Testosterone influences the accumulation of carotenoids in the retina of a wild bird (39.4)

Abstract

Carotenoids accumulate at high concentrations in the avian retina, where they filter incoming light, tune spectral sensitivity, and provide protection from damaging UV light. Among wild house finches (Haemorhous mexicanus), we have observed significant seasonal variation in retinal carotenoid levels, with a peak during the non‐reproductive winter period and lowest levels during the spring/summer breeding season. We hypothesized that these seasonal patterns of accumulation could be driven by the direct influence of photoperiod and/or indirectly through the influence of seasonally sensitive sex steroid hormones (testosterone) on retinal carotenoid physiology. To test these hypotheses, we brought wild caught male and female adult house finches into captivity, gonadectomized a subset of the male birds, and maintained groups on long (16:8 light:dark) or short (8:16) photoperiods for two months. At the conclusion of the study, gonadectomized males had significantly higher carotenoid levels in their retinas and much lower circulating testosterone levels than males that were sham‐treated, but did not differ significantly from intact females. Photoperiod alone had no significant effect on retinal carotenoid levels; however there was a significant interactive effect of gonad status, photoperiod, and time on plasma carotenoid levels. Sham‐treated males on the long photoperiod showed a significant decline in plasma carotenoid levels in the first month of the experiment, but recovered in the second month. These results suggest that testosterone maybe influencing the uptake, transport, and/or accumulation of carotenoids in the avian retina and driving seasonal patterns of accumulation. These shifts in retinal carotenoid accumulation represent a previously unrecognized cost of testosterone‐mediate traits (e.g. song, territoriality).Grant Funding Source: Supported by NSF‐IOS‐0910357, 0923694 and DBI‐1202776