Expansion Front Research Articles

Slow expanders invade by forming dented fronts in microbial colonies

Most organisms grow in space, whether they are viruses spreading within a host tissue or invasive species colonizing a new continent. Evolution typically selects for higher expansion rates during spatial growth, but it has been suggested that slower expanders can take over under certain conditions. Here, we report an experimental observation of such population dynamics. We demonstrate that mutants that grow slower in isolation nevertheless win in competition, not only when the two types are intermixed, but also when they are spatially segregated into sectors. The latter was thought to be impossible because previous studies focused exclusively on the global competitions mediated by expansion velocities, but overlooked the local competitions at sector boundaries. Local competition, however, can enhance the velocity of either type at the sector boundary and thus alter expansion dynamics. We developed a theory that accounts for both local and global competitions and describes all possible sector shapes. In particular, the theory predicted that a slower on its own, but more competitive, mutant forms a dented V-shaped sector as it takes over the expansion front. Such sectors were indeed observed experimentally, and their shapes matched quantitatively with the theory. In simulations, we further explored several mechanisms that could provide slow expanders with a local competitive advantage and showed that they are all well-described by our theory. Taken together, our results shed light on previously unexplored outcomes of spatial competition and establish a universal framework to understand evolutionary and ecological dynamics in expanding populations.

Genetic divergence and range expansion in a western North Pacific coral

Coral poleward range expansions have recently been observed in response to warming oceans. Range expansion can lead to reduced genetic diversity and increased frequency of deleterious mutations that were rare in core populations, potentially limiting the ability for adaptation and persistence in novel environments. Successful expansions that overcome these founder effects and colonize new habitat have been attributed to multiple introductions from different sources, hybridization with native populations, or rapid adaptive evolution. Here, we investigate population genomic patterns of the reef-building coral Acropora hyacinthus along a latitudinal cline that includes a well-established range expansion front in Japan using 2b-RAD sequencing. A total of 184 coral samples were collected across seven sites spanning from ~24°N to near its northern range front at ~33°N. We uncover the presence of three cryptic lineages of A. hyacinthus, which occupy discrete reefs within this region. Only one lineage is present along the expansion front and we find evidence for its historical occupation of marginal habitats. Within this lineage we also find evidence of bottleneck pressures associated with expansion events including higher clonality, increased linkage disequilibrium, and lower genetic diversity in range edge populations compared to core populations. Asymmetric migration between populations was also detected with lower migration from edge sites. Lastly, we describe genomic signatures of local adaptation potentially attributed to lower winter temperatures experienced at the more recently expanded northern populations. Together these data illuminate the genomic consequences of range expansion in a coral and highlight how adaptation to discrete environments along expansion fronts may facilitate further range expansion in this temperate coral lineage.

Human influence on brown trout juvenile body size during metapopulation expansion.

Change in body size can be driven by social (density) and non-social (environmental and spatial variation) factors. In expanding metapopulations, spatial sorting by means of dispersal on the expansion front can further drive the evolution of body size. However, human intervention can dramatically affect these founder effects. Using long-term monitoring of the colonization of the remote Kerguelen islands by brown trout, a facultative anadromous salmonid, we analyse body size variation in 32 naturally founded and 10 human-introduced populations over 57 years. In naturally founded populations, we find that spatial sorting promotes slow positive changes in body size on the expansion front, then that body size decreases as populations get older and local density increases. This pattern is, however, completely different in human-introduced populations, where body size remains constant or even increases as populations get older. The present findings confirm that changes in body size can be affected by metapopulation expansion, but that human influence, even in very remote environments, can fully alter this process.

Characteristics of Impulse Carburization LPC Process.

In the present work, Pyrowear53 steel was subjected to the impulse carburizing LPC process. After carburation, the material was quenched and tempered. Postprocessing analyses included the measurement of hardness, carbon content, residual austenite, and residual stresses. The results revealed that the thermochemical treatment resulted in the formation of an approximately 1200 µm wide carburized layer. The results of hardness, carbon content, and residual austenite measurement showed a continuous gradient (drop) in the measured values within the carburized layer. However, the results of residual stresses revealed the existence of a local extremum, namely, a zone with higher compressive stresses at the depth between 600 and 1000 µm. This was explained by a different temperature for initiation of martensite transformation as a function of carbon content. This difference resulted in the occurrence of two martensite expansion fronts at two different depths, resulting in an increase in compressive stresses at the noted depth range. Moreover, it was concluded that this region was present for material containing between 0.8 and 0.4 wt% carbon for Pyrowear53.

