|
Rob Gendron's Research
|
|
|
| My primary research interest involves a study of the gall-forming aphid Hormaphis hamamelidis. I also collaborated recently with Jim Reichman in developing a computer model of food caching behavior in small mammals. | |||
|
|
|||
| Gall-forming aphids | |||
|
|
|||
|
Witch hazel is a common understory plant in eastern deciduous forests, best
known for its use as an astringent and in dowsing ("water witching"). Sometimes
there are red cone-shaped structures on the surface of witch hazel leaves.
These are galls produced by the aphid Hormaphis hamamelidis. Like
most aphids, Hormaphis has a complex life cycle. In Pennsylvania there
are three generations per year. In early spring females (the "stem mothers")
hatch out and crawl onto the leaf buds. As the leaves begin to expand the
stem mothers inject chemicals into the leaf tissue which causes a hollow
gall to form. Once inside her gall the stem mother reproduces asexually until
the gall is filled with 50-70 offspring, all female. This second generation
develops wings and disperses to other plants where they also reproduce asexually.
The third generation includes both males and females. In late summer this
final generation reproduces sexually and lays eggs on the branches of the
witch hazel plant. The following spring the cycle begins anew. You can download
a 6K GIF file that illustrates this life cycle.
For several years, with the assistance of a group of students (see below), I have been investigating the distribution patterns of Hormaphis on its host plant. Stem mothers tend to aggregate on some leaves while avoiding others. This seems to be related to variation among leaves in the density of protective hairs (trichomes) on the surface. Presumably the trichomes make it more difficult for the aphids to feed. |
|
||
|
|||
|
|
|||
|
Aphids are also aggregated among trees; some plants are heavily infested
while their neighbors remain virtually untouched. The same trees seem to
get hit year after year, suggesting that there may be a genetic basis for
this variation in susceptibility to attack.
In addition to looking at the distribution of the aphids we are also looking at other aspects of their ecology, including population dynamics, predator-prey interactions and insect-plant interactions. |
|||
|
|
|||
|
Caching Behavior
Many animals store food for long periods of time to prevent starvation. One problem these animals face is deciding what food types to store and what to eat immediately. This is complicated because often the most nutritious foods spoil the fastest. It seems likely that natural selection has equipped caching species with the ability to make the correct decision. In an attempt to understand these decisions Jim Reichman (now director of the National Center for Ecological Analysis and Synthesis) and I developed of a model of food caching behavior in small mammals. The following paragraph is the abstract of our paper which was recently published in the American Naturalist. Food stored for an extended period may change substantially in value (e.g., ripen or spoil). Consequently, when selecting food for a long-term cache an animal should consider what the value of each food item will be when it is eaten rather than when it is collected. This adds considerable complexity to the problem of food selection compared to the situation addressed by most prey choice models. Beginning with the premise that an animal should store no more of a food type than can be consumed before the remainder spoils, we developed a numerical computer simulation to evaluate three cache management strategies under various conditions of food availability and duration of the cache-use-period. On the basis of deterioration rates, the simulation predicts how much of each food type an animal should store. The results indicate that animals should adjust the composition of their cache to reflect food perishability, and that no one inventory strategy is optimal under all conditions. |
|||
|
|
|
|
The Aphid Team
|
|
|
|
|
|
Jendy McElhinney has worked on the aphid project from the beginning
and is an indispensable member of the aphid team. She is a graduate of IUP
with degrees in Biology and Education. When she is not watching aphids or
working on her farm she is a substitute teacher in a local high school. |
|
|
|
|
|
Kevin Madden came to IUP as a graduate student. For his master's research he
worked on sexual selection in fish. |
|
|
|
|
| Mario Giazzon worked on the aphid project in both 1997 and 1998. He graduated from IUP and earned his Master's degree at Illinois State University. |
|
|
|
|
| Lynn Patti joined us for both the 1994 and 1995 seasons. She also did an independent study looking at various factors that influence leaf preference by stem mother aphids. Now she is happily teaching 8th grade science at Gateway Middle School. | |
|
|
|
| Aaron Doverspike worked on the aphid project during the summer of 1996. He was a graduate student and did his thesis research on olfactory search images in mice. |
|
|
|
|
The other members of the aphid team, each of whom worked on the project for
a summer or two, are
Mary-Margaret Conjelko |
|
|
|
 |
[Home]
[Research]
[Personal] [Links]
[Software]
[Labs] |
|
Send comments to:
Robert P. Gendron Biology Department Indiana University of Pennsylvania Indiana, PA 15705 rgendron@iup.edu copyright © 1997-2003, Robert P. Gendron, Revised - 3 October 2003. |