Moustached Bats, Ghost-faced Bats

In the theatre of mammal diversity, there are two groups that loom above all their competitors. The most diverse of the generally recognised mammalian orders, by a healthy margin, is the rodents. Nevertheless, they are still given a good run for their money by the silver medalist, the bats. There is somewhere in the region of 1100 known living species of bat, a number that has continued to increase in recent years as study progresses. This post will focus on one particular group of bats, the Mormoopidae.

Ghost-faced bat Mormoops megalophylla, copyright Merlin Tuttle.

Mormoopids are a group of bats found in warmer parts of the Americas. They commonly go by the names of moustached bats or funnel-eared bats, at least to the extent that any type of bat can be said to 'commonly' go by anything. They are fast-flying, insectivorous bats that roost in colonies in hot, humid caves. These colonies can be sizable: at least one colony of Wagner's moustached bat Pteronotus personatus was estimated to include more than 16,000 individuals (de la Torre & Medellín 2010). In the United States, mormoopids are currently restricted to the south-west (in the form of the ghost-faced bat Mormoops megalophylla) but subfossil from Florida indicate a wider distribution in the past (Simmons & Conway 2001).

Mormoopids belong to the Noctilionoidea, a distinctly Neotropical group of bats that also includes the leaf-nosed bats of the Phyllostomidae and the Noctilio bulldog bats (and also possibly the short-tailed bat Mystacina of New Zealand, because why make things simple?) The biggest difference between mormoopids and other noctilionoids lies in the structure of their shoulders. In most bats, the trochiter (one of the tubercles at the top of the humerus) is enlarged to form a secondary articulation with the scapula. This strengthens the shoulder joint, presumably allowing the production of more power for flight. Mormoopids, however, lack this enlarged trochiter. I must confess to being unsure just what is the significance of this alteration; mormoopids remain fast fliers (de la Torre & Medellín 2010). Are they perhaps sacrificing a bit of endurance for the sake of higher mobility?

Wagner's moustached bat Pteronotus personatus, copyright Bernard Dupont.

Current classifications of the mormoopids recognise two genera in the family, Mormoops and Pteronotus. Mormoops species have a shorter head than Pteronotus species (so short, in fact, that the braincase is wider than it is long), with a markedly upturned snout. Basically, they have a skull like a pug dog. In a revision of the family, Simmons & Conway (2001) recognised two living species of Mormoops and six of Pteronotus, plus an additional species of each described from subfossil remains from Cuba. Pteronotus was also divided between three subgenera. The type subgenus included two species, Pt. davyi and Pt. gymnonotus, known as naked-backed bats because the membrane for their wings attaches close to the spine so the body fur is not visible in dorsal view (in other mormoopids, the wings attach along the sides of the body). Three of the remaining species (Pt. personatus, the sooty moustached bat Pt. quadridens and Macleay's moustached bat Pt. macleayi) were placed in a morphologically generalised subgenus Chilonycteris. The remaining living species was Parnell's moustached bat Pt. parnellii, placed in its own subgenus Phyllodia.

Pteronotus parnellii was the only known mormoopid, and in fact the only Neotropical bat of any kind, to use high duty cycle echolocation. Echolocation, of course, works through the bat emitting calls and listening for when they bounce back from surrounding objects. The problem is that the noise produced while emitting calls can drown out returning echoes. As a result, most echolocating bats use what is called low duty cycle echolocation. Individual echolocation calls are spaced apart so the bat has time between each call to listen for echoes. High duty cycle echolocation is used by two Old World bat families, the Rhinolophidae and Hipposideridae, as well as Pteronotus parnellii. These bats have learnt the trick of emitting calls continuously and recognising returning echoes by their different frequency. This allows each bat to build up a more detailed picture of its surrounds, allowing for greater mobility in complex environments such as around dense forest.

Parnell's moustached bat Pteronotus parnellii, copyright Alex Borisenko.

In recent years, however, mormoopid systematics have been given a shake-up. Many of the mormoopid species recognised by Simmons & Conway (2001) could be divided between multiple subspecies. Recently, a molecular analysis of Pteronotus species by Pavan & Marroig (2016) found strong genetic divergence between most of these subspecies. As a result, they proposed raising the distinct subspecies to species level, effectively raising the number of living Pteronotus species from six to fifteen. Some of these species could also be separated on the basis of morphometric and acoustic data; others exhibited morphometric overlap but were geographically distinct. 'Pteronotus parnellii' was the most diverse, being divided into eight named species plus an unnamed population that may warrant species recognition. The question that this immediately raises: is the use of high duty cycle echolocation a feature of all nine of these species, or might it turn out that not all members of the P. parnellii group are high duty echolocators?

REFERENCES

de la Torre, J. A., & R. A. Medellín. 2010. Pteronotus personatus (Chiroptera: Mormoopidae). Mammalian Species 42 (869): 244–250.

Pavan, A. C., & G. Marroig. 2016. Integrating multiple evidences in taxonomy: species diversity and phylogeny of mustached bats (Mormoopidae: Pteronotus). Molecular Phylogenetics and Evolution 103: 184–198. Simmons, N. B., & T. M. Conway. 2001. Phylogenetic relationships of mormoopid bats (Chiroptera: Mormoopidae) based on morphological data. Bulletin of the American Museum of Natural History 258: 1–97.