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Selection, Sexual

Dominy, Abby [1], Loew, Ellis R [2], Spotila, James R. [1], Avery, Harold W. [3].

Turtles in a different light: underwater visual ecology and mate selection in the diamondback terrapin.

Diamondback terrapins (Malaclemys terrapin) are colorful turtles inhabiting estuaries along the Eastern and Gulf coasts of the United States. Terrapins, like some reptiles and many birds, have tetrachromatic vision (found in this study) which enables them to utilize colors and color combinations not visible to mammalian predators. The ability to see and express colors in the UV, blue, green, and red portions of the light spectrum has led to conspicuous coloration and patterns on the skin, carapace, and plastron, especially in UV and long-wavelength colors. Ultraviolet and red colors are frequently cited as sexually selected traits in other species, especially birds. However, very little is known about the visual ecology of turtles or estuarine vertebrates. Current knowledge of terrapin mating behavior is limited to the fact that mating aggregates will form in the Spring near the surface of the water column, and males will arrive early to prepare for what appears to be lekking behavior. Our research seeks to evaluate the visual ecology of the diamondback terrapin, which is potentially important in mate selection. To determine whether terrapins select mates based on coloration and/or patterning, we collected blood samples from captured gravid females, their hatchlings, and all captured potential fathers. Six microsatellite loci were genotyped to determine paternity of hatchlings with known mothers. The color phenotypes of males that were identified as fathers are being compared to the distribution of color phenotypes in the study population. Color phenotypes were measured using reflectance spectrophotometry and digital photography. These data show a strong correlation between colors expressed in the UV and red portions of the spectrum, suggesting that these colors are co-selected. The strength and saturation of these color signals can vary greatly between individuals, suggesting assortative mate selection. To determine the underwater visual environment of these highly aquatic animals, downwelling and upwelling irradiance in the water column were measured at 0.5m intervals in the water column. For downwelling irradiance, UV light dominates at the water surface but attenuates quickly within 0.5m below the surface. For upwelling irradiance, long-wavelength red colors can be detected at the surface. This suggests that mate selection should occur near the surface of the water column for optimal display of the correlated UV and red colors expressed by the terrapin. Optimized visual detection of conspecifics just below the water surface would suggest that mating aggregations are leks designed to allow for visual assessment of mate quality.

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1 - Drexel University, Biodiversity, Earth and Environmental Science, 3245 Chestnut St., Philadelphia, PA, 19104, USA
2 - Cornell University, Biomedical Sciences, Ithaca, NY, 14853, USA
3 - The Leatherback Trust, Cherry Hill, NJ, 08003, USA

sexual selection
sensory ecology
Reflectance spectrophotometry.

Presentation Type: Regular Oral Presentation
Session: 4
Location: Cotton A/Snowbird Center
Date: Saturday, June 22nd, 2013
Time: 8:45 AM
Number: 4002
Abstract ID:211
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation

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