The Dynamics of the Transition from Kardashev Type II to Type III Galaxies Favor Technosignature Searches in the Central Regions of Galaxies

Abstract We present a video of a simulation showing the expansion front of a technological species settling a Milky Way-like galaxy, created using the model described in Carroll-Nellenback et al. It illustrates how even very conservative rates of settlement ship launches and ship ranges can quickly lead to a galaxy endemic with technology, and how the rotational and peculiar motions of stars contributes to the expansion. This video confirms and validates previous work showing that the centers of galaxies are promising search directions for SETI.

Recovery process of genetic diversity through seed and pollen immigration at the northernmost leading‐edge population of Fagus crenata

AbstractThe range expansion of a plant species begins with colonization of ecological empty patches from posterior source populations. This process involves stochastic loss of genetic diversity. However, the founder population could restore genetic diversity by gene flow from posterior populations via seeds and pollen and its recovery affects evolutionary potential for species expansion. To clarify the recovery process of genetic diversity during species range expansion, gene flow via seeds and pollen was investigated at the expansion front of Fagus crenata. Based on eight nuclear microsatellite genotypes of a total of 150 individuals and 225 seeds at the northernmost leading‐edge population, genetic diversity, fine‐scale spatial genetic structure (FSGS), and genetic differentiation from other five northern populations were investigated. Moreover, both seed and pollen immigration and their effects on genetic diversity at different successional stages were analyzed. The leading‐edge population showed lower genetic diversity and substantial genetic differentiation, reflecting its strong genetic drift. Non‐significant FSGS and a negative inbreeding coefficient for mature trees may indicate that the earliest generation consisted of founders from foreign seed sources. The significant proportion of seed and pollen immigration increased the number of different alleles for later successional stages. The effective number of pollen parents from foreign sources (20.8) was markedly higher than that from the local source (2.1). These results indicated that pollen immigration incorporated new and rare alleles and increased the genetic diversity of the population. However, the proportion of foreign gene flow decreased during succession, probably due to the increased reproductive success of local individuals as they reached maturity and grew in size.

The Effect of the Recombination Rate between Adaptive Loci on the Capacity of a Population to Expand Its Range.

AbstractPrevious theoretical work on range expansions over heterogeneous environments showed that there is a critical environmental gradient where range expansion stops. For populations with freely recombining loci underlying the trait under selection (hereafter, "adaptive loci"), the critical gradient in one-dimensional habitats depends on the fitness cost of dispersal and the strength of selection relative to genetic drift. Here, we extend the previous work in two directions and ask, What is the role of the recombination rate between the adaptive loci during range expansions? And what effect does the ability of selfing as opposed to obligate outcrossing have on range expansions? To answer these questions, we use computer simulations. We demonstrate that while reduced recombination rates between adaptive loci slow down range expansions as a result of poor purging of locally deleterious alleles at the expansion front, they may also allow a species to occupy a greater range. In addition, we find that the allowance of selfing may improve the ability of populations to expand their ranges, for example, because selfing among potentially rare high-fitness individuals facilitates the establishment and maintenance of locally well-adapted genotypes. We conclude that during range expansions there is a trade-off between positive and negative effects of recombination within and between individuals.

Evolution of cold tolerance and thermal plasticity in life history, behaviour and physiology during a poleward range expansion

Many species that are moving polewards encounter novel thermal regimes to which they have to adapt. Therefore, rapid evolution of thermal tolerance and of thermal plasticity in fitness-related traits in edge populations can be crucial for the success and speed of range expansions. We tested for adaptation in cold tolerance and in life history, behavioural and physiological traits and their thermal plasticity during a poleward range expansion. We reconstructed the thermal performance curves of life history (survival, growth and development rates), behaviour (food intake) and cold tolerance (chill coma recovery time) in the aquatic larval stage of the damselfly Ischnura elegans that is currently showing a poleward range expansion in northern Europe. We studied larvae from three edge and three core populations using a common-garden experiment. Consistent with the colder annual temperatures, larvae at the expansion front evolved an improved cold tolerance. The edge populations showed no overall (across temperatures) evolution of a faster life history that would improve their range-shifting ability. Moreover, consistent with damselfly edge populations from colder latitudes, edge populations evolved at the highest rearing temperature (28°C) a faster development rate, likely to better exploit the rare periods with higher temperatures. This was associated with a higher food intake and a lower metabolic rate. In conclusion, our results suggest that the edge populations rapidly evolved adaptive changes in trait means and thermal plasticity to the novel thermal conditions at the edge front. Our results highlight the importance of considering besides trait plasticity and the evolution of trait means, also the evolution of trait plasticity to improve forecasts of responses to climate change.

