SREL Reprint #2367

Male ontogeny and size-related variation in mass allocation of bluenose shiners (Pteronotropis welaka)

Dean E. Fletcher

Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29802

Abstract: During the spawning season of Pteronotropis welaka (bluenose shiners), three types of males were present in the population that differed in size, coloration, morphology, and mass allotment. The smallest males (initial males) were less dimorphic in both coloration and morphology, whereas the largest males (terminal males) represented the peak in sexually dimorphic development. Intermediate-sized males (transitional males) were also intermediate in size and coloration. The three types of males represent phases of a continual ontogenetic sequence in which initial males were in the first phase of ontogeny of sexually mature males followed by transitional males that were in transition to the terminal phase, the climax of development. Transition into a terminal male involved the expansion of median fins and pelvic fins, formation of blue on the head, increase in iridescent patches on scales, loss of yellow pigment in the dorsal fin, and general intensification of black pigment. Variation in mass allocation among somatic, reproductive, and storage components occurred among phases of P. welaka males. Initial and terminal males allocated a similar relative amount of mass to testicidar tissue. Transitional males, however, during the period of increased development of secondary sexual characters and growth allocated a lower proportion of their mass to reproduction. Simultaneously, transitional males allocated the same relative mass to storage (fat deposits). Either transitional males allocated less mass to a functional testes, or delayed gonad maturation. Similar testes gross morphology observed among the types of males may indicate the former. This may represent a trade-off of current reproductive tissue development for somatic growth and development of secondary sexual characters, while not utilizing fat reserves that may be needed for future activities.

SREL Reprint #2367

Fletcher, D.E. 1999. Male ontogeny and size-related variation in mass allocation of bluenose shiners (Pteronotropis welaka). Copeia 2:479-486.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).