For humans, maintaining proper blood sugar levels is crucial for overall health and for providing energy to our cells. Both insufficient and excessive blood sugar can lead to severe health issues, with high blood sugar being a key indicator of metabolic disorders like diabetes. Recent findings from the Stowers Institute for Medical Research suggest that looking at evolutionary adaptations, particularly those of bats, may offer new strategies for tackling metabolic diseases.
Published in Nature Ecology and Evolution on August 28, 2024, a study led by co-first authors Postdoctoral Research Associate Jasmin Camacho, Ph.D., and former Stowers researcher Andrea Bernal-Rivera, under the guidance of Stowers Associate Investigator Nicolas Rohner, Ph.D., highlights the highest blood sugar levels ever documented in mammals. This indicates that bats have evolved unique mechanisms that allow them to survive and thrive under conditions that would be fatal to other mammals.
“Our research shows blood sugar levels that are unprecedented in nature — levels that would be life-threatening and could induce coma in other mammals, but not in bats,” noted Camacho. “We’re uncovering a trait that was previously thought to be impossible.”
Thirty million years ago, the Neotropical leaf-nosed bat primarily consumed insects. Over time, these bats have evolved into various species, expanding their diets to include fruits, nectar, meat, and even blood.
“Studying animals that have thrived for millions of years allows us to begin cataloging the evolutionary changes they have undergone,” Camacho explained. “What makes Neotropical leaf-nosed bats particularly fascinating is their diverse diet across numerous species, enabling us to explore how dietary adaptations occur. Our goal is to extend these insights to other mammals, including humans, to potentially improve our health.”
To delve into how bats have diversified their diets, the research team ventured into the jungles of Central and South America, as well as the Caribbean, conducting fieldwork over several years. Their catch-and-release missions focused on performing glucose tolerance testing — which measures blood sugar levels — on nearly 200 wild bats from 29 different species after giving them a single feeding of one of three types of sugars related to their diets: insects, fruits, or nectar.
“We observed various methods of how sugar is processed, absorbed, stored, and utilized in the body, revealing how these processes have adapted in accordance with different dietary needs,” remarked Bernal-Rivera.
The process of keeping blood sugar levels within a healthy range is known as glucose homeostasis, typically managed by the hormone insulin, whose dysfunction leads to diabetes. Different species of leaf-nosed bats demonstrate a range of adaptations for glucose homeostasis, including changes in their digestive anatomy and genetic alterations that affect how sugar is transported from the bloodstream into cells.
“Fruit bats have fine-tuned their insulin signaling pathways to reduce their blood sugar levels,” stated Camacho. “In contrast, nectar bats can endure high blood sugar levels, similar to those seen in individuals with uncontrolled diabetes, through a different mechanism that appears to operate independently of insulin.”
Although the specifics of how nectar bats regulate their glucose levels remain under investigation, the researchers have found potential indicators of alternative metabolic strategies. Bats with sugar-heavy diets possess longer intestines and intestinal cells with higher surface areas for nutrient absorption than bats with different diets. Moreover, nectar bats consistently express a gene crucial for sugar transport, a characteristic also seen in a type of hummingbird.
“This research provides critical resources for the field,” said Nadav Ahituv, Ph.D., a bioengineering and genetics professor at the University of California, San Francisco. “It not only outlines the metabolic characteristics of various bat species with differing diets but also their intestinal structure and potential genomic regions responsible for these dietary adaptations.”
“The collected data will drive future studies aimed at understanding mammalian dietary variations and could lead to the development of innovative treatments for various metabolic disorders in humans,” Ahituv added.
Additional authors include Valentina Peña, Sofia Robb, Ph.D., Jonathon Russell, Kexi Yi, Ph.D., Yongfu Wang, Ph.D., Dai Tsuchiya, Ph.D., and Oscar Murillo-GarcÃa, Ph.D.
This research was funded by the National Science Foundation’s Postdoctoral Research Fellowships in Biology (Award: 2109717), the Burroughs Wellcome Fund Postdoctoral Diversity Enrichment Program (Award: G-1022339), the Howard Hughes Medical Institute Hanna H. Gray Fellows Program (Award: GT15991), and received institutional support from the Stowers Institute for Medical Research. Part of the fieldwork was supported by Contribución a la conservación del Bosque seco Tropical del Valle del Cauca (CVC Permit: 1122) from the Institute for Research and Preservation of the Cultural and Natural Heritage of Valle del Cauca.
