Progress 08/01/00 to 07/31/04
Outputs
Barbed goatgrass, Aegilops triuncialis L., is a noxious annual grass that has been present in the California flora since the early part of this century, but which has been rapidly expanding its range in recent years. In addition to invading grasslands on normal soil, this species is unusual in that it is capable of invading habitats generally thought to be invasion resistant, such as serpentine habitats and other low fertility soils. We know very little about the importance of adaptive evolutionary change in promoting the spread of weed populations. In particular, the role of maternal environmental effects (also known as trans-generational phenotypic plasticity) in promoting the expansion of weed populations is essentially unknown. A recently completed growth chamber study on photosynthesis and water-use efficiency suggested that maternal environment influences a variety of physiological and morphological traits in goatgrass seedlings. Seedlings produced from mothers
grown in two soil types within a common garden exhibited significantly different rates of photosynthesis. Photosynthetic rates were higher in seedlings from mothers grown in more fertile sandy loam soils compared to progeny from mothers grown in nutrient deficient serpentine soil. This overall maternal environment effect on seedling photosynthesis was also found for progeny produced from reciprocal transplant studies along serpentine soil gradients in the field. When compared in a common garden, seedlings whose mothers grew in nutrient poor "edge" habitats had lower rates of photosynthesis than seedlings of mothers grown in higher nutrient "core" habitats. Seed size has been shown to be an important trait in studies of maternal environmental effects in plants. This appears to be true in goatgrass; seed size in progeny produced by mothers in edge habitats was larger than in progeny produced in core habitats (regardless of maternal genotype). For example, at one serpentine site, seeds
produced in edge habitats were over 25% larger than seeds produced in core habitats. This maternally induced difference in seed size may have fitness consequences because it translates into subsequent differences in plant size. The likelihood that maternal environmental effects are adaptive is greatly increased if the environment of the offspring is similar to that of the mother. This similarity of maternal and progeny environments is, in turn, more likely if dispersal of progeny from the mother is limited. Demographic studies on goatgrass indicate that local dispersal of goatgrass seed is highly limited. Greater than 90% of the seeds fall within a meter of the parent plant and the longest dispersal distance recorded was less than 5 meters. This demographic data suggests that local dispersal within a site is limited and thus may foster the expression of adaptive maternal effects. Taken together, the initial results from our growth chamber, common garden, reciprocal transplant, and
demographic studies suggest that maternal effects may be an important form of adaptive phenotypic plasticity in goatgrass populations invading serpentine sites in California.
Impacts
Barbed goatgrass is a noxious annual grass that has been rapidly expanding its range in recent years. The rapid invasion of rangelands by this unpalatable forage grass has increased economic loss by reducing range productivity and forage quality. We investigated the mechanisms by which goatgrass adapts to different rangeland environments in order to help develop effective control measures. We found that both genetic changes and phenotypic plasticity were important in facilitating the spread of this range weed.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Barbed goatgrass, Aegilops triuncialis L., is a noxious annual grass that has been present in the California flora since the early part of this century, but which has been rapidly expanding its range in recent years. The rapid colonization of rangelands by this unpalatable forage grass has resulted in increasing economic loss in terms of range productivity and forage quality. In addition to invading grasslands on normal soil, this species is unusual in that it is capable of invading habitats generally thought to be invasion resistant, such as serpentine habitats and other low fertility soils. Although it is likely that selective gradients are strong along weed invasion fronts, we know very little about the importance of adaptive evolutionary change in promoting the spread of weed populations. The relative role of phenotypic plasticity and genetic differentiation in promoting the expansion of weed populations is essentially unknown. Common garden study. We sampled ten
spreading populations of A. triuncialis located throughout California to investigate the interaction between biotic and abiotic selection pressures during invasion and the characteristics that enable this species to be a successful invader. Using a common garden approach that simulates edge and core growth environments for both competitive and stress gradients, we studied the relative importance of adaptive selection and phenotypic plasticity in the invasion process. Analyses of flowering time in the common garden study indicate that phenotypic variation in goatgrass phenology is highly dependent on the type of gradient under consideration. In the serpentine gradient plantings there was a strong effect of planting environment on flowering time while in the competition gradient there was little variation between core and edge plantings. The delay in flowering that we observed for goatgrass populations in the serpentine soils may result from the well-known low fertility and coarse
texture of these soils. Reciprocal transplant study. To examine the potential for rapid local adaptation along invasion fronts, field reciprocal transplant experiments using bulked seed from six of the populations (three from stress gradients and three from competitive gradients) were initiated at each of the seed collection sites. Data on establishment suggest that there may be significant genetic differences between core and edge populations in seedling survival. Analyses partitioned by gradient type indicated that differences between core and edge sources were significant only for the serpentine stress gradient. In both core and edge planting sites along serpentine gradients, percent seedling survival of edge populations was higher than percent survival in core populations. The difference in seedling survival for serpentine edge populations may be caused by differences in seed size and may reflect selection for larger seed size along the edges of invasion fronts into serpentine
habitats.
