Water-induced stress influences the relative investment in cleistogamous and chasmogamous flowers of an invasive grass, Microstegium vimineum (Poaceae)

Abstract

Background: Global climate change has the potential to shape evolutionary trajectories of invasive species via many routes, including through changes in mating systems. Many cleistogamous (CL) plants adjust investment in CL (selfed) vs. chasmogamous (CH, potentially outcrossed) progeny across environmental gradients. However, the details of such adjustments are lacking for highly invasive plant species.

Aims: We used a highly invasive grass, Microstegium vimineum, as a model for understanding how changes in water-induced stress (including potential associated changes in soil nutrient availability) might affect mating systems and thus evolutionary change in invasive species. We predicted that plants would respond to increased water-induced stress through a relative reduction in investment in CL vs. CH reproduction (i.e., a decrease in the CL:CH ratio).

Methods: Under greenhouse conditions, we measured fecundity (number of inflorescences and florets per plant) as well as relative investment in CL vs. CH florets (CL:CH ratios for number of inflorescences, florets per inflorescence, overall florets) in response to three watering treatments approximating mesic (low) to inundated (high) conditions.

Results: Plant biomass was significantly lower in high-watering treatment relative to intermediate and low treatments, indicating that the high-water condition was stressful. Contrary to expectations, stressed plants significantly increased relative investment in CL reproduction, a pattern associated with decreased inflorescence number and increased numbers of CL florets per inflorescence.

Conclusions: We conclude that changes in water-induced stress could strongly influence realised rates of outcrossing in this invasive plant, leading to mating system evolution, and altered invasiveness.

Keywords:

• cleistogamy
• invasive species
• mating system
• phenotypic plasticity
• soil moisture
• water gradient

Acknowledgements

The authors thank L. Flory and J. Rudgers for providing seed and technical advice, and N. Deshpande and M. King for assistance in the greenhouse. The project was supported by Rice University funds and NSF DEB 0716868.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Division of Environmental Biology: [Grant Number 0716868]; Rice University.

Notes on contributors

Lesley G. Campbell

Lesley Campbell is a plant evolutionary ecologist interested in how plant mating systems affect the evolutionary trajectories of populations, especially focusing on weedy and invasive plants.

Loren P. Albert

Loren Albert is a Ph.D. candidate in Ecology and Evolutionary Biology, studying plant ecological physiology with a focus on forest responses to climate change.

Esra D. Gumuser

Esra Gumuser graduated from Rice University with a B.S. in EEB, is finishing her masters in biomedical science at Texas A&M and is planning to attend medical school in the near future.

Kenneth D. Whitney

Ken Whitney is an evolutionary ecologist with interests in the causes and consequences of interspecific hybridisation, maintenance and effects of genetic diversity, the evolution of genome size, and plant–animal interactions.