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opencc-zeroApr 2020View details →

Experimental modification of morphology reveals the effects of the zygosphene-zygantrum joint on the range of motion of snake vertebrae

Variation in joint shape and soft tissue can alter range of motion (ROM) and create trade-offs between stability and flexibility. The shape of the distinctive zygosphene–zygantrum joint of snake vertebrae has been hypothesized to prevent axial torsion (twisting), but its function has never been tested experimentally. We used experimental manipulation of morphology to determine the role of the zygosphene–zygantrum articulation by micro-computed tomography (μCT) scanning and 3D printing two mid-body vertebrae with unaltered shape and with the zygosphene digitally removed for four species of phylogenetically diverse snakes. We recorded the angular ROM while manipulating the models in yaw (lateral bending), pitch (dorsoventral bending) and roll (axial torsion). Removing the zygosphene typically increased yaw and dorsal pitch ROM. In the normal vertebrae, roll was <2.5 deg for all combinations of pitch and yaw. Roll increased in altered vertebrae but only for combinations of high yaw and ventral pitch that were near or beyond the limits of normal vertebra ROM. In the prairie rattlesnake and brown tree snake, roll in the altered vertebrae was always limited by bony processes other than the zygosphene, whereas in the altered vertebrae of the corn snake and boa constrictor, roll ROM was unconstrained when the pre- and post-zygapophyses no longer overlapped. The zygosphene acts as a bony limit for yaw and dorsal pitch, indirectly preventing roll by precluding most pitch and yaw combinations where roll could occur and potentially allowing greater forces to be applied across the vertebral column than would be possible with only soft-tissue constraints.

opencc-zeroDec 2017View details →

Data from: Does metabolism constrain bird and mammal ranges and predict shifts in response to climate change?

Mechanistic approaches for predicting the ranges of endotherms are needed to forecast their responses to environmental change. We test whether physiological constraints on maximum metabolic rate and the factor by which endotherms can elevate their metabolism (metabolic expansibility) influence cold range limits for mammal and bird species. We examine metabolic expansibility at the cold range boundary (MECRB) and whether species' traits can predict variability in MECRB and then use MECRB as an initial approach to project range shifts for 210 mammal and 61 bird species. We find evidence for metabolic constraints: the distributions of metabolic expansibility at the cold range boundary peak at similar values for birds (2.7) and mammals (3.2). The right skewed distributions suggest some species have adapted to elevate or evade metabolic constraints. Mammals exhibit greater skew than birds, consistent with their diverse thermoregulatory adaptations and behaviors. Mammal and bird species that are small and occupy low trophic levels exhibit high levels of MECRB. Mammals with high MECRB tend to hibernate or use torpor. Predicted metabolic rates at the cold range boundaries represent large energetic expenditures (>50% of maximum metabolic rates). We project species to shift their cold range boundaries poleward by an average of 3.9° latitude by 2070 if metabolic constraints remain constant. Our analysis suggests that metabolic constraints provide a viable mechanism for initial projections of the cold range boundaries for endotherms. However, errors and approximations in estimating metabolic constraints (e.g., acclimation responses) and evasion of these constraints (e.g., torpor/hibernation, microclimate selection) highlight the need for more detailed, taxa‐specific mechanistic models. Even coarse considerations of metabolism will likely lead to improved predictions over exclusively considering thermal tolerance for endotherms.

opencc-zeroNov 2019View details →

Comparing raccoon MHC diversity in native and introduced ranges: evidence for the importance of functional immune diversity for adaptation and survival in novel environments.

The adaptive potential of invasive species is related to the genetic diversity of the invader, which is influenced by genetic drift and natural selection. Typically, the genetic diversity of invaders is studied with neutral genetic markers, however, the expectation of reduced diversity has not been consistently supported by empirical studies. Here, we describe and interpret genetic diversity at both neutral microsatellite loci and the immune related MHC-DRB locus of native and invasive populations of raccoon to better understand of how drift and selection impact patterns of genetic diversity during the invasion process. We found that despite the loss of many MHC alleles in comparison with native populations, functional MHC supertypes are preserved in the invasive region. In the native raccoon population the number of supertypes within individuals was higher than expected under a neutral model. The high level of individual functional divergence may facilitate the adaptation to local conditions in the invasive range. These results suggest that selection is driving divergent allele combinations despite drift causing allelic loss. In the invasive populations, we also detected increased population structure at microsatellites compared to the MHC locus, further suggesting that balancing selection is acting on adaptively important regions of the raccoon genome. Finally, we found that alleles known to exhibit resistance to rabies in the native range, Prlo-DRB*4, Prlo-DRB*16 and Prlo-DRB*102, were the most common alleles in the European populations, suggesting directional selection is acting on this locus. Our research shows empirical support for the importance of functional immune diversity for adaptation and survival in novel environments.

