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bioRxiv2019

ASSEMBLY MECHANISMS OF NEOTROPICAL BUTTERFLY COMMUNITIES ALONG AN ENVIRONMENTAL GRADIENT

Our goal was to test the hypothesis that assembly processes that limit species similarity (i.e., competition) predominantly occur in more stable abiotic environments, whereas habitat filtering (i.e., habitat characteristics) is a major driver of community composition within more variable environments at regional (e.g., aseasonal vs seasonal forests) and local scales (e.g., understory vs. canopy). A combined approach of phylogenetic- and functional trait-based analyses using forewing length and aspect ratio as traits, were used to this hypothesis.\n\nA 3-year survey was carried out at three sites (i.e., wet, transition and dry forests) across a climatic gradient in western Ecuador. Transition and dry forests were considered as seasonal, whereas wet forest were considered aseasonal. Butterflies were sampled using traps baited with rotting banana and prawn every two months from Nov 2010 to Sep 2013. Traps were set up at two heights, in the understory and canopy. DNA was extracted to sequence the barcode section of the mitochondrial gene cytochrome oxidase 1 (COI) for phylogenetic analyses. Measurements of morphological traits, forewing length and aspect ratio were done using digital photographs of specimens.\n\nA total of 6466 specimens representing 142 species of Nymphalidae were recorded. Based on phylogenetic- and trait-based analyses, we rejected the hypothesis that assembly processes that limit species similarity (i.e., competition) are likely to predominantly occur in more stable abiotic environments, whereas habitat filtering can be a major driver of community composition within more variable environments at regional (i.e., aseasonal forest vs seasonal forests) and local scales (i.e., understory vs. canopy). My study of assembly mechanisms revealed the opposite pattern, with stronger evidence for the action of ecological filters in the assembly of butterfly communities from the wet aseasonal forests, and competition likely to be a major assembly process within dry seasonal forests. The present study therefore provided new insights into community assembly mechanisms in one of the richest butterfly faunas worldwide.

ecology↗

bioRxiv2019

Global ecotypes in the ubiquitous marine clade SAR86

SAR86 is an abundant and ubiquitous heterotroph in the surface ocean that plays a central role in the function of marine ecosystems. We hypothesized that despite its ubiquity, different SAR86 subgroups may be endemic to specific ocean regions and functionally specialized for unique marine environments. However, the global biogeographical distributions of SAR86 genes, and the manner in which these distributions correlate with marine environments, have not been investigated. We quantified SAR86 gene content across globally-distributed metagenomic samples and modeled these gene distributions as a function of 51 environmental variables. We identified five distinct clusters of genes within the SAR86 pangenome, each with a unique geographic distribution associated with specific environmental characteristics. Gene clusters are characterized by strong taxonomic enrichment of distinct SAR86 genomes and partial assemblies, as well as differential enrichment of certain functional groups, suggesting differing functional and ecological roles of SAR86 ecotypes. We then leveraged our models and high-resolution, remote sensing-derived environmental data to predict the distributions of SAR86 gene clusters across the worlds oceans, creating global maps of SAR86 ecotype distributions. Our results reveal that SAR86 exhibits previously unknown, complex biogeography, and provide a framework for exploring geographic distributions of genetic diversity from other microbial clades.

ecology↗

bioRxiv2019

A genomic approach to inferring kinship reveals limited intergenerational dispersal in the yellow fever mosquito

