Trait-mediated indirect interactions (TMIIs) are important mediators of community diversity and structure and associated ecosystem processes. Elucidating the genetic basis of ecologically important phenotypic traits is the first step toward understanding the complex interactions that occur among community members. Molecular markers routinely used in quantitative trait loci (QTL) analyses (e.g., amplified fragment length polymorphisms (AFLPs), simple sequence repeats (SSRs)) have provided researchers with a toolbox for investigating the genetic basis of heritable traits. A goal of this research is to link genetically based traits to community interactions and ecosystem function. Ultimately, this insight can open a window onto the evolutionary dynamics that shape community structure and associated ecosystem processes (e.g., nutrient cycling). Such an approach is important as it bears on the continued development of the field of community genetics, which seeks to understand the genetic interactions that occur between species and their abiotic environment in complex communities (e.g., Whitham et al. 2003, 2006; Johnson and Agrawal 2005; LeRoy et al. 2006; Bangert et al. 2006a, b; Schweitzer et al. 2008; Crutsinger et al. 2009; Bailey et al. 2009).
Three fundamental patterns of phenotypic expression exist for alternative mating strategies. These patterns include Mendelian strategies, developmental strategies, and behavioral strategies. Each pattern of expression is revealed by hormonal and neurological factors that regulate the timing and degree to which phenotypic differences appear; however, the nature of each regulatory mechanism depends fundamentally on its underlying mode of inheritance. The genetic architectures underlying such inheritance in turn depend on the circumstances in which mating opportunities arise, including the intensity of selection favoring distinct reproductive morphologies, and the predictability of mating opportunities within individual lifespans. This chapter concerns the nature of this variation and its possible causes, with illustrations from the Crustacea.
Although crustaceans were among the first recorded examples of alternative mating strategies (Orchestia darwinii: Darwin 1874, p. 275; Tanais spp.: Darwin 1874, p. 262), there is currently no synthetic treatment of how such polymorphisms are expressed within this group. The apparent scarcity of reports of male polymorphism among crustaceans is unexpected given the frequency with which sexual selection has been demonstrated within this taxon (Holdich 1968, 1971, Manning 1975, Stein 1976, Thompson and Manning 1981, Knowlton 1980, Shuster 1981, Christy 1983, Hatziolos and Caldwell 1983, reviews in Salmon 1984, Koga et al. 1993). As explained below, when sexual selection occurs, alternative mating strategies are likely to evolve. This chapter provides an evolutionary framework for understanding the expression of alternative mating strategies, with illustrations from the Crustacea (Table 9.1).
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