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opencc-zeroDec 2009View details →

Data from: Significant genetic boundaries and spatial dynamics of giant pandas occupying fragmented habitat across southwest China

Understanding population history and genetic structure are key drivers of ecological research. Here we studied two highly fragmented and isolated populations (Xiaoxiangling and Daxiangling) of giant pandas (Ailuropoda melanoleuca) at the extreme southwestern edge of their distribution. This area also contains the Dadu River, national road 108 and various human infrastructure and development, providing an ideal region in which we can identify the effects of different barriers on animal movements. We used partial mitochondrial control region (mtDNA) and nine microsatellite loci (nuclear DNA) data derived from 192 fecal and one blood sample collected from the wild. We found 136 genotypes corresponding to 53 unique multilocus genotypes and eight unique control region haplotypes (653 bp). Significant genetic boundaries correlated spatially with the Dadu River (K=2). We estimate that a major divergence took place between these populations 26 000 YBP, at around the similar time the rock surface of valley bottom formed in Dadu River. The national road has resulted in further recent population differentiation (Pairwise FS on mtDNA and nuclear DNA) so that in effect, four smaller sub-populations now exist. Promisingly, we identified two possible first generation migrants and their migration paths, and recommended the immediate construction of a number of corridors. Fortunately, the Chinese government has accepted our advice and is now planning corridor construction.

Data from: Using a 'time machine' to test for local adaptation of aquatic microbes to temporal and spatial environmental variation

Local adaptation occurs when different environments are dominated by different specialist genotypes, each of which is relatively fit in its local conditions and relatively unfit under other conditions. Analogously, ecological species sorting occurs when different environments are dominated by different competing species, each of which is relatively fit in its local conditions. The simplest theory predicts that spatial, but not temporal, environmental variation selects for local adaptation (or generates species sorting), but this prediction is difficult to test. Although organisms can be reciprocally transplanted among sites, doing so among times seems implausible. Here we describe a reciprocal transplant experiment testing for local adaptation or species sorting of lake bacteria in response to both temporal and spatial variation in water chemistry. The experiment used a −80 °C freezer as a 'time machine'. Bacterial isolates and water samples were frozen for later use, allowing transplantation of older isolates 'forward in time' and newer isolates 'backward in time'. Surprisingly, local maladaptation predominated over local adaptation in both space and time. Such local maladaptation may indicate that adaptation, or the analogous species sorting process, fails to keep pace with temporal fluctuations in water chemistry. This hypothesis could be tested with more finely-resolved temporal data.

Data from: The ghost of introduction past: spatial and temporal variability in the genetic diversity of invasive smallmouth bass

Understanding the demographic history of introduced populations is essential for unravelling their invasive potential and adaptability to a novel environment. To this end, levels of genetic diversity within the native and invasive range of a species are often compared. Most studies, however, focus solely on contemporary samples, relying heavily on the premise that the historic population structure within the native range has been maintained over time. Here, we assess this assumption by conducting a three-way comparison of the genetic diversity of native (historic and contemporary) and invasive (contemporary) smallmouth bass (Micropterus dolomieu) populations. Analyses of a total of 572 M. dolomieu samples, representing the contemporary invasive South African range, contemporary and historical native USA range (dating back to the 1930s when these fish were first introduced into South Africa), revealed that the historical native range had higher genetic diversity levels when compared to both contemporary native and invasive ranges. These results suggest that both contemporary populations experienced a recent genetic bottleneck. Furthermore, the invasive range displayed significant population structure, whereas both historical and contemporary native USA populations revealed higher levels of admixture. Comparison of contemporary and historical samples showed both a historic introduction of M. dolomieu, as well as a more recent introduction, thereby demonstrating that undocumented introductions of this species have occurred. Although multiple introductions might have contributed to the high levels of genetic diversity in the invaded range, we discuss alternative factors that may have been responsible for the elevated levels of genetic diversity and highlight the importance of incorporating historic specimens into demographic analyses.

