High Dispersal Rates Research Articles

Lasting through the ice age: The role of the proglacial refugia in the maintenance of genetic diversity, population growth, and high dispersal rate in a widespread freshwater crustacean

Abstract The severe climatic changes during the Pleistocene ice ages have shaped the genetic structure and distribution of biota in Europe. We aimed to reveal in detail the genetic diversity, geographical population structure, historical and present demography, migration patterns, and the presence of possible glacial refugia within the nominative subspecies Asellus aquaticus aquaticus. We analysed DNA sequences of the mitochondrial cytochrome c oxidase subunit I gene and nuclear noncoding internal transcribed spacer II region, from populations inhabiting post‐glacial Europe (from the British Isles and Scandinavia to the northern Mediterranean and Black Sea coasts). The origin of the taxon, including establishment in the Dinaric Western Balkans, dates to the Middle/Late Pliocene, but most of its genetic diversity emerged during the Middle/Late Pleistocene before the Last Glacial Maximum. Despite the general absence of spatial genetic structure with population growth, we discovered two different phylogeographic stories across 11 clusters revealed by a coalescent approach. Firstly, the periglacial cluster group—spatially restricted mainly to the northern Balkans, Pannonian Basin, and Pontic Region—is older and more divergent. It apparently retained a relatively stable population size during the glacial‐interglacial cycles. Conversely, the proglacial cluster group—widely distributed in areas close to the glacier margins (north of the Alps, Sudetes, Carpathians) and in the Pannonian Basin—is younger and composed of closely related individuals. It originated in Pleistocene and lasted continuously through the Last Glacial Maximum in numerous high latitude refugia. This was probably due to the vast network of proglacial lakes and rivers, which played a crucial role in the maintenance of genetic diversity, population growth, and high dispersal rate. The evolutionary history of A. a. aquaticus reveals unexpected patterns and is an important lesson when making predictions for other aquatic taxa. Our results suggest that we should stop perceiving the proglacial habitats as lifeless ice desert.

Dispersion Overrides Environmental Variability as a Primary Driver of the Horizontal Assemblage Structure of the Mesopelagic Fish Family Myctophidae in the Northern Gulf of Mexico

The lanternfishes (Myctophidae) are a highly speciose, globally-distributed family of fishes that constitute a dominant component of the global pelagic fauna. As a vertically-migrating taxon of oceanic micronekton, myctophids play vital ecological roles in the biological carbon pump and as an important prey group for several commercially-important species. However, our knowledge of the ecology of this taxon remains incomplete, and as anthropogenic impacts continue to develop and extend into deeper waters, there is a clear need for a better understanding of its ecological role and assemblage dynamics. The aim of the present study was to examine the distribution patterns of the myctophid assemblage within a 200 × 700 km grid of the northern Gulf of Mexico (GoM) in relation to major mesoscale hydrographic features. The 22 dominant myctophid species (> 0.05% by relative abundance) were analysed from a total of 302 trawl samples collected between January and September 2011, from 0 – 1000 m depth. Redundancy analysis (RDA) indicated that measured environmental variables and spatial patterning explained an average of 12% (range 0 – 27%) of the observed variance in the myctophid assemblage. Distance-based Moran’s Eigenvector Mapping (dbMEM) and trend analysis (RDA) indicated limited significant spatial coherence within the assemblage at the scales considered. Local contribution to beta diversity (LCBD) scores corroborated these findings, indicating that the majority of samples were not significantly different from the mean assemblage structure. Taken together, these results suggest that the myctophid assemblage in the northern GoM is well-mixed and highly dispersed at the sub-basin scale (at least), likely the result of the interaction between vertical migration and depth-specific lateral advection. Findings such as these inform our approach to assessing impacts in a large, dynamic, pelagic ecosystems. It is essential to know over what spatial scales assessments of pelagic faunal impacts, and potential recoveries, must be based. In cases of large, spatially integrated pelagic assemblages, high dispersal rates may serve to either ameliorate the effects of a disturbance through immigration or spread the effects across a wider spatial area than the disturbance phenomenon footprint itself.

