Experimental admixture among geographically disjunct populations of an invasive plant yields a global mosaic of reproductive incompatibility and heterosis

1. Invasive species have the ability to rapidly adapt in the new regions where they are introduced. Classic evolutionary theory predicts that the accumulation of genetic differences over time in allopatric isolation may lead to reproductive incompatibilities resulting in decreases in reproductive success and, eventually, to speciation. However, experimental evidence for this theoretical prediction in the context of invasive species is lacking. We aimed to test for the potential of allopatry to determine reproductive success of invasive plants, by experimentally admixing genotypes from six different native and non‐native regions of Centaurea solstitialis, an invasive forb for which preliminary studies have detected some degree of reproductive isolation between one native and non‐native region. 2. We grew plants under common garden conditions and outcrossed individuals originating from different source populations in the native and introduced range to evaluate reproductive success in terms of seed to ovule ratio produced. We also assessed geographical and genetic isolation among C. solstitialis regions as a potential driving factor of reproductive success. 3. Experimental admixture generated mixed fitness effects, including significant increases, decreases and no differences in reproductive success as compared to crosses within population (control). Centaurea solstitialis invasive populations in the Americas generated preponderantly negative fitness interactions, regardless of the pollen source, suggesting selection against immigrants and reinforcement. Other non‐native populations (Australia) as well as individuals from the native range of Spain demonstrated an increase in fitness for between‐region crosses, indicating inbreeding. These differences show an asymmetrical response to inter‐regional gene flow, but no evidence of isolation by distance. 4. Synthesis. The speed of adaptation and the accumulation of reproductive incompatibilities among allopatric populations of invasive species might be more rapid than previously assumed. Our data show a global mosaic of reproductive outputs, showcasing an array of evolutionary processes unfolding during colonization at large biogeographical scales

Experimental admixture among geographically disjunct populations of an invasive plant yields a global mosaic of reproductive incompatibility and heterosis

Invasive species have the ability to rapidly adapt in the new regions where they are introduced. Classic evolutionary theory predicts that the accumulation of genetic differences over time in allopatric isolation may lead to reproductive incompatibilities resulting in decreases in reproductive success and, eventually, to speciation. However, experimental evidence for this theoretical prediction in the context of invasive species is lacking. We aimed to test for the potential of allopatry to determine reproductive success of invasive plants, by experimentally admixing genotypes from six different native and non-native regions of Centaurea solstitialis, an invasive forb for which preliminary studies have detected some degree of reproductive isolation between one native and non-native region. We grew plants under common garden conditions and outcrossed individuals originating from different source populations in the native and introduced range to evaluate reproductive success in terms of seed to ovule ratio produced. We also assessed geographical and genetic isolation among C. solstitialis regions as a potential driving factor of reproductive success. Experimental admixture generated mixed fitness effects, including significant increases, decreases and no differences in reproductive success as compared to crosses within population (control). Centaurea solstitialis invasive populations in the Americas generated preponderantly negative fitness interactions, regardless of the pollen source, suggesting selection against immigrants and reinforcement. Other non-native populations (Australia) as well as individuals from the native range of Spain demonstrated an increase in fitness for between-region crosses, indicating inbreeding. These differences show an asymmetrical response to inter-regional gene flow, but no evidence of isolation by distance. Synthesis. The speed of adaptation and the accumulation of reproductive incompatibilities among allopatric populations of invasive species might be more rapid than previously assumed. Our data show a global mosaic of reproductive outputs, showcasing an array of evolutionary processes unfolding during colonization at large biogeographical scales.Fil: Irimia, Ramona E.. Eberhard Karls Universität Tübingen; Alemania. Universidad de Coimbra; PortugalFil: Hierro, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Branco, Soraia. Universidad de Coimbra; PortugalFil: Sotes, Gastón Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina. Universidad de Chile; ChileFil: Cavieres, Lohengrin A.. Universidad de Chile; Chile. Universidad de Concepción; ChileFil: Eren, Ozkan. Adnan Menderes Universitesi; TurquíaFil: Lortie, Christopher J.. University of York; Reino UnidoFil: French, Kristine. No especifíca;Fil: Callaway, Ragan M.. University of Montana; Estados UnidosFil: Montesinos, Daniel. Universidad de Coimbra; Portuga

