Paedomorphic Tendencies in the Evolution of Daphnia (Daphnia) longispina s. l. Species Group (Crustacea: Cladocera: Daphniidae)

Abstract

Paedomorpic tendencies in the evolution of pelagic daphniids with respect to the Daphnia longispina s. l. species group (Crustacea: Cladocera: Daphniidae) are discussed. They concern the reduction of the total length, body length and relative length of the rostrum, relative length of postabdominal processes and decrease in the number of postabdominal teeth, elongation of the caudal spine, swimming antennae, and postabdominal setae. Paedomorphic tendencies in the males of Daphnia cucullata Sars are manifested in their similarity to females, and, in males of Daphnia galeata Sars, they are mainly manifested in their similarity to juvenile males of Daphnia longispina (O. F. Müller). Paedomorphic evolution and adaptation to the pelagic mode of life may be strongly interrelated, and occuring in parallel and even independently from each other due to the mosaic pattern of evolution.