RT-qPCR reveals opsin gene upregulation associated with age and sex in guppies (Poecilia reticulata)-a species with color-based sexual selection and 11 visual-opsin genes
Date
2011-03-29
Authors
Laver, Christopher R.J.
Taylor, John S.
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: PCR-based surveys have shown that guppies (Poecilia reticulata) have an unusually large visual-opsin
gene repertoire. This has led to speculation that opsin duplication and divergence has enhanced the evolution of
elaborate male coloration because it improves spectral sensitivity and/or discrimination in females. However, this
conjecture on evolutionary connections between opsin repertoire, vision, mate choice, and male coloration was
generated with little data on gene expression. Here, we used RT-qPCR to survey visual-opsin gene expression in
the eyes of males, females, and juveniles in order to further understand color-based sexual selection from the
perspective of the visual system.
Results: Juvenile and adult (male and female) guppies express 10 visual opsins at varying levels in the eye. Two
opsin genes in juveniles, SWS2B and RH2-2, accounted for >85% of all visual-opsin transcripts in the eye, excluding
RH1. This relative abundance (RA) value dropped to about 65% in adults, as LWS-A180 expression increased from
approximately 3% to 20% RA. The juvenile-to-female transition also showed LWS-S180 upregulation from about
1.5% to 7% RA. Finally, we found that expression in guppies’ SWS2-LWS gene cluster is negatively correlated with
distance from a candidate locus control region (LCR).
Conclusions: Selective pressures influencing visual-opsin gene expression appear to differ among age and sex.
LWS upregulation in females is implicated in augmenting spectral discrimination of male coloration and courtship
displays. In males, enhanced discrimination of carotenoid-rich food and possibly rival males are strong candidate
selective pressures driving LWS upregulation. These developmental changes in expression suggest that adults
possess better wavelength discrimination than juveniles. Opsin expression within the SWS2-LWS gene cluster
appears to be regulated, in part, by a common LCR. Finally, by comparing our RT-qPCR data to MSP data, we were
able to propose the first opsin-to-λmax assignments for all photoreceptor types in the cone mosaic.
Description
BioMed Central
Keywords
Citation
Laver and Taylor: RT-qPCR reveals opsin gene upregulation associated with age and sex in guppies (Poecilia reticulata)-a species with color-based sexual selection and 11 visual-opsin genes. BMC Evolutionary Biology 2011 11:81.