Craniometric variations in a population of the spotted souslik

Abstract

The aim of these investigations was to analyse sex dimorphism and variations in the development of the skull of Citellus suslicus (G u 1-denstaedt, 1770) on the basis of a sample consisting of 194 individuals. Fisher's discriminant analysis was the method used, and the significance of the results obtained was checked by the Mahalanobis D 2 test. Sex dimorphism was found in the skull of the souslik, it being particularly marked even in young animals. With the exception of postorbital breadth the mean measurements are greater in males. In young sousliks all the characters are non-discriminant. In adult sousliks the following characters were found to be discriminant in definition of sex dimorphism: maximum length of the skull, maximum nasal breadth, postorbital breadth, maximum height of brain case, mandible length. Changes with development were found in the craniometric characters, the majority of them exhibiting growth with age. Nasal length, frontal length and inter-orbital constriction are most probably stable, altering very little with age, while postorbital breadth even decreases. The most distinctive characters from the aspect of changes with age are: maximum length of the skull, postorbital breadth (in males),, and nasal breadth in females. The following regularities in development of the souslik's skull can be distinguished: a) rate of development of different parts of the skull is uneven, and in consequence different discriminant characters dominate in different periods of the animal's life, and different correlations occur; b) proportion between height and length of the skull is maintained in both age groups; c) development of the mandible takes place evenly in all planes; d) the muscles of the mandible exert a considerable effect on the development of the parts of the skull connected with them; e) the frontal region exhibits considerable developmental stability. I. PROBLEMS DISCUSSED IN THE STUDYThe aim of this study is to investigate the sex dimorphism and variations in development of the skull of the Spotted souslik, Citellus suslicus (Guldenstaedt, 1770) in one population at Sławęcin near Hrubieszów in the Lublin province. The area inhabited by this population is uniform from the ecological aspect. The skulls were collected over a period of one month. The material is therefore of the required uniformity from the geographical, ecological and seasonal aspects, which permits of assuming that the basic factors forming the variations observed are the sex and age of the animals.Present address: B. Ciesielska, Warsaw, Komarowa 88 m 37, W. Kupść, Warsaw, J. Bruna 6 m 32.[151]