Decreasing glucocorticoid levels towards the expansion front suggest ongoing expansion in a terrestrial mammal.

Understanding the causes of range expansions in abundant species can help predict future species distributions. During range expansions, animals are exposed to novel environments and are required to cope with new and unpredictable stressors. Glucocorticoids (GCs) are mediators of the hormonal and behavioural mechanisms allowing animals to cope with unpredictable changes in the environment and are therefore expected to differ between populations at expansion edge and the historic range. However, to date, very few studies have evaluated the relationship between GCs and range expansion. The Egyptian mongoose has been rapidly expanding its range in Portugal over the past 30years. In this study, we applied an information theoretic approach to determine the most important spatial and environmental predictors of hair GCs (hGCs) in the population, after controlling for normal patterns of hGC variation in the species. We observed a decrease in hGC as distance from the historic range increased (i.e. closer to the expansion front). This distance term was present in all of the top models and had a 95% confidence interval (95% CI) that did not overlap with zero, strongly supporting its influence on hGC. We estimated a 0.031pg/mg (95% CI: -0.057, -0.004) decrease in hGCs for each kilometre distance to the Tagus River, which was once the limit of the species' distribution. Our results indicate that the species' expansion is unlikely to be limited by mechanisms related to or mediated by the physiological stress response. The decrease in hGC levels towards the expansion edge coupled with limited evidence of a negative effect of human population density suggests that the species' northward expansion in Portugal could continue.

Geographic Patterns In Pollen Production In The Plant Ring SpeciesEuphorbia tithymaloidesIn The Caribbean

Abstract—We examine investment in male function in the context of geography and floral morphology in the plant ring speciesEuphorbia tithymaloides, which colonized the Caribbean from Mexico/Guatemala along two fronts that roughly correspond to the Greater and the Lesser Antilles and that meet in the vicinity of the Anegada Passage. Our results on investment in pollen relative to ovule production are consistent withE. tithymaloidesrelying on pollinators for reproduction across its range in the Caribbean. We document a geographic pattern of reduction in anther number and pollen:ovule ratios in populations ofE. tithymaloidestowards the Anegada Passage, which is consistent with a possible geographic transition towards a mixed breeding system where selfing has increased importance in this area where its two expansion fronts meet. The reduction in pollen production is correlated with inflorescence morphology, which converges to relatively shorter cyathia towards the Anegada Passage along both fronts. We discuss alternative scenarios and potential drivers of the patterns we document.

Isotopic niche breadth of a generalist mesopredator increases with habitat heterogeneity across its range

AbstractAlthough generalists are becoming increasingly abundant and widespread, little is known about their response to ecological variation they encounter across their range. For example, the generalist’s flexible diet is cited to help explain recent range expansions, but no study has directly examined this claim. Here, we use stable isotope values of the Virginia opossum (Didelphis virginiana), a true generalist, to examine an extension of MacArthur’s habitat heterogeneity hypothesis for a single generalist species. If a generalist’s diet reflects local food abundance, then more heterogeneous landscapes should result in broader niches. We used stable isotope analysis, landcover indices, and WorldClim data to further evaluate how the opossum’s use of its environment varies across ancestral regions, expansion fronts, and regions of human‐facilitated introductions. Niche breadth varied across its range, especially between expansion fronts. We found a positive relationship between landcover diversity and isotopic niche breadth. WorldClim variables linked to aridity and C4 plant abundance were most strongly associated with nitrogen (δ15N) and carbon (δ13C) values, respectively. Our results reveal that a generalist’s stable isotope signature reflects its local environment, demonstrating their flexible diet is captured with stable isotopes and supporting the generalist habitat heterogeneity hypothesis.

Simulated expansion and ion front formation of ultracold plasma

We report the direct molecular dynamics simulation results of the ultracold two-component plasma expansion. Interaction between charges is described by Coulomb's law. The number of particles varies from 103 to 105. It is shown in this article that the expansion of the plasma begins with the evaporation of some of the electrons and with the transfer of their kinetic energy to the energy of the electric field. After that, the field increases the kinetic energy of the ions. An important result is the detection of the supersonic ion wave formation. On the basis of the calculation results, equations and self-similar solutions are obtained. General dependences on plasma parameters are determined, which are compared with experimental data.

Weak founder effects but significant spatial genetic imprint of recent contraction and expansion of European beech populations.

