Life-long testosterone and antiandrogen treatments affect the survival and reproduction of captive male red-legged partridges (Alectoris rufa)

Sexual steroids can play an important role as life-history organizers. In males, high circulating testosterone levels induce physiological/behavioral costs and benefits, leading to trade-offs. However, studies simultaneously testing the impact of these levels in both fitness components (survival and fecundity) during lifetime are scarce and limited to wild birds. To determine the mortality causes or hormonal manipulation impacts on male fertility is, nonetheless, a difficult task in free-ranging animals that could be easier in captivity. We longitudinally monitored captive red-legged partridges (Alectoris rufa) and exposed males to high exogenous testosterone levels, anti-androgens, or a control treatment during each breeding period throughout their lives. Theory predicts that individuals maintaining high androgen levels should obtain higher fitness returns via reproduction, but suffer reduced longevity. Testosterone-treated male partridges, accordingly, lived shorter compared to controls, since they were more prone to die from a natural bacterial infection. However, the same birds seemed to have a lower capacity to fertilize eggs, probably due to endocrine feedback reducing testicular mass. These results show that exogenous testosterone can exert unpredicted effects on fitness parameters. Therefore, caution must be taken when drawing conclusions from non-fully controlled experiments in the wild. Males treated with the androgen-receptor blocker flutamide did not outlive controls as predicted by the life-history trade-off theory, but their mates laid eggs with higher hatching success. The latter could be due to mechanisms improving sperm quality/quantity or influencing maternal investment in egg quality. Testosterone receptor activity/amount could thus be as relevant to fitness as testosterone levels.Open access funding provided by University of Turku (UTU) including Turku University Central Hospital. Financial support was obtained from the projects PII1I09-0271-5037, PII1C09-0128-4724, SBPLY/17/180501/000468 from the JCCM (co-financed with European Regional Development Fund-ERDF), CGL2009-10883-C02-02 from Ministerio de Ciencia e Innovación (MICIN, Spain), CGL2015-69338-C2-2-P from Ministerio de Economía, Industria y Competitividad (MINECO), and PID2019-109303GB-I00 from MICIN. AC and LP-R were supported by a “Juan de la Cierva-formación” postdoctoral grant (MINECO, FJCI-2015-23536) and a SECTI postdoctoral contract from the University of Castilla-La Mancha (UCLM), respectively. AC is currently supported by a postdoctoral fellowship from Fundación Ramón Areces. AAR-H is funded by a Marie Skłodowska-Curie grant (agreement 842085).Peer reviewe