Prior exposure to stress allows the maintenance of an ecosystem cycle following severe acidification

Ecosystem processes vary temporally due to environmental fluctuations, such as when variation in solar energy causes diurnal cycles in primary production. This normal variation in ecosystem functioning may be disrupted and even lost if taxa contributing to functioning go extinct due to environmental stress. However, when communities are exposed to the stress at sub-lethal levels over several generations, they may be able to develop community-level stress tolerance via ecological (e.g. species sorting) or evolutionary (e.g. selection for tolerant genotypes) mechanisms and thus avoid the loss of stability, as defined by the resistance of a process. Community tolerance to a novel stressor is expected to increase the resistance of key processes in stressed ecosystems. In freshwater communities we tested whether prolonged prior exposure to an environmental stressor, i.e. acidification, could increase ecosystem stability when the communities were exposed to a subsequent press perturbation of more severe acidification. As a measure of ecosystem stability, we quantified the diurnal variation in dissolved oxygen (DO), and the resistance of the DO cycle and phytoplankton biomass. High-frequency data from oxygen loggers deployed in 12 mesocosms showed that severe acidification with sulfuric acid to pH 3 could cause a temporary (i.e. two-week long) loss of diurnal variation in dissolved oxygen concentration. The loss of diurnal variation was accompanied by a strong reduction in phytoplankton biomass. However, the pre-exposure to acidification for several weeks resulted in the maintenance of the diurnal cycle and higher levels of phytoplankton biomass, though they did not return to as rapidly to pre-exposure functioning as non-exposed mesocosms. These results suggest that ecosystem stability is intrinsically linked to community-wide stress tolerance, and that a history of exposure to the stressor may increase resistance to it, though at the cost of some resilience

Prior selection prevents the loss of an ecosystem cycle during acidification

Ecosystem processes vary temporally due to variation in environmental variables, such as when diurnal variation in sunlight causes diurnal cycles in net primary production. This variability can be characterized by its frequency and amplitude, used to define “normal” functioning of an ecosystem. Relatively little research has addressed how normal modes of variability, such as diurnal cycles, are lost or recovered, following anthropogenic stress. We conducted an aquatic mesocosm experiment to test whether prior application of environmental stress, in the form of moderate acidification, affected the diurnal cycle of dissolved oxygen when exposed to severe acidification. High-frequency data from sensor loggers deployed in 12 mesocosms showed that severe acidification caused a temporary loss of diurnal variation in dissolved oxygen concentration. However, pre-exposure to an acidic environment resulted in the persistence of the diurnal cycle. We hypothesize that pre-exposure shifted the community to acid tolerant genotypes and/or species of algae and other photosynthetic organisms. Our findings suggest that the stability of ecosystem cycles is intrinsically liked to the stress tolerance of the species assemblage

Prioritizing taxa for genetic reference database development to advance inland water conservation

Biodiversity loss has accelerated over the past century and freshwater species overall are among those experiencing greatest declines. Genetic resources have the potential to help evaluate the full magnitude of this loss and represent a key tool to effectively allocate conservation resources and monitor the success of restoration efforts. The full power of genetic resources will be realized when the daunting task of referencing all DNA sequences of freshwater organisms is complete. Here, we quantified the availability and distribution of barcode and genome data for freshwater macroscopic organisms in Canada, a country rich in inland water resources and thus particularly vulnerable to aquatic species losses. Impressively, most inland water species (86 %) were represented by barcodes recorded in the BOLD Systems database, while very few had full genomes available (<4 %) in the NCBI database. We identified barcode data deficiencies in northern regions and for taxa assessed as most at risk or without sufficient information for conservation status classification. As expected, the speciose insect group had a lower-than-average number of records per species and a high proportion of data deficient species without adequate barcode coverage. This study highlights where future sequencing resources should be prioritized within initiatives such as the Canada BioGenome Project and BIOSCAN Canada and provides a workflow that could be applied internationally to inform conservation management plans and to mitigate biodiversity loss

QCBS beta diversity workshop

R workshop on beta diversit

Impacts of land use on Ugandan rainforest streams: From fish physiology to ecosystem functioning

