The karyotype of Myotis horsfieldi

The karyotype of Myotis horsfieldi was 2n = 44, FN = 50, consisting of three large and one small metacentric or submetacentric pairs and 17 medium-sized to small acrocentric pairs in autosomes, a medium-sized submetacentric X chromosome, and a small acrocentric Y chromosome (Fig. 4A). The karyotype of Myotis horsfieldi from Hainan Island does not differ from conspecific population in Borneo [32]. The vespertilionid genus Myotis is one of the most diverse mammalian genera and includes 103 species [26], but it is also one of the most karyologically conservative genera. A diploid number 2n = 44 characterizes all 47 species for which karyotypes have been reported [22, 33]. Chromosomal variation is essentially restricted to the presence of heterochromatic short arms on the smaller autosomes, variation in the location of active nucleolus organizer regions (NORs), as well as differences in the size of the Y chromosome [22, 33, 34]. In addition, an inverted autosome and a duplicated translocation involving the X chromosome have been reported in M. pruinosus [35]. An extra pair of acrocentric autosomes (2n = 46) has also been reported in M. annectans from Thailand [36] and in M. davidii from Guangdong [16]. The karyotype of M. horsfieldi in this study is the conservative one and showed no additional translocation.