Understanding past dispersal and breeding events can provide insight into ecology and evolution, and can help inform strategies for conservation and the control of pest species. However, parent-offspring dispersal can be difficult to investigate in rare species and in small pest species such as mosquitoes. Here we develop a methodology for estimating parent-offspring dispersal from the spatial distribution of close kin, using pairwise kinship estimates derived from genome-wide single nucleotide polymorphisms (SNPs). SNPs were scored in 162 Aedes aegypti (yellow fever mosquito) collected from eight close-set, high-rise apartment buildings in an area of Malaysia with high dengue incidence. We used the SNPs to reconstruct kinship groups across three orders of kinship. We transformed the geographical distances between all kin pairs within each kinship category into axial standard deviations of these distances, then decomposed these into components representing past dispersal events. From these components, we isolated the axial standard deviation of parent-offspring dispersal, and estimated neighbourhood area (129 m), median parent-offspring dispersal distance (75 m), and oviposition dispersal radius within a gonotrophic cycle (36 m). We also analysed genetic structure using distance-based redundancy analysis and linear regression, finding isolation by distance both within and between buildings and estimating neighbourhood size at 268 individuals. These findings indicate the scale required to suppress local outbreaks of arboviral disease and to target releases of modified mosquitoes for mosquito and disease control. Our methodology is readily implementable for studies of other species, including pests and species of conservation significance.

ecology↗

bioRxiv2019

An Empiricist’s Guide to Modern Coexistence Theory for Competitive Communities

While most ecological theories have historically invoked niche differences as the primary mechanism allowing species coexistence, we now know that species coexistence in competitive communities actually depends on the balance of two opposing forces: niche differences (ND) that determine how species limit their own growth rate versus that of their competitor, and relative fitness differences (RFD) that establish competitive hierarchies among species. Several different empirical methods have been proposed for measuring ND and RFD in order to make predictions about coexistence of species, yet it remains unclear which method(s) are appropriate for a given empirical study and whether or not those methods actually yield the same information. Here we summarize and compare five different empirical methods, with the aim of providing a practical guide for empiricists who want to predict coexistence among species. These include two phenomenological methods that estimate ND and RFD based on observing competitive interactions among species; two mechanistic methods that estimate ND and RFD based solely on information about species resource requirements; and a fifth method that does not yield ND and RFD but describes the impacts of those forces within communities. Based on the specific requirements, limitations, and assumptions of each approach, we offer a series of decision steps that can be used to determine which method(s) are best for a given study system. In particular, we show there are important tradeoffs between mechanistic methods, which require detailed understanding of species niches and physiology but are more tractable experimentally, and phenomenological methods which do not require this detailed information but can be impractical for some study designs. Importantly, we show that although each method can be used to estimate ND and RFD, the methods do not always yield the same values. Therefore we caution against future syntheses that compile these estimates from different empirical studies. Finally, we highlight several areas where modern coexistence theory could benefit from additional empirical work.

ecology↗

bioRxiv2019

Microbial evolution reshapes soil carbon feedbacks to climate change

Microbial decomposition of soil organic matter is a key component of the global carbon cycle. As Earths climate changes, the response of microbes and microbial enzymes to rising temperatures will largely determine the soil carbon feedback to atmospheric CO2. However, while increasing attention focuses on physiological and ecological mechanisms of microbial responses, the role of evolutionary adaptation has been little studied. To address this gap, we developed an ecosystem-evolutionary model of a soil microbe-enzyme system under warming. Constraining the model with observations from five contrasting sites reveals evolutionary aggravation of soil carbon loss to be the most likely outcome; however, temperature-dependent increases in mortality could cause an evolutionary buffering effect instead. We generally predict a strong latitudinal pattern, from small evolutionary effects at low latitude to large evolutionary effects at high latitudes. Accounting for evolutionary mechanisms will likely be critical for improving projections of Earth system responses to climate change.