opencc-zeroAug 2019View details →

Data from: Impact of the spatial uncertainty of seed dispersal on tree colonization dynamics in a temperate forest

An aggregated distribution of dispersed seeds may influence the colonization process in tree communities via inflated spatial uncertainty. To evaluate this possibility, we studied 10 tree species in a temperate forest: one primarily barochorous, six anemochorous and two endozoochorous species. A statistical model was developed by combining an empirical seed dispersal kernel with a gamma distribution of seedfall density, with parameters that vary with distance. In the probability density, the fitted models showed that seeds of Fagaceae (primarily barochorous) and Betulaceae (anemochorous) were disseminated locally (i.e., within 60 m of a mother tree), whereas seeds of Acer (anemochorous) and endozoochorous species were transported farther. Greater fecundity compensated for the lower probability of seed dispersal over long distances for some species. Spatial uncertainty in seedfall density was much greater within 60 m of a mother tree than farther away, irrespective of dispersal mode, suggesting that seed dispersal is particularly aggregated in the vicinity of mother trees. Simulation results suggested that such seed dispersal patterns could lead to sites in the vicinity of a tree being occupied by other species that disperse seeds from far away. We speculate that this process could promote coexistence by making the colonization rates of the species more similar on average and equalizing species fitness in this temperate forest community.

Data from: The effects of spatial scale and isoscape on consumer isotopic niche width

1. The mean and variance of ecological variables are dependent on sampling attributes such as the coverage of environmental heterogeneity (sampling extent) and spatial scale. Trophic niche width is often approximated by bulk tissue stable isotopes of C and N, i.e. the population isotopic niche. However, recent studies suggest that environmental heterogeneity (experienced by individuals) may be more important in defining the isotopic niche width than trophic variability. We hypothesised that isotopic niche width will increase monotonically with spatial scale, largely produced by environmental variation, e.g. nutrient source. 2. To refine this hypothesis, by describing the shapes of isotope scaling curves, we explored a previously published dataset describing three Chilean intertidal species representing different feeding guilds (grazing snails, suspension feeding mussel). We tested these hypotheses on a new, larger dataset describing three functionally-analogous intertidal species from Northern Ireland. We generated isotopic variance-area curves from a spatially-explicit bootstrap and investigated the scale-dependency of environment-isotope relationships, including wave exposure and sub-habitat heterogeneity. 3. Spatial scale explained 50% of the variance in population isotopic niche widths (bivariate C-N ellipse area) by simple, non-linear relationships. Finer scales (< 1 to 10 km lag) accounted for most variance. Scale dependence was strong for ẟ15N variance, of which > 40% was explained by modelling linear coefficients. A ẟ15N baseline gradient, or isoscape, dominated ẟ15N variance scaling patterns, from sheltered, terrestrially-influenced embayments to exposed, pelagic-dominated coastline. Consumer ẟ13C variance had a weaker scale-dependence, plateauing at mesoscales (> 20 km lag). 4. We show that isotopic niche width is strongly dependent on sampling spatial extent, which controls the environmental heterogeneity experienced by individual consumers. Environmental heterogeneity must be accounted for before isotopic niche width can be considered to accurately represent trophic niche width. Studies conducted at different spatial scales are likely to identify different environment-isotope relationships. 5. We recommend that spatial scale should be incorporated into sampling designs explicitly, easiest by maintaining a consistent lag distance or area within which populations are sampled. Identified isoscapes can be de-trended, where necessary.

opencc-zeroOct 2019View details →

Data from: Differences in epiphyte biomass and community composition along landscape and within-crown spatial scales

