The means by which new species arise is without doubt one of the most fundamental concerns of evolutionary biology. Under the biological species concept, species are defined as groups of actually or potentially interbreeding natural populations isolated from other such groups (Mayr 1963), systems of populations, the gene exchange between which is limited or prevented in nature by a reproductive isolating mechanism or by a combination of such mechanisms (Dobzhansky 1970). The restriction of gene flow between populations was considered largely essential to the speciation process (Mayr 1963), and allopatric models of speciation - in which geographically isolated populations diverge genetically to such an extent that they become reproductively isolated from one another - are widely accepted and considered by many to be the primary means of speciation. However, others have challenged this view (e.g. Maynard Smith 1966, Bush 1969, Ehrlich & Raven 1969), arguing that if natural selection is sufficiently strong, speciation can occur even if gene flow is continuing between speciating populations. Such divergence-with-gene-flow models led to renewed interest in, and growing support for models of sympatric speciation (e.g. Bush 1994, Schluter 1998). In sympatric speciation models, a single population in a homogeneous environment experiences simultaneous selection for two opposing phenotypes, with reproductive isolation subsequently developing between the two divergent phenotypes (reviewed in Maynard Smith 1966, Endler 1977, Felsenstein 1981, Rice & Hostert 1993, Johnson and Gullberg 1998).

Large and small morphs of Rhinolophus philippinensis occur syntopically throughout this species’ range and in some cases have been designated as subspecies (Flannery 1995). Extensive size differentiation in the population captured in Kakenauwe Forest Reserve (Buton Island) (2 large individuals and 6 small) was not reflected in the depth of genetic divergence. Large morphs (forearm length (FA) 56.4 ± 1.1 mm; weight 11.5 ± 1.1 g) exhibited an almost Hutchinsonian relationship to small morphs (FA 47.3 ± 1.0 mm; 6.7 ± 0.4 g), but preliminary genetic analysis, based on the first 1033 base pairs of the ND2 gene, revealed that some inter-morph differences (1.55 – 3.0%) barely exceeded intra-morph divergence (1.45%)). Thus while the morphological data indicates two species, genetic information is not inconsistent with a single species, or a species in the process of diverging. The extreme size difference and the relatively limited genetic divergence presents the possibility that local processes, namely size-mediated resource partitioning, may be driving a form of ecological speciation (sensu Schluter 1998). As a working hypothesis, we propose a model in which there is simultaneous selection for large and small morphs to exploit prey of different sizes. For divergent selection to lead to reproductive isolation between the two morphs, the character under selection (body size) has to influence the mate recognition system. In rhinolophid bats, call frequency scales with body size (Kingston et al. 2000), so selection on body size is likely to take lead to changes in call frequency between the two morphs. In many bat families, echolocation calls have no function in intraspecific communication (Fenton 1985), but rhinolophid bats the echolocation system is highly specialized and greatly constrains the production and reception of sound for communication purposes. As a consequence, adult rhinolophid bats emit sound consisting predominantly of a pure-tone frequency in both a communicative and an echolocation context (Möhres 1966). Call frequency is therefore likely to be an essential part of the mate recognition system. Furthermore, the frequency of the call is closely matched to an ‘acoustic fovea’ – an area of the ear and brain that is extremely sensitive and over-represents the pure-tone frequencies to enable the bat to detect the tiny changes in the echo created by the fluttering of insect wings (Schnitzler & Flieger 1983). This tight link between call frequency and acoustic sensitivity means that individuals should be most receptive to communication signals from conspecifics that are closest to their own call frequency as these will fall within their acoustic fovea and elicit the greatest auditory neurological response (i.e. small morphs will respond most readily to communication signals from other small morphs because these are most apparent to them; and large morphs will respond to other large morphs). Put simply, the ecological selection on body size could result in shifts in the mate recognition system (echolocation call frequency) that eventually lead to reproductive isolation and speciation. From this model arise a number of predictions that we will test in this field season. Specifically: 1) Large and small morphs differ in their diet, with large morphs including larger prey items in their diet; 2) Large morphs use lower echolocation call frequencies than do small morphs; 3) Large and small morphs exhibit ecological segregation.

