Size matters in vampire bats, new study finds

The female common vampire bat is larger than its male counterpart, according to a new study from Virginia Tech researchers.

Luis E. Escobar and Analorena Cifuentes-Rincon were recently part of an international team that studied almost 500 specimens spanning over a century of the species, Desmodus rotundus, that live throughout Colombia. Published in PLOS One, the researchers believe their findings could be foundational to better understanding how sex differences influence the spread of viruses, particularly rabies, and their mitigation.

“Desmodus rotundus is one of the most interesting bats in the world — and not just because it is one of just three species that feed exclusively on blood, but also because they can harbor viruses while showing a unique tolerance to infection,” said Cifuentes-Rincon, a Ph.D. student in the Department of Fish and Wildlife Conservation and first author.  

The researchers verified that the female vampire bat is larger than the male by measuring several different features, but they found that their forearm and tibia, or shinbone, lengths were the most accurate indicators of size. 

An associate professor in the College of Natural Resources and Environment, Escobar said the work is the first step in exploring if the bats’ virus transmission rates follow the same pattern as that of mosquitoes.   

“[Female] mosquitoes bite more because they are bigger and need more meals, and it seems they transmit more virus.” said Escobar, an affiliate with the Center for Emerging Zoonotic and Arthropod-borne Pathogens and Rincon’s mentor. This is a much-needed area of research for mammals carrying diseases of direct transmission.” 

Similar to mosquitos, the common vampire bat is a reservoir for rabies, a widespread zoonotic disease. It is estimated that bat-to-cattle rabies transmission results in a more than $8 billion loss in South America. And he believes that estimate to be low. 

“We are really interested in rabies because bat-borne rabies is on the rise in Latin America,” said Cifuentes-Rincon, a native of Colombia. “And rabies is one of the most mortal diseases in the world for humans and for all mammals.”

Colombia is home to all three vampire bat species, according to Cifuentes-Rincon. In the case of the common vampire bat, its climatic flexibility allows them to easily adapt to the tropical climate at sea level as well as the cold temperatures at the higher elevation of the Andes mountains. 

Cifuentes-Rincon said the common vampire bats are very social, which contributes to the constant transmission of pathogens among each colony. Their feeding habits – regurgitation of food for younger bats – and frequent grooming among the colony also contribute to pathogen transmission. 

Escobar said the common vampire bat’s natural diet of more than 100 species is replaced in many sites by cattle when the forest is cleared. Wild creatures naturally move throughout the landscape and finding them may be difficult. Cattle are easy prey. This plays into the natural feeding patterns of the common vampire bats, as they prefer to go back to feed on the same individual night after night. 

“In the wild, when common vampire bats bite all these different wildlife species, many of the animals attacked, such as birds, don’t die,” said Escobar, an affiliate with the Fralin Life Sciences Institute’s Global Change Center and Invasive Species Collaborative. “It’s just when we modify the landscape, remove wildlife, and put only cattle that we have these frequent and large outbreaks in the tropics. There seems to be an association between an increase of attacks to cattle that is followed by attacks to people. But we need more research to be sure.” 

Escobar said the current study hinged on the researchers’ ability to tap into the many Colombian museums’ specimens and was unique. About 444 specimens studied were from  museums and represented climactically diverse regions, which allowed the team to confirm the long-term trend that females have been larger. 

“Females are larger, likely due evolutionary selection linked to reproductive investment,” Cifuentes-Rincon said. “They experience a long gestation – about seven months – followed by lactation that can last up to five months, and they provide prolonged and intensive maternal care, all of which impose substantial energetic demands.” 

Future studies will look at not only evolutionary traits but also the effects of sexual dimorphisms, or different features of males and females in the same species, on the prevalence of pathogens the bats carry, the transmission paths, and the bats’ own immunity.  

Escobar, who holds an adjunct and visiting professorship at the Universidad de La Salle, Bogotá, Colombia, believes this foundational research contributes to the mission of Virginia Tech’s land-grant mission. By conducting workshops and training all the researchers how to identify the bat species, how to measure them, and how to collect specimens from the wild for natural history museums, Escobar is ensuring that further research on bats continues in Colombia and Latin America.  

“The people that lost a cow could be a big rancher or could be a small family that is trying to survive,” said Escobar, who is also an adjunct and visiting professor with One Health Institute, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile. “That’s why we are doing this research.”  

The other participants in the research include: 

• Karen D. Sarmiento-Arias – Laboratorio de Biodiversidad, Instituto de Ciencias, Benemerita Universidad Autonoma de Puebla, Mexico  
• Diego Soler-Tovar – Epidemiology and Public Health Research Group, Faculty of Agricultural Sciences, Universidad de La Salle, Bogotá, Colombia 
• Abelardo Rodriguez-Bolanos – Programa de Biología, Facultad de Ciencias Matemáticas y Naturales. Grupo de Investigación Biodiversidad de Alta Montant, Museo de Historia Natural, Universidad Distrital Francisco José de Caldas, Bogotá, Colombia 
• Carlos Bravo-Garcia – Programa de Biología, Facultad de Ciencias Matemáticas y Naturales. Grupo de Investigación Biodiversidad de Alta Montant, Museo de Historia Natural, Universidad Distrital Francisco José de Caldas, Bogotá, Colombia; Colección de mamíferos, Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, Villa de Leyva, Boyacá, Colombia 
• Nicolas Reyes-Amaya – Colección de mamíferos, Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, Villa de Leyva, Boyacá, Colombia 
• Laura Avila-Vargas – Epidemiology and Public Health Research Group, Faculty of Agricultural Sciences, Universidad de La Salle, Bogotá, Colombia