Vascular epiphytes contribute to the structural, compositional, and functional complexity of tropical montane cloud forests because of their high biomass, diversity, and ability to intercept and retain water and nutrients from atmospheric sources. However, human-caused climate change and forest-to-pasture conversion are rapidly altering tropical montane cloud forests. Epiphyte communities may be particularly vulnerable to these changes because of their dependence on direct atmospheric inputs and host trees for survival. In Monteverde, Costa Rica, we measured vascular epiphyte biomass, community composition, and richness at two spatial scales: (1) along an elevation gradient spanning premontane forests to montane cloud forests; and (2) within trees along branches from inner to outer crown positions. We also compared epiphyte biomass and distribution at these scales between two different land-cover types, comparing trees in closed canopy forest to isolated trees in pastures. An ordination of epiphyte communities at the level of trees grouped forested sites above versus below the cloud base, and separated forest versus pasture trees. Species richness increased with increasing elevation and decreased from inner to outer branch positions. Although richness did not differ between land-cover types, there were significant differences in community composition. The variability in epiphyte community organization between the two spatial scales and between land-cover types underscores the potential complexity of epiphyte responses to climate and land-cover changes.

Data from: Do North Atlantic Eels show parallel patterns of spatially varying selection?

Background: The two North Atlantic eel species, the European and the American eel, represent an ideal system in which to study parallel selection patterns due to their sister species status and the presence of ongoing gene flow. A panel of 80 coding-gene SNPs previously analyzed in American eel was used to genotype European eel individuals (glass eels) from 8 sampling locations across the species distribution. We tested for single-generation signatures of spatially varying selection in European eel by searching for elevated genetic differentiation using FST-based outlier tests and by testing for significant associations between allele frequencies and environmental variables. Results: We found signatures of possible selection at a total of 11 coding-gene SNPs. Candidate genes for local selection constituted mainly genes with a major role in metabolism as well as defense genes. Contrary to what has been found for American eel, only 2 SNPs in our study correlated with differences in temperature, which suggests that other explanatory variables may play a role. None of the genes found to be associated with explanatory variables in European eel showed any correlations with environmental factors in the previous study in American eel. Conclusions: The different signatures of selection between species could be due to distinct selective pressures associated with the much longer larval migration for European eel relative to American eel. The lack of parallel selection in North Atlantic eels could also be due to most phenotypic traits being polygenic, thus reducing the likelihood of selection acting on the same genes in both species.

Data from: Impact of habitat fragmentation on the spatial structure of the Eastern Arc Forests in East Africa: implications for biodiversity conservation

The Eastern Arc Mountains in Tanzania and Kenya are one of 35 global biodiversity hotspots. The Eastern Arc forests are, as are many other tropical biodiversity hotspots, highly fragmented. Understanding the impact of habitat fragmentation (i.e., habitat loss and subdivision) on the spatial structure of the Eastern Arc forests is important because forest spatial structure highly influences species richness, persistence, and extinction debt. Here we examine the impact of habitat fragmentation on the spatial structure of the Eastern Arc forests at a patch scale using very high resolution aerial imagery having a spatial resolution of 0.5–1.5 m. Forest area across the 13 Eastern Arc Mountains is 405,852 ha and is distributed into 311 fragments ≥ 10 ha in size with a median fragment size of 84 ha. The 18 largest forest fragments in the Eastern Arc Mountains contain greater than three-quarters of total forest area. Average fragment isolation, as assessed by median distance to nearest fragment and median distance to the nearest larger fragment, is 867 and 1533 m, respectively. Of total forest area, 14% is < 100 m from the forest edge and 33% is < 300 m from the forest edge. Establishing forested linkages among the largest and closest forest fragments through forest regeneration and protection of secondary regenerating forest as well as providing protected area status to the remaining non-protected forest including unprotected smaller forest fragments are important to enhancing the long-term persistence of many plant and animal species here.

Data from: The density and spatial arrangement of the invasive oyster Crassostrea gigas determines its impact on settlement of native oyster larvae

