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Effect of reproductive tactics and leg amputation on male survival in an intrasexually dimorphic arachnid

Grant number: 23/10628-9
Support Opportunities:Scholarships in Brazil - Master
Effective date (Start): April 01, 2024
Effective date (End): March 31, 2025
Field of knowledge:Biological Sciences - Ecology - Theoretical Ecology
Principal Investigator:Glauco Machado
Grantee:Wellen Cristina Alves Bezerra
Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil


Male armaments are sexually selected traits widely distributed in nature. Given the costs associated with the production and maintenance of armaments, not all males can afford them. Therefore, when competition among males is intense, intrasexual dimorphism can evolve. Heavily armed males usually engage in fights to secure females or resources, while less armed males adopt alternative reproductive tactics. In the harvestman species Longiperna concolor, males possess an extremely elongated fourth pair of legs (legs IV) compared to females. Males with elongated legs IV (majors) defend reproductive territories on rocks and fallen trunks, whereas males with short legs IV (minors) invade territories and engage in sneaky copulations. In this project, we will test whether there are differences in the survival of males from each morph. We have two alternative hypotheses: (1) the reproductive tactic of minors leads to greater vagility, which may expose them to increased predation by ambush predators and consequently reduce male survival; (2) the exaggerated size of the legs IV in majors hampers their locomotion ability, affecting predator evasion, food acquisition, and thus male survival. Additionally, we will investigate whether leg amputations occurring during agonistic interactions influence the survival of males from both morphs. Our hypothesis is that amputations impair the locomotion of males from both morphs but are more detrimental to majors due to the greater length of their legs. The study will utilize previously collected mark-recapture data following Pollock's robust design, which will be analyzed through hierarchical modeling. This project innovates by using modern statistical techniques to estimate survival in a species with intrasexual dimorphism, and in which the structure used in male combat also serves an ambulatory function, which can directly impact locomotion, food foraging, and predator evasion abilities. The results obtained will be of interest to those studying agonistic interactions among males, ecological costs of armaments, and alternative reproductive tactics.

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