Brassica fruticulosa
Photo: Sílvia Busoms, UAB.
Imagine you're a design engineer tasked to design part of a manufacturing process to be used in two different factories. You produce a solution which works in one factory, so what do you do for the second factory?
If you're creationism putative designer, you forget all about the solution that works, and you design a completely different method for the second factory. It would be far too simple to use the first method you designed for the second factory, obviously. It would be as though there is no communication between the two factories and no sharing of ideas or testing to see which method was the most efficient in terms of time, materials and labor. Each factory would work to its own methods, oblivious of anywhere else or any better solutions.
And that just what creationism's alleged creator appears to have done with two populations of a common coastal plant in Catalonia - a wild member of the cabbage family, Brassica fruticulosa - where different populations have adapted to soil salinity in two different ways.
What can you tell me about the plant Brassica fruticulosa, its distribution and adaptation to different soil conditions? Brassica fruticulosa, commonly known as Mediterranean cabbage, is a wild species within the Brassicaceae family. It is native to the Mediterranean region, where it thrives in a variety of habitats, including rocky, disturbed, and coastal areas. The species is highly adapted to different environmental conditions, including poor, dry, and calcareous soils, which is a key feature of its resilience.This was discovered by three researchers from the Universitat Autònoma de Barcelona (UAB) Plant Physiology Lab, in collaboration with researchers from the University of Nottingham (UK), the Max Planck Institute for Biology (Germany), and Charles University in Prague (Czech Republic).
Distribution:
Brassica fruticulosa is primarily found in Southern Europe, North Africa, and parts of the Middle East. Its distribution spans countries like Spain, Italy, Greece, Turkey, and Algeria, extending into coastal regions with Mediterranean climates.
Adaptation to Soil Conditions:
This adaptation to different soil conditions is likely linked to its ecological strategy of thriving in marginal habitats, where competition from other plants is less intense.
- Drought Resistance: The plant is well-suited to dry and nutrient-poor soils, a characteristic of Mediterranean ecosystems. Its deep root system allows it to access water in arid environments, contributing to its drought tolerance.
- Calcareous Soils: The species is adapted to alkaline soils, often thriving in limestone-rich areas. It can tolerate high pH levels, which would limit the growth of less adapted species.
- Disturbed and Rocky Soils: Brassica fruticulosa also thrives in disturbed habitats, such as roadsides and rocky outcrops. Its ability to grow in these challenging environments shows its resilience to various soil types and disturbances.
Their findings are the subject of a recent open access research paper in Proceedings of the National Academy of Science (PNAS) and a UAB news release.
Different adaptation strategies to saline soils identified in neighbouring populations of the same plant species
Researchers from the Faculty of Biosciences have identified two divergent adaptive responses to soil salinity in populations of the same wild species found in the Catalonia’s coastal area, the Brassica fruticulosa, and have pinpointed the genes involved. The study will help to investigate the ways to improve resilience in agricultural species of the same plant family, such as rapeseed and mustard, in the face of a globally relevant stressor as is soil salinization.
The study was recently published in Proceedings of the National Academy of Sciences (PNAS) and is signed by researchers Sílvia Busoms, Glòria Escolà and Charlotte Poschenrieder from the UAB Plant Physiology Lab, in collaboration with researchers from the University of Nottingham (UK), the Max Planck Institute for Biology (Germany), and Charles University in Prague (Czech Republic).
Over the past few years, UAB researchers have worked in close collaboration with members of the University of Nottingham to develop a study model along the Catalan coast to understand the interaction between environmental factors such as salinity and the adaptation of wild populations of the Brassicaceae family. They developed several studies focused on populations of Arabidopsis thaliana, a model organism for biological research, but in this case, they focused on Brassica fruticulosa, a species genetically and morphologically closer to cultivated brassicas such as rapeseed (Brassica napus) and mustard (Sinapis alba).
This research has allowed them to demonstrate that in Catalonia coastal populations of B. fruticulosa use two different strategies to tolerate soil salinity: those from the north (Cap de Creus region) are able to restrict root-to-shoot sodium transport, preventing the damage of the aerial parts. In contrast, those from the centre accumulate sodium in the leaves, but they use efficient mechanisms of osmotic adjustment and compartmentalisation that allow them to tolerate high concentrations of this compound.
The fact that two populations of the same plant species located so close geographically have evolved differently under the same environmental conditions surprised the researchers.
“In general, in all organisms it is expected that species adapting to similar stressors also evolve in a similar way. In our case, however, although in the coastal habitats of the Catalan coast soil salinity can be considered the main selective agent, there must be other factors that have altered the recent evolutionary process of this Brassicaceae species.
Sílvia Busoms, lead author
Department of Plant Physiology
Universitat Autònoma de Barcelona, Barcelona, Spain
This divergence in plant populations so close to each other has rarely been described, not so much because it is an exception, but because in many cases the studies are carried out at the macro-scale.
The Tramontane wind may explain this divergence
In their study, researchers examined in detail the characteristics of the soils and the climatology of all the populations’ location. The only parameter that showed significant differences was evapotranspiration, which was higher in the north due to the Tramontane wind that regularly blows there.
