“Neglected patterns of variation in phenotypic plasticity: Age- and sex-specific antipredator plasticity in a cichlid fish”

Posted on by Denis Meuthen & Timo Thünken

Denis Meuthen, Sebastian A. Baldauf, Theo C. M. Bakker, and Timo Thünken (Apr 2018)

The DOI will be http://dx.doi.org/10.1086/696264

This study indicates sex- and age-specific phenotypic plasticity whose patterns correspond to theoretical predictions

Growing up with predators: cichlid fish fine-tune their expression of defense traits and ornaments during development in response to predator presence

Organisms are to some extent able to flexibly adjust their morphology, physiology, and behavior to current environmental conditions. This so-called “phenotypic plasticity” is beneficial because the environment often fluctuates and so does the presence of predators. However, long-term effects of developing and living in the presence of predator cues are largely unexplored. Denis Meuthen, Timo Thünken, and colleagues from the Theo Bakker lab at the University of Bonn, Germany, aimed to fill this gap by conducting a comprehensive experiment on Pelvicachromis taeniatus, an African cichlid fish with bright coloration in both sexes. Over more than two years, they investigated morphological and color development of fish that were regularly exposed to conspecific alarm cues – which signal the presence of predators. Based on photographs taken at six developmental stages from juveniles to reproductively active adults, the researchers show that predator effects are present, but neither consistently nor uniformly expressed across sexes and life stages. In an early juvenile stage, alarm-cue exposed fish developed beneficial morphological responses such as increased body size, longer dorsal spines and increased eye diameters, all of which are adaptations to reduce predation risk. In an early adult stage, alarm-cue exposed males showed delayed expression of nuptial body coloration, but invested in body size. In males of other developmental stages as well as in adult females, the researchers did not find any significant effects. These results suggest that phenotypic plasticity optimizes predator-defense traits during vulnerable developmental stages such as during early life and shortly prior to reproduction.

This study is part of Denis Meuthen’s PhD thesis focusing on intragenerational antipredator phenotypic plasticity. As postdoc he is currently studying transgenerational phenotypic plasticity in fathead minnows at the University of Saskatchewan, Canada. The senior author Timo Thünken is interested in how variation in the developmental environment affects animals’ behavior and also in sexual selection, focusing on adaptive inbreeding in P. taeniatus.

Male (top) and female (bottom) Pelvicachromis taeniatus at the six developmental stages examined in the present study. Sexes are not distinguishable during the first two developmental stages, thus only one individual is shown, respectively. (Credit: Denis Meuthen)

Abstract

The ability of organisms to plastically respond to changing environments is well studied. However, variation in phenotypic plasticity during ontogeny is less well understood despite its relevance of being an important source of phenotypic variation in nature. Here, we comprehensively study ontogenetic variation in morphological antipredator plasticity across multiple traits in Pelvicachromis taeniatus, a Western African cichlid fish with sexually dimorphic ornamentation. In a split-clutch design, fish were raised under different levels of perceived predation risk (conspecific alarm cues or distilled water). Morphological plasticity varied substantially across ontogeny: it was first observable at an early juvenile stage where alarm cue-exposed fish grew faster. Subsequently, significant plasticity was absent until the onset of sexual maturity. Here, alarm-cue-exposed males were bigger than control males, which led to deeper bodies, longer dorsal spines, bigger caudal peduncles and increased eye diameters. Sexual ornamentation emerged delayed in alarm cue-exposed males. In later adulthood, the plastic responses receded. Despite small effect sizes, these responses represent putative adaptive plasticity as they are likely to reduce predation risk. In females, we did not observe any plasticity. In accordance with theory, these results suggest fine-tuned expression of plasticity that potentially increases defenses during vulnerable developmental stages and reproductive output.