Juvenile Life Stages Research Articles

Spatial and temporal distributions of Dreissena spp. veligers in Lake Huron: Does calcium limit settling success?

The larval stage of invasive Dreissena spp. mussels (i.e., veligers) are understudied despite their seasonal numerical dominance among plankton. We report the spring and summer veliger densities and size structure across the main basin, North Channel, and Georgian Bay of Lake Huron, and seek to explain spatiotemporal variation. Monthly sampling was conducted at 9 transects and up to 3 sites per transect from spring through summer 2017. Veliger densities peaked in June and July, and we found comparable densities and biomasses of veligers between basins, despite differences in density of juvenile and adult mussels across these regions. Using a generalized additive model to explain variations in veliger density, we found that temperature, chlorophyll a, and nitrates/nitrites were most important. We generated an index of veliger attrition based on size distributions that revealed a higher rate of attrition in the North Channel than the rest of the lake. A logistic model indicated a threshold calcium concentration of around 22 mg/L was necessary for veligers to survive to larger sizes and recruit to their juvenile and benthic adult life stages. Improved understanding of factors that regulate the production and survival of Dreissena veligers could improve the ability of managers to assess future invasion threats as well as explore potential control options.

The effects of temperature and salinity on the endocrinology in two life stages of juvenile rainbow/steelhead trout (Oncorhynchus mykiss)

The San Francisco Bay Delta is experiencing seasonally warmer waters and saltwater intrusion into historically freshwater ecosystems due to climate change. Steelhead/rainbow trout (Oncorhynchus mykiss) are resident in the Bay-Delta from juvenile development through the smoltification process. Due to increases