Authors: Sagi, Liran; Bouskila, Amos ;

Isolation by time can lead to sympatric speciation based only on different reproduction times (allochrony). The few known examples of such separation operate due to a life cycle longer than a year in a semelparous organism (reproduces once in its lifetime). There were no examples of this phenomenon among terrestrial vertebrates. We found that Chamaeleo chamaeleon musae, a desert chameleon, has several characteristics that may lead to this separation. These chameleons reproduce a year after hatching and only 0.2% of the population survives to the second reproductive season. This forms two subpopulations: the first reproduces during even years and their eggs are incubated during odd years, while the second subpopulation uses opposite years. As a result, the two subpopulations rarely have the opportunity to mix. We found that survival varies depending on the subpopulation and on precipitation during incubation. This unique lifestyle can be a consequence of climatic changes and may become more common in the coming decades. This chameleon is the first terrestrial vertebrate that exhibits a potential allochronic lifestyle that can lead, or has already led, to genetic divergence between sympatric subpopulations. This is a rare opportunity to study this unique form of separation in progress.