Paula Mathiasen

Out in the cold: genetic variation of Nothofagus pumilio (Nothofagaceae) provides evidence for latitudinally distinct evolutionary histories in austral South America

Nothofagus pumilio is the dominant and almost ubiquitous tree species in mountainous environments of temperate South America. We used two types of molecular markers (cpDNA and isozymes) to evaluate the effects of the Paleogene paleogeography of Patagonia and more recent climatic oscillations of the Neogene on such cold‐tolerant species’ genetic makeup. Phylogeographic analysis on sequences of three cpDNA non‐coding regions at 85 populations yielded two latitudinally disjunct monophyletic clades north and south of c. 42°S containing 11 and three haplotypes, respectively. This indicates a long‐lasting vicariant event due to the presence of an extended open paleobasin at mid latitudes of Patagonia. Also distribution patterns of cpDNA haplotypes suggest regional spread following stepping‐stone models using pre‐Cenozoic mountains as corridors. Comparable genetic diversity measured along 41 sampled populations using seven polymorphic isozyme loci provides evidence of local persistence and spread from multiple ice‐free locations. In addition, significantly higher heterozygosity and allelic richness at high latitudes, i.e. in areas of larger glacial extent, suggest survival in large and isolated refugia. While, higher cpDNA diversity in lower latitudes reflects the complex orogeny that historically isolated northern populations, lower isozyme diversity and reduced FST values provide evidence of local glacial survival in numerous small locales. Therefore, current genetic structure of N. pumilio is the result of regional processes which took place during the Tertiary that were enhanced by contemporary local effects of drift and isolation in response to Quaternary climatic cycles.

Phylogeographically concordant chloroplast DNA divergence in sympatric Nothofagus s.s. How deep can it be

• Here, we performed phylogenetic analyses and estimated the divergence times on mostly sympatric populations of five species within subgenus Nothofagus. We aimed to investigate whether phylogenetic relationships by nuclear internal transcribed spacer (ITS) and phylogeographic patterns by chloroplast DNA (cpDNA) mirror an ancient evolutionary history that was not erased by glacial eras. Extant species are restricted to Patagonia and share a pollen type that was formerly widespread in all southern land masses. Weak reproductive barriers exist among them. • Fifteen cpDNA haplotypes resulted from the analysis of three noncoding regions on 330 individuals with a total alignment of 1794 bp. Nuclear ITS data consisted of 822 bp. We found a deep cpDNA divergence dated 32 Ma at mid-latitudes of Patagonia that predates the phylogenetic divergence of extant taxa. Other more recent breaks by cpDNA occurred towards the north. • Complex paleogeographic features explain the genetic discontinuities. Long-lasting paleobasins and marine ingressions have impeded transoceanic dispersal during range expansion towards lower latitudes under cooler trends since the Oligocene. • Cycles of hybridization-introgression among extant and extinct taxa have resulted in widespread chloroplast capture events. Our data suggest that Nothofagus biogeography will be resolved only if thorough phylogeographic analyses and molecular dating methods are applied using distinct genetic markers.

Retracing the evolutionary history of Nothofagus in its geo-climatic context: new developments in the emerging field of phylogeology

Phylogeographic studies have made a significant contribution to the interpretation of genetic lineage distribution in response to climate changes, such as during glaciation events of the Neogene. However, the effects of ancient landscapes associated with global sea level rises, tectonic processes, and climatology driving lineage evolution have been largely overlooked. These effects can be tested in widespread lineages of cold-tolerant species that have endured cooling, and thus, phylogeographic patterns may reflect large-scale processes that were not reset by the ice ages. We hereby combine geological evidence from marine sedimentary basins, Andean orogeny, and climatology with molecular dating and statistical phylogeography to infer how geological and climatic processes affected the distribution of lineages in cold-tolerant Nothofagus species during the Cenozoic. A total of 239 populations along the entire range of all species within the genus Nothofagus (N. antarctica, N. betuloides, N. dombeyi, N. nitida, and N. pumilio) were sampled and analyzed by sequencing three non-coding regions of the chloroplast. We found 30 chloroplast DNA haplotypes that were geographically structured. Molecular dating calibrated with fossils revealed that ancestral lineages appeared in Eocene/Oligocene, whereas most divergences took place during the Miocene; in turn, Bayesian skyline plots showed that population expansion occurred in the Early Pleistocene (1.5-1 million years ago). Lineage divergence from all wide-ranging Nothofagus was spatially and temporally concordant with episodic marine transgressions and warmer times in Patagonia during Eocene/Miocene Epochs. Long-lasting stable raised areas preserved haplotype diversity throughout Patagonia, from where cold-tolerant taxa expanded their ranges during pre-Quaternary times. The detailed study of such ancient divergences is novel and allows us to infer the effects of geological processes on distribution patterns of ancient lineages, that is, phylogeology.