Understanding how the density and spatial arrangement of invaders is critical to developing management strategies of pest species. The Pacific oyster, Crassostrea gigas, has been translocated around the world for aquaculture and in many instances has established wild populations. Relative to other species of bivalve, it displays rapid suspension feeding, which may cause mortality of pelagic invertebrate larvae. We compared the effect on settlement of Sydney rock oyster, Saccostrea glomerata, larvae of manipulating the spatial arrangement and density of native S. glomerata, and non-native C. gigas. We hypothesized that while manipulations of dead oysters would reveal the same positive relationship between attachment surface area and S. glomerata settlement between the two species, manipulations of live oysters would reveal differing density-dependent effects between the native and non-native oyster. In the field, whether oysters were live or dead, more larvae settled on C. gigas than S. glomerata when substrate was arranged in monospecific clumps. When, however, the two species were interspersed, there were no differences in larval settlement between them. By contrast, in aquaria simulating a higher effective oyster density, more larvae settled on live S. glomerata than C. gigas. When C. gigas was prevented from suspension feeding, settlement of larvae on C. gigas was enhanced. By contrast, settlement was similar between the two species when dead. While the presently low densities of the invasive oyster C. gigas may enhance S. glomerata larval settlement in east Australian estuaries, future increases in densities could produce negative impacts on native oyster settlement. Synthesis and applications: Our study has shown that both the spatial arrangement and density of invaders can influence their impact. Hence, management strategies aimed at preventing invasive populations reaching damaging sizes should not only consider the threshold density at which impacts exceed some acceptable limit, but also how patch formation modifies this.

Data from: Phylogeography of African locust bean (Parkia biglobosa) reveals genetic divergence and spatially structured populations in West and Central Africa

The evolutionary history of African savannah tree species is crucial for the management of their genetic resources. In this study, we investigated the phylogeography of Parkia biglobosa and its modelled distribution under past and present climate conditions. This tree species is very valued and widespread in West Africa, providing edible and medicinal products. A large sample of 1 610 individuals from 84 populations, distributed across 12 countries in Western and Central Africa, were genotyped using eight nuclear microsatellites. Individual-based assignments clearly distinguished three genetic clusters, extreme West Africa (EWA), centre of West Africa CWA), and Central Africa (CA). Overall, estimates of genetic diversity were moderate to high, with lower values for populations in EWA (AR=6.4, HE=0.78 and HO=0.7) and CA (AR=5.9, HE=0.67 and HO=0.61) compared to populations in CWA (AR=7.3, HE=0.79 and HO=0.75). The overall population differentiation was found to be moderate (FST=0.09). A highly significant isolation-by-distance pattern was detected, with a marked phylogeographic signature suggesting possible effects of past climate and geographic barriers to migration. Modelling the potential distribution of the species showed a contraction during the last glaciations followed by expansion events. The exploratory Approximate Bayesian Computation conducted suggests a best-supported scenario in which the cluster CWA traced back to the ancestral populations and a first split between EWA and CWA took place about 160 000 years BP, then a second split divided CA and CWA, about 100 000 years BP. However, our genetic data do not enable to conclusively distinguish among a few alternative possible scenarios.

Data from: How do similarities in spatial distributions and interspecific associations affect the coexistence of Quercus species in the Baotianman National Nature Reserve, Henan, China

Congeneric species often have similar ecological characteristics and use similar resources. These similarities may make it easier for them to co-occur in a similar habitat but may also lead to strong competitions that limit their coexistence. Hence, how do similarities in congeneric species affect their coexistence exactly? This study mainly used spatial point pattern analysis in two 1 hm2 plots in the Baotianman National Nature Reserve, Henan, China, to compare the similarities in spatial distributions and interspecific associations of Quercus species. Results revealed that Quercus species were all aggregated under the complete spatial randomness null model, and aggregations were weaker under the heterogeneous Poisson process null model in each plot. The interspecific associations of Quercus species to non-Quercus species were very similar in Plot 1. However, they can be either positive or negative in different plots between the co-occurring Quercus species. The spatial distributions of congeneric species, interspecific associations with non-Quercus species, neighborhood richness around species, and species diversity were all different between the two plots. We found that congeneric species did have some similarities, and the closely related congeneric species can positive or negative associate with each other in different plots. The co-occurring congeneric species may have different survival strategies in different habitats. On one hand, competition among congenerics may lead to differentiation in resource utilization. On the other hand, their similar interspecific associations can strengthen their competitive ability and promote local exclusion to non-congeneric species to obtain more living space. Our results provide new knowledge for us to better understand the coexistence mechanisms of species.

