General Research Interests:

Overall, I am interested in ecology and evolution.  More specifically, my work focuses on how pollinator behavior and floral-display size (i.e., the number of flowers on a plant) interact to influence plant reproductive success.

To answer questions about pollinator behavior and floral display I have utilized Asclepias spp. (milkweeds) as my model system.  Milkweeds have a derived pollination system that relies on insect vectors for pollen dispersal.  Specifically, they do not have individual pollen grains, but aggregates of pollen grains called pollinia.

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Apis mellifera (Western Honey Bee) exhibiting a phenomenon called chaining, where a series of pollinia (black and yellow objects) attach to each other and the bee’s feet (Photograph by Dillon Alderfer, F&M ’18).

I have been able to collect pollinia that have been deposited by pollinators (like the Western Honey Bee in the video below), genotype them using microsatellites, and quantify self-pollination rates.  Self pollen deposition may significantly influence reproductive success of a plant, especially if the plant is self-incompatible like many milkweed species.

 Apis mellifera (Western Honey Bee) visiting an Asclepias syriaca (Common Milkweed) inflorescence (video source: youtube=

Additionally, many milkweed species are clonal (particularly the Common Milkweed).  This characteristic may result in increased floral-display size, as a result of spatially aggregated stems, and self pollen deposition.  To investigate this phenomenon I wrote a simulation (using R) to model pollen dispersal in plant populations with varying amounts of clonality and spatial autocorrelation.

Representative plots of simulated aggregated plant populations with different levels of clonality.

Please contact me via email ( for more details about my research!


  • Howard, A. F.  2018.  Asclepias Syriaca (Common Milkweed) flowering date shift in response to climate change.  Scientific Reports 8:17802.  Retrieve from
  • Ollerton et al.  (in press).  The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study.  Anals of Botany 1–15.  PDF.
  • Mallory, H. S., A. F. Howard, and M. R. Weiss. 2016. Timing of Environmental Enrichment Affects Memory in the House Cricket, Acheta domesticus. PLoS ONE 11(4). Retrieve from
  • Howard, A. F. and E. M. Barrows. 2014. Self-pollination rate and floral-display size in Asclepias syriaca with regard to floral-visitor taxa. BMC Evolutionary Biology 14. Retrieve from
  • Barrows, E. M., A. F. Howard, and B. W. Steury. 2013. Phenology and Floral Visitors of Lithospermum virginianum L. (Boraginaceae) in Great Falls Park and Chub Sandhill Natural Area Preserve, Virginia. Marilandica 4:6–9.
  • Barrows, E. M., A. F. Howard, and B. W. Steury. 2012. Fruit Production and Phenology of Phacelia covillei S. Watson (Hydrophyllaceae) in the Potomac Gorge Area of Maryland and Virginia. Marilandica 3:10–16.
  • Barrows, E. M., A. F. Howard, and B. W. Steury. 2011. Phenology and floral visitors of Valeriana pauciflora Michaux (Valerianaceae) in the Potomac River Gorge Area of Maryland and Virginia, United States. Marilandica 2:6–10.
  • Brenner, F. J., A. F. Howard, and R. Pearson. 2008. Successional changes in plant community in an acid mine drainage treatment wetland. Journal of the Pennsylvania Academy of Science 82: 62–66.
  • Howard, A. F., H. A. Bookstein, and E. M. Barrows. (in prep.). Pollinium removal from Asclepias syriaca flowers and the size of Apis mellifera and Bombus griseocollis.
  • Howard, A. F. and E. M. Barrows. (in prep.). Geitonogamy and Mating Patterns in Monoecious, Pollen-bearing Clonal Plants.
  • Howard, A. F., E. M. Barrows, and M. B. Hamilton. (in prep.). Selection on multiple levels of floral-display size through female fitness in Asclepias incarnata.
  • Howard, A. F. (under review). Branching patterns and reproductive success in the Swamp Milkweed (Asclepias incarnata).

