset of sexual maturation, we focus on studying these two developmental stages in particular For this purpose, we manipulated perceived predation risk by regularly exposing fish from hatchlings onwards to conspecific alarm cues. We expected to observe that these defences differ between sexes at the point of maturation
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