1. Life in a leaf
What are the fitness consequences of simultaneous or serial attack by different natural enemies? Does this influence population dynamics or community structure?
We are focusing on these three-way interactions between plants, herbivores and plant pathogens. We use Scaptomyza leafminers, and mustard plants hosts and Pseudomonas plant pathogens in laboratory and field experiments. In the field we work principally at the Rocky Mountain Biological Laboratory (RMBL). At the RMBL we take advantage of the fact that the mustard Cardamine cordifolia is heavily attacked by the host-specific Scaptomyza nigrita and Pseudomonas bacteria (Parris Humphrey, Ph.D. student and Martha Villalobos, undergraduate student). We focus on understanding the strength and direction of interactions between each. We are also focusing on understanding the contribution of the microbiome of the Scaptomyza gut to its ecology. A preliminary screen by Parris Humphrey has indicated the presence of several bacterial symbionts in larvae and adult flies, which may play a key role in their ability to colonize and use resources from toxic host plants...recent work by Artyom Kopp's laboratory has shown that diverse Drosophila species seem to have fairly predictable associations with bacterial lineages from diverse phyla. Whether this extends to herbivorous Scaptomyza species is unknown and something in which are are keenly interested.
We are focusing on these three-way interactions between plants, herbivores and plant pathogens. We use Scaptomyza leafminers, and mustard plants hosts and Pseudomonas plant pathogens in laboratory and field experiments. In the field we work principally at the Rocky Mountain Biological Laboratory (RMBL). At the RMBL we take advantage of the fact that the mustard Cardamine cordifolia is heavily attacked by the host-specific Scaptomyza nigrita and Pseudomonas bacteria (Parris Humphrey, Ph.D. student and Martha Villalobos, undergraduate student). We focus on understanding the strength and direction of interactions between each. We are also focusing on understanding the contribution of the microbiome of the Scaptomyza gut to its ecology. A preliminary screen by Parris Humphrey has indicated the presence of several bacterial symbionts in larvae and adult flies, which may play a key role in their ability to colonize and use resources from toxic host plants...recent work by Artyom Kopp's laboratory has shown that diverse Drosophila species seem to have fairly predictable associations with bacterial lineages from diverse phyla. Whether this extends to herbivorous Scaptomyza species is unknown and something in which are are keenly interested.
2. Adaptive divergence between sun and shade populations of the mustard plant Cardamine cordifolia
What factors shape species distributions? Can populations diverge even when gene flow is high? Is there habitat specialization by plants when herbivory rates and light quality are consistently inversely related?
To address these questions we study phenotypic plasticity and adaptation to sun and shade populations of Cardamine cordifolia and in desert mistletoe (see below). For the C. cordifolia work, a bit of background is necessary. Professor Svata Louda studied the interaction between C. cordifolia and its herbivore community for years at the RMBL showing that the fly causes significant declines in host plant fitness and likely drives the skewed distribution of this plant. It is largely restricted to the shade, where herbivores are less active--a textbook exmaple of how natural enemies can shape primary producer population structure. We are testing if local adaptation to shade vs. sun has occurred in the host plant using common gardens, herbivory assays and functional genomics at RMBL and, more broadly, whether there is local adaptation for common host genotypes in S. nigrita across its geographic range, from British Columbia to New Mexico (Andy Gloss, Ph.D. student). Evidence from herbaria suggests that the interaction between plant and leafminer is long-standing and we are uncovering the genetic bases of reciprocal evolution between the two species, which is facilitated by their close relationships with model organisms. Photos from a large common garden experiment (3 sun and 3 shade gardens) involving 500 plants at RMBL and a lot of hard work are below, led by Andy Gloss (Ph.D. student) and Joey Frazier (undergraduate researcher) in 2011. Andy and Joey built a Swiss Family Robinson-esque watering system when the spring we were using to water our garnens dried up, bringing down water from several hundred feet uphill to our six gardens located hundreds of feet apart on the side of Gothic Mountain. This research has revealed some new evidence for potential local adaptation in C. cordifolia growing in deep shade and open bog (sunny) habitats, a manuscript exists that is being led by Parris Humphrey (Ph.D. student) and Andy Gloss (Ph.D. student). We are now pursuing genome scans using next-generation sequencing technology to determine if alleles can be identified associated with each habitat type in bittercress.