Presentations and Posters:

  • Plant Composition Comparison of Constructed Wetland and Naturally Occurring Wetland. Slippery Rock Watershed Coalition, Investigating Watershed Issues, Westminster College, April 14, 2005.
  • Asclepias pollination and floral display. Annual Blandy Experimental Farm Research Symposium, Blandy Experimental Farm, July 23, 2008
  • Pollinator-mediated Floral-display Evolution in an Herbaceous, Hermaphroditic Angiosperm (Asclepias syriaca, Apocynaceae). Evolution Conference, University of Idaho, June 24, 2009.
  • Impact of Pollinators on the Reproductive Success and Floral Display of Milkweeds (Asclepias sp.). Washington Biologists’ Field Club, July 9, 2009.
  • Impact of Pollinators on Self-pollination Rate and Floral-Display of Asclepias syriaca. Evolution Conference, Portland State University, June 28, 2010.
  • Self-pollination and Fitness in Pollen Bearing Clonal Plants. Evolution Conference, University of Oklahoma, June 20, 2011.
  • Pollinium Acquisition in Three Pollinator Taxa of Asclepias syriaca, Common Milkweed (Apocynaceae). Ecology Conference, Portland, OR, August 2012.
  • Branching Patterns and Reproductive Success in the Swamp Milkweed (Asclepias incarnata). Chicago Area Undergraduate Research Symposium, Chicago, IL, April 5, 2014.
  • The Influence of Floral-visitor Anatomy on Pollen Removal from Asclepias syriaca (Common Milkweed). To be presented at the Annual SACNAS National Conference in Los Angeles, CA, October 2014.

Research Awards and Grants:

  • Washington Biologists’ Field Club Award, Washington Biologist’s Field Club, 2007–2008: Quantified the distribution and Phenology of the Maryland Endangered Plant Phacelia covillei (Hydrophyllaceae) in Plummers Island and adjacent areas, Chesapeake and Ohio Canal National Historical Park (COCNHP), Maryland. Enumerated the basic ecology of P. covillei on Plummers Island including: abundance, distribution, flowering phenology, and pollination biology.
  • Washington Biologists’ Field Club Award, Washington Biologist’s Field Club, 2008–2009: Impact of Insect Pollinator Group on Outcrossing Pollination Rates of Asclepias syriaca (Apocynaceae) at the Audubon Naturalist Society, Chevy Chase, MD. Measured the effect of various pollinator taxa (including bees, butterflies, and moths) on the mating system of A. syriaca.
  • Washington Biologists’ Field Club Award, Washington Biologist’s Field Club, 2009–2010: Impact of Pollinators on the Reproductive Success and Floral Display of Asclepias (Milkweed) in the Potomac Valley. Determined how plant male and female reproductive successes are influenced by the behaviors of various pollinator taxa and how do the effects of pollinator behavior on reproductive success influence the evolution of floral display.
  • Grants-in-Aid of Research Award, Sigma Xi, 2008–2009: Pollinator Behavior as a Driver of Angiosperm Floral-display Evolution. Determined the effect of various pollinator taxa on the floral-display size and architecture evolution of Asclepias syriaca.
  • Blandy Experimental Farm Graduate Fellowship, Blandy Experimental Farm and State Arboretum, 2008–2010: Plant Reproductive Success, Floral Display, and Pollinator Behavior. Quantified the influence of pollination on the mating system, fitness and floral display evolution in Asclepias syriaca and Asclepias incarnata.
  • Graduate School Travel Grant, Georgetown University, 2009: I was awarded a grant to present my original research at the Society for the Study of Evolution conference at the University of Idaho in Norman, ID.
  • Georgetown Center for the Environment Travel Grant, Georgetown University, 2010–2011: I was awarded grants in 2010 and 2011 to present my original research at the Society for the Study of Evolution conferences at the University of Portland and University of Oklahoma in Portland, OR, and Oklahoma City, OK, respectively.
  • Biology Department Travel Grant, Georgetown University, 2010: I was awarded a grant to present my original research at the Society for the Study of Evolution conference in Oklahoma City, OK
  • Summer Research with Undergraduates, Student Center for Science Engagement, Northeastern Illinois University, 2014: I was awarded a grant to work with an undergraduate student on a project entitled “The Influence of Pollinator Anatomy on Common Milkweed (Asclepias syriaca) Pollination”.