Effects of in vitro metamorphosis on survival, growth, and reproductive success of freshwater mussels
Captive breeding is an effective conservation strategy, but it has risks, especially when a life history stage of an organism is bypassed. Freshwater mussels (Unionida) are critically imperiled, and their larvae are parasites on fishes. Traditional mussel captive breeding involves artificially infesting fishes with larvae (in vivo), but increasingly used in vitro methods allow larval metamorphosis in culture media, bypassing the parasitic stage. We provide the first comparisons of mussel performance between in vitro and in vivo methods in the wild and throughout the mussel life cycle using two mussel species. In six streams, survival and growth did not differ between in vitro- and in vivo-produced Lampsilis cardium. Metamorphosis of Sinanodonta woodiana differed sharply between two in vitro protocols (methods 1 and 2), but metamorphosis for method 2 was twice as high as in vivo. Survival and growth after eight days was lower for in vitro method 1 than method 2 and in vivo, showing that suboptimal in vitro protocols can have lingering effects on juvenile performance. However, survival and growth did not differ among methods by the end of the first and second growing seasons. Most importantly, in vitro-produced mussels survived, grew to maturity, and produced F2 juveniles naturally on fishes, all at rates that did not differ from in vivo-produced mussels. We detected no strong side effects of bypassing the mussel host-fish stage, but this study illustrates the importance of assessing consequences of captive breeding methods for any organism in a variety of environmental and life history contexts.