Research Interests

My research focuses on understanding evolutionary patterns and processes among populations and species as outlined below. My primary focus is on islands, particularly remote hotspot islands of the Pacific. Hotspot archipelagoes – in which islands emanate from a single volcanic hotspot from which they are progressively carried away by a geological plate – allow us to examine how communities have changed over time and thus gain insight into the nature of processes shaping communities over evolutionary time. These archipelagoes make it possible to visualize snapshots of evolutionary history. For example, the geological history of the Hawaiian archipelago is relatively well understood, with individual islands arranged linearly by age. Thus, early stages of diversification and community formation can be studied on the island of Hawaii, an island still forming, and compared to progressively later stages on the older islands of Maui, Lanai, Molokai, Oahu, and Kauai. A roughly similar chronological arrangement is found in the archipelagoes of both the Marquesas and the Societies in French Polynesia

Adaptive Radiation in the Remote Islands of Polynesia. In common with most Hawaiian spiders, representatives of the genus Tetragnatha remain largely unknown and undescribed. Over the last few years I have described an additional 19 species and have collected more than 50 new species . This species radiation encompasses a huge spectrum of colors, shapes, sizes, ecological affinities, and behaviors. Many species are web-building, with structural modifications of the abdomen that allow concealment within specific microhabitats.  I am generating phylogenetic patterns of relationship for different groups of Hawaiian Tetragnatha, and establishing relationships to mainland congeners, employing morphological and various molecular approaches. Using this information, I can test the role of morphological, ecological and behavioral attributes in dictating patterns of speciation.

Evolution of Communities on Remote Islands. I have been examining how communities are assembled through speciation. These studies make use of the chronological arrangement of the Hawaiian Islands to visualize snapshots of evolutionary history. Within this context, we can study the spiders' adaptive radiations over time in a natural time-series laboratory of evolution. We have found that, (1) species assembly is not random; (2) within any community, similar sets of distinct ecological types, or ecomorphs ("green" which sits on leaves; "maroon," which is mostly on moss; "small brown," among twigs; and "large brown," on tree bark) arise through both dispersal and evolution; and (3) species assembly is dynamic with maximum species numbers in communities of intermediate age. The similar dynamics of species accumulation through evolutionary (species accumulate through evolutionary adaptation) and ecological (species accumulate through immigration) processes suggests universal principles underlie community assembly. Recent studies on web-building species have shown that similar web types have evolved independently in different Hawaiian spiders, suggesting convergence in web-building behaviors between quite disparate species on different islands.

In 1999 I expanded the research in Hawaii to other remote islands in Polynesia, in particular, the Society and Marquesas archipelagoes (1999, 2001) and the Australs (2002), as well as to Fiji and Micronesia. Recent studies in the islands of French Polynesia indicate that a number of the groups that have diversified here are the same as those that have diversified in Hawaii , though species diversity is not as high as that in Hawaii. Over the last few years I have been describing new species on these islands, determining their relationships within the archipelagoes, and how they are related between isolated archipelagoes. This work is based out of UC Berkeley's Gump Research Station in Moorea and also in collaboration with the Délégation à la Recherche in Papeete, Tahiti. In December 2002 I completed an expedition, funded by the Délégation à la Recherche, with Jean-Yves Meyer (pictured right on Mt Perau summit), Benoit Fontaine, Olivier Gargominy, and Ron Englund, to the southernmost Austral island of Rapa (photograph on right from near the suimmit of Mt Perau). Here we conducted a survey of the plants and invertebrates of the island, work which was made possible by the gracious hospitality of M. and Mme. Cerdan Faraire (photograph on left). Most recently (July 2005) I started field work on the spiders of Fiji as part of a survey on the arthropods of the Fijian Islands (with Eli Sarnat, Andy Bennet, and Moala Tokota'a, left). Similar work is planned for the islands of eastern Micronesia (Pohnpei, Kosrae, and Chuuk).

Comparative biogeography of spiders in the Indian & Pacific Oceans.  In collaboration with Christophe Thébaud,  Université Paul Sabatier, Toulouse, I have started examining spiders from the Mascarene Islands of the Indian Ocean. This work is part of a much larger project (ANR-BIOTAS) funded by the French government (Dominique Strasberg, Serge Quilici, and Christophe Thébaud "Analyse de la diversification des biota terrestres et marins au sein du 'hotspot' de biodiversié du Sud-Ouest de l'océan Indien" (Henrich Bruggemann, Dominique Strasberg, Christophe Thébaud, Gustav Paulay, Brent Emerson, Serge Planes, Marie Louise Cariou, Emmanuel Paradis). The goal of the spider project is to understand how communities form on isolated land masses over similar time scales, but with very different sets of potential colonists. Moreover, the islands of the Mascarenes are considerably less remote than many of the Pacific islands, Reunion being only 724 km east of Madagascar. This project will form the basis of the PhD research of Julianne Casquet, Université Paul Sabatier, Toulouse.

Evolution of color  polymorphism in the Hawaiian Happy face spider.  The Hawaiian happy face spider Theridion grallator (Theridiidae) exhibits a spectacular array of color morphs, which can be plain either 'yellow' or 'patterned' (red, black or white patches differing in form and extent, on the yellow background). In Maui populations abdominal color is controlled by simple Mendelian alleles, with 'yellow' morphs recessive to all patterned morphs. The progeny always segregate for the parental color alleles in Mendelian ratios. Fundamental differences exist in the genetics underlying color polymorphism in different populations. For example, the polymorphism appears to be controlled at a single major locus on Maui, two on Hawaii; and there is no evidence of associations of any morphs with a particular sex on Maui, whereas on Hawaii island, 4 morphs are limited to a single sex. I am investigating the mechanisms whereby these differences have arisen during colonization of the different islands.  Selection appears to be operating to maintain similar frequencies of color alleles in different populations.  Hawaiian bird predators are the most likely selective agent capable of modifying their feeding effort according to the frequency of a morph. This work is being conducted in collboration is Geoff Oxford, York University, England.
     

Adaptive radiation in Hawaiian Argyrodes (Theridiidae).  Kleptoparasitism (feeding on the webs of other spiders) is common in the theridiid genus Argyrodes. However, Argyrodes is a composite of several probably monophyletic groups, formerly recognized as distinct genera. Kleptoparasitism is characteristic of the A. argyrodes group; the rhomphaea group has a predatory attack behavior, while the ariamnes group appears to be free living, and can attack vagrant spiders, and flies that rest on the web. There are two lineages of Argyrodes endemic to the Hawaiian Islands - A small lineage of kleptoparasites in the argyrodes group, and a much larger radiation of long-bodied species. The Hawaiian representatives of the long-bodied ineage are characterized by variably elongate abdomens; all are nocturnal. While most are free-living, several species have been found as kleptoparasites on the webs of different species of  endemic Hawaiian web-building Orsonwelles (Linyphiidae) and are also found as free-living individuals. It appears, therefore, that kleptoparasitism is facultative, unlike many species groups of Argyrodes in which it appears to be obligate. Their affinities to other representatives of the genus outside the Hawaiian Islands are unclear. Current research focuses on the phylogeny of the Hawaiian long-bodied Argyrodes to determine how they diversified within and between islands. This work is being conducted with Malia Rivera.