Adaptation of an Invasive Cladoceran (Daphnia Lumholtzi) to Temperature
Daphnia lumholtzi, a cladoceran native to the Old World tropics, has successfully invaded lakes and rivers of North America. This invasive species has been successful, in part, due to similarities between native habitats and warm, eutrophic southern lakes and reservoirs, in which summer conditions are poorly tolerated by Daphnia species native to the US. However, D. lumholtzi has more recently invaded waterways in the northern US with thermal regimes very different from its native conditions. In order to determine the ability of this species to acclimate to different temperatures, I carried out life table experiments with animals isolated from lakes over a latitudinal (temperature) gradient across the US. Isofemale lineages were established from lakes in Texas, Oklahoma Georgia, Missouri, and Minnesota. Fitness measures included survival, fertility and intrinsic rate of increase. A comparison of clones from Lake Somerville (Texas) and Lake Pepin (Minnesota) at 20 and 30°;C showed that, despite strong effects of temperature, no significant difference was detected for the main effect of population for any fitness measure. These results suggest that D. lumholtzi can acclimate to cooler conditions without microevolutionary adaptation to temperature.
Daphnia lumholtzi, intrinsic rate of increase, invasive species, thermal gradient, temperature acclimation, Biology
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