PLANT RESPONSE TO INCREASED TEMPERATURE AND HERBIVORY Dejeanne Doublet // Terrestrial Ecology // John Parker Lab

WITH CLIMATE CHANGE, GLOBAL TEMPERATURES WILL CONTINUE TO RISE Why temperature and herbivory? Climate change is a powerful driver of ecological, social, and economic change, and Is expected to increase with ongoing globalization. Environmental temperature drives a number of important ecological interactions, including competition, predation, and herbivory, by determining the metabolic rates of ectothermic organisms In summary, we show that herbivory, and therefore potential top-down control of plant biomass, is highly contingent upon environmental temperature. Source: NASA

INSECT HERBIVORY DRIVES ECOLOGICAL AND EVOLUTION CHANGE IN PLANTS The consumption of plants by insect herbivores represents one of the dominant species interactions on Earth and has been hypothesized to play a strong role in the diversification of plant species and their traits

But little is known about how TEMPERATURE AFFECTS HERBIVORY The ecology and evolution of plant-herbivore relationships is, in part, governed by the reciprocal nature of their interaction and the complexity of communities. For example, plant traits and plant community structure are critical for determining insect occurrence and attack rates 

TEMPERATURE INCREASES CHANGE INSECT HERBIVORY PATTERNS In 2014, Lemoine, Parker and Burkepile showed that increased temperature had variable effects on herbivory rates.  Here we characterized the effect of temperature on herbivory rates for 21 herbivore-plant pairs, encompassing 14 herbivore and 12 plant species. We show that overall consumption rates increase with temperature between 20 and 30 °C but do not increase further with increasing temperature. However, there is substantial variation in thermal responses among individual herbivore-plant pairs at the highest temperatures. 

TEMPERATURE INCREASES CAN CAUSE CHANGES IN INSECT HERBIVORY PATTERNS In 2014, Lemoine et al. showed that increased temperature had variable effects on herbivory rates. But how does this relate to climate change? Next step: Grow plants under different temperatures with and without herbivores Not related to climate change because plants were not grown under different temps, next step grow plants under diff temps with and without herbivores

Our Question: How do temperature and herbivory affect plant fitness?

THE SET-UP Study site is right here on SERC property. Garden by the green house out back towards Education Center that Nate has spent the last couple of years putting together. Made up of 16 main plots where we can manipulate both temperature and herbivory.

THE SET-UP WARMED + HERBIVORY WARMED, NO HERBIVORY AMBIENT + HERBIVORY AMBIENT, NO HERBIVORY 4 treatments

Bird’s Eye View of Plots Warm Ambient Herbivory (Exposed to insects) No Herbivory (Netted) No Herbivory (Netted) Factorial, split-plot design N= 32

Heated vs. Ambient Temperatures Infrared heat, 3-4 degree increase, nighttime temp differences are greater, which actually portrays a climate change scenario more realistically than if temps were evenly increased all day.

A geneticist's dream plant Oenothera biennis aka common evening primrose A geneticist's dream plant Planted at the end of last summer

Why Oeonothera biennis? Native to eastern and central North American Little genetic variability between plants Host for various pollinators, seed predators and herbivores

The dominant herbivore: Japanese beetles (Popillia japinoca)

Introduced “Pest” Source: National Agricultural Pest Information System

BEETLES ARRIVED IN EARLY JUNE AND STAYED THROUGH MID AUGUST So the plants were allowed to grow under the different temperatures, then in June, the hungry Japanese beetles showed up and started doing their thing

Nearly all observed damage caused by JAPANESE BEETLES

Estimated Leaf Damage Percent Leaf Damage No Herbivory Herbivory

38% more beetles were found in ambient plots

PLANTS WITH NO HERBIVORY BEGAN FLOWERING FIRST, AND DISPLAYED MORE FLOWERS (AT FIRST)

AFFECT FLOWER PHENOLOGY? HOW DOES HERBIVORY AFFECT FLOWER PHENOLOGY? And how will temperature play a role?

Weekly Flower Counts

Flower Phenology Timeline Ambient Herbivory Treatment No herbivory Herbivory Flowers per Plant Warm

Flower Phenology Timeline Ambient Herbivory Treatment No herbivory Herbivory Peak # 1: Delayed by Herbivory Flowers per Plant Warm

Flower Phenology Timeline Peak # 2: Delayed by Herbivory + Expedited by Warming Ambient Herbivory Treatment No herbivory Herbivory Flowers per Plant Warm

Flower Phenology Timeline Ambient Herbivory Treatment No herbivory Herbivory Flowers per Plant Beginning of season: More flowers in NO Herbivory + Warmed treatments Warm

Flower Phenology Timeline Ambient Herbivory Treatment No herbivory Herbivory Flowers per Plant End of season: More flowers in Herbivory + Ambient treatments Warm

INSECT HERBIVORY DELAYS FLOWERING UNDER NORMAL AND WARM CONDITIONS BUT WHAT DOES THIS MEAN FOR OVERALL PLANT FITNESS?

What Defines Plant Fitness? Fitness is defined by a plant’s ability to reproduce. Fruit and seed production is a direct measurement of fitness. Ability to reproduce  Drives evolutionary changes

To estimate fitness: 1. Count fruit 2. Estimate seed production 3 To estimate fitness: 1. Count fruit 2. Estimate seed production 3. Estimate seed mass

Fruit Count No Herbivory Herbivory Average Fruit / Plant

Fruit Count No Herbivory Herbivory Average Fruit / Plant

Seed Density within Fruit Ambient Warm No Herbivory Herbivory Number of Seeds per Gram Fruit

Seed Mass Ambient Warm No Herbivory Herbivory Seed Mass (mg)

Seed Mass Ambient Warm Seed Mass (mg) No Herbivory Herbivory Seed Mass (mg) Lots of small, light-weight seeds

To Summarize…. AMBIENT, NO HERBIVORY WARMED, NO HERBIVORY HIGH # of Fruit per Plant LOW Density of Seeds HIGH Seed Mass WARMED, NO HERBIVORY HIGH # of Fruit per Plant HIGH Density of Seeds LOW Seed Mass AMBIENT + HERBIVORY LOW # of Fruit per Plant HIGH Density of Seeds LOW Seed Mass WARMED + HERBIVORY HIGH # of Fruit per Plant HIGH Density of Seeds LOW Seed Mass Under Ambient conditions, Herbivory caused plants to produce fewer fruit concentrated with more, light-weight seeds When Warmed, Herbivory did not matter and plants produced a high amount of fruit that had lots of small, light-weight seeds

Conclusions 1 2 3 4 Both herbivory and temperature change the timing of flowering Herbivory decreased fruit production, only in ambient temperatures Warming deterred herbivory, contributing to an increase in the plant’s fruit production Temperature and herbivory have striking effects on plant phenology and fitness In summary, we show that herbivory, and therefore potential top-down control of plant biomass, is highly contingent upon environmental temperature.

Current Literature Herbivory reduced seed predation by 77% Plant benefits from leaf herbivory Leaf herbivory has little impact on lifetime reproductive output However, only 5 beetles were placed on each plant for 5 days

Furthering Current Research Our methods provide a more realistic approach to understanding herbivory effects on plant fitness Takes into account climate change, showing that temperature plays a major role in how herbivory affects plant fitness Potential further studies: taking into account seed predators, pollinators

Acknowledgements Nate Lemoine Dr. John Parker Megan Palmer Alison Cawood Dozens of volunteers and citizen scientists SERC Maintenance Lauren, Dan and everybody else who work hard to make SERC a wonderful place to live and work