When there is high evapotranspiration, plants absorb more water and at the same time more sodium if they do not have mechanisms to exclude it. Therefore, the strategies used by the plants of the central coastal areas may be insufficient in the conditions of the northern coast. In the study we hypothesise that although they are neighbouring populations, the northern B. fruticulosa evolved differently in order to tolerate both high salinity levels and high evapotranspiration.
Charlotte Poschenrieder, co-author Department of Plant Physiology
Universitat Autònoma de Barcelona, Barcelona, Spain
To characterise the genetic basis of the two adaptive strategies identified, researchers first created the reference genome of B. fruticulosa, which will contribute to the expansion of the catalogue of reference genomes of eukaryotic species from the Catalan-speaking territories (within the Earth Biogenome Project) and will allow further research with this species. Subsequently, the sequencing of 18 populations and the subsequent genetic and transcriptomic analyses validated the two strategies observed and allowed researchers to propose candidate genes involved in the mechanisms of salinity tolerance.
Salinity is a threat to the planet's agricultural soils and its consequences are greater when it affects impoverished soils such as those found in the Mediterranean basin. A better understanding of the mechanisms of salt tolerance used by plants living there and which have adapted to these conditions is essential to improve the resilience of cultivars that must adapt to the new environmental conditions. “This study, therefore, establishes B. fruticulosa as a promising source of desirable alleles, and the population diversity present in Catalonia as a powerful model for the study of adaptations to saline soils,” researchers conclude.
Original article:Silvia Busoms, Ana C. da Silva, Glòria Escolà and Levi Yant.
Local cryptic diversity in salinity adaptation mechanisms in the wild outcrossing Brassica fruticulosa.
September 24, 2024. Proc Natl Acad Sci. https://doi.org/10.1073/pnas.2407821121
This example is interesting in that it shows the process of allopatric speciation in progress even though the two populations are still regarded as the same species. It's not clear from this paper whether the two population can or do interbreed, but if they do, what would be the consequences for the hybrids? Depending on the mode of inheritance, the offspring's genes could express in three different ways:Significance
One might expect that closely related populations of a given species should adapt to the same environmental stressor in the same way due to genetic or physiological constraints. However, this is not commonly tested due to practical limitations. Here, we show that, even at the level of neighboring populations, contrasting adaptive strategies control adaptive responses to high coastal salinity in Brassica fruticulosa, a close wild relative of many crops of worldwide importance. This indicates multiple options for engineering an agriculturally crucial adaptation: soil salinization. These results will be of interest to not only those studying fundamental mechanisms of adaptation, but also resilience improvement in Brassica species.
Abstract
It is normally supposed that populations of the same species should evolve shared mechanisms of adaptation to common stressors due to evolutionary constraint. Here, we describe a system of within-species local adaptation to coastal habitats, Brassica fruticulosa, and detail surprising strategic variability in adaptive responses to high salinity. These different adaptive responses in neighboring populations are evidenced by transcriptomes, diverse physiological outputs, and distinct genomic selective landscapes. In response to high salinity Northern Catalonian populations restrict root-to-shoot Na+ transport, favoring K+ uptake. Contrastingly, Central Catalonian populations accumulate Na+ in leaves and compensate for the osmotic imbalance with compatible solutes such as proline. Despite contrasting responses, both metapopulations were salinity tolerant relative to all inland accessions. To characterize the genomic basis of these divergent adaptive strategies in an otherwise non-saline-tolerant species, we generate a long-read-based genome and population sequencing of 18 populations (nine inland, nine coastal) across the B. fruticulosa species range. Results of genomic and transcriptomic approaches support the physiological observations of distinct underlying mechanisms of adaptation to high salinity and reveal potential genetic targets of these two very recently evolved salinity adaptations. We therefore provide a model of within-species salinity adaptation and reveal cryptic variation in neighboring plant populations in the mechanisms of adaptation to an important natural stressor highly relevant to agriculture.
Today’s accumulation of high-profile cases detailing repeated evolution capture the fascination of biologists. Independently evolved adaptive coloring shifts in mammals and insects, defensive armor in fish, and serpentine and altitude adaptation in plants: these all present not only additional evidence for candidate mechanisms underlying adaptations, but also an optimistic outlook toward “predicting” the course of evolution and inspiring expositions for the public (1–6). Given these iconic cases, an expectation may arise that even at the functional level, neighboring populations of the same species should, due to genetic or developmental constraints and mutation limitation, share evolved strategies of adaptation to the same stressors (7). The logical extension is that natural selection might be expected to predictably drive the origin and maintenance of adaptations at strategic or mechanistic levels. However, this idea has not been sufficiently tested due to restraints on study systems, sampling, resolution, and scale (8). We thus lack a clear understanding of how often an expectation of uniform or repeatable species-wide adaptation strategies is violated in favor of diversity even within single species.