Living on the edge: adaptive and plastic responses of the tree Nothofagus pumilio to a long-term transplant experiment predict rear-edge upward expansion.

Current climate change affects the competitive ability and reproductive success of many species, leading to local extinctions, adjustment to novel local conditions by phenotypic plasticity or rapid adaptation, or tracking their optima through range shifts. However, many species have limited ability to expand to suitable areas. Altitudinal gradients, with abrupt changes in abiotic conditions over short distances, represent “natural experiments” for the evaluation of ecological and evolutionary responses under scenarios of climate change. Nothofagus pumilio is the tree species which dominates as pure stands the montane forests of Patagonia. We evaluated the adaptive value of variation in quantitative traits of N. pumilio under contrasting conditions of the altitudinal gradient with a long-term reciprocal transplant experimental design. While high-elevation plants show little response in plant, leaf, and phenological traits to the experimental trials, low-elevation ones show greater plasticity in their responses to changing environments, particularly at high elevation. Our results suggest a relatively reduced potential for evolutionary adaptation of high-elevation genotypes, and a greater evolutionary potential of low-elevation ones. Under global warming scenarios of forest upslope migration, high-elevation variants may be outperformed by low-elevation ones during this process, leading to the local extinction and/or replacement of these genotypes. These results challenge previous models and predictions expected under global warming for altitudinal gradients, on which the leading edge is considered to be the upper treeline forests.

Identifying Genetic Hotspots by Mapping Molecular Diversity of Widespread Trees: When Commonness Matters

Conservation planning requires setting priorities at the same spatial scale at which decision-making processes are undertaken considering all levels of biodiversity, but current methods for identifying biodiversity hotspots ignore its genetic component. We developed a fine-scale approach based on the definition of genetic hotspots, which have high genetic diversity and unique variants that represent their evolutionary potential and evolutionary novelties. Our hypothesis is that wide-ranging taxa with similar ecological tolerances, yet of phylogenetically independent lineages, have been and currently are shaped by ecological and evolutionary forces that result in geographically concordant genetic patterns. We mapped previously published genetic diversity and unique variants of biparentally inherited markers and chloroplast sequences for 9 species from 188 and 275 populations, respectively, of the 4 woody dominant families of the austral temperate forest, an area considered a biodiversity hotspot. Spatial distribution patterns of genetic polymorphisms differed among taxa according to their ecological tolerances. Eight genetic hotspots were detected and we recommend conservation actions for some in the southern Coastal Range in Chile. Existing spatially explicit genetic data from multiple populations and species can help to identify biodiversity hotspots and guide conservation actions to establish science-based protected areas that will preserve the evolutionary potential of key habitats and species.

Predominant regeneration strategy results in species-specific genetic patterns in sympatric Nothofagus s.s. congeners (Nothofagaceae)

Life-history traits affect plant performance. Predominant regeneration modes, sprouting v. non-sprouting, will result in contrasting evolutionary and ecological responses that may be traced by nuclear markers. Sympatric Nothofagus Blume species provide the natural setting to test whether sprouters have a greater ability to maintain genetic diversity. In total, 28 populations along the entire distribution range of N. antarctica (G. Forst.) Oerst. were screened by eight polymorphic isozyme loci. We compared pairwise genetic patterns of the predominant sprouter N. antarctica with the mainly non-sprouter N. pumilio (Poepp. & Endl.) Krasser at 20 sympatric locations along their geographically concordant widespread range. Overall, the sprouter N. antarctica showed higher genetic variation throughout its range than did the non-sprouter N. pumilio. Mid-latitude populations of N. antarctica have maintained isozyme diversity, as inferred using genetic-landscape analysis. Despite the potential for inter-specific gene flow and past hybridisations, species identity was preserved by divergent selective forces acting on sympatric populations with distinct autoecological traits. Predominantly sprouting, as compared with mainly non-sprouting, has favoured long-term persistence of genet diversity in relatively large populations that were probably less affected by drift through time, thereby preserving molecular variants along its range. These variants, in combination with plasticity in diverse habitats, have resulted in greater resilience of N. antarctica under changing scenarios.

Population Genetic Structure of the Giant Cactus Echinopsis terscheckii in Northwestern Argentina Is Shaped by Patterns of Vegetation Cover