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bioRxiv2019

Microbial networks inferred from metabarcoding data lack replicability: consequences for next-generation biomonitoring

Plant-associated microbial interaction networks protect plants against disease. There is, therefore, a need to monitor in real time their responses to environmental changes to predict disease risk and adjust crop protection strategies. Next-Generation Biomonitoring (NGB) proposes to reconstruct automatically these networks from metabarcoding data, to complement ecological community properties commonly used for ecosystem health assessment. This study aimed to evaluate the benefits and shortcomings of community-level and network-level properties for biomonitoring. We specifically investigated whether microbial networks inferred from metabarcoding data show robust responses to agricultural practices, using the grapevine microbiota as a study system. Our results demonstrate a strong footprint of the agricultural practice on the metabarcoding data, when analyzed at the community level. The richness, diversity and evenness of fungal communities were significantly higher in organic than conventional plots. The cropping system also affected the composition of grapevine foliar fungal communities significantly. Contrary to our expectations, microbial networks were less sensitive to changes in agricultural practices than microbial communities, confirming that NGB should not only consider network-level properties but also community-level properties. Moreover, we found that microbial networks lacked replicability within a cropping system but that consensus networks, built from several network replicates, could generate relevant hypotheses of microbial interactions. As things stand, community-level properties appear to be a more reliable and statistically powerful monitoring option than network-level properties. Future developments, especially in network inference methods, are likely to challenge our findings and help to improve the monitoring of the ecosystem services provided by the plant microbiota.

ecology↗

bioRxiv2019

The Importance of Mesozooplankton Diel Vertical Migration for Sustaining a Mesopelagic Food Web

We used extensive ecological and biogeochemical measurements obtained from quasi-Lagrangian experiments during two California Current Ecosystem Long-Term Ecosystem Research cruises to analyze carbon fluxes between the epipelagic and mesopelagic zones using a linear inverse ecosystem model (LIEM). Measurement constraints on the model include 14C primary productivity, dilution-based microzooplankton grazing rates, gut pigment-based mesozooplankton grazing rates (on multiple zooplankton size classes), 234Th:238U disequilibrium and sediment trap measured carbon export, and metabolic requirements of micronekton, zooplankton, and bacteria. A likelihood approach (Markov Chain Monte Carlo) was used to estimate the resulting flow uncertainties from a sample of potential flux networks. Results highlight the importance of mesozooplankton active transport (i.e., diel vertical migration) for supplying the carbon demand of mesopelagic organisms and sequestering carbon dioxide from the atmosphere. In nine water parcels ranging from a coastal bloom to offshore oligotrophic conditions, mesozooplankton active transport accounted for 18% - 84% (median: 42%) of the total carbon supply to the mesopelagic, with gravitational settling of POC (12% - 55%; median: 37%) and subduction (2% - 32%; median: 14%) providing the majority of the remainder. Vertically migrating zooplankton contributed to downward carbon flux through respiration and excretion at depth and via consumption loses to predatory zooplankton and mesopelagic fish (e.g. myctophids and gonostomatids). Sensitivity analyses showed that the results of the LIEM were robust to changes in nekton metabolic demands, rates of bacterial production, and mesozooplankton gross growth efficiency. This analysis suggests that prior estimates of zooplankton active transport based on conservative estimates of standard (rather than active) metabolism should be revisited.\n\nContribution to the FieldUnderstanding the flows of carbon within the ocean is important for predicting how global climate will shift; yet even after decades of research, the magnitude with which the ocean sequesters carbon is highly uncertain. One reason behind this uncertainty is that a variety of mechanisms control the balance between carbon input and carbon output within the ocean. The topic of this work is to inspect the role of biological organisms in physically transferring organic carbon from the surface to the deep ocean. As opposed to other mechanisms--such as sinking particles, the biological transfer of carbon is difficult to measure directly and is often quite variable, leading to large uncertainties. Here we use an extensive set of in situ observations off the coast of southern California to model the flow of carbon through the ecosystem. The model determined that in our study area nearly half of the total transfer of carbon from the surface ocean to deep was carried out by zooplankton that swim up to the surface each night to feed. This finding has direct implications for global carbon budgets, which often underestimate this transfer of carbon.

ecology↗

bioRxiv2019

Co-occurrence or dependence? Using spatial analyses to explore the interaction between palms and triatomines.