Here, we test this expectation by taking a “hyperlocal” approach in the study of plant adaptation to coastal stressors, focusing on adaptation to high coastal salinity in a strip of coastline in Catalunya, Northern Spain. Previous work on local adaptation of Arabidopsis thaliana in this region detailed geographically and temporally fine-scale adaptive variation in fitness-related traits across environmental salinity gradients, even at the scale of a few kilometers (9, 10). This region is characterized by a positive gradient of soil salinity from inland to the coast, shaping plant species communities and driving the evolution of salinity tolerance mechanisms at the local population- (deme-) level (11). Plant evolutionary responses to these conditions have been observed even in the selfer A. thaliana at fine (3 to 5 km) scale, resulting in functionally adaptive variation (12). Functional confirmation of this is evidenced by selective sweep of a hypomorphic ion transporter HKT1;1, which modulates Na+ leaf concentrations in response to rapid (monthly) temporal and spatial variation in rainfall and soil salinity (9).
Unfortunately, work in A. thaliana has two major limitations: first, due to its overwhelmingly selfing reproductive mode, relative to its outcrossing relatives A. thaliana has 10-fold lower genetic diversity and high rates of spontaneous, population-specific mutations (13). This low diversity also has important consequences in respect to increased homozygosity and effective population size, resulting in genetic drift, reduced effective recombination rates, genomic background effects, and the fixation of maladaptive alleles (reviewed in ref. 14). Second, Arabidopsis is substantially divergent from important Brassica crops, limiting the translational potential of discoveries in this otherwise convenient lab model. Wild outcrossing Brassicas, on the other hand, harbor higher levels of genetic diversity, directly facilitating studies of adaptation (15). Motivated by these considerations, we searched for wild Brassicaceae species with contrasting, recently evolved (within-species) phenotypes in complex coastal adaptations, focusing specifically on salinity tolerance. This resulted here in the identification of a model for local adaptation to coastal salinity, Brassica fruticulosa, and allows us to test hypotheses regarding the scale of local adaptation to high coastal salinity.
The genus Brassica belongs to the Brassicaceae (mustard) family and contains nearly 100 species, many of which are grown globally as vegetables like cabbage, broccoli, kale, and radish, as mustards, as oil crops (placing 3rd after palm and soy), and as fodder for animal feed (16). Brassicas are widely proficient at adapting to new habitats due to recent and recurrent polyploidy events, hybridization, and plastic genomes. These characteristics also make them great targets for genetic manipulation to further enhance resilience (17).
Here, we first perform a large-scale, genus-wide natural variation survey of diverse, wild outcrossing Brassicas in coastal Northeast Spain, eventually testing six candidate species for within-species adaptation to high salinity. From these, we identify and develop one particularly promising model of within-species variation in adaptation to extreme salinity and complex coastal stressors, B. fruticulosa. First described in 1792 by Cirillo (18), B. fruticulosa has not yet been recognized as harboring population-specific salinity adaptation. This has been a missed opportunity, as B. fruticulosa is closely related to Brassica rapa (19, 20) and shares many affinities with this global crop. We then assemble the B. fruticulosa genome using Oxford Nanopore long read sequencing polished with Illumina short reads, and sequence 90 individuals from 18 populations (nine coastal, nine inland) contrasting in salinity and soil parameters defined by ionome levels in leaves and soil in the root space of every individually sequenced wild plant. Using transcriptome data of leaves and roots, we reveal divergent adaptive strategies in response to high salinity in neighboring plant populations. We then perform common garden, physiological, and ion homeostasis experiments to detail these different strategies that evolved in closely neighboring adapted plant populations. Finally, we perform environmental association analysis (EAA) (with soil ionome as phenotype) and genome scans by ecotype to seek a genomic basis of divergent adaptative strategies to high salinity in neighboring B. fruticulosa populations. Taken together, these experiments reveal contrasting adaptive responses to extreme salinity, at the local scale, differing mechanistically at the scale of kilometers.
Fig 6.
Overview of the contrasting salinity tolerance strategies of the North and Central B. fruticulosa coastal metapopulations. Hypothetical model of genes, ion transport, and signaling pathways involved in salinity tolerance mechanisms. Gene symbols are shown in bold letters. Ion fluxes are indicated with black arrows. Gene activation/repression and molecule increase/decrease are indicated with red arrows. Star-framed symbols denote signaling pathways and hormone molecules are circled in green. “ST” = Salt tolerant.
- Adapted like the northern population.
- Adapted like the southern population.
- Adapted like both populations.
So, hybridization would be wasteful with reduced survival of the hybrids. This is environmental pressure to establish barriers to hybridization because plants that don't hybridize will tend to produce more successful offspring than those which do.
From an intelligent [sic] design perspective, this example of doing the same thing in two different ways makes no sense as the work of the same designer. However, given that there is no mechanism for isolated populations to share information and make informed decisions about the best way to adapt to local conditions, then ensure they evolved that way, this makes perfect sense from an evolutionary perspective.
Again, the detail behind a superficial appearance of designs reveals that there was no intelligence involved in the process; instead, the process was a mindless utilitarian process that produced two different solutions to the same problem.
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