Robust jaws and a (sometimes) 'greenish' pelt: house bats (vesper bats part IX)

Hey, if anyone out there is bored with the bats, just gimme a shout. If you're loving it, say so, and urge me to post more - there's still a lot to come! Yes, welcome once again to the vesper bat series: for previous installments see the list of links at the bottom of this article. We continue our trek through vesper bat diversity with another of the clades often regarded as a 'tribe' within the vesper bat 'subfamily' Vespertilioninae: the house bats or yellow bats, conventionally grouped together in Scotophilini.

House bats - the approximately 15 species of Scotophilus - are handsome, robustly built vesper bats that occur across Africa, Madagascar and Asia [adjacent composite shows Yellow-bellied house bat S. dinganii above (from Professor Paul's Guide to Mammals) and head of Lesser Asiatic house bat S. kuhlii (from wikipedia)]. The Réunion house bat S. borbonicus is present on Réunion*, the Lesser Asiatic house bat has a range that extends from Pakistan to the Nicobar Islands, Sulawesi, the Philippines and Flores, and a few other species occur on Sulawesi and the Philippines too. House bats look rather like noctules, but have long, tapering tragi (noctules have short, mushroom-shaped tragi) and their jaws and teeth are large and capable of powerful biting. As is the case with quite a few vesper bat genera, the number of species is likely to rise since cryptic species have recently been discovered (Jacobs et al. 2006); more are sure to come (the Yellow-bellied house bat in particular seems to be a species complex). Two species have recently been described from Madagascar: S. tandrefana Goodman et al., 2005 and S. marovaza Goodman et al., 2006.

* Or it was, since it now seems to be extinct. Claims of its presence on Madagascar and Mauritius are apparently erroneous, though the Madagascan animal (represented by a single specimen) remains unidentified and is generally referred to as S. cf. borbonicus.

This strong, robust house bat skull (typically with a very prominent sagittal crest, just a single pair of large, conical upper incisors, and large, tall-cusped premolars and molars) may be related to a diet that incorporates a lot of beetles [Lesser Asiatic house bat skull shown below; from Ingle & Heaney (1992)]. One intriguing fact is that the Greater Asiatic house bat S. heathii has been reported to eat fruit in captivity. I don't know if this occurs in the wild, but if so it might be unique for a vesper bat. The head shape is sometimes described as dog-like: with a bit of imagination, there is a superficial similarity with short-faced dog breeds like boxers or mastiffs [adjacent head-shot of Lesser Asiatic house bat from Professor Paul's Guide to Mammals].

As you might guess, house bats are well known for frequenting houses - they're associated with urban and suburban areas across Africa and Asia - and they often roost in or close to ceilings, sometimes in between wooden rafters and/or close to metal roofs. They presumably enjoy the heat present in such locations. In wilder habitats, typical roosts include woodpecker and barbet holes, hollow trees and beneath palm fronds.

A tent-building vesper bat?

Lesser Asiatic house bats might construct 'tents' in fan palms: on the Philippines, they were observed roosting in modified fronds of the fan palm Livistona rotundifolia (Rickart et al. 1989) [unmodified and modified fronds shown below: from Rickart et al. (1989)]. Various other bats - certain phyllostomids and fruit bats - construct tents: they hang from the undersides of large leaves, and bite into the leaf on either sides of the central rib, causing the sides to droop down and thus form the walls of the 'tent'. However, the house bats were never observed constructing the tents, and for this reason it's possible that another bat species was the real tent-maker. Maybe the house bats were just being opportunistic.

The Greater Asiatic house bat S. heathii at least undergoes winter dormancy. Little information is available, but I presume that this occurs across the cooler or drier parts of its range.

Twins and triplets are frequent in some species and the Greater Asiatic house bat in particular is well known for practising delayed implantation. When first discovered (during the 1970s) this was (so I understand) a bit surprising, as it had previously been hypothesised that sperm storage and delayed implantation - already well known in temperate vesper bats - correlated with a hibernating habit and associated drop in body temperature (Hartman 1933). Yet here it was in a tropical, non-hibernating group (Krishna & Dominic 1978). Ok, granted, delayed implantation had been documented during the early 1970s in two kinds of tropical vesper bats already (flat-headed bats (Tylonycteris) and in the tropical pipistrelle Pipistrellus ceylonicus). In the extremely widespread Greater Asiatic house bat*, males and female associate and mate in January and/or February, and - get this - the vagina then becomes "occluded because of extensive cornification of the vaginal epithelium" (Krishna & Dominic 1978, p. 319). This occlusion persists to late February at least. Fertilization occurs in April (remember, this is two or three months after mating), and babies are born - after a gestation of about 90 days - in June.

* It occurs from Afghanistan in the west to the Philippines in the east. Some sources mention its presence on Sulawesi, but the house bats on that islands are best regarded as a separate species, the Sulawesi yellow house bat S. celebensis.

As suggested by one of their common names, many Scotophilus bats are yellowish-brown (in some species, the belly is entirely yellow), but some have an off-white pelt [Lesser Asiatic house bat shown above; image from here]. Robbins (1978) and Kingdon (1997) variously described "greenish brown", "olive-green" and "greenish olive" as present in some species. So, these bats join the elite group of greenish-furred mammals. Like noctules, they tend to have a short-haired, glossy pelt.