BackgroundTriatomine kissing bugs are responsible for the vectorial transmission of the parasite Trypanosoma cruzi, etiological agent of Chagas disease, a zoonosis affecting 10 million people and with 25 million at risk of infection. Triatomines are associated with particular habitats that offer shelter and food. Several triatomine species of the Rhodnius genus have close association with palm crowns, where bugs can obtain blood from the associated fauna. The Rhodnius - palm interaction has been reported in several places of Central and South America. However, the association in the distributions of Rhodnius species and palms has not been quantitatively determined.\n\nMethodology/Principal FindingsBroad distributions of eight Rhodnius species and 16 palm species with Rhodnius-infestation reports were estimated using Ecological Niche Models. Rhodnius species distributions in their total range were compared to their distributions in areas with palms. Rhodnius species presence was found to be higher in areas with palms. However, that tendency notoriously depended on palm species. Rhodnius species presence increased several times in areas with particular palm species. Moreover, a possible relationship was found between Rhodnius and palm species richness, indicating the Amazon region as the convergent region where several Rhodnius and palm species intersected. Finally, palm distribution was evaluated as predictor of Rhodnius species distributions, but their inclusion in the distributions models did not improve their performance.\n\nConclusions/SignificanceThe distributions of some Rhodnius and palm species showed a high spatial association, which can be based on species interaction or niche similarity. Based on distribution convergence, the Amazon region appear to be the origin of the Rhodnius-palm association. The direct relationship between palms and Rhodnius species richness could be based on the habitat heterogeneity offered by different palm species. Despite spatial association, palm presence would not be a relevant predictor of Rhodnius species distributions in comparison to other environmental variables. Inclusion of other input data as hosts distribution could help to increase model predictability.\n\nAuthor summaryThe infestation of palms with Rhodnius genus kissing bugs (Chagas disease vectors) is important from the public health perspective, since insects living in palms can infest nearby houses. The migration of these bugs to households could threaten vector control programs since reinfestation of treated dwellings can occur. Association between Rhodnius and palms species distributions has been previously suggested but never quantitatively determined. The strong association between one palm species and one Rhodnius species can be used as a factor to predict the presence of Rhodnius bugs in definite areas. In this study, we estimated by models the distributions of eight Rhodnius species and 18 Rhodnius-infested palm species. Rhodnius distributions models showed a biased presence toward areas with certain palm species. That specific association was very strong in some cases; however, the presence of associated palm species was used in Rhodnius distributions models, but that did not improve the predictability of the models. Palm presence appear to be not essential for the Rhodnius current distribution because they could inhabit other habitats; but that association could be relevant to the Rhodnius evolutionary and biogeographic history.

ecology↗

bioRxiv2019

Combining statistical and mechanistic models to unravel the drivers of mortality within a rear-edge beech population

AO_SCPLOWBSTRACTC_SCPLOWSince several studies have been reporting an increase in the decline of forests, a major issue in ecology is to better understand and predict tree mortality. The interactions between the different factors and the physiological processes giving rise tree mortality, as well as the inter-individual variability in mortality risk, still need to be better assessed. This study investigates mortality in a rear-edge population of European beech (Fagus sylvatica L.) using a combination of statistical and process-based modelling approaches. Based on a survey of 4323 adult beeches since 2002 within a natural reserve, we first used statistical models to quantify the effects of competition, tree growth, size, defoliation and fungi presence on mortality. Secondly, we used an ecophysiological process-based model (PBM) to separate out the different mechanisms giving rise to temporal and inter-individual variations in mortality by simulating depletion of carbon stocks, loss of hydraulic conductance and damage due to late frosts in response to climate. The combination of all these simulated processes was associated with the temporal variations in the population mortality rate. The individual probability of mortality decreased with increasing mean growth, and increased with increasing crown defoliation, earliness of budburst, fungi presence and increasing competition, in the statistical model. Moreover, the interaction between tree size and defoliation was significant, indicating a stronger increase in mortality associated to defoliation in smaller than larger trees. Finally, the PBM predicted a higher conductance loss together with a higher level of carbon reserves for trees with earlier budburst, while the ability to defoliate the crown was found to limit the impact of hydraulic stress at the expense of the accumulation of carbon reserves. We discuss the convergences and divergences obtained between statistical and process-based approaches and we highlight the importance of combining them to characterize the different processes underlying mortality, and the factors modulating individual vulnerability to mortality.