opencc-zeroJan 2020View details →

Data From: An artificial habitat increases the reproductive fitness of a range-shifting species within a newly colonized ecosystem

When a range-shifting species colonizes an ecosystem it has not previously inhabited, it may experience suboptimal conditions that challenge its continued persistence and expansion. Some impacts may be partially mitigated by artificial habitat analogues: artificial habitats that more closely resemble a species' historic ecosystem than the surrounding habitat. If conditions provided by such habitats increase reproductive success, they could be vital to the expansion and persistence of range-shifting species. We investigated the reproduction of the mangrove tree crab Aratus pisonii in its historic mangrove habitat, the suboptimal colonized salt marsh ecosystem, and on docks within the marsh, an artificial mangrove analogue. Crabs were assessed for offspring production and quality, as well as measures of maternal investment and egg quality. Aratus pisonii found on docks produced more eggs, more eggs per unit energy investment, and higher quality larvae than conspecifics in the surrounding salt marsh. Yet, crabs in the mangrove produced the highest quality larvae. Egg lipids suggest these different reproductive outcomes result from disparities in the quality of diet-driven maternal investments, particularly key fatty acids. This study suggests habitat analogues may increase the reproductive fitness of range-shifting species allowing more rapid expansion into, and better persistence in, colonized ecosystems.

opencc-zeroDec 2017View details →

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.

Data from: Ecological release of the Anna's Hummingbird during a northern range expansion

During range expansions species can experience rapid population growth if changes in climate or interspecific interactions remove limits on growth rates in novel habitats. Here I document a century of range expansion in the Anna's Hummingbird (Calypte anna) and investigate the causes of its recent abundance through a combination of demographic, climatic, and phenological analyses. Christmas Bird Count records show that populations have been growing within the native range since the early twentieth century. Sites across the Pacific Northwest show striking fits to simple models of exponential growth following colonization in the 1960's and 70's, and nest records indicate that the species now delays the start of the nesting season by at least 16 days in the north. Although the species now occurs in a much wider range of climates than it did in its native range, the fastest growing sites in the northwest are in regions with minimum breeding season temperatures similar to those occupied by the species prior to the expansion. Range expansions in the Anna's Hummingbird thus reflect an ecological release likely caused by a mix of human facilitation, introduced plants, and phenological acclimation that allowed a California native to expand across western North America.

Data from: Relatedness with plant species in native community influences ecological consequences of range expansions

Global warming is enabling many plant species to expand their range to higher latitudes and altitudes, where they may suffer less from natural aboveground and belowground enemies. Reduced control by natural enemies can enable climate warming-induced range expanders to get an advantage in competition with natives and become disproportionally abundant in their new range. However, so far studies have examined individual growth of range expanders, which have common congeneric plant species in their new range. Thus it is not known how general is this reduced effect of above- and belowground enemies and how it operates in communities, where multiple plant species also interact with each other. Here we show that range-expanding plant species with and without congenerics in the invaded habitats differ in their ecological interactions in the new range. In a community-level experiment, range-expanding plant species, both with and without congenerics, suppressed the growth of a herbivore. However, only range expanders without congenerics reduced biomass production of the native plant species. In the present study, range expanders without congenerics allocated more biomass aboveground compared to native plant species, which can explain their competitive advantage. Competitive interaction and also biomass allocation of native plants and their congeneric range expanders were similar. Our results highlight that information about species phylogenetic relatedness with native flora can be crucial for improving predictions about the consequences of climate warming-induced range expansions.

opencc-zeroFeb 2020View details →

Spatiotemporal population dynamics of the Caddo Madtom (Noturus taylori), a narrow-range endemic of the Ouachita Highlands