Population genetics of the invasive wasp Vespula germanica in South Africa

The German wasp (Vespula germanica) is a highly successful invader on a global scale. These wasps were first observed in the Western Cape region in South Africa in 1972, and they have the potential to expand their range and cause significant damage to the native biodiversity. Our study used nuclear (DNA microsatellites) and mitochondrial DNA (mtDNA) from 42 wasp colonies to analyse the population genetics of V. germanica in their invaded South African range. We sequenced three mitochondrial genes; cytochrome c oxidase I, cytochrome b and cytochrome c oxidase II. We found six mtDNA haplotypes present in South Africa. Although only a single fertilized queen is sufficient for the establishment of a wasp nest, the probability of a single introduced queen to successfully establish a nest and a population is very small. If multiple queens were introduced at the same time, the probability for more than one haplotype being transferred to the new population increases. Therefore, the true number of queen introductions occurred in South Africa can be inferred to be between two and six. We examined nine microsatellite loci and found weak-to-no genetic sub-structuring, likely due to high dispersal rates. We concluded that German wasps in South Africa maintain a homogenous population with movement of individuals between localities.

Ecological Connectivity in Two Ancient Lakes: Impact Upon Planktonic Cyanobacteria and Water Quality

The ancient lakes Mikri Prespa and Megali Prespa are located in SE Europe at the transnational triangle and are globally recognized for their ecological significance. They host hundreds of flora and fauna species, and numerous types of habitat of conservational interest. They also provide a variety of ecosystem services. Over the last few decades, the two lakes have been interconnected through a surface water channel. In an attempt to explore whether such a management practice might alter the ecological properties of the two lakes, we investigated a series of community metrics for phytoplankton by emphasizing cyanobacteria. Our results demonstrate that the cyanobacterial metacommunity structure was affected by directional hydrological connectivity and high dispersal rates, and to a lesser extent, by cyanobacterial species sorting. Cyanobacterial alpha diversity was twofold in the shallow upstream Lake Mikri Prespa (Simpson index average value: 0.70) in comparison to downstream Lake Megali Prespa (Simpson index average value: 0.37). The cyanobacterial assemblage of the latter was only a strict subset of that in Mikri Prespa. Similarly, beta diversity components clearly showed a homogenization of cyanobacteria, supporting the hypothesis that water flow enhances fluvial translocation of potentially toxic and bloom-forming cyanobacteria. Degrading of the water quality in the Lake Megali Prespa in anticipation of improving that of the Lake Mikri Prespa is an issue of great concern for the Prespa lakes’ protection and conservation.

Artificial selection for increased dispersal results in lower fitness.

Dispersal often covaries with other traits, and this covariation was shown to have a genetic basis. Here, we wanted to explore to what extent genetic constraints and correlational selection can explain patterns of covariation between dispersal and key life-history traits-lifespan and reproduction. A prediction from the fitness-associated dispersal hypothesis was that lower genetic quality is associated with higher dispersal propensity as driven by the benefits of genetic mixing. We wanted to contrast it with a prediction from a different model that individuals putting more emphasis on current rather than future reproduction disperse more, as they are expected to be more risk-prone and exploratory. However, if dispersal has inherent costs, this will also result in a negative genetic correlation between higher rates of dispersal and some aspects of performance. To explore this issue, we used the dioecious nematode Caenorhabditis remanei and selected for increased and decreased dispersal propensity for 10 generations, followed by five generations of relaxed selection. Dispersal propensity responded to selection, and females from high-dispersal lines dispersed more than females from low-dispersal lines. Females selected for increased dispersal propensity produced fewer offspring and were more likely to die from matricide, which is associated with a low physiological condition in Caenorhabditis nematodes. There was no evidence for differences in age-specific reproductive effort between high- and low-dispersal females. Rather, reproductive output of high-dispersal females was consistently reduced. We argue that our data provide support for the fitness-associated dispersal hypothesis.

Patterns of population structure and complex haplotype sharing among field isolates of the green alga Chlamydomonas reinhardtii.