ecology↗

bioRxiv2019

Deconstructing higher-order interactions in the microbiota: A theoretical examination

O_LIA major objective of microbial ecology is to identify how the composition of gut microbial taxa shapes host phenotypes. However, most studies focus solely on community-level patterns and pairwise interactions and ignore the potentially significant effects of higher-order interactions involving three or more component taxa. C_LIO_LIStudies on higher-order interactions among microbial taxa are scarce for many reasons, including experimental intractability, daunting diversity and complexity of many microbial systems, and the potential confounding role of the environment. Moreover, we still lack the empirical and statistical tools to isolate and understand the role of higher-order interactions on the host. C_LIO_LIHere, we apply a mathematical approach to quantifying the effects of higher-order interactions among taxa on host infection risk. To do so, we adapt the Hadamard-Walsh method recently used in evolutionary genetics to quantify the nonlinear effects of mutations on fitness. We apply our approach to an in silico dataset built to resemble a population of insect hosts with gut-associated microbial communities at risk of infection from an intestinal parasite. Critically, we examine these interactions across a breadth of environmental contexts, using nutrient content of the insect diet as a model for context. C_LIO_LIWe find that the effect of higher-order interactions is considerable and can change appreciably across environmental contexts. Strikingly, the relative eminence of different orders (pairwise vs. third order, fourth order, and fifth order) changes as a function of environmental context. Furthermore, we show-in our theoretical microcosm-that higher-order interactions can stabilize community structure thereby reducing host susceptibility to parasite invasion. C_LIO_LIOur approach illustrates how incorporating the effects of higher-order interactions among gut microbiota across environments can be essential for understanding their effects on host phenotypes. We conclude that higher-order interactions among taxa can profoundly shape important organismal phenotypes, and they deserve greater attention in host-associated microbiome studies. C_LI

ecology↗

bioRxiv2019

Reconsidering the management paradigm of fragmented populations

Habitat fragmentation and population declines call for informed management of many endangered species. The dominant paradigm for such management focuses on avoiding deleterious inbreeding effects in separated populations, by facilitating migration to maintain connectivity between them, an approach epitomized by the \"one migrant per generation\" rule. We show that this paradigm fails to take into account two important factors. First, it ignores an inherent trade-off: maintaining within-population genetic diversity is at the expense of maintaining global diversity. Migration increases local within-population genetic diversity, but also homogenizes the meta-population, which may lead to erosion of global genetic diversity. Second, this paradigm does not consider that because many fragmented species have declined in numbers only within the last century, they still carry much of the high genetic diversity characteristic of the historically large population. The conservation of a species global diversity, crucial for evolutionarily adaptation to ecological challenges such as epidemics, industrial pollutants, or climate change, is paramount to a species long-term survival. Here we discuss how consideration of these factors can inform management of fragmented populations and provide a framework to assess the impact on genetic diversity of different management strategies. We also propose two alternative management strategies to replace the \"one migrant per generation\" dogma.