Species inhabiting drylands commonly depend on the surrounding vegetation for recruitment under stress, while competition may affect populations in moister environments. Our objective was to analyze how different climates and vegetation affect the fine-scale spatial genetic structure (SGS) of the columnar cactus Echinopsis terscheckii. At 4 sites, we estimated vegetation cover by digitized patches and the normalized difference vegetation index (NDVI). We mapped 30 individuals per population and collected tissue for isozyme electrophoresis using 15 putative loci. Spatial autocorrelation between all possible genotype pairs and the number of genetically homogeneous groups and families were calculated for each population. Greater cover (66%) and average NDVI values were detected in the most humid habitat that consisted of fewer, larger, and more dispersed vegetation patches. All populations were genetically diverse and showed significant SGS. Positive correlations were found between the distance at which maximum autocorrelation and kinship values were reached and vegetation area and patch size. Also higher NDVI values were associated with lower number of patches. Populations exposed to higher precipitation and vegetation cover consisted of sparse individuals that clustered at larger distances whereas vegetation patches in arid climates produced groups of closely related genotypes at small distances. These results support the stress-gradient genetic hypothesis. Under water stress, facilitation promotes establishment underneath patchy vegetation resulting in fine-scale family structure. In moister xerophilous forests, competition for resources, that is, light, results in sparse individuals and thus coarse-scale neighborhoods. This information can guide conservation and/or restoration efforts, such as the spatial scale to be considered in germplasm collection.

Variación genética en Nothofagus (subgénero Nothofagus)

El subgenero Nothofagus consiste de cinco especies lenosas que estan presentes en diversas asociaciones forestales de los bosques templados de Argentina y Chile. Dadas las variaciones del medio fisico se esperan variaciones intraespecificas estructurales y funcionales con base genetica. El analisis del acervo genetico de multiples poblaciones de las distintas especies a escala regional, mediante marcadores nucleares y citoplasmaticos con baja tasa de mutacion, permitio resolver las relaciones filogeneticas y reconstruir su historia biogeografica en Patagonia, respectivamente. Secuencias nucleares ITS mostraron que N. pumilio divergio tempranamente y que N. antarctica resulto ser hermana del grupo monofiletico conteniendo las tres especies siempreverdes (N. betuloides, N. dombeyi y N. nitida). Analisis filogeograficos mediante secuencias de ADN del cloroplasto reconstruyeron rasgos antiguos del paisaje del Oligoceno-Mioceno de Patagonia y develaron la existencia de paleohibridaciones. La senal contemporanea provista por polimorfismos isoenzimaticos contribuyo al analisis de patrones espaciales de variacion como el efecto del rango geografico, la formacion de clines y ecotipos, las consecuencias geneticas de los disturbios naturales en relacion con el modo predominante de regeneracion (rebrotante y no-rebrotante) y la hibridacion. Estudios en distintos ambientes habitados por N. antarctica y experimentales en jardin comun y trasplantes reciprocos de N. pumilio en alturas contrastantes, mostraron que caracteres ecofisiologicos y morfologicos de los individuos son el resultado de seleccion natural y plasticidad. Las especies del subgenero Nothofagus son linajes antiguos que han desarrollado adaptaciones a lo largo de su historia evolutiva y, por lo tanto, tendrian el potencial de responder a cambios en el clima.

First presence records of Nothofagus nitida (Nothofagaceae) in Argentina and estimation of its potential distribution area

Nothofagus nitida es una especie arborea siempreverde considerada endemica de los bosques humedos del sur de Chile. En este estudio, se informa el hallazgo de individuos de N. nitida al este de Los Andes en Argentina, ampliandose su area de distribucion geografica potencial, hasta ahora documentada solo para zonas humedas al oeste de la Cordillera de Los Andes, en Chile. Las nuevas localidades corresponden al Brazo Sur del Lago Menendez a orillas de los rios Alerce y del Paso Viejo, en el Parque Nacional Los Alerces, Provincia de Chubut, Argentina. Se tomaron muestras de follaje fresco de cinco individuos que fueron considerados N. nitida putativos a base de la morfologia foliar y corteza. Se extrajo ADN, se amplifico mediante PCR y se secuencio de manera automatica la region ITS del ADN nuclear que permite identificar las distintas especies del subgenero Nothofagus. Las secuencias de ADN obtenidas de cuatro individuos correspondieron de manera inequivoca a N. nitida. Por otro lado, se realizo un modelado de la distribucion de la especie que mostro otras areas potenciales de ocurrencia en Argentina. Este hallazgo amerita la realizacion de esfuerzos para su busqueda en otras localidades al este de Los Andes, utilizando como herramienta los mapas de distribucion potencial a fin de determinar su distribucion y utilizar marcadores geneticos para confirmar su presencia.*Autor de correspondencia: a Universidad Nacional del Comahue, INIBIOMA-CONICET, Quintral 1250, 8400 Bariloche, Río Negro, Argentina, tel.: +54 294 4428505 Int. 110, andrea.premoli@gmail.com b Guardaparque (R), 9211 Lago Puelo, Chubut, Argentina. c Cuerpo de Guardaparques, Parque Nacional Los Alerces, Administración de Parques Nacionales, 9201 Villa Futalaufquen, Chubut, Argentina. d Universidad Nacional de Córdoba, Instituto Multidisciplinario de Biología Vegetal (IMBIV)-CONICET, Córdoba, Argentina. e Universidad Nacional del Comahue, Departamento de Zoología, Bariloche, Río Negro, Argentina.