opencc-zeroDec 2014View details →

Data from: Unraveling conflicting density- and distance-dependent effects on plant reproduction using a spatially-explicit approach

1. Density- and distance-dependent (DDD) mechanisms are important determinants of plant reproductive success (PRS). Different components of sequential PRS can operate either in the same or in different directions and thus reinforce or neutralize each other, and they may also operate at different spatial scales. Thus, spatially-explicit approaches are needed to detect such complex DDD effects across multiple PRS components and spatial scales. 2. To reveal DDD effects of different components of early PRS of the Iberian pear (Pyrus bourgaeana) sampled over three consecutive years, we used marked point pattern analysis. Our special interest is to identify conflicting processes that regulate populations at different spatial scales, e.g. whether DDD on fruit initiation and on fruit development acted in opposite directions. To evaluate the significance of observed mark correlation functions based on empirical data (e.g. fruiting success) we compared them to expectations given by spatially-explicit null models. 3. Diverse DDD processes affected several aspects of PRS in a variable extent over the three seasons. First, early fruit set was higher for individuals with more neighbors at small distances (i.e. up to 40m). However, late P. bourgaeana fruit set decreased with increasing number of nearby neighbors, but these effects canceled for overall fruit set that did not show DDD effects. Second, the absolute number of fruits produced (crop sizes) by trees showed positive density dependence in 2011 and 2012 but not in 2013. Finally, the total number of seeds produced did not show DDD effects, indicating that conflicting demographic processes can disrupt the initial spatial pattern of tree investment in reproduction. 4. Synthesis: Understanding complex spatial effects of density- and distance-dependent (DDD) processes requires dissection of component processes to attain the complete picture since contrasting DDD processes may be hidden behind a single cumulative measure of reproductive success. The combination of novel and classic mark correlation functions used here constitute a powerful spatially-explicit tool that can be broadly applied to unravel conflicting mechanisms of DDD regulating the persistence of sessile organisms at a range of spatial scales. Our findings help to explain why some authors failed to find expected DDD of PRS and highlight the importance of detailed multi-year field studies on plant reproductive success.

opencc-zeroDec 2011View details →

Data from: Spatially explicit models of dynamic histories: examination of the genetic consequences of Pleistocene glaciation and recent climate change on the American Pika.

A central goal of phylogeography is to identify and characterize the processes underlying divergence. One of the biggest impediments currently faced is how to capture the spatiotemporal dynamic under which a species evolved. Here we described an approach that couples species distribution models (SDMs), demographic and genetic models in a spatiotemporally explicit manner. Analyses of American Pika (Ochotona priniceps) from the sky islands of the central Rocky Mountains of North America are used to provide insights into key questions about integrative approaches in landscape genetics, population genetics and phylogeography. This includes (i) general issues surrounding the conversion of time-specific SDMs into simple continuous, dynamic landscapes from past to current, and (ii) the utility of SDMs to inform demographic models with deme-specific carrying capacities and migration potentials, as well as (iii) the contribution of the temporal dynamic of colonization history in shaping genetic patterns of contemporary populations. Our results support that the inclusion of a spatiotemporal dynamic is an important factor when studying the impact of distributional shifts on patterns of genetic data. Our results also demonstrate the utility of SDMs to generate species-specific predictions about patterns of genetic variation that account for varying degrees of habitat specialization and life-history characteristics of taxa. Nevertheless, the results highlight some key issues when converting SDMs for use in demographic models. Because the transformations have direct affects on the genetic consequence of population expansion by prescribing how habitat heterogeneity and spatiotemporal variation is related to the species-specific demographic model, it is important to consider alternative transformations when studying the genetic consequences of distributional shifts.

opencc-zeroDec 2015View details →

Data from: Limited gene dispersal and spatial genetic structure as stabilizing factors in an ant-plant mutualism