ecology↗

bioRxiv2019

Predator-induced selection on urchin activity level depends on urchin body size

Temporally consistent individual differences in behavior impact many ecological processes. We simultaneously examined the effects of individual variation in prey activity level, covering behavior, and body size on prey survival with predators using an urchin-lobster system. Specifically, we tested the hypothesis that slow-moving purple sea urchins (Strongylocentrotus purpuratus) and urchins who deploy extensive substrate (pebbles and stones) covering behavior will out-survive active urchins that deploy little to no covering behavior when pitted against a predator, the California spiny lobster (Panulirus interruptus). We evaluated this hypothesis by first confirming whether individual urchins exhibit temporally consistent differences in activity level and covering behavior, which they did. Next, we placed groups of four urchins in mesocosms with single lobster and monitored urchin survival for 108 hours. High activity level was negatively associated with survival, whereas urchin size and covering behavior independently did not influence survival. The negative effect of urchin activity level on urchin survival was strong for smaller urchins and weaker for large urchins. Taken together, these results suggest that purple urchin activity level and size jointly determine their susceptibility to predation by lobsters. This is potentially of great interest, because predation by recovering lobster populations could alter the stability of kelp forests by culling specific phenotypes, like foraging phenotypes, from urchin populations.

ecology↗

bioRxiv2019

Incomplete resilience of a shallow lake to a brownification event

Dissolved organic carbon (DOC) concentrations in many freshwater ecosystems of the northern hemisphere have increased in recent decades due to additional terrestrial inputs. This phenomenon, known as brownification, can strongly alter the physical, chemical, and biological traits of aquatic ecosystems. Extreme rainfall can also cause sudden brownification, known as blackwater events in rivers, while longer term effects on lakes are unknown. Here, we investigated the resilience of a small, temperate, shallow lake to a strong natural flooding-induced brownification event in 2011-2012. From initial DOC and total phosphorus (TP) concentrations of ~12 and 0.04 mg L-1, respectively, the lake rapidly reached peak DOC and TP concentrations of 60 and 0.35 mg L-1, respectively. By the following year, water levels had returned close to initial values, yet two additional years of monitoring (until summer 2015) and a more recent sample in spring 2019 showed that the lake did not fully return to its pre-brownification state. Instead, DOC and TP concentrations plateaued at concentrations respectively 1.5-fold and twofold greater than pre-brownification values within less than two years and remained at these concentrations in spring 2019. During this initial recovery period the lake exhibited a decline of phytoplankton and a partial recovery of summer periphyton biomass and production, albeit a full return to pre-brownification values was not recorded in either case. DOC and TP concentrations were positively correlated to phytoplankton biomass and negatively to periphyton. As increases in phytoplankton production outpaced decreasing periphyton production, the net result of this brownification event has been an increase in whole-lake areal summertime primary production. This incomplete resilience to a flooding-induced brownification event implies consequences for several ecological and biogeochemical functions of shallow lakes that warrant further investigation and might contribute to the gradual increase of freshwater DOC concentrations in the northern hemisphere.

ecology↗

bioRxiv2019

DO THESE CRAYFISH MAKE ME LOOK FAT? BODY CONDITION CORRELATES TO PREY ABUNDANCE IN THREE HELLBENDER (CRYPTOBRANCHUS ALLEGANIENSIS) POPULATIONS

In ecological studies body condition is often measured as an indicator of animal health or well-being. The Hellbender (Cryptobranchus alleganiensis) is a threatened salamander species found throughout the montane regions of the eastern United States. Although few young individuals have historically been found in the wild, recent studies in Blue Ridge Physiographic Regions have uncovered larvae in several streams. In Little River, Tennessee, differences in the crayfish population, the principal component of the adult Hellbender diet, was hypothesized as a potential reason for the large number of immature individuals, and lack of large adults. To investigate this hypothesis, we compared body condition of Hellbenders in three streams with different crayfish relative frequencies. Body condition of Hellbenders was positively correlated with crayfish relative frequencies, with Hellbenders in the stream with the highest crayfish relative frequency exhibiting the highest expected mass per total length.