The nature of population structure in microbial eukaryotes has long been debated. Competing models have argued that microbial species are either ubiquitous, with high dispersal and low rates of speciation, or that for many species gene flow between populations is limited, resulting in evolutionary histories similar to those of macroorganisms. However, population genomic approaches have seldom been applied to this question. Here, we analyse whole-genome resequencing data for all 36 confirmed field isolates of the green alga Chlamydomonas reinhardtii. At a continental scale, we report evidence for putative allopatric divergence, between both North American and Japanese isolates, and two highly differentiated lineages within N. America. Conversely, at a local scale within the most densely sampled lineage, we find little evidence for either spatial or temporal structure. Taken together with evidence for ongoing admixture between the two N. American lineages, this lack of structure supports a role for substantial dispersal in C.reinhardtii and implies that between-lineage differentiation may be maintained by reproductive isolation and/or local adaptation. Our results therefore support a role for allopatric divergence in microbial eukaryotes, while also indicating that species may be ubiquitous at local scales. Despite the high genetic diversity observed within the most well-sampled lineage, we find that pairs of isolates share on average ~9% of their genomes in long haplotypes, even when isolates were sampled decades apart and from different locations. This proportion is several orders of magnitude higher than the Wright-Fisher expectation, raising many further questions concerning the evolutionary genetics of C.reinhardtii and microbial eukaryotes generally.

Synthesis of Nano Copper Shell for Conductive Ink in Wearable Electronics

Number of emerging synthesis techniques were revealed to synthesize the copper nanoparticles (CuNp) with reduced oxide states to improve the conductivity by various researchers. This research work highlights about the synthesis of surface oxide layer free copper nanoparticles (CuNp) using less expensive chemical reduction method by reducing the oxide states. Poly Vinyl Pyrolidone were used as a capping agent and Ascorbic acid as reducing agents for minimizing the oxide layer of CuNp. SEM, XRD, FTIR and Zeta Potential by particle size analyzer of synthesized powder were characterized.SEM images shows the particle size in the range of 100-300nm. XRD peaks expressed at 43.3482, 50.4653 and 74.1109 correspondence to the planes of (111), (200) and (220) confirms the presence of nanocopper in the sample. Particle size analyzer results exhibits the average particle size of CuNp as 141.2 nm. The peaks of FTIR spectrum at 3747 cm-1, 1887 cm-1, and 1690 cm-1 confirm the presence of polyhydroxyl groups, which indicates the high dispersion rate of CuNp in the taken solvent. Further, the work reviewed to find the suitable binding agent to fabricate nanoconductive ink. The outcome of the study takes us closer towards to fabricate nano conductive ink using CuNp for flexible electronics.

Experimental and theoretical landscape influences on Spodoptera frugiperda movement and resistance evolution in contaminated refuge areas of Bt cotton

Transgenic cotton plants producing Bacillus thuringiensis (Bt) (Berliner) insecticidal proteins have contributed to the management of key lepidopteran pests. Larval high dispersal rates between non-Bt and Bt plants in landscapes with seed contamination can speed the evolution of insect resistance to Bt plants. We evaluated the effect of Bt and non-Bt cotton plants on the larval dispersal pattern and survival of susceptible, heterozygous and Cry1F-resistant Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) genotypes in pure and contaminated artificial micro-landscape. A computer model was used to analyse the consequences of S. frugiperda larval dispersal behaviour on resistance evolution in refuge areas with different contamination levels and migration of different adult genotype combinations. The biological data from artificial micro-landscape experiments were used in simulations of macro-landscape scales. The Cry1F-resistant genotype avoided non-Bt cotton. The heterozygote had a similar larval dispersal behaviour as the susceptible genotype when non-Bt cotton was the central plant. Our simulations provide evidence that in refuge areas contaminated with Bt cotton plants, the evolution of resistance may be > 75-fold faster in relation to a contamination-free refuge. In conclusion, S. frugiperda resistance management practices on regional scales with contamination-free refuges are important to prevent loss in different crops.

Ant diversity patterns across tropical elevation gradients: effects of sampling method and subcommunity