Understanding the ecological and evolutionary processes occurring during species range shifts is important in the current context of global change. Here, we investigate the interplay between recent expansion, gene flow and genetic drift, and their consequences for genetic diversity and structure at landscape and local scales in European beech (Fagus sylvatica L.) On Mont Ventoux, South-Eastern France, we located beech forest refugia at the time of the most recent population minimum, ~150 years ago, and sampled 71 populations (2042 trees) in both refugia and expanding populations over an area of 15,000 ha. We inferred patterns of gene flow and genetic structure using 12 microsatellite markers. We identified six plots as originating from planting, rather than natural establishment, mostly from local genetic material. Comparing genetic diversity and structure in refugia versus recent populations did not support the existence of founder effects: heterozygosity (He = 0.667) and allelic richness (Ar = 4.298) were similar, and FST was low (0.031 overall). Still, significant spatial evidence of colonization was detected, with He increasing along the expansion front, while genetic differentiation from the entire pool (βWT) decreased. Isolation by distance was found in refugia but not in recently expanding populations. Our study indicates that beech capacities for colonization and gene flow were sufficient to preserve genetic diversity despite recent forest contraction and expansion. Because beech has long distance pollen and seed dispersal, these results illustrate a 'best case scenario' for the maintenance of high genetic diversity and adaptive potential under climate-change-related range change.

Changes in Ecosystem Nitrogen and Carbon Allocation with Black Mangrove (Avicennia germinans) Encroachment into Spartina alterniflora Salt Marsh

Increases in temperature are expected to facilitate encroachment of tropical mangrove forests into temperate salt marshes, yet the effects on ecosystem services are understudied. Our work was conducted along a mangrove expansion front in Louisiana (USA), an area where coastal wetlands are in rapid decline due to compounding factors, including reduced sediment supply, rising sea level, and subsidence. Marsh and mangrove ecosystems are each known for their ability to adjust to sea-level rise and support numerous ecosystem services, but there are some differences in the societal benefits they provide. Here, we compare carbon and nitrogen stocks and relate these findings to the expected effects of mangrove encroachment on nitrogen filtration and carbon sequestration in coastal wetlands. We specifically evaluate the implications of black mangrove (Avicennia germinans) encroachment into Spartina alterniflora-dominated salt marsh. Our results indicate that black mangrove encroachment will lead to increased aboveground carbon and nitrogen stocks. However, we found no differences in belowground (that is, root and sediment) nitrogen or carbon stocks between marshes and mangroves. Thus, the shift from marsh to mangrove may provide decadal-scale increases in aboveground nitrogen and carbon sequestration, but belowground nitrogen and carbon sequestration (that is, carbon burial) may not be affected. We measured lower pore water nitrogen content beneath growing mangroves, which we postulate may be due to greater nitrogen uptake and storage in mangrove aboveground compartments compared to marshes. However, further studies are needed to better characterize the implications of mangrove encroachment on nitrogen cycling, storage, and export to the coastal ocean.

História do contado pelos Akuntsú: ocupação territorial e perdas populacionais

Este artigo descreve o histórico de ocupação territorial e as perdas populacionais relatadas pelos monolíngues Akuntsú. Um povo que sofreu inúmeras perseguições e testemunharam a morte de seus parentes com a chegada das frentes de expansão nacional no estado de Rondônia. Hoje vivem em proteção, devido ao contato feito pela Funai em 1995, quando, então, com suas terras interditadas, conseguiram dar continuidade aos seus processos culturais e atividades cotidianas. Consideramos, assim, neste artigo, relatos de diferentes histórias contadas, principalmente, pelos integrantes mais velhos do grupo: Konibú, já falecido, e sua esposa Pugapia. Atualmente, o povo está reduzido a três pessoas, as quais são memórias vivas de uma história de massacre, perseguições e fugas que aconteceram no estado de Rondônia nas décadas de 80 e 90.

Niche opportunity created by land cover change is driving the European hare invasion in the Neotropics

The European hare (Lepus europaeus) was introduced in the late 19th century in Argentina and has since rapidly expanded northwards, currently occupying the Brazilian south and southeast. Although European hare is known to be a farmland specialist in its native Europe, what habitat types or landscape features are facilitating its expansion in the Neotropics are not yet clear. Here we assessed support to the disturbance and biotic resistance hypotheses as general drivers of this invasion. We sampled with camera-traps and track surveys 205 sites in three landscapes in southeastern Brazil. We used occupancy models that corrected for both false positive and false negative errors. The disturbance hypothesis was the top-ranked (w = 0.66) with the amount of field, sugarcane, and managed forests all affecting strongly and positively hare occupancy. Support to the biotic resistance hypothesis was lower (ΔAICc = 2.14; w = 0.23) and partial, since only native forests showed a negative effect on hare occupancy. Our findings indicate that in the expansion front occupancy of this invader is mainly dictated by niche opportunities created by native habitat transformation into agricultural lands. The biotic resistance imposed by remaining native habitats seems to play a secondary role and only due to native forests. We conclude that hare geographical expansion should increase given the prominent role of Brazil as a commodity producer and exporter. Nevertheless, fomenting forested protected areas and improving adherence of rural owners to the Brazilian Forest Act, which protects forests in private rural properties, might help lessen this spread.

