Megabat

Description

Most fruit bats are larger than insectivorous bats or Microchiroptera, however there are a number of small fruit bats also. The smallest species is 6 cm (2.4 in) long and thus smaller than some microbats, for example, the Mauritian tomb bat. The largest attain a wingspan of 1.7 m (5.6 ft), weighing in at up to 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 bat Rousettus 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 tongue, 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 for bats. 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. Megabats are frugivorous or nectarivorous, i.e., they eat fruits or lick nectar from flowers. Often, the fruits are crushed and only the juices are consumed. The teeth are adapted to bite through hard fruit skins.

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).

As disease reservoirs

Fruit bats have been found to act as reservoirs for ebola virus, though the bats themselves sometimes have no signs of infection. Three species of bats have tested positive for ebola, but had no symptoms of the virus. This indicates that the bats may be acting as a reservoir for the virus. Of the infected animals identified during these field collections, immunoglobulin G (IgG) specific for ebola virus was detected in hammer-headed bats, Franquet's epauletted fruit bats, and little collared fruit bats.

The epidemical Marburg 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.

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.

Classification

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.

List of species

The family Pteropodidae is divided into seven subfamilies with 186 total extant species, represented by 44–46 genera:

Family Pteropodidae