AbstractsBiology & Animal Science

Abstract

Cynipid galls are atypical plant growths induced by wasps in the family Cynipidae that provide larvae with shelter and nutrition. Larvae gain control of attacked plant organs and send them on a new developmental trajectory, with three developmental phases known as initiation, growth, and maturation. Each of the approximately 1400 species of cynipid gall wasps manipulates plant tissues in a slightly different manner such that galls of each species are structurally distinct. Although the means by which cynipids initiate galls has fascinated naturalists for hundreds of years, the basic events in gall induction are still poorly understood. In an attempt to understand the galling strategies and developmental processes responsible for species-specific galls, I chose to compare the intimate details of life history strategies of two taxonomically related species attacking the same plant organs. The strategies included host specificity, phenology, and oviposition strategies, along with gall development to highlight basic events in gall biology and reveal possible stages in past speciation events. It is argued that differences in phenology and gall development played a role in driving speciation and thus, the patterns observed today are a result of extensive ecological interactions in the past that have influenced the evolution of these complex insect-plant relationships. Two species of cynipid wasps of the genus Diplolepis that occur on the wild roses of central Ontario proved to be ideal candidates for the study. One species, Diplolepis polita, induces single-chambered, prickly galls found in clusters on the adaxial surface of leaflets of Rosa acicularis whereas, the other species, D. nebulosa, induces single- iv chambered, smooth-surfaced galls found in clusters on the abaxial surface of the leaflets of Rosa blanda. Galls at all stages of development, from freshly oviposited eggs to maturation, were found in large numbers for both species. Leaf tissues from the bud stage to maturity of both species of rose were fixed in FAA, embedded in paraffin, sectioned and stained for histological study. Likewise, leaf tissues with freshly oviposited eggs of both species and galls from immaturity to maturity were fixed, sectioned, and stained. Comparing the several thousand slides made for the study revealed that galls of D. polita and D. nebulosa differ in their developmental events as well as the anatomy of their mature galls. Like the galls of all species of cynipids, those of D. polita and D. nebulosa are composed of distinct layers of gall cells known as nutritive, parenchymatous nutritive, sclerenchyma, cortex, and epidermis. Galls of D. polita consist of nutritive cells, parenchymatous nutritive cells, and an epidermis throughout the initiation and growth phases. Larvae remain small in relation to chamber volume until the maturation phase, when a hard layer of sclerenchyma differentiates. In contrast, galls of D. nebulosa have a delayed initiation phase, where galls remain nearly undetectable on leaflets for several weeks…