AbstractLocal diversity may be influenced by niche assembly processes involving competition for limited resources, or by niche conservatism and the length of time clades have had to diversify. Mid‐elevation peaks in ant diversity on wet forest elevational gradients are most consistent with niche conservatism effects. However, it is possible that subsets of the ant community vary in the degree to which niche assembly processes are important, and this may be revealed by sampling methods that bias toward particular subsets. A previous study of ant‐elevation patterns in Middle American wet forest relied on Winkler sampling, a method that samples much of the ant community that occurs in leaf litter and rotten wood on the forest floor. Here, we evaluate richness patterns at the same sites as the previous study, using two alternative methods: baiting and beating. Baiting attracts ants to a concentrated resource and might be expected to attract a community more shaped by competitive interactions. Diversity patterns at baits were nearly identical to patterns from Winkler samples, for all ants combined and for the genus Pheidole, which are abundant omnivorous ants that are among the most common at baits. There was no evidence that stronger competitive effects influenced the shape of the diversity curve. Beating samples capture ants that forage on low vegetation, a distinct arboreal community with lower phylogenetic diversity than litter ants and inhabiting a more variable microclimate. Arboreal ants differed from litter ants in having a less distinct mid‐elevation peak, with less of a decline from 500 m to sea level. The lowland decline in litter ant diversity may be caused by the recent upslope shift in temperature associated with the current interglacial period. Arboreal ants may be buffered from this effect by adaptation to canopy life, tolerating broader extremes of temperature, or by high rates of dispersal from warmer regions.

The disappearing periglacial ecosystem atop Mt. Kilimanjaro supports both cosmopolitan and endemic microbial communities

Microbial communities have not been studied using molecular approaches at high elevations on the African continent. Here we describe the diversity of microbial communities from ice and periglacial soils from near the summit of Mt. Kilimanjaro by using both Illumina and Sanger sequencing of 16S and 18S rRNA genes. Ice and periglacial soils contain unexpectedly diverse and rich assemblages of Bacteria and Eukarya indicating that there may be high rates of dispersal to the top of this tropical mountain and/or that the habitat is more conducive to microbial life than was previously thought. Most bacterial OTUs are cosmopolitan and an analysis of isolation by geographic distance patterns of the genus Polaromonas emphasized the importance of global Aeolian transport in the assembly of bacterial communities on Kilimanjaro. The eukaryotic communities were less diverse than the bacterial communities and showed more evidence of dispersal limitations and apparent endemism. Cercozoa dominated the 18S communities, including a high abundance of testate amoebae and a high diversity of endemic OTUs within the Vampyrellida. These results argue for more intense study of this unique high-elevation “island of the cryosphere” before the glaciers of Kilimanjaro disappear forever.

Establishment Limitation Constrains the Abundance of Lactic Acid Bacteria in the Napa Cabbage Phyllosphere.

Patterns of phyllosphere diversity have become increasingly clear with high-throughput sequencing surveys, but the processes that control phyllosphere diversity are still emerging. Through a combination of lab and field experiments using Napa cabbage and lactic acid bacteria (LAB), we examined how dispersal and establishment processes shape the ecological distributions of phyllosphere bacteria. We first determined the abundance and diversity of LAB on Napa cabbage grown at three sites using both culture-based approaches and 16S rRNA gene amplicon sequencing. Across all sites, LAB made up less than 0.9% of the total bacterial community abundance. To assess whether LAB were low in abundance in the Napa cabbage phyllosphere due to a limited abundance in local species pools (source limitation), we quantified LAB in leaf and soil samples across 51 vegetable farms and gardens throughout the northeastern United States. Across all sites, LAB comprised less than 3.2% of the soil bacterial communities and less than 1.6% of phyllosphere bacterial communities. To assess whether LAB are unable to grow in the phyllosphere even if they dispersed at high rates (establishment limitation), we used a gnotobiotic Napa cabbage system in the lab with experimental communities mimicking various dispersal rates of LAB. Even at high dispersal rates, LAB became rare or completely undetectable in experimental communities, suggesting that they are also establishment limited. Collectively, our data demonstrate that the low abundance of LAB in phyllosphere communities may be explained by establishment limitation.IMPORTANCE The quality and safety of vegetable fermentations are dependent on the activities of LAB naturally present in the phyllosphere. Despite their critical role in determining the success of fermentation, the processes that determine the abundance and diversity of LAB in vegetables used for fermentation are poorly characterized. Our work demonstrates that the limited ability of LAB to grow in the cabbage phyllosphere environment may constrain their abundance on cabbage leaves. These results suggest that commercial fermentation of Napa cabbage proceeds despite low and variable abundances of LAB across different growing regions. Propagule limitation may also explain ecological distributions of other rare members of phyllosphere microbes.

