Population dynamics and reproductive ecology of the gynodioecious prairie species Lobelia spicata Lam. (Campanulaceae)

Ruffatto, Danielle

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Description

Title

Population dynamics and reproductive ecology of the gynodioecious prairie species Lobelia spicata Lam. (Campanulaceae)

Author(s)

Ruffatto, Danielle

Issue Date

2012-06-27T21:19:06Z

Director of Research (if dissertation) or Advisor (if thesis)

Molano-Flores, Brenda

Department of Study

Plant Biology

Discipline

Plant Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Date of Ingest

2012-06-27T21:19:06Z

Keyword(s)

• Gynodioecy
• Lobelia spicata
• female frequency
• latitudinal gradient
• abiotic conditions

Abstract

Lobelia spicata Lam. (Campanulaceae) is a common prairie species found throughout Illinois. Its breeding system, gynodioecy, is relatively rare, and is characterized by having female and hermaphrodite plant morphs coexisting within populations. Although some data on the reproductive ecology of L. spicata has been gathered, the population and breeding system dynamics of this species remain unexplored. Consequently, a literature review and a field study were conducted where population and reproductive output and fitness data were collected for 11 L. spicata populations across northern and central Illinois during 2008 and 2009. Chapter 1 provides a summary of the literature review and includes the classification of and phylogenetic relationships within Lobelia L. for determination of L. spicata’s closest relatives. Information is also provided on breeding system distribution within Lobelia, as well as patterns of variation in pollination type, floral compatibility and pollination syndrome for the closest relatives of L. spicata. It was found that the classification of Lobelia has undergone multiple transformations throughout history, but the most recent system divides the genus into 18 sections based on phenotypic characters, biogeographical patterns and molecular phylogenies. L. spicata is grouped with the 21 other eastern North American species into Lobelia section Lobelia. Members of Lobelia are exclusively synoecious with the exception of section Hypsela, which contains dioecious species, and section Lobelia, which contains two gynodioecious species including L. spicata. For L. spicata’s closest relatives in Lobelia section Lobelia, only 6 species out of 22 have had data on pollination type and floral compatibility collected, and among those species the combinations are highly variable. Further, 21 of the 22 species (e.g. L. spicata) are insect-pollinated with white, blue or purple corollas. L. cardinalis is the only species exhibiting an avian pollination syndrome, most likely due to its large, red flowers. It was concluded that the construction of comprehensive, molecular-based phylogenies for the North American Lobelia as well as additional research on individual Lobelia species will increase understanding of breeding system evolution within the genus. Chapter 2 examines the population dynamics of L. spicata overall by examining the impact of population size and density on reproductive output and fitness measurements. No relationship was found between population size or density and any of the four reproductive measurements across two sampling years with three exceptions. Population size exhibited a marginally significant negative correlation with fruit set in 2008 and a positive correlation with seed number per fruit in 2009, while population density was positively correlated with seed number per fruit in 2008. Size of L. spicata populations may be having an indirect impact on fruit set and seed number per fruit during intermittent years due to its influence on the availability of compatible, out-crossed pollen. Alternatively, high plant density may be linked to increased visitation of flowers by pollinators, causing an increase in the number of seeds produced per fruit. Thus, population dynamics such as size and density could impact future reproductive success and population persistence in L. spicata. Chapter 3 examines the gynodioecious breeding system of L. spicata to determine if reproductive differences exist between plant genders, and if so how those differences are impacted by female frequency and/or gender density. Female plants were found to produce greater fruit sets, seed numbers per fruit and percent seed germination than hermaphrodites, though these reproductive gender differences varied among populations and between 2008 and 2009. Female frequency, female density and hermaphrodite density did impact the gender-based reproductive measurements, particularly fruit set, presumably due to their influence on pollen quantity and quality. Chapter 4 assesses whether two abiotic factors, temperature and precipitation, are driving the relationship between female frequency, gender morph density and reproduction measurements across a latitudinal gradient. Female frequency within L. spicata populations was negatively correlated with latitude, such that there were higher percentages of females in southern than in northern populations. Temperature is likely the driving force behind the latitude/female frequency relationship because it negatively correlated with latitude and positively correlated with temperature across sampling years. However, less precipitation in southern populations during intermittent years may also account for some of the latitudinal variation in female frequency. Gender-based reproductive success measurements and female advantage did not correlate with geographic location or abiotic conditions with few exceptions. Both hermaphrodite and female seed biomass and percent seed germination were negatively correlated with latitude and positively correlated with temperature. Thus, stressful conditions such as high temperatures and low precipitation may somehow favor the success of female plants within populations of L. spicata, while high temperatures result in the production of larger and better germinating seeds by hermaphrodite and female plants. In summary, this study has provided detailed information on many aspects of Lobelia spicata’s reproductive ecology that was formerly unknown. By starting with the larger issues of breeding system distribution within Lobelia (Chapter 1) and species-level reproductive variation with population size and density (Chapter 2), it was possible to critically evaluate trends existing due to L. spicata’s gynodioecious breeding system such as gender morph differences and the impact of female frequency and gender morph density on female advantage in reproduction (Chapter 3). Further, formerly unknown patterns of latitudinal variation in female frequency and reproduction were uncovered for the species (Chapter 4). In a broader context, these data could have important implications for the management of species with polymorphic breeding systems in the face of global climate change.

Graduation Semester

2012-05

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Copyright 2012 Danielle Ruffatto

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