The Caddo Madtom, Noturus taylori, is endemic to three river drainages of the Ouachita Highlands in the southeastern United States. Conservation concern for N. taylori has been heightened by recent studies based on analyses of allozyme data suggesting population decline and a possible extirpation event, which lead to N. taylori petitioned for listing under the Endangered Species Act in 2011. The objective of this study was to determine if contemporary factors, historic processes, or a combination of both, using microsatellite DNA loci and mitochondrial (mt) DNA, have influenced patterns of genetic structuring for N. taylori to better inform conservation management strategies. Phylogeographic and Bayesian cluster analyses suggest that genetic structuring between Caddo and Ouachita river drainages was shaped by historical processes prior to construction of reservoir dams that dissect the drainages. We found no evidence that reservoir dams influenced contemporary patterns of genetic structure, thus it is likely that larger river courses, and life-history characteristics conducive to headwater habitats, play important roles in limiting gene flow between drainages, and to some extent within drainages. Genetic diversity of N. taylori was relatively high compared to other endangered madtom species; however, compared to the Ouachita River population, genetic diversity was significantly lower for the Caddo River population. Collectively, these results suggest that N. taylori populations are not heavily impaired, and the genetic variation and structuring is most attributable to historic processes. However, the endemic status and narrowly fragmented distribution still renders N. taylori populations vulnerable to extirpation or extinction by stochastic events.

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: 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.

Data from: Late Pleistocene range expansion of North American topminnows accompanied by admixture and introgression.

Aim: We used genome-scale sampling to assess the phylogeography of a group of topminnows in the Fundulus notatus species complex. Two of the species have undergone extensive range expansions resulting in broadly overlapping distributions, and sympatry within drainages has provided opportunities for hybridization and introgression. We assess the timing and pattern of range expansion in the context of late-Pleistocene-Holocene drainage events, and evaluate the evidence for introgressive hybridization between species. Location: Central and southern United States including drainages of the Gulf of Mexico Coastal Plain and portions of the Mississippi River drainage in and around the Central Highlands. Taxon: Topminnows, Genus Fundulus, subgenus Zygonectes - Fundulus notatus, Fundulus olivaceus, Fundulus euryzonus Methods: We sampled members of the F. notatus species complex throughout their respective ranges, including numerous drainage systems where species co-occur. We collected genome-wide Single Nucleotide Polymorphisms (SNPs) using the Genotype by Sequencing (GBS) method, and subjected data to population genetic analyses to infer the population histories of both species, including explicit tests for admixture and introgression. The methods employed included STRUCTURE, Principle Coordinates Analysis, TreeMix and Approximate Bayesian Computation. Results: Genetic data are presented for 749 individuals sampled from 14 F. notatus, 20 F. olivaceus, and two F. euryzonus populations. Members of the species complex differed in phylogeographic structure, with F. notatus exhibiting geographic clusters corresponding to Pleistocene coastal drainages, and F. olivaceus comparatively lacking in phylogeographic structure. Evidence for interspecific introgression varied by drainage. Main Conclusions: Populations of F. notatus and F. olivaceus exhibited contrasting patterns of lineage diversity among coastal drainages, indicating inter-specific differences in their Pleistocene southern refugia. Phylogeographic patterns in both species indicated that range expansions into the northern limits of contemporary distributions coincided with and continued subsequent to the Last Glacial Maximum. There was evidence of introgression between species in some, but not all drainages where the species co-occur, in a pattern that is correlated with previous estimates of hybridization rates.

opencc-zeroMar 2020View details →

Data from: Why do bugs perish? range size and local vulnerability traits as surrogates of Odonata extinction risk

Despite claims of an insect decline worldwide, our understanding of extinction risk in insects is incomplete. Using bionomic data of all odonate (603 dragonflies and damselflies) North American species, we assessed: a) regional extinction risk and whether this is related to local extirpation; b) whether these two patterns are similar altitudinally and latitudinally; and, c) areas of conservation concern. We used geographic range size as a predictor of regional extinction risk and body size, thermal limits and habitat association as predictors of local extirpation. We found that: a) greater regional extinction risk is related to narrow thermal limits, lotic habitat use and large body size (this in damselflies but not dragonflies); b) southern species are more climate-tolerant but with limited geographic range size than northern species; and, c) two priority areas for odonate conservation are the cold-temperate to sub-boreal Northeast USA and the Transversal Neo-Volcanic System. Our approach can be used to estimate insect extinction risk as it compensates for the lack of abundance data.

