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| Burmogerris rarus Fu, Cai, Chen, Xuan, Myint & Huang, 2024 |
Abstract
Fossilized mating insects are irreplaceable material for comprehending the evolution of the mating behaviours and life-history traits in the deep-time record of insects as well as the potential sexual conflict. However, cases of mating pairs are particularly rare in fossil insects, especially aquatic or semi-aquatic species. Here, we report the first fossil record of a group of water striders in copulation (including three pairs and a single adult male) based on fossils from the mid-Cretaceous of northern Myanmar. The new taxon, Burmogerris gen. nov., likely represents one of the oldest cases of insects related to the marine environment, such as billabongs formed by the tides. It exhibits conspicuous dimorphism associated with sexual conflict: the male is equipped with a specialized protibial comb as a grasping apparatus, likely representing an adaptation to overcome female resistance during struggles. The paired Burmogerris show smaller males riding on the backs of the females, seemingly recording a scene of copulatory struggles between the sexes. Our discovery reveals a mating system dominated by males and sheds light on the potential sexual conflicts of Burmogerris in the Cretaceous. It indicates the mating behaviour remained stable over long-term geological time in these water-walking insects.
Keywords: mating behaviour, group mating fossil, sexual conflict, Myanmar amber, palaeoecology
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| The paired water striders Burmogerris rarus gen. et sp. nov., from mid-Cretaceous Burmese amber, under bright-field microscopy. (a) An overall view of the amber piece; red and blue arrows indicate adult males and females, respectively; the middle pair consists of the holotype (NIGP201886, male) and the allotype (NIGP201887, female). (b) Paratypes, NIGP201888 and NIGP201889. (c) Paratypes, NIGP201890 and NIGP201891. Scale bars: 5 mm in (a), 1 mm in (b,c). |
Systematic palaeontology
Infraorder Gerromorpha Popov, 1971
Superfamily Gerroidea Leach, 1815
Family incertae sedis
Burmogerris Fu, Cai, Chen & Huang, gen. nov.
Etymology: The generic name is a combination of the prefix ‘Burma-’ referring to Myanmar, and Gerris, the type genus of the family Gerridae. Gender masculine.
Diagnosis: The genus is characterized by a combination of the following characters: macropterous; head without median impressed line on the dorsal surface (a typical median line on the dorsal surface of head in veliids); antennal segment II elongate, slightly shorter than segment I and more than twice as long as two apical segments, segment IV widened, less spindle-shaped. All tarsi three-segmented (two-segmented in all gerrids), first tarsomere extremely short, subcylindrical; forelegs prolonged, almost as long as body length; male protibia bearing numerous discontinuous clusters of pegs (absent in male gerrids); protarsus more than one-half length of the protibia, with second tarsomere about 1.20 times as long as the apical tarsomere; mesotibia bearing a row of long and slender trichobothria-like hairs; mesofemur as long as or slightly longer than the mesotibia; mesotibia almost as long as the mesotarsus; metatarsus with the second tarsomere much longer than the apical tarsomere; claws inserted on the apex of apical tarsomere; arolia absent.
Burmogerris rarus Fu, Cai, Chen & Huang, sp. nov.
Etymology: The specific epithet ‘rarus’ (Latin, adjective, meaning rare) refers to some odd morphological characters and its rare existence.
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| Ecological reconstruction of Burmogerris rarus gen. et sp. nov. in the Burmese amber forests during the mid-Cretaceous. reconstructive illustration by Jie Sun. |
Yanzhe Fu, Chenyang Cai, Pingping Chen, Qiang Xuan, Tin Aung Myint and Diying Huang. 2024. Group Mating in Cretaceous Water Striders. Proc. R. Soc. B. 291: 20232546. DOI: 10.1098/rspb.2023.2546
