- University of Illinois
- University of Toronto
Summary
Male bluegill (Lepomis macrochirus) display a complex reproductive behavior involving two alternative life history pathways: delay of sexual maturation to become “parentals” or precocious maturation as “cuckolders.” The purpose of our study was to investigate the association of two androgens, 11-ketotestosterone (11KT) and testosterone (T), with reproduction in these two types of males. Radioimmunoassay techniques were used to measure daily levels of the two androgens in the blood serum of parental male bluegill captured during the prespawning, spawning, and nesting periods throughout the reproductive season. Dramatic changes in the levels of 11KT and T were observed among parental males during these periods. Peaks occurred at the onset of spawning activity during each breeding bout. Compared to spawning parental males, spawning cuckolder males had significantly lower serum levels of 11KT. In contrast, the serum levels of T among parental and cuckolder males were not significantly different. These findings suggest that the elevated levels of 11KT are associated with the behaviors displayed by spawning parental males. The levels of T, however, seem to be associated with the occurrence of a phenomenon common to both parental and cuckolder males, such as development of gonads and/or spermiation.
Methodology
All fish were collected from Lake Opinicon (44°34’N,76°19’W), Ontario. Because the Lake Opinicon bluegill population is under intensive study, individual males within a breeding colony can be sampled during each component of the reproductive cycle. Individual fish were captured without disturbing the colony by swimmers using hand nets. Three sets of collections were made. In 1986, parental males were collected from each of the five colonies that formed sequentially at the same breeding site through the entire reproductive season (June-July). In June 1987, both parental and cuckolder males were sampled over a 2-day period from within several colonies in the lake during spawning. Cuckolder males were individually assigned to either the sneaker or satellite category based on the spawning behavior observed by divers during collection. Finally, in 1986, about 200 live adult male and female bluegill were transported to Illinois Natural History Survey (INHS) experimental ponds in Champaign, Illinois. These adults successfully bred during the 1987 reproductive season and were sampled in May 1988, prior to and during the first breeding bout.