Egyptian Fruit Bat

The Egyptian fruit bat or Egyptian rousette (Rousettus aegyptiacus) is a species of megabat that is found in Africa, the Middle East, the Mediterranean, and the Indian subcontinent. It is one of three Rousettus species with an African-Malagasy range, though the only species of its genus found on continental Africa. The common ancestor of the three species colonized the region in the late Pliocene or early Pleistocene. The species is traditionally divided into six subspecies. It is considered a medium-sized megabat, with adults weighing 80–170 g (2.8–6.0 oz) and possessing wingspans of approximately 60 cm (24 in). Individuals are dark brown or grayish brown, with their undersides paler than their backs.

The Egyptian fruit bat is a highly social species, usually living in colonies with thousands of other bats. It, along with other members of the genus Rousettus, are some of the only fruit bats to use echolocation, though a more primitive version than used by bats in other families. It has also developed a socially-complex vocalization system to communicate with conspecifics. The Egyptian fruit bat is a frugivore that consumes a variety of fruits depending on the season and local availability. Because of its consumption of commercially-grown fruits, the Egyptian fruit bat is considered a pest by farmers. It also acts as a pollinator and seed disperser for many species of trees and other plants.^[3]

Taxonomy and etymology

Other pteropodid species

R. amplexicaudatus

R. spinalatus

R. leschenaultii

R. aegyptiacus

R. madagascariensis

R. obliviosus

Relationship of R. aegyptiacus within Pteropodidae (not all Rousettus species included) based on 2016 study of mitochondrial and nuclear DNA^[7]

The Egyptian fruit bat was described as a new species in 1810 by French naturalist Étienne Geoffroy Saint-Hilaire, who gave it the name Pteropus egyptiacus.^[8] He later revised the specific epithet to ægyptiacus, given as 1812^[3] or 1818.^[9][2] In 1870, John Edward Gray placed it in the now-defunct genus Eleutherura, treating the taxon as two species (E. unicolor and E. ægyptiaca).^[4] Danish mammalogist Knud Andersen was the first reviser of the taxon; he used Rousettus ægyptiacus and wrote that egyptiacus "may [...] be considered a slip or misprint corrected by the author himself".^[10]

In 1992, G. B. Corbet and J. E. Hill argued that Geoffroy's revision from egyptiacus to ægyptiacus was invalid according to the ICZN Code, and changed the name back to egyptiacus.^[11] The 1999 Mammalian Species review used egyptiacus as well.^[3] However, Geoffroy's revision was supported in 2001 by D. Kock.^[12] He notes that aegyptiacus was "accepted almost universally by the scientific community", emphasizing its use by Andersen in 1912.^[12] Kock argued that even if it was an unjustified emendation at first, it became a justified emendation through widespread use, as the use of aegyptiacus was undisputed until Corbet and Hill (the ICZN Code also mandates that use of "æ" become "ae", hence ægyptiacus is no longer in use).^[12][13] Kock also writes that since the Latin adjective for "Egyptian" is aegyptiacus, egyptiacus is a simple misspelling in the original description.^[12] The Agreement on the Conservation of Populations of European Bats was amended to use the specific name aegyptiacus in 2003.^[14][15] Books like Mammal Species of the World (2005) and Mammals of Africa (2013) follow Kock and use the name aegyptiacus.^[6][2]

Two other members of Rousettus have an African-Malagasy range: the Madagascan rousette (R. madagascariensis) and the Comoro rousette (R. obliviosus). Based on an analysis of both mitochondrial and nuclear genetics, the Egyptian fruit bat forms a clade with the Madagascan and Comoro rousettes. The Rousettus lineage colonized Africa in a single event in the late Pliocene or early Pleistocene. Diversification into three species followed soon after, with the Egyptian fruit bat the first to branch—the Comoro and Madagascan rousettes have a more recent common ancestor with each other than with the Egyptian fruit bat.^[16]

Subspecies

There are six subspecies of Rousettus aegyptiacus.^[17][3][2]

Description

The Egyptian fruit bat is considered a medium-sized megabat. Adults have an average total body length of 15 cm (5.9 in) and an average wingspan of about 60 cm (24 in). Its forearm length is 81–102 mm (3.2–4.0 in) and its thumb length is 22–31 mm (0.87–1.22 in).^[3] Adults weigh 80–170 g (2.8–6.0 oz).^[3] Males are larger than females and can be easily distinguished by their large scrotums and the prominent, stiff strands of hair around their throats.^[19][2] It has a dental formula of 2.1.3.22.1.3.3 for a total of 34 teeth.^[3]

The fur on its body is relatively short and consists of soft and sleek strands.^[3][2] On its back, the fur's coloration ranges from dark brown to gray-brown, while the coloration on its underside is pale brown with a yellowish-brown collar around its neck.^[3] Its wings are of a darker brown than its body and the wing membranes attach to the leg at the first toe. Males and females have similar coloration. Similar to other megachiropteran species, the Egyptian fruit bat only has claws on its first and second digits, while the other digits have extremities made of cartilage.^[3]

