First evidence of yearly allochrony in a terrestrial vertebrate: A case study of an annual chameleon

Isolation through differences in reproductive timing, known as allochrony, is a unique life history trait that can lead to the separation of a population into two distinct populations. Yearly allochrony, where reproductive events are separated between years, is extremely rare and has been documented <10 times. It requires a single reproductive event at a fixed age and a life cycle of 2 years or more. Among terrestrial vertebrates, documented examples of yearly allochrony are nonexistent. Our study reveals that Chamaeleo chamaeleon musae possesses the potential for allochronic separation. These chameleons reproduce 1 year after hatching, with only 0.2% of the population surviving to a second reproductive season. Their eggs require 11 months to hatch. This combination of factors results in two distinct subpopulations: one that incubates eggs during even years while adults reproduce in odd years and another that follows the reverse pattern. This separation prevents intermixing between the two subpopulations. C. c. musae is currently the only known terrestrial vertebrate exhibiting yearly allochrony. Population and evolutionary ecologists must consider yearly allochrony when studying animal life cycles, given its significant implications for speciation, species conservation, and monitoring programs.