New paper: Primary productivity explains size variation across the Pallid bat’s western geographic range

Pallid bat skullWhy do some species have larger individuals in certain parts of their range?  In many animal species, body size tends to increase with latitude. This famous ecological pattern, known as Bergmann’s Rule, was originally thought to be an adaptation for heat conservation. However, several hypotheses have been proposed, such as resource availability, resistance to starvation, and heat dissipation. We evaluate which of these hypotheses best explain geographic size variation in the Pallid bat in our new paper (Kelly et al., in press). We also investigate potential consequences of size variation by testing whether skull shape (an indicator of bite performance) changes in tandem with size.

Our results suggest that primary productivity (a proxy for resource availability) and to a lesser extent, heat conservation, best explain size variation across the Pallid bat’s western range. We also found that larger individuals have cranial traits associated with greater bite force production. This may help explain why larger individuals tend to consume larger and harder prey. Our results suggest that resource availability is a major factor explaining size, morphology, and possibly feeding performance in a wide-ranging and omnivorous bat species.

New paper on the hindlimb membrane musculature of bats

Virtual dissections in ventral view of the calcar-depressor muscle complex of one hindlimb of (a) Myotis californicus, (b) Molossus molossus, and (c) Artibeus jamaicensis.

Ph.D. student Katie Stanchak just published a new paper describing  the variation in the membrane and limb musculature associated with the calcar – a neomorphic skeletal structure found in the hind limbs of most bats. By combining diffusible iodine-based contrast enhanced computed tomography (diceCT) and standard histological techniques, Katie found that the arrangement of the calcar musculature varies among bat species that have different flight ecologies. These results suggest that the calcar may have a functional role in flight maneuverability, an idea that Katie will be testing in later stages of her Dissertation.

Katie’s article has also been featured in the diceCT blog.

More papers! Behavioral correlates of cranial muscle functional morphology

Check out the new issue of the Anatomical Record, co-edited with Adam Hartstone-Rose and Damiano Marchi! It is full of anatomical goodness, and showcases new findings and cutting-edge techniques in the study of muscle functional morphology. This issue contains several papers by Santana lab members:

Curtis A.A. and Santana S.E. 2018. Jaw-dropping: functional variation in the digastric muscle in bats. The Anatomical Record 301: 279–290. PDF

Santana S.E. 2018. Comparative anatomy of bat jaw musculature via Diffusible Iodine-Based Contrast-Enhanced Computed Tomography. The Anatomical Record 301: 267–278. PDF

Hartstone-Rose and Santana S.E. 2018. Behavioral correlates of cranial muscle functional morphology. The Anatomical Record 301: 197–201. PDF

Arbour J.A. and López-Fernández H. 2018. Intrinsic Constraints on the Diversification of Neotropical Cichlid Adductor Mandibulae Size. The Anatomical Record 301: 216–226.

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New paper: Auditory opportunity and visual constraint enabled the evolution of echolocation in bats

Why are there bats that do not echolocate, and how has body size and morphology constrained or facilitated the evolution of sensory diversity in bats? In a collaborative paper in Nature Communications, we present a broad phylogenetic comparative analysis that illuminates the trade-offs between vision and echolocation during bat evolution. You can access the open-access paper here. Enjoy!

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The evolution of anterior coloration in carnivorans

Why does the spectacled bear have facial stripes? Or why do canids have relatively plain faces? In a new article with the Caro and Stankowich labs, we explored the behavioral factors that might predict the diversity in facial and chest colors in carnivorans. Much to our surprise, we found that there might be different factors associated with the evolution facial and chest coloration in different lineages. Find out more by reading  the full article in Behavioral Ecology and Sociobiology, or its press coverage from Science.

Caro et al. 2017
Caro et al. 2017

Team returns from Costa Rica

Ada and Leith have returned from a successful trip to La Selva Biological Station, Costa Rica! This field trip was part of our project investigating the coevolution between plant chemical signals and frugivorous bats. The team collected  scent samples from fruits, and conducted behavioral experiments to measure what scents bats prefer.  They were joined by our collaborators at the Dávalos and Rossiter labs, who are working on the sensory genomics of tropical bats.

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Habitat diversity & bat activity in vineyards

Rochelle setting up bat acoustic monitoring equipment in a Napa Vineyard
Rochelle setting up bat acoustic monitoring equipment in a Napa Vineyard

For her undergraduate honors thesis, Rochelle studied bat activity in North Coast vineyards. Using acoustic equipment, she tested whether local or landscape-scale habitat diversity influenced vineyard bat activity. Rochelle and her colleagues found that local habitat diversity significantly increased overall bat activity, especially for two of the most common bat species detected (the Yuma myotis & Big brown bat).

These species are also known to consume agricultural pests. Thus, promoting their activity in agricultural landscape will not only benefit bats, but may also help suppress agricultural pests. Rochelle’s research was published last week in the journal Agriculture, Ecosystems, and the Environment.

Summer of Fieldwork: Grenada 2015

Grenada is a 344 Km2 island located in the Southeastern Caribbean. Despite its small size, it is famous for being one of the major producers of nutmeg and mace in the world. Exotic trees of many commercially important fruits, including the iconic Myristica fragrans, have been planted throughout the island’s mountainous landscape. For fruit bats, this means one thing: lots and lots of food.

Leith and I visited Grenada last summer thanks to an invitation to Saint George’s University by Dr. Sonia Cheetam Brow and Dr. Diana Stone. Sonia and Diana are virologists at SGU’s School of Veterinary Medicine, and they were interested in doing research on viruses that may be hosted by Grenadian bats. This research is very important because bats in Grenada are abundant and use many man-made structures for roosting, putting them in close proximity to humans. Additionally, we were interested in surveying what bat species still live in Grenada. Very few studies have characterized the island’s bat fauna and the last inventory precedes the damage caused by Hurricane Ivan to the region.

Much of our efforts went into finding bat roosting sites nearby population settlements, while at the same time spanning all of Grenada’s parishes to get a full coverage of the island major habitats. Our collaborators put a lot of effort networking with locals to find bat roosting sites. While people in Grenada are very familiar with the presence of bats, locating bat colonies proved trickier. First, there is little knowledge about natural roosts, with the exception of one small cave that is home to hundreds of Artibeus jamaicensis and Glossophaga longirostris. Second, bats are considered “pests” by most locals, and any group of roosting bats found in or near a house is usually exterminated quickly.

Luckily for us and the bats, natural disasters and economic downturns have resulted in many buildings (e.g., large vacation houses, bars, barns) to be left completely abandoned throughout the island. We found that these structures now provide new and relatively conflict-free roosts for hundreds of bats in Grenada. Walking into some of these houses felt sort of post-apocalyptic: lianas and other plants growing inside, bats hanging from the ceiling or flying around by the dozens, walls covered in guano, and floors covered in a thick layer of bat-dispersed seeds that were meant to grow in the forest.

In all, through roost searches and mistnetting, we collected only four species of the 12 that have been previously reported in Grenada: Artibeus lituratus, Artibeus jamaicensis, Glossophaga longirostris, and Molossus molossus. It is unclear if the diversity of bats has decreased due to human activity and natural disasters in the island, or if the findings are due to the need of a bigger sampling effort.

While in Grenada, we were also able to give guest lectures at SGU, talk with locals about bats, learn methods for necropsy and pathobiology sampling, and learn about the rich Grenadian history and culture. Leith and Sonia are now creating a guide to the bats of Grenada, which we hope can contribute to educating the population on the importance of bats for ecosystems and aid in their conservation.

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.