Unraveling the mechanisms driving transitions to parthenogenesis in a ladybug
Résumé
Parthenogenesis in animals is a reproductive mode enabling females to produce offspring without fertilization. While the evolutionary advantages and limitations behind the transition from sexual reproduction to parthenogenesis are well understood, the specific mechanisms by which transitions occur in each case remain unclear. Hybridization, infection by a parthenogenesis-inducing bacterial endosymbiont, and odd-numbered polyploidization are often associated with transitions to parthenogenesis in arthropods. With these parthenogenesis-associated characteristics in mind, we investigated the origin of the first case of parthenogenesis in a ladybug by generating a long-read genome assembly of Nephus voeltzkowi individuals from one of several recently discovered parthenogenetic populations to uncover any indications of the presence of these features. We found a rare combination of parthenogenesis-associated characteristics as parthenogenetic individuals appear to be of hybrid origin, infected with Wolbachia bacteria, and possess triploid genomes, whereas the sexual populations are diploid and lack these features. We performed a Wolbachia elimination experiment to determine the role that the infection plays in the reproduction of the parthenogenetic N. voeltzkowi. The experiment demonstrated that the elimination of Wolbachia resulted in a reduction in egg hatching rate, followed by a drastic reduction in egg production among treated females. This suggests that infection by these bacteria is necessary for successful reproduction in the parthenogenetic females, and Wolbachia may even play a two-part role by facilitating egg laying and early embryo development. Understanding how different features underlie transitions to parthenogenesis and how they relate to each other will provide new insights into the diversity and evolutionary consequences of alternative reproductive modes in animals.
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