Empirical evidence for the continuity of semelparity and iteroparity

Abstract Semelparity—the life history featuring a single, massive bout of reproduction followed by death—has been traditionally considered as a discrete trait, and mathematical models that compare the intrinsic rates of increase between annual semelparity and perennial iteroparity are often used to explain why organisms have semelparous or iteroparous reproductive strategies. However, some authors have proposed that semelparity and iteroparity may represent different extremes along a continuum of possible modes of parity, rather than discrete alternatives. In this thesis, I provide experimental evidence for this “continuum” hypothesis by assessing the degree of variation in the simultaneity and uniformity of semelparous reproduction in the herbaceous monocarp Lobelia inflata (Campanulaceae). I report four points of interest: (1) that reproductive characters can strategically vary among offspring within a semelparous reproductive episode; (2) that phenotypically plastic responses to constrained reproduction cause variation in the “semelparousness” of a semelparous reproductive episode; (3) that L. inflata is capable of deferring reproductive effort to another season, and that this deferral is also phenotypically plastic; and (4) that the degree of genetic variation in a field population of L. inflata suggests non-random survival of ecotypes related to differences in parity. I conclude that the continuum hypothesis more accurately characterizes life history variation among semelparous organisms.