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Abstract There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti‐predator) behaviour inDaphnia. We set‐up replicate experimental populations ofDaphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50‐day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases inDaphniadensity favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti‐predator behaviour.Daphniafrom the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti‐predator behaviour. Such trends provide new insights into selection on eye size and behaviour.
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Sensory evolution in a cavefish radiation: patterns of neuromast distribution and associated behaviour in Sinocyclocheilus (Cypriniformes: Cyprinidae)
The genus Sinocyclocheilus , comprising a large radiation of freshwater cavefishes, are well known for their presence of regressive features (e.g. variable eye reduction). Fewer constructive features are known, such as the expansion of the lateral line system (LLS), which is involved in detecting water movements. The precise relationship between LLS expansion and cave adaptation is not well understood. Here, we examine morphology and LLS-mediated behaviour in Sinocyclocheilus species characterized by broad variation in eye size, habitat and geographical distribution. Using live-staining techniques and automated behavioural analyses, we examined 26 Sinocyclocheilus species and quantified neuromast organ number, density and asymmetry within a phylogenetic context. We then examined how these morphological features may relate to wall-following, an established cave-associated behaviour mediated by the lateral line. We show that most species demonstrated laterality (i.e. asymmetry) in neuromast organs on the head, often biased to the right. We also found that wall-following behaviour was distinctive, particularly among eyeless species. Patterns of variation in LLS appear to correlate with the degree of eye loss, as well as geographical distribution. This work reveals that constructive LLS evolution is convergent across distant cavefish taxa and may mediate asymmetric behavioural features that enable survival in stark subterranean microenvironments.
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- Award ID(s):
- 2205928
- PAR ID:
- 10425664
- Date Published:
- Journal Name:
- Proceedings of the Royal Society B: Biological Sciences
- Volume:
- 289
- Issue:
- 1984
- ISSN:
- 0962-8452
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1098/rspb.2022.1641
