More Like this

1. Allopatry, hybridization, and reproductive isolation in Arctostaphylos

   https://doi.org/10.1002/ajb2.1576  

   Parker, V. Thomas ; Rodriguez, Christina Y. ; Wechsler, Gail ; Vasey, Michael C. ( December 2020 , American Journal of Botany)

   Hybridization plays a key role in introgressive adaptation, speciation, and adaptive radiation as a source of evolutionary innovation. Hybridization is considered common inArctostaphylos, yet species boundaries are retained in stands containing multiple species.Arctostaphyloscontains diploids and tetraploids, and recent phylogenies indicate two clades; we hypothesize combinations of these traits limit or promote hybridization rates.

   We statistically analyzed co‐occurrence patterns of species by clade membership and ploidy level from 87 random 0.1 ha plots. We sampled multiple sites to analyze for percent hybridization based on morphology. Finally, phenophases were analyzed by scoring herbarium sheets for a large number of taxa from both clades as well as tetraploids, and second, surveying three field sites over two years for divergence in phenological stages between co‐occurring taxa.

   Most taxa inArctostaphylosare allopatric relative to other congenerics. When two taxa co‐occur, the patterns are a diploid with a tetraploid, or two diploids from different clades. When three taxa co‐occur, the pattern is two diploids from different clades and a tetraploid. Field and herbarium data both indicate flowering phenology is displaced between diploids from the two clades; one of the diploid clades and tetraploids overlap considerably.

   The two deep clades inArctostaphylosare genetically distant, with hybrids rare or non‐existent when taxa co‐occur. Reproductive isolation between clades is enhanced by displaced flowering phenology for co‐occurring species. Within clades, taxa appear to have few reproductive barriers other than an allopatric distribution or different ploidy levels.

    

   more » « less
2. Polyploidy in creosote bush ( Larrea tridentata ) shapes the biogeography of specialist herbivores

   https://doi.org/10.1111/jbi.13490  

   O'Connor, Timothy K. ; Laport, Robert G. ; Whiteman, Noah K. ( January 2019 , Journal of Biogeography)

   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.

   Warm deserts of North America.

   Gall midges (Asphondylia auripilagroup, Diptera: Cecidomyiidae) that attack three parapatric cytotypes of creosote bush (Larrea tridentata, Zygophyllaceae).

   We surveyedAsphondyliaspecies diversity at 177 sites across a 2300‐km extent. After noting a correspondence between the distributions of eightAsphondyliaspecies andL. tridentatacytotypes, we fine‐mappedAsphondyliaspecies 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 (SDMs) to determine if climatically suitable habitat for each midge species extended beyond cytotype contact zones.

   The range limits of 6/17Asphondyliaspecies (including two novel putative species confirmed withCOIsequencing) perfectly coincided with the contact zone of diploid and tetraploidL. tridentata. One midge species was restricted to diploid host plants while five were restricted to tetraploid and hexaploid host plants. Where diploid and tetraploidL. tridentataare sympatric, cytotype‐restricted midge species more frequently attacked their typical host andAsphondyliacommunity structure differed markedly between cytotypes.SDMs predicted that distributions of cytotype‐restricted midge species were not constrained by climatic conditions near cytotype contact zones.

   Contact zones between plant cytotypes are dispersal barriers for manyAsphondyliaspecies due to plant–insect interactions. The distribution ofL. tridentatacytotypes 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.

    

   more » « less
3. Pollinator assemblage and pollen load differences on sympatric diploid and tetraploid cytotypes of the desert‐dominant Larrea tridentata

   https://doi.org/10.1002/ajb2.1605  

   Laport, Robert G. ; Minckley, Robert L. ; Pilson, Diana ( February 2021 , American Journal of Botany)

   Whole‐genome duplication (polyploidy) is an important force shaping flowering‐plant evolution. Ploidy‐specific plant–pollinator interactions represent important community‐level biotic interactions that can lead to nonrandom mating and the persistence of mixed‐ploidy populations.