Data from: Evidence for adaptive responses to historic drought across a native plant species range

As climatic conditions change, species will be forced to move or adapt to avoid extinction. Exacerbated by ongoing climate change, California recently experienced a severe and exceptional drought from 2011-2017. To investigate whether an adaptive response occurred during this event, we conducted a "resurrection" study of the cutleaf monkeyflower (Mimulus laciniatus), an annual plant, by comparing trait means and variances of ancestral seed collections ("pre-drought") with contemporary descendant collections ("drought"). Plants were grown under common conditions to test whether this geographically-restricted species has the capacity to respond evolutionarily to climate stress across its range. We examined if traits shifted in response to the recent, severe drought and included populations across an elevation gradient, including populations at the low- and high-elevation edges of the species range. We found that time to seedling emergence in the drought generation was significantly earlier than in the pre-drought generation, a response consistent with drought adaptation. Additionally, trait variation in days to emergence was reduced in the drought generation, which suggests selection or bottleneck events. Days to first flower increased significantly by elevation, consistent with climate adaptation across the species range. Drought generation plants were larger and had greater reproduction, which was likely a carryover effect of earlier germination. These results demonstrate that rapid shifts in trait means and variances consistent with climate adaptation are occurring within populations, including peripheral populations at warm and cold climate limits, of a plant species with a relatively restricted range that has so far not shifted its elevation distribution during contemporary climate change. Thus, rapid evolution may mitigate, at least temporarily, range shifts under global climate change. This study highlights the need for better understanding rapid adaptation as a means for plant communities to cope with extraordinary climate events.

Data from: Local range boundaries versus large-scale tradeoffs: climatic and competitive constraints on tree growth

Species often respond to human‐caused climate change by shifting where they occur on the landscape. To anticipate these shifts, we need to understand the forces that determine where species currently occur. We tested whether a long‐hypothesised trade‐off between climate and competitive constraints explains where tree species grow on mountain slopes. Using tree rings, we reconstructed growth sensitivity to climate and competition in range centre and range margin tree populations in three climatically distinct regions. We found that climate often constrains growth at environmentally harsh elevational range boundaries, and that climatic and competitive constraints trade‐off at large spatial scales. However, there was less evidence that competition consistently constrained growth at benign elevational range boundaries; thus, local‐scale climate‐competition trade‐offs were infrequent. Our work underscores the difficulty of predicting local‐scale range dynamics, but suggests that the constraints on tree performance at a large‐scale (e.g. latitudinal) may be predicted from ecological theory.

Data from: Influence of range position on locally adaptive gene-environment associations in Populus flowering time genes

Local adaptation is pervasive in forest trees, which are characterized by large effective population sizes spanning broad climatic gradients. In addition to having relatively contiguous populations, many species also form isolated populations along the rear edge of their range. These rear-edge populations may contain unique adaptive diversity reflecting a history of selection in marginal environments. Thus, discovering genomic regions conferring local adaptation in rear edge populations is a key priority for landscape genomics to ensure conservation of genetic resources under climate change. Here, we report on adaptive gene-environment associations in SNPs from 27 genes in the Populus flowering time gene network, analyzed on a range-wide collection of >1000 balsam poplar trees, including dense sampling of the southern range edge. We use a combined approach of local adaptation scans to identify candidate SNPs, followed by modeling the compositional turnover of adaptive SNPs along multivariate climate gradients using Gradient Forests (GF). Flowering time candidate genes contained extensive evidence of climate adaptation, namely outlier population structure and gene-environment associations, along with allele frequency divergence between the core and edge of the range. GF showed strong allele frequency turnover along gradients of elevation and diurnal temperature variability, as well as threshold responses to summer temperature and precipitation, with turnover especially strong in edge populations that occur at high elevation but southerly latitudes. We discuss these results in light of how climate may disrupt locally adaptivegene-environment relationships, and suggest that rear edge populations hold climate-adaptive variants that should be targeted for conservation.

opencc-zeroApr 2020View details →

Community-level interactions between plants and soil biota during range expansion

