Jurassic scorpionflies (Mecoptera) with swollen first metatarsal segments suggesting sexual dimorphism

Evolving longer for a mate: A new scorpionfly (Mecoptera: Panorpoidea: Panorpidae) with exaggeratedly elongated male abdominal segments

Male scorpionflies often evolve exaggeratedly elongated abdominal segments (EEAS) that are used as a sexual display to the females, and a combat weapon in intra-sexual disputes. EEAS have independently evolved several times since the Jurassic till the present day in at least eight genera and four families. In this paper, Neopanorpa exaggerata sp. n. with EEAS is described from Yunnan Province, China. Through comparisons among extinct and extant species, our current knowledge is summarized for the evolution, copulatory mechanism, and biogeography of the scorpionflies with EEAS. Also discussed are the trade-offs between the benefits of "looking sexy" and the negative impacts associated with a long abdomen. Additionally, further clarification is provided on the multiple origins of EEAS in Panorpoidea.

Evolution of sexual conflict in scorpionflies

Sexual conflict – opposite reproductive/genetic interests between sexes – can be a significant driver of insect evolution. Scorpionflies (Insecta: Mecoptera) are models in sexual conflict research due to their large variety of mating practices, including coercive behaviour and nuptial gift provisioning. However, the role of palaeontology in sexual conflict studies remains negligible, namely due to the paucity of well-preserved fossils. Here, we describe three male scorpionflies from Cretaceous and Eocene ambers. The structure of notal and postnotal organs is analysed in extant and extinct forms; a depression below the base of the notal organ in different panorpid species spatially matches the anterior fold of the female’s wing. Based on disparate abdominal configurations and correlations in extant relatives, we posit that each new fossil taxon had a different mating approach along a nuptial gifting-coercive spectrum. The Eocene specimen possesses extreme female clamping abdominal armature, suggesting a degree of sexual coercion greater than in any other known scorpionfly, extinct or extant. The fossil record of abdominal modifications in male scorpionflies documents a relatively late evolution (Eocene) of long notal organs indicating oppressive behaviour toward a female during mating. Our findings reveal a wider array of mating-related morphological specialisations among extinct Panorpoidea, likely reflecting more diversified past mating strategies and behaviours in this group, and represent first steps towards gaining a deep-time perspective on the evolution of sexual conflict over mating among insects.