Diversity in rest-activity patterns among Lake Malawi cichlid fishes suggests a novel axis of habitat partitioning.

Evan Lloyd,Andrew J Conith,R Craig Albertson,Brian Chhouk,Alex C Keene

doi:10.1242/jeb.242186

Evan Lloyd, Andrew J Conith + Show 3 more

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https://doi.org/10.1242/jeb.242186

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Abstract

ABSTRACTAnimals display remarkable diversity in rest and activity patterns that are regulated by endogenous foraging strategies, social behaviors and predator avoidance. Alteration in the circadian timing of activity or the duration of rest–wake cycles provide a central mechanism for animals to exploit novel niches. The diversity of the >3000 cichlid species throughout the world provides a unique opportunity to examine variation in locomotor activity and rest. Lake Malawi alone is home to over 500 species of cichlids that display divergent behaviors and inhabit well-defined niches throughout the lake. These species are presumed to be diurnal, though this has never been tested systematically. Here, we measured locomotor activity across the circadian cycle in 11 Lake Malawi cichlid species. We documented surprising variability in the circadian time of locomotor activity and the duration of rest. In particular, we identified a single species, Tropheops sp. ‘red cheek’, that is nocturnal. Nocturnal behavior was maintained when fish were provided shelter, but not under constant darkness, suggesting that it results from acute response to light rather than an endogenous circadian rhythm. Finally, we showed that nocturnality is associated with increased eye size after correcting for evolutionary history, suggesting a link between visual processing and nighttime activity. Together, these findings identify diversity of locomotor behavior in Lake Malawi cichlids and provide a system for investigating the molecular and neural basis underlying variation in nocturnal activity.

Highlights

IntroductionThe timing of locomotor activity and rest can differ dramatically between closely related species, or even between individuals of the same species, raising the possibility that it can be adaptive and subject to selection (Brown et al, 2018; Duboué et al, 2011; Hammond et al, 2018)
Animals display remarkable diversity in rest and activity patterns
Following an initial 24 h period of acclimation, activity was recorded in individually housed juvenile fish across 24 h in standard light:dark conditions, with infrared lighting used to monitor locomotor activity during the night as previously described in A. mexicanus (Yoshizawa et al, 2015)

Summary

Introduction

The timing of locomotor activity and rest can differ dramatically between closely related species, or even between individuals of the same species, raising the possibility that it can be adaptive and subject to selection (Brown et al, 2018; Duboué et al, 2011; Hammond et al, 2018). Alteration in the circadian timing of activity or the duration of rest–wake cycles provide a central mechanism for animals to exploit novel niches. In two closely related species of the tephritid fruit fly, hybridization in the wild appears to be prevented only by circadian differences in mating times (Raphael et al, 2019; Smith, 1979)

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