Parasitism is always costly to the host
Nan Lyu, 北京师范大学生命科学学院生物多样性科学与生态工程教育部重点实验室，北京 100875，中国, Wei Liang, 海南师范大学生命科学学院热带岛屿生态学教育部重点实验室，海南省热带动植物生态学重点实验室，海南 海口 571158，中国
Abstract
Recent studies have examined the cost of raising parasitic cuckoos and highlighted the importance of “no extra cost” in explaining the low levels of defense in hosts. To clarify the reasons for parasitization in typical hosts, we present a simple model to explore the immediate and future costs of parasitism in shaping the evolution of defense behavior in hosts. Our results suggest that any cost of parasitization is maladaptive to the host and learned egg recognition is always favored to overcome these costs. Furthermore, although facing a potential cost of mis-imprinting, learned nestling recognition may still evolve when there is a non-zero immediate cost from raising a parasitic nestling. Therefore, we contend that “no extra cost” does not provide sufficient evidence to explain the low levels of defense behavior in hosts <i>per se</i>.