Impacts
Barbed goatgrass is a noxious annual grass that has been rapidly expanding its range in recent years. The rapid invasion of rangelands by this unpalatable forage grass has increased economic loss by reducing range productivity and forage quality. We investigated the mechanisms by which goatgrass adapts to different rangeland environments in order to help develop effective control measures.
Publications
- Rice KJ, Gerlach JD, Dyer AR, and McKay J 2003 Evolutionary changes along invasion fronts in a range weed. Seventh International Rangeland Congress Proceedings. (N, Allsop, A.R. Palmer, S.J. Milton, G.H. Kerley, K.P. Kirkman, R. Hurt, and C. Brown, eds.). Durban, South Africa.
- Dyer AR, Rice KJ, and Gerlach JD 2003 Adaptive variation in an invasive annual grass: germination patterns of Aegilops triuncialis in California, USA. Seventh International Rangeland Congress Proceedings. (N, Allsop, A.R. Palmer, S.J. Milton, G.H. Kerley, K.P. Kirkman, R. Hurt, and C. Brown, eds.). Durban, South Africa.
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Progress 01/01/02 to 12/31/02
Outputs
To examine the potential for rapid local adaptation along invasion fronts, field reciprocal transplant experiments using bulked seed from six of the populations (three from stress gradients and three from competitive gradients) were initiated at each of the seed collection sites. At each site we established 10 seed planting blocks within both edge and core microsites. Within each block, core and edge seed were planted separately in subplots with nine seeds from each microsite seed source. To measure the potential for local adaptation, within each plot the demographic parameters of plant survival and net reproductive rate (seed "out" / seed "in") were measured for each of the microsite planting cohorts. In addition, to better understand potential mechanisms of local adaptation, we also measured individual plant traits such as plant flowering time, plant height, and plant leaf/tiller number. A full demographic analysis of the reciprocal transplant experiment is still
underway but data on establishment suggest that there may be significant genetic differences between core and edge populations in seedling survival. Gradient type (competitive vs. stress) by microsite population interactions were significant (p < 0.05) indicating that population differences in seedling survival between edge and core seed sources are gradient dependent. Analyses partitioned by gradient type indicated that differences between core and edge sources were significant (p < 0.0005) only for the serpentine stress gradient. In both core and edge planting sites along serpentine gradients, percent seedling survival of edge populations was higher (mean + 1 s.e. = 63.9 + 3.4 %) than percent survival in core populations (51.3 + 3.5 %). In contrast, seedling survival along competitive gradient microsites was almost identical for core and edge populations (66.7 + 2.2 % and 67.4 + 2.5 %, respectively). The difference in seedling survival for serpentine edge populations may be caused
by differences in seed size and may reflect selection for larger seed size along the edges of invasion fronts into serpentine habitats. These analyses focus only on early survival; demographic analysis is currently underway of the reproductive output from these populations. These additional analyses, when coupled with studies currently underway on the role of maternal effects on seed size, will allow a better understanding of the role of adaptation and plasticity in goatgrass invasion dynamics.
Impacts
Barbed goatgrass is a noxious annual grass that has been rapidly expanding its range in recent years. The rapid invasion of rangelands by this unpalatable forage grass has increased economic loss by reducing range productivity and forage quality. We will investigate the mechanisms by which goatgrass adapts to different rangeland environments in order to help develop effective control measures.
Publications
- Rice K., Gerlach J., Dyer A., and McKay J. 2003. Evolutionary changes along invasion fronts in a range weed. Proceedings of the International Rangeland Congress, Durban, South Africa. (IN PRESS)
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Progress 01/01/01 to 12/31/01
Outputs
Barbed goatgrass, Aegilops triuncialis L., is a noxious annual grass that has been present in the California flora since the early part of this century, but which has been rapidly expanding its range in recent years. The rapid colonization of rangelands by this unpalatable forage grass has resulted in increasing economic loss in terms of range productivity and forage quality. In addition to invading grasslands on normal soil, this species is unusual in that it is capable of invading habitats generally thought to be invasion resistant, such as serpentine habitats and other low fertility soils. Although it is likely that selective gradients are strong along weed invasion fronts, we know very little about the importance of adaptive evolutionary change in promoting the spread of weed populations. The relative roles of phenotypic plasticity and genetic differentiation in promoting the expansion of weed populations across highly heterogeneous landscapes is essentially
unknown. Using a target-neighborhood approach, we examined the performance of goatgrass targets from several different seed sources planted within neighborhoods of intraspecific or interspecific competition. In addition the substrate within the common garden was varied to simulate the edaphic conditions of both core and edge populations. Although all reponse variables have yet to be analyzed, it is clear that phenotypic plasticity is an important factor in phenological variation in barbed goatgrass. All populations, regardless of seed source flowered earlier in serpentine soil substrate. An extensive, within-site reciprocal transplant experiment was established this autumn at six different sites in the coast ranges of California that will examine the potential for local adaptation along goatgrass invasion fronts.
Impacts
Barbed goatgrass is a noxious annual grass that has been rapidly expanding its range in recent years. The rapid invasion of rangelands by this unpalatable forage grass has increased economic loss by reducing range productivity and forage quality. We will investigate the mechanisms by which goatgrass adapts to different rangeland environments in order to help develop effective control measures.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
Barbed goatgrass, Aegilops triuncialis L., is a noxious annual grass that has been present in the California flora since the early part of this century, but which has been rapidly expanding its range in recent years. The rapid colonization of rangelands by this unpalatable forage grass has resulted in increasing economic loss in terms of range productivity and forage quality. In addition to invading grasslands on normal soil, this species is unusual in that it is capable of invading habitats generally thought to be invasion resistant, such as serpentine habitats and other low fertility soils. Although it is likely that selective gradients are strong along weed invasion fronts, we know very little about the importance of adaptive evolutionary change in promoting the spread of weed populations. The relative roles of phenotypic plasticity and genetic differentiation in promoting the expansion of weed populations across highly heterogeneous landscapes is essentially
unknown. In this project we have begun to investigate the demographic and adaptive mechanisms by which A. triuncialis adapts to 1) the variation in competition intensity (intra- and interspecific) between core and peripheral areas of invasive populations and 2) the abiotic stress gradients that characterize different habitats types currently being invaded. We will focus specific attention on the interaction between genetic differences within invading populations and the adaptive strategies, i.e., local adaptation or plastic response, that characterize different patterns of invasion, such as coherent invasion fronts and satellite patches. Because of substantial prior study by molecular geneticists, A. triuncialis is an excellent model species for using molecular tools to investigate invasion dynamics; the ability to estimate gene flow will allow unusual power for gauging the relative strength of selection during the invasion process.
Impacts
Barbed goatgrass is a noxious annual grass that has been rapidly expanding its range in recent years. The rapid invasion of rangelands by this unpalatable forage grass has increased economic loss by reducing range productivity and forage quality. We will investigate the mechanisms by which goatgrass adapts to different rangeland environments in order to help develop effective control measures.
Publications
- No publications reported this period
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