Comparative studies of the population genetics of closely associated species are necessary to properly understand the evolution of these relationships because gene flow between populations affects the partners' evolutionary potential at the local scale. As a consequence (at least for antagonistic interactions), asymmetries in the strength of the genetic structures of the partner populations can result in one partner having a co-evolutionary advantage. Here, we assess the population genetic structure of partners engaged in a species-specific and obligatory mutualism: the Neotropical ant-plant, Hirtella physophora, and its ant associate, Allomerus decemarticulatus. Although the ant cannot complete its life cycle elsewhere than on H. physophora and the plant cannot live for long without the protection provided by A. decemarticulatus, these species also have antagonistic interactions: the ants have been shown to benefit from castrating their host plant and the plant is able to retaliate against too virulent ant colonies. We found similar short dispersal distances for both partners, resulting in the local transmission of the association and, thus, inbred populations in which too virulent castrating ants face the risk of local extinction due to the absence of H. physophora offspring. On the other hand, we show that the plant populations probably experienced greater gene flow than did the ant populations, thus enhancing the evolutionary potential of the plants. We conclude that such levels of spatial structure in the partners' populations can increase the stability of the mutualistic relationship. Indeed, the local transmission of the association enables partial alignments of the partners' interests, and population connectivity allows the plant retaliation mechanisms to be locally adapted to the castration behaviour of their symbionts.

opencc-zeroDec 2016View details →

Data from: Measuring site fidelity and spatial segregation within animal societies

1.Animals often display a marked tendency to return to previously-visited locations that contain important resources, such as water, food, or developing brood that must be provisioned. A considerable body of work has demonstrated that this tendency is strongly expressed in ants, which exhibit fidelity to particular sites both inside and outside the nest. However, thus far many studies of this phenomena have taken the approach of reducing an animal's trajectory to a summary statistic, such as the area it covers. 2.Using both simulations of biased random walks, and empirical trajectories from individual rock ants, Temnothorax albipennis, we demonstrate that this reductive approach suffers from an unacceptably high rate of false negatives. 3.To overcome this, we describe a site-centric approach which, in combination with a spatially-explicit null model, allows the identification of the important sites towards which individuals exhibit statistically significant biases. 4.Using the ant trajectories we illustrate how the site-centric approach can be combined with social network analysis tools to detect groups of individuals whose members display similar space-use patterns. 5.We also address the mechanistic origin of individual site fidelity; by examining the sequence of visits to each site, we detect a statistical signature associated with a self-attracting walk - a non-Markovian movement model that has been suggested as a possible mechanism for generating individual site fidelity.

Data from: Spatial dynamics and mixing of bluefin tuna in the Atlantic Ocean and Mediterranean Sea revealed using next generation sequencing

The Atlantic bluefin tuna is a highly migratory species emblematic of the challenges associated with shared fisheries management. In an effort to resolve the species' stock dynamics, a genome-wide search for spatially informative single nucleotide polymorphisms (SNPs) was undertaken, by way of sequencing reduced representation libraries. An allele frequency approach to SNP discovery was used, combining the data of 555 larvae and young-of-the-year (LYOY) into pools representing major geographical areas and mapping against a newly assembled genomic reference. From a set of 184,895 candidate loci, 384 were selected for validation using 167 LYOY. A highly discriminatory genotyping panel of 95 SNPs was ultimately developed by selecting loci with the most pronounced differences between western Atlantic and Mediterranean Sea LYOY. The panel was evaluated by genotyping a different set of LYOY (n= 326) and from these 77.8% and 82.1% were correctly assigned to western Atlantic and Mediterranean Sea origins, respectively. The panel revealed temporally persistent differentiation among LYOY from the western Atlantic and Mediterranean Sea (FST = 0.008, p=0.034). The composition of six mixed feeding aggregations in the Atlantic Ocean and Mediterranean Sea was characterized using genotypes from medium (n = 184) and large (n = 48) adults, applying population assignment and mixture analyses. The results provide evidence of persistent population structuring across broad geographic areas and extensive mixing in the Atlantic Ocean, particularly in the mid-Atlantic Bight and Gulf of St. Lawrence. The genomic reference and genotyping tools presented here constitute novel resources useful for future research and conservation efforts.