The Egyptian fruit bat has one of the greatest ratios of brain weight to body weight of any bat species. It is well adapted to seeing in low light and possesses a highly developed sense of smell. The regions of the brain associated with sight and smell are similarly well-developed. Its eyes are large and well-developed, while its ears are considered medium-length. As in all megabats, the choroid of the eye (vascular region between retina and sclera) has tiny projections known as papillae, which is where its photoreceptor cells are located.^[3]

Behavior and ecology

Diet and foraging

The Egyptian fruit bat is frugivorous, consuming mostly fruit,^[19] though it also consumes leaves.^[3] As a nocturnal animal, it is more active in the evening. It leaves its roost at dusk to begin foraging.^[2] The Egyptian fruit bat has a flexible diet, consuming any soft, pulpy fruit from nearby fruiting trees. Common fruits eaten by the Egyptian fruit bat are Persian lilacs, loquat, figs, and wild dates.^[19] The type of fruit consumed is influenced by overall availability depending on the season and habitat type.^[20] Its dietary flexibility includes eating unripe fruits or those damaged by insects or fungi, allowing them to persist in habitats where ripe fruits are not perennially available.^[21]

The Egyptian fruit bat usually makes multiple, short flights from its roost to various fruiting trees. It prefers to pick fruit and carry it back to the roost or another tree before eating it.^[3][19] A study of Egyptian fruit bats in Cyprus noted that if Egyptian fruit bats are aware of an abundant fruit source somewhere, they will travel distances of about 15–20 km (9–12 mi) to reach it.^[20] It eats large quantities of fruit each evening, equivalent to about 50 to 150 percent of its weight.^[3] While eating, it will hold the fruit tightly against its body to prevent theft by other bats.^[3] Its intestinal transit time is rapid, with food passing through the small and large intestines in 18–100 minutes.^[3][19] The Egyptian fruit bat serves as a seed disperser of large and small seeds. Seeds are dispersed 25–400 m (82–1,312 ft) away from parent trees. Even seeds too large to ingest are dispersed due to its habit of picking fruits in one tree and consuming them in another, where larger seeds are spat out.^[22]

Egyptian fruit bats are ecologically important as pollinators or seed dispersers for many species of trees and plants. The baobab tree, for instance, relies almost exclusively on fruit bats to pollinate its flowers.^[3][23]

Mating, reproduction and life cycle

The Egyptian fruit bat has two breeding seasons: the first is from April to August, while the second season is from October to February.^[24] When the breeding season begins, the bats within the colony separate based on sex. The males gather together to form bachelor groups while the females form maternity colonies.^[3] Female bats have control over copulation; therefore, to increase the chances of mating, male Egyptian fruit bats will provide a nuptial gift to the female bat. The nuptial gifts are fruits that the male allows the female to scrounge.^[25] By allowing the female to scrounge, it strengthens the bond between the pair, thus increasing the probability of the female copulating with a given male.^[25] Females typically give birth to only a single offspring each year (called a "pup"), but twins are occasionally born, after a gestation period of around 115 to 120 days.^[3][26] Newborn Egyptian fruit bat pups are altricial at birth with their eyes shut until they are nine days old.^[3] The female carries the pup until it is six weeks old, which is when it can hang in the roost on its own. Afterwards, the pup is left in the roost while the mother forages. Before the pup is left in the roost, the mother repeatedly transports the pup to the same tree and is left there for the night while the mother forages. The pup learns this location and visits it first when at about three months of age, the pup will leave the roost on its own to forage for its food.^[27] They only become independent from their mothers after nine months, once they have finally reached their adult physique. Offspring typically stay with the same colony as the parents for their entire lives.^[3]

In the wild, the average lifespan of the Egyptian fruit bat ranges from 8 to 10 years, while in captivity its lifespan is about 22 years with proper care.^[3][28] The significant difference between the lifespan of Egyptian fruit bats in the wild versus ones in captivity is mostly because of the wild bats’ increased exposure to predation and vitamin D deficiency.^[3]

Predators and parasites

The Egyptian fruit bat has several avian predators, including hawks, owls, and falcons, specifically the lanner falcon. A mammalian predator is the genet.^[3] External parasites (ectoparasites) of the Egyptian fruit bat include parasitic mites like Spinturnix lateralis, Liponyssus, and several Ancystropus species. Others parasitic taxa are flies like Eucampsipoda, Nycteribosca, and Nycteribia. Fleas that parasitize it include Archaeopsylla and Thaumapsylla, and it has also been documented with the tick Alectorobius camicasi. Internal parasites (endoparasites) are the hemosporidian Plasmodium roussetti, which causes malaria, and the roundworm Nycteridocoptes rousetti.^[3]

Vocalization

Egyptian fruit bats, along with other species in the genus Rousettus, are some of the only megabats to use echolocation, though it is considered a primitive form compared to non-megabat species.^[3][29] A few other megabat species echolocate via creating clicks with their wings.^[29] It echolocates by emitting a series of sharp clicks with its tongues and by altering teeth and lip positions.^[30] The clicks are normally slow and constant, but speed up dramatically when the bat approaches an object. This allows it to effectively navigate in darkness.^[31][32]

