Plant plasticity in reproductive allocation in
response to mate and herbivore environment
Emily Dudaitis1 and Deidra Jacobsen2
1Dept. of Geology and Environmental Earth Science, Miami University, Oxford OH 45056
2Dept. of Biological Sciences, Miami University Regionals, Hamilton OH 45011
Plants must allocate a limited amount of resources among growth, reproduction, and defense.
Resources devoted to flowers and fruits can depend on the relative benefit of selfing (i.e. reproductive assurance) and outcrossing (i.e. genetic diversity).1
Herbivore stress may reinforce selective seed development, favoring outcrossed over selfed seeds if insect damage limits overall seed production and fitness.2
Many plants have mechanisms such as fruit abortion or abscission to reduce damage from frugivores that feed on developing fruits and seeds.3
In this study, we examined whether flower or fruit abscission prior to seed maturation serves as a mechanism for preferential development of outcrossed seeds, particularly under herbivore stress.
We used Physalis pubescens (Solanaceae), an annual plant that can produce seeds through both selfing and outcrossing.
This species was also selected because of its interaction with a specialist frugivore moth, Chloridea subflexa, whose larvae cause significant fruit damage and are known to trigger selective fruit abscission3 (Fig. 1).
H1: Because of the potential value of outcrossing, we expected higher abscission rates for self-pollinated flowers and fruits, leading to preferential maturation of outcrossed fruits.4,5
H2: We expected that frugivore damage would exacerbate this effect, leading to a stronger bias toward the maturation of outcrossed seeds over selfed seeds.
Physalis pubescens plants (N = 34) were grown at The Conservatory at Miami Hamilton.
Individual flowers on each plant were tagged and assigned to controlled self-pollination (N = 137) or outcrossing treatments (N = 127) (Fig. 2).
To test H1: We recorded the number of flowers in each treatment that began fruit enlargement.
Enlarged fruits from both selfing and outcrossing treatments were assigned to either undamaged/control treatments or a damage treatment where half the fruit was cut off to mimic Chloridea subflexa larval damage.
To test H2: We recorded the number of days until fruit abscission and scored whether fruits were immature or mature (Fig. 3).
Fisher’s Exact Tests were used to compare numbers of abscised and mature flowers and fruits across treatments.
Contrary to our prediction (H1), selfed and outcrossed flowers showed similar rates of flower drop or early fruit failure (75% and 72% respectively) (P = 0.692).
When fruits were damaged, they were more likely to abscise fruits before they fully matured. Consistent with our prediction in H2, the negative effect of damage on fruit maturation was especially strong in selfed fruits (Fig. 4).
While damaged selfed fruits were significantly less likely to reach maturity than undamaged/control selfed fruits (P < 0.001), damaged outcrossed fruits experienced only a marginal decrease in fruit maturity at abscission compared with undamaged/control outcrossed fruits (P = 0.065).
Our results suggest that fruit damage increases abscission of selfed more than outcrossed fruits in Physalis pubescens.
Under frugivore pressure in natural settings, fruit and seed maturation decisions may become more selective, particularly if overall seed production is reduced. However, the strength of this selectivity likely depends on the level of inbreeding depression.
Funding: Miami University Undergraduate Summer Scholars (USS) Program
Plant Care: Savannah Ballweg and student workers at The Conservatory
1. Anderson et al. 2003. Am. J. Bot. 2. Barrett and Harder 2017. Annu. Rev. Ecol. Evol. Syst. 3. Benda et al. 2009. Entomol Exp. Appl. 4. Lloyd 1980. New Phytol. 5. Korbecka et al. 2002. Plant Biol.
Through the completion of this research project, I was able to gain skills that furthered my career and self-development skills. I was able to stay motivated and determined in order to perform my best work and collect meaningful results. My research mentor and I were able to schedule our project in a way that allowed us to reach our goals in a timely manner.
Professionalism was gained through this project by strengthening skills such as time management, work ethic, collaboration, and oral and written presentation. Throughout this project I made sure to be diligent, thorough, and responsible just as I would have to be in a professional work environment.
Being able to work with a team is a very important and useful skill in college and in the workplace. Although I was the only undergraduate student working on this research project, I had the pleasure of having a research mentor that I worked very well with. Her expectations for this project were clearly defined and made it easy for me to complete my work the best as I could.