New beginnings for dead ends: polyploidy, -SSE models, and the dead-end hypothesis.

Background: Since the mid-twentieth century, it has been argued by some that the transition from diploidy to polyploidy is an "evolutionary dead end" in plants. While this point has been debated ever since, multiple definitions of "dead end" have been used in the polyploidy literature without sufficient differentiation between alternative uses.

Scope: Here, we focus on the two most common conceptions of the dead-end hypothesis currently discussed: the "lowering diversification" hypothesis and the "rarely successful" hypothesis. We discuss the evidence for both hypotheses, and we employ a recently developed method of inferring tip diversification rates to demonstrate tests for the effect of ploidy on diversification in Solanaceae.

Conclusions: We find that diversification rates in the family are not strongly correlated with ploidy or with the closely related trait of breeding system. We also outline recent work in the field that moves beyond the relatively simple question of whether polyploidy increases, decreases, or does not significantly affect diversification rates in plants.