Hipposideros galeritus Cantor 1846

Hipposideros galeritus Cantor, 1846 New material: one adult male (VN 18-143 [16 May 2018], voucher, in alcohol, skull extracted), two released lactating females (VN 18-121, VN 18-189, [16 May 2018]) and two pregnant females (VN 19-49 [15 March 2019], VN 20-0087 [03 March 2020], vouchers, in alcohol); five adult males (VN 19-50, VN 19-51, VN 19-52 [15 March 2019], VN 19-63, VN 19-64 [16 March 2019], vouchers, in alcohol); four adult males (20191203.1, 20191203.3, 20191204.3, 20191204.4 [3-4 December 2019], vouchers, in alcohol). All were collected in secondary lowland mixed forests, Co To mountain, Tri Ton district, An Giang province (10.388637 oN, 104.995033 oE [AG1, Figure 1]). Morphology: Mensural data from our specimens (e.g., FA = 48.1 ± 1.0 mm, range 46.5–50.0 mm; CCL = 14.96 mm; Table 2) accord with published measurements for H. galeritus from Vietnam (FA: 45–51 mm; CCL: 14.6–15.8 mm) (Kruskop 2013) and Southeast Asia (FA: 47.8 ± 1.68 mm; CCL: 14.46 ± 0.28 mm) (Srinivasulu et al. 2025). External characters also match previous descriptions: the noseleaf is broad, covering the entire muzzle. The anterior leaf lacks a medial emargination and possesses two well-developed supplementary leaflets; the proximal leaflets are expanded and fused to form a single, impaired structure surrounding the anterior leaf which considerably exceeds it in width. The intermediate leaf is simple, equal to or wider than the posterior leaf. The posterior leaf is subdivided into four septa. Males possess a frontal sac behind the posterior leaf. The ears are triangularly pointed and the antitragal lobe is subangular, approximately one-third of the ear length. The pelage is thick and soft, dark to reddish brown dorsally, paler ventrally; hairs have pale bases. The muzzle and ears are variably pigmented (Figure 2B). The skull is small and elongated (GLS = 17.66 mm), with the mastoid width exceeding zygomatic breadth (Table 2). In lateral profile, the skull is elevated over the frontal and parietal regions of the braincase. The sagittal crest is low, moderately developed anteriorly but indistinct posteriorly, extending into the parietal region. The lambdoid crests are weakly developed. The interorbital region is narrow. Three pairs of rostral inflations are present: the anterior rostral chambers are similar in length to the posterior-median rostral chambers. The posterior-lateral chambers are much wider than kidney-shaped posterior-median chambers. The dentition includes robust and tall upper canines; the small first upper premolars (P²) situated within the toothrow between the upper canines and second upper premolars (P 4); and the crown area of the first lower premolar (P 2) is approximately equal to that of the second lower premolar (P 4) but only about half its height (Figure 3B). Echolocation: The constant frequency (CF) component of echolocation calls emitted by our bats ranged between 84–85 kHz (Table 2; Appendix 4). As tabulated in Srinivasulu et al. (2025) and our own data, only populations of H. galeritus found in the Thai-Malay peninsula and Bokor National Park, Cambodia (close to the AG1) are known to emits calls at similar frequencies (80.7–92.0 kHz and 86–87 kHz respectively), whereas populations elsewhere in mainland Southeast Asia and on Borneo produce significantly higher constant frequency components (typically ≥ 98–110 kHz). Genetics: Consistent with previous studies (Francis et al. 2010; Murray et al. 2012; Srinivasulu et al. 2025), our Bayesian trees based on COI and Cytb datasets strongly support the monophyly of Southeast Asian H. galeritus s.l. (PP=1). In our COI tree, the H. galeritus s.l clade is subdivided into three well-supported geographic subclades (PP=1): A– insular Sundaic (Borneo (Kalimantan, Indonesia and Sarawak, Malaysia) + Java), B– mainland Sundaic or the Thai-Malay Peninsula, and C—Indochinese comprising Thailand excluding the peninsula, Cambodia, Laos, Vietnam, including our specimens in the VMD. In our Cytb tree, bats from insular Sundaic and Indochinese subregions appeared in two divergent and highly supported lineages (PP=1) (Figure 6). Genetic divergences based on COI / Cytb sequences within three recognized subclades A, B, C Southeast Asian H. galeritus s.l. are between 0– 4.9% / 0.3–2.8%, 0.3/–, and 0–2.7 / 0.2–0.9%, respectively; distances between these clades are between 11.4–14.6% / 10.7–11.5% and comparable with interspecific variations in the Hipposideros genus (Appendix 7). Taxonomic notes: Hipposideros galeritus was historically regarded as a widespread species across the Indomalayan Region, comprising four geographic subspecies: H. g. galeritus (distributed in the Thai-Malay peninsula, including Tarutao, Penang, and Bangka islands, Sumatra, SE Thailand, S. Laos, Cambodia, and C-S. Vietnam), H. g. brachyotus Dobson, 1874 (India, Bangladesh, Sri Lanka), H. g. insolens Lyon, 1911 (endemic to Borneo), and H. g. longicauda Peters, 1861 (restricted to Java) (Corbet & Hill 1992; Monadjem et al. 2019; Simmons 2005). Based on analyses of COI gene sequences, morphological and acoustic data, Srinivasulu et al. (2025) revised this classification by: (1) re-elevating brachyotus to species rank for Indian populations, (2) describing the Sri Lankan population as H. srilankaensis, and (3) concluding that Southeast Asian H. galeritus s.l. represents several distinct species. This conclusion aligns with earlier studies (Francis et al. 2010; Murray et al. 2012) which found substantial genetic divergence and distinct echolocation call frequencies among allopatric populations (e.g., ~115 kHz in Borneo, 89.1 ± 1.5 kHz in Peninsular Malaysia, ~108 kHz in Laos), supporting their status as evolutionarily and ecologically distinct species. However, Srinivasulu et al. (2025) interpreted the observed call frequency variation across Southeast Asian COI lineages as vocal plasticity. Our genetic results confirm deep geographic structuring within Southeast Asian H. galeritus s.l. but delimiting these taxa and elucidating their evolutionary history remains challenging. For instance, despite similar isolation by marine barriers, COI p-distances between one Javan and two Bornean bats were unexpectedly low (4.7–4.9%), contrasting sharply with higher divergences between insular and continental Southeast Asian populations (11.4– 14.6%; Appendix 7). These distances exceed maximum intraspecific variations in the Indochinese H. galeritus (pdistances ≤2.7%) and interspecific variations between certain pairs of sister species such as 3.3% between H. kunzi and H. kingstonae or 3.5% between H. rotalis and H. khaokhouayensis. However, they are lower than the intraspecific variation between Bornean and Peninsular Malaysian populations of H. cervinus (5.9–6.2%; Appendix 7). This pattern suggests allopatric populations in insular Southeast Asia either represent deeply structured populations of a single species or recently diverged sister species (Francis et al. 2010; Murray et al. 2012). Likewise, our low-frequency emitters in the VMD (AG1: 84–85 kHz) are phylogenetically nested within the high-frequency Indochinese clade (~110 kHz), yet genetically divergent from the low-frequency emitters of the Thai-Malay Peninsula (mainland Sundaic subregion). While call plasticity may be a plausible explanation for frequency variation in the Indochinese subregion clade, these mtDNA phylogenetic patterns can stem from either incomplete lineage sorting of ancestral polymorphisms after diversification or introgression following secondary contact (Ballard & Whitlock 2004; Funk & Omland 2003). Long branches in the mtDNA phylogenetic tree, especially among the two phonic forms (excluding individuals showing potential introgression) indicate that these lineages have had substantial time to evolve independently after their divergence from a common ancestor. Instead, the “low-frequency” bats carrying mtDNA haplotypes of “high-frequency” congeners was not found randomly but specifically in parapatric zones (including AG1 and KG1-3 [Figure 1] and in Bakor National Park, Cambodia), suggesting historical or ongoing introgression between previously isolated incipient species following secondary contact(s) (Mao et al. 2010, 2013; Zhou et al. 2023). As proposed by Srinivasulu et al. (2025) and supported by regional phylogeographic studies (Khan et al. 2010; Tu et al. 2017a, 2018b), the evolutionary history of taxa within the H. galeritus s.l. complex in mainland Southeast Asia was likely shaped by climatic fluctuations and associated changes in forest range and sea levels during the Pliocene–Pleistocene. In line with this hypothesis, cycles of forest contraction and expansion, along with the submersion and re-emergence of the Isthmus of Kra due to sea-level oscillations, may have facilitated allopatric speciation, followed by secondary contact and asymmetric introgressive hybridization. Given the limitations of our study (incomplete geographic sampling, reliance solely on mtDNA markers), future research incorporating nuclear DNA data is needed to (1) test gene flow hypotheses and clarify species boundaries within mainland Southeast Asia; and (2) resolve the taxonomy and phylogeography of insular Sundaic populations (Borneo, Sumatra, Java, Sulawesi). Distribution and ecological notes: Given the unresolved taxonomy of Hipposideros galeritus s.l. in mainland Southeast Asia, our records of low-frequency-emitting bats in the VMD (AG1, KG1-3 [Figure 1]) and Bakor National Park, Cambodia, suggest that the distribution range of this phonic form may extend from the Thai-Malay Peninsula to the Mekong Delta. Targeted surveys between southern Cambodia and southeastern Thailand may confirm this. Similar to other hipposiderids, our low-frequency bats were observed roosting in caves or rock crevices and foraging for insects in the understorey of secondary forest. Records of pregnant females in March and lactating females in May indicate that their breeding season spans f