Phylogeny, biogeography and evolution of life-history traits of Megastigmidae (Hymenoptera: Chalcidoidea)
Abstract
Megastigmidae comprises ca 220 species that mostly occur in the Australian region, with few genera in other biogeographic regions. Megastigmidae exhibits contrasted life-history strategies. Several genera are seed-feeders of angiosperms or gymnosperms, other are parasitoids and one genus appears to be a gall-maker. The aims of our study were to 1) produce a robust phylogeny for Megastimidae; 2) use it to determine the area of its origin; 3) identify the ancestral feeding strategy and clarify the number of transitions between parasitic and phytophagous lifestyle. We sequenced ca 900 UCE for
>100 species representing all known genera. We also sequenced numerous outgroups, including two genera of Pteromalidae, Keirana and Chromeurytoma.
Our analyses demonstrated that the circumscription of Megastigmidae should be revised to include
Keirana and Chromeurytoma. Three subfamilies should be recognized within Megastigmidae:
Keiraninae, Chromeurytominae and Megastigminae. The family originated in the Australian region and subsequently colonized the world. The biologies of Keiraninae is poorly known but
Chromeurytoma is a hyperparasitoid of gall-making Fergusonina (Diptera: Fergusoninidae).
Megastigminae is subdivided into three clades. The first comprises phytophagous species (including gall-formers). The second clade likely includes only parasitoid species. Within the third clade, the parasitic Mangostigmus is recovered sister to all other species, and phytophagy has evolved at least twice independently. Our analyses suggest that parasitoidism is the most likely ancestral feeding strategy of the family and of Megastigmus as well with subsequent shift to seed predation. From a parasitoid lifestyle, return to phytophagy has evolved at least three times independently within
Megastigmidae.