opencc-zeroDec 2011View details →

Data from: Defining spatial and temporal patterns of phylogeographic structure in Madagascar's iguanid lizards (Genus Oplurus)

Understanding the remarkably high species diversity and levels of endemism found among Madagascar's flora and fauna has been the focus of many studies. One hypothesis that has received much attention proposes that Pleistocene climate fluctuations spurred diversification. However, while spatial patterns of distribution and phylogenetic relationships can provide support for biogeographic predictions, temporal estimates of divergence are required to determine the fit of these geospatial patterns to climatic or biogeographic mechanisms. We use multilocus DNA sequence data to test whether divergence times among Malagasy iguanid lizards of the subfamily Oplurinae are compatible with a hypotheses of Quaternary diversification. We estimate the oplurine species tree and associated divergence times under a relaxed clock model. In addition, we examine the phylogeographic structure and population divergence times within two sister-species of Oplurus primarily distributed in the northwest and southwest of Madagascar (O. cuvieri and O. cyclurus, respectively). We find that divergence events among oplurine lineages occurred in the Oligocene and Miocene and are thus far older and incompatible with the hypothesis that recent climate fluctuations are related to current species diversity. However, the timing of intraspecific divergences and spatial patterns of population genetic structure within O. cuvieri and O. cyclurus suggest a role for both intrinsic barriers and recent climate fluctuations at population-level divergences. Integrating information across spatial and temporal scales allows us to identify and better understand the mechanisms generating patterns diversity.

Data from: Population genetic structure of the tree-hole tick Ixodes arboricola (Acari: Ixodidae) at different spatial scales

The endophilic tick Ixodes arboricola infests cavity-nesting birds, and its dispersal strongly depends on the movements of its host. Population genetic structure of I. arboricola was studied with seven polymorphic microsatellite markers. We collected 268 ticks from 76 nest boxes in four woodlots near Antwerp, Belgium. These nest boxes are mainly used by the principal hosts of I. arboricola, the great tit Parus major and the blue tit Cyanistes caeruleus. As these birds typically return to the same cavity for roosting or breeding, ticks within nest boxes were expected to be highly related, and tick populations were expected to be spatially structured among woodlots and among nest boxes within woodlots. In line with the expectations, genetic population structure was found among woodlots and among nest boxes within woodlots. Surprisingly, there was considerable genetic variation among ticks within nest boxes. This could be explained by continuous gene flow from ticks from nearby tree holes, yet this remains to be tested. A pairwise relatedness analysis conducted for all pairs of ticks within nest boxes showed that relatedness among larvae was much higher than among later instars, which suggests that larvae are the most important instar for tick dispersal. Overall, tick populations at the studied spatial scale are not as differentiated as predicted, which may influence the scale at which host–parasite evolution occurs.

opencc-zeroSep 2019View details →

Data from: Testing the limits of pheromone stigmergy in spatially constrained robotic swarms

Area coverage and collective exploration are key challenges for swarm robotics. Previous research in this field has drawn inspiration from ant colonies, with real, or more commonly virtual, pheromones deposited into a shared environment to coordinate behaviour through stigmergy. Repellent pheromones can facilitate rapid dispersal of robotic agents, yet this has been demonstrated only for relatively small swarm sizes (N<30). Here, we report findings from swarms of real robots (Kilobots) an order of magnitude larger (N>300), and from realistic simulation experiments up to N=400. We identify limitations to stigmergy in a spatially constrained environment – a free but bounded two-dimensional workspace – using repellent binary pheromone. At larger N a simple, stigmergic avoidance algorithm becomes first no better, then inferior to, the area coverage of non-interacting random walkers. Thus, with ever-increasing swarm sizes, the assumption of robustness and scalability for such approaches may need to be re-examined. Instead, subcellular biology, and diffusive processes, may prove a better source of inspiration at large N in spatially constrained or high agent density environments.