EARLY ONTOGENY OF 3 GYMNOCEPHALUS SPECIES (PISCES, PERCIDAE) - REFLECTIONS ON THE EVOLUTION OF THE GENUS

A brief description of the early development of ruff, Gymnocephalus ce rnuus, Balon's ruff, G. baloni, and yellow pope, G. schraester, is pre sented. Developmental steps and thresholds, as well as patterns in the development of the three Gymnocephalus species, are discussed with re gard to saltatory ontogeny and alprehost theory. Most of the patterns in all three Gymnocephalus species were found to be very similar to ea ch other, and a new model of speciation for the genus Gymnocephalus is proposed. The hypothesis that the subgenus Gymnocephalus (G. schraets er and G. acerinus) has been evolving precocially and the subgenus Ace rina (G. cernuus and G. baloni) altricially is based on the following patterns: (1) embryos and larvae of yellow pope grow and develop faste r than those of ruff and Balon's ruff, (2) yellow pope females become mature when older and larger, (3) relative fecundity in yellow pope is considerably lower, (4) eggs of yellow pope are larger, containing a greater amount of yolk, and (5) typical elongation of the snout (preor bital distance) in yellow pope seems to be a deviation from the ancest ral state. Several patterns of development in the precocial form (body depth, head depth and shape of mouth) indicate that juvenilisation (p aedomorphosis) may have played an important role in the divergence of these subgenera.