Semilunar follicular cycle of an intertidal fish: the Fundulus model.
In their habitat, Fundulus heteroclitus (Cyprinodontidae) spawn against a variety of specific substrates that become available only at spring tides; they thus exhibit a semilunar reproductive cyclicity. In the laboratory at 28 +/- 0.6 degrees C and 14L:10D, this cyclicity is free-running and can be observed by means of daily egg collection and frequent ovarian sampling. Daily egg collection cycles gathered from three different spawning groups were pooled chronologically; the cycles were determined by nonlinear regression sine-curve matching and so were dated from Days -6 to +6, with Day 0 as the peak egg collection day. Ovaries were sampled on Days -6, -4, -2, -1, +1, +2, and +4. The pooled data indicated that early-maturing follicles (1.3- to 1.6-mm diameter) are recruited from a constant reserve of vitellogenic follicles (0.7- to 1.2-mm diameter) and become abundant early in the cycle but are depleted during Days -6 to +4 by the formation of late-maturing follicles and ovulated eggs. A midcycle peak of ovulated eggs in the ovary corresponds to the egg collection peak. This progression of follicles followed by spawning decreases the total count of the follicles (> or = 0.7-mm diameter) and eggs in the ovary by 52% (from 454 to 219 per 10 g of female weight). The semilunar follicular cycle in this Fundulus model thus includes 1) an early-cycle follicle recruitment, 2) an early- and midcycle follicle maturation, and 3) a midcycle egg ovulation and spawning. This follicular cycle also proceeds in fish deprived of a spawning substrate. A female in the wild would thus execute the follicular cycling in a timely sequence, in anticipation of each recurring spring tide, whether or not a natural substrate becomes available. We conclude that F. heteroclitus provides a useful nonmammalian model for the study of cyclic reproductive activity in the laboratory.
Hsiao
S M
SM
Whitney Laboratory, University of Florida, St. Augustine 32086, USA.
Limesand
S W
SW
Wallace
R A
RA
D000818:Animals; D003530:Cyprinidae / Q000502:physiology*; D005260:Female; D008297:Male; D016081:Moon; D006080:Ovarian Follicle / Q000254:growth & development*; D010060:Ovulation / Q000502:physiology; D010507:Periodicity; D012726:Sexual Behavior, Animal / Q000502:physiology; D014817:Vitelline Membrane / Q000502:physiology