Signal perception in swordtails

Male green swordtail

Project Overview

Animals assess one another using signals—such as colour patterns, ornaments, and displays—in contexts that are critically important for survival and reproduction, such as mate choice. Many animal signals vary along a continuum, and this variation reflects variation in the quality of the signaller. For example, males of a given species may vary continuously in body size, with larger males being better quality mates. An implicit assumption in most research on animal signalling is that signal perception is continuous, meaning that receivers can both perceive and respond to each difference in signal magnitude between signallers. However, although the stimulus (the signal) varies continuously across individuals, increasing evidence suggests that not all of that variation is perceived by the receiver, or processed in the brain.

To understand how and why a signal receiver responds to a signal in a given way, it is crucial to understand how the receiver actually perceived the signal. Signal perception is a function of several factors, including the physiology of the sensory organs and perceptual processes that occur after a signal is transduced by the sensory organ. This research uses fishes in the family Poeciliidae, primarily swordtails in the genus Xiphophorus, and uses an integrative approach to examine proportional processing in animal signalling, and its relation to sensory physiology, signaller and receiver behaviour, and signal evolution. Understanding how signal receivers perceive signal variation is crucial to understanding how signallers place selection on the evolution of signalling traits; how signal receivers evaluate and compare signallers; and ultimately, how the incredible diversity of signalling traits and structures found in the animal kingdom has evolved. Additionally, studying perception in non-human animals can help us understand the diversity of perceptual processing across species, and establish new model systems for cognitive and perceptual studies.

We are grateful to the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement for funding recent research

Prior work and current areas of research

In a recent project led by Eleanor Caves funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement, we focused on the green swordtail Xiphophorus helleri. Results from that project have shown (1) that visual acuity, the ability to perceive detail, is low in green swordtails, approximately 1/20th that of humans, but is higher in females than males, and that (2) perception of body size, an important mate choice signal in swordtails, is proportional, rather than continuous. Specifically, when choosing between two males of different sizes, female green swordtails expressed stronger preferences for the larger male when both males in a pair were small, compared to when both males were larger. This challenges many assumptions inherent in animal signalling studies, and suggests that female perceptual processes can be a selective force limiting the evolution of signal elaboration.

Future work in this system will focus on (1) continuing to investigate proportional processing in green swordtails, for example investigating the effects of changes in the viewing environment, social environment, or prior experience on perception, and (2) extend these studies on both sensory physiology and behaviour to additional species, to examine how sensory physiology and proportional processing shape animal perception.

Female green swordtails