Bioacoustics of Myotis (Myotis) annatessae

Comparison to other species The new species mostly resembles M. muricola s. lato in general appearance. It differs in smaller average size (both in external and cranial measurements) and weaker dentition with particularly small upper canines. The thumb and its claw is longer than in Indochinese and Malayan M. muricola ; thumb measured without claw about 15% of forearm length (13.7–16.9 vs. 9.2–12.3% in M. muricola ). The calcar lobe is less developed than in M. muricola . The notch on the posterior edge of the ear conch is noticeably better developed in M. muricola . Penis is somewhat smaller and less bulbous than in Indochinese M. muricola and M. ater , but definitely thicker than in M. mystacinus s.lato. Indochinese specimens of M. muricola also have, on average, a proportionally shorter hind foot (about 38% of tibia length). From M. ater , the new species also clearly differs in smaller size and lighter coloration. From M. nipalensis , it differs in a smaller upper canine and proportionally higher braincase: the average OH/MW ratio is 0.75 in M. annatessae , and 0.69 in M. nipalensis . From M. siligorensis and its allies the new Myotis differs by distinctively myotodont lower molars, larger canines (which exceed the corresponding large premolars in height), rectangular (not U or W shaped) posterior edge of palate and a more robust rostrum. The new species also differs from other morphologically similar Myotis in baculum shape. In the M. siligorensis complex, the baculum is minute and peg-like, often lacking the urethral groove. In Indochinese M. muricola and M. ater it is clearly different, with a constricted distal end. Amongst all the specimens analyzed, the baculum of M. annatessae bears closest resemblance to that of the Nepalese M. muricola , but the latter is more robust, more curved upward and has very shallow basal concavity ( Fig. 3 , h). From M. laniger and small individuals of M. horsfieldii , the new species is easily distinguishable by a smaller hind foot (about half of tibia length in both species and definitely shorter in M. annatessae ), by the place of the wing membrane attachment (above the base of the outer toe in both M. laniger and M. horsfieldii ) and by shorter canines; from M. rosseti — by larger foot, larger overall size, absence of the adhesive pads on thumbs and both small middle upper premolars well developed. According to published data ( Allen, 1938 ; Smith and Xie, 2008), M. davidii — another East Asian mouseeared bat of similar size — has a larger hind foot and posterior upper small premolars displaced inward from the tooth rows. Several other named forms of small-sized Myotis have been described from adjacent parts of mainland South-East Asia and were traditionally treated as subspecies of M. muricola ( Simmons, 2005 ) . Myotis lobipes from western Burma has long been regarded as a full synonym of M. muricola s. str. (Tate, 1941). Its type specimen resembles M. muricola specimens from Indochina in size and qualitative features. Myotis moupinensis from China (not included into our analysis) is also usually treated as a partial synonym of M. muricola (Tate, 1941; Simmons, 2005 ). Its average smaller size ( Allen, 1938 ) gives it superficial resemblance to M. annatessae . However, six alcohol-preserved specimens in ZISP, labelled as M. moupinensis and collected from within the known distributional range of this form, possess nyctalodont lower molars and other morphological traits in common with the Taiwanese M. latirostris . Thus they are more likely to be affiliated with this distinct species (M. Ruedi, personal communication). The same is probably true for M. blanfordi and M. caliginosus . Specimens of these forms (including types of M. blanfordi ) processed in the Berlin Zoological Museum match M. latirostris in cranial shape and dentition. This entire species complex, while similar in size to M. annatessae , differs markedly in having a lower braincase, shallower frontal profile, proportionally larger canines, and nyctalodont lower molars. Finally, available skull measurements of the form niasensis , described from Nias Island as “a small form of Myotis muricola ” ( Lyon, 1916: 442 ) , resemble those of the new species, but niasensis has short- er forearm and ear lengths (31.2–31.5 and 9.8–10.2 vs. 32.6–35.3 and 11.6–13.8, respectively). Tate, who apparently saw the type of niasensis , reports that it has a low brain case, in contrast to the proportionally high brain case in M. annatessae . Genetic analysis As mentioned earlier, neighbour-joining analysis of COI sequences ( Fig. 4 ) corroborates the observed morphological distinctiveness of M. annatessae from both M. muricola and M. siligorensis complexes, as well as from the extralimital M. mystacinus and allied species. Available genetic data are insufficient to infer phylogenetic relationships between the new species and other Myotis , but its deep genetic divergence from the most morphologically similar representatives of this genus is clear. Closely related lineages, labelled on the tree as ‘ Myotis cf. muricola ’, most probably represent undescribed forms. However their divergence from M. annatessae also corresponds to specific level. Comments on natural history All Vu Quang specimens in the type series were captured over the Song Con River. Bats were observed foraging about 1–7 m above the water surface, over ripples as well as over backwaters. In the latter case M. annatessae were observed togeth- er with M. horsfieldii , although the latter was foraging immediately above the water surface; thus two species partitioned the foraging space by altitude. Echolocation calls recorded with a QMC Mini heterodyning ultrasound detector were FM, low intensity, with frequency ranging from 45–50 kHz. All specimens captured in July–August were reproductively inactive.