Parasitism offers large rewards but carries high risks: predicting parasitic strategies under different life history conditions in lampreys

The loss of parasitism in metazoan lineages is often seen as unlikely, but it has occurred in some lineages (e.g., leeches, lampreys). How and why parasitism is lost is aptly addressed by studying lampreys, because extant species include a range of feeding modes and parasitism has been lost repeatedly. An individual‐based model was developed to determine if variations in survival and growth rates in the larval and juvenile stages could favor parasitic or non‐parasitic strategies. A realization of the model for a Lampetra spp. population, a genus which includes parasitic and non‐parasitic animals, indicated that both strategies could be successful. A different model realization of the non‐parasitic species Lethenteron appendix also agreed with expectations, only non‐parasitic strategies were successful. Modeling anadromous Petromyzon marinus produced only parasitic animals, as expected, but suggested two different adult sizes should appear in the population, which has not been reported i...