Submitted to: The International Journal of Organic Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2013
Publication Date: 6/7/2013
Publication URL: http://handle.nal.usda.gov/10113/58844
Citation: Litman, J., Praz, C., Danforth, B., Griswold, T.L., Cardinal, S. 2013. Origins, evolution and diversification of cleptoparasitic lineages in long-tongued bees. The International Journal of Organic Evolution. 67(10):2982-2998. Interpretive Summary: Most bees are pollen collectors, utilizing the pollen as food for their offspring. They are the principal pollinators of many crops and play a prominent role in pollinating plants in natural environments. These bees reproduce by collecting pollen and nectar, depositing it in individual pockets called cells, then laying an egg on these provisions. Some bees, however, have evolved from these pollen-collecting nesters to become parasites of such nesters. Here we explore the pathway that led to various parasitic lifestyles and the evolutionary consequences of becoming a parasite. Analysis of the family tree for bees suggests that the first step in parasitism was a strategy where parasites open the completed bee cells, destroy the host egg, then lay their own egg on the pollen and nectar provisions. Subsequently, some parasites transitioned into a strategy where they enter cells that are in the process of being provisioned by the host bee, while she is out foraging, and deposit their eggs in these open, partially completed nest cells. Within this group there are two subgroups, one where the female parasite destroys the host egg, and one where the parasite egg hatches and the parasite larva destroys the host egg or larva. Results show that adopting a parasitic strategy comes at an evolutionary cost in terms of the rate of speciation (number of species that result) compared to non-parasitic bees. In most cases (8 out of 10) parasitism has resulted in lower rates of speciation. The distribution of parasitic groups among bee families is discussed.
Technical Abstract: The evolution of parasitic behavior may catalyze the exploitation of new ecological niches yet also binds the fate of a parasite to that of its host. It is thus not clear whether evolutionary transitions from free-living organism to parasite lead to increased or decreased rates of diversification. We explore the evolution of brood parasitism in long-tongued bees and find decreased rates of diversification in eight of 10 brood parasitic clades. We propose a pathway for the evolution of brood parasitic strategy and find that a strategy in which a closed host nest cell is parasitized and the host offspring is killed by the adult parasite represents an obligate first step in the appearance of a brood parasitic lineage; this ultimately evolves into a strategy in which an open host cell is parasitized and the host offspring is killed by a specialized larval instar. The transition to parasitizing open nest cells expanded the range of potential hosts for brood parasitic bees and played a fundamental role in the patterns of diversification seen in brood parasitic clades. We address the prevalence of brood parasitic lineages in certain families of bees and examine the evolution of brood parasitism in other groups of organisms.