The Role of Phenotypic Plasticity in Marine Biological Invasions

The outcome of a species introduction depends, in large measure, on the abilities of the invader and species in the receiving community to respond to their new environments. A successful invader must survive changing environmental conditions at all stages leading to and following its introduction. Residents in the invaded community, in turn, must cope with environmental changes that result from the arrival of the new species. Adaptive responses (i.e., those that confer a fitness benefit) by either party have been viewed primarily to result from evolutionary changes in fixed traits in populations (Thompson 1998; Mooney and Cleland 2001; Cox 2004). Although intense selection can result in rapid phenotypic shifts across generations (Huey et al. 2000; Gilchrist et al. 2001; Reznick and Ghalambor 2001), this process does not encompass fully the dynamic nature of many invasions. A burgeoning literature indicates that individual organisms are capable of modifying ecologically important physiological, morphological, behavioral, and life-history features within a lifetime in response to environmental cues (Harvell 1986; Stearns 1989; Kingsolver and Huey 1998; Schlichting and Pigliucci 1998; West-Eberhard 2003; DeWitt and Scheiner 2004a). This phenomenon, known as phenotypic plasticity, provides a means by which an invader can respond relatively quickly to its new biotic or abiotic environment. Similarly, phenotypic plasticity may allow resident species to mitigate changes wrought by the invader. The role of adaptive phenotypic plasticity in biological invasions, however, has been largely ignored in marine settings.

Our understanding and interpretation of marine biological invasions will be incomplete on several counts if we fail to acknowledge or test for the potential influence of phenotypic plasticity. First, phenotypic plasticity can provide a mechanistic explanation to understand and predict (1) why and how some individuals or species invade and others do not, (2) what the ecological effects and eventual ranges of the invader might be, and (3) how native species might respond to the introduction. In particular, knowledge of the type, direction, and magnitude of induced responses is critical if we are to decipher direct and indirect ecological effects stemming from species introductions. Second, recognition of phenotypic plasticity's influence should aid in our interpretation of spatial patterns or temporal changes that develop following marine introductions. In particular, changes in characteristics of populations following an invasion cannot necessarily be assumed to reflect selection (rapid or otherwise). Rather, studies need to test for environmental and genetic influences and their interactive contribution to phenotype across ecologically relevant environments. Such studies will give a better indication of factors driving short- and long-term evolutionary responses to marine invasions.