Interactions between neighboring plants are critical for biodiversity maintenance in plant populations and communities. Intraspecific trait variation and genome duplication are common in plant species and can drive eco‐evolutionary dynamics through genotype‐mediated plant–plant interactions. However, few studies have examined how species‐wide intraspecific variation may alter interactions between neighboring plants. We investigate how subspecies and ploidy variation in a genetically diverse species, big sagebrush (
- Award ID(s):
- 1757324
- NSF-PAR ID:
- 10252777
- Date Published:
- Journal Name:
- Plants
- Volume:
- 9
- Issue:
- 12
- ISSN:
- 2223-7747
- Page Range / eLocation ID:
- 1717
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Artemisia tridentata ), can alter the demographic outcomes of plant interactions. Using a replicated, long‐term common garden experiment that represents range‐wide diversity ofA. tridentata , we ask how intraspecific variation, environment, and stand age mediate neighbor effects on plant growth and survival. Spatially explicit models revealed that ploidy variation and subspecies identity can mediate plant–plant interactions but that the effect size varied in time and across experimental sites. We found that demographic impacts of neighbor effects were strongest during early stages of stand development and in sites with greater growth rates. Within subspecies, tetraploid populations showed greater tolerance to neighbor crowding compared to their diploid variants. Our findings provide evidence that intraspecific variation related to genome size and subspecies identity impacts spatial demography in a genetically diverse plant species. Accounting for intraspecific variation in studies of conspecific density dependence will improve our understanding of how local populations will respond to novel genotypes and biotic interaction regimes. As introduction of novel genotypes into local populations becomes more common, quantifying demographic processes in genetically diverse populations will help predict long‐term consequences of plant–plant interactions. -
Current and past climatic changes can shift plant climatic niches, which may cause spatial overlap or separation between related taxa. The former often leads to hybridization and introgression, which may generate novel variation and influence the adaptive capacity of plants. An additional mechanism facilitating adaptations to novel environments and an important evolutionary driver in plants is polyploidy as the result of whole genome duplication. Artemisia tridentata (big sagebrush) is a landscape-dominating foundational shrub in the western United States which occupies distinct ecological niches, exhibiting diploid and tetraploid cytotypes. Tetraploids have a large impact on the species’ landscape dominance as they occupy a preponderance of the arid spectrum of A. tridentata range. Three distinct subspecies are recognized, which co-occur in ecotones – the transition zone between two or more distinct ecological niches – allowing for hybridization and introgression. Here we assess the genomic distinctiveness and extent of hybridization among subspecies at different ploidies under both contemporary and predicted future climates. We sampled five transects throughout the western United States where a subspecies overlap was predicted using subspecies-specific climate niche models. Along each transect, we sampled multiple plots representing the parental and the potential hybrid habitats. We performed reduced representation sequencing and processed the data using a ploidy-informed genotyping approach. Population genomic analyses revealed distinct diploid subspecies and at least two distinct tetraploid gene pools, indicating independent origins of the tetraploid populations. We detected low levels of hybridization (2.5%) between the diploid subspecies, while we found evidence for increased admixture between ploidy levels (18%), indicating hybridization has an important role in the formation of tetraploids. Our analyses highlight the importance of subspecies co-occurrence within these ecotones to maintain gene exchange and potential formation of tetraploid populations. Genomic confirmations of subspecies in the ecotones support the subspecies overlap predicted by the contemporary climate niche models. However, future mid-century projections of subspecies niches predict a substantial loss in range and subspecies overlap. Thus, reductions in hybridization potential could affect new recruitment of genetically variable tetraploids that are vital to this species’ ecological role. Our results underscore the importance of ecotone conservation and restoration.more » « less
