February 14 2019

5:00 pm 1100 TLSB

EcoEvoPub Series

Graduate Student Presentations


Nick Russo
Department of Ecology and Evolutionary Biology, UCLA

Title:Avian Spring Migration as a Dispersal Mechanism for a Forest Insect Invasion

Birds act as long-distance dispersal agents for plants, animals, and other organisms during migration, and can contribute to the range expansion of invasive species. The hemlock woolly adelgid (Adelges tsugae) is a largely sessile, invasive insect that decimates eastern hemlock forests and relies on vectors to continue spreading northward. Since dispersing adelgid nymphs (crawlers) are most abundant from late April to late May in the Northeast U.S., we investigated the potential for birds to disperse this invasive insect over long distances during spring migration. We experimentally tested two modes of adelgid crawler transfer between hemlock branches and mounted passerine specimens, collecting crawlers from the birds feathers after a period of contact with infested branches. Crawler transfer was greater when birds actively brushed against an infested branch than when they simply perched, and transfer rates peaked in May, coinciding with the phenological peak emergence of adelgid crawlers. We also sampled the plumage of wild birds captured in Connecticut hemlock forests over two years of crawler activity and found significantly more crawlers on birds during spring migration than during the subsequent breeding seasons. The crawler load of sampled birds mirrored the phenological variability in crawler abundance in the forests of capture. Finally, we confirmed experimentally that crawlers move off bird plumage and settle on uninfested hemlock foliage. Our results implicate an influence of avian ecology and life history in the dispersal of this invasive insect.

Evan Doughty
Department of Ecology and Evolutionary Biology, UCLA

Title: Ecological and Evolutionary Dynamics of Body Mass in North American Ungulates

Body mass is deeply integrated with an organisms ecology, physiology, morphology, and overall life history. Accordingly, the evolution of mammalian body mass has seen considerable attention, particularly with in the context of climate and environmental change throughout the Cenozoic. Specifically, prior analyses document persistent increases in body mass among numerous groups of mammals throughout the Cenozoic. To date, most studies have focused strictly on documenting the general pattern of these trends (e.g. Copes Rule) across various taxonomic scales and relate them to environmental changes. Revealing the drivers of these trends, and the precise mechanisms by which they drive body mass evolution requires more detailed quantitative analysis. In this study, we use phylogenetic comparative methods to estimate the rates of body mass evolution of North American ungulate mammals (orders Artiodactyla and Perissodactyla). Abiotic drivers of body mass evolution are expected to place similar selective pressures on distantly related lineages (e.g., horses and camels). We therefore determined whether evolutionary rates shift across all ungulate clades throughout the Cenozoic (55 to 5 Ma). We estimated body mass of 678 species North American ungulates from measurements of their cheek teeth. Using a framework phylogenetic hypothesis, we fit Brownian motion models of increasing complexity to determine the number and timing of significant rate shifts. Our results indicate the evolutionary history of ungulate body mass is characterized by multiple rate shifts throughout the Cenozoic. Median evolutionary rate initially is high during the early diversification of ungulates, and shows a sharp increase in the late Middle to latest Eocene (~42 - 34Ma), with highest rates near the Eocene/Oligocene boundary. Median rates then decline precipitously throughout the remainder of the Oligocene, and continue at low levels throughout the Miocene. These results indicate that the apparently gradual increase in median ungulate body mass throughout the Cenozoic is actually underlain by fluctuating evolutionary rates. Notably, the dramatic global cooling at the Eocene-Oligocene boundary seems to coincide with a substantial change in evolutionary dynamics.











































































































































































































































































































































































































































































































































































































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