Find research datasets worth reusing

Data from: Testing range-limit hypotheses using range-wide habitat suitability and occupancy for the scarlet monkeyflower (Erythranthe cardinalis)

Determining the causes of geographic range limits is a fundamental problem in ecology, evolution, and conservation biology. Range limits arise due to fitness and dispersal limitation, which yield contrasting predictions about habitat suitability and occupancy of suitable habitat across geographic ranges. If a range edge is limited primarily by fitness, occupancy of suitable habitat should be high, habitat suitability should decline towards the edge, and no suitable habitat should exist beyond it. In contrast, a range edge limited primarily by dispersal should have unoccupied but suitable habitat at and beyond the edge. We built ecological niche models relating occurrence records for the scarlet monkeyflower (Erythranthe cardinalis) to climatic variables, and applied these models to independent data from systematic, range-wide surveys of presence and absence to estimate the availability and occupancy of climatically suitable habitat. We found that fitness limitation predominated over dispersal limitation, but dispersal limitation also played a role at the poleward edge. These results are consistent with the hypothesis that dispersal limitation is more important along shallow environmental gradients and also suggest that synergy between dispersal and fitness limitation can contribute to colonization failure. The framework used here is validated by independent data and could be readily applied to inferring causes of range limits in many other species.

opencc-zeroDec 2018View details →

Data from: Rarity does not limit genetic variation or preclude subpopulation structure in the geographically restricted desert forb Astragalus lentiginosus var. piscinensis

Premise of the study: Characteristics of rare taxa include small population sizes and limited geographical ranges. The genetic consequences of rarity are poorly understood for most taxa. A small geographical range could result in reduced opportunity for isolation by distance or environment, thereby limiting genetic structure and variation, but few studies explore genetic structure at small spatial scales with sufficient resolution to test this hypothesis. Moreover, few comparative genetic studies exist among infrataxa differing in rarity. Here, we compare genetic variation among varieties of Astragalus lentiginosus differing in range size. Additionally, we ask if genetic structure exists in A. l. var. piscinensis, a rare taxon consisting of several thousand individuals that persist on ~8 km2 of alkaline soil. Methods: We compared genetic variation among 11 varieties of A. lentiginosus differing in range size using a genotyping by sequencing (GBS) approach, which generated 11,475 single nucleotide polymorphisms (SNPs). We characterized genetic structure among subpopulations of A. l. var. piscinensis using a second GBS dataset of 7,274 SNPs and explored associations between genetic structure and environmental variation. Key results: We found no association between genetic variation and range size among varieties of A. lentiginosus. Additionally, despite the extremely small range of A. l. var. piscinensis, we report a well-defined genetic structure among subpopulations associated with microhabitat variation in soil composition. Conclusion: Our results suggest that fine scale genetic structure may exist within other rare Astragalus taxa and that rarity does not preclude the maintenance of genetic diversity in this genus. In compliance with data protection regulations, please contact the publication office if you would like to have your personal information removed from the database.

Data from: High specialization and limited structural change in plant‐herbivore networks along a successional chronosequence in tropical montane forest

Secondary succession is well‐understood, to the point of being predictable for plant communities, but the successional changes in plant‐herbivore interactions remains poorly explored. This is particularly true for tropical forests, despite the increasing importance of early successional stages in tropical landscapes. Deriving expectations from successional theory, we examine properties of plant‐herbivore interaction networks while accounting for host phylogenetic structure along a succession chronosequence in montane rainforest in Papua New Guinea. We present one of the most comprehensive successional investigations of interaction networks, equating to >40 person years of field sampling, and one of the few focused on montane tropical forests. We use a series of nine 0.2ha forest plots across young secondary, mature secondary and primary montane forest, sampled almost completely for woody plants and larval leaf chewers (Lepidoptera), using forest felling. These networks comprised of 12,357 plant‐herbivore interactions and were analysed using quantitative network metrics, a phylogenetically controlled host‐use index and a qualitative network beta diversity measure. Network structural changes were low and specialisation metrics surprisingly similar throughout succession, despite high network beta diversity. Herbivore abundance was greatest in the earliest stages, and hosts here had more species‐rich herbivore assemblages, presumably reflecting higher palatability due to lower defensive investment. All herbivore communities were highly specialised, using a phylogenetically narrow set of hosts, while host phylogenetic diversity itself decreased throughout the chronosequence. Relatively high phylogenetic diversity, and thus high diversity of plant defenses, in early succession forest may result in herbivores feeding on fewer hosts than expected. Successional theory, derived primarily from temperate systems, is limited in predicting tropical host‐herbivore interactions. All succession stages harbour diverse and unique interaction networks, which together with largely similar network structures and consistent host use patterns, suggests general rules of assembly may apply to these systems.

opencc-zeroJun 2019View details →

Data from: Limits to environmental masking of genetic quality in sexual signals

There is considerable debate over the value of male sexual ornaments as signals of genetic quality. Studies alternately report that environmental variation enhances or diminishes the genetic signal, or leads to crossover where genotypes perform well in one environment but poorly in another. A unified understanding is lacking. We conduct a novel experimental test examining the dual effects of distinct categories of genetic (inbred versus crossed parental lines) and environmental quality (low, through high to extreme larval food stress) on a condition-dependent male ornament. We find that differences in genetic quality signalled by the ornament (male eyespan in Diasemopsis meigenii stalk-eyed flies) become visible and are amplified under high stress but are overwhelmed in extreme stress environments. Variance among independent genetic lines increases with environmental stress in both genetic quality classes, but at a slower rate in high quality outcrossed flies. Individual genetic lines generally maintain their ranks across environments, except among high quality lines under low environmental stress, where low genetic variance among lines precludes differentiation between ranks. Our results provide a conceptual advance, demonstrating a unified pattern for how genetic and environmental quality interact. They show when environmental conditions lead to the amplification of differences in signals of genetic quality and thereby enhance the potential indirect genetic benefits gained by female mate choice.

Data from: Limited hatchery introgression into wild brook trout (Salvelinus fontinalis) populations despite reoccurring stocking

Due to increased anthropogenic pressures on many fish populations, supplementing wild populations with captive-raised individuals has become an increasingly common management practice. Stocking programs can be controversial due to uncertainty about the long-term fitness effects of genetic introgression on wild populations. In particular, introgression between hatchery and wild individuals can cause declines in wild population fitness, resiliency, and adaptive potential, and contribute to local population extirpation. However, low survival and fitness of captive-raised individuals can minimize the long-term genetic consequences of stocking in wild populations, and to date the prevalence of introgression in actively stocked ecosystems has not been rigorously evaluated. We quantified the extent of introgression in 30 populations of wild brook trout (Salvelinus fontinalis) in a Pennsylvania watershed, and examined the correlation between introgression and 11 environmental covariates. Genetic assignment tests were used to determine the origin (wild vs. captive-raised) for 1742 wild-caught and 300 hatchery brook trout. To avoid assignment biases, individuals were assigned to two simulated populations that represented the average allele frequencies in wild and hatchery groups. Fish with intermediate probabilities of wild ancestry were classified as introgressed, with threshold values determined through simulation. Even with reoccurring stocking at most sites, over 93% of wild-caught individuals probabilistically assigned to wild origin, and only 6% of wild-caught fish assigned to introgressed. Models examining environmental drivers of introgression explained less than 3% of the among-population variability, and all estimated effects were highly uncertain. This was not surprising given overall low introgression observed in this study. Our results suggest that introgression of hatchery-derived genotypes can occur at low rates, even in actively stocked ecosystems and across a range of habitats. However, a cautious approach to stocking may still be warranted, as the potential effects of stocking on wild population fitness and the mechanisms limiting introgression are not known.

opencc-zeroDec 2019View details →

Data from: Molecular responses to freshwater limitation in the mangrove tree Avicennia germinans (Acanthaceae)

Environmental variation along the geographical space can shape populations by natural selection. In the context of global warming and changing precipitation regimes, it is crucial to understand the role of environmental heterogeneity in tropical trees adaptation, given their disproportional contribution to water and carbon biogeochemical cycles. Here, we investigated how heterogeneity in freshwater availability along tropical wetlands has influenced molecular variations of the Black Mangrove (Avicennia germinans). Fifty-seven trees were sampled in seven sites differing markedly in precipitation regime and riverine freshwater inputs. Using 2,297 genome-wide single nucleotide polymorphic markers, we found signatures of natural selection by the association between variations in allele frequencies and environmental variables, including the precipitation of the warmest quarter and annual precipitation. Additionally, we found candidate loci for selection based on statistical deviations from neutral expectations of interpopulation genetic differentiation. Most candidate loci within transcribed sequences were functionally associated with central aspects of drought-tolerance or plant response to drought. Moreover, our results suggest the occurrence of rapid evolution of a population, likely in response to sudden and persistent limitation in plant access to soil water, following a road construction in 1974. Observations supporting rapid evolution included the reduction in tree size and changes in allele frequencies and in transcripts expression levels associated with increased drought-tolerance, through accumulation of osmoprotectants and antioxidants, biosynthesis of plant cuticle, protection against stress-induced proteins degradation, stomatal closure, photorespiration and photosynthesis. We describe a major role of spatial heterogeneity in freshwater availability in the specialization of this typically tropical tree.

Data from: Is there a disease-free halo at species range limits? The co-distribution of anther-smut disease and its host species

1. While disease is widely recognized as affecting host population size, it has rarely been considered to play a role in determining host range limits. Many diseases may not be able to persist near the range limit if host population density falls below the critical threshold level for pathogen invasion. However, in vector- and sexually-transmitted diseases, pathogen transmission may be largely independent of host density and theory demonstrates that diseases with frequency-dependent transmission may persist in small populations near the range limit. 2. Empirical studies of disease at species range limits have lagged behind the theory, and to date, no previous study has tested the hypothesis that vector or sexually transmitted diseases can be maintained at host range limits. 3. We studied the distribution of anther-smut disease, a sterilizing pollinator-transmitted disease, on four alpine plant species to determine whether disease was present at the host range limits. 4. We found that host abundance declined towards the elevational range limits, and disease extended to the most extreme elevational range limits in three of the four host species. Maximum likelihood estimation of the magnitude of the disease-free halo showed that it was small or non-existent for all host species. Moreover, disease prevalence within populations was often higher nearer the host's range limit than in the range center and was independent of host density. 5. Synthesis: Our results show that diseases where transmission is frequency-dependent have the potential to affect host distributions not just in theory, but also in real world populations.

opencc-zeroDec 2019View details →

Data from: Diet variability among insular populations of Podarcis lizards reveals diverse strategies to face resource-limited environments

Access to resources is a dynamic and multi-causal process that determines the success and survival of a population. It is therefore often challenging to disentangle the factors affecting ecological traits like diet. Insular habitats provide a good opportunity to study how variation in diet originates, in particular in populations of mesopredators such as lizards. Indeed, high levels of population density associated with low food abundance and low predation are selection pressures typically observed on islands. In the present study, the diet of eighteen insular populations of two closely related species of lacertid lizards (Podarcis sicula and Podarcis melisellensis) was assessed. Our results reveal that despite dietary variability among populations, diet taxonomic diversity is not impacted by island area. In contrast, however, diet disparity metrics, based on the variability in the physical (hardness) and behavioral (evasiveness) properties of ingested food items, are correlated with island size. These findings suggest that an increase in intraspecific competition for access to resources may induce shifts in functional components of the diet. Additionally, the two species differed in the relation between diet disparity and island area suggesting that different strategies exist to deal with low food abundance in these two species. Finally, sexual dimorphism in diet and head dimensions is not greater on smaller islands, in contrast to our predictions.

opencc-zeroAug 2019View details →

Data from: Pollen limitation and autonomous selfing ability interact to shape variation in outcrossing rate across a species range

Premise of the study: Hermaphroditic plants commonly reproduce through a mixture of selfing and outcrossing. The degree to which outcrossing rates reflect the availability of outcross pollen, genetic differentiation in the ability to autonomously self-fertilize, or both is often unclear. Despite the potential for autonomy and the pollination environment to jointly influence outcrossing, this interaction is rarely studied. Methods: We reviewed literature testing whether the pollination environment or floral traits causing autonomous selfing predict outcrossing rate variation among populations. We also measured outcrossing rates in 23 populations of Campanula americana and examined associations with the pollination environment, autonomy, and their interaction. Key Results: Our review revealed that traits facilitating selfing were often negatively associated with outcrossing rates while most aspects of the pollination environment poorly predicted outcrossing. Populations of C. americana varied from mixed mating to highly outcrossing but variation was unrelated to population size, density, pollen limitation, or autonomous selfing ability. Outcrossing rate was significantly influenced by an interaction between autonomous selfing ability and pollen limitation. In highly autonomous populations, elevated pollen limitation was associated with reduced outcrossing, while there was no relationship for less autonomous populations. Conclusions: Both the ability to self autonomously and pollen limitation interact to shape outcrossing rates in C. americana. This work suggests autonomy affords mating system flexibility, though it is not ubiquitous in all populations across the species range. Interactions between traits influencing autonomy and pollen limitation are likely to explain variation in outcrossing rates among populations of flowering plants.

