Devadatta argyoides

Competition to find a mate and reproduce the next generation is always very intense in the animal kingdom. Sometimes even a successful mating might not necessary guarantee the offsprings are sired by the original male.

Males of dragonflies and damselflies are especially adapted to displace the sperm of the previous male from a female. The discovery of sperm displacement in odonates by Prof. Jonathan Waage in 1979 is considered a significant finding in odonatology. Since then, it is now known there are four distinct ways a male can displace a rival male’s sperm: 1) physical removal by means of hooks or horns on the penis; 2) moving rivals’ sperm to sites in the females where its least likely to be used; 3) stimulation of female to induce sperm expulsion; 4) flushing out of rival’s sperm using the copulating male’s sperm.

These are fascinating behaviours. An earlier post mentioned this casually. Recently, I observed the copulation of Devadatta argyoides, enabling me a better understanding of sperm displacement.

Devadatta argyoides is from the family Amphipterygidae. This is a small and primitive family with only one species present in Peninsular Malaysia and Singapore. In fact Singapore is the type locality for this damselfly. It is rather common and usually found perching near small forest streams.

This couple had just gotten into tandem when I first spotted them. The male then flew with the female in tow for a short distance before perching above the stream. Slowly the female bent her abdomen to form the 'wheel’ thus interlocking their genitalia. Almost immediately, the male started displacing rivals’ sperm. This can be seen clearly by the male abdomen’s active movement. It lasted for about 2-3 minutes before the male stopped moving to transfer in his own sperm.

After copulation, the couple separated with the female flying off a distance away. The male did not seem interested in mate guarding nor did the female oviposit after I followed her for almost 10 minutes. I’m not familiar with the mating system of D. argyoides. Perhaps during this post-copulatory rest, the female was assessing the male’s guarding capacity, or the suitability of ovipositing site, or she’s manipulating the recently received sperm for fertilisation and evaluating its quality. The mating systems in odonates are varied with six systems currently recognised by scientists. There are lots more to discover on odonates mating behaviour especially species rarely encountered due to their elusive nature.

Pictures and video taken at: Bukit Timah Nature Reserve, October & November 2008



References:

Corbet, P. S. & S. J. Brooks, 2008. Dragonflies, HarperCollins Publishers, London, UK.

Lieftinck, M. A., 1954. ‘Handlist of Malaysian Odonata’, Treubia, vol 22, pp. 1-202.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Vestalis amoena; Vestalis amethystina

Vestalis amoena

Among Singapore’s damselflies, species from the genus Vestalis probably have the most attractive wings. Depending on the viewing angle and reflecting sunlight, the clear wings of these damselflies can appear to sparkle with purplish iridescence. We have two species in Singapore, Vestalis amoena and Vestalis amethystina. Both species look very much alike with the same metallic green colouration. In fact, the nine species known to exist in Sundaland are so similar in appearance that even differences in wings venation, body colouration and male penis structure are too ambiguous for species recognition. The only sure way to distinguish the species is by examining the male’s anal appendages.

Vestalis amethystina

Although it seems difficult but with a good digital camera giving a close-up shot of the male’s anal appendages, it is actually rather easy to identify our two Vestalis species in the field without having to capture them. For Vestalis amoena, the appendages are less curved towards each other and appear shaped like a horseshoe.

On the other hand, Vestalis amethystina has their appendages more curved towards each other. Females can be separated by the yellow labium of V. amoena and black labium of V. amethystina.

The geographical distribution of these two species is interesting. Both of them occur together from southern Thailand, Malay Peninsula to Sumatra. But V. amoena extends into Borneo while V. amethystina does not. In Borneo a close relative V. amaryllis, not found in the Malay Peninsula or Sumatra, exists. So it seems V. amaryllis became isolated in Borneo, differentiate into an independent species and occupies an ecological niche before V. amethystina could establish itself.

In Singapore, both V. amoena and V. amethystina occupy similar habitat: flowing streams in dense forest vegetation. However V. amoena is reportedly less common than V. amethystina. This seems to be very true as I encounter V. amoena less often during regular trips into the nature reserves. One very possible reason is that V. amoena prefers larger and faster flowing streams.
As forests degradation occurs, silt and sediments become accumulated causing streams to flow slower thus making it a more suitable habitat for V. amethystina. Historical records show that V. amoena was once found in Ulu Pandan. This is a perfect case in point of how much forests we have lost and how vulnerable forest damselflies are.



Pictures taken at: Central Catchment Nature Reserve, June 2008.



References:

Laidlaw, F. F., 1931. ‘A list of the dragonflies (Odonata) of the Malay Peninsula with descriptions of new species’, Journal of the Federated Malay States Museums, Singapore, vol 16, pp. 175-233.

Lieftinck, M A., 1965. ‘The species-group of Vestalis amoena Selys, 1853, in Sundaland (Odonata, Calopterygidae)’, Tijdschrift voor Entomologie, vol 108, pp. 325-364.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia