Realized thermal niche approach eliminates temperature bias in bioenergetic model estimates.

Bioenergetics models estimate ectotherm growth, production, and prey consumption - all key for effective ecosystem management during changing global temperatures. Based on species-specific allometric and thermodynamic relationships, these models typically use the species' lab-derived optimum temperatures (physiological optimum) as opposed to empirical field data (realized thermal niche) that reflect actual thermal experience. Yet, dynamic behavioral thermoregulation mediated by biotic and abiotic interactions may provide substantial divergence between physiological optimum and realized thermal niche temperatures to significantly bias model outcomes. Here, using the Wisconsin bioenergetics model and in-situ year-round temperature data, we tested the two approaches and compared the maximum attainable lifetime weight and lifetime prey consumption estimates for two salmonid species with differing life histories. We demonstrate that using the realized thermal niche is the better approach because it eliminates significant biases in estimates produced by the physiological optimum. Specifically, using the physiological optimum, slower-growing Salvelinus namaycush maximum attainable lifetime weight was underestimated, and consumption overestimated, while fast-growing Oncorhynchus tshawytscha maximum attainable weight was overestimated. While the physiological optimum approach is useful for theoretical studies, our results demonstrate the critical importance that models used by management utilize up-to-date system- and species-specific field data representing actual in-situ behaviors (i.e., realized thermal niche).

Host species and habitat shape fish-associated bacterial communities: phylosymbiosis between fish and their microbiome.

BACKGROUND: While many studies have reported that the structure of the gut and skin microbiota is driven by both species-specific and habitat-specific factors, the relative importance of host-specific versus environmental factors in wild vertebrates remains poorly understood. The aim of this study was to determine the diversity and composition of fish skin, gut, and surrounding water bacterial communities (hereafter referred to as microbiota) and assess the extent to which host habitat and phylogeny predict microbiota similarity. Skin swabs and gut samples from 334 fish belonging to 17 species were sampled in three Laurentian Great Lakes (LGLs) habitats (Detroit River, Lake Erie, Lake Ontario). We also collected and filtered water samples at the time of fish collection. We analyzed bacterial community composition using 16S metabarcoding and tested for community variation. RESULTS: We found that the water microbiota was distinct from the fish microbiota, although the skin microbiota more closely resembled the water microbiota. We also found that environmental (sample location), habitat, fish diet, and host species factors shape and promote divergence or convergence of the fish microbiota. Since host species significantly affected both gut and skin microbiota (separately from host species effects), we tested for phylosymbiosis using pairwise host species phylogenetic distance versus bacterial community dissimilarity. We found significant phylogenetic effects on bacterial community dissimilarity, consistent with phylosymbiosis for both the fish skin and gut microbiota, perhaps reflecting the longstanding co-evolutionary relationship between the host species and their microbiomes. CONCLUSIONS: Analyzing the gut and skin mucus microbiota across diverse fish species in complex natural ecosystems such as the LGLs provides insights into the potential for habitat and species-specific effects on the microbiome, and ultimately the health, of the host. Video Abstract.

Burkholderia spp.-based biopesticide controls wireworms (Coleoptera: Elateridae) in potatoes.

Wireworms (Coleoptera: Elateridae) are economically significant pests of potatoes (Solanum tuberosum), damaging the marketable portion of the crop by feeding and tunneling into tubers. While conventional potato growers use the few registered synthetic insecticides to control wireworms, certified organic growers are left with less options due to the limited effectiveness of the available insecticides. Biologically derived pesticides provide an additional alternative for both systems. Certain gram-negative proteobacteria, such as Burkholderia spp., possess insecticidal compounds. However, very little is known about their efficacy on wireworms. From 2018 to 2021, we conducted experiments in Virginia to assess the efficacy of a Burkholderia spp.-based commercial pesticide, Majestene, as a wireworm control in potatoes. In a lab experiment, soil drench application of this insecticide at a rate of 66 g a.i. per 1 liter resulted in 30% wireworm mortality and significantly reduced wireworm feeding damage on potato tubers. In the field, in-furrow applications of Burkholderia spp. at a rate of 17.66 kg a.i. per ha significantly reduced wireworm damage to tubers in 2 of 7 field experiments conducted. By comparison, the commercial standard insecticide, bifenthrin, significantly reduced tuber damage in 3 of the 7 field experiments. Our study demonstrates the prospect for proteobacteria-derived insecticides for control of wireworms and potentially other soil-dwelling insects. In conclusion, findings present growers with another option to combat wireworm pressure, especially in organic systems.

Watercraft decontamination practices to reduce the viability of aquatic invasive species implicated in overland transport.

Recreational boating activities enable aquatic invasive species (AIS) dispersal among disconnected lakes, as invertebrates and plants caught on or contained within watercraft and equipment used in invaded waterbodies can survive overland transport. Besides simple preventive measures such as "clean, drain, dry", resource management agencies recommend decontaminating watercraft and equipment using high water pressure, rinsing with hot water, or air-drying to inhibit this mode of secondary spread. There is a lack of studies assessing the efficacy of these methods under realistic conditions and their feasibility for recreational boaters. Hence, we addressed this knowledge gap via experiments on six invertebrate and plant AIS present in Ontario. Washing at high pressures of 900-1200 psi removed the most biological material (90%) from surfaces. Brief (< 10 s) exposure to water at ≥ 60 °C caused nearly 100% mortality among all species tested, except banded mystery snails. Acclimation to temperatures from 15 to 30 °C before hot water exposure had little effect on the minimum temperature required for no survival. Air-drying durations producing complete mortality were ≥ 60 h for zebra mussels and spiny waterfleas, and ≥ 6 days among plants, whereas survival remained high among snails after a week of air-drying. Hot water exposure followed by air-drying was more effective than either method separately against all species tested.

Subsidy accessibility drives asymmetric food web responses.

Global change is fundamentally altering flows of natural and anthropogenic subsidies across space and time. After a pointed call for research on subsidies in the 1990s, an industry of empirical work has documented the ubiquitous role subsidies play in ecosystem structure, stability, and function. Here, we argue that physical constraints (e.g., water temperature) and species traits can govern a species' accessibility to resource subsidies, which has been largely overlooked in the subsidy literature. We examined the input of a high-quality, point-source anthropogenic subsidy (aquaculture feed) into a recipient freshwater lake food web. Using a combined bio-tracer approach, we detect a gradient in accessibility of the anthropogenic subsidy within the surrounding food web driven by the thermal preferences of three constituent species, effectively rewiring the recipient lake food web. Because aquaculture is predicted to increase significantly in coming decades to support growing human populations, and global change is altering temperature regimes, then this form of food web alteration may be expected to occur frequently. We argue that subsidy accessibility is a key characteristic of recipient food web interactions that must be considered when trying to understand the impacts of subsidies on ecosystem stability and function under continued global change.

Evaluation of muscle lipid extraction and non-lethal fin tissue use for carbon, nitrogen, and sulfur isotope analyses in adult salmonids.

RATIONALE: Chemical lipid extraction or using alternative tissues such as fish fin as opposed to muscle may alter isotopic ratios and influence interpretations of δ13 C, δ15 N, and previously unassessed δ34 S values in stable isotope analyses (SIA). Our objectives were to determine if lipid extraction alters these isotope ratios in muscle, if lipid normalization models can be used for lipid-rich salmonids, and if fin isotope ratios are comparable with those of muscle in adult salmonids. METHODS: In six adult salmonid species (n = 106) collected from Lake Ontario, we compared three isotope ratios in lipid-extracted (LE) muscle with bulk muscle, and LE muscle with fin tissue, with paired t-tests and linear regressions. We compared differences between δ13 C values in LE and bulk muscle with predicted values from lipid normalization models and the log-linear model of best fit and determined model efficiency. RESULTS: The δ15 N values in LE muscle increased (<1‰) relative to bulk muscle for most salmonids, with relationships nearing 1:1. There were either no differences or strong 1:1 relationships in δ34 S values between species-specific bulk and LE muscle. One lipid normalization model had greater model efficiency (97%) than the model of best fit (94%). Fin had higher δ13 C values than LE muscle while δ15 N trends varied (<1‰); however, both isotope ratios had either no or weak linear relationships with fin and LE muscle within species. The δ34 S values in fin were similar to those in LE muscle and had strong 1:1 relationships across species. CONCLUSIONS: We recommend using the lipid normalization model to adjust for δ13 C values in lipid-rich muscle (C:N >3.4). LE muscle could be used without δ15 N or δ34 S adjustments, but the minimal increase in δ15 N values may affect SIA interpretation. With high unexplained variability among adult species in fin-muscle δ13 C and δ15 N relationships, species-specific fin-muscle adjustments are warranted. No fin-muscle tissue adjustment would be required for δ34 S values.

Application of machine learning to identify predators of stocked fish in Lake Ontario: using acoustic telemetry predation tags to inform management.

Understanding predator-prey interactions and food web dynamics is important for ecosystem-based management in aquatic environments, as they experience increasing rates of human-induced changes, such as the addition and removal of fishes. To quantify the post-stocking survival and predation of a prey fish in Lake Ontario, 48 bloater Coregonus hoyi were tagged with acoustic telemetry predation tags and were tracked on an array of 105 acoustic receivers from November 2018 to June 2019. Putative predators of tagged bloater were identified by comparing movement patterns of six species of salmonids (i.e., predators) in Lake Ontario with the post-predated movements of bloater (i.e., prey) using a random forests algorithm, a type of supervised machine learning. A total of 25 bloater (53% of all detected) were consumed by predators on average (± S.D.) 3.1 ± 2.1 days after release. Post-predation detections of predators occurred for an average (± S.D.) of 78.9 ± 76.9 days, providing sufficient detection data to classify movement patterns. Tagged lake trout Salvelinus namaycush provided the most reliable classification from behavioural predictor variables (89% success rate) and was identified as the main consumer of bloater (consumed 50%). Movement networks between predicted and tagged lake trout were significantly correlated over a 6 month period, supporting the classification of lake trout as a common bloater predator. This study demonstrated the ability of supervised learning techniques to provide greater insight into the fate of stocked fishes and predator-prey dynamics, and this technique is widely applicable to inform future stocking and other management efforts.

Long-term retention of acoustic telemetry transmitters in temperate predators revealed by predation tags implanted in wild prey fish.

Bloater Coregonus hoyi (n = 48) were implanted with V9DT-2x predation transmitters and monitored on 105 acoustic receivers in eastern Lake Ontario for >6 months. Twenty-three predation events were observed, with predator retention of tags ranging from ≤1 to ≥194 days and 30% of retentions lasting >150 days. Long tag retention times raise concerns for acoustic telemetry analysis and the health of piscivorous predators retaining tags.

Effects of intracoelomic transmitter implantation on metabolic rate, swimming performance, growth and survival in juveniles of two salmonids.

In this study, we investigated the effects of acoustic tag implantation on standard and routine metabolic rate (SMR and RMR, estimated via oxygen consumption), critical swimming speed (Ucrit ), survival and growth in juveniles of rainbow trout Oncorhynchus mykiss and lake trout Salvelinus namaycush. Tag burdens ranged from 1.8% to 7.5% across the two species. Growth rates in acoustic-tagged fish were equal to or higher than those in other treatments. Acoustic-tagged S. namaycush had a marginally lower Ucrit than controls but that effect was not replicated in the O. mykiss experiment. Tagging did not have clear effects on metabolic rate but there was an interaction whereby SMR and RMR tended to increase with time since surgery in tagged O. mykiss but not in other treatments (the same trend did not occur in S. namaycush). Survival was high across treatments (mean 98% survival among O. mykiss, 97.5% among S. namaycush). There were no statistically significant effects of tag burden (percentage of body mass) except for a weak negative relationship with growth rate (across species) and a weak positive relationship with Ucrit but only in the O. mykiss. Collectively, our findings suggest there were minor, context-dependent effects of acoustic tagging in juvenile S. namaycush and O. mykiss during an eight-week laboratory experiment. Further research will be required to assess whether tagging can cause meaningful behavioural effects in these species in captivity or in the wild and whether there is a tag burden threshold above which deleterious effects consistently occur.

Benefits of Turbid River Plume Habitat for Lake Erie Yellow Perch (Perca flavescens) Recruitment Determined by Juvenile to Larval Genotype Assignment.

Nutrient-rich, turbid river plumes that are common to large lakes and coastal marine ecosystems have been hypothesized to benefit survival of fish during early life stages by increasing food availability and (or) reducing vulnerability to visual predators. However, evidence that river plumes truly benefit the recruitment process remains meager for both freshwater and marine fishes. Here, we use genotype assignment between juvenile and larval yellow perch (Perca flavescens) from western Lake Erie to estimate and compare recruitment to the age-0 juvenile stage for larvae residing inside the highly turbid, south-shore Maumee River plume versus those occupying the less turbid, more northerly Detroit River plume. Bayesian genotype assignment of a mixed assemblage of juvenile (age-0) yellow perch to putative larval source populations established that recruitment of larvae was higher from the turbid Maumee River plume than for the less turbid Detroit River plume during 2006 and 2007, but not in 2008. Our findings add to the growing evidence that turbid river plumes can indeed enhance survival of fish larvae to recruited life stages, and also demonstrate how novel population genetic analyses of early life stages can contribute to determining critical early life stage processes in the fish recruitment process.

Novel molecular approach demonstrates that turbid river plumes reduce predation mortality on larval fish.

Turbidity associated with river plumes is known to affect the search ability of visual predators and thus can drive 'top-down' impacts on prey populations in complex ecosystems; however, traditional quantification of predator-prey relationships (i.e. stomach content analysis) often fails with larval fish due to rapid digestion rates. Herein, we use novel molecular genetic methods to quantify larval yellow perch (YP) in predator stomachs in western Lake Erie to test the hypothesis that turbidity drives variation in larval predation. We characterize predator stomach content DNA to first identify YP DNA (single nucleotide polymorphism) and then quantify larval YP predation (microsatellite allele counting) in two river plumes differing in turbidity. Our results showed elevated larval YP predation in the less turbid river plume, consistent with a top-down impact of turbidity on larval survival. Our analyses highlight novel ecological hypothesis testing using the power of innovative molecular genetic approaches.

Validation of rapid assimilation of PCBs following IP dosing in the round goby (Neogobius melanostomus).

The assimilation of polychlorinated biphenyls (PCBs) in round gobies (Neogobius melanostomus) after intraperitoneal (IP) injection was compared to PCBs bioaccumulated by the same fish through natural exposure ("native" PCBs). Lipid equivalent corrected dorsal muscle: whole body concentration ratios for native PCB 153 averaged 1.16 ± 0.77 and ranged from 1.19 to 1.24 for three IP dosed non-native PCBs within 6 h after dosing. Variation in tissue distribution of IP-dosed congeners was reduced after benchmarking to PCB 153, reinforcing that assimilation of the IP dose occurred into muscle rapidly after injection. Despite the use of small oil volumes during injection (<10 µL per fish), coefficients of variation of IP-dosed PCBs were equivalent to those observed for native PCBs. The results suggest that IP dosing provides a precise method to achieve target concentrations of hydrophobic chemicals in small fish and does not require several days to achieve assimilation into highly perfused tissues.

T-maze learning in weanling lambs.

A major advantage of sheep models in experimental studies of neurodevelopmental disorders (e.g., with prenatal neurotoxicant exposure) is that the equivalent of all three trimesters of human brain development occurs in sheep entirely in utero. However, studies of learning and memory in sheep are limited. The goal of this study was to extend the analysis of spatial learning and memory in adolescent sheep using several traditional T-maze tasks. Both 9- and 14-week-old lambs acquired a delayed nonmatching-to-place task, but the older lambs learned the task significantly faster. In contrast, acquisition of a matching-to-place task was significantly more difficult. Lambs, like rodents, appear to have a predisposition toward learning "win-shift" spatial problems in a T-maze under appetitive motivation. Lambs also rapidly acquired a position habit and showed typical reversal learning curves. These findings support the use of T-maze tasks to assess behavioral outcomes in various sheep models.

Seasonal variation in mercury and food web biomagnification in Lake Ontario, Canada.

Seasonal variation in mercury (Hg) concentrations and food web structure was assessed for eastern Lake Ontario. Hg concentrations, measured in 6 species of invertebrates and 8 species of fishes, tended to be highest in the spring and lowest in the summer for most biota. Yellow perch (Perca flavescens) exhibited significant ontogenetic shifts in diet and Hg, although such patterns were not evident for other species. Food web structure, as indicated by stable isotope values (δ(15)N, δ(13)C) was not static. Log-transformed Hg data were strongly and consistently correlated with δ(15)N values for the whole food web in each of the three seasons (slopes, 0.17-0.24) and across the entire year (slope, 0.2). While significantly different between seasons, the regression slope values are still consistent with published global Hg biomagnification rates. Our results indicate that the assessment of Hg trends in Great Lakes must take into account seasonal patterns and time of sampling.

Resource switching in fish following a major food web disruption.

Dreissenid mussels (Dreissena polymorpha and D. bugensis) have re-engineered Great Lakes ecosystems since their introduction in the late 1980s. Dreissenids can have major indirect impacts on profundal habitats by redirecting nutrients and energy away from pelagic production (which supplies profundal production) and depositing nutrients and energy in the nearshore zones that they occupy. However, strong empirical evidence for the effects of this redirection of resources on fish populations is currently lacking. Here, we report significant shifts in isotopic signatures, depth distribution and diets of a coldwater profundal fish population that are all consistent with a greater reliance on nearshore resources after the establishment of dreissenid mussels in South Bay, Lake Huron. Isotopic signatures of scales collected from 5-year-old lake whitefish (Coregonus clupeaformis) demonstrated remarkable stability over the 50-year period prior to the establishment of dreissenids (1947-1997) and a sudden and significant change in isotopic signatures (3 per thousand enrichment in delta13C and 1 per thousand depletion in delta(15)N) after their establishment (2001-2005). These dramatic shifts in isotopic signatures were accompanied by a coincident shift in the mean depth of capture of lake whitefish towards the nearshore. A comparison of previously unpublished pre-invasion diets of lake whitefish from South Bay with contemporary diets collected between 2002 and 2005 also indicate a greater reliance on nearshore prey after the invasion of dreissenid mussels. This study is the first to report changes in the carbon source available to lake whitefish associated with restructured benthic communities after the appearance of dreissenid mussels. Further, this study contributes to a growing body of work that demonstrates the ecological insights that can be gained through isotopic analysis of archived fish bony tissues in ecosystems that have experienced significant levels of disturbance.

Eyeblink classical conditioning in the preweanling lamb.

Classical conditioning of eyeblink responses has been one of the most important models for studying the neurobiology of learning, with many comparative, ontogenetic, and clinical applications. The current study reports the development of procedures to conduct eyeblink conditioning in preweanling lambs and demonstrates successful conditioning using these procedures. These methods will permit application of eyeblink conditioning procedures in the analysis of functional correlates of cerebellar damage in a sheep model of fetal alcohol spectrum disorders, which has significant advantages over more common laboratory rodent models. Because sheep have been widely used for studies of pathogenesis and mechanisms of injury with many different prenatal or perinatal physiological insults, eyeblink conditioning can provide a well-studied method to assess postnatal behavioral outcomes, which heretofore have not typically been pursued with ovine models of developmental insults.

Eyeblink classical conditioning and interpositus nucleus activity are disrupted in adult rats exposed to ethanol as neonates.

Neonatal exposure to ethanol in rats, during the period of brain development comparable to that of the human third trimester, produces significant, dose-dependent cell loss in the cerebellum and deficits in coordinated motor performance. These rats are also impaired in eyeblink conditioning as weanlings and as adults. The current study examined single-unit neural activity in the interpositus nucleus of the cerebellum in adults following neonatal binge ethanol exposure. Group Ethanol received alcohol doses of 5.25 g/kg/day on postnatal days 4-9. Group Sham Intubated underwent acute intragastric intubation on postnatal days 4-9 but did not receive any infusions. Group Unintubated Control (from separate litters) did not receive any intubations. When rats were 3-7 mo old, pairs of extracellular microelectrodes were implanted in the region of the interpositus nucleus. Beginning 1 wk later, the rats were given either 100 paired or 190 unpaired trials per day for 10 d followed by 4 d of 100 conditioned stimulus (CS)-alone trials per day. As in our previous study, conditioned response acquisition in Group Ethanol rats was impaired. In addition, by session 5 of paired acquisition, Group Sham Intubated and Group Unintubated Control showed significant increases in interpositus nucleus activity, relative to baseline, in the CS-unconditioned stimulus interval. In contrast, Group Ethanol failed to show significant changes in interpositus nucleus activity until later in training. These results indicate that the disruption in eyeblink conditioning after early exposure to ethanol is reflected in alterations in interpositus nucleus activity.

Selective and enduring deficits in spatial learning after limited neonatal binge alcohol exposure in male rats.

BACKGROUND: In rats, heavy bingelike alcohol exposure during the neonatal brain growth spurt [postnatal days (PD) 4-9] can impair development of spatial learning. This study tested whether binge exposure limited to the latter half of this period (PD 7-9) produced selective spatial learning deficits that endured into adulthood. METHODS: On PD 7 to 9, Long-Evans rats were given intubations of alcohol (5.25 g/kg/day), sham intubations, or no intubations. Rats were tested as adults (>or=PD 70) in the Morris water maze under one of three different conditions: place (submerged escape platform in the same location each trial), random (submerged platform in a different, random location each trial), or redundant (visible platform that protruded above the water, in the same location for each trial). A 60-sec probe trial (with no platform present) followed the last acquisition trial. RESULTS: The mean peak blood alcohol concentration was 401 mg/dl on PD 7. Neonatal alcohol treatment significantly impaired acquisition and reduced place biases on the probe trial in place-trained males, but not females. Neonatal alcohol treatment had no significant effects on acquisition performance of the random or redundant groups. Redundant training yielded rapid acquisition for all groups. The visible cue overshadowed place cues for all treatment groups, but small place biases were evident in controls. After random training, no group showed place biases. CONCLUSIONS: Heavy alcohol exposure in rats limited to the last half of the neonatal brain growth spurt caused enduring deficits in spatial learning, but only in males. The deficits were specific to place learning in the Morris water maze and emerged only when learning and performance depended on the use of distal place cues.