Megabats constitute the suborderMegachiroptera, and its only family Pteropodidae of the order Chiroptera (bats). They are also called fruit bats, Old World fruit bats, or, especially the genera Acerodon and Pteropus, flying foxes. Megabats are found in tropical and subtropical areas of Eurasia, Africa, and Oceania. Compared to insectivorous bats, fruit bats are relatively large, and with some exceptions, do not navigate by echolocation. They are herbivores and rely on their keen senses of sight and smell to locate food.
Most fruit bats are larger than insectivorous bats or Microchiroptera, but a number of small fruit bats exist, also. The smallest species is 6 cm (2.4 in) long, thus smaller than some microbats, for example, the Mauritian tomb bat. The largest attain a wingspan of 1.7 m (5.6 ft), and weigh as much as 1.6 kg (3.5 lb). Most fruit bats have large eyes, allowing them to orient themselves visually in twilight and inside caves and forests.
Their sense of smell is excellent. In contrast to the microbats, the fruit bats do not use echolocation (with one exception, the Egyptian fruit batRousettus egyptiacus, which uses high-pitched tongue clicks to navigate in caves).
Loss of echolocation
Megabats make up the only family (Pteropodidae) in order Chiroptera that is not capable of laryngeal echolocation. Echolocation and flight evolved early in the lineage of chiropterans. Although echolocation was later lost in family Pteropodidae, bats in the genus Rousettus are capable of primitive echolocation through clicking their tongues, and some species have been shown to create clicks similar to those of echolocating bats using their wings.
Both echolocation and flight are energetically expensive processes. The nature of the flight and echolocation mechanism of bats allows for creation of echolocation pulses with minimal energy use. Energetic coupling of these two processes is thought to have allowed for both energetically expensive processes to evolve in bats. The loss of echolocation may be due to the uncoupling of flight and echolocation in megabats. The larger average body size of megabats compared to echolocating bats suggests that a larger body size disrupts the flight-echolocation coupling and made echolocation too energetically expensive to be conserved in megabats.
Behavior and ecology
Megabats mostly roost in trees and shrubs. Only those that possess echolocation venture into the dark recesses of caves. Because they eat fruit, some megabat species are unpopular with orchard owners. They are frugivorous or nectarivorous, i.e., they eat fruits or lick nectar from flowers. Often, the fruits are crushed and only their juice is consumed, while the remaining fibrous matter is discarded. The teeth are adapted to bite through hard fruit rinds, and ridges on the soft palate help to squeeze out the juices within.
Frugivorous bats aid the distribution of plants (and therefore forests) by carrying the fruits with them and spitting the seeds or eliminating them elsewhere. Nectarivores actually pollinate visited plants. They bear long tongues that are inserted deep into the flower; pollen passed to the bat is then transported to the next blossom visited, thereby pollinating it. This relationship between plants and bats is a form of mutualism known as "chiropterophily". Examples of plants that benefit from this arrangement include the baobabs of the genus Adansonia and the sausage tree (Kigelia).
The epidemicalMarburg virus was found in 2007 in specimens of the Egyptian fruit bat, confirming the suspicion that this species may be a reservoir for this virus.
Other viral diseases which can be carried by fruit bats include Australian bat lyssavirus and henipavirus (notably Hendra virus and Nipah virus), both of which can prove fatal to humans. These bats have been shown to infect other species (specifically horses) with Hendra virus in Australian regions. Later, humans became infected with Hendra virus after being exposed to horse bodily fluids and excretions. The discovery of this Australian bat lyssavirus was in 1996, before this all bats on all continents, except Australia, had been recorded to carry this rabies-like disease.
Fruit bats are considered a delicacy by South Pacific Islanders, as well as in Micronesia. Consumption has been suggested as a cause of Lytico-Bodig disease on the Micronesian island of Guam, through bioaccumulation of a plant toxin to which the bats are immune. The transmission of Nipah virus from flying foxes to pigs is thought to be due to an increasing overlap between bat habitats and piggeries in peninsular Malaysia. At the index farm, fruit orchards were in close proximity to the piggery, allowing the spillage of urine, faeces, and partially eaten fruit onto the pigs. Retrospective studies demonstrate that viral spillover into pigs may have been occurring in Malaysia since 1996 without detection. During 1998, viral spread was aided by the transfer of infected pigs to other farms, where new outbreaks occurred.
Fox Island, Australia, is believed to be home to the largest colony of flying foxes on the continent.
Bats have been traditionally thought to belong to one of two monophyletic groups, a view that is reflected in their classification into two suborders (Megachiroptera and Microchiroptera). According to this hypothesis, all living megabats and microbats are descendants of a common ancestor species that was already capable of flight.
However, other views have been shared, and a vigorous debate persists to this date. For example, in the 1980s and 1990s, some researchers proposed (based primarily on the similarity of the visual pathways) that the Megachiroptera were in fact more closely affiliated with the primates than the Microchiroptera, with the two groups of bats having therefore evolved flight via convergence (see Flying primates theory). However, a recent flurry of genetic studies confirms the more longstanding notion that all bats are indeed members of the same clade, the Chiroptera. Other studies have recently suggested that certain families of microbats (possibly the horseshoe bats, mouse-tailed bats, and the false vampires) are evolutionarily closer to the fruit bats than to other microbats.
^Holland RA, Waters DA, Rayner JM (December 2004). "Echolocation signal structure in the Megachiropteran bat Rousettus aegyptiacus Geoffroy 1810". The Journal of Experimental Biology. 207 (Pt 25): 4361-9. doi:10.1242/jeb.01288. PMID15557022.
^Monson CS, Banack SA, Cox PA (2003). "Conservation implications of Chamorro consumption of flying foxes as a possible cause of amyotrophic lateral sclerosis-parkinsonism dementia complex in Guam". Conservation Biology. 17 (3): 678-686. doi:10.1046/j.1523-1739.2003.02049.x.
^Pettigrew JD, Jamieson BG, Robson SK, Hall LS, McAnally KI, Cooper HM (1989). "Phylogenetic relations between microbats, megabats and primates (Mammalia: Chiroptera and Primates)". Philosophical Transactions of the Royal Society B. 325 (1229): 489-559. Bibcode:1989RSPTB.325..489P. doi:10.1098/rstb.1989.0102.