Herbivory Weakens the Stability of a Floral Polymorphism

Herbivory Weakens the Stability of a Floral Polymorphism

Mia Gaughan1-2,7-8, Vincent S. Pan2-4,7-8, Sylvie Martin-Eberhardt2-3,5, William C. Wetzel6, Kadeem J. Gilbert2-5.

1:Department of Biology, Washington University in St. Louis, St. Louis, MO, USA

2: W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI, USA

3: Department of Integrative Biology, Michigan State University, East Lansing, MI, USA

4: Ecology, Evolution, and Behavior Program, Michigan State University, Easting Lansing, MI, USA

5: Department of Plant Biology, Michigan State University, East Lansing, MI, USA

6: Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana, USA

7: Corresponding authors: vsbpan [at] gmail [dot] com, gmia [at] wustl [dot] edu

8: Co-first authors

Dataset DOI: 10.5281/zenodo.18807895

General descriptions

480 Hesperis matronalis were subjected to an induction (clipping) treatment across 40 sites. We measured a bunch of fitness surrogates to look at whether herbivory affects frequency dependent selection. We performed a choice/no-choice assay to confirm what was going on with the herbivores. See the associated manuscript for more details on the methods.

Manuscript abstract

Herbivores have profound impacts on the maintenance of plant diversity. While simple optimal foraging models predict that herbivores should selectively attack common plant phenotypes, models that allow for differential plant resource acquisition can predict a preference towards rarer phenotypes, leading to the destabilization of intraspecific polymorphism. We show that herbivores may play such a destabilizing role in the dimorphic Hesperis matronalis system by weakening negative frequency-dependence. Across 40 patches of varying morph ratios, locally rarer H. matronalis morphs grew larger in the early season but received disproportionately more herbivory in the mid- and late season, leading to lower female fitness and survival. We rescued the advantage of being rare by experimentally reducing later herbivory through a plant immunity induction treatment. Feeding assays with a mustard-feeding caterpillar Trichopulsia ni confirmed that herbivores had higher survival on locally rare morphs and preferred to feed on rarer morphs. Our results are consistent with the hypothesis that herbivores may have evolved to use rarity as a cue to track resources, potentially weakening the advantage of being rare, a critical component of stable coexistence. We argue that this phenomenon of insect herbivores weakening the maintenance of plant diversity is extremely common in stable polymorphic systems.

Data descriptions

We use 'NA' to denote missing values in general.

base_map.jpg

This is a screen shot of google maps displaying the sites studied.

DRFDS_manuscript_cleaned_field_data_03_06_2025.csv

This is the field data + no-choice experiment. Each row is a plant or caterpillar that ate the specific plant.

This is the field data + no-choice experiment. Each row is a plant or caterpillar that ate the specific plant.

siteID: The unique identifier of the 40 sites

plantID: Unique plant identifier

trt: the clipping treatment of the plant (c = control, a = aggregated clipping, d = dispersed clipping)

leaf_number_pre: number of leaves counted before the leaves were clipped

largest_leaf_len_pre: largest leaf length in cm two days after the leaves were clipped

height: the height of the plant in cm roughly a month later clipping when the plant is flowering

herb_intensity: herbivory severity at the time of flower survey (n = no damage, l = low damage, m = medium damage, h = high damage)

flower_count: the number of flowers counted

date_flower_survey: moth-day-year of flower survey

date_trt: the date of clipping treatment (month-day-year)

lat: the latitude in degree decimals of the plant

lon: the longitude in degree decimals of the plant

notes: general notes

date_pollen_processed: the date pollen is scored

pollen_alive: the number of pollen grains counted that were stained red with tetrazolium (0.5% TTC for >24h)

pollen_dead: the number of pollen grains counted that did not stain with TTC

anther_prop_red: the proportion surface area of anther stained red in the TTC staining solution

anther_prop_red_logit: logit transformed anther_prop_red.

num_stalks: the number of stalks (either flowering or not flowering) of the same plant

leaf_feeding_start: the year-month-day H:M:S of when the no-choice leaf feeding assay with T. ni started

leaf_feeding_end: the year-month-day H:M:S of when the no-choice leaf feeding assay with T. ni ended

cat_wt: the milligram of the T. ni caterpillar post weight (after leaf feeding trial)

cat_dead: is the caterpillar dead after the no-choice feeding trial (1 = yes, 0 = no)

herbivory_assay_notes: notes specific to the no-choice herbivory assay

seed_collection_date: year-month-day of when the seeds were collected.

late_herb_prop: Proportion of herbivory on the plant in the late season survey

late_herb_survey_date: year-month-day of when late season herbivory was surveyed

late_herb_sruvey_notes: Notes specific to late season herbivory survey

silique_count: Number of siliques counted

silique_weight: the weight in grams of the siliques collected.

PC1: the first principal component of the RGB values of the scanned flower color

hex: the hex code of the scanned flower color

red: the red intensity (0-1) of the flower color

green: the green intensity (0-1) of the flower color

blue: the blue intensity (0-1) of the flower color

clipped: which clipping treatment did the plant get? (clipped: clipped; control: not clipped)

site_PC: The average PC1 value of all plants measured at a site

flower_color: a rough classification of flower color as either purple or white.

alive_next_year: whether the plant survived until next year (1: yes, 0: no)

next_year_survey_date: year-month-day of when the plant survival was surveyed

next_year_notes: notes specific to survival survey

DRFDS_manuscript_cleaned_choice_experiment_10_22_2023.csv

This is the choice experiment. Each row is a caterpillar.

containerID: The experimental arena ID

cat_sourceID: colony ID of where the caterpillar comes from

cat_pre_wt: Caterpillar pre-weight in milligrams

leaf_trt: Whether the leaf disk comes from a purple (p) or white (w) morph. Each leaf disk is ordered in a clockwise fashion, separated by a dash.

percent_herb: Percent herbivory on each leaf disk in the same order is leaf_trt

cat_post_wt: Caterpillar post weight in milligrams

date_experiment_setup: year-month-day of when of the experiment was setup

date_experiment_takedown: year-month-day of when the experiment ended

notes: general notes

dead: Did the caterpillar die by the end of the experiment? (1: yes, 0: no)

Code

DRFDS_analysis.html

The knitted output of the manuscript analyses

DRFDS_analysis.Rmd

The code for manuscript analyses

DRFDS_analysis_utils.R

Some functions used in DRFDS_analysis.Rmd for analysis.

Dependencies

A list of code dependencies, including their version numbers, can be found in the file dependencies.txt

Usage

Do whatever you want with the data. For questions, email Vincent Pan (vsbpan [at] gmail [dot] com).