Fringed bat COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

Myotis thysanodes Miller 1897 belongs to the Order Chiroptera, Family Vespertilionidae. A phenetic analysis of morphological traits led Findley (1972) to assign Myotis thysanodes to his Nattereri group, which included the Palaearctic species Myotis natteri and Myotis pequinus. A more recent analysis based on mtDNA sequences in 33 species of Myotis led Ruedi and Mayer (2001) to conclude that M. thysanodes and M. natteri evolved in different clades. Morphological similarity among these taxa (notably the distinctive fringe on the trailing edge of the interfemoral membrane) reflects convergence and is a poor predictor of genetic or ancestral similarities. Among the North American long-eared Myotis species, M. thysanodes is the most morphologically distinct but it shares a close affinity with the Western Long-eared Myotis (Myotis evotis) and Miller's Myotis (Myotis milleri) in allozyme and chromosomal traits (Reducker et al. 1983). Recent mtDNA analyses by Tanya Dewey (unpubl. data) have shown that M. thysanodes is most closely related to M. evotis and in some regions there has been mitochondrial introgression between these two species.

Although four subspecies are recognized: M. t. aztecus-southern Mexico, M. t. thysanodes-most of western North America including British Columbia, M. t. pahasapensis-the Black Hills, and M. t. verspertinus-coastal Oregon and California (Hall 1981; Manning and Jones 1988), the phylogeographic structure revealed from the mtDNA analysis by Tanya Dewey (unpubl. data) is inconsistent with this subspecies taxonomy.

Another common English name for this species is the Fringed Myotis. The French common name is Vespertilion à queue frangée, or chauve-souris à queue frangée.

Description

The largest Myotis species in Canada, the Fringed Bat (Figure 1A) has pale brown dorsal fur, blackish wing and tail membranes, and long black ears. The ventral fur tends to be buffy. The outer edge of the interfemoral membrane has a fringe of stiff hairs visible with the naked eye. The calcar (a cartilaginous spur on the heel bone) is not keeled. The skull has a relatively narrow rostrum and a steep sloping forehead region. The dental formula is: incisors 2/3, canines 1/1, premolars 3/3, and molars 3/3. Representative body measurements (range in parentheses) for adults from the Canadian population are: total length 90 mm (88-93), ear length 19 mm (18-20), tragus length 9 mm (8-11), forearm length 42.3 mm (40.0-44.5), body mass 7.1 g (5.4-8.4) (Nagorsen 2002).

The only other long-eared Myotis bat known to occur within its Canadian range is the Western Long-eared Myotis (M. evotis).  The Fringed Bat is discriminated by its longer forearm (usually >42 mm), and a very prominent fringe of hairs on the outer edge of the tail membrane (Figure 1B) that is visible with the naked eye (van Zyll de Jong 1985; Nagorsen 2003). The skull of M. thysanodes has a broader palate (width across upper molars (M³-M³) >6.2 mm, and longer than maxillary toothrow length).