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Research in the Eppley Lab

 

Spatial segregation of the sexes in Distichlis spicata: Understanding the evolution of ecological niches is a focal area of evolutionary ecology. This project examines the genetic, physiological, and ecological factors that allow male and female plants in the wetland grass species Distichlis spicata to have evolved and maintain different ecological niches. Despite the fact that sex ratio theory suggests that such a spatial structure should be highly disadvantageous in a sessile organism because it reduces mating success, patterns of intraspecific niche dimorphism, also known as spatial segregation of the sexes, are quite common in dioecious plants. Currently, we are using greenhouse experiments and plan to set up long-term reciprocal transplant experiments in the field to test evolutionary hypotheses and physiological mechanisms that have been proposed to explain spatial segregation of the sexes in D. spicata.

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More information on spatial segregation of the sexes in D. spicata can be found on our project website: SSS in Distichlis spicata

Students planting D. spicata seedlings at Tomales Bay, CA

 

 

 

Sex and extreme environments: Producing offspring by sexual reproduction is potentially genetically and physically risky, yet most Eukaryotes reproduce primarily via sexual rather than asexual reproduction. Many studies have found positive correlations between environmental stress and sexual reproduction, suggesting that under stressful conditions sex has an adaptive function. However, the correlation between sex and stress has not been found to extend to extreme environments, although there has been only a few studies in this area. Understanding how sex functions in extreme environments has striking implications for the evolution of sex, which may have evolved in organisms in extreme environments, and the maintenance of sex in organisms that inhabit extreme environments today. It has been suggested that when environmental stress is extremely high only a few genotypes are adaptive; if this is the case, then recombination would not be an adaptive strategy.

To test whether the positive correlation between genetic variation, sexual reproduction, and environmental stress occurs in the majority of environments except extreme environments, we are using bryophytes around geothermally heated hot springs as a model system. Preliminary data for this project were collected around hot springs on New Zealand’s North Island, and we are currently developing this project at Lassen Volcanic National Park, California. We plan to use a series of greenhouse experiments to determine the effects of environment and genetics in sexual versus asexual reproduction in extreme environments and to develop microsatellite markers for a handfull of bryophyte species to estimate the relationship between sexual reproduction and environmental stress.

We are growing several bryophyte species in the greenhouse that were collected from around fumeroles at Boiling Spring Lake and Devil's Kitchen at Lassen Volcanic National Park to determine the heat tolerance of individual species. Moss plants were found green and growing (see photo below) at soil surface temperatures above 58ºC, and soil temperatures at 10 cm of 77ºC.

PSU student, Camille Graves, collecting data on

moss communities at Lassen Volcanic National Park

Moss community around a fumarole

Boiling Spring Lake, Lassen

 

 

Moss mating systems: Although land plants evolved with mating systems that relied on motile sperm swimming across stressful environments for fertilization, this reliance has often been considered the weak link in the life-history of non-vascular plants. New research, however, suggests that moss sperm may actually move an order of magnitude farther than previously believed and possibly be dispersed by microarthropods, building on much earlier work suggesting arthropods as sperm vectors. We are using the emerging model system Ceratodon purpureus to comprehensively examine male mating success in light of recent findings.

Sex ratio variation in Bryum argenteum : We are testing hypotheses to explain the extreme female-biased sex ratio found in B. argenteum. Most moss species (>55 %) have separate sexes, and female-biased sex ratios predominate in moss species with this type of breeding system. However, little information is available on whether sex-specific differences in clonal growth or mortality account for the sex bias and whether these differences correlate with sex-specific differences in allocation to reproduction. Sex-ratio bias and environmental stress in mosses is particularly interesting in comparison to what we know about such interactions in angiosperms. In angiosperms with separate sexes, allocation to reproduction is generally higher in females than males, and females often occur in less stressful areas than males. In mosses, however, when conditions become stressful, male plants become less frequent and often disappear from populations altogether. Whether this indicates a difference in sex-specific stress-tolerance patterns in bryophytes versus angiosperms is unknown. For B. argenteum, a cosmopolitan moss species with separate sexes, this project aims to determine the relative costs of reproduction in males and females, the relative clone sizes of males and females, population sex ratios, and ecological correlates (if any) with sex ratio variation. These data will allow us to assess the proximate and ultimate mechanisms responsible for the extreme female-biased sex ratios found in this species.

The effects of Hedra helix management strategies in Portland, Oregon’s urban ecosystems: The aim of this project is to test the effects of management strategies for an invasive plant, Hedra helix (English Ivy), and overall habitat disturbance on native biodiversity in Portland, Oregon’s urban environment. The project is being conducted by undergraduates at Portland State University in collaboration with The No Ivy League, Forest Park, Portland and the City of Portland’s Parks and Recreation Department. The No Ivy League is a non-profit organization that has been removing H. helix from Portland parks for many years and has reliable management records that can be used for this study. Long term plots have been established in Himes Park to assess the effects of ivy management strategies on understory vegetation.

Collaborators:
Dr. Travis Glenn, University of Georgia, Savannah River Ecology Laboratory

Dr. Linley Jesson, University of Victoria, Wellington; University of New Brunswick

Dr. Phil Garnock-Jones, University of Victoria, Wellington

Dr. Nicholas McLetchie, University of Kentucky

Dr. John Pannell, University of Oxford

Dr. Todd Rosenstiel, Portland State University

Dr. Lloyd Stark, University of Navada, Las Vegas

Phil Taylor, University of Victoria, Wellington

Dr. Olga Tsyusko, University of Georgia, Savannah River Ecology Laboratory

Funding: