Latest finding - Integrative Zoology
- Photopic adaptations to a changing environment in two Lake Victoria cichlids
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During the past 30 years, Lake Victoria cichlid fishes have encountered severe environmental and ecological changes including an introduced predator, new prey types, and increased eutrophication. Increased eutrophication reduced water transparency and shifted the spectral composition of underwater light to longer wavelengths (red-green light).
Collections of two cichlid species, Haplochromis pyrrhocephalus and Haplochromis tanaos, from before and after the environmental changes were compared with respect to their photopic resolution and sensitivity. Of both species, eyes were dissected and retinal features were measured from tangential sections.
In both species the eyes became smaller independent of body size, possibly to make space for other structures that increased in size such as the gills. In H. pyrrhocephalus, a significantly lower long wavelength (red-green light) sensitive double cone size density was found. This resulted in a lower resolution which concurs with the changed diet to larger prey types. However, the double cone size remained unchanged. This means that the photopic sensitivity, the smaller eyes, remained unchanged.
In the modern populations of H. tanaos, by contrast, no change in resolution was found. While the double cone size increased in relation to eye size, so that the photopic sensitivty of the smaller fish remained the same as well.
A reduction or complete absence of single short wavelength (blue light) sensitive cones was found for both species. This implies that there might no longer be a “need” for single cones in the current turbid environment (see figure).
Our results imply that these resurgent zooplanktivores are capable of adapting their eye morphology to the changed environmental conditions without losing crucial aspects used for survival and reproduction.
- Old and modern cichlid retinas
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Double cone patterns; DC, double cone; S, single cone. A: Row pattern of double cones with presence of some single cones in caudal region of H. pyrrhocephalus from 1978 (316-131). B: Row pattern of double cones with no single cones present in the rostral-ventral region in H. pyrrhocephalus from 2001 (316-205). C: Square pattern of double cones around single cones in the rostral region in H. tanaos from 1978 (320-09). D: Diamond pattern of double cones around tiny single cones in the rostral-ventral region in H. tanaos from 2001 (320-15).
- Publication
The results of this study have been published DOI:j.1095-8312.2012.01859.x in the Biological Journal of the Linnean Society (2012) 106, 328-341, impact factor 2.17.
