The influence of correlated traits in the process of reproductive character displacement in the upland chorus frog, Pseudacris feriarum

Behavioral interactions among individuals can have complex effects on trait evolution. In this study I quantify the strength of correlation between aggressive and advertisement calls in the chorus frog, Pseudacris feriarum, to assess whether male-male aggressive interactions may have contributed to observed patterns of reproductive character displacement (RCD) in the advertisement call. Male frogs use aggressive vocal signals in defense of calling sites and to facilitate spacing in breeding choruses. Males that successfully defend their calling site likely benefit from higher reproductive success. Consequently, intrasexual selection may act on the evolution of aggressive signals. Selection acting on one call type (aggressive or advertisement) could promote evolution of other calls in the vocal repertoire via indirect selection. If call types are evolving together, selection on aggressive signals may indirectly cause RCD of advertisement calls. Given the similarities of aggressive call characteristics to the displaced traits of advertisement call characteristics in Pseudacris feriarum, I hypothesize that male-male aggressive interactions may have influenced the observed RCD in advertisement signals. To assess whether this is a possible mechanism of observed RCD in populations of P. feriarum, I compare aggressive and advertisement vocalizations among individuals and across populations to determine if call types covary and may be evolving together. Both advertisement and aggressive calls were recorded from the same individual and an average of 15 individuals were recorded per population. Populations targeted include those where RCD has been observed (FL, GA and SC - sympatry) and where it has not been observed (AL, NC, VA and SC - allopatry).;I find that all homologous signal traits measured between call types are positively correlated, and that patterns of character displacement are largely consistent between call types. Furthermore, evidence suggests strong selection on both signal types, supporting a role for intrasexual selection in contributing to character divergence in this species. This research has important implications for our understanding of the mechanisms of character displacement and the evolution of vocal signals in anuran amphibians. Intra- and intersexual selection may not be mutually exclusive forces driving character divergence (Berglund 1996). This research contributes to our understanding of the mechanisms of character displacement by exploring an understudied potential agent of selection in promoting signal divergence: intrasexual selection via male-male competition. Research in reproductive character displacement has long focused on inter-species interactions. Few studies have examined the role of aggression in reproductive character displacement (but see Adams 2004; Grether 2009 for interspecific aggression studies) and to my knowledge no study has probed the role of intraspecific competition in influencing reinforcement. If traits contributing to RCD exhibit correlated evolution with other secondary sexual traits, then it becomes necessary to re-evaluate the target(s) of selection. This system is ideal for addressing these questions because it has multiple lines of evidence in support of RCD via reinforcement, asymmetric character displacement resulting in study populations of high variability in the traits of interest, a lek breeding system in which it is likely that both female choice and male-male competition play a role in mating success, and structurally similar secondary sexual characteristics used in mate choice and conspecific competition (acoustic signals) which may evolve together given the likelihood of constraints on anuran call production.