Biological Sciences, School of


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A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Sciences (Ecology, Evolution, & Behavior), Under the Supervision of Professor Eileen A. Hebets. Lincoln, Nebraska: July, 2011

Copyright 2011 Dustin J. Wilgers


Evidence of signal complexity is seemingly pervasive across animal communication systems. Exploring signal function may provide insight into how these displays evolved and are maintained. This dissertation examines the courtship signal function in a grassland wolf spider. Rabidosa rabida lives in an extremely complex environment, and males use complex displays incorporating both visual and seismic modalities. Using several approaches I provide insight into the content and efficacy of the various signal components, as well as how variation in these displays influence female mating decisions in isolation and combined.

First, I manipulated male and female body condition using diet quantity manipulations and performed mate choice trials using females of each diet across two different age classes. Female mate choice decisions varied with diet and age. Overall, younger females were choosy, mating more often with good condition males, while older females mated indiscriminately. Next, to determine which signal components may be useful in female mate assessment, I explored the condition-dependence of the signal components and tested their efficacy by performing mate choice trials in environments that differed in modality transmission. Both visual and seismic components are condition-dependent, and are sufficient to maintain copulation success when detected in isolation. Thus, each signal component may serve as both a content- and efficacy-backup when facing variable sensory environments. Lastly, I manipulated both foreleg ornamentation and the seismic display, and presented them to females both in isolation and combined, to determine if and how variation in each component influences female mating decisions. Females were choosy based on the seismic display alone, and only discriminated males based on foreleg ornamentation when detected along with a seismic signal, suggesting an inter-signal interaction.

Together, these experiments suggest that the sources of selection acting on male R. rabida are just as complex as the courtship displays used during mating interactions. The courtship signal components making up the display appear to function by maintaining both copulation success and mate assessment across a variety of environments encountered.