Subtropical Florida is an important region for the production of freshwater aquarium fish, rearing hundreds of species and varieties. However, relatively few small-bodied aquarium fish have successfully established, which could be due to insufficient propagule pressure, biotic resistance due to native competitors and predators, and traits of the fishes and varieties in production. Through the process of domestication, popular aquarium species such as the green swordtail, Xiphophorus hellerii, have up to 100 varieties in trade, which has led to exaggerated traits such as enhanced coloration and elongate fins, trails that should have fitness consequences upon return to the wild. However, aquaculture production can also increase propagule pressure, which might counteract the fitness consequences of domestication. Our objectives were to 1) identify persistent feral populations of green swordtail in Florida, 2) compare feral phenotypes to those in trade, 3) examine the influence of biotic resistance, and 4) determine how propagule pressure interacts with domestication. A combination of field surveys, feeding trials, and pond experiments were used to address these objectives.
Results/Conclusions
Field surveys revealed persistent populations of green swordtail, dominated by a wild-type variety lacking the striking color patterns of most traded varieties. In control ponds, the number of fish captured at the conclusion of the experiment for each variety followed propagule size. However, biotic resistance increased with community complexity and affected survival and reproduction; a native poeciliid competitor and a native predatory fish were strong resistors. The wild-type variety, reflecting less advertent domestication, increased relative to other varieties despite low propagule pressure, as biotic resistance increased. At least for ornamental species, these results suggest propagule pressure is attenuated when moving across levels of biotic resistance due to advertent domestication. Future studies should focus on examining the degree to which feral phenotypes mirror wild phenotypes in the native range, providing insight into the reversibility of domestication selection.