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Crotaphytus Collaris) POSSIBLE SEXUAL SELECTION IN PRE-REPRODUCTIVE HATCHLING COLLARED LIZARDS (CROTAPHYTUS COLLARIS) By ANDREA ACEVEDO CROSBY Bachelor of Science in Biology Pontificia Universidad Javeriana Bogotá, Colombia 2003 Master of Science in Biology University of Texas at Arlington Arlington, Texas 2009 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY July, 2015 POSSIBLE SEXUAL SELECTION IN PRE-REPRODUCTIVE HATCHLING COLLARED LIZARDS (CROTAPHYTUS COLLARIS) Dissertation Approved: Dr. Stanley F. Fox Dissertation Adviser Dr. Jennifer Grindstaff Dr. Matthew B. Lovern Mark Gregory M.S. ii Name: ANDREA ACEVEDO CROSBY Date of Degree: JULY, 2015 Title of Study: POSSIBLE SEXUAL SELECTION IN PRE-REPRODUCTIVE HATCHLING COLLARED LIZARDS (CROTAPHYTUS COLLARIS) Major Field: ZOOLOGY Abstract: We studied the possible adaptive significance of precocial sexual signaling in collared lizard hatchlings. Male hatchlings display intense dorsolateral orange bars at hatching or within the first weeks of life. Hatchling orange bars (HOB) increased in saturation with body size until reaching a threshold, and then faded as adult coloration began to show. In most organisms, sexual dichromatism (usually present only in adults) has been related to androgens and aggressive behavior. It is unknown how androgen levels are related to the expression of the orange bars in male hatchling collared lizards. We tested the hypothesis that male hatchlings with higher levels of androgens would show greater proportion of orange, higher orange saturation (color purity), and more aggressive behavior than those with lower levels of androgens. We first tested this hypothesis by manipulating androgen levels through implants of testosterone (T) and dihydrotestosterone (DHT). Both proportion of orange and orange saturation increased the most with DHT. When DHT was implanted, almost 40% of the variation in aggression was explained by DHT. We then examined relationships of unmanipulated levels of T and DHT with coloration and aggressive behavior in wild-ranging male hatchlings. Although not statistically significant, our results showed a positive trend between orange saturation and DHT. Hatchlings with higher saturated orange bars tended to behave more aggressively than those with less saturated bars. Finally, to determine if HOB are related to fitness in sexually mature males, we measured inferred fitness in yearlings and adults at the same population and related it to the proportion of orange and orange saturation that those yearlings and adults had when hatchlings. Our results suggested that hatchlings with more orange coloration had a higher probability of pair- bonding, displaced less from their natal locations, had larger home range areas (as adults, but not as yearlings), and had higher inferred fitness (as adults, but not as yearlings). Thus, it is suggested that precocial sexual signaling in hatchlings is positively related to estimated fitness in adults as estimated from spatial data, but not so in yearlings when yearling males, unlike adults, likely gain their fitness by sneaking copulations. iii TABLE OF CONTENTS Chapter Page I. ONTOGENETIC CHANGES IN COLORATION OF MALE HATCHLING COLLARED LIZARDS (CROTAPHYTUS COLLARIS) ....................................... 1 Abstract ................................................................................................................... 1 Introduction ............................................................................................................. 2 Methods ................................................................................................................... 9 Results ................................................................................................................... 12 Discussion ............................................................................................................. 13 Literature Cited ..................................................................................................... 16 Tables .................................................................................................................... 23 Figures ................................................................................................................... 25 II. EFFECTS OF EXOGENOUS ANDROGENS ON DIMORPHIC ORANGE COLORATION AND AGGRESSIVE BEHAVIOR IN HATCHLING COLLARED LIZARDS (CROTAPHYTUS COLLARIS) ........................................................... 29 Abstract ................................................................................................................. 29 Introduction ........................................................................................................... 30 Methods ................................................................................................................. 32 Results ................................................................................................................... 37 Discussion ............................................................................................................. 41 Literature Cited ..................................................................................................... 44 Figures ................................................................................................................... 49 III. RELATIONSHIPS AMONG ANDROGENS, COLORATION, AND AGGRESSION IN WILD-RANGING HATCHLING COLLARED LIZARDS (CROTAPHYTUS COLLARIS) ........................................................................................................... 57 Abstract ................................................................................................................. 57 Introduction ........................................................................................................... 58 Methods ................................................................................................................. 59 Results ................................................................................................................... 62 Discussion ............................................................................................................. 65 Literature Cited ..................................................................................................... 68 Figures ................................................................................................................... 70 iv Chapter Page IV. HATCHLING ORANGE COLORATION AND FITNESS IN THE COLLARED LIZARD (CROTAPHYTUS COLLARIS) ....................................... 77 Abstract ................................................................................................................. 77 Introduction ........................................................................................................... 78 Methods ................................................................................................................. 82 Results ................................................................................................................... 87 Discussion ............................................................................................................. 91 Literature Cited ..................................................................................................... 96 Figures ................................................................................................................. 100 v LIST OF TABLES Table Page 1.1 Fixed effects of body size (Slope Estimate), measured as snout-vent length (mm) on color variables (Dependent Variable), estimated with linear mixed-effects models to account for repeated measurements on individual lizards. Degrees of freedom and P-values were estimated using Satterthwaite’s approximation .................................................................................................... 23 1.2 Quadratic model of fixed effects of body size, measured as snout-vent length (SVL) on subjective orange coloration categories assigned to individual male hatchling collared lizards, using a linear mixed-effects model to account for repeated measurements on individual lizards. Degrees of freedom and P-values were estimated using Satterthwaite’s approximation. ......................... 24 vi LIST OF FIGURES Figure Page 1.1 Male hatchling Crotaphytus collaris showing orange bars. ................................. 25 1.2 Correlation between subjective orange categories and spectral data for a sample of hatchling collared lizards re-measured multiple times over their life in 2013 ....... 26 1.3 Regression of orange brightness, saturation and hue against body size (snout-vent length) for male hatchling collared lizards re-measured multiple times over their life in 2013 .................................................................................................. 27 1.4 Change in subjective orange coloration over hatchling growth. The curve is a significant quadratic regression (see text for statistics) .............................................. 28 2.1 Top two panels: circulating androgen levels measured 30 days after T implantation in 2012. Bottom two panels: circulating androgen levels measured 30 days after DHT implantation in 2013 .................................................................... 49 2.2 Principal Components Analysis (PCA) of residuals of brightness, saturation and hue for T (left panel, n = 17) and DHT
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