|Triumph the Insult Comic Dog|
I’ve already blogged about evening one of the conference, which you can read about here, so I’m skipping directly to the first full day. I woke up Friday morning at 4:30am, excited, nervous, and sweating after making the mistake of turning off the noisy swamp-cooler in my room before hitting the sack. I recited my mantra from back when I was a Landscape Architecture student, “sleep is overrated,” jumped into the shower and got dressed. I jotted down directions to the Trinkle Center and read from a book penned by that day’s keynote speaker until the hotel’s continental breakfast was open. After breezing through the lobby for bean juice and a handful of generic cheerios I was out the door.
|Early Friday morning at the Trinkle Center|
The following is a recap of Herbivory Affects Morphology, Physiology and Sex of a Common Perennial Vine, Passiflora incarnata, a research presentation given by C. Bennington of Stetson University’s Department of Biology:
|Gulf Fritillary caterpillar|
The researcher’s goal was to determine how P. incarnata allocates its energy in the face of herbivory, and whether an increase in production of defense mechanisms is conversely related to the energy it puts into reproduction and growth.
|Trichomes can impale soft-bodied caterpillars|
|Closeup of nectaries on a species of Passiflora|
The flowers of this vine are self-incompatible (cannot successfully produce seed from their own pollen), open synchronously and last for only one day. They are andromonoecious, which is a fancy way of saying that they have both bisexual and male flowers on the same plant. At this point I became a bit confused with what the researcher was describing as “male,” and the photos she was showing, since it had been my understanding that male flowers had only male reproductive organs, i.e. anther-topped filaments. I learned later on that, in andromonoecious plants, flowers with non-functioning female organs are classified as male. With that piece of information the researcher's description of the difference between the male and bisexual flowers (males do not drop their stigmas whereas bisexual flowers’ stigmas do a sort of backbend and end up in a boy-girl circle alongside the anthers) made perfect sense.
|Bisexual (L) and male (R) flowers of P. incarnata|
Testing and Data Collection
- 9 genotypes (plants of the same genus and species but not necessarily the same parents) of Passiflora incarnata were collected from sites separated by a considerable distance.
- In a screened area, 6 pots of each genotype were cultivated, of which 3 were the control and three were subject to simulated herbivory (leaf clipping). By potting the plants, each genotype could be positively identified; had they been planted in the ground, the vines’ rhizomatous tendencies might have lead to the creation of offshoots whose origin could be difficult to pinpoint.
- The amount of nectar each plant produced was quantified, all flowers were tagged and data regarding the flowers’ sex, size, pollen count and quantity of ovules was recorded. Additionally, an average trichome count was calculated from leaf samples of each plant.
- At the end of the experiment, each plant’s specific leaf area (SLA) was determined by dividing the area of a portion of a leaf by the dry weight of that same portion of leaf. SLA is (more or less) related to leaf thickness; flat, thin leaves have a high SLA, and tough, dense leaves have a low SLA.
- Although it was presumed that low SLA and high trichome count went hand-in-hand, and that, when resources were allocated towards producing trichomes, nectar quantity would be low, data from the “herbivory group” suggested otherwise. This group both produced more nectar AND had a lower SLA than the control group.
- Herbivory did not appear to effect flower production.
- Genotype seemed to have a large impact on male flower production.
- Plants that produced male flowers tended to be larger than their counterparts, and were of higher fitness overall.
Following the presentation, the lecturer reflected upon what role, if any, the caterpillar’s saliva might have had on the vine’s response herbivory, and whether simulated herbivory by manual leaf cutting was a comparable substitute for the real thing. Although I am in no way a scientist or researcher, it seems to me that rhizomatous growth would be an excellent way for vines subject to herbivory to channel their resources. Perhaps we will hear more on the subject during next year’s conference in Jacksonville.
- Triumph: http://www.endalldisease.com/wp-content/uploads/2011/08/Triumph.jpg
- Fritillary caterpillar: http://www.flickr.com/photos/kevinclick/4894217920/sizes/n/in/photostream/
- Trichome impalement: http://uts.cc.utexas.edu/~gilbert/teaching/zoo369/lec6graphics/impale.jpg
- Nectaries: http://www.wmrs.edu/people/BIOs/john%20smiley/heliconius-passiflora-flea%20beetle/passiflora/lobata/lobata%20slide.jpg
- Inflorescences: http://www.jstor.org/stable/2444737?origin=JSTOR-pdf
- Dai, C. and Galloway, L. F. (2012), Male flowers are better fathers than hermaphroditic flowers in andromonoecious Passiflora incarnata. New Phytologist, 193: 787-796.
- McLain, D. Kelly (1983), Ants, Extrafloral Nectaries and Herbivory on the Passion Vine, Passiflora incarnata. American Midland Naturalist, 110 #2: 433-439.
- Triumph the Dog video