The Distribution and Reproduction of the Plains Spadefoot Toad, "Scaphiopus Bombifrons", in Iowa
McMullen, Catherine J. Mabry
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The problem. The northeastern extreme of the range of "Scaphiopus bombifrons" occurs in Iowa. This study was designed to determine whether the species should continue to be classified as threatened with extinction in Iowa. At the onset of this study, the species had been found only in a few localities in the loess hills. The study attempted to determine whether or not the species occurred beyond the dry loess soil and adjacent flood plain. Little has been published concerning the reproduction of the plains spadefoot toad. This study attempted to determine time of breeding, number of eggs produced, and the possible relationship among fat, breeding, and above-ground activity. Procedure. The range was determined by searching for specimens throughout the loess hills on roads during rain or on warm, humid nights. Body length, testes, ovaries and fat bodies were measured to determine size at sexual maturity, cycle of activity and breeding, and gonadal and fat body cycles. Findings. "S. bombifrons" was found to occur throughout the loess hills, and no longer merits threatened status. It was not found beyond the deep loess soil. Adult females were more abundant than males, were larger, and attained maturity at a more consistent size. Most individuals were not active below 60°F air temperature, and breeding probably occurred once in a season, usually in June. Mature females produce an average of about 2600 egqs each year. As many as two years were needed for juveniles to attain sexual maturity. Gonads were largest in June, although reproductive capability could apparently be attained through much of spring and summer. Aestivation and hibernation appeared to consume more fat than did the production of gametes. Conclusions. "S. bombifrons" is a moderately abundant, possibly recent invader of the loess hills. It appears limited to loess habitats. The species produces a large number of egqs in Iowa, which may help to account for the abundance it seems to have achieved over a period of less than 40 years. Recommendations. A study of a marked, breeding population should be conducted. It will answer questions concerning life span of individuals, survival over winter, number of breedinq periods per year, growth, and could enable estimation of local populations.
49 leaves. Advisor: James L. Christiansen