Chimerism occurs when two genetically distinct conspecific individuals fuse together generating a single entity. Coalescence and chimerism in red seaweeds has been positively related to an increase ...in body size, and the consequent reduction in susceptibility to mortality factors, thus increasing survival, reproductive potential and tolerance to stress in contrast to genetically homogeneous organisms. In addition, they showed that a particular pattern of post-fusion growth maintains higher genetic diversity and chimerism in the holdfast but homogenous axes. In Chilean kelps (brown seaweeds), intraorganismal genetic heterogeneity (IGH) and holdfast coalescence has been described in previous research, but the extent of chimerism in wild populations and the patterns of distribution of the genetically heterogeneous thallus zone have scarcely been studied. Since kelps are under continuous harvesting, with enormous social, ecological and economic importance, natural chimerism can be considered a priceless in-situ reservoir of natural genetic resources and variability. In this study, we therefore examined the frequency of IGH and chimerism in three harvested populations of Lessonia spicata. We then evaluated whether chimeric wild-type holdfasts show higher genetic diversity than erect axes (stipe and lamina) and explored the impact of this on the traditional estimation of genetic diversity at the population level. We found a high frequency of IGH (60-100%) and chimerism (33.3-86.7%), varying according to the studied population. We evidenced that chimerism occurs mostly in holdfasts, exhibiting heterogeneous tissues, whereas stipes and lamina were more homogeneous, generating a vertical gradient of allele and genotype abundance as well as divergence, constituting the first time "within- plant" genetic patterns have been reported in kelps. This is very different from the chimeric patterns described in land plants and animals. Finally, we evidenced that IGH affected genetic differentiation among populations, showed lower levels of FST index when we compared holdfast than lamina samples. In the light of this, future studies should evaluate the significance of chimeric holdfasts in their ability to increase kelps resilience, improve restoration and ecosystem service.
Genetic diversity is a key factor for population survival and evolution. However, anthropogenic habitat disturbance can erode it, making populations more prone to extinction. Aiming to assess the ...global effects of habitat disturbance on plant genetic variation, we conducted a meta‐analysis based on 92 case studies obtained from published literature. We compared the effects of habitat fragmentation and degradation on plant allelic richness and gene diversity (equivalent to expected heterozygosity) and tested whether such changes are sensitive to different life‐forms, life spans, mating systems, and commonness. Anthropogenic disturbance had a negative effect on allelic richness, but not on gene diversity. Habitat fragmentation had a negative effect on genetic variation, whereas habitat degradation had no effect. When we examined the individual effects in fragmented habitats, allelic richness and gene diversity decreased, but this decrease was strongly dependent on certain plant traits. Specifically, common long‐lived trees and self‐incompatible species were more susceptible to allelic richness loss. Conversely, gene diversity decreased in common short‐lived species (herbs) with self‐compatible reproduction. In a wider geographical context, tropical plant communities were more sensitive to allelic richness loss, whereas temperate plant communities were more sensitive to gene diversity loss. Our synthesis showed complex responses to habitat disturbance among plant species. In many cases, the absence of effects could be the result of the time elapsed since the disturbance event or reproductive systems favoring self‐pollination, but attention must be paid to those plant species that are more susceptible to losing genetic diversity, and appropriate conservation should be actions taken.
