THE EFFECTS OF POND DURATION ON THE LIFE-HISTORY TRAITS OF AN EPHEMERAL POND CRUSTACEAN, EULIMNADIA-TEXANA

We examined the relationship between pond duration and life history ch aracters of the clam shrimp Eulimnadia texana, a species inhabiting ep hemeral ponds in southwestern North America. Since the shrimp live in temporary habitats, we predicted that there should be high selection p ressure on life history characteristics associated with rapid developm ent (e.g., fast growth, early maturity, etc.), rather than selection f or increased longevity. Pond duration was estimated using a combinatio n of average monthly rainfall and pond size (surface to volume ratio). Shrimp that live in smaller ponds thigh surface to volume ratio) in a reas with low average rainfall should, on average, experience a shorte r total time available for development than those in larger ponds or i n areas of higher rainfall. These shrimp should have an earlier age at maturity, reduced longevity, lower fecundity, and faster growth. Five replicate populations of clam shrimp were collected as cysts from fiv e ponds. These shrimp were raised in a common garden experiment in the laboratory. Daily measurements of growth and egg production were take n and ages at maturity and death were recorded. Shrimp from areas with higher average rainfall had slower growth, higher fecundity, greater longevity, and an earlier age at maturity than those from areas with l ower average rainfall. If average rainfall is an accurate measure of p ond duration, then the first three of these life history traits differ in the directions expected. However, age at maturity varied in a mann er opposite to that expected, being earlier in the ponds with longer d uration. Surface to volume ratio was not helpful in further resolving differences in these life history characters.