Award Abstract # 1655772
Effects of mating system change on population dynamics: an experimental test across competitive contexts

NSF Org: DEB
Division Of Environmental Biology
Recipient: TEMPLE UNIVERSITY-OF THE COMMONWEALTH SYSTEM OF HIGHER EDUCATION
Initial Amendment Date: March 28, 2017
Latest Amendment Date: June 23, 2022
Award Number: 1655772
Award Instrument: Continuing Grant
Program Manager: Betsy Von Holle
mvonholl@nsf.gov
 (703)292-4974
DEB
 Division Of Environmental Biology
BIO
 Directorate for Biological Sciences
Start Date: September 15, 2017
End Date: August 31, 2024 (Estimated)
Total Intended Award Amount: $677,357.00
Total Awarded Amount to Date: $721,425.00
Funds Obligated to Date: FY 2017 = $156,815.00
FY 2018 = $87,133.00

FY 2019 = $435,409.00

FY 2022 = $42,068.00
History of Investigator:
  • Rachel Spigler (Principal Investigator)
    rachel.spigler@temple.edu
Recipient Sponsored Research Office: Temple University
1805 N BROAD ST
PHILADELPHIA
PA  US  19122-6104
(215)707-7547
Sponsor Congressional District: 02
Primary Place of Performance: Temple University
1900 N. 12th St.
Philadelphia
PA  US  19122-6018
Primary Place of Performance
Congressional District:
02
Unique Entity Identifier (UEI): QD4MGHFDJKU1
Parent UEI: QD4MGHFDJKU1
NSF Program(s): Population & Community Ecology,
POP & COMMUNITY ECOL PROG
Primary Program Source: 01002223DB NSF RESEARCH & RELATED ACTIVIT
01001718DB NSF RESEARCH & RELATED ACTIVIT

01001819DB NSF RESEARCH & RELATED ACTIVIT

01001920DB NSF RESEARCH & RELATED ACTIVIT

01002021DB NSF RESEARCH & RELATED ACTIVIT

01002122DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 097Z, 102Z, 1228, 9178, 9251, SMET
Program Element Code(s): 112800, 118200
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.074

ABSTRACT

Habitat fragmentation, global pollinator declines, and land use change are rapidly transforming ecological conditions in plant populations. What is the fate of plant populations in this increasingly altered world? Interactions between plants and their pollinators are being disrupted in human-disturbed habitats, leading to increased rates of self-fertilization (seeds produced with pollen from the same flower vs. from another plant) by plants. Because offspring produced by self-fertilization are more likely to have decreased survival and reproduction, a major conservation concern relates to whether and how loss of pollinator services for individual plants scales up to influence plant population growth and persistence. This research will experimentally evaluate the impact of changes in the frequency of self-fertilization on population growth under different ecological conditions. The focal species is affected by habitat fragmentation and is classified as imperiled in several states. Findings will contribute broadly to our understanding of and ability to predict the fates of these and other similar plant and animal species in a changing world. Additionally, the researcher will implement outreach programs, leading educational programs in plant-pollinator interactions at yearly K-6 summer camps. Yearly survey data of wild populations will be collected by citizen scientists. A postdoctoral associate, graduate student, and numerous undergraduates will be trained in research and outreach skills.


This project employs a powerful experimental demographic approach to evaluate the impact of mating system (pattern of inbreeding) on population growth of a self-compatible plant, Sabatia angularis (rosepin), across competitive contexts. Selfing rate (0%, 25%, 50%, 75%, 100%) and competitive context (high vs. low interspecific competition) of experimental populations will be directly manipulated through hand pollinations and contrasting mowing regimes. The demographic fates of all individuals will be followed over three generations. Demographic data will be used to parameterize models from which population dynamics can be derived. The impact of selfing rate, competitive context, and their interaction on vital rates (growth, survival, fecundity) and population growth rate will be evaluated, including non-linear relationships. The underlying causes of observed changes (or similarities) in growth rate across experimental treatments will be investigated with additional demographic analyses. Demographic models will also be constructed to mimic the experimental mating-system gradient by incorporating prior static inbreeding depression estimates in silico and outcomes compared to experimental results. Research findings will further address the ecological impacts of genetic load, demographic costs of selection, and impacts of intraspecific variation on species coexistence.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Emel, Sarah L. and Wang, Shichen and Metz, Richard P. and Spigler, Rachel B. "Type and intensity of surrounding human land use, not local environment, shape genetic structure of a native grassland plant" Molecular Ecology , v.30 , 2021 https://doi.org/10.1111/mec.15753 Citation Details
Godineau, Claire and Theodorou, Konstantinos and Spigler, Rachel B "Effect of the Seed Bank on Evolutionary Rescue in Small Populations: Univariate and Multivariate Demogenetic Dynamics" The American Naturalist , v.204 , 2024 https://doi.org/10.1086/731402 Citation Details
Spigler, Rachel B. and Charles, Annmarie "Inbreeding Reduces Floral Longevity and Flower Size in the Mixed-Mating Biennial Sabatia angularis" International Journal of Plant Sciences , v.184 , 2023 https://doi.org/10.1086/724030 Citation Details
Spigler, Rachel B. and Maguiña, Rossana "Changes in female function and autonomous selfing across floral lifespan interact to drive variation in the cost of selfing" American Journal of Botany , v.109 , 2022 https://doi.org/10.1002/ajb2.1816 Citation Details
Spigler, Rachel B. and Woodard, Alyssa J. "Context?dependency of resource allocation trade?offs highlights constraints to the evolution of floral longevity in a monocarpic herb" New Phytologist , v.221 , 2018 10.1111/nph.15498 Citation Details
Walker, Mark J and Spigler, Rachel B "Experimental evidence of inbreeding depression for competitive ability and its population-level consequences in a mixed-mating plant" Frontiers in Plant Science , v.15 , 2024 https://doi.org/10.3389/fpls.2024.1398060 Citation Details