The Sulawesi Naked Bat (Cheiromeles parvidens) is an intriguing bat about which very little is known. Found only in Sulawesi, the Philippines and the Moluccas, it is a distinctive, large bat that appears almost devoid of fur. Not only is the naked appearance quite striking, but a glandular throat sack on the lower neck means that these bats can be very pungent as well. Moreover, the long, narrow wings can be folded into pockets at the sides of the body so the bat can move about on all four limbs, further distinguishing this bat from other insectivorous species.

Despite these unique features, almost nothing is known of the ecology and conservation status of the Sulawesi Naked Bat. In fact, so few have been captured that its taxonomic status is currently considered uncertain (Corbet & Hill 1992) and it has been suggested as conspecific with the Malaysian Cheiromeles torquatus. In 2000 two individuals were captured in mistnets positioned over a river near Labundo Bundo (Buton Island). As for specimens known from the Moluccas (Flannery 1995), they were much (FA 69.7 mm, 69.4mm; 73.0g, 76.0g) than representatives of C. torquatus from Peninsular Malaysia (FA: 78.1-86.2 mm; 155-185 g), suggesting that they are indeed a separate species.

• To establish the taxonomic status of Rhinolophus philippinensis. Are the size morphs of Rhinolophus philippinensis separate taxa or a single species?
• To test the predictions of the ecological speciation model and determine how ecological differentiation is achieved. Do the morphs differ in roosting ecology (assumption being that assortative roosting is indicative of assortative mating), foraging ecology, diet?
• To determine the taxonomic status of Cheiromeles parvidens as it relates to Cheiromeles torquatus and investigate the ecology of this unique bat.

1. Taxonomic status of Rhinolophus philippinensis. Harp traps were set on established trails in the Kakenauwe Forest Reserve. For each individual captured, morphological data were collected and wing tracings drawn. Echolocation resting frequency (kHz) was recorded with an Ultrasound Advice S-25 bat detector linked to a the S350 ultrasound processor for time expansion and recording on a Professional Walkman (Sony). Tissue punches were taken from the wing membranes for molecular comparisons of the two morphs.
2. Ecological differentation between large and small morphs; testing the predictions of the ecological speciation model. To determine the extent to which the two Rhinolophus philippinensis morphs differ in their foraging and roosting ecology, radio transmitters were attached to each of the three individuals captured (following Wilkinson & Bradbury 1988). Biotrack refurbished tags weighing 0.6g with a lifespan of 7 to 10 days were used in each case. Each bat was tracked on release from the point of capture to obtain an approximate initial bearing. Up to three tracking teams in radio-contact were utilized to triangulate the point of origin of the signal each night. Trackers were then positioned at the point of signal origin the subsequent night in an attempt to back-track to the roost
3. Taxonomic status of C. parvidens. Mist nets were set over the Umala Dongkula (near Labundo Bundo) on approximately 14 nights between 18:00 and 20:00.

Three further individuals of Rhinolophus philippinensis were captured in 2001, bringing the total to four large (three male and one female) and six small morphs - collected in 2000 and 2001. Alpha-level taxonomy, acoustic and molecular comparisons of the two morphs will now be conducted to resolve their status. The intensive radio-tracking program of the Rhinolophus philippinensis morphs suggests that the home range for the large morph may be larger than originally predicted based on wing morphology. Both the male and female large morph appeared to originate each night from the same direction, but it was not possible to locate the roost before the radio transmitters failed. This project will continue next year Despite the intensibeData collected on the large morph suggest that home range size may be larger than originally predicted based on wing morphology; radiotracking was continued for each individual until the radiotransmitters died, but no roosts were located. This project will continue next year.

Two further specimens of Cheiromeles parvidens (one male and one female) were collected for morphological and genetic comparisons with Cheiromeles torquatus from Peninsular Malaysia (held at the American Museum of Natural History).

The taxonomic status of both Rhinolophus philippinensis and Cheiromeles parvidens will be resolved and incorporated into the publication describing the bats of Buton and Kabaena (‘Bat species of Buton and Kabaena Islands’ by Dr. Tigga Kingston (Boston University), Dr. Stephen Rossiter (Queen Mary and Westfield, University of London) & Dr. Boeadi (Museum of Zoology, Bogor) to be submitted by May 2002). Further publications describing the extent to which ecological speciation is occuring in the the Rhinolophus philippinensis morphs may follow the 2002 field season.

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