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Abstract Increased ecological disturbances, species invasions, and climate change are creating severe conservation problems for several plant species that are widespread and foundational. Understanding the genetic diversity of these species and how it relates to adaptation to these stressors are necessary for guiding conservation and restoration efforts. This need is particularly acute for big sagebrush (Artemisia tridentata; Asteraceae), which was once the dominant shrub over 1,000,000 km2 in western North America but has since retracted by half and thus has become the target of one of the largest restoration seeding efforts globally. Here, we present the first reference-quality genome assembly for an ecologically important subspecies of big sagebrush (A. tridentata subsp. tridentata) based on short and long reads, as well as chromatin proximity ligation data analyzed using the HiRise pipeline. The final 4.2 Gb assembly consists of 5,492 scaffolds, with nine pseudo-chromosomal scaffolds (nine scaffolds comprising at least 90% of the assembled genome; n = 9). The assembly contains an estimated 43,377 genes based on ab initio gene discovery and transcriptional data analyzed using the MAKER pipeline, with 91.37% of BUSCOs being completely assembled. The final assembly was highly repetitive, with repeat elements comprising 77.99% of the genome, making the Artemisia tridentata subsp. tridentata genome one of the most highly-repetitive plant genomes to be sequenced and assembled. This genome assembly advances studies on plant adaptation to drought and heat stress and provides a valuable tool for future genomic research.more » « less
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Abstract Aim Whole‐genome duplication (polyploidy) can influence the biogeography and ecology of plants that differ in ploidy level (cytotype). Here, we address how two consequences of plant polyploidy (parapatry of cytotypes and altered species interactions) shape the biogeography of herbivorous insects.
Location Warm deserts of North America.
Taxa Gall midges (
Asphondylia auripila group, Diptera: Cecidomyiidae) that attack three parapatric cytotypes of creosote bush (Larrea tridentata , Zygophyllaceae).Methods We surveyed
Asphondylia species diversity at 177 sites across a 2300‐km extent. After noting a correspondence between the distributions of eightAsphondylia species andL. tridentata cytotypes, we fine‐mappedAsphondylia species range limits with transects spanning cytotype contact zones. We then tested whether plant–insect interactions and/or abiotic factors explain this coincidence by (a) comparing attack rates and gall midge communities on alternative cytotypes in a narrow zone of sympatry and (b) using species distribution models (SDM s) to determine if climatically suitable habitat for each midge species extended beyond cytotype contact zones.Results The range limits of 6/17
Asphondylia species (including two novel putative species confirmed withCOI L. tridentata . One midge species was restricted to diploid host plants while five were restricted to tetraploid and hexaploid host plants. Where diploid and tetraploidL. tridentata are sympatric, cytotype‐restricted midge species more frequently attacked their typical host andAsphondylia community structure differed markedly between cytotypes.SDM s predicted that distributions of cytotype‐restricted midge species were not constrained by climatic conditions near cytotype contact zones.Main conclusions Contact zones between plant cytotypes are dispersal barriers for many
Asphondylia species due to plant–insect interactions. The distribution ofL. tridentata cytotypes therefore shapes herbivore species ranges and herbivore community structure across North American deserts. Our results demonstrate that polyploidy in plants can affect the biogeography of ecological communities. -
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Abstract Western North America has been experiencing persistent drought exacerbated by climate change for over two decades. This extreme climate event is a clear threat to native plant communities.
Artemisia tridentata is a keystone shrub species in western North America and is threatened by climate change, urbanization, and wildfire. A drought Genotype × Environment (G × E) experiment was conducted to assess phenotypic plasticity and differential gene expression inA. tridentata . The G × E experiment was performed on diploidA. tridentata seedlings from two populations (one from Idaho, USA and one from Utah, USA), which experience differing levels of drought stress during the summer months. Photosynthetic data, leaf temperature, and gene expression levels were compared between treatments and populations. The Utah population maintained higher photosynthetic rates and photosynthetic efficiency than the Idaho population under drought stress. The Utah population also exhibited far greater transcriptional plasticity than the Idaho population and expressed genes of response pathways distinct from those of the Idaho population. Populations ofA. tridentata differ greatly in their drought response pathways, likely due to differences in response pathways that have evolved under distinct climatic regimes. Epigenetic processes likely contribute to the observed differences between the populations.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/plants9121717
