Geology topics

John F. Gaskin

Publications and source records attributed to John F. Gaskin.

5 recordsLinked to original sources

USGS2025

Low genetic diversity in populations of a clonal invasive plant limits sexual reproduction

Premise Clonality, a form of asexual reproduction and spread, is common among invasive plants, though sexual reproduction via seeds is often still important for their long-range dispersal. In small populations, clonality has been hypothesized to interfere with sexual reproduction by limiting outcrossing opportunities of a plant. Methods We developed a structural equation model based on estimates of genetic diversity and seed production of Lepidium draba , a problematic invasive clonal plant, at 26 sites in Colorado to test whether site characteristics relating to small founder populations resulted in low genetic diversity and sexual reproduction. The next year, in pollen supplementation experiments at six sites (three with high genetic diversity, three with low), we tested whether populations with low genetic diversity were limited by non-self pollen. Results Large populations and populations associated with rivers tended to have higher genetic diversity. Percentage seed fill and total seed production were considerably higher at sites with higher genetic diversity. At populations with low genetic diversity, supplementation with pollen from outside of the site, but not from within the site, increased seed production. At populations with high genetic diversity, pollen supplementation from off-site did not increase seed production. Conclusions Our study shows that, in low-diversity populations that are dominated by a few large clones, L. draba produces few seeds compared to high-diversity populations and that this appears to be due to limited availability of non-self pollen. The data indicate that low genetic diversity decreases sexual reproduction, which may greatly reduce long-distance dispersal from these populations.

Colorado↗

USGS2020

Managing invasive plants on Great Plains grasslands: A discussion of current challenges

The Great Plains of North America encompass approximately 1,300,000 km 2 of land from Texas to Saskatchewan. The integrity of these lands is under continual assault by long-established and newly-arrived invasive plant species, which can threaten native species and diminish land values and ecological goods and services by degrading desired grassland resources. The Great Plains are a mixture of privately and publicly owned lands, which leads to a patchwork of varying management goals and strategies for controlling invasive plants. Continually updated knowledge is required for efficient and effective management of threats posed by changing environments and invasive plants. Here we discuss current challenges, contemporary management strategies, and management tools and their integration, in hopes of presenting a knowledge resource for new and experienced land managers and others involved in making decisions regarding invasive plant management in the Great Plains.

Great Plains↗

USGS2014

Hybridization of an invasive shrub affects tolerance and resistance to defoliation by a biological control agent

Evolution has contributed to the successful invasion of exotic plant species in their introduced ranges, but how evolution affects particular control strategies is still under evaluation. For instance, classical biological control, a common strategy involving the utilization of highly specific natural enemies to control exotic pests, may be negatively affected by host hybridization because of shifts in plant traits, such as root allocation or chemical constituents. We investigated introgression between two parent species of the invasive shrub tamarisk ( Tamarix spp.) in the western United States, and how differences in plant traits affect interactions with a biological control agent. Introgression varied strongly with latitude of origin and was highly correlated with plant performance. Increased levels of T. ramosissima introgression resulted in both higher investment in roots and tolerance to defoliation and less resistance to insect attack. Because tamarisk hybridization occurs predictably on the western U.S. landscape, managers may be able to exploit this information to maximize control efforts. Genetic differentiation in plant traits in this system underpins the importance of plant hybridization and may explain why some biological control releases are more successful than others.

Colorado↗

USGS2014

From hybrid swarms to swarms of hybrids

Science has shown that the introgression or hybridization of modern humans ( Homo sapiens ) with Neanderthals up to 40,000 YBP may have led to the swarm of modern humans on earth. However, there is little doubt that modern trade and transportation in support of the humans has continued to introduce additional species, genotypes, and hybrids to every country on the globe. We assessed the utility of species distributions modeling of genotypes to assess the risk of current and future invaders. We evaluated 93 locations of the genus Tamarix for which genetic data were available. Maxent models of habitat suitability showed that the hybrid, T. ramosissima x T. chinensis , was slightly greater than the parent taxa (AUCs > 0.83). General linear models of Africanized honey bees, a hybrid cross of Tanzanian Apis mellifera scutellata and a variety of European honey bee including A. m. ligustica , showed that the Africanized bees (AUC = 0.81) may be displacing European honey bees (AUC > 0.76) over large areas of the southwestern U.S. More important, Maxent modeling of sub-populations (A1 and A26 mitotypes based on mDNA) could be accurately modeled (AUC > 0.9), and they responded differently to environmental drivers. This suggests that rapid evolutionary change may be underway in the Africanized bees, allowing the bees to spread into new areas and extending their total range. Protecting native species and ecosystems may benefit from risk maps of harmful invasive species, hybrids, and genotypes.

Environment and Ecology Research↗

USGS2008

Latitudinal variation in cold hardiness in introduced Tamarix and native Populus

To investigate the evolution of clinal variation in an invasive plant, we compared cold hardiness in the introduced saltcedar ( Tamarix ramosissima , Tamarix chinensis , and hybrids) and the native plains cottonwood ( Populus deltoides subsp. monilifera ). In a shadehouse in Colorado (41°N), we grew plants collected along a latitudinal gradient in the central United States (29–48°N). On 17 occasions between September 2005 and June 2006, we determined killing temperatures using freeze-induced electrolyte leakage and direct observation. In midwinter, cottonwood survived cooling to −70°C, while saltcedar was killed at −33 to −47°C. Frost sensitivity, therefore, may limit northward expansion of saltcedar in North America. Both species demonstrated inherited latitudinal variation in cold hardiness. For example, from September through January killing temperatures for saltcedar from 29.18°N were 5–21°C higher than those for saltcedar from 47.60°N, and on September 26 and October 11, killing temperatures for cottonwood from 33.06°N were >43°C higher than those for cottonwood from 47.60°N. Analysis of nine microsatellite loci showed that southern saltcedars are more closely related to T. chinensis while northern plants are more closely related to T. ramosissima . Hybridization may have introduced the genetic variability necessary for rapid evolution of the cline in saltcedar cold hardiness.

Evolutionary Applications↗