Relationships between soil seed bank composition and standing vegetation along chronosequences in a tropical dry forest in north-eastern Brazil

AbstractTo better understand the role of seed banks in ecological succession of dry forests, we compared similarities between vegetation and seed banks and assessed the relative contributions of seed dispersal and persistence in chronosequences in the Brazilian semi-arid region. To sample the standing vegetation and the seed bank, we collected data in three sites with three successional ages in each one (5 y, 25 y and 45 y). A total of 180 soil samples (three sites × three successional ages × 10 plots × two components) were collected. The composition of the seed bank was assessed by the seedling emergence method. Of 166 species identified in the standing vegetation, only 50 (30.1%) were also present in the seed bank, resulting in low similarity (Jaccard index = 0.02–0.21) and reflecting the rarity of woody species and the dominance of annuals (71% of richness). The relative importance of seed persistence and seed dispersal to seed banks composition were balanced in most cases (difference was not rejected in four out six comparisons). Those results suggest that seed banks in tropical dry forests are largely the result of high dispersal rates and the persistence of allochthonous annual species that contribute to decoupling seed bank and vegetation composition.

Comparing Pool-seq, Rapture, and GBS genotyping for inferring weak population structure: The American lobster (Homarus americanus) as a case study.

Unraveling genetic population structure is challenging in species potentially characterized by large population size and high dispersal rates, often resulting in weak genetic differentiation. Genotyping a large number of samples can improve the detection of subtle genetic structure, but this may substantially increase sequencing cost and downstream bioinformatics computational time. To overcome this challenge, alternative, cost‐effective sequencing approaches, namely Pool‐seq and Rapture, have been developed. We empirically measured the power of resolution and congruence of these two methods in documenting weak population structure in nonmodel species with high gene flow comparatively to a conventional genotyping‐by‐sequencing (GBS) approach. For this, we used the American lobster (Homarus americanus) as a case study. First, we found that GBS, Rapture, and Pool‐seq approaches gave similar allele frequency estimates (i.e., correlation coefficient over 0.90) and all three revealed the same weak pattern of population structure. Yet, Pool‐seq data showed F ST estimates three to five times higher than GBS and Rapture, while the latter two methods returned similar F ST estimates, indicating that individual‐based approaches provided more congruent results than Pool‐seq. We conclude that despite higher costs, GBS and Rapture are more convenient approaches to use in the case of species exhibiting very weak differentiation. While both GBS and Rapture approaches provided similar results with regard to estimates of population genetic parameters, GBS remains more cost‐effective in project involving a relatively small numbers of genotyped individuals (e.g., <1,000). Overall, this study illustrates the complexity of estimating genetic differentiation and other summary statistics in complex biological systems characterized by large population size and migration rates.

Comparative spatial genetic structure of two rodent species in an agro-ecological landscape in southern Africa

Determining the scale of genetic variation informs studies of dispersal, connectivity, and population dynamics particularly in heterogeneous landscapes. Mastomys natalensis and Mus minutoides are generalist rodents that utilize multiple habitat types within the agro-ecological landscapes of southern African savannas. To study the comparative spatial genetic structure of these species we developed 9 new microsatellites for Mus and used 14 microsatellite loci previously developed for Mastomys, to genotype rodents sampled across an agro-ecological landscape (˜200 km2). Spatial genetic structure was measured using spatial autocorrelation and Moran’s Eigenvector Maps analysis. In both species, non-random genetic similarity was limited to only the smallest spatial scales (<600 m), and at that scale, it was significantly greater in Mastomys than in Mus. Only a small proportion of the genetic signal across the landscape was due to spatial signal in Mastomys, and there was no spatial signal detected for Mus. The lack of spatial autocorrelation beyond the first six hundred meters for both species illustrated that they are capable of high rates of dispersal, while the observed patterns of genetic panmixia found for both species is the predicted genetic outcome for species with omnivorous habits and plastic habitat use. These findings have implications for both pest management and rodent-borne disease control.

