Biology subjects

Braasch, J.

Publications and source records attributed to Braasch, J..

5 recordsLinked to original sources

bioRxiv2025

Soil composition structures genetic variation across small spatial scales in a rare serpentine endemic plant

Studies of population genetic structure are typically conducted at the scale of species distributions and encompass large distances and substantial environmental variation. However, population genetic structure could also be present in species with highly restricted global distributions, such as habitat specialists with threatened or vulnerable conservation status. For these organisms, low dispersal distances coupled with fine-scale environmental heterogeneity could influence population genetic composition, potentially creating spatial genetic structure and genotype by environment associations. Here we use the serpentine endemic plant Calochortus tiburonensis, with a global distribution of 160 ha, to evaluate whether fine-scale structure in soil composition and low seed dispersal distances result in the development of population genetic structure. We paired soil elemental analysis with a RAD-seq SNP dataset for 24 C. tiburonensis individuals. Although no population structure was detected between C. tiburonensis sampling locations, multiple analyses identified associations between soil composition and genetic distance between individuals. This included associations with nickel and magnesium, two elements that were expected a priori to impact plant fitness in serpentine landscapes. However, redundancy analyses and a generalized dissimilarity model both suggest that total soil variation better explains differences in genetic composition between individuals, implying that selection from the holistic soil environment has a role in matching plant genotypes to the microenvironment. Our results indicate that fine-scale environmental heterogeneity could influence genetic differences between individuals in plant populations, even in the absence of population genetic structure. Additionally, these associations between genetic composition and fine-scale environmental heterogeneity implicate extremely fine-scale environmental heterogeneity as an essential mechanism for preserving genetic variation, particularly within range-limited species.

ecology↗

bioRxiv2022

Environmental contributions to the evolution of trait differences in Geum triflorum: implications for restoration

Premise of the StudyUnderstanding how environment influences the distribution of trait variation across a species range has important implications for seed transfer during restoration. Heritable genetic differences associated with environment could impact fitness when transferred into new environments. Here, we test the degree to which the environment shapes the evolution and distribution of genetic effects for traits important to adaptation. MethodsIn a common garden experiment, we quantified trait differentiation for populations of Geum triflorum sourced from three distinct ecoregions and evaluated the ability of climate to predict trait variation. Populations were sourced from alvar ecoregions which experience predictable extremes in seasonal water availability and the prairie ecoregion which exhibits unpredictable changes in water availability. Key ResultsPlants sourced from alvar ecoregions exhibited smaller but more numerous stomata and greater intrinsic water use efficiency relative to prairie plant populations supporting the evolution of ecotypic differences. Estimates of standing genetic variance and heritable genetic variation for quantitative traits suggest alvar populations have greater adaptive potential. However, reduced evolvability suggest all populations of G. triflorum may have limited capacity to evolve in response to environmental change. ConclusionsThese results point towards the importance of understanding the role of environment in shaping the distribution and evolution of genetic differences across seed populations and how these data may inform recommendations for seed transfer across novel environments and our expectations of populations adaptive potential.

evolutionary biology↗

bioRxiv2021

Testing for evolutionary change in restoration: a genomic comparison between ex situ, native and commercial seed sources of Helianthus maximiliani

