The simulations assessed how variation in three key genetic parameters affects patterns of allotypic similarity and compatibility frequencies among (1) full sibships; (2) half sibships; and (3) randomly drawn pairs using a simple additive model.
Next, we used this information to identify threshold proportions of allotypic similarity (i.e., number of allorecognition alleles actually shared/number of alleles potentially shared) for different combinations of L and n that yielded frequencies of fusion, transitory fusion, and rejection that most closely matched our empirical estimates.
Consequently, the overall [TABULAR DATA FOR TABLE 4 OMITTED] allotypic similarity among siblings across loci will also decrease, as reflected in the downward "migration" of a given coded section as n increases.
High levels of allotypic specificity could, however, result from any number of genetic alternatives, ranging from one or a few loci with tens to hundreds of alleles per locus (characteristic of populations of botryllid ascidians: Milkman 1967; Mukai and Watanabe 1975a,b; Scofield et al.
The ability to distinguish among these genetic alternatives, and to circumscribe the rules governing compatibility, determines how the expression of allorecognition-dependent behaviors influences the evolution of allotypic variation.
Our data show that, as in botryllid ascidians, allotypic identity is not a prerequisite for compatibility in H.
This study also generally confirms prior studies of the inheritance of allotypic specificity in Hydractinia, in showing that the likelihood of tissue fusion declines according to the relatedness of interacting pairs (e.g., Teissier 1929; Crowell 1950; Hauenschild 1954, 1956; Muller 1964; Ivker 1972; Mokady and Buss 1996).
symbiolongicarpus, several lines of evidence argue that along the continuum of genetic models that could confer allotypic specificity, relatively few loci with a moderate number of alleles govern allotypic specificity in this species.
simulations), an outcome consistent with the existence of distinguishable allotypic groupings within sibships.
If five loci carrying six equal frequent alleles per locus governed allotypic specificity in H.
Such high levels of allotypic diversity could, at least in part, represent a balance between the generation of new allotypic variants by mutation and their loss via drift (Neigel 1988; Brown and Eklund 1994).
In the case of cnidarians such as Hydractinia, in which allorecognition systems determine whether individuals will fuse or fight, frequency-dependent selection acting at the level of the individual can favor the accumulation of allotypic variation when the fitness costs of intergenotypic fusion exceed the benefits of aggression (Grosberg and Quinn 1988).