Date of Award
Doctor of Philosophy
Ecology and Evolutionary Biology
Susan E. Riechert
Brian C. O'Meara, Gary McCracken, Todd Freeberg, Haileab Hilafu
Organisms have evolved complex behavioral, morphological and physiological traits in response to various selection pressures. These phenotypes are usually composed of many traits that may or may not be genetically or phenotypically correlated. Correlations of both types can lead to evolutionary trade-offs, which may be broken over long evolutionary time periods through such mechanisms as the decoupling of genetic linkages and the development of phenotypic plasticity. Behavioral traits associated with temperament provide an excellent system in which to evaluate underlying mechanisms of the establishment and decoupling of genetic linkages. Other traits, such as the type of web that a spider builds, may not be so labile since there is greater complexity associated with, for example, web spinning organs and prey specialization. I initiated my investigation into these questions by examining the extent to which behavioral traits and their correlations change over ontogeny and how this varies between males and females of the grass spider Agelenopsis lisa (Chapter 1). I then considered how these behavioral traits change over macro-evolutionary time by using a dated phylogeny of 19 spider species of the RT3 spider clade (Chapter 2). Finally, I considered web evolution across all of spiders (Araneae) to examine how web type influences spider diversification (Chapter 3). My results indicate that behavioral traits are highly repeatable at certain life-stages, such as the penultimate stage in males that corresponds with increased prey consumption in preparation for searching for mates as an adult. While there are very few significant behavioral trait correlations that would suggest the presence of a behavioral syndrome, the weak correlations are consistent across ontogeny. Behavioral trait correlations are not conserved across macro-evolutionary time, suggesting that temperament traits are likely free to evolve independently from other behavioral traits. Several of the traits examined are evolving towards phenotypic optima related to the habitat they reside in. However, some traits are particularly slow to evolve, which may result in maladaptive scenarios where species get “stuck” when the environment changes quickly. Finally, I found that weblessness is associated with higher diversification rates in spiders and reduced rates of diversification in orb weaving spiders.
Bosco, Jennifer Marie, "Trait Evolution in Spiders: Perspectives on the Evolution of Behavioral Syndromes and Web Structures. " PhD diss., University of Tennessee, 2017.