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Intellectual merit

Human activities are fragmenting natural habitats, shrinking plant populations that are vital to ecosystems. These smaller populations face higher inbreeding levels, as fewer plants mean closer relatives and more self-pollination in pollinator-poor areas. Inbreeding can reduce growth, survival, and reproduction, threatening population health. However, the role of ecological factors like competition and resource availability in shaping these effects is often overlooked. Our research investigated how inbreeding, competition, and environmental conditions interact to affect natural selection and population growth, using the native plant Sabatia angularis as a focal study system. We employed a multifaceted approach, including large-scale field experiments, demographic monitoring in both experimental and wild populations, multiple greenhouse experiments, and modeling.  At a broader scale, this comprehensive strategy enabled us to examine how ecological, genetic, and demographic processes interact to shape evolutionary outcomes and population persistence.

 

Our findings revealed that human land use isolates populations across the landscape, increasing inbreeding and reducing genetic diversity, with urban development having the strongest effects. In experimental populations, the effects of inbreeding varied with plant density and the type and frequency of competitors (outcrossed vs. inbred, presence/absence of other species). Outcrossed plants generally grow better and are superior competitors. However, this means that they compete more aggressively with each other for resources, leading to stronger density-dependent dynamics compared to inbred populations. As a result, average plant size at high densities is similar across populations regardless of inbreeding levels. These results highlight how competition can mask effects of inbreeding depression on growth, potentially providing a misleading impression of population stability.

 

Simulation models provided deeper insights into the interaction between competition and inbreeding. While inbreeding depression in initial plant size showed limited impact under resource competition, even small disadvantages in growth rate for inbred individuals could lead to significant fitness reductions. Competitive gains by outcrossed plants and reduced competition among inbred plants with higher rates of inbreeding are predicted to moderate population declines but not eliminate them.

 

Further experimental studies revealed novel effects of inbreeding, such as shortening the lifespan of individual flowers, which could hinder reproduction in areas with fewer pollinators by reducing the time available for pollen transfer. Resource availability emerged as a critical factor in how plants allocate resources between maintaining existing flowers and producing new ones, suggesting unexpected ways in which inbreeding depression and resource availability can interact to influence fitness outcomes.

 

Through mathematical and simulation models, we investigated how interactions between population dynamics and evolution shape population persistence under environmental change. Many plant species have seed banks—dormant seeds in the soil that remain viable for years. While seed banks may harbor outdated traits that reduce fitness, we demonstrate that under certain conditions, storing seeds from extreme years can enhance adaptation and promote population persistence by acting as steppingstones to novel environments. These findings have broad implications for a wide range of organisms with long-lived dormant stages and offer valuable insights for conservation strategies, such as prioritizing seeds from stressful years to preserve traits better aligned with future environmental challenges.

 

Broader Impacts

The project offered extensive training and mentorship opportunities, fostering the development of two PhD students and a postdoctoral associate while providing research experiences for 24 undergraduate students. These undergraduates gained valuable hands-on experience and developed essential skills through their involvement in fieldwork, laboratory experiments, and greenhouse studies. Additionally, the project employed and trained three research technicians, enhancing their professional growth and future career opportunities.

 

Our research advances the understanding of factors driving population declines, providing critical insights for the conservation of plant species in fragmented habitats. Focusing on S. angularis, a species at risk of extinction throughout its range, this study was conducted in the serpentine grasslands of eastern North America—a rare and ecologically significant habitat. The research team shared findings with stakeholders and advised on restoration measures and conservation planning in these unique ecosystems.

 

Educational outreach remained a core component of the project. The research team developed hands-on learning activities for elementary school-aged children, enriching summer nature camps and kindergarten classrooms. These activities not only provided valuable public education but also offered critical outreach training for graduate and undergraduate students. 


Last Modified: 12/06/2024
Modified by: Rachel B Spigler

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