Costly sexually-selected weapons are predicted to trade off with post-copulatory traits, such as testes. Although weapons can be important for achieving access to females, individuals of some species can permanently drop (i.e. autotomize) their weapons to escape danger. We capitalized on this natural behavior to experimentally address whether the loss of a sexually-selected weapon leads to increased testes investment in the leaf-footed cactus bug, Narnia femorata (Hemiptera: Coreidae). In a second experiment, we measured offspring production for males that lost a weapon during development. We found that those that dropped a hind limb during development grew significantly larger testes than the control treatments. Hind-limb autotomy did not result in the enlargement of other nearby traits. Our results are the first to show that males may compensate for natural weapon loss by investing more in testes. In a second experiment we found that females paired with males that lost a hind limb had 40% lower egg hatching success. Yet, in those cases where viable offspring were produced, males missing a hind limb produced 42% more offspring than males with intact limbs. These results suggest that the loss of a hind-limb weapon can, in some cases, lead to greater fertilization success
