Do longer genital spines in male seed beetles function as better anchors during mating?

► In a wide variety of taxa, males are equipped with harmful genital structures. ► One suggested function for genital spines has been that they function as an anchor. ► We used five populations of seed beetles to test this hypothesis. ► We show that longer genital spines do not function as better anchors during mating. ► We also show that females suffer fitness costs when mating to males with long spines.