Shanna Carney

Lab Research:

Locoweed Hybridization
Origin and Hybridization of Knapweeds
Invasive Ants and Seed Dispersal
Ant Dispersal of Invasive Plant Seeds
Literature Cited


Locoweed Hybridization

        Colorado has several species of Oxytropis or locoweed, and hybridization between O. sericea and O. lambertii occurrs when the two species come in contact.  The white-flowered locoweed, O. sericea, flowers earlier than the purple-flowered species, O. lambertii.  It has been suggested that introgression (i.e., movement of genes from one species into another due to hybridization) may be unidirection due to this phenological difference (Bill Weber, pers. comm.).  Thus, I am investigating patterns of gene flow in hybridizing populations of the two species, such as that seen to the left from Phantom Canyon Ranch, Livermore, CO.  I also am interested in factors that affect hybridization frequencies in this species pair.  During the summer (2001), with the assistance of grad students Linda Courter and Brooke Byerley, I studied patterns of pollinator visitation to determine whether pollinator constancy or pollinator specificity affects interspecific movement of pollen in mixed populations.  This study utilized artificial arrays of cut inflorescences in addition to natural mixed populations.  It does not appear that pollinators discriminated among the two species and their hybrids in their visitation patterns, but those data are currently being analyzed.
 

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Origin and Hybridization of Knapweeds

        This project is being done in collaboration with Dr. Ruth Hufbauer from the Department of Bioagricultural Sciences and Pest Management at Colorado State University and our joint graduate student Robin Marrs.  See thier web pages for more details.  My own efforts are focused specifically on the hybridization aspects of the project.
        The invasions of diffuse and spotted knapweed (Centaurea diffusa and C. maculosa) into the western United States in general, and the state of Colorado in particular, are associated with reductions in biodiversity and in forage for wildlife and livestock.  The fundamental goals of this collaborative research are to pinpoint the origins of these economically important invasive weeds and examine the genetic and ecological effects of their introductions.  These invasive weeds share multiple biological control agents, thus knowing their origins will allow for more precise efforts at their joint control.  If the species are hybridizing in their introduced range in addition to their native range, then this interspecific recombination could have significant impacts on biocontrol efforts. Therefore, knowledge of the extent of hybridization in the United States will be important for successful biocontrol efforts as well.  Finally, results will provide information about the role of selection on invading plant species in increasing weediness in the introduced range.

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Invasive Ants and Seed Dispersal

         Invasive species are a major threat to biodiversity because they outcompete or predate native species, sometimes leading to their extinction.  Direct effects of invasive species on communities have been well documented.  Less well understood are the indirect effects of invasions due to the loss of mutualists.  Because the invasive Argentine ant,Linepithema humile, decreases the diversity of native ants (and other arthropods) where it is found, it is possible that invasions of this species may have dramatic fitness consequences for plants with ant-dispersed seeds (i.e., myrmecochores).  The long-term goal of this research is to investigate the indirect effects of Argentine ant presence on the fitness of myrmecochores found in invaded regions of coastal Southern California.  Specifically, I am focusing on two California myrmecochores, Claytonia perfoliata (miner's lettuce) and Dendromecon rigida (tree poppy).   I am comparing the collection behavior of native and Argentine ants toward seeds of these species. I also am examining the effects of seed dispersal by ants (or a lack thereof) on predation by rodents and other larger seed predators.  The fates of these seeds following collection by native and Argentine ants will then be compared in the lab of my collaborator, Dr. David Holway, at UC San Diego.  This aspect of the project will allow me to determine whether seeds are suffering predation by ants after they enter a nest, or if they have been taken to a safe site where predation is minimized.  This project will allow a more complete understanding of the importance of indirect effects of biological invasions.  Additionally, the magnitude of the resulting effects will inform the question of how strong the links among plants and their ant dispersers are.

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Native Ant Dispersal of Alien Plant Seeds

        Although myrmecochory is referred to as a seed dispersal mutualism, the interaction between ant and plant species is facultative and loosely coupled.  The result of this generalized interaction is that the mutualism may still function under novel conditions, such as when the plant species is alien and has not coevolved with the ant species present.  This interaction and its outcome is the focus of another of my research projects.

        Despite the fact that many of the country’s most important rangeland weeds bear seeds with elaiosomes (Pemberton and Irving 1990), structures that attract ants and lead to seed dispersal by ants, few studies have examined the role of native ants in plant invasions.  Thus, the role of ants in plant invasions still remains unclear.  I currently am investigating this question using several invasive plant species found in Fort Collins, CO and the surrounding area.  These include Canada thistle (Cirsium arvense), musk thistle (Carduus nutans), and leafy spurge (Euphorbia esula).  Studying the role of native ants in alien plant persistence and spread involves assessing the behavior of ants toward seeds of these species, observing the frequency of dispersal of the seeds, and assessing the fitness consequences of dispersal by ants.

        I recently (summer 2003) participated in the Ant Course at the Southwestern Research Station in Portal, AZ.  I highly recommend this course to any aspiring myrmecologists as a way to learn about taxonomy, behavior, and ecology of ants.  This course gave me a better understanding of ants and an increased ability to identify them.  In addition, it was tons of fun!



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The Carney Lab

Last Updated 8/26/03 by Shanna Carney.
secarney@lamar.colostate.edu
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