   At a naturally occurring diploid–tetraploid contact zone of the autopolyploid desert shrubLarrea tridentata, we combined flower phenology analyses, collections of bees on plants of known cytotype, and flow cytometry analyses of bee‐collected pollen loads to investigate whether (1) diploid and tetraploid plants have unique bee pollinator assemblages, (2) bee taxa exhibit ploidy‐specific visitation and pollen collection biases, and (3) specialist and generalist bee taxa have ploidy‐specific visitation and pollen collection biases.

   Although bee assemblages overlapped, we found significant differences in bee visitation to co‐occurring diploids and tetraploids, with the introduced honeybee (Apis mellifera) and one native species (Andrenaspecies 12) more frequently visiting tetraploids. Consistent with bee assemblage differences, we found that diploid pollen was overrepresented among pollen loads on native bees, while pollen loads onA. melliferadid not deviate from the random expectation. However, mismatches between the ploidy of pollen loads and plants were common, consistent with ongoing intercytotype gene flow.

   Our data are consistent with cytotype‐specific bee visitation and suggest that pollinator behavior contributes to reduced diploid–tetraploid mating. Differences in bee visitation and pollen movement potentially contribute to an easing of minority cytotype exclusion and the facilitation of cytotype co‐occurrence.

    

   more » « less
4. Intraspecific variation mediates density dependence in a genetically diverse plant species

   https://doi.org/10.1002/ecy.3502  

   Zaiats, Andrii ; Germino, Matthew J. ; Serpe, Marcelo D. ; Richardson, Bryce A. ; Caughlin, T. Trevor ( September 2021 , Ecology)

   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 (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.

    

   more » « less
5. Host-Induced Genome Instability Rapidly Generates Phenotypic Variation across Candida albicans Strains and Ploidy States

   https://doi.org/10.1128/mSphere.00433-20  

   Smith, Amanda C. ; Hickman, Meleah A. ( June 2020 , mSphere)

   Mitchell, Aaron P. (Ed.)

   ABSTRACT Candida albicans is an opportunistic fungal pathogen of humans that is typically diploid yet has a highly labile genome tolerant of large-scale perturbations including chromosomal aneuploidy and loss-of-heterozygosity events. The ability to rapidly generate genetic variation is crucial for C. albicans to adapt to changing or stressful environments, like those encountered in the host. Genetic variation occurs via stress-induced mutagenesis or can be generated through its parasexual cycle, in which tetraploids arise via diploid mating or stress-induced mitotic defects and undergo nonmeiotic ploidy reduction. However, it remains largely unknown how genetic background contributes to C. albicans genome instability in vitro or in the host environment. Here, we tested how genetic background, ploidy, and the host environment impacts C. albicans genome stability. We found that host association induced both loss-of-heterozygosity events and genome size changes, regardless of genetic background or ploidy. However, the magnitude and types of genome changes varied across C. albicans strain background and ploidy state. We then assessed if host-induced genomic changes resulted in fitness consequences on growth rate and nonlethal virulence phenotypes and found that many host-derived isolates significantly changed relative to their parental strain. Interestingly, diploid host-associated C. albicans predominantly decreased host reproductive fitness, whereas tetraploid host-associated C. albicans increased host reproductive fitness. Together, these results are important for understanding how host-induced genomic changes in C. albicans alter its relationship with the host. IMPORTANCE Candida albicans is an opportunistic fungal pathogen of humans. The ability to generate genetic variation is essential for adaptation and is a strategy that C. albicans and other fungal pathogens use to change their genome size. Stressful environments, including the host, induce C. albicans genome instability. Here, we investigated how C. albicans genetic background and ploidy state impact genome instability, both in vitro and in a host environment. We show that the host environment induces genome instability, but the magnitude depends on C. albicans genetic background. Furthermore, we show that tetraploid C. albicans is highly unstable in host environments and rapidly reduces in genome size. These reductions in genome size often resulted in reduced virulence. In contrast, diploid C. albicans displayed modest host-induced genome size changes, yet these frequently resulted in increased virulence. Such studies are essential for understanding how opportunistic pathogens respond and potentially adapt to the host environment. 

   more » « less