Facultative parthenogenesis in the Ryukyu drywood termite Neotermes koshunensis

Abstract

Parthenogenesis is a relatively rare reproductive mode in nature compared to sex. In social insects, the evolution of parthenogenesis has a notable impact on their life histories. Some termites with parthenogenetic ability produce numerous non-dispersing supplementary queens asexually, whereas other castes are produced via sexual reproduction. This asexual queen succession (AQS) system is adaptive because hundreds of the asexual queens improve the reproductive potential of the colony and maintain the genetic diversity within the colony. However, the evolutionary process of the AQS system remains unclear because parthenogenetic species without this system are unknown. Here, we report facultative parthenogenesis in the drywood termite Neotermes koshunensis. Although the eggs produced by females isolated from males hatched, the hatching rate of those eggs was lower than that of the eggs produced by females kept with males. These parthenogenetic offspring inherited only the maternal alleles and showed high homozygosity, which indicates that the mechanism of ploidy restoration is terminal fusion. A previous study showed that most colonies of this species have a single queen or orphan; thus, the AQS system has not evolved despite their parthenogenetic ability. Further investigations of N. koshunensis will reveal how parthenogenesis evolved and its role in the insect societies.

Figure 1. The total number of eggs and larvae produced by female-male (FM) and female-female (FF) pairs at each the observation period.

Filled and open points represents mean of the data of FM and FF pairs, respectively. The shapes of the points correspond to the number of eggs (circle) and larvae (triangle). Each bar on the point indicates its standard error.

Figure 2

Rearing condition for the colony-founding experiments (a) and photographs of a typical result of the experiments (b–d). In these photographs, a female-female pair founded their colony through digging through the two chips of pine wood (b) and produced their eggs (indicated by the arrow) via parthenogenesis (c). We observed the larvae (indicated by arrows) in this experimental colony (d).