Reproductive and lipid patterns of four West Texas Anurans

The strategy employed by a species in partitioning stored energy among the requirements for growth, body maintenance, and reproduction has been examined in various ectothermic vertebrates. However, few studies have examined patterns of lipid use by semi-arid amphibians. In order to assess the lipid storage/mobilization strategy employed by amphibians that have moisture-restricted activity periods, the toads Bufo cognatus and Scaphiopus hammondi were collected throughout their activity season, and lipid content and reproductive status of individuals were determined. For comparative purposes, the same parameters were also examined for Acris crepitans and Bufo woodhousei, anuran species which are adapted to semiaquatic and mesic environments, respectively.

Females of all species showed a reduction of body lipid as ovarian development proceeded. Bufo cognatus showed no seasonal lipid variation after accounting for ovarian lipid requirements. In this species, liver lipidfree dry mass was reduced during winter dormancy suggesting a non-lipid component was used for metabolism. Scaphiopus hammondi utilized lipid for metabolism during dormancy and during pre-breeding activity. Liver nonlipid material served no significant metabolic importance. Acris crepitans showed significant variation in both body lipid and liver non-lipid seasonal group values, as has been identified for other semi-aquatic anurans. Male, but not female, B. woodhousei exhibited seasonal variation in lipid stores attributable to metabolism. Females, but not males, showed seasonal variation in quantified liver glycogen.

Ovulation of all ovarian follicles in a given year was only observed in A. crepitans. Females of the other species retained mature or almost mature follicles throughout the year. Retainment of mature follicles might be reproductively advantageous for these species by allowing breeding preparedness throughout the activity season. Bufo cognatus and §. hammondi typically reproduce in the spring when rain fills the ephemeral playas in which they breed. If sufficient rainfall occurred in late summer, they would be reproductively prepared for an additional opportunity to lay eggs. Testicular patterns were similar for all species; though synchronized with the time of annual breeding activity which varied among species.

It appears there is no one reproductive or lipid mobilization strategy common to all anurans. Instead, these physiologically controlled functions are modified to fit a particular species' life history.