Finding a 'home' for these bats within the vesper bat radiation is difficult, since different studies report rather different possibilities. Morphological similarities (a similar baculum shape) led Hill & Harrison (1987) to consider house bats allied with the Harlequin bat Scotomanes ornatus in the 'tribe' Scotophilini. However, any similarity between house bats and the Harlequin bat now seems convergent: the latter is most likely a member of the serotine clade, and house bats don't seem at all closely related to this group (Hoofer & Van Den Bussche 2003). Roehrs et al. (2010) found Scotophilini to be the sister-group to Antrozoini (the clade that includes the Pallid bat, little yellow bats and others). That possible position is shown here. The fact that both house bats and pallid bats have robust teeth and jaws (see the skull diagrams above) makes this proposed relationship rather satisfying. The similarities might represent convergence, but a comparatively large and obvious dentition in little yellow bats makes me wonder.

Meanwhile, Agnarsson et al. (2011) found house bats to be outside the clade that included all other vesper bats except Cistugo! This position would indeed demonstrate a highly divergent position for this lineage, and could even mean that - like Cistugo - house bats should be given their own 'family' name.... I suppose this would be Scotophilidae, wouldn't it?

A phylogeny for house bats was recently published by Trujillo et al. (2009). The Lesser Asiatic house bat seems to be the most basal species. A clade of mostly African species has S. nux as its most basal member; Asian species like the Greater Asiatic house bat (sister-taxon to the Yellow-bellied house bat) are also within this clade. The Madagascan species do not form a clade, indicating independent invasions of the island.

And that's that. More vesper bats to come, much more. But, hey, other stuff too.

For previous Tet Zoo articles in the vesper bats series, see...

• Introducing the second largest mammalian 'family': vesper bats, or vespertilionids
• The vesper bat family tree: of myotines, plecotins, antrozoins, and all those cryptic species (vesper bats part II)
• Bent-winged bats: wide ranges, very weird wings (vesper bats part III)
• Of southern African wing-gland bats, woolly bats, and the ones with tubular nostrils (vesper bats part IV)
• The many, many mouse-eared bats, aka little brown bats, aka Myotis bats (vesper bats part V)
• Long-eared bats proper: Plecotus and other plecotins (vesper bats part VI)
• Desert long-eared bats - snarling winged gremlins that take scorpion stings to the face and just don't care (vesper bats part VII)
• Hairy-tailed bats: a tale of furry tails, red coats, cold tolerance, migration and sleeping out in the open (vesper bats part VIII)

And for previous Tet Zoo articles on bats, see...

• Desmodontines: the amazing vampire bats
• Giant extinct vampire bats: bane of the Pleistocene megafauna
• Camazotz and the age of vampires
• Dark origins: the mysterious evolution of blood-feeding in bats
• A new hypothesis on the evolution of blood-feeding: food source duality involving nectarivory. Catchy, no?
• Oh no, not another giant predatory flightless bat from the future
• The most terrestrial of bats
• I stroked a pipistrelle
• Red bats
• We flightless primates
• Big animalivorous microbats
• Hidden in plain sight: discovering cryptic vesper bats in the European biota
• PROTOBATS: visualising the earliest stages of bat evolution

Refs - -

Agnarsson, I., Zambrana-Torrelio, C. M., Flores-Saldana, N. P. & May-Collado, L. J. 2011. A time-calibrated species-level phylogeny of bats (Chiroptera, Mammalia). PLoS Currents 011 February 4; 3: RRN1212. doi: 10.1371/currents.RRN1212.

Hartman, C. G. 1933. On the survival ofspermatozoa in the female genital tract of the bat. Quarterly Review of Biology 8, 185-193.

Hill, J. E. & Harrison, D. L. 1987. The baculum in the Vespertilioninae (Chiroptera: Vespertilionidae) with a systematic review, a synopsis of Pipistrellus and Eptesicus, and the descriptions of a new genus and subgenus. Bulletin of the British Museum of Natural History (Zoology) 52, 225-305.

Hoofer, S. R. & Van Den Bussche, R. A. 2003. Molecular phylogenetics of the chiropteran family Vespertilionidae. Acta Chiropterologica 5, supplement, 1-63.

Ingle, N. R. & Heaney, L. R. 1992. A key to the bats of the Philippine Islands. Fieldiana Zoology, New Series 69, 1-44.

Jacobs, D. S., Eick, G. N., Schoeman, M. C. & Matthee, C. A. 2006. Cryptic species in an insectivorous bat, Scotophilus dinganii. Journal of Mammalogy 87, 161-170.

Kingdon, J. 1997. The Kingdon Field Guide to African Mammals. Academic Press, San Diego.

Krishna A, & Dominic CJ (1978). Storage of spermatozoa in the female genital tract of the vespertilionid bat, Scotophilus heathi. Journal of reproduction and fertility, 54 (2), 319-21 PMID: 569203

Rickart, E. A., Heideman, P. D. & Utzurrum, R. C. B. 1989. Tent-roosting by Scotophilus kuhlii (Chiroptera: Vespertilionidae) in the Philippines. Journal of Tropical Ecology 5, 433-436.

Robbins, C. B. 1978. Taxonomic identification and history of Scotophilus nigrita (Schreber) (Chiroptera: Vespertilionidae). Journal of Mammalogy 59, 212-213.

Roehrs, Z. P., Lack, J. B. & Van Den Bussche, R. A. 2010. Tribal phylogenetic relationships within Vespertilioninae (Chiroptera: Vespertilionidae) based on mitochondrial and nuclear sequence data. Journal of Mammalogy 91, 1073-1092.

Trujillo, R. G., Patton, J. C., Schlitter, D. A. & Bickham, J. W. 2009. Molecular phylogenetics of the bat genus Scotophilus (Chiroptera: Vespertilionidae): perspectives from paternally and maternally inherited genomes. Journal of Mammalogy 90, 548-560.