Today's Reading

In the spring of 1991, and not long after entering my doctorate program in zoology, I started thinking about potential topics for thesis-related research. As these sorts of things tend to go, I was expected to pick a topic that fell under the expertise of the graduate committee chairperson. In my case, it was John Hermanson, a young faculty member whose only other grad student had departed the year before. Hermanson, who taught anatomy at Cornell University's veterinary school (though he was not himself a vet) had a strong background in muscle biochemistry, especially variants of the famous contractile protein duo actin and myosin. In the presence of calcium and adenosine triphosphate (the energy currency of the cell, better known as ATP), the chain-like molecules of actin and myosin ratchet past each other. Occurring simultaneously millions of times over, this molecular movement produces the muscle contraction responsible for actions like walking and galloping—activities formerly popular with the horses whose leg muscles Hermanson kept stored in an ultracold freezer.

Hermanson was at the forefront of the relatively new field of functional morphology, a modern take on classical anatomy. Practitioners of "func morph" studied the relationship between the structures of an organism (i.e., its anatomy) and the function of those structures. Hitting the literature hard, I quickly became intrigued. It also became apparent that Hermanson's favorite study animals were clearly off the beaten horse track—some of them in fact flitting over said tracks after dusk.

Having spent at least a third of my childhood free time peering under rocks and logs for snakes, salamanders, and other creepy-crawlies, another third maintaining a collection of exotic pets (I had a monkey named Guggie and, later, a boa constrictor named Alice), and the remainder of my time watching horror movies, it took me approximately five seconds to choose bats over biochemistry.


WHEN THE FIFTEENTH-and sixteenth-century Europeans returned from their flag-planting exploits in the New World, along with the loot they had pillaged and the Indigenous people they had kidnapped and enslaved, they also brought back tales of strange creatures—of sea monsters, of cyclopean humans with tails, and of bats that attacked men in the night and drank their blood. The latter were generally described as hideous creatures sporting five-foot wings. With these Westerners far more concerned with gold, God, and geography, it would take another 250 years for the first naturalists to begin closely examining and classifying the natural wonders they either encountered in places like Central and South America or pulled out of bottles and shipping crates returned from those regions.

When it came to unmasking the identity of the vampire bats, though...they blew it. Undoubtably, most of these scientist types saw only the results of vampire bat attacks, which took place in the dead of night, but not the attacks themselves. And the majority of the accounts they collected were likely secondhand tales or worse. Many of the bats they did see had spear-shaped nasal structures projecting vertically from their snouts. Unfortunately, this led the naturalists to the mistaken belief that these nose leaves were wielded like fleshy stilettos. The thought was that after impaling their victims, the vampires would then drain their blood through the resulting gash. Taxonomists began assigning scary-sounding names to any specimens with a nose leaf, names like Vampyrops, Vampyressa, Vampyrodes, and Vampyrum, though, in truth, none of these bats were vampires. Along the way, the group picked up the common name New World leaf-nosed bats. Things went further off the rails as the presence of nose leaves in two Old World bat families (Rhinolophidae and Megadermatidae) likely contributed to the incorrect belief that vampire bats could also be found throughout Europe, Africa, the Indo-Pacific, and Asia.

Today, vampire bats belong to the large (with approximately 170 species) and diverse family Phyllostomidae (in which all but three species do not feed on blood). Though they are still commonly referred to as New World leaf-nosed bats, we now understand that nose leaves aren't weapons but are instead employed, megaphone-style, to direct the larynx-generated echolocation calls that characterize the bats that possess them. I've always found the earlier interpretation of nose-leaf function more than a bit odd, basically because nose leaves are soft and pliable, and in no way capable of inflicting wounds of any kind. Perhaps it was the permanently stiffened condition they were in when they arrived at museums and universities across Europe that misled taxonomists.

It is nearly always a surprise to non-bat biologists that there are but three species of blood-feeding bats alive today. Their ranges are confined to parts of Mexico, Central and South America, and two Caribbean islands (Trinidad and Margarita). The fact that they lack elongate nose leaves, which aren't a modern-day requirement for inclusion in the Phyllostomidae family, but instead possess pad-shaped versions of these structures, goes a long way to explain the nonvampiric scientific names the trio was assigned in the nineteenth century: Desmodus rotundus, Diphylla ecaudata, and Diaemus youngi. But even without sinister-sounding scientific names, each of these bats is wonderfully equipped for a life of obligate sanguivory (blood feeding only)—and several of their adaptations are related to their choppers.

Vampire bats have the fewest teeth of any bat species: twenty-six in Diphylla ecaudata, the hairy-legged vampire bat; twenty-two in Diaemus youngi, the white-winged vampire bat; and twenty in Desmodus rotundus, the common vampire bat. Desmodus is also the only bat with a single upper and lower molar on each side of the jaw. Interestingly, the fact that vampire bat molars are few in number and tiny in size makes perfect sense. Molars generally serve as the functional equivalent of grinding mills. In many mammals, their job is to smash food items into near pulp—which not only increases the surface area available for digestive enzymes to start doing their jobs but makes it easier to swallow that saliva-moistened mouthful of whatever. Vampire bats consume no solid food, so molars are not required—especially given the metabolic expense of growing and maintaining them.
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