February 13, 2020
5:00pm 1100 TLSB
" Graduate Student Presentations "
Department of Ecology and Evolutionary Biology, UCLA, Kraft Lab
“Rich forest, poor soil: Leaf nutrients and habitat specialization in an Amazonian forest”
The non-flooded forests of the Central Amazon are among the most diverse forests on Earth, yet they grow on extremely weathered and infertile soils. Even within these forests, however, soil fertility can vary substantially and is often associated with local topography, thus creating very contrasting habitats such as the top of plateaus and the bottom of stream gullies. While some plant species seem indifferent to these topo-edaphic gradients, several species have specialized and are thus restricted to one of these habitats. Habitat specialization in plants might be the result of a growth-survival tradeoff: species that can tolerate the harsher conditions of the plateau may be outcompeted by the faster-growing species found in the gullies. Because the concentration of nutrients in the leaves are the link between soil fertility and plant growth, in this talk I will explore how leaf stoichiometry relates to the habitat specialization of hundreds of tree species. Furthermore, I will show how intraspecific variance in leaf nutrient content can predict the degree of specialization of a subset of common Amazonian tree species.
Department of Ecology and Evolutionary Biology, UCLA, Alfaro Lab
“Phylogenomic Analysis Resolves Contentious Relationships and Divergence Times of a Global Radiation of Small Fishes”
Gobiarian fishes, exemplified by gobies, sleepers and cardinalfishes, have successfully radiated across coastal marine and aquatic habitats worldwide, yet the biological traits considered responsible for generating their great diversity, such as small body size and rapid rates of evolution, have also mired resolution of their phylogeny. Currently accepted relationships within Gobiaria rest largely upon molecular studies, and although consensus has emerged regarding core relationships along major lineages, the root topology is contentious, with multilocus and phylogenomic studies resolving nursery (Kurtidae) and cardinalfishes (Apogonidae) either as reciprocal or sequential sister taxa to other gobiarians. Here I use comprehensive sampling of higher taxa and phylogenomic analyses incorporating more than 700 loci to resolve systematic relationships of gobiarians and estimate a timescale for their diversification. My results reveal that uncertainty in the position of nursery and cardinalfishes at the root of the tree can be attributed to incomplete lineage sorting. I place the origin of Gobiaria in the youngest age of the Early Cretaceous (104 Ma), find major clades of gobies, sleepers, and cardinalfishes appear in the early Eocene (~50 Ma), and identify diversification of goby lineages in the Oligocene and Miocene. These results support the current two-order classification placing nursery and cardinalfishes in Kurtiformes and the remaining gobiarians in Gobiiformes, confirm the clade-based phylogenetic classification of eleven gobiarian families, and provide evidence for classifying wrigglers in a twelfth gobiarian family, Xenisthmidae.