Investment in regeneration versus asexual reproduction is resource‐dependent in a freshwater annelid

The post‐embryonic developmental processes of regeneration and asexual agametic reproduction are widespread and often co‐occur in animals. These traits are of great ecological significance, but their physiological dynamics within species are not well understood. In naid annelids, regeneration and asexual reproduction via fission are evolutionarily related and mechanistically similar yet distinct, making these animals useful systems in which to study resource allocation strategies between the two processes. How asexual reproductive investment varies as a function of somatic investment demands was tested in the naid Pristina leidyi by repeatedly amputating the heads of individual worms, allowing regeneration to proceed, and measuring reproductive output over time. Treatments were replicated under high and low food levels to determine to what extent the investment dynamic between regeneration and fission is affected by the resource pool. Reproductive output was affected by injury and regeneration frequency in a resource‐dependent manner, such that only worms with less food availability exhibited reproductive deficits; injury and regeneration did not affect reproductive output of worms under the high food condition. When reproductive output was decreased, this occurred not through a reduction in offspring quantity but a reduction in offspring quality. In the offspring of experimental animals, body size and fission speed were dependent on parental feeding level and to a lesser and inconsistent extent on parental injury history, but regeneration speed was unaffected by parental treatment. These findings suggest that, in a species capable of both regeneration and asexual reproduction: (1) the resource pool is a key factor mediating the resource investment pattern between regeneration and fission; (2) sacrificing per‐offspring investment rather than fecundity may be an optimal strategy if resources are limiting; (3) regeneration and fission have evolved distinct resource allocation pathways. This work prompts further questions about the physiological dynamics between regeneration and asexual reproduction in animals, such as whether and to what extent these have evolved adaptively, including in response to injury and resource pressures. Read the free Plain Language Summary for this article on the Journal blog.