Increase of genetic diversity indicates ecological opportunities in recurrent-fire landscapes for wall lizards

Socioeconomic and climatic factors are modifying fire regimes with an increase of fire frequency and extension. Unfortunately, the effects of recurrent fires on biological processes that ultimately affect the genetic diversity of animal populations are mostly unknown. We examined genetic patterns of diversity in the wall lizard Podarcis guadarramae in northern Portugal, one of the European regions with the highest percentage of burnt land. This species is a small saxicolous lizard as it inhabits natural outcrops and artificial stone walls, likely in recurrent-fire landscapes. We genotyped nine microsatellites from ten populations selected according to a gradient in fire recurrence, and compared genetic diversity indexes and demographic patterns among them. At the population level, we hypothesize that a high level of mortality and population bottlenecks are expected to reduce genetic heterozygosity in sampled localities affected by recurrent fires. Alternatively, genetic signatures are expected to be absent whether fire did not cause high mortality. Regardless of levels of mortality, we expect a gain in genetic diversity whether recurrent fires facilitate lizard dispersal and migration due to the increased quality of the habitat for wall lizards. At the regional level, we examine whether a recurrent fire regime may disrupt the spatial structure of populations. Our results showed an increase in genetic diversity in recurrently burnt populations, and a decline in longer-unburnt populations. We did not detect bottleneck effects in repeatedly-burnt populations. High genetic diversity in recurrent fire populations suggests a high dispersion rate between adjacent metapopulations and perhaps immigration from outside the fire boundary. At the regional level, lizard populations show low differentiation and weak genetic structure, suggesting no effects of fire. This study confirms field-based censuses showing that recurrent-fire regimes give ecological opportunities to wall lizards that benefit from habitat openness.

Offspring Microbiomes Differ Across Breeding Sites in a Panmictic Species.

High dispersal rates are known to homogenize host’s population genetic structure in panmictic species and to disrupt host local adaptation to the environment. Long-distance dispersal might also spread micro-organisms across large geographical areas. However, so far, to which extent selection mechanisms that shape host’s population genetics are mirrored in the population structure of the enteric microbiome remains unclear. High dispersal rates and horizontal parental transfer may homogenize bacterial communities between breeding sites (homogeneous hypothesis). Alternatively, strong selection from the local environment may differentiate bacterial communities between breeding sites (heterogeneous hypothesis). Furthermore, selection from age-specific environmental or physiological factors may differentiate the microbiome between juveniles and adults. Here, we analyzed the cloacal bacterial 16S rRNA gene of fledgling greater flamingos, Phoenicopterus roseus, across nine western Mediterranean breeding sites and four breeding seasons (n = 731) and adult birds (n = 27) from a single site. We found that fledgling cloacal microbiome, as measured by alpha diversity, beta diversity, the relative abundance of assigned sequence variants (ASVs) belonging to a phylum and genus composition within phylum, varied significantly between sampling sites and across time within site despite high adult dispersal rates. The spatio-temporal effects were stronger on individual ASV absence/presence than on ASV abundance (i.e., than on core microbiome composition). Spatial effects had a stronger effect than temporal effects, particularly on ASV abundance. Our study supports the heterogeneous hypothesis whereby local environmental conditions select and differentiate bacterial communities, thus countering the homogenizing effects of high-dispersing host species. In addition, differences in core microbiome between adult vs. fledgling samples suggests that differences in age-specific environmental and/or physiological factors result in differential selection pressure of core enteric microbiome between age classes, even within the same environment. In particular, the genus Corynebacterium, associated with both seasonal fat uptake and migration in previous studies, was much more abundant in high-dispersing fledglings than in more resident adults. To conclude, selection mechanisms that shape the host’s genetic structure cannot be extended to the genetic structure of the enteric microbiome, which has important implications regarding our understanding of both host local adaptation mechanisms and enteric microbiome population genetics.

Anthropogenic impacts on aquatic bacteria: a perspective from the tropics

Abstract Bacterioplankton comprises a highly diverse group of microorganisms, which are dominant in aquatic ecosystems, and play a central role in ecosystem functioning and biogeochemical cycles. Due to their high turnover and dispersal rates, as well as high adaptability and plasticity, microbes are likely to respond quickly to environmental changes and perturbations on their ecosystems. In this opinion paper, we reviewed some studies that addressed bacterial community’s responses to anthropogenic impacts in their aquatic environments. Inorganic nutrients and organic matter inputs from the catchment areas are likely to increase due to changes in climate and land use. These changes will impact the microbial community composition and metabolism, as well the amount of energy and carbon flowing through aquatic food webs as mostly demonstrated in studies from temperate and boreal systems. However, due to the low number of studies on microbial communities in tropical ecosystems, our understanding of how they will respond to perturbations in this distinct environmental context is still limited. Research in microbial ecology in southern countries is still in its infancy and deserves more attention in the future, since tropical aquatic ecosystems are hotspots of biodiversity, host most of the world freshwater reserves, and play a key role in global biogeochemical cycles.

