Measuring the costs of alternative reproductive tactics in horseshoe crabs, Limulus polyphemus

► We examined a cost of the attached tactic in male horseshoe crabs. ► Feeding ability of males is restricted when they are attached to females. ► Increased δ15N values of attached males signify a period of nutritional stress. ► Satellite males, which are in poorer condition, may not be able to afford this cost. ► Our study sheds light on why the different tactics take the form they do.