Previous research in vertebrates has demonstrated that selection can cause rapid evolutionary changes in cranial modularity, that is, how many and which parts of the skull vary and evolve together. Mammals, however, seem to have maintained a simple pattern of cranial modularity throughout their evolutionary history and across tremendous ecological and morphological diversity. All mammals studied to date have two cranial modules, the braincase and rostrum. But what happens when parts of the skull acquire novel functions? Does cranial integration remain the same? We just published a study in which we test whether skull modularity has been remodeled in rhinolophid bats due to the novel and critical function of their nasal cavity in echolocation. Rhinolophids have greatly enlarged nasal cavities that vary in shape across species, thus we predicted that nasal echolocation resulted in the evolution of a third cranial module, the ‘nasal dome’, in addition to the braincase and rostrum modules. Remarkably, despite large variation in the shape of the nasal dome, we found that the integration of the rhinolophid skull still follows the two-module pattern found in other mammals. In other words, the shape of the nasal cavity changes together with the shape of the snout across species. We also found distinct trends in the evolution of skull shape across these bats’ geographic distribution. Our findings highlight that broad morphological and functional diversity can still be achieved in spite of a relatively simple modular template.
After the Belize warm up, I went to Costa Rica to work at two main sites, the Tirimbina Forest Reserve and OTS La Selva research station. The major goal of this trip was to collect fecal samples for molecular dietary analyses in foliage-gleaning bats, along with performance data across bats and other mammals. These data will allow us to understand patterns and mechanisms of food resource partitioning within and across dietary guilds. With the help of collaborator Dr. Bernal Rodríguez Herrera and his students at the Universidad de Costa Rica, we were able to collect data for a total of 24 species of bats, plus several kinkajous.
One of the trip highlights included catching Honduran white bats (Ectophylla alba), a very small frugivore that builds tents in the vegetation. Findings about Ectophylla’s tent construction behavior have changed the paradigm that only male bats build these roosts as part of a resource-defense polygynous system; female Ectophylla also contribute to building tents. A second high point was collecting a wrinkle-faced bat (Centurio senex), a very rare and morphologically derived stenodermatine that is built to bite. Just as impressive, the second largest bat in the Neotropics (Phyllostomus hastatus) made its appearance in our nets and contributed to our dataset. With such stunning biodiversity, we are very much looking forward to continue work and collaborations in Costa Rica. Pura vida!
The field season 2013 started with a bang! This May, I joined an international team of over 40 bat biologists in an expedition to Lamanai, Belize. The trip was led by Dr. Brock Fenton, a bat expert from the University of Western Ontario who has been visiting the site for over 20 years. Lamanai is impressive with biodiversity and archeological remains; jaguar faces not only decorate the Mayan temples, but these animals can be seen around the area as well.
With a few dozen bat researchers in the group, projects were as diverse as the bats: morphology of wings, muscles, skulls and reproductive tracts, echolocation, feeding behavior, diet, flight aerodynamics, radio tracking, viruses, and more. We caught around 500 bats from 28 species, the great majority of which were released unharmed. The voucher specimens that were kept will serve as the basis of studies in labs across five institutions, which is an impressive use of field-collected specimens. These will continue to be available to researchers at the American Museum of Natural History’s Mammal Collection.
Why do primates have such colorful and distinct faces? We have been trying to answer this question in a broad comparative context by integrating data on the two most likely drivers of primate facial diversity: sociality and ecology. A major challenge during this research has been to quantify the facial patterns in a way that is comparable across hundreds of primates species. So, we devised a metric, “facial complexity”, which represents how many colors there are in a primate’s face. Much to my own surprise, the evolution of facial complexity seems to be tightly linked to social group size and species sympatry. This is usually a positive relationship (Neotropical primates are the oddball), indicating that differences in the number of colors in primate faces provide cues that might be used for species and/or individual recognition.
This research has been getting a lot of media coverage (I guess everyone likes monkeys!), and a new article in Discover magazine does an excellent job at decribing our complexity scale. Check it out:
Welcome to the Santana Lab at the University of Washington and the Burke Museum of Natural History and Culture. We combine studies on the morphology, performance, behavior and ecology of mammals to understand their evolution and diversity. We are interested in questions such as:
- Why are there differences in diversity across mammal groups?
- How is variation in morphology related to the performance of organisms in nature?
- What is the impact of behavior in the evolution of performance and morphology?
- What is the role of ecomorphology in shaping ecological communities and in diversification?
Browse this site to learn more about the lab and find out about opportunities to join. Follow this site for lab news.