Assessment of soil physical properties' statuses under different land covers within a landscape dominated by exotic industrial tree plantations in south-central Chile

Land use and land cover changes (LULCC) within a highly anthropized Mediterranean landscape dominated by industrial tree plantation leads to degradation of soil physical properties. This process has been more intense in the coastal range of south-central Chile due to its soils, which are highly susceptible to erosion, combined with a long history of intensive land use changes during the last century, transitioning from native forest (NF) to agriculture and the more recent establishment of Pinus radiata and Eucalyptus spp. exotic tree plantations. In this context, the aim of this study was to assess the statuses of soil physical properties over different land cover situations. Historical land cover maps were determined via supervised classifications using the maximum likelihood classifier applied to satellite imagery. Five land use and land cover categories (LULC) were defined according to main land cover transitions associated with active and abandoned forestry operations that have been reported in the region: NF, pine plantation (P), eucalyptus plantation (Eu), early successional (E-S), and secondary successional (S-S). Successional stages were generated using change detection statistics considering changes between 2001 and 2014 maps. Soil samples were collected at three depths in 39 plots that describe the five LULC. High clay contents were found in all the LULC except Eu and P. These sites have shown more signs of degradation, with lower organic matter (SOM) and macropores and higher shear strength (ShS). Soil organic matter was consistent with litter contribution and quality, establishing lower bulk density (Db) for NF and S-S and higher values for Eu and E-S. ShS and dispersion rate (DR) exhibit a correlation with SOM with lower ShS and higher DR when SOM increased. Relevant differences were identified for structural stability index (SSI) between LULC depending on soil physical quality, besides a positive correlation with SOM. Those results show the need to generate appropriate conditions of vegetation cover in order to recover soils subjected to current forestry management of industrial plantations.

The introduction, spread and ecology of redclaw crayfish Cherax quadricarinatus in the Zambezi catchment

Two of the four crayfish species brought to Zambia for aquaculture since 1979 are now naturalised. Procamburus clarkii occurs in the Maramba River at Livingstone, close to a former fish farm, whereas Cherax quadricarinatus, deliberately introduced to a number of sites in the Zambezi and Kafue River catchments since 2001, is now widespread and highly invasive. High rates of dispersal, up to 111 km y−1 downstream, might be the result of passive transport on floating vegetation. Significantly more synodontid Synodontis sp. catfish were caught in Fladen traps in the Kafue River in crayfish-free areas compared with crayfish-infested areas, but the possibility that synodontids became trap averse in the presence of crayfish was not ruled out. No difference was found in the numbers of Single-spined River Crab Potamonautes unispinus caught in crayfish-free and infested areas. Alien temnocephalans, commonly found on crayfish, are now also present on crabs P. unispinus on the Kafue Flats. The artisanal gill net fishery has been harmed by the introduction of C. quadricarinatus and no significant commercial fishery has developed. However, without more information on the adverse impacts, and stronger fisheries regulation, there is a high risk C. quadricarinatus and P. clarkii will be introduced to uninfested catchments with irreversible consequences for artisanal fishermen and the environment.

Factors affecting the biological control of the spiralling whitefly Aleurodicus dispersus (Hemiptera: Aleyrodidae) in banana plantations in Costa Rica: a study case

ABSTRACTA study was conducted to reveal the causes for Aleurodicus dispersus outbreak in commercial banana plantations in Costa Rica. Biotic and abiotic factors affecting the abundance of the spiralling whitefly were determined. Four nymph parasitoids and nine predators were found to affect A. dispersus population. Seventeen families of host plants for A. dispersus in the banana area were identified, allowing the whitefly to reach a high reproductive and dispersal rate and pest status in short periods. The use of nematicides during the dry season was the key factor for mortality of natural enemies responsible for maintaining pest populations under economic levels.