For example, many teleost species display robust diurnal locomotor rhythms including the goldfish ( Carassius auratus), the Mexican tetra ( Astyanax mexicanus) and the zebrafish ( Danio rerio) ( Duboué et al., 2011 Iigo and Tabata, 1996 Zhdanova et al., 2001). For example, 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).Īcross phyla the timing of rest and activity is regulated by a circadian clock that persists under constant conditions, as well as acute response to environmental cues that include light and food availability ( Huang et al., 2011). Indeed, there is some evidence that alterations in daily rhythms can be a major factor in speciation events. Alteration in the circadian timing of activity or the duration of rest–wake cycles provide a central mechanism for animals to exploit novel niches. Indeed, circadian regulation of locomotor activity is strongly associated with foraging strategies, social behaviors and predator avoidance, which are critical factors in organismal fitness ( Siegel, 2005 Vaze and Sharma, 2013). 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). 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.Īnimals display remarkable diversity in rest and activity patterns. 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. 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. In particular, we identified a single species, Tropheops sp. We documented surprising variability in the circadian time of locomotor activity and the duration of rest. Here, we measured locomotor activity across the circadian cycle in 11 Lake Malawi cichlid species. These species are presumed to be diurnal, though this has never been tested systematically. Lake Malawi alone is home to over 500 species of cichlids that display divergent behaviors and inhabit well-defined niches throughout the lake. The diversity of the >3000 cichlid species throughout the world provides a unique opportunity to examine variation in locomotor activity and rest. Animals display remarkable diversity in rest and activity patterns that are regulated by endogenous foraging strategies, social behaviors and predator avoidance.
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