Features of decomposition of gas hydrate when exposed to microwave radiation

The article summarizes the results of numerical monitoring of the decomposition of gas hydrates in a high frequency electromagnetic field. The results of the numerical experience of the decay process are summarized. In addition, the distribution of temperature and pressure is presented, but in addition, the relationship with the coefficient of permeability. In this article, the features of decomposition of methane hydrate under the influence of microwave radiation are studied. It is shown that the values of temperature and pressure in the reservoir decrease with time and distance from the source of microwave radiation. The dependence of the expansion front coordinate on time for different values of the permeability coefficient is presented.

The novel features of Plantagoovata seed mucilage accumulation, storage and release

Seed mucilage polysaccharide production, storage and release in Plantagoovata is strikingly different to that of the model plant Arabidopsis. We have used microscopy techniques to track the development of mucilage secretory cells and demonstrate that mature P.ovata seeds do not have an outer intact cell layer within which the polysaccharides surround internal columellae. Instead, dehydrated mucilage is spread in a thin homogenous layer over the entire seed surface and upon wetting expands directly outwards, away from the seed. Observing mucilage expansion in real time combined with compositional analysis allowed mucilage layer definition and the roles they play in mucilage release and architecture upon hydration to be explored. The first emergent layer of hydrated mucilage is rich in pectin, extremely hydrophilic, and forms an expansion front that functions to ‘jumpstart’ hydration and swelling of the second layer. This next layer, comprising the bulk of the expanded seed mucilage, is predominantly composed of heteroxylan and appears to provide much of the structural integrity. Our results indicate that the synthesis, deposition, desiccation, and final storage position of mucilage polysaccharides must be carefully orchestrated, although many of these processes are not yet fully defined and vary widely between myxospermous plant species.

Invisibilidade dos negros na história de Gramado/RS

O município de Gramado, no Estado do Rio Grande do Sul, é reconhecido destino turístico no Brasil, e apresentado como um espaço de colonização alemã, italiana e portuguesa. A ausência dos negros na história oficial, a inexistência de pesquisas acadêmicas sobre o assunto e a necessidade de material pedagógico para auxiliar no ensino de história e cultura afro-brasileira, promoveu o início dessa pesquisa que está em estágio preliminar. Pesquisas acadêmicas no entorno de Gramado comprovam significativa população de descendência africana no século XIX, além disso uma extensa rede de compadrio entre proprietários de terras e afro-brasileiros. A ausência de dados oficiais conduz a pesquisa para a análise dos lugares de memória, por meio de indícios encontrados em livros de memorialistas locais, fotografias e paisagens. Os resultados coletados até o presente indicam que os negros sempre estiveram presentes na história da região, tanto na frente de expansão quanto na frente pioneira, e também apontam para um provável esquecimento proposital dessa população.

Genetic Melting Pot in Blacklegged Ticks at the Northern Edge of their Expansion Front.

Blacklegged ticks (Ixodes scapularis) are considered to be the main vector of Lyme disease in eastern North America. They may parasitize a wide range of bird and mammal hosts. Northward dispersal of blacklegged ticks has been attributed largely to movement of hosts to areas outside of the current range of the tick, in conjunction with climate change. To better understand the drivers of range expansion in the blacklegged tick, we need investigations of the genetic connectivity and differentiation of tick populations at a fine spatial scale using appropriate markers. In this study, we investigated genetic connectivity and differentiation in blacklegged ticks, in an area of putatively recent advance in Ontario and Quebec, Canada, using microsatellite markers. Our findings suggest patchy differentiation of alleles, no spatial pattern of genetic structure, and genetic subdivision within sites, which are consistent with the very limited evidence available near the leading edge of range expansion of blacklegged ticks into Canada. These findings are consistent with the prevailing hypothesis, drawn from a variety of fields of study, suggesting that migratory birds from a variety of regions may be bringing hitchhiking ticks northward into Canada.