Data from: Frequency dependence limits divergent evolution by favouring rare immigrants over residents

Two distinct forms of natural selection promote adaptive biological diversity. Divergent selection occurs when different environments favour different phenotypes, leading to increased differences between populations. Negative frequency-dependent selection occurs when rare variants within a population are favoured over common ones, increasing diversity within populations. These two diversifying forces promote genetic variation at different spatial scales, and may act in opposition, but their relative effects remain unclear because they are rarely measured concurrently. Here we show that negative frequency-dependent selection within populations can favor rare immigrants over locally adapted residents. We reciprocally transplanted lake and stream ecotypes of threespine stickleback into lake and stream habitats, while manipulating the relative abundance of residents versus immigrants. We found negative frequency-dependence: survival was highest for the locally rare ecotype, rather than natives. Also, individuals with locally rare major histocompatibility complex (MHC) class IIb genotypes were infected by fewer parasites. This negative frequency-dependent selection will tend to favour rare immigrants over common residents, amplifying the effect of migration and undermining the efficacy of divergent natural selection to drive population differences. The only signal of divergent selection was a tendency for foreign fish to have higher parasite loads than residents, after controlling for MHC genotype rarity. Frequency-dependent ecological interactions have long been thought to promote speciation. Our results suggest a more nuanced view in which negative frequency dependence alters the fate of migrants to promote or constrain evolutionary divergence between populations.

Data from: Malagasy cichlids differentially limit impacts of body shape evolution on oral jaw functional morphology

Patterns of trait covariation, like integration and modularity, are vital factors that influence the evolution of vertebrate body plans. In functional systems, decoupling of morphological modules buffers functional change in one trait by reducing correlated variation with another. However, for complex morphologies with many-to-one mapping of form to function (MTOM), resistance to functional change may also be achieved by constraining morphological variation within a functionally stable region of morphospace. For this research, we used geometric morphometrics to evaluate the evolution of body shape and its relationship to jaw functional morphology in two independent radiations of endemic Malagasy cichlid (Teleostei: Cichlidae). Our results suggested that the two subfamilies used different strategies to mitigate impacts of body shape variation on a metric of jaw function, maxillary kinematic transmission (MKT): (1) modularity between cranial and postcranial morphologies, and (2) integration of body and jaw evolution, with jaw morphologies varying in a manner that limits change in MKT. This research shows that, unlike modularity, MTOM allows traits to retain strong evolutionary covariation while still reducing impacts on functionality. These results suggest that MTOM, and its influence on the evolution of correlated traits, is likely much more widespread than is currently understood.

Data from: Habitat geometry and limited perceptual range affect habitat choice of a trap-building predator

By considering various biotic and abiotic factors, organisms are expected to distinguish among suitable habitats of different quality and choose the one that offers them the highest fitness payoff. According to the ideal-free-distribution model, density drives organism choice and ultimately distribution among habitats. However, deviations from the basic model are common, as it does not take into account intrinsic and extrinsic constraints. Two important constraints are those of habitat geometry (e.g., habitat area, habitat shape), and perceptual range. We used a trap-building predator, the wormlion larva, to examine these constraints. We manipulated the geometry of the preferred shaded microhabitat and the distance of individuals from it, and assessed their effect on wormlion habitat choice, distribution patterns and performance. Habitat geometry affected wormlion microhabitat choice and distribution patterns, measured as distance from the habitat center and spatial pattern type, but had no effect on performance, expressed as the area of the pit-trap constructed. The interaction between habitat geometry and density was inconsistent regarding the distribution patterns, affecting distance from the center but not the spatial pattern type. Furthermore, we found that wormlions demonstrated a low perceptual range, which limited their ability to sense proximate shaded conditions. We highlight the importance of incorporating the interplay between habitat geometry, density and perceptual range when studying habitat choice and spatial patterns, and suggest that spatial patterns should be analyzed in more than a single way.

