Pietro Pollo, Danilo G. Muniz, Eduardo S. A. Santos

Male preference for high-quality females is expected to evolve when male reproductive potential is restricted. However, when there is competition among males, some models predict the evolution of assortative male mate choice, in which good competitors choose high quality females while poor competitors choose lower quality females to avoid competition. In Trichonephila clavipes spiders, males have limited sperm supply and fight for access to females. We tested whether female quality and male size (a proxy of fighting ability) influence male decisions in T. clavipes. We used field experiments in which males could choose among two available females in a scenario free of competition. We found that males choose their mates based on both female size and female recent pairing status (whether the female was accompanied by a male before the experiment). Importantly, male mate choice exhibited plasticity, and varied with male size, as large males preferred larger females that were recently unpaired, medium-sized males showed no preference, and small males preferred smaller, recently paired females. Because all females appear to attract males, we predict that variation on male mate choice attenuates sexual selection on females. Our findings confirm the prediction of variable male mate choice when there is male-male competition and male reproductive potential is restricted, a pattern that may be common, but hard to detect.