Advertent domestication attenuates the influence of propagule pressure

Abstract

The process of domestication affects fitness following return to the wild. For the invasion of non-native species, however, captive rearing is thought to increase propagule pressure, the quantity and rate that individuals are introduced. Invasion success for domesticated species may represent a balance between survival and propagule pressure. Survival is likely affected by selective breeding (advertent versus inadvertent selection) and predator populations, which contribute to biotic resistance, the ability of communities to resist invasion. Ornamental species are subjected to deliberate selection (advertent) for phenotypic traits such as coloration, as is the case with the green swordtail (Xiphophorus hellerii). Wild-type varieties are also produced without deliberate selection (inadvertent) and resemble their wild counterparts. In Florida, swordtails are produced in aquaculture and propagule pressure is high, yet few colorful individuals are encountered in the wild. Here we examined how invasion success is influenced by the interactive effects of biotic resistance, selective breeding, and propagule pressure. We used outdoor ponds to examine intraspecific variation in invasion success for five swordtail varieties across increasing biotic resistance. Propagule pressure over 14 weeks was varied proportional to trade volume for the five varieties. Biotic resistance increased with community complexity and affected swordtail survival and reproduction. In control ponds the number of fish for each variety followed propagule size. Despite lower propagule pressure, the wild-type variety increased relative to the advertently produced varieties, but only in ponds with greater biotic resistance. These results suggest propagule pressure is attenuated by increased biotic resistance and deliberate breeding.