Experimental evolution under predation reduces body size in dung flies but courtship displays persist in males (Diptera: Sepsidae)

• Published in: Behavioural processes Vol. 220; p. 105073
• Main Authors: Lee, Nicole L.Y., Kuan, Pamela S.Y., Hua, Qiaz Q.H., Puniamoorthy, Nalini
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.2024
• Subjects: Allometry; Animals; Biological Evolution; body size; Body Size - physiology; Courtship; Diptera - physiology; directed evolution; dung flies; feces; Female; females; Male; males; Mantis; Mantodea - physiology; Mating behaviour; Predation; Predatory Behavior - physiology; risk; Sepsidae; Sexual Behavior, Animal - physiology; Sexual selection; Sexual Selection - physiology; species; spermatozoa; Mating behaviour; Sexual selection; Predation; Allometry; Sepsidae
• ISSN: 0376-6357; 1872-8308; 1872-8308
• DOI: 10.1016/j.beproc.2024.105073

Exaggerated sexual traits, such as ornaments and courtship displays, are crucial for mate acquisition in many species and are often subject to directional runaway selection. However, in the face of high predation risk, natural selection can result in a reduction of conspicuous precopulatory displays to avoid detection by potential predators. Sexual selection may then favour increased investment in inconspicuous postcopulatory traits. Here, we investigated the transgenerational effects of predation on precopulatory male courtship and postcopulatory sexual traits (testes size, sperm length) in a dung fly, Sepsis punctum (Sepsidae). Behavioural assays prior to selection document a marked decrease in male courtship displays in the presence of a predator, the Asian Ant Mantis (Odontomantis planiceps). However, after ten generations of experimental evolution, flies exhibited a marked increase in courtship, both in the absence and presence of a predator. Additionally, under sustained predation pressure, male and female body size decreased but male postcopulatory traits were not significantly affected. These results suggest that precopulatory courtship can be under strong sexual selection even in the face of predation pressure. Larger flies were more susceptible to predation, and there could be canalisation of postcopulatory traits that are crucial for fertilisation. •Male courtship activity increased over generations regardless of predation risk•Adult body size decreased over generations of sustained predation pressure•Male postcopulatory traits (testes volume, sperm length) were not significantly affected•Crucial postcopulatory traits may be under strong stabilising selection due to their role in fertilisation