opencc-zeroJan 2020View details →

Data from: Fullerene-like structures of Cretaceous crinoids reveal topologically limited skeletal possibilities

In general there are few cases where numbers or types of possible phenotypes are known, although vast state spaces have been postulated. Rarely applied in this context, graph theory and topology enable enumeration of possible phenotypes and evolutionary transitions. Here, we generate polyhedral calyx graphs for the Late Cretaceous, stemless crinoids Marsupites testudinarius and Uintacrinus socialis (Uintacrinoidea Zittel 1879) revealing structural similarities to carbon fullerenes and fulleroids (respectively). The Uintacrinus calyx incorporates numerous plates (e.g. |V| ≥ 197), which are small, light, low-density and have 4 to 8 sides. Therefore, the corresponding number of possible plate arrangements, given by the number of polyhedral graphs, is large (>> 〖1×10〗^14). Graph vertices representing plates with sides > 6 introduce negative Gaussian curvature and topological instability. However, observed Uintacrinus graph cardinalities (|V|) do not allow more stable pentaradial configurations. In contrast, the Marsupites calyx dual graph has 17 faces that are pentagonal or hexagonal. Therefore, it is structurally identical to a carbon fullerene, specifically C30-D5h. Corresponding graph restrictions result in radical constraint to only three structural options. Further restriction to pentaradial symmetry allows only one possibility: the Marsupites phenotype. This robust, stable topology is consistent with adaptation to the predation pressures of the Mesozoic marine revolution. Consequently, the most plausible evolutionary pathway between unitacrinoid phenotypes was a mixed heterochronic trade-off to fewer, larger calyx plates. Therefore, topological limitations radically constrained uintacrinoid skeletal possibilities but thereby aided evolution of a novel adaptive phenotype.

Data from: Toward a geography of omnivory: omnivores increase carnivory when sodium is limiting

1. Toward understanding the geography of omnivory, we tested three hypotheses that predict the proportion of animal tissue consumed: The Sodium Limitation Hypothesis predicts that omnivores increase animal consumption in Na-poor environments because Na bioaccumulates from plants to predators; thus, heterotrophs are Na-rich sources. The Nitrogen Limitation and Habitat Productivity Hypotheses use the same logic to predict more animal consumption in N-poor and productive environments respectively. 2. Omnivory is a common trophic strategy, but what determines the balance of plant and animal tissue omnivores consume is relatively unexplored. Most of what we know comes from single populations at local scales. Here we quantitatively test these three hypotheses at a large geographic scale and across 20 species of omnivorous ants. 3. We tested each hypothesis using N stable isotopes (δ 15 N) to quantify the degree of carnivory in ant populations in 20 forests that span 12° latitude from Georgia to Maine, USA. We used the difference in δ 15 N between 20 ant conspecifics in 10 genera between two paired forests (10 pairs of 20 forests) that consisted of a coastal and inland forests on the same latitude to determine if the proportion of animal tissue consumed could be predicted based on Na, N or NPP. 4. Sodium gradients accounted for 18% of the variation in δ 15 N, 45% if one outlier ant species was omitted. In contrast, the Nitrogen Limitation and Habitat Productivity Hypotheses, which predict more animal consumption in N-poor and more productive environments respectively, failed to vary with δ 15 N. 5. Our results reveal a geography of omnivory driven in part by access to Na.