To address these questions we study phenotypic plasticity and adaptation to sun and shade populations of Cardamine cordifolia and in desert mistletoe (see below). For the C. cordifolia work, a bit of background is necessary. Professor Svata Louda studied the interaction between C. cordifolia and its herbivore community for years at the RMBL showing that the fly causes significant declines in host plant fitness and likely drives the skewed distribution of this plant. It is largely restricted to the shade, where herbivores are less active--a textbook exmaple of how natural enemies can shape primary producer population structure. We are testing if local adaptation to shade vs. sun has occurred in the host plant using common gardens, herbivory assays and functional genomics at RMBL and, more broadly, whether there is local adaptation for common host genotypes in S. nigrita across its geographic range, from British Columbia to New Mexico (Andy Gloss, Ph.D. student). Evidence from herbaria suggests that the interaction between plant and leafminer is long-standing and we are uncovering the genetic bases of reciprocal evolution between the two species, which is facilitated by their close relationships with model organisms. Photos from a large common garden experiment (3 sun and 3 shade gardens) involving 500 plants at RMBL and a lot of hard work are below, led by Andy Gloss (Ph.D. student) and Joey Frazier (undergraduate researcher) in 2011. Andy and Joey built a Swiss Family Robinson-esque watering system when the spring we were using to water our garnens dried up, bringing down water from several hundred feet uphill to our six gardens located hundreds of feet apart on the side of Gothic Mountain. This research has revealed some new evidence for potential local adaptation in C. cordifolia growing in deep shade and open bog (sunny) habitats, a manuscript exists that is being led by Parris Humphrey (Ph.D. student) and Andy Gloss (Ph.D. student). We are now pursuing genome scans using next-generation sequencing technology to determine if alleles can be identified associated with each habitat type in bittercress.
3. Mistletoes, birds, and mesquites
What factors shape species distributions? Can populations diverge even when gene flow is high? What is the role of genetic diversity in disease transmission dynamics? What is the role of vector behavior in shaping parasite distributions? Do parasites have ecosystem-level consequences?
This project, which is just getting underway in the lab, is examining current and historical interactions among three key players in the Sonoran Desert: The desert mistletoe, Phoradendron californicum, its main disperser, the Phainopepla (Phainopepla nitens), and its host trees in the bean family (Palo verdes, acacias, mesquites and Ironwood). We are developing a panel of variable microsatellite loci for the mistletoe and the bird to test hypotheses on whether these two interacting and mutually interdependent species exhibit population genetic co-structure. Phainopepla home ranges will be estimated using banding and radio telemetry. We are testing for local adaptation to different host plant species by the mistletoe using reciprocal transplants. Ultimately, we'd like to know how mistletoe infections influence host plant population growth rates, community structure and ecosystems.
Importantly, this system has been studied in detail by other scientists formerly at the University of Arizona (Dr. Julian Aukema and Dr. Carlos Martínez del Rio), and their insight has given us fantastic hypotheses to test, particularly relating to how interactions between these species shapes their population genetic structures.
Mistletoes are a native and natural part of the Sonoran Desert, typically only killing trees during extreme droughts (http://www.sciencedirect.com/science/article/pii/S0140196306002874). They are not introduced species, but rather are indigenous, keystone species for myriad other species that use their fruits and vegetative tissues as food and habitat. For example the Phainopepla (called kuigam, meaning 'mesquite dweller' by the O'odham people--Nabhan et al. 1982) is specially adapted to process fruits from the mistletoe. Without this plant, the bird would most likely not be able to survive in the Sonoran Desert winters. The same is true for the beautiful Great Purple Hairstreak butterfly, which cannot survive without foliage from this plant. Remarkably, desert mistletoe fossils are present in packrat middens from the Sonoran Desert that were radiocarbon dated to > 8,000 years before present. University of Arizona undergraduate honors thesis student Lauren Johnston and PERT postdoctoral fellow Dr. Jen Koop are involved in this project.
This project, which is just getting underway in the lab, is examining current and historical interactions among three key players in the Sonoran Desert: The desert mistletoe, Phoradendron californicum, its main disperser, the Phainopepla (Phainopepla nitens), and its host trees in the bean family (Palo verdes, acacias, mesquites and Ironwood). We are developing a panel of variable microsatellite loci for the mistletoe and the bird to test hypotheses on whether these two interacting and mutually interdependent species exhibit population genetic co-structure. Phainopepla home ranges will be estimated using banding and radio telemetry. We are testing for local adaptation to different host plant species by the mistletoe using reciprocal transplants. Ultimately, we'd like to know how mistletoe infections influence host plant population growth rates, community structure and ecosystems.
Importantly, this system has been studied in detail by other scientists formerly at the University of Arizona (Dr. Julian Aukema and Dr. Carlos Martínez del Rio), and their insight has given us fantastic hypotheses to test, particularly relating to how interactions between these species shapes their population genetic structures.
Mistletoes are a native and natural part of the Sonoran Desert, typically only killing trees during extreme droughts (http://www.sciencedirect.com/science/article/pii/S0140196306002874). They are not introduced species, but rather are indigenous, keystone species for myriad other species that use their fruits and vegetative tissues as food and habitat. For example the Phainopepla (called kuigam, meaning 'mesquite dweller' by the O'odham people--Nabhan et al. 1982) is specially adapted to process fruits from the mistletoe. Without this plant, the bird would most likely not be able to survive in the Sonoran Desert winters. The same is true for the beautiful Great Purple Hairstreak butterfly, which cannot survive without foliage from this plant. Remarkably, desert mistletoe fossils are present in packrat middens from the Sonoran Desert that were radiocarbon dated to > 8,000 years before present. University of Arizona undergraduate honors thesis student Lauren Johnston and PERT postdoctoral fellow Dr. Jen Koop are involved in this project.
