We examined the relationship between pond duration and life history characters of the clam shrimp Eulimnadia texana, a species inhabiting ephemeral ponds in southwestern North America. Since the shrimp live in temporary habitats, we predicted that there should be high selection pressure on life history characteristics associated with rapid development (e.g., fast growth, early maturity, etc.), rather than selection for increased longevity. Pond duration was estimated using a combination of average monthly rainfall and pond size (surface to volume ratio). Shrimp that live in smaller ponds (high surface to volume ratio)in areas with low average rainfall should, on average, experience a shorter total time available for development than those in larger ponds or in 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 five ponds. These shrimp were raised in a common garden experiment in the laboratory. Daily measurements of growth and egg production were taken 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 lower average rainfall. If average rainfall is an accurate measure of pond duration, then the first three of these life history traits differ in the directions expected. However, age at maturity varied in a manner opposite to that expected, being earlier in the ponds with longer duration. Surface to volume ratio was not helpful in further resolving differences in these life history characters.
Conchostraca evolution of aging senescence branchiopod