Aj. Danylchuk et Wm. Tonn, Effects of social structure on reproductive activity in male fathead minnows (Pimephales promelas), BEH ECOLOGY, 12(4), 2001, pp. 482-489
The selection of alternative reproductive phenotypes is often thought to be
the result of physiological state, with small individuals forced energetic
ally to postpone the allocation of resources to reproduction. However, for
male fathead minnows (Pimephales promelas), we show that seasonal reproduct
ive activity is modulated by social status. In enclosure and pond experimen
ts, small males advanced their reproductive condition, held nesting territo
ries, and spawned earlier in the reproductive season only when lat ge males
were absent or removed from the population. Since differences in the timin
g of reproduction among small males were not size- or condition-dependent,
the common explanation for the selection of alternative reproductive phenot
ypes, based on state-dependence, is insufficient. In the absence of large,
socially dominant individuals, small males produced comparable numbers of o
ffspring as the treatment with large males, although the offspring of these
uninhibited small males were smaller at the end of the growing season than
the young of large males. Thus, interactions among conspecifics may accoun
t for much of the phenotypic diversity observed within and among natural fa
thead minnow populations, through their direct and indirect effects our gro
wth, recruitment and survival.