Developmental effects of environmental light on male nuptial coloration in Lake Victoria cichlid fish
- Published
- Accepted
- Subject Areas
- Evolutionary Studies
- Keywords
- Pundamilia, plasticity, reproductive isolation, visual signals, mate choice
- Copyright
- © 2017 Wright et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2017. Developmental effects of environmental light on male nuptial coloration in Lake Victoria cichlid fish. PeerJ Preprints 5:e3298v1 https://doi.org/10.7287/peerj.preprints.3298v1
Abstract
Background. Efficient communication requires that signals are well transmitted and perceived in a given environment. Natural selection therefore drives the evolution of different signals in different environments. In addition, environmental heterogeneity at small spatial or temporal scales may favour phenotypic plasticity in signaling traits, as plasticity may allow rapid adjustment of signal expression to optimize transmission. In this study, we explore signal plasticity in the nuptial coloration of Lake Victoria cichlids, Pundamilia pundamilia and Pundamilia nyererei. These two species differ in male coloration, which mediates species-assortative mating. They occur in adjacent depth ranges with different light environments. Given the close proximity of their habitats, overlapping at some locations, plasticity in male coloration could contribute to male reproductive success but interfere with reproductive isolation.
Methods. We reared P. pundamilia, P. nyererei, and their hybrids under light conditions mimicking the two depth ranges in Lake Victoria. From photographs, we quantified the nuptial coloration of males, spanning the entire visible spectrum. In experiment 1, we examined developmental colour plasticity by comparing sibling males reared in each light condition. In experiment 2, we assessed colour plasticity in adulthood, by switching adult males between conditions and tracking coloration for 100 days.
Results. We found that nuptial colour in Pundamilia did respond plastically to our light manipulations, but only in a limited hue range. Fish that were reared in light conditions mimicking the deeper habitat were significantly greener than those in conditions mimicking shallow waters. The species-specific nuptial colours (blue and red) did not change. When moved to the opposing light condition as adults, males did not change colour.
Discussion. Our results show that species-specific nuptial colours, which are subject to strong divergent selection by female choice, are not plastic. We do find plasticity in green coloration, a response that may contribute to visual conspicuousness in darker, red-shifted light environments. These results suggest that light-environment-induced plasticity in male nuptial coloration in P. pundamilia and P. nyererei is limited and does not interfere with reproductive isolation.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Natural and experimental light conditions
Experimental light environments were created to mimic natural light conditions experienced by P. pundamilia and P. nyererei at Python Islands, Lake Victoria. Vertical lines indicate the peak sensitivities of the three main Pundamilia photoreceptors: SWS2a (453nm), RH2 (531nm), LWS (565nm) (Carleton et al., 2005) .
Interspecific colour differences
Interspecific differences in coloration, presented as principal components (PC1-PC4), for body and each fin. Error bars represent 95% CI,• indicates P < 0.1, * indicates P < 0.05, **indicates P < 0.01, *** indicates P < 0.001.
Increased green coloration in each species group
There was no evidence of species-specific response to the light manipulations, as all three species groups exhibited increased green colour in the deep light condition.
Fish coloration (whole fish PC3) during 100 days after switching light conditions (experiment 2)
There was a significant three-way interaction between species, treatment, and date for ‘whole fish’ PC3. However, colour differed little between control (SS/DD) and switched fish (SD/DS). Error bars represent 95% CI.
Fish coloration (body PC4) during 100 days after switching light conditions (experiment 2)
There was a significant three-way interaction between species, treatment, and date for ‘body’ PC4. However, change across the 100-day period differed little between control (SS/DD) and treatment fish (SD/DS). Error bars represent 95% CI.
Experiment 1 test families
Sample size (males) for each cross, separated by family and by deep (D) and shallow (S) rearing light. Family names are expressed as mother x father, such that ‘PN’ indicates P. pundamilia female x P. nyererei male (F1) and ‘PNPN’ indicates a second generation cross of ‘PN’ female x ‘PN’ male - F1 and F2 hybrids were pooled in the analyses. Superscripted numbers indicate families with the same mothers; superscripted letters indicate families with the same fathers.
Experiment 2 test families
Sample size (males) for each cross, separated by family and treatment group; for example: ‘DS’ indicates a deep-reared fish that was moved to shallow light. Once again, family names are expressed as mother x father and were pooled in the analyses. Superscripted numbers indicate families with the same mothers; superscripted letters indicate families with the same fathers.
Colour parameters
Colour space parameters based on those defined by Selz et al. (2016), modified slightly to accommodate our photography set up, and including ‘green’ and ‘violet’ to cover the entire hue range. Black was defined using the YUV colour space.
PCA loading matrix (experiment 1)
PCA loading matrices from experiment 1, with the cumulative amount of variance accounted for per PC. All PCs were calculated independently for each section.
PCA loading matrix (experiment 2)
PCA loading matrixes from experiment 2, with the cumulative amount of variance accounted for per PC. All PC’s were calculated independently for each section.
Continued colour change
Fish continued to change colour throughout the experiment, as evidenced by the significance of ‘date’ in nearly all analyses. t-values and degrees of freedom presented from linear mixed models; • indicates P < 0.1, * indicates P < 0.05, **indicates P < 0.01, *** indicates P < 0.001.