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Summer of fieldwork: Costa Rica

In July, Jeff Riffell, David Villalobos and I went to La Selva Biological Station in Costa Rica to work on our NSF-funded project “Chance or necessity? Adaptive vs. non adaptive evolution in plant-frugivore interactions”. Going in the middle of the rainy season during an El Niño year made for a very stormy, wet, muddy and soggy couple of weeks. In what I’d like to call “the field season triathlon” (hiking, trawling, and reaching up), we were able to collect Volatile Organic Compounds (VOC) from the fruits of over a dozen species of Piper and other bat-dispersed plants, and fecal and tissue samples from nearly 100 bats. While mapping the VOC profiles onto phylogenies will enable us to investigate how fruit scent evolves in this system, analyses of the bat fecal samples will allow us to expand our current understanding of how much the bats rely on the different Piper species for food.

This autumn, Leith Miller and Ada Kaliszewska are continuing sample collection and analysis for this project in La Selva. Meanwhile, Laurel Yohe (a PhD student at our collaborating lab) gave a talk at the North American Symposium for Bat Research in which she presented preliminary results  on the olfactory receptors of short-tailed fruit bats.

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Summer of fieldwork: The Philippines

Time flies when you’re having fun, or if you are catching bats around the world, which is basically the same thing. This is the first post reporting our fieldwork trips this summer, which included four countries across four ecogeographic regions!

It all started with a trip to the Philippines with a team composed by the Sears, Dávalos, Dumont and Santana labs, Dr. Susan Tsang, and colleagues from the National Museum of the Philippines. Our main goal was to collect Old World fruit bats (Pteropodidae) for a study that will contribute to understanding why these bats have much lower cranial diversity than their New World counterparts (Phyllostomidae). Answering this question involves integrating studies on cranial development, bite force and feeding behavior across a range of pteropodid and phyllostomid species.

What impressed me the most upon arriving to the Philippines was the overwhelming population density (Luzon is the 4th most populated island in the world). Our field sites were near, Liliw, a highland town in the southern portion of the Laguna province. Even several hours away from the capital, there were no apparent sights of the kind of habitats that I would expect could sustain bats. Yet, despite the loss of habitat and the pollution, some bat species still seem to fly through this landscape and take advantage of fruiting trees during their nightly foraging activities. Using mist nets suspended a few dozen meters above the ground, and skipping on any form of night sleep, we were able to collect five of these bat species: Cynopterus brachyotis, Eonycteris spelaea, Macroglossus minimus, Ptenochirus jagori, and Rousettus amplexicaudatus. Though this was a considerably lower diversity than what I’m used to experiencing in the Neotropics, it was astonishing to see these species live for the first time.

From the beginning, it was quite evident that pteropodids are a different ballgame than phyllostomids when it comes to recording performance and feeding behavior. Although both Cynopterus and Ptenochirus were reminiscent of Neotropical Artibeus species in their extravagant use of distress calls in the mist net, their approach towards scary things (like a bite force meter) seemed quite different. These species, as well as the rest of the pteropodids we caught, tended to rely more on their flight response when faced with experimental situations – cue adorable bat covering its face with its wings. With much patience and creativity, however, we were able to get bite force data for new species to complement previous datasets for our study. Likewise, Karen Sears and Dan Urban set up a lab in the field that allowed them to conduct unprecedented experiments and observations on the skull development of several pteropodid species.

My favorite catch of this trip was Rousettus, despite the fact that their activity peaked between 2-4 AM, sending the sleep-deprived team into panic mode to quickly release dozens of bats from the nets before sunrise. Rousettus were extremely gentle bats, and it was a treat to hear their tongue clicks (a form of echolocation) as they flew about and while we handled them. The young of at least one species of Rousettus may learn vocalizations in similar ways to the way human babies do. What’s not to love?

The data and samples collected during this trip will serve for dozens of studies that will expand the understanding of this diverse and still obscure group of bats. As it often happens, I came back with many more research questions than when I left. Here’s to hoping there will be more pteropodids in our future.

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Notes from the field: Ectophylla alba

Ectophylla alba, the Honduran white bat, is a unique species of Neotropical leaf-nosed bat. Not only they are among the very few species of bats that are almost completely white, but they are extremely specialized in their diets and roosting ecology. Males and females of the species skillfully construct delicate tents from the leaves of Heliconia plants, and their diet is restricted to fruits of Ficus colubrinae plants. During our most recent trip to Costa Rica, we had the opportunity to record and measure these bats as they frantically fed from a F. colubrinae fruiting tree (below). Fruiting events in Ficus plants occur in short bursts and are scattered throughout the landscape, and E. alba likely choose places to “camp out” according to the potential for food availability.

 

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Integration of bat skulls

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.

Does nasal echolocation influence the modularity of the mammal skull? – Santana & Lofgren (2013) – Journal of Evolutionary Biology