Behaviour 2019
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Male spiders choose to produce worthless gifts under sperm competition  
Camila Pavón-Peláez1, Mauro Martínez Villar1, Valentina Franco-Treccu1, María J Albo1,2. 1Departamento de Ecología y Evolución, Facultad de Ciencias, UdelaR, Montevideo, Montevideo, Uruguay; 2Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Montevideo, Uruguay

Sexual selection in the form of mate competitioncan drive the maintenance of male alternative mating tactics. Males from the spider Paratrechalea ornatahave two mating tactics, they offer either nutritive (fresh prey) or worthless gifts (prey leftovers)wrapped in silk and are plastic inthis decision making. We examined howgift type production and mating successis influenced by matecompetitionwhen prey availability is constant. Weexposedmales to court females intothree experimental groups: to unmated females in the presence of a competitor male (pre-copulatory competition), to already mated females (post-copulatory competition), and to unmated females in the absence of a competitor (no competition). We found that post-copulatory competition increased the probability of worthless gifts production. Additionally,without competitionmales offering either gift typeacquiredsimilar mating duration, whileoffering worthless gifts decreased mating durations when post-copulatory competition occurred. Our findings show that males under sperm competition minimize gift content investment and consequently suffer a reduction in their matings success.