Hairy legs in the Nursery

2014 REU Intern Anne Gibbons

ANNE GIBBONS

Junior Environmental Studies major at University of Michigan - Ann Arbor

REU Mentors: Dr. Petra Sierwald (Curator, Arachnida and Myriapoda, S&E) and Dr. Estevam da Silva (Postdoctoral Researcher, Arachnida and Myriapoda, S&E)

Symposium Presentation Title: Fishing around the world: spiders of the genus Dolomedes

Symposium Presentation Abstract: With 44,906 species described, spiders rank seventh in species diversity among other orders of organisms. Spiders can be found on all continents except Antarctica, living on vegetation, webs, and even water. The family Pisauridae is commonly known as nursery web spiders. In this family, the female spider builds a silken nest for her young and protectively guards it until the juvenile spiders are mature enough to leave. Of the 48 genera of Pisaurid spiders, one cosmopolitan genus, Dolomedes, is the most diverse, with 98 described species. Many species of Dolomedes are called “fishing spiders” because they are usually found near bodies of fresh water and are able to run across the surface of the water, even submerging to hunt small fish. Using the Dolomedes collection in the Field Museum, as well as loans from other museums, the goal of the project was to add images, descriptions, and measurements to the morphological atlas of Dolomedes specimens. Using this data, we created a phylogenetic tree to tell us the evolutionary history of the genus. To do this, spiders were examined with a light microscope, dissected, mounted and dried on stubs for the scanning electron microscope (SEM). We dissected the tarsal claw and male and female genitalia because they are the most complex morphological features of spiders used for identification. In addition, spine patterns on the leg from each species were recorded and coded into characters. Microscope and digital images were used to compare morphological characters between species, eventually using these characters to create a phylogenetic tree with programs Mesquite and TNT. Finally, during the examination of material from a Chinese collection, we found the male of Dolomedes raptoroides, which was illustrated using SEM images and photos. The specimen was measured and described and we prepared a manuscript for publication in the periodic Zootaxa. In the final phylogenetic analysis, our data generated 5 most parsimonious trees, using equally-weighted characters. The final consensus tree included 23 taxa and 39 characters (116 steps, Ci=39, Ri=50), but the results did not related the morphological resemblance between species and the geographic distribution. This may be due to gaps in the species sampling from Africa and Europe. In the future, an analysis with a more geographically diverse sample of Dolomedes species will allow for a greater understanding of past evolutionary events.


Original Project Title: Hairy legs in the Nursery

Original Project Description: With over 300 species, the nursery web spiders (family Pisauridae) have conquered the world; they can be found on every continent. The family members hunt on the water, in the vegetation, in trees, on the forest floor, and in webs. Females of the family carry their silken egg sacs in their fangs, and build a nursery web for the spiderlings, when these are hatching. As in other spiders, the Pisauridae have complex male and female copulatory organs, and hairy legs, often with an intricate spine pattern. Analyzing the evolutionary relationships among the over 40 genera of the family using morphological and molecular characters in conjunction with their geographic distribution will enable us to explain speciation events, and trace geologic events, such as glaciations, climate and vegetation changes of the past.

Research methods and techniques: The intern will be trained in spider morphology, identification, and dissections. S/He will acquire skills to operate  light and scanning electron microscopes, to produce and to manipulate images using sophisticated software. The newly generated morphological data will be added to the existing data pool, allowing comparative analyses and phylogenetic inference using these data.