The main objective of this PhD thesis is to document impacts of deforestation and agricultural land use on afrotropical streams at the organismal, community, and ecosystem levels. Using a meta-analysis and systematic literature review comparing global distributions of current deforestation, freshwater fish diversity, consumption and trade of freshwater fishes by human populations, and research effort on deforestation impacts on inland waters, I first demonstrate that tropical Africa is the only region of the world that has rapid deforestation, high biodiversity, and a high reliance of human populations on inland waters for income and food security, and yet a low research effort. In the remainder of the dissertation, I present an empirical case study comparing rainforest and agricultural streams in and around Kibale National Park, Uganda. I first quantified alpha and beta diversity of invertebrates in 34 farm and forest stream sites in and around Kibale, and showed that deforestation reduces alpha diversity but increases beta diversity of Kibale streams. I then focused in on one forest-farm stream pair in each of two watersheds in the Kibale region to measure various ecosystem stocks and functions. Farm streams, compared to forested streams, had lower standing stock biomass of invertebrates despite abundant basal resources, as well as higher primary production, slower invertebrate-mediated litter decomposition, and lower secondary production of invertebrates. Finally, I adopted an evolutionary and eco-physiological perspective to examine adaptive divergence in various populations of a cyprinid fish occurring in both forest and farm streams. I asked whether deforestation-associated stream warming influences the metabolism, growth, and top-down trophic interactions of fish populations in farm streams, which was tested using a combination of acclimation experiments, respirometry, a mark-recapture study, and bioenergetics modeling. I showed that the metabolic costs of warming had little impact on either fish growth or trophic interactions, and that other effects of land use such as changes in predator and prey density have a much stronger impact on energy flow in these food webs. Overall, this thesis demonstrates strong effects of deforestation and agricultural land use on afrotropical streams at different levels of biological organization (organism, community, and ecosystem), but also identifies important knowledge gaps currently limiting the development of a fully global picture of the impacts of deforestation on the structure and function of stream ecosystems.L'objectif principal de cette thèse est de documenter les impacts de la déforestation et de l'utilisation agricole des terres sur les ruisseaux d'Afrique tropicale, aux niveaux de l'individu, de la communauté et de l'écosystème. Dans un premier temps, j'ai effectué une méta-analyse et une revue de littérature systématique comparant les distributions globales de la déforestation actuelle, la diversité de poissons, le commerce et la consommation de poissons d'eau douce par les populations humaines, de même que l'effort de recherche sur les impacts de la déforestation sur les eaux continentales. J'ai ainsi pu démontrer que l'Afrique tropicale est la seule région au monde qui présente une déforestation rapide, une forte biodiversité et où les populations humaines dépendent grandement des eaux continentales en termes de revenu monétaire et de sécurité alimentaire, avec pourtant un faible effort de recherche. Dans les autres chapitres de cette thèse, je présente une étude de cas comparant les ruisseaux de milieux agricoles et de forêts tropicales humides situés au sein, ou près, du parc national de Kibale, Ouganda. J'ai d'abord quantifié la diversité alpha et bêta des invertébrés dans 34 ruisseaux de fermes et forêts à l'intérieur ou aux alentours de Kibale, ce qui m'a permis de montrer que la déforestation réduit la diversité alpha, mais augmente la diversité bêta des ruisseaux de Kibale. Par la suite, j'ai focalisé sur une paire de ruisseaux forêt-ferme dans deux bassins versants de la région de Kibale afin de mesurer divers lots ('stocks') et fonctions écosystémiques. Comparativement aux ruisseaux de forêt, les ruisseaux agricoles avaient une biomasse d'invertébrés plus faible, malgré les ressources de base abondantes, ainsi qu'une plus grande production primaire, une décomposition plus lente par les invertébrés et une plus faible production secondaire d'invertébrés. Finalement, j'ai adopté une perspective évolutive et écophysiologique pour examiner la divergence adaptative de plusieurs populations de poissons cyprin présents dans les ruisseaux de ferme et de forêt. J'ai cherché à savoir si le réchauffement des ruisseaux induit par la déforestation influençait le métabolisme, la croissance et/ou les interactions trophiques de type "top-down" des populations de poissons des ruisseaux de ferme, ce qui a été testé par le biais d'une combinaison d'expériences d'acclimatation, de respirométrie, une étude de marquage-recapture ainsi que de la modélisation bioénergétique. J'ai montré que les coûts métaboliques du réchauffement avaient un faible impact sur la croissance des poissons et sur les interactions trophiques, mais que les autres effets liés à l'utilisation des terres, tel un changement dans la densité de prédateurs et de proies, ont un impact bien plus fort sur le flux d'énergie dans ces réseaux trophiques. Dans son ensemble, cette thèse démontre que la déforestation et l'utilisation agricole des terres affectent fortement les ruisseaux afro-tropicaux à différents niveaux d'organisation biologique (organisme, communauté et écosystème), tout en identifiant d'importantes lacunes dans nos connaissances limitant actuellement notre possibilité d'atteindre une compréhension réelement globale des impacts de la déforestation sur la structure et le fonctionnement des écosytèmes de ruisseaux