It also makes use of a range of vocalizations for communication, including grunts and screeches, to communicate with other bats within the colony. As a result, a large roosting colony can be a deafening cacophony. Additionally, according to several studies, it is thought that because of their constant exposure to thousands of other individuals, they can form their own language to interact with one another about specific topics such as food. Colonies of Egyptian fruit bats develop their own dialects, producing sounds at different frequencies.^[33] Egyptian fruit bat pups acquire the dialect of their colonies by listening to their mothers' vocalizations.^[33][34]

Range and habitat

The Egyptian fruit bat is vastly dispersed across various locations and can be found throughout Africa, the Middle East, Pakistan, and the northern regions of the Indian subcontinent.^[21] Other populations can additionally be found in the Mediterranean on the mainland coasts of Cyprus and Turkey. It is the only frugivorous bat species in Europe.^[20] Outside of its natural distribution, an Egyptian fruit bat was observed in the Greek island of Kastellorizo during a zoological expedition in 2017.^[35] Usually found in various kinds of habitats such as tropical rain forests, savannas, or other forests, the Egyptian fruit bat tends to live in large colonies that consist of thousands of individuals in their established roosts.^[20][3] It prefers to establish roosts wherever there are plenty of fruiting trees nearby; most roosts are in caves.^[19] When no caves are nearby, it establishes roosts in cave-like human structures, such as abandoned depots and hangars.^[19][2]

Relationship with humans

As pests

Since fruit bats also eat commercially grown fruits intended for human consumption, many of them are poisoned or otherwise persecuted and eliminated by farmers to prevent crop loss.^[20][19] In Turkey, Israel, and Cyprus, farmers have poisoned Egyptian fruit bats via insecticides and pesticides. Other techniques used to kill the bats include using dynamite to destroy cave roosts, or fumigating cave entrances with sulfur to exterminate entire bat colonies.^[19] While Egyptian fruit bats do eat commercially grown fruits, the percentage of crops lost to bats may be overestimated.^[20][19]

In the 1950s in Israel, Egyptian fruit bats were declared pests, which led to an eradication campaign starting in 1958. Its roosting caves were poisoned with the pesticides 1,2-Dibromoethane or lindane, which not only killed Egyptian fruit bats, but many insectivorous bat species. Populations of insectivorous bats declined by approximately 90% in fifteen years as a result of the fumigation of caves, despite being protected under the Israeli Wild Animals Protection Law.^[36]

As disease reservoir

The Egyptian fruit bat has been a suspected reservoir for several human diseases under surveillance. It is hypothesized that it can spread Marburg virus to conspecifics through contact with infected excretions such as guano, but a 2018 review concluded that more studies are necessary to determine the specific mechanisms of exposure that cause Marburg virus disease in humans. Exposure to guano could be a route of transmission to humans.^[37] It has been documented with antibodies against Ebola virus in its blood, known as being seropositive, but has not tested positive for the virus itself. Evidence that it or any other megabat species is the natural reservoir of Ebola virus is "far from decisive".^[38]

In captivity

The Egyptian fruit bat is well represented in zoos around the world. As of 2015, there were 616 Egyptian fruit bats housed in twenty-three Association of Zoos and Aquariums (AZA) member facilities, slightly more than 5% of all captive bat individuals of twenty-eight different species.^{[39]: 12–13} In the future, the AZA emphasized the need to ensure that males are rotated among facilities to promote genetic variation within the captive population. Captive individuals are susceptible to hemochromatosis (iron overload), necessitating further research into the dietary risk factors for this condition, as well as general nutritional requirements for the Egyptian fruit bat.^{[39]: 34–35} While import of fruit bats into the US is usually closely regulated, a procedural error in 1994 allowed the importation of thousands of Egyptian fruit bats (and other species).^[40][41] Given that the Egyptian fruit bat is highly adaptable, there are concerns that, through the pet trade, it could become an introduced species in the Southern US, competing with native animals and causing destruction to fruit agriculture.^[40]

As model animals

The Egyptian fruit bat is used as a model animal in navigation research.^[42][43][44] They are especially suitable for this kind of research, because they use visual inputs in conjunction with echolocation to navigate.^[45][30] Additionally, their head is large enough to hold a wireless device that holds both electrodes that go into the brain and measure electrical activity of the cells, as well as a tracking device.^[42] This method was used to show that bats have place cells,^[46][47] which are cells that track their location, as well as head direction cells, which track the orientation of their head.^[43] Additionally they have vector cells, which contain a representation of the location relative to an important object.^[42] The bats are of particular interest, because these three types of cells have been shown to represent location and direction in 3D.^[43][47] Bats also have cells that represent the location of other bats, which researchers have called 'social place cells'.^[44] This finding was published in conjunction with a similar finding in rats.^[44][48]

References