THE ABDOMINAL GLANDULAR SYSTEM IN DUNG BEETLES (COLEOPTERA, SCARABAEIDAE) - EVOLUTIONARY TRENDS AND RELATIONSHIPS WITH NESTING HABITS

The abdominal glandular system in Scarabaeidae s. str. evolved by elaboration from simple glandular units scattered around the integument. Within the family, every evolutionary step towards increasing complexity can be observed. Glandular complexity and complexity of nesting behaviour, it seem, are correlated. In tunnelers with a primitive nesting behaviour, the glandular units show only an increase in density in some abdominal areas. In tunnelers with more elaborate nesting behaviour, and in rollers, differentiated glandular patches are to be found. In rollers, this glands are more numerous and show a more complex structure. A regression seems responsible for the relatively poor glandular development in Mentophiline Canthonines, considered as "non-rolling rollers". Sternal glands always exhibit a sexual dimorphism. In females they probably play a role in brood-ball making, an activity restricted to females. In males, they are mainly present in species in which a close collaboration exists between both sexes in nesting behavior. The female android (male-like) sternal glands and the male sternal glands have probably a similar function. Pygidial glands are probably connected with food transport far from its source. Meanwhile, no relationships could be discovered between the abdominal glands and the parental brood care.