Electric signals and species recognition in gymnotiform fish

Gymnotiformes are South American weakly electric fish that produce weak electric organ discharges (EOD) for orientation, foraging and communication purposes. Because EOD properties vary widely across species, electric signals could serve a species recognition function. We quantified the electric signals of various species and used discriminant function analyses to verify whether these signals are species-specific based on different signal parameters. We found that the EOD waveform was a more specific cue than EOD frequency. Using Apteronotus leptorhynchus as a focal species, we complemented these measurements with playback experiments using stimuli of different species (varying in frequency, waveform, or both). In both a free-swimming experiment and a communication assay with restrained fish, we found that the subjects' behaviour was strongly influenced by the frequency of the stimuli but, opposite to what we predicted, the waveform of the stimuli had no measurable effect on either communication or locomotor behaviors.Les gymnotes sont des poisons faiblement électriques d'Amérique du Sud utilisant leur électro-sens à des fins de navigation, d'approvisionnement et de communication. Les décharges électriques varient énormément d'une espèce à l'autre et pourrait ainsi être utilisées pour la reconnaissance des espèces. Nous avons quantifié la décharge de plusieurs espèces et avons utilisé des analyses discriminantes afin de vérifier si les décharges sont spécifiques aux espèces selon différents paramètres. La forme de la décharge semble plus spécifique que la fréquence de celle-ci. Pourtant, en réalisant des expériences comportementales avec le gymnote Apteronotus leptorhynchus et des stimuli de différentes espèces, nous avons découvert que le comportement des sujets varie beaucoup en fonction de la fréquence du stimulus alors que, contrairement à ce que nous avions prédis, la forme de la décharge du stimulus n'eut aucun impact mesurable sur les comportements moteurs ou communicatifs des sujets

Fugere et al 2018 Funct Ecol data

File includes all data used in linked publication, namely data on: stream water temperature (diel trends and time series), growth and metabolic rates in the lab temperature acclimation experiment, body size measurements for the field mark-recapture study, and invertebrate abundance and biomass data used in the bioenergetics model. The last sheet also includes results of said energetics model

Electrical signalling of dominance in a wild population of electric fish

Animals often use signals to communicate their dominance status and avoid the costs of combat. We investigated whether the frequency of the electric organ discharge (EOD) of the weakly electric fish, Sternarchorhynchus sp., signals the dominance status of individuals. We correlated EOD frequency with body size and found a strong positive relationship. We then performed a competition experiment in which we found that higher frequency individuals were dominant over lower frequency ones. Finally, we conducted an electrical playback experiment and found that subjects more readily approached and attacked the stimulus electrodes when they played low-frequency signals than high-frequency ones. We propose that EOD frequency communicates dominance status in this gymnotiform species

Data for Bell et al. 2019 Proc B

Spreadsheet containing the pH, phytoplankton, and zooplankton measurements taken in all mesocosms on all sampling occasions. A treatment key is also provided