Male colour variation in a eurytopic African cichlid: the role of diet and hypoxia

Abstract

Species that cross strong environmental gradients are expected to face divergent selective pressures that can act on sexually-selected traits. In the present study, we examine the role of hypoxia and carotenoid availability in driving divergence in two sexually-selected traits, male colour and reproductive behaviour, in the African cichlid Pseudocrenilabrus multicolor victoriae. Low-dissolved oxygen (DO) (hypoxic) environments are expected to be energetically challenging; given that male nuptial colour expression and courtship displays can be costly, we expected fish in low-DO versus high-DO environments to differ in these traits. First, a field survey was used to describe natural variation in male nuptial colour patterns and diet across habitats divergent in DO. Next, using wild-caught fish from a low-DO and high-DO habitat, we tested for differences in reproductive behaviour. Finally, a laboratory rearing experiment was used to quantify the interaction of DO and diet (low-versus high-carotenoid availability) on the expression of male colour during development. In energetically challenging low-DO environments, fish were more red and, in high-DO environments, fish were typically brighter and more yellow. The frequency of reproductive displays in fish of low-DO origin was 75% lower, although this had no consequence for brooding frequency (i.e. both populations produced the same number of broods on average). Our laboratory rearing study showed carotenoid availability to be important in colour production with no direct influence of DO on colour. Additionally, weak patterns of diet variation across wild populations suggest that other factors in combination with diet are contributing to colour divergence.

Habitat constraints on carotenoid‐based coloration in a small euryhaline teleost

“…It is generally assumed that bright yellow, orange, and red carotenoid-based colorations are honest signals of the general health of an individual (Grether et al, 1999;Johnson & Fuller, 2014;Kodric-Brown, 1989;Olson & Owens, 1998), giving information about an individual's vigor, resistance to parasites/pathogens, and ability to find food resources (Kodric-Brown, 1998). Indeed, this coloration is costly to express, as vertebrates are inefficient carotenoid assimilators (Grether et al, 1999), and carotenoids used as pigments cannot contribute to various physiological processes regarding antioxidant protection, immune function, and reproduction (Brown, Leonard, McGraw, & Clotfelter, 2014;McGraw, 2005;McNeil, Friesen, Gray, Aldredge, & Chapman, 2016;Pike et al, 2010;Svensson, Pelabon, Blount, Surai, & Amundsen, 2006). As only a small fraction of the carotenoids ingested through the diet can be assimilated, the availability of these pigments in nature can strongly influence the intensity of such coloration.…”

The effects of commonly used anaesthetics on colour measurements across body regions in the poeciliid fish, Girardinus metallicus

“…In summary, our results suggest that photographing fish in a water-filled glass chamber without anaesthetics may be an effective way to obtain digital images for colour analysis, especially when HSB are variables of interest (Maan et al, 2004;McNeil et al, 2016).…”

“…In summary, our results suggest that photographing fish in a water‐filled glass chamber without anaesthetics may be an effective way to obtain digital images for colour analysis, especially when HSB are variables of interest (Maan et al ., ; McNeil et al ., ). Photographing without anaesthetic under standardised light conditions is a minimally invasive process that can be used to obtain images prior to behavioural observations and may give a more accurate measurement of natural colour based on how fish appear to conspecifics.…”

“…However, quantification of coloration traits in live poeciliids can pose challenges because the fish are so small. Colour measurement techniques involve using either reflectance spectrophotometry to, for example, address perceptual abilities, or to quantify the effects of pigment content on coloration (Grether et al ., ), or software‐based measurements taken from digital images, which are more suitable for examining patterns without necessarily obtaining absolute values of traits (Langkilde & Boronow, ; Maan et al ., ; McNeil et al ., ; Parolini et al ., ; Pike, ; Stevens et al ., ). Researchers wishing to measure coloration with minimal stress to the animal, for example because they will perform subsequent behavioral observations, often elect to use digital images (Bergman & Beehner, ; Foo et al ., ; Pike, ; Stevens et al ., ).…”

“…based measurements taken from digital images, which are more suitable for examining patterns without necessarily obtaining absolute values of traits (Langkilde & Boronow, 2012;Maan et al, 2004;McNeil et al, 2016;Parolini et al, 2018;Pike, 2011;Stevens et al, 2007). Researchers wishing to measure coloration with minimal stress to the animal, for example because they will perform subsequent behavioral observations, often elect to use digital images (Bergman & Beehner, 2008;Foo et al, 2017;Pike, 2011;Stevens et al, 2007).…”