Globally imperiled ecosystems often depend upon collection, propagation, and storage of seed material for use in restoration. However, during the restoration process demographic changes, population bottlenecks, and selection can alter the genetic composition of seed material, with potential impacts for restoration success. The evolutionary outcomes associated with these processes have been demonstrated using theoretical and experimental frameworks, but no studies to date have examined the impact these processes have had on the seed material maintained for conservation and restoration. In this study, we compare genomic variation across seed sources used in conservation and restoration for the perennial prairie plant Helianthus maximiliani, a key component of restorations across North American grasslands. We compare individuals sourced from contemporary wild populations, ex situ conservation collections, commercially produced restoration material, and two populations selected for agronomic traits. Overall, we observed that ex situ and contemporary wild populations exhibited a similar genomic composition, while four of five commercial populations and selected lines were differentiated from each other and other seed source populations. Genomic differences across seed sources could not be explained solely by isolation by distance nor directional selection. We did find evidence of sampling effects for ex situ collections, which exhibited significantly increased coancestry relative to commercial populations, suggesting increased relatedness. Interestingly, commercially sourced seed appeared to maintain an increased number of rare alleles relative to ex situ and wild contemporary seed sources. However, while commercial seed populations were not genetically depauperate, the genomic distance between wild and commercially produced seed suggests differentiation in the genomic composition could impact restoration success. Our results point towards the importance of genetic monitoring of species used for conservation and restoration as they are expected to be influenced by the evolutionary processes that contribute to divergence during the restoration process.

genomics↗

bioRxiv2019

Introduced species dominate different responses of grassland communities to climate change on serpentine and nonserpentine soils

Introduced species are a common feature of modern plant communities and experience environmental challenges alongside native species. Changes to the environment may reveal distinct species-environment relationships for native and introduced components of plant communities. Extreme environmental change, such as drought, is predicted to result in declines in native species and increased opportunities for invasion, but empirical support for these ideas remains mixed. We tested for differences in the response of native and invaded species to environmental changes by analyzing a longterm dataset of species abundance in California grasslands collected during a period of severe drought. Sampling sites included a combination of stressful serpentine soils, which are resilient against invasion and maintain diverse native species assemblages, and more benign nonserpentine soils, which are heavily invaded and harbor low levels of native species cover. We found a significant correlation between sampling year and species composition for nonserpentine sites, but not for serpentine sites. These patterns were repeated when only introduced species were included in the analysis but no pattern of change was found for native species. The species most strongly associated with directional change on nonserpentine soils were three invasive Eurasian grasses, Bromus hordaceus, Taeniatherium caput-medusae, and Avena fatua. Differences in species composition on both serpentine and nonserpentine soils were significantly correlated with specific leaf area, a trait which has been linked to drought tolerance in these communities, although changes in abundance for the three Eurasian grasses most strongly associated with change did not consistently follow this pattern. Our analyses indicate relatively stable native community composition and strong directional change in introduced species composition, contradicting predictions for how native and introduced species will respond to environmental shifts, but supporting the hypothesis that native and invading species groups have important functional differences that shape their relationships to the environment.

ecology↗

bioRxiv2017

The Prevalence And Benefits Of Admixture During Species Invasions: A Role For Epistasis?

Species introductions often bring together genetically divergent source populations, resulting in genetic admixture. This geographic reshuffling of diversity has the potential to generate favorable new genetic combinations, facilitating the establishment and invasive spread of introduced populations. Observational support for the superior performance of admixed introductions has been mixed, however, and the broad importance of admixture to invasion questioned. Under most underlying mechanisms, admixtures benefits should be expected to increasewith greater divergence among and lower genetic diversity within source populations. We use a literature survey to quantify the prevalence of admixture and evaluate whether it occurrs under circumstances predicted to be mostbeneficial to introduced species. We find that 39% of species are reported to be admixed when introduced. Admixed introductions come from sources with a wide range of genetic variation, but are disproportionately absent where there is high genetic divergence among native populations. We discuss multiple potential explanations for these patterns, but note that negative epistatic interactions should be expected at high divergence amongpopulations (outbreeding depression). As a case study, we experimentally cross source populations differing in divergence in the invasive plant Centaurea solstitialis. We find many positive (heterotic) interactions, but fitness benefits decline and are ultimately negative at high source divergence, with patterns suggestingcyto-nuclear epistasis. We conclude that admixture is common in species introductions and often happens under conditions expected to be beneficial to invaders, but that these conditions may be constrained by predictable negativegenetic interactions, potentially explaining conflicting evidence for admixture's benefits to invasion.

evolutionary biology↗