Multivariate analysis of Morphological characters of Pipistrellus Pipistrellus (Schreber, 1774) and P. Nathusii (Keyserling & Blasius, 1839) (Mammalia: Chiroptera) from the Netherlands

Within the Vespertilionidae the genus Pipistrellus Kaup, 1829 is characterized by the presence of a calcar lobe (epiblema) attached to the calcar bone, the presence of two upper premolars on each side and a forearm length smaller than 38 mm. Two representatives of this genus occur in The Netherlands: Pipistrellus pipistrellus (Schreber, 1774) and P. nathusii (Keyserling & Blasius, 1839). These two species probably are closely related and are difficult to distinguish. Many authors over the years have used different morphological, dental and skull characters to differentiate these species. In this study the characters are divided into two groups: descriptive characters and biometric characters. Scanning electron photographs indicate a more pronounced dentition of the apical hair scales in the fur on the breast and back of P. nathusii than in that of P. pipistrellus. In P. nathusii the second upper incisor reaches beyond the caudal cusp of the first upper incisor in more than 72% of the skulls, while this feature occurs in only 8% of the skulls of P. pipistrellus. A gap between the second and third incisor is found in 84% of the lower jaws of P. nathusii and in only 21% of the lower jaws of P. pipistrellus. The BIOPAT computer program was used in analysing the biometric characters. A multivariate analysis including a principal component analysis of biometric characters was applied, for which purpose these characters were divided into four groups: skull, dental, external and X-ray characters. A total of 165 specimens, mainly from The Netherlands, have been examined. A discriminant analysis was used to select those characters by which these two species may best be separated. Important biometric skull characters are: condylobasal length, length of lower jaw and toothrow length (I1 - M 3) and, to a lesser extent, occipital width. The most important dental character is the relative length of I2. However, for a better separation a discriminant function of eight dental characters is required. Essential external or X-ray characters are: length of fifth finger, third finger and forearm length. The X-ray characters show a high correlation with the external characters. The X-ray method, however, can be useful for identification of dry skins.