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bioRxiv2019

Invasive plants facilitated by socioeconomic change shelter vectors of scrub typhus and spotted fever

BackgroundEcological determinants of most emerging vector-borne diseases are little studied, particularly for neglected tropical disease; meanwhile, although socioeconomic change can have significant downstream effect on human risks to vector-borne diseases via a change in land cover, particularly facilitating the invasion of exotic plants, related studies remain very scarce. Scrub typhus and spotted fever are neglected diseases emerging around the globe and are transmitted by chigger mites and ticks, respectively, with small mammals as the primary hosts of both vectors.\n\nMethodology/Principal findingsWe investigated how invasion of Leucaena leucocephala plant after extensive abandonment of farmlands driven by industrialization in Penghu Islands of Taiwan affected abundance of chiggers and ticks by trapping small mammals in three types of habitats (invasion site, agricultural field, human residence) every two months for a year. Invasion sites sheltered more chiggers and ticks than the other two habitats; moreover, both vectors maintained higher abundance in early winter and populations of chiggers were more stable across seasons in invasion sites, suggesting that the invasive sites could be a temporary refuge for both vectors and might help mitigate the negative influence of unfavorable climate. Infective rates of etiologic agents in chiggers and ticks were also higher in invasion sites. Top soil temperature and relative humility were similar across the three habitats, but invasion sites harbored more Rattus losea rat, on which infested chiggers and ticks were more well fed than those from the most commonly trapped species (Suncus murinus shrew), implicating that abundance of superior hosts instead of microclimate, might determine the abundance of both vectors.\n\nConclusions/SignificanceThis study highlights an important but largely neglected issue that socioeconomic change can have unexpected consequence for human health mediated particularly through invasive plants, which could become a hotspot for emerging infectious diseases but usually are very hard to be eradicated. In the future, a more holistic perspective that integrates socioeconomy, land use, exotic species, and human health should be considered to fully understand potential emergence of vector-borne diseases.\n\nAuthor summaryUnderstanding how environmental factors, such as land use change, affect risks to vector-borne diseases helps control and prevent human diseases, but ecological preference of vectors of most neglected diseases remain little investigated. In this study, we found that vectors of scrub typhus (chigger mites) and spotted fever (hard ticks), two emerging neglected diseases, were much more abundant in sites invaded by exotic plants than the other major land cover types in a small island of Taiwan; moreover, populations of chigger mite in invasion sites were more stable across seasons, suggesting that plant invasion sites could be a refuge for disease vectors under unfavorable climate. Higher abundance of chigger mites and ticks was related to higher abundance of a superior rodent host instead of a difference in soil micro-climate. More significantly, these invasive plants are facilitated by extensive abandonment of farmlands driven by industrialization and rural to urban migration, thus demonstrating an important but largely neglected issue that socioeconomic change, when mediated through a change in land cover, can have unexpected downstream effect on emerging neglected tropical diseases.

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bioRxiv2019

The conspicuousness of the toxic Heliconius butterflies across time and habitat

Forests are a mosaic of light spectra, and colour signal efficiency might change in different light environments. Local adaptation in Heliconius butterflies is linked to microhabitat use and the colourful wing colour patterns may be adapted for signalling in different light environments. These toxic butterflies exhibit conspicuous colours as a warning to predators that they should be avoided, but also find and choose potential mates based on colour signals. The two selection pressures of predation and mate preference are therefore acting together. Colour conspicuousness should show habitat-specific contrast for the butterflies, which would facilitate detection and species identification. On the other hand, selection for signal stability would be stronger in the avian visual system. In this study we analysed the contrast of two Heliconius mimicry rings in their natural habitats under varying degrees of forest fragmentation and light conditions. We used digital image analyses and mapped the bird and butterfly vision colour space in order to examine whether warning colours have greater contrast and if they transmit a consistent signal across time of the day and habitat in a tropical forest. We tested conspicuousness using opponent colour channels against a natural green background. For avian vision, colours are generally very stable through time and habitat. For butterfly vision, there is some evidence that species are more contrasting in their own habitats, where conspicuousness is higher for red and yellow bands in the border and for white in the forest. Light environment affects Heliconius butterflies warning signal transmission to a higher degree through their own vision, but to a lesser degree through avian predator vision. This work provides insight into the use of colour signals in sexual and natural selection in the light of ecological adaptation.

