A RESOURCE RANGE INVARIANCE RULE FOR OPTIMAL OFFSPRING SIZE PREDICTS PATTERNS OF VARIABILITY IN PARENTAL PHENOTYPES

Previous analysis of the rules regarding how much more a female should invest in a litter of size C rather than producing a litter with one more offspring revealed an invariance relationship between litter size and the range of resources per offspring in any litter size. The rule is that the range of resources per offspring should be inversely prop ortional to litter size. Here we present a modification of this rule t hat relates litter size to the total resources devoted to reproduction at that litter size. The result is that the range of resources devote d to reproduction should be the same for all litter sizes. When parent al phenotypes covary linearly with resources devoted to reproduction, then those traits should also show equal ranges within each litter siz e category (except for litters of one). We tested this prediction by e xamining the range in body size (= total length) of female mosquito fi sh (Gambusia hubbsi) at different litter sizes. Because resources devo ted to reproduction may take many forms (e.g., nest defense), this pre diction may have broad applicability.