1. Plant species that expand their range in response to current climate change will encounter soil communities that may hinder, allow, or even facilitate plant performance. It has been shown repeatedly for plant species originating from other continents that these plants are less hampered by soil communities from the new than from the original range. However, information about the interactions between intra-continental range expanders and soil communities is sparse, especially at community level. 2. Here we used a plant-soil feedback experiment approach to examine if the interactions between range expanders and soil communities change during range expansion. We grew communities of range-expanding and native plant species with soil communities originating from the original and new range of range expanders. We determined the composition of fungi, bacteria and nematodes in these conditioned soils by high-throughput amplicon sequencing of the ITS region and the 16S rRNA gene and using morphological methods, respectively. Then we tested how these soil communities influence the growth of subsequent communities of range expanders and natives. 3. We found that after the conditioning phase soil bacterial, fungal and nematode communities differed by origin and by conditioning plant communities. Despite differences in bacterial, fungal and nematode communities between original and new range, soil origin did not influence the biomass production of plant communities. Both native and range expanding plant communities produced most aboveground biomass in soils that were conditioned by plant communities distantly related to them. 4. Synthesis. We conclude that communities of range-expanding plant species shape specific soil communities in both original and new range soil. Plant-soil interactions of range expanders in communities can be similar to the ones of their closely related native plant species.

opencc-zeroSep 2019View details →

Data from: Corralling a black swan: natural range of variation in a forest landscape driven by rare, extreme events

The natural range of variation (NRV) is an important reference for ecosystem management, but has been scarcely quantified for forest landscapes driven by infrequent, severe disturbances. Extreme events such as large, stand-replacing wildfires at multi-century intervals are typical for these regimes; however, data on their characteristics are inherently scarce, and, for land management, these events are commonly considered too large and unpredictable to integrate into planning efforts (the proverbial 'Black Swan'). Here, we estimate the NRV of late-seral (mature/old-growth) and early-seral (post-disturbance, pre-canopy-closure) conditions in a forest landscape driven by episodic, large stand-replacing wildfires: the Western Cascade Range of Washington, USA (2.7 million ha). These two seral stages are focal points for conservation and restoration objectives in many regions. Using a state-and-transition simulation approach incorporating uncertainty, we assess the degree to which NRV estimates differ under a broad range of literature-derived inputs regarding: a) overall fire rotations, and b) how fire area is distributed through time – as relatively frequent smaller events (less episodic), or fewer but larger events (more episodic). All combinations of literature-derived fire rotations and temporal distributions (i.e. 'scenarios') indicate that the largest wildfire events (or episodes) burned up to 10^5-10^6 hectares. Under most scenarios, wildfire dynamics produced 5th-95th percentile ranges for late-seral forests of ~47-90% of the region (median 70%), with structurally complex early-seral conditions composing ~1-30% (median 6%). Fire rotation was the main determinant of NRV, but temporal distribution was also important, with more episodic (temporally clustered) fire yielding wider NRV. In smaller landscapes (20,000 ha; typical of conservation reserves and management districts), ranges were 0-100% because fires commonly exceeded the landscape size. Current conditions are outside the estimated NRV, with the majority of the region instead covered by dense mid-seral forests (i.e. a regional landscape with no historical analog). Broad consistency in NRV estimates among widely varied fire regime parameters suggests these ranges are likely relevant even under changing climatic conditions, both historical and future. These results indicate management-relevant NRV estimates can be derived for seral stages of interest in extreme-event landscapes, even when incorporating inherent uncertainties in disturbance regimes.

Data from: Costs of immunity and their role in the range expansion of the house sparrow in Kenya

There are at least two reasons to study traits that mediate successful range expansions. First, dispersers will found new populations and thus impact the distribution and evolution of species. Second, organisms moving into new areas will influence the fate of resident communities, directly competing with or indirectly affecting residents by spreading non-native or spilling-back native parasites. The success of invaders in new areas is likely mediated by a counterbalancing of costly traits. In new areas where threats are comparatively rare, individuals that grow rapidly and breed prolifically should be at an advantage. High investment in defenses should thus be disfavored. In the present study, we compared the energetic, nutritional and collateral damage costs of an inflammatory response among Kenyan house sparrow (Passer domesticus) populations of different ages, asking whether costs were related to traits of individuals from three different capture sites. Kenya is among the world's most recent range expansions for this species, and we recently found that the expression of Toll-like receptors (TLRs), leukocyte receptors that instigate inflammatory responses when bound to microbial elements, was related to the range expansion across the country. Here, we found (contrary to our expectations) that energetic and nutritional costs of inflammation were higher, but damage costs were lower, in range-edge compared with core birds. Moreover, at the individual level, TLR-4 expression was negatively related to commodity costs (energy and a critical amino acid) of inflammation. Our data thus suggest that costs of inflammation, perhaps mediated by TLR expression, might mitigate successful range expansions.