Reproductive behaviour of Libellago semiopaca on a Bornean rainforest stream (Odonata: Chlorocyphidae)


The reproductive behaviour of Libellago semiopaca was studied on a swift-flowing shallow forest stream in Brunei. Females oviposited just below the water-line, commonly in groups, only on large, firm-textured, semi-submerged logs, usually guarded by males. Both sexes were very sedentary. Suitable sites, with good illumination and deep deposits of fine gravel and leaf mulch in dead water immediately behind the log were scarce. When stream levels were high, no oviposition sites were available. When possible, females generally oviposited every day, arriving between 10:00 and 15:00 h, and usually remaining on site for at least two hours. Males arrived earlier, between 09:00 and 13:00 h, and established small territories along the log. Females apparently began reproductive activity only when all oocytes were mature, and the egg load diminished daily as eggs were laid. Most matings occurred before 12:00 h with early-arriving females. Females mated every 2-3 days, probably to replenish sperm supplies. Male density was at its highest after 11:00 h and males shared territories, spending much of their time flying in low intensity confronting contests. Removal of males from a site, just as it was becoming available by falling water levels, resulted in little use of the site by females. Pinning decoy dead females at a good oviposition site failed to attract females if males had been removed. It is suggested that the prolonged male agonistic display attracts females to the site, and possibly commits them to future matings with the territory holders.

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