Data from: Climate variability predicts thermal limits of aquatic insects across elevation and latitude

Janzen's extension of the climate variability hypothesis posits that increased seasonal variation at high latitudes should result in greater temperature overlap across elevations, and favor wider thermal breadths in temperate organisms compared to their tropical counterparts. We tested these predictions by measuring stream temperatures and thermal breadths (i.e. the difference between the critical thermal maximum and minimum) of 62 aquatic insect species from temperate (Colorado, USA) and tropical (Papallacta, Ecuador) streams spanning an elevation gradient of ca. 2000m. Temperate streams exhibited greater seasonal temperature variation and overlap across elevations than tropical streams, and as predicted, temperate aquatic insects exhibited broader thermal breadths than tropical insects. However, elevation had contrasting effects on patterns of thermal breadth. In temperate species, thermal breadth decreased with increasing elevation because CTMAX declined with elevation while CTMIN was similar across elevations. In tropical insects, by contrast, CTMAX declined less sharply than CTMIN with elevation, causing thermal breadth to increase with elevation. These macrophysiological patterns are consistent with the narrower elevation ranges found in other tropical organisms, and they extend Janzen's climate variability hypothesis to freshwater streams. Furthermore, because lowland tropical aquatic insects have the narrowest thermal breadths of any region, they may be particularly vulnerable to short-term extreme changes in stream temperature.

opencc-zeroDec 2015View details →

Data from: Ant community and habitat limit colony establishment by the fire ant, Solenopis invicta

Hypotheses of community assembly include limitation through habitat physical attributes, as well as competition among species. Such hypotheses must be resolved through experimental tests. Previous experiments have shown that: (i) fire ants of the monogyne social form occur mostly in highly disturbed habitat where they do not compete with mature colonies of co-occurring ants; (ii) in native pine forests of northern Florida, habitat disturbance favours fire ants while simultaneously reducing native ants; (iii) fire ants thrive in these disturbances but do not persist as these become less disturbed over time; and finally, (iv) newly mated, dispersing/colony-founding fire ant queens settle preferentially in such disturbed sites. We now show that by choosing disturbed sites, newly mated, monogyne fire ant queens greatly increase their chances of successful colony establishment. Experimental plots were created in the native ground cover of a north Florida pine forest with all combinations of tilling, shading or reduction of the native ant community. Newly mated fire ant queens, incipient colonies and small colonies were planted in these plots. Only five of 980 (0·5%) newly mated queen nests survived after 120 days, and only five of 400 incipient colonies (1·3%) survived after 30 days. All survivors were in plots with tilling and/or native ant reduction. Extrapolation indicated that 0·04% of newly mated queens and 0·1% of incipient colonies were likely to have survived at 1 year. In contrast, planting small colonies resulted in much higher rates of survival – in plots with native ant reduction, fire ants increased on baits throughout the year but decreased in unreduced control plots. Fifteen months after planting 108 colonies, 21 mounds (19%) were found in the ant-reduced plots, but <2% of 108 colonies survived in the control plots. Taken together, these results show that by landing in disturbed habitat with its reduced native ant population, newly mated fire ants queens increase their chances of successful colony establishment. In contrast to much of the previous literature, our results suggest that ant community assembly proceeds primarily by queen habitat choice and secondarily by filtering and competition.

Data from: Declining demographic performance and dispersal limitation influence the geographic distribution of the perennial forb, Astragalus utahensis (fabaceae)

1. A central goal of ecology is understanding the determinants of species' distributions. 'Metapopulation' models for the existence of distributional boundaries predict that species' geographic ranges arise from the landscape-scale deterioration of habitat suitability towards the range edge (i.e. niche mechanisms), which simultaneously hinders demographic performance and limits dispersal to suitable habitat beyond the edge (i.e. dispersal limitation). However, few studies have examined both of these mechanisms for the same species by examining abundance and comprehensive measures of demographic performance across the distribution and beyond its boundary. 2. We tested the predictions of metapopulation models for range limits by contrasting abundance, demographic performance, and population growth (λ) of the perennial forb Astragalus utahensis in central and northern range edge populations. We tested for dispersal limitation by transplanting individuals at and beyond the northern range boundary and monitoring their demographic performance. 3. Astragalus abundance and stochastic λ decreased from the range center to the northern range edge, with stochastic λ falling to or below replacement in range edge populations. However, transplants at some sites beyond the northern range edge survived and reproduced at levels similar to transplants within the range. Thus, in addition to deteriorating conditions at the range edge, dispersal limitation appears to contribute to limiting A. utahensis' northern distribution. 4. Synthesis: Our results support metapopulation models for range limits by suggesting that decreased demographic performance constrains the viability of range edge populations while contributing to dispersal limitation of A. utahensis' distribution. Thus, the tandem action of niche and dispersal processes appears to play an important role in constraining this species' northern latitudinal range.