Meta‐Análisis de los Efectos Diferenciales de la Fragmentación y Degradación del Hábitat sobre la Diversidad Genética de las Plantas
Resumen
La diversidad genética es un factor clave para la supervivencia y evolución de las poblaciones. Sin embargo, la perturbación antropogénica de los hábitats puede dañar esta diversidad, volviendo a las poblaciones más susceptibles a la extinción. Con el objetivo de evaluar los efectos globales de la perturbación del hábitat sobre la variación genética de las plantas, realizamos un meta‐análisis basado en 92 estudios de caso obtenidos de la literatura publicada. Comparamos los efectos de la degradación y fragmentación del hábitat sobre la riqueza de alelos y la diversidad de genes (equivalente a la heterocigosidad esperada) de las plantas y probamos si dichos cambios son sensibles para diferentes formas de vida, tiempos de vida, sistemas de apareamiento y preponderancia. La perturbación antropogénica tuvo un efecto negativo sobre la riqueza de alelos, pero no sobre la diversidad genética. La fragmentación del hábitat tuvo un efecto negativo sobre la variación genética, mientras que la degradación del hábitat no tuvo efecto. Cuando examinamos los efectos individuales en los hábitats fragmentados, la riqueza de alelos y la diversidad genética disminuyeron, pero esta disminución estuvo vinculada fuertemente con ciertas características de las plantas. Específicamente, los árboles de larga vida y las especies auto‐incompatibles fueron más susceptibles a la pérdida de la riqueza de alelos. De manera contraria, la diversidad genética disminuyó en especies comunes de vida corta (hierbas) con reproducción auto‐compatibles. En un contexto geográfico más amplio, las comunidades de plantas tropicales fueron más sensibles a la pérdida de la riqueza de alelos, mientras que las comunidades de plantas de zonas templadas fueron más sensibles a la pérdida de diversidad de genes. Nuestra síntesis mostró respuestas complejas a la perturbación del hábitat entre las especies de plantas. En muchos casos, la ausencia de efectos podría ser el resultado del tiempo transcurrido desde el evento de perturbación o los sistemas reproductivos que favorecen la auto‐polinización, pero se le debe prestar atención a aquellas especies de plantas que son más susceptibles a la pérdida de la diversidad genética, para así poder realizar las acciones de conservación apropiadas.
摘要
遗传多样性是种群存活和演化的关键因素。然而, 人类对生境的干扰会侵蚀遗传多样性, 导致种群更容易灭绝。为了评估全球生境干扰对植物遗传变异的影响, 我们对 92 项已发表文献中的案例研究进行了荟萃分析。我们比较了生境破碎化和退化对植物等位基因丰富度和基因多样性 (相当于期望杂合度) 的影响, 并检验了植物的遗传多样性变化是否容易受到不同的生活型、寿命、繁殖方式和稀有性的影响。人类干扰对等位基因丰富度有负面影响, 但对基因多样性没有作用。生境破碎化对遗传变异有负面影响, 而生境退化则没有影响。我们检测了破碎化生境中影响因素的单独作用, 发现等位基因丰富度和基因多样性均下降, 但下降程度与植物的某些性状密切相关。具体来说, 寿命长的常见种和自交不亲和的物种更容易丧失等位基因丰富度。相反地, 寿命短的常见种 (草本植物) 与自交亲和的物种更容易发生基因多样性下降。在更广泛的地理环境中, 热带植物群落更可能丧失等位基因丰富度, 而温带植物群落则更可能丧失基因多样性。我们的总结表明不同植物对生境干扰表现出复杂的响应。在许多情况下, 没有观察到影响可能与干扰事件发生的时间有关, 或是因为该植物的繁殖方式倾向于自花授粉, 但必须注意那些对遗传多样性丧失更敏感的植物, 并采取适当的保护措施。【翻译: 胡怡思; 审校: 聂永刚】
Article impact statement: Effects of disturbance on plant genetic diversity are influenced by disturbance type, plant biological traits, and geographical context.
Chimerism is produced by the somatic fusion of two or more genetically distinct conspecific individuals. In animals, the main cost of fusion is competition between genetically different cell lineages ...and the probability of original cell line replacement by more competitive invasive lines, which limits its natural frequency (3%–5%). In red and brown seaweeds, chimerism is widespread (27%–53%), seemingly without the negative outcomes described for animals. The rigidity of cell walls in macroalgae prevents cell motility and invasions. In addition, in moving waters, most somatic fusions involve the holdfast. Histological observations in laboratory‐built bicolor macroalgal chimeras indicated that upright axes emerge from the base of plants by proliferation and vertical growth of discrete cell groups that include one or just a few of the cell lineages occurring in the holdfasts. Laboratory experiments showed growth competition between cell lineages, thus explaining lineage segregation during growth along originally chimeric erect axes. Genotyping of the axes showed more heterogeneous tissues basally, but apically more homogeneous ones, generating a vertical gradient of allele abundance and diversity. The few chimeric primary branches produced, eventually became homogenous after repeated branching. Therefore, coalescing macroagae exhibit a unique pattern of post‐fusion growth, with the capacity to reverse chimerism. This pattern is significantly different from those in animals and land plants, suggesting chimerism is a biologically heterogeneous concept.