Trait evolution during a rapid global weed invasion despite little genetic differentiation

Invasive species often possess a great capacity to adapt to novel environments in the form of spatial trait variation, as a result of varying selection regimes, genetic drift, or plasticity. We explored the geographic differentiation in several phenotypic traits related to plant growth, reproduction, and defense in the highly invasive Centaurea solstitialis by measuring neutral genetic differentiation (FST), and comparing it with phenotypic differentiation (PST), in a common garden experiment in individuals originating from regions representing the species distribution across five continents. Native plants were more fecund than non-native plants, but the latter displayed considerably larger seed mass. We found indication of divergent selection for these two reproductive traits but little overall genetic differentiation between native and non-native ranges. The native versus invasive PST–FST comparisons demonstrated that, in several invasive regions, seed mass had increased proportionally more than the genetic differentiation. Traits displayed different associations with climate variables in different regions. Both capitula numbers and seed mass were associated with winter temperature and precipitation and summer aridity in some regions. Overall, our study suggests that rapid evolution has accompanied invasive success of C. solstitialis and provides new insights into traits and their genetic bases that can contribute to fitness advantages in non-native populations

Biogeographic differences in the allelopathy of leaf surface extracts of an invasive weed

Allelopathy, the release of chemicals byplants that inhibit the germination and growth ofcompeting species, can be an important trait forinvasive success. However, little is known aboutpotential biogeographical differences in allelopathydue to divergent regional eco-evolutionary histories.To test this, we examined the allelochemical potentialof the highly invasive species Centaurea solstitialisfrom six world regions including native (Spain,Turkey) and non-native ranges (Argentina, Chile, California and Australia). Seeds from several populationsin each region were collected and grown undercommon garden conditions. Allelopathic potential andchemical composition of three leaf extract concentrationsof C. solstitialis from each region: 0.25%, 0.5%0.75% (w/v-1) were assessed on the phytometerLactuca sativa. The main allelochemicals present inthe leaf-surface extract were sesquiterpene lactonesthat varied in major constitutive compounds acrossregions. These leaf extracts had strong inhibitoryeffects on L. sativa seed germination and net growth.Summed across regions, the 0.25% concentrationsuppressed germination by 72% and radicle elongationby 66%, relative to the controls. At the 0.5% concentration, no seeds germinated when exposed toextracts from the non-native ranges of Argentina andChile, whereas germination and radicle growth werereduced by 98% and 89%, respectively, in theremaining regions, relative to controls. Germinationand seedling growth were completely inhibited at the0.75% concentration extract for all regions. Some nonnativeregions were characterized by relatively lowerconcentrations of allelochemicals, suggesting thatthere is biogeographical variation in allelopathicexpression. These findings imply that rapid selectionon the biochemical signatures of an exotic invasiveplant species can be highly region-specific across theworld.Fil: Irimia, Ramona E.. Universidad de Coimbra; PortugalFil: Lopes, Susana M. M.. Universidad de Coimbra; PortugalFil: Sotes, Gastón. Universidad de Tarapaca.; Chile. Universidad de Chile; ChileFil: Cavieres, Lohengrin A.. Universidad de Chile; Chile. Universidad de Concepción. Facultad de Ciencias Naturales y Oceanografía; ChileFil: Eren, Ozkan. Adnan Menderes Universitesi; TurquíaFil: Lortie, Christopher J.. York University; CanadáFil: French, Kristine. University Of Wollongong. School Of Earth And Enviromental Sciences; AustraliaFil: Hierro, Jose Luis. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Confluencia. Instituto de Ciencias de la Tierra y Ambientales de la Pampa. Grupo Vinculado Fundacion Centro de Salud E Investigaciones Medicas | Universidad Nacional de la Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de la Pampa. Grupo Vinculado Fundacion Centro de Salud E Investigaciones Medicas.; ArgentinaFil: Rosche, Christoph. University of Montana; Estados Unidos. Martin Luther University Halle Wittenberg; AlemaniaFil: Callaway, Ragan M.. University of Montana; Estados UnidosFil: Pinho e Melo, Teresa M. V. D.. Universidad de Coimbra; PortugalFil: Montesinos, Daniel. Universidad de Coimbra; Portugal. James Cook University; Australi