ecology↗

bioRxiv2019

Estimating abundance with interruptions in data collection using open population spatial capture-recapture models

O_LIThe estimation of population size remains one of the primary goals and challenges in ecology and provides a basis for debate and policy in wildlife management. Despite the development of efficient non-invasive sampling methods and robust statistical tools to estimate abundance, maintenance of field sampling is still subject to economic and logistic constraints. These can result in intentional or unintentional interruptions in sampling and cause gaps in data time series, posing a challenge to abundance estimation, and ultimately conservation and management decisions.\nC_LIO_LIWe applied an open population spatial capture-recapture (OPSCR) model to simulations and a real case study to test the reliability of abundance inferences models to interruption in data collection. Using individual detections occurring over consecutive sampling occasions, OPSCR models allow the estimation of abundance from individual detection data while accounting for lack of demographic and geographic closure between occasions. First, we simulated sampling data with interruptions in field sampling of different lengths and timing. We checked the performance of an OPSCR model in deriving abundance for species with slow and intermediate life history strategies. Finally, we introduced artificial sampling interruptions of various magnitudes and timing to a five-year non-invasive monitoring data set of wolverines (Gulo gulo) in Norway and quantified the consequences for OPSCR model predictions.\nC_LIO_LIInferences from OPSCR models were reliable even with temporal interruptions in monitoring. Interruption did not cause any systematic bias, but increased uncertainty. Interruptions occurring at occasions towards the beginning and the end of the sampling caused higher uncertainty. The loss in precision was more severe for species with a faster life history strategy.\nC_LIO_LIWe provide a reliable framework to estimate abundance even in the presence of sampling interruptions. OPSCR allows monitoring studies to provide contiguous abundance estimates to managers, stakeholders, and policy makers even when data are non-contiguous. OPSCR models do not only help cope with unintentional interruptions during sampling but also offer opportunities for using intentional sampling interruptions during the design of cost-effective population surveys.\nC_LI

ecology↗

bioRxiv2019

Effects of temperature and pCO2 on the respiration, biomineralization and photophysiology of the giant clam Tridacna maxima

Such as many other reef organisms, giant clams are today confronted to global change effects and can suffer mass bleaching or mortality events mainly related to abnormally high seawater temperatures. Despite its strong ecological and socio-economical importance, its responses to the two most alarming threats linked to global change (i.e., ocean warming and acidification) still need to be explored. We investigated physiological responses of 4-years-old Tridacna maxima specimens to realistic levels of temperature and partial pressure of carbon dioxide (pCO2) (+1.5{degrees}C and +800 atm of CO2) predicted for 2100 in French Polynesian lagoons during the warmer season. During a 65-days crossed-factor experiment, individuals were exposed to two temperatures (29.2{degrees}C; 30.7{degrees}C) and two pCO2 (430 {micro}atm; 1212 {micro}atm) conditions. Impact of each parameter and their potential synergetic effect were evaluated on respiration, biomineralization and photophysiology. Kinetics of thermal and acidification stress were evaluated by performing measurements at different times of exposure (29, 41, 53, 65 days). At 30.7{degrees}C, the holobiont O2 production, symbiont photosynthetic yield, and density were negatively impacted. High pCO2 had a significant negative effect on shell growth rate, symbiont photosynthetic yield and density. Shell microstructural modifications were observed from 41 days in all temperature and pCO2 conditions. No significant synergetic effect was found. Today thermal conditions (29.2{degrees}C) appeared to be sufficiently stressful to induce a host acclimatization process. All these observations indicate that temperature and pCO2 are both forcing variables affecting T. maxima physiology and jeopardize its survival under environmental conditions predicted for the end of this century.

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