Mexico harbors great cultural and ethnic diversity, yet fine-scale patterns of human genome-wide variation from this region remain largely uncharacterized. We studied genomic variation within Mexico ...from over 1000 individuals representing 20 indigenous and 11 mestizo populations. We found striking genetic stratification among indigenous populations within Mexico at varying degrees of geographic isolation. Some groups were as differentiated as Europeans are from East Asians. Pre-Columbian genetic substructure is recapitulated in the indigenous ancestry of admixed mestizo individuals across the country. Furthermore, two independently phenotyped cohorts of Mexicans and Mexican Americans showed a significant association between subcontinental ancestry and lung function. Thus, accounting for fine-scale ancestry patterns is critical for medical and population genetic studies within Mexico, in Mexican-descent populations, and likely in many other populations worldwide.
Mexico harbors great cultural and ethnic diversity, yet fine-scale patterns of human genome-wide variation from this region remain largely uncharacterized. We studied genomic variation within Mexico ...from over 1000 individuals representing 20 indigenous and 11 mestizo populations. We found striking genetic stratification among indigenous populations within Mexico at varying degrees of geographic isolation. Some groups were as differentiated as Europeans are from East Asians. Pre-Columbian genetic substructure is recapitulated in the indigenous ancestry of admixed mestizo individuals across the country. Furthermore, two independently phenotyped cohorts of Mexicans and Mexican Americans showed a significant association between subcontinental ancestry and lung function. Thus, accounting for fine-scale ancestry patterns is critical for medical and population genetic studies within Mexico, in Mexican-descent populations, and likely in many other populations worldwide.
The selective role of pollinators on the floral phenotype has been identified as the main force behind angiosperm diversification. However, in generalized plant–pollinator interactions this ...association may not be that evident, since pollinator assemblages vary in composition among populations, possibly influencing the direction and intensity of floral trait selection. In this study we determine whether there was spatial variation in pollinator assemblages and the selective forces they exert in ten populations of
Alstroemeria ligtu
var.
simsii
. We characterized the whole pollinator assemblage in ten populations, quantified four floral attraction traits and determined potential selection targets in each of the study populations. Our results revealed that populations differed in the composition of their pollinator assemblages, and the pollinators with the highest visitation rates also differed among populations. Using phenotypic selection analysis we detected significant differentials and selection gradients only in two of the ten populations, for corolla tube length and ratio of the nectar guide. The spatial variation in selection showed that linear selection acting upon these traits differed significantly among the studied populations. Our study indicates that selection can be detected in generalized plant–pollinator systems and brings new evidence of phenotypic selection variation in space for this endemic plant species. Future studies are needed to determine whether the selective patterns described here are consistent over time and whether they produce evolutionary change in the populations under study.
In brown macroalgae, intraspecific holdfast coalescence has only been studied in two species of Lessonia (Lessonia spicata and Lessonia berteroana). In both species coalescence followed the same ...general pattern: once the connection between holdfasts was established, the contact areas showed significant cellular morphological modifications. Typical epidermal cells became polygonal and similar to cortical cells. In addition, coalescence involved the de novo formation of secondary plasmodesmata, establishing a direct cytoplasm connection within neighbouring cells, where dense materials, vacuoles and organelles can be observed. In the present study, we demonstrate intraspecific holdfast coalescence in two additional kelp species, Lessonia trabeculata and Macrocystis pyrifera, as well as in the kelp-like seaweed, Durvillaea antarctica. The process of holdfast fusions in these species is similar to that described previously and suggests that this is a generalized phenomenon among kelp and kelp-like brown algae. In addition, the formation of cytoplasmic connections between genetically different brown algal individuals is shown for the first time.
