Gibbons—endangered and inadequately studied small apes—are species-rich compared to great apes. Their species-level phylogeny has been largely resolved, although certain discordances exist, perhaps because of hybridization between species. My research draws upon wild gibbon specimens housed in museum collections around the world to expand knowledge about suspected interspecific hybridization of gibbons in Southeast Asia, which could yield a valuable evolutionary perspective on potential interbreeding between late coexisting hominin lineages, such as Neanderthals and anatomically modern humans. The use of both genetic (mitogenome and exome) and 3D morphological (surface scanning and geometric morphometrics) data from the same specimens to detect hybridization also provides the opportunity to test how hybridization manifests in skull shape. Moreover, my research has applications for conservation biology. Most gibbon species are classified as “Endangered” or “Critically Endangered”, yet conservation efforts are often focused on great apes rather on these small-bodied relatives. Targeted action is acutely needed to promote gibbon conservation, and one way to achieve this is to confirm taxon identity as a basis for appropriate recognition of individuals for reproduction in captivity with a view to subsequent reintroduction into their natural habitats.
The “island rule” is a generalization which states that over evolutionary time on islands, small-bodied species become larger because of reduced predation, and large-bodied species become smaller due to severely limited food resources. However, it is unclear how certain anatomical parts change with the evolution of smaller body sizes. Therefore, a portion of my research is dedicated to (1) establishing whether or not island dwarfing is universal among large-bodied Southeast Asian mammals, (2) determining how brain size scales to body size on the mainland versus islands of various sizes, and (3) analyzing little-studied changes in dimensions of the skull between mainland and island-living individuals.
Southeast Asia and museums
Southeast Asia is a spectacular region for studies of evolution on islands because there are thousands of islands of various sizes and types. Specifically, there are oceanic islands (land surrounded by water and never connected to the mainland) and continental islands (continental shelf elevations isolated by water that may connect with the mainland when sea levels are low). Due to deforestation and the pet trade, many organisms in the region are endangered. So instead of focusing on individuals in the field, I utilize extensive collections in state-of-the-art natural history museums around the world, where the remains of Southeast Asian mammals are kept. So I spend quite a bit of time behind the scenes at these museums to collect data.
Island dwarfing has often been assumed to be universal, and the degree of dwarfing depends on island size. So I am interested in testing whether or not island dwarfing is a general rule for mammals from Southeast Asia. Additionally, I am using allometric scaling, the study of size relationships, to analyze how brain size scales to body size in island mammals. Since the discovery of the small-brained Homo floresiensis, a new hominin species, on the island of Flores, in Indonesia, scientists have debated over hypotheses for why it has such a tiny brain. Through my research, I hope to shed some light on the specimen by answering a sidelined but fundamental question: How does brain size scale to body size in island-living mammals generally?
3D Geometric morphometrics
Geometric morphometrics is a method that allows me to analyze the morphology of museum specimen skulls by collecting 3D coordinates of designated landmarks on the skull. To collect data, either a microscribe or a NextEngine 3D surface scanner is utilized. We then use Procrustes superimposition and principal component analyses to answer our questions.
It is clear that relatedness between and within species is a key issue when analyzing comparative data, and the need to use these phylogenetic techniques for comparative data in evolutionary anthropology and biology have been stressed by Felsenstein (1985), Nunn (2011) and Stone et al. (2011). Therefore, I am using next generation techniques in ancient DNA labs to sequence the genomes of organisms. The tissues used for my research are collected by scraping residual dried tissue flakes from 50-100 year old museum specimens. With these data, we tease apart relationships between populations to better understand phylogeography and to control for phylogenetic relatedness in morphological analyses.