To Thine Own Self be True? An Addendum to Feldgarden and Yund's Report on Fusion and the Evolution of Allorecognition in Colonial Marine Invertebrates.

Feldgarden and Yund (1) recently re-examined a question central to understanding the evolution of allorecognition systems in colonial and clonal marine invertebrates: “How does the genetic polymorphism necessary to restrict intergenotypic fusion to kin and clonemates accumulate in natural populations?” They argue that explanations invoking kin selection account fully for neither the extensive allelic polymorphism that characterizes the genetic systems that control allorecognition specificity, nor the apparent phenotypic instability of genetic chimeras. As a more parsimonious explanation than kin selection for these observations, they propose that frequency-dependent selection, acting at the level of the individual, promotes the accumulation of allotypic polymorphism by favoring fusion with self (and preventing fusion with nonself). To place this proposition into a conceptual framework, they cite two of my papers (2, 3) and assert that, “Several authors have noted that kin selection does not provide an obvious explanation for high allotype diversity.” As far as it goes, this is an accurate statement, at least with respect to intergenotypic fusion in populations lacking kin structure. In these papers, however, J. F. Quinn and I developed a series of analytical models showing how individual selection could easily maintain allotypic polymorphism through the control of intergenotypic fusion. So that there can be no misunderstanding about what we said, I quote a summary of our work on allotypic specificity and fusion from a paper published in 1988 (2, pp. 402-403; full references can be found in the original text):