Raffica J. La Rosa, Ph.D.

Postdoctoral Research Associate


Adaptation to a variable environment

California vernal pools - Lasthenia

This research is in collaboration with Nancy Emery at the University of Colorado-Boulder where her lab focuses on the patterns of plant distribution and understanding the key ecological and evolutionary factors that determine why certain species are where they are.

I am working on a project studying plant adaptation to a variable environment using several Lasthenia plant species that are associated with California vernal pools. These pools flood over the rainy season and can remain flooded for several months. Lasthenia species inhabit different depths from the base of the pools to the surrounding upland. Seeds germinate as the rains begin and become flooded as seedlings. As the water level drops, the plants quickly bolt and set seed before the dry season sets in.

We are conducing experiments to understand the effects of mean water levels and hydrological fluctuations (during the flooded period) on plant fitness, competition, and root and leaf physiology.

Adaptive floral traits in Asclepias

Present-day natural selection on floral traits

My dissertation research is on the adaptation and evolution of floral traits. I am interested in understanding how adaptive traits function and how they are maintained. Milkweeds have unusual flowers that:

  1. Package their pollen into pairs of pollen sacs called pollinia.
  2. The male and female reproductive tissue is fused to form a cylindrical gynostegium.
  3. Surrounding the gynostegium there is a ring of five hoods called a corona.

There are six linear traits of the gynostegium and corona that I have been studying on five species in the genus Asclepias. I hypothesize that the traits are adaptations to increase pollination and am using selection gradient analysis to identify which traits are under selection, and therefore likely to be adaptations. In addition, I am analyzing video of pollinator visits to determine how the floral traits function to increase pollination.

A. exaltata: six traits

I have measured selection in five species in southwest Michigan; I collected data on two of them (A. exaltata and A. incarnata) for three or more consecutive years.

Selection measurements only address present-day selection, so I am also doing a comparative analysis across Asclepias comparing traits and their pollinators to better understand how past selection may have determined the size and shape of these floral traits across species. I predict I will find relationships between traits and their pollinators that cannot be explained by phylogeny alone.

Five Asclepias species

Five species native to Michigan, USA.

Past selection on floral traits across the North American Asclepias.

Details on the way!