Judging a book by its cover: Evaluating the relationship between sexual signals and fitness in an iteroparous species

Abstract

With this dissertation, we evaluated the relationship between sexually selected traits and reproductive success, considering alternative perspectives by which we quantify, evaluate, and interpret these traits. Sexually selected traits, such as cranial appendages in ungulates, can serve as indicators of condition, and researchers often discuss them interchangeably when comparing their role in obtaining greater reproductive success. We discussed the evolution and physiological constraints associated with the development of antlers and horns and propose that permanent versus temporary traits likely communicate vastly different messages in long-lived species. We investigated age-related patterns in antler allometry utilizing 16 years of data from a population of known-aged, freely breeding white-tailed deer (Odocoileus virginianus). We observed a positive, nonlinear relationship between antler and body size across all age classes, where for every for every 10% increase in body size, we observed an 8.05% increase in antler size (± 0.017 SE, P < 0.001). For ages 1.5-5.5 years, antler allometry value had no significant relationship with increased annual reproductive success (P = 0.33-0.79). However, for deer aged 6.5+ years, allometry value was positively associated with annual reproductive success (P = 0.002). We also identified antler characteristics that may facilitate either armament or ornament utility and assessed their relationship to annual reproductive success (ARS). We found sum of antler tine lengths (armament and ornament characteristic) and number of antler points (armament characteristic) to be associated with ARS within our top antler characteristic models, and that gross antler score better predicted this relationship than either variable alone. The relationship between sum of the antler tine lengths, number of antler points, gross antler score and ARS varied quadratically with age, peaking at approximately 5.5 years of age. Additionally, the relationship between number of antler points and ARS declined as the male population age increased (-0.06 ± 0.02, p = 0.007). Despite temptation to identify antlers as either armaments or ornaments, our findings suggest a complex relationship between antler characteristics and ARS, contingent upon age and population dynamics.