Origin of Polyploidy in Parthenogenetic Weevils

Parthenogenesis and, in particular, polyploidy are rare in animals. A number of cases are known among weevils. Previous models have assumed that parthenogenesis originated in a diploid lineage, involving first an automictic (meiotic) mechanism that then evolves into apomixis. New degrees of polyploidy are added through hybridization events with males of the same or related species. A model is advanced here that proposes that triploidy and parthenogenesis arise through a single event and the first stage is a diploid gamete that has arisen through defective meiosis that fuses with a haploid gamete. New degrees of polyploidy arise through disjunction events that involve one or several haploid chromosome sets. This model is in accord with the available evidence.