An increase in the aberration rate of the acoustical signal in peripheral populations of the Marmota bobac, Müller (1776) [Augmentation du taux d'aberration du signal acoustique dans les populations périphériques de la Marmota bobac, Müller (1776)].

Résumé

Analysis of the alarm call of the Marmota bobac Müller, 1776 has revealed aberrations – deviations from the species-normal signal type. In contrast to the normal, the signal shows a different type of frequency modulation: the gentle frequency change is distributed by its rapid increase and attenuation. The above character is, presumably, recessive: related individuals may demonstrate both a presence and an absence of the aberrant signal. The animals with an aberrant signal form loose groups. Chrono-populations may show variation in aberration frequency, nevertheless the difference between local populations remain. The aberration rate is higher in peripheral populations (western Ukraine and eastern Kazakhstan) compared with the central part of the range. In local populations the aberration rate ranges from 9 to 61%. The peripheral populations are isolated for a long time from the core of the range, which aggravates the “periphery” effect (reduction in the gene flow). In the West, the major isolation mechanisms are anthropogenic factors – human settlements, farmlands, and roads. In the East, an extra ecological effect is created by the Turgaai Hollow. Today, it is rather an ecological than geographical barrier (Rumyantsev 1977): the soils of the hollow are alkali soils and solonchaks inherited from the ancient lake basin (Boboyedova 1966). In addition to “regular” aberrations the steppe marmot populations show some rare forms of aberrations with a rate not exceeding 3%. The latter show the traits characteristic of other bobak-group species.