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Trophic niche differentiation within the adaptive radiation of Hawaiian Tetragnatha spiders


The Hawaiian Tetragnatha spiders are a remarkable and well-documented example of adaptive radiation. With ca. 50 species exhibiting a diverse range of morphologies and ecological affinities, all having evolved within the last few million years, this system has a great deal to offer for studies of evolutionary ecology. Furthermore, due to Hawaii’s age-structured arrangement of islands, it is possible to infer past processes in this lineage’s evolutionary history by using a space-for-time substitution. Although the ecological affinities of some Hawaiian Tetragnatha, notably the members of the Spiny Leg (actively hunting) clade, have been well documented, much is still unknown about the ecological niches of web-builders, and about the precise nature of ecological interactions that occur among both Spiny Leg and web-building species. Importantly, little is yet known about the dietary compositions of different Hawaiian Tetragnatha species. Diet is likely to play a critical role in the ecology of these spiders, all of which are obligate predators and therefore potentially compete for prey; and because the need to hunt prey can exert significant selective pressure, trophic ecology may also have played a part in driving the evolutionary diversification of this lineage.

The work presented here examines the trophic niche ecology of Hawaiian Tetragnatha in a geographic and evolutionary context. Working at multiple geographic scales – within a single forest site, among sites on an island, and across sites on three different islands – I characterize the trophic niches of several Tetragnatha species and probe the extent to which these niches overlap. I use multiple types of data to describe trophic niche, including web architecture (i.e., hunting behavior), stable isotope signatures of N and C in the spiders’ tissues, and molecular identification of gut contents. Additionally, I present a phylogenetic hypothesis for the entire adaptive radiation, which lays the foundation necessary for analyzing ecological dynamics in the context of the spiders’ evolutionary history. My work adds critical information to our knowledge of the natural history, evolutionary history and ecology of Hawaiian Tetragnatha, and builds on our understanding of the ecological and evolutionary dynamics of adaptive radiation.

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