TP16 Multiple Stressors in Amphibian Ecotoxicology
Tuesday, 15 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(MCM-1118-076641) Spleen cellularity in spadefoot toads collected from cropland and rangeland playas.

Dupler, K¹, Gutierrez, M¹, Smith, L¹, McMurry, S¹, ¹ Texas Tech University, Lubbock, Texas, USA

ABSTRACT- We conducted a study in 2004 to determine if spleen cellularity in spadefoot toads differed between playa wetlands in cropland or rangeland watersheds. Playas in cropland watersheds are characterized by increased sediment loads and reduced hydroperiods compared to rangeland playas. A shorter hydroperiod can alter normal development of amphibians, resulting in faster time to metamorphosis and reduced body size in newly morphed individuals. Amphibians reorganize many aspects of their immune system during metamorphosis, and it has been proposed that alterations in normal development rate during metamorphosis could alter the normal process of reorganizing immunological parameters. Our study was designed to examine one aspect of the immunological changes that occur during metamorphosis; apotosis of splenic lymphocytes. Two species of toads (Spea multiplicata and S. bombifrons) were collected at three stages of development from playa wetlands in cropland (n=4) and rangeland (n=5) watersheds. We measured total weight, SVL, spleen weight, total splenic leukocytes, and total splenic lymphocytes. Species identification was confirmed using electrophoretic markers. In general, body weight and SVL were reduced in toads collected from cropland playas compared to rangeland playas. These differences were most pronounced in S. multiplicata compared to S. bombifrons. Likewise, tadpoles showed the largest differences in body size between playa types, with an overall convergence of weight and length with later development. Spleen weight was reduced in S. multiplicata in cropland playas at all development stages. However, difference in spleen weight in S. bombifrons was generally restricted to the tadpole group. Lymphocytes constituted the bulk of the spleen cell population (ca. 90%). Total number of cells in the spleen was generally lower in toads captured from cropland playas, and followed the same pattern as observed for spleen weight. Overall, results indicate that toads collected from cropland playas are smaller, with smaller spleens and fewer splenocytes.

Key words: amphibians, immunity, agriculture, sedimentation