Reproductive and Somatic Effort Distribution of a plant parasite on its host and Reproductive and Somatic Effort BIOL 3060

Distribution of a plant parasite on its host: gall distribution on the flowering dogwood, Cornus florida

Flowering dogwood, Cornus florida

Midge fly, Resseliella clavula

Purpose To determine the distribution of midge galls on dogwood trees and to investigate some environmental factors that might influence distribution. Questions 1) How are the galls distributed spatially? Random vs. clumped vs. uniform 2) Could # or distribution of galls be related to: Size/age of the plant? Nearest neighbor distance? Sunny versus shady microhabitat?

P 1 : Random Distribution Parasites are randomly distributed within the environment. If midges flew until they “hit” a dogwood haphazardly …

P 2 : Even Distribution “Regular”: Organisms are evenly spaced in the environment. In our case, every tree would have the same number of galls. This would suggest that the parasites are competing for the trees. 10

P 3 : Clumped Distribution Most trees have few parasites, and some a lot. Typically associated with: – disease outbreaks – tree densities (“contagious”) – age-related effects

Tree size Older and infirm trees might be more likely to be attacked by the midge parasite. Distance to nearest neighbor If trees are close together, they might be more likely to attract galls. Collect gall data in two habitats Some microhabitats might be better for galls than others. Environmental Factors We are Measuring

Flower buds (reproductive) Leaf bud (somatic) Both

Bark: dark brown with squarish, scaly blocks. Young trees will be smooth and not as distinctive.

Examples of different numbers of bud scales Dogwood with two bud scales. Twigs are slender, green or purple.

Dogwood leaf scars are opposite, small, and encircle twig. Example of alternate leaf scars Opposite leaf scars Terminal bud

Flowers: white, four petals (spring) Fruit: bright red, in clusters (late summer, fall) Leaves: opposite, veins curved