Female accompaniment by male whiptail lizards: is it mate guarding?

Post-copulatory female accompaniment by males is often interpreted as mate guarding. However, several alternative hypotheses for the function of accompaniment have received little attention. We analysed potential functions of post-copulatory accompaniment in whiptail lizards, Aspidoscelis costata, by comparing 23 accompanied females and 54 unaccompanied females in the field. Male companions closely followed females for 1 to 2 days around ovulation, after which females became unreceptive. Unaccompanied females were in all stages of the reproductive cycle, including 12 nearly-ovulating females. Male companions were aggressive to other males and, on average, won 98.7% of interactions. Only pairs in accompaniment performed consensual copulations (1 to 3 per pair). Solitary males attempted opportunistic copulations but did not selectively target nearly-ovulating females. Male companions attacked rivals attempting opportunistic copulations, but did not copulate in retaliation when attempts were successful. Accompaniment reduced lunges and pursuits from other males on females, but did not reduce opportunistic copulations or predation, or increase foraging opportunities for females. Through accompaniment, males likely (1) copulate repeatedly, (2) swamp rival sperm, (3) inseminate females more and (4) monopolise access to fertile females, whereas females may receive (1) post-copulatory courtship, (2) copulations with high quality males and (3) sufficient sperm for fertilisation.