Effects of photoperiod length on Sungaya inexpectata (Phasmida: Heteropterygidae) reproduction and detection of potential reproductive manipulators in S. inexpectata and diverse phasmids

Abstract

Phasmida peculiarities aroused increasing interests last years. However, some aspects of their biology such as parameters influencing their reproduction mode (e.g. photoperiod, food availability or symbiosis) remain largely understudied. Within other insects such as aphids, photoperiod is known to impact reproductive events, their success rate but also their reproduction mode like the complete switch from asexuality to sexuality. Otherwise, symbionts-hosts associations allow a species to colonize new ecological niches or prevent pathogenic infection or even host’s reproduction mode. Some symbionts are indeed able to direct host’s reproduction for enhancing their own transmission by inducing phenotypes that increases daughter investment. These reproductive manipulators are intensively studied, with Wolbachia in the first line. Phasmids like Sungaya inexpectata could be alternatively sexual and parthenogenetic and are suited to study the potential effect of photoperiod and symbiont presence on reproduction. We exposed late S. inexpectata nymphs to short/long photoperiods and assigned them to parthenogenetic or sexual reproduction condition when adults. We recorded several reproductive parameters: pre-copulation time, copulation length, time at first oviposition, eggs number and mass for each focal female. A shorter pre-copulation time and time at first oviposition of sexual compared to parthenogenetic females were observed under the long photoperiod. Uni- and multivariate analysis further tended to show that sexual laid more eggs of a larger mass than their parthenogenetic relatives under long photoperiod. We then tested the presence of four symbionts (Wolbachia, Spiroplamsa, Rickettsia and Cardinium) on S. inexpectata subjects and ten other species by diagnostic Polymerase Chain Reaction. We only found Spiroplasma in S. inexpectata and four other species without reproductive or photoperiodic association. This suggests that photoperiod could influence the rate of reproductive events and the fitness of reproductive modes while symbiont-regulated reproduction is partially avoided even if further study on Spiroplasma-Phasmid association would be interesting.