Photopic adaptations to a changing environment in two Lake Victoria cichlids

Abstract

During the past 30 years, Lake Victoria cichlid fishes have encountered severe environmental and ecological changes including an introduced predator and new prey types. Furthermore, increased eutrophication has led to reduced water transparency and shifted the spectral composition of underwater light to longer wavelengths. In the present study, 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. Eyes of both species were dissected and retinal features were measured from tangential sections. In both species, the eyes became smaller, independently of body size. This decrease possibly occurred to make space for other structures that increased in size. In H. pyrrhocephalus, a significantly lower resolution was found. However, the size, and thus photon‐catching ability of the double cones, remained unchanged, despite the smaller eyes. In the modern populations of H. tanaos, the double cone size increased in relation to eye size, so that the photon‐catching ability of the smaller fish remained the same. However, no significant decrease in resolution was found. Shortwave sensitivity was found to be lower in both modern populations because of a reduction or the complete absence of single cones. The results obtained in the present study 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. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 328–341.

Fast adaptive responses in the oral jaw of Lake Victoria cichlids

“…Third, the decreased water transparency of the lake and decreased eye size of the resurgent cichlids (van Rijssel and Witte ). These smaller eyes (which are probably due to a morphological trade‐off), but especially the lower resolution of the eyes of some species (van der Meer et al ), may have made it harder to distinguish small‐sized prey types (e.g., zooplankton) in more turbid water.…”

Two new species of zooplanktivorous haplochromine cichlids from Lake Victoria, Tanzania

“…In the successfully recovering zooplanktivorous haplochromine species, morphological changes were observed, which may have been caused by adaptive responses to the environmental changes, both through natural selection and phenotypic plasticity (Wanink and Witte 2000, Witte et al 2008, Chapman et al 2008, van der Meer et al 2012; van Rijssel and Witte 2012). In some cases (introgression through) hybridization may have also taken place among zooplanktivores (Mzighani et al 2010).…”

Contemporary phenotypic change in correlated characters in the African cyprinid, Rastrineobola argentea

“…Our study adds to a growing number of examples of Lake Victoria fishes that have undergone rapid phenotypic changes in response to anthropogenic changes over the past half century (Witte et al, 2008;Sharpe et al, 2012;Van Der Meer et al, 2012;van Rijssel & Witte, 2013;van Rijssel et al, 2014van Rijssel et al, , 2016, and more broadly to the increasing body of evidence that humans are major drivers of contemporary phenotypic change (Hendry, Farrugia & Kinnison, 2008). Lake Victoria is typical of many lakes in densely populated catchments that have experienced pollution, eutrophication, over-fishing, and the introduction of non-indigenous species either simultaneously or in close succession (Dudgeon et al, 2006).…”