Data from: Day/night upper thermal limits differ within Ectatomma ruidum ant colonies

In the tropics, daily temperature fluctuations can pose physiological challenges for ectothermic organisms, and upper thermal limits may affect foraging activity over the course of the day. Variation in upper thermal limits can occur among and within species, and for social insects such as ants, within colonies. Within colonies, upper thermal limits may differ among individuals or change for an individual throughout the day. Daytime foragers of the Neotropical ant Ectatomma ruidum have higher critical thermal maxima (CTmax) than nocturnal foragers, but whether these differences occur among or within colonies was not previously known. We investigated the potential mechanisms accounting for day/night variation in CTmax of E. ruidum foragers by testing whether CTmax varied among or within colonies or due to individuals within colonies acclimating to changes in temperature over a short time scale (3 h). We found within- but not among-colony differences in CTmax on a diel cycle, and we found no evidence for among- or within-colony partitioning of foraging times by individual workers. Individuals did not acclimate to experimental manipulations of temperature, although additional experiments with more ecologically relevant temperature manipulations are needed to rule out this mechanism. In summary, we have shown that day/night differences in upper thermal limits can occur within ant colonies, but further investigation is needed to elucidate the mechanisms driving this variation.

Data from: Cryptic diversity in the Mexican highlands: thousands of UCE loci help illuminate phylogenetic relationships, species limits and divergence times of montane rattlesnakes (Viperidae: Crotalus)

With the continued adoption of genome-scale data in evolutionary biology comes the challenge of adequately harnessing the information to make accurate phylogenetic inferences. Coalescent-based methods of species tree inference have become common, and concatenation has been shown in simulation to perform well, particularly when levels of incomplete lineage sorting are low. However, simulation conditions are often overly simplistic, leaving empiricists with uncertainty regarding analytical tools. We use a large ultraconserved element (UCE) data set (>3000 loci) from rattlesnakes of the Crotalus triseriatus group to delimit lineages and estimate species trees using concatenation and several coalescent-based methods. Unpartitioned and partitioned maximum-likelihood and Bayesian analysis of the concatenated matrix yield a topology identical to coalescent analysis of a subset of the data in bpp. ASTRAL analysis on a subset of the more variable loci also result in a tree consistent with concatenation and bpp, whereas the SVDquartets phylogeny differs at additional nodes. The size of the concatenated matrix has a strong effect on species-tree inference using SVDquartets, warranting additional investigation on optimal data characteristics for this method. Species-delimitation analyses suggest up to 16 unique lineages may be present within the C. triseriatus group, with divergences occurring during the Neogene and Quaternary. Network analyses suggest hybridization within the group is relatively rare. Altogether, our results reaffirm the Mexican highlands as a biodiversity hotspot and suggest that coalescent-based species-tree inference on data subsets can provide a strongly supported species tree consistent with concatenation of all loci with a large amount of missing data.

Data from: Rising CO2 accelerates phosphorus and molybdenum limitation of N2-fixation in young tropical trees

Background and Aims: Nitrogen fixation may be critical for supplying the nitrogen (N) needed to maintain the tropical carbon sink in a world of rising atmospheric CO2. However, we do not know whether increased CO2 acts to exacerbate nutrient limitation on the fixation process itself. We experimentally test this idea by growing N2-fixing plants in pre-Industrial (280 ppm), present-day (400 ppm), and doubled (800 ppm) atmospheric CO2. Methods: In a greenhouse experiment, we grew tree seedlings from N2-fixing species and a non-fixing species at three CO2 concentrations with control, +P (phosphorus), +Mo (molybdenum), and +P+Mo nutrient treatments. Results: We found nutrient limitation to be minimal at pre-Industrial CO2, but with increasing CO2 fixer growth and fixation became increasingly limited by P and by a P-by-Mo interaction. At 400 ppm, plants with +P grew ~50% faster and fixed 10-15x more N2 based on nodule mass and nitrogenase activity. At 800 ppm, plants with +P+Mo grew 200% more, and fixed 25x more N2, suggesting Mo-P co-limitation at elevated CO2. Conclusion: Our findings imply that complex patterns of nutrient limitation can develop as CO2 rises, potentially suppressing tropical N2-fixation and new inputs of N needed to sustain the tropical carbon sink.