Chimerism theoretically increases the genetic heterogeneity of coalescing organisms, which in turn may increase phenotypic variability in chimeras, allowing them greater tolerance to environmental ...changes when compared with non-coalescing individuals. In order to test this hypothesis, we compared abiotic stress tolerance between coalescing and non-coalescing organisms. The specific daily growth was compared using discs formed with 1, 5, and 20
Mazzaella laminarioides
carpospores. These were cultivated under three different temperature (6, 12, and 25 °C) and salinity (10, 35, and 50 g L
−1
) conditions. Growth of the disc area was measured after 30 days of cultivation under controlled conditions. Sporeling survival similarly was calculated under each of these temperatures and salinities in order to record whether stress-resistant phenotypes were present. The results showed that, under stressful conditions, non-coalescing specimens experienced a significant reduction in the specific growth rate compared with those under non-stressful conditions. The reduction in growth falls off, however, as the number of coalescing spores increases. The cultivation of spore populations also indicates the presence of sporelings with the capacity to survive alone in stressful situations. The results suggest that the coalescing discs exhibit higher tolerance to environmental stressors than non-coalescing discs, allowing them to survive and grow under these conditions. This can be explained by an increase in phenotypic plasticity, resulting from greater genetic heterogeneity due to somatic fusion of a larger number of spores.
Genetic diversity is considered a key factor of population survival and evolution, especially in changing environments. Genetic diversity arises from mutations in the DNA sequence of cell lines and ...from there it reaches the level of organisms, populations, and regions. However, many previous studies have not considered the organism architecture or pattern of thallus construction, ignoring the potential genetic complexities that intraorganismal genetic heterogeneity could generate in modular organisms. In seaweeds, modularity and clonality exist in many species. Modular organization has been related to advantages in terms of rapid construction and recovery after the loss of individual modules, which have their own demographic properties as they generate, mature, senesce, and die. Based on recent evidence from the literature, we suggest that modules also have their own genetic properties. Specifically, modular seaweeds have two possible sources of genetic diversity at the individual level: the heterozygosity of the genotypes composing the genet, and genetic heterogeneity among the modules within a genet (i.e., intraclonal genetic variability). Both sources of genetic diversity can have ecological and evolutionary consequences, and most of them must be considered in research on modular seaweeds. Linking intraorganismal genetic diversity with clonal architecture and propagation styles may help us to understand important ecological and evolutionary processes such as speciation modes, invasive capacities, or farming potential.
Most individuals throughout the Americas are admixed descendants of Native American, European, and African ancestors. Complex historical factors have resulted in varying proportions of ancestral ...contributions between individuals within and among ethnic groups. We developed a panel of 446 ancestry informative markers (AIMs) optimized to estimate ancestral proportions in individuals and populations throughout Latin America. We used genome-wide data from 953 individuals from diverse African, European, and Native American populations to select AIMs optimized for each of the three main continental populations that form the basis of modern Latin American populations. We selected markers on the basis of locus-specific branch length to be informative, well distributed throughout the genome, capable of being genotyped on widely available commercial platforms, and applicable throughout the Americas by minimizing within-continent heterogeneity. We then validated the panel in samples from four admixed populations by comparing ancestry estimates based on the AIMs panel to estimates based on genome-wide association study (GWAS) data. The panel provided balanced discriminatory power among the three ancestral populations and accurate estimates of individual ancestry proportions (R² > 0.9 for ancestral components with significant between-subject variance). Finally, we genotyped samples from 18 populations from Latin America using the AIMs panel and estimated variability in ancestry within and between these populations. This panel and its reference genotype information will be useful resources to explore population history of admixture in Latin America and to correct for the potential effects of population stratification in admixed samples in the region.
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