Behavioral and morphological plasticity in an adaptive radiation of Hawaiian 'spiny leg' Tetragnatha spiders (Araneae: Tetragnathidae)

Adaptive radiation is characterized by the rapid diversification of a lineage into an array of morphologically divergent species that have adapted to exploit different environments or resources. This dissertation quantifies morphological, behavioral and cognitive variation associated with the diversification of Hawaiian "spiny leg" Tetragnatha spiders. This clade is notable for both its breadth of morphological diversity, and the constraints within which this diversity has evolved: Most of the seventeen currently described species can be assigned to one of four ecomorphological groups that share similar shapes, colors and ecological affinities associated with crypsis. Communities of "spiny leg" Tetragnatha often include multiple sympatric species, but not multiple members of the same ecomorph.;Chapter 1 focuses on a single basal species, T. kauaiensis, that displays two ecomorphs depending on the age of the animal. Principal components analyses of morphological characters associated with crypsis demonstrate that the ontogenetic disparity within this species corresponds to adult morphological diversity of several derived species. Heterochrony is proposed as a significant factor in the diversification of the clade. Further exploring the role of ontogenetic diversity in this group, Chapter 2 describes differences in activity patterns that vary with age, using loss of web building behavior to determine the specific role of the web in dictating differences in movement. Immature individuals are found to be less itinerant than mature spiders, but no differences are found between species or between sexes.;Chapter 3 describes ecological differences in selections of cryptic substrates for different species and concludes that substrate selection is unlikely to reduce competition between species, inviting alternative hypotheses for the observed community structure. Frequency-dependent selection by visual predators is proposed as a process that could facilitate colonization of communities by novel phenotypes leading to limiting similarity without direct competition. Frequency-dependent processes are also hypothesized to play a role in selection for the cognitive differences described in Chapter 4. Here, intraspecific and interspecific differences in reaction to two aversive stimuli reveal a broad diversity of response norms in the clade, as well as behavioral consistency within individuals.