November 21, 2019

5:00 TLSB 1100

EcoEvoPub

" Graduate Student Presentations "

Aidan Couzens

Department of Ecology and Evolutionary Biology,

Sears Lab, UCLA

“Kangaroo Evolution and the Grassland Revolution in Australian Ecosystems”

Kangaroos are the most diverse herbivores in Australian ecosystems but the factors driving their success, especially the role of environmental change, is poorly understood. The most ecologically successful living group of kangaroos are the grass-eating macropodin kangaroos which include the largest living marsupial, the red kangaroo, as well as diminutive members like the quokka. Up until around 40 thousand years ago these modern kangaroos shared ecosystems with a now extinct clade of short-faced kangaroos which included species up to three-meters tall. Previous evidence, especially molecular phylogenetic dating has tended to implicate the spread of arid biomes during the Miocene as key to the origin of many Australian vertebrate groups. To better understand the role of environmental change in kangaroo evolution we measured changes in molar tooth crown height and dental wear, a proxy for levels of dietary abrasion, on fossil and modern kangaroo specimens spanning the past 25 million years. The results reveal that during the mid-Pliocene many modern kangaroo lineages shifted toward consuming abrasive grasses which prompted a rapid evolutionary increase in their molar tooth crown height. In contrast, the extinct short-faced kangaroos were primarily browsers but there is evidence that they became more generalist consumers as aridity intensified during the Pleistocene. Strikingly, when compared with browsing herbivores on other continents, short-faced kangaroos appear to have diversified despite declining ecosystem productivity. Our results suggest that grazing herbivore niches originated relatively recently in Australian ecosystems compared with the northern continents and do not support climate change as the key extinction driver of the short-faced kangaroos.

 

Sarah J. Jacobs

Department of Ecology and Evolutionary Biology,

Zapata Lab, UCLA

“Peering into the nature of species: considering genomic and phenotypic evidence on an equal footing”

Species are a fundamental unit in the biological sciences—they are central to biological theory and often the primary unit of experimental work. Additionally, they are a unit of measure and assessment in biodiversity questions, which directly impacts how we protect, conserve, and manage the world around us. Subsequently, the way we delimit species is important. Current species delimitation approaches seek either to identify ‘good species’—those with congruent genomic and phenotypic patterns of differentiation—or they prioritize molecular evidence when delineating species. This is in the face of growing genomic evidence that species are much more reticulate than previously thought, calling into question the dominant paradigm about the nature of species. Similarly, our awareness of biological entities that do not align with the idea of a ‘good species’ (i.e., cryptic species and syngameons), suggests that prioritizing a single line of evidence over another could mislead species delimitation efforts and have downstream consequences when using the species as a unit of analysis. Here, I present a framework for species delimitation that considers genomic and phenotypic evidence on equal footing, combining current tools and techniques, utilized in a novel way, to peer into the nature of species.

 

Thursday, November 21st, 2019 @ 5 PM

1100 Terasaki Life Sciences Building [TLSB]