AsianScientist (Mar. 30, 2017) – Ancient damselfly ancestors trapped in amber have shed light on early insect courtship behavior. These findings have been published in Scientific Reports.
Courtship behaviours, common in modern insects, have left extremely few fossil traces. In dragonflies and damselflies (odonates), the male must persuade the female to mate in tandem. Many territorial odonatans initiate courtship by high-frequency wing-beats directed towards an approaching female. However, most courtship, mating and parenting (social-sexual) behavior cannot be captured by the fossil record and therefore remain poorly understood.
In the present study, Dr. Zheng Daran and Professor Wang Bo from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences describe the courtship behavior of three male damselflies trapped in mid-Cretaceous Burmese amber. The fossils were named Yijenplatycnemis huangi after Mr. Huang Yijen from Taiwan, for his generous donation of the type specimen.
Y. huangi has spectacular extremely expanded, pod-like legs, helping to fend off other suitors as well as attract mating females, increasing the chances of successful mating. The new findings provide suggestive evidence of damselfly courtship behaviour as far back as the dinosaur age.
Modern Platycnemididae (white-legged damselflies) and Chlorocyphidae (jewel damselflies) convergently acquired similar but less developed structures. During courtship, male Platycypha caligata wave the white anterior surface of all six of their laterally enlarged leg at the females, but use the posterior surface of their legs for intra-sexual signaling during territorial defense.
Similarly, male East Asian Platycnemis species with expanded, feather-like legs that are well differentiated from the females, exhibiting a strong sexual dimorphism. The males display their white legs in a fluttering flight in front of females before mating.
By morphological inference, the six extremely expanded legs of Y. huangi could also have a signaling function for courtship displays. Both Platycypha and Platycnemis have elaborate legs but Y. huangi legs are even larger. These more exaggerated legs suggest an extreme adaptation for courtship behaviour.
More importantly, unlike Platycypha and Platycnemis, the legs of Y. huangi are asymmetric and pod-shaped, particularly the hindleg which has a semi-circular outline. This pod-like shape would make waving slower due to air resistance.
The leg shape of Y. huangi also resembles the wings of some members of extinct net-winged insects. The legs of Y. huangi are translucent and partly covered with two narrow brown bands, making them resemble pigmented wings. In addition, there is an eye-shaped spot in the middle of the hindleg, similar to the wing spots of a species of extinct lacewings. These well-developed eyespots are typically used to make a conspicuous and contrasting display to intimidate vertebrate predators or protect the body by deflecting an attack to the wings.
Deflective eyespots in butterflies and fossil lacewings are smaller than the ones used for threat behavior and are never on found on the legs, but dragonflies are predators with good eyesight, and the tiny ones on Y. huangi may have less to do with deflecting nearby predators. Instead, the authors suggest that Y. huangi eyespots may have more to do with attracting females. That none of the pigmented legs in Y. huangi are damaged further suggests they were not used as part of an aggressive response.
The article can be found at: Zheng et al. (2017) Extreme Adaptations for Probable Visual Courtship Behavior in a Cretaceous Dancing Damselfly.
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Source: Chinese Academy of Sciences; Photo: Yang Dinghua.
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