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Fruit bats

The Pteropodidae encompass a diverse assemblage of fruit-eating bats, represented by over 30 species in mainland Africa (Happold and Happold 2013, Nesi et al. 2013, Hassanin et al. 2015), of which 21 species in 11 genera occur in southern Africa. The only mainland genera not recorded in southern Africa are Nanonycteris and Scotonycteris, which are restricted within the rainforest zone. Nevertheless, museum records of Scotonycteris bergmansi Matschie 1894 mapped by Bergmans (1990) extend nearly to 4°S in the Congo basin. So, it is likely that S. bergmansi occurs in our area, if not resident, then possibly as a migrant.

Furthermore, several species of Pteropus breed on islands in the Indian Ocean, some very close to the mainland (at Pemba and Zanzibar).

The Pteropodidae are a distinctive group, readily distinguished from other bats by the possession of two claws on the wing (all other bats have only one wing claw, which is the homologue of our thumb) (Figure 43b). Traditionally, they are also viewed as being larger than ‘microbats’, but this is not always so. For example, at 13 g, the diminutive pteropodid Megaloglossus woermanni is smaller than many ‘micro-bat’ species. However, it is true that the largest bats belong to this family. In Africa, Hypsignathus and Eidolon may have forearm lengths of over 120 mm, and a large male of the former can exceed 400 g. By comparison, the largest ‘microbats’ weigh less than 200 g. The other typical features of the Pteropodidae are their dog-like faces with elongated muzzles and large eyes (Figure 43a), and their diet of fruit. In contrast to the ‘microbats’, eyesight is important in the Pteropodidae – they rely on this sensory organ for perception of their environment. A distinctive form of echolocation has developed in only one genus, Rousettus (Neuweiler 1990).

Figure 43. A typical Pteropodidae species: (a) head showing the large eyes and absence of noseleafs, and (b) wing showing the presence of claws on the first and second digits.

Figure 44. (a) The absence of a tail (e.g. Epomophorus species), and (b) the presence of a short tail (e.g. Rousettus species)

Figure 45. The configuration of palatal ridges in three Pteropodidae species: (a) Epomophorus wahlbergi, (b) E. crypturus, and (c) E. angolensis.

Associations between food plants and fruit bats, worldwide, are important to the dispersal and reproduction of many species of tropical angiosperms. In the Usambara Mountains, Tanzania, where at least seven species of pteropids occur, approximately 20% of the submontane tree flora is bat-dispersed (Seltzer et al. 2013). Globally, fruit bats are known to pollinate at least 528 species of flowering plants (Fleming et al. 2009). In Africa, the pollination of selected plants by fruit bats has been studied in West African fruit bats only (Rosevear 1965). an inaugural study revealed that fruit bats pollinate the baobab, Adansonia digitata (Jaeger 1945), and subsequent studies focused on pollination of the sausage tree, Kigelia africana, and other West African trees by pteropids (Baker and Harris 1957, Harris and Baker 1958, 1959). A recent study of the genus Rousettus across its Afrotropical range invokes the co-evolutionary relationships between pteropids and many tropical angiosperms; it suggests that seed dispersal by Rousettus bats, which have the ability to colonise dry habitats, could have led to the expansion of forest refugia in Africa and Asia during the Pleistocene (Stribna et al. 2019). In light of the latter, it is interesting to note the persistence of the isolated outlying population of Eidolon helvum, confined to the Aïr Massif, northern Niger, deep within the Sahara Desert (Bergmans 1990, Cotterill 2001c). These interesting subjects of the ecology and co-evolution of Afrotropical plants and pteropids await deserving study – improving our understanding of bat–plant interactions in pollination and seed dispersal in tropical landscapes has important significance for biodiversity conservation (Bermingham et al. 2005, Fleming et al. 2009). Such exigency and the dearth of knowledge on these subjects challenges evolutionary biologists – in southern Africa especially – with interesting opportunities.

The phylogenetic relationships within the Pteropodidae have recently been clarified using molecular techniques (Almeida et al. 2011, 2016). Previous studies based on morphology suggested that African fruit bats comprised two subfamilies: Epomophorinae (including the tribes Epomophorini, Myonycterini, Plerotini and Scotonycterini) and Rousettinae (including the genera Rousettus and Eidolon) (Bergmans 1997), with the genus Pteropus restricted to offshore islands (O’Brien et al. 2009). Molecular phylogenies do not support this division (Almeida et al. 2016). For a start, the genus Eidolon represents an independent lineage not closely related to other fruit bats, and is placed in its own subfamily Eidolinae. All other mainland African fruit bats (i.e. excluding Pteropus) group together as an independent lineage represented by the subfamily Rousettinae, with the Asian genus Eonycteris the only non-African member of this taxon (Giannini and Simmons 2003, Almeida et al. 2011, 2016). Thus, the highly distinctive genus Megaloglossus with its unique, extensible tongue and nectivorous diet, does not group with other Asian nectivorous fruit bats (e.g. Macroglossus), but is embedded within the Rousettinae. Fruit bats have colonised the African mainland at least four times (Almeida et al. 2016), with the genus Pteropus having independently colonised offshore Indian Ocean islands on three occasions (O’Brien et al. 2009).

In summary, African fruit bats can be divided into the following seven tribes: (1) Eidolini (Eidolon); (2) Scotonycterini (Scotonycteris, Casinycteris); (3) Rousettini (Rousettus); (4) Stenonycterini (Stenonycteris); (5) Epomophorini (Epomophorus, Epomops, Hypsignathus, Micropteropus, Nanonycteris); (6) Myonycterini (Myonycteris, Megaloglossus); and (7) Plerotini (Plerotes).

The Epomophorini include bats with distinctive white ear patches and shoulder epaulettes (but absent in Hypsignathus). The Scotonycterini also have white facial markings. The remaining genera have less striking faces and lack shoulder epaulettes, rendering these bats far drabber in appearance. Some genera (e.g. Rousettus and Myonycteris) have a short tail (Figure 44). The taxonomic position of Lissonycteris was in dispute for a long time – this taxon was previously placed in its own genus, and prior to that considered a subgenus of Rousettus. This species has now been confirmed to belong to the genus Myonycteris (Nesi et al. 2013). Before the advent of molecular techniques, relationships within the Pteropodidae were inferred from a number of morphological characters; one of the most important of these was the configuration of palatal ridges (Figure 45). If not particularly useful for understanding systematic relationships, the palatal ridges are still useful in species identification.

Hypsignathus and Nanonycteris are monotypic genera, and their taxonomic status is not currently disputed. Micropteropus, Epomophorus and Epomops, however, are not as clearly distinct and there is still debate on the position of species within them (Almeida et al. 2016). Epomophorus grandis was originally described as Micropteropus grandis (hence the species epithet), and may still be a member of the latter genus but this awaits molecular analysis; the palatal ridges in this species appear to be intermediate between that of the two genera. Similarly, Epomops dobsonii (but not the other two Epomops species, E. franqueti and E. buettikoferi) has recently been transferred to Epomophorus based on molecular analysis (Almeida et al. 2016); we also suggested this in the first edition judging by its biogeography and its intermediate palatal ridges (Monadjem et al. 2010b). Externally, Micropteropus and Nanonycteris are almost identical (to the point that they cannot be identified with certainty on external features alone), but they are morphologically (palatal ridges) and genetically quite different, justifying generic separation. (Note that Nanonycteris does not occur in southern Africa.) Finally, the relationship between Micropteropus and Epomophorus is not yet clearly established and requires further molecular studies, particularly the inclusion of M. grandis, M. intermedius and most of the species of Epomophorus (Almeida et al. 2016).

TABLE 5.

TABLE 5. IDENTIFICATION MATRIX FOR GENERA WITHIN THE FAMILY PTEROPODIDAE

GENUS	FA (MM)	TAIL	WHITE EAR PATCHES	GLANDULAR PATCH/HAIRS (MALES)	PALATAL RIDGES1	WING	OTHER
Megaloglossus	39–49	very short	no	throat – ruff of longer whitish hairs	7 ridges, 4+2+1	inserts on 2nd or 3rd toe or between	Africa’s smallest fruit bat; pointed snout and elongated tongue
Casinycteris	50–62	absent	yes	unknown	2 series: 3–4 thick + 1 thin, then 13–16 thin, irregular, serrated	unknown	shortened palate and upturned rostrum
Plerotes	45–53	absent	yes	unknown	8 simple ridges, 4+0+4	unknown	narrow interfemoral membrane, calcar absent
Micropteropus	49–64	very short	yes	shoulders – long white hair	6 prominent ridges (1st undivided, remainder divided by prominent medial gap), followed by variable number of narrow serrated ridges, 1+5+2–4	unknown
Myonycteris	66–88	short	no	throat – ruff of long sticky hair	usually 8 or 9 ridges, 3+4+2	inserts on 2nd toe	metacarpal and first phalanx of 5th digit = (or >) forearm length
Epomophorus	60–95	absent	yes	shoulders – long white hair	6 thin ridges, typically 4+2+0, except E. dobsonii which has 5 thick ridges and 3–4 thin ridges (see genus matrix)	inserts on 2nd toe	face as long as braincase
Epomops	80–104	absent	yes	shoulders – long white hair	3 thick undivided and 5–8 thin ridges, 3+0+5–8	inserts on 2nd toe	face much shorter than braincase
Rousettus	86–106	short	no	two restricted glandular areas with stiffened hairs on sides of neck	typically 8 ridges, 4+3+1	inserts on 1st toe or between 1st and 2nd	metacarpal and first phalanx of 5th digit much shorter than forearm length
Stenonycteris*	85–95	short	no	two restricted glandular areas with stiffened hairs on sides of neck	8 ridges, 4+3+1	inserts on 1st toe or between 1st and 2nd	metacarpal and first phalanx of 5th digit much shorter than forearm length
Eidolon	110–130	short (∼15 mm)	no	glandular hairs on neck	8–11 ridges, 4+3+1–4 or 3+4+1–4	inserts on 1st toe; naked wing	dorsal fur restricted to narrow band
Hypsignathus	114–134	absent	yes	absent	10–11 ridges, the first 5 are thick while the remainder are thin	unknown	large, swollen muzzle, especially pronounced in males

¹ Palatal formula indicates, from front to back, three groups: undivided ridges, divided ridges and thin serrated ridges near the posterior end of the palate^* Stenonycteris can be readily distinguished from Rousettus by its comparatively long fur

TABLE 6.

TABLE 6. IDENTIFICATION MATRIX FOR SPECIES WITHIN THE GENUS EPOMOPHORUS (PTEROPODIDAE)

SPECIES	FA (MM)	DISTINGUISHING COLOUR AND MARKS	PALATAL RIDGES	ROOST	RANGE IN SOUTHERN AFRICA
E. labiatus	58–66	-	2nd to 4th ridges not divided	banana trees, palm roofs of huts	widespread in Malawi and Zambia
E. grandis	62–66	-	2nd to 6th ridges divided by narrow groove	not known	restricted to Angola and DRC
E. anselli	64–77	-	2nd to 4th ridges not divided	not known	known from northeast Malawi and southern DRC (and may occur in eastern Zambia)
E. wahlbergi	69–93	broad muzzle	only 1 post-dental palatal ridge	dense foliage of tall trees	widespread and abundant in eastern parts
E. crypturus	75–88	narrow muzzle	2 post-dental palatal ridges; 4th ridge is midway between 3rd and 5th ridges	dense foliage of tall trees	widespread and abundant in eastern parts
E. angolensis	76–94	narrow muzzle	2 post-dental palatal ridges; 4th ridge closer to 3rd than 5th ridge	not known	restricted to southwestern Angola and northwestern Namibia
E. dobsonii	80–92	broad muzzle	2 thick post-dental palatal ridges, each with 2 triangular projections	probably dense foliage of tall trees	widespread in northern parts

TABLE 7.

TABLE 7. IDENTIFICATION MATRIX FOR SPECIES WITHIN THE GENUS MYONYCTERIS (PTEROPODIDAE)

SPECIES	FA (MM)	PALATAL RIDGES	ROOST	RANGE IN SOUTHERN AFRICA
M. torquata	< 65	typically 9 ridges, 3+4+2	probably trees	marginal into region: restricted to rainforests of Central and West Africa
M. relicta	69–71	typically 8 ridges, 3+3+2	not known	widespread along eastern coastal parts
M. angolensis	72–83	typically 9 ridges, 3+4+2	hollow trees, entrance to caves	marginal into region: restricted to rainforests of Central and West Africa
M. goliath	75–90	typically 9 ridges, 3+4+2	probably as above	southern African endemic: highlands of eastern Zimbabwe and central Mozambique

TABLE 8.

TABLE 8. IDENTIFICATION MATRIX FOR SPECIES WITHIN THE GENUS MICROPTEROPUS (PTEROPODIDAE)

SPECIES	FA (MM)	DISTINGUISHING COLOUR AND MARKS	PALATAL RIDGES	ROOST	RANGE IN SOUTHERN AFRICA
M. pusillus	49–56	white ear base	1+5+2–4, 2nd and 3rd ridges fused	trees	marginal, northern Angola
M. intermedius	57–64	white ear base	1+5+2–4, no ridges fused	not known	marginal, northern Angola