Title:
Visual sensitivities tuned by heterochronic shifts in opsin gene expression
Visual sensitivities tuned by heterochronic shifts in opsin gene expression
Author(s)
Carleton, Karen L.
Spady, Tyrone C.
Streelman, J. Todd
Kidd, Michael R.
McFarland, William N.
Loew, Ellis R.
Spady, Tyrone C.
Streelman, J. Todd
Kidd, Michael R.
McFarland, William N.
Loew, Ellis R.
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Abstract
Background: Cichlid fishes have radiated into hundreds of species in the Great Lakes of Africa.
Brightly colored males display on leks and vie to be chosen by females as mates. Strong
discrimination by females causes differential male mating success, rapid evolution of male color
patterns and, possibly, speciation. In addition to differences in color pattern, Lake Malawi cichlids
also show some of the largest known shifts in visual sensitivity among closely related species. These
shifts result from modulated expression of seven cone opsin genes. However, the mechanisms for
this modulated expression are unknown.
Results: In this work, we ask whether these differences might result from changes in
developmental patterning of cone opsin genes. To test this, we compared the developmental
pattern of cone opsin gene expression of the Nile tilapia, Oreochromis niloticus, with that of several
cichlid species from Lake Malawi. In tilapia, quantitative polymerase chain reaction showed that
opsin gene expression changes dynamically from a larval gene set through a juvenile set to a final
adult set. In contrast, Lake Malawi species showed one of two developmental patterns. In some
species, the expressed gene set changes slowly, either retaining the larval pattern or progressing
only from larval to juvenile gene sets (neoteny). In the other species, the same genes are expressed
in both larvae and adults but correspond to the tilapia adult genes (direct development).
Conclusion: Differences in visual sensitivities among species of Lake Malawi cichlids arise through
heterochronic shifts relative to the ontogenetic pattern of the tilapia outgroup. Heterochrony has
previously been shown to be a powerful mechanism for change in morphological evolution. We
found that altering developmental expression patterns is also an important mechanism for altering
sensory systems. These resulting sensory shifts will have major impacts on visual communication
and could help drive cichlid speciation.
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Date Issued
2008-05-23
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