Abstract
Numerous sex-related morphological adaptations are connected to reproductive behavior in animals. For example, females of some insect species can submerge during oviposition, which may lead to sex-related adaptations in the hydrophobicity (water-repellency) due to specialization of certain morphological structures. On the other hand, ageing can cause changes in hydrophobicity of the surface, because the morphological structures can wear with age. Here, we investigated sex-and age-related differences in wing hydrophobicity and in morphology (spine density, wax cover characteristics, size of females' pseudopterostigma) potentially related to hydrophobicity of Calopteryx splendens damselflies. Hydrophobicity was measured with two methods, by measuring the contact angle (CA) between a wing and water droplet, and by dipping a wing into water and measuring forces needed to submerge, withdraw, and pull-out a wing from water. We found that C. splendens wings are superhydrophobic, having mean CAs of 161°. The only sex and age related difference in the hydrophobicity measurements was that young females had stronger amplitude of force fluctuations during withdrawal of wings from water than young males. This suggests that young females may form less uniform air pockets on their wings while submerged. From the morphological structures measured here, the only sex related finding was that old females had denser spine cover than young females in their wing veins. The difference may be explained by better survival of females with denser spine cover. The most important morphological character that predicted superhydrophobicity was the prevalence of long wax rods on wing veins. In addition, female pseudopterostigma area (a trait present only in females) was negatively related to pull-out force, suggesting that large pseudopterostigmas might help females to emerge from water following oviposition. The subtle sex-related differences in hydrophobicity could be explained by the fact that both sexes must resist rain, and males are occasionally in contact with water.
Highlights
Selection pressures due to sex specific behavior can cause adaptations in morphological structures
Contact angle measurements All wings were superhydrophobic with contact angles varying between 156u and 165u
Cryo-Scanning electron microscope (SEM) revealed that water droplets have spherical shape on wing surface (Fig. 4), verifying the superhydrophobic nature of the wing surface
Summary
Selection pressures due to sex specific behavior can cause adaptations in morphological structures. Females lay their eggs while partly or totally submerged in water [1] [2], and may be expected to have greater water repellency than males as a result of natural selection. Support for this kind of adaptation is found in the damselfly Calopteryx cornelia, in which females submerge during oviposition [1]. Females of this species are able to survive under water longer than males, suggesting that there could be sex-specific adaptations related to submerging. There are some indications that the wings of female damselflies might have denser bristle cover than males, which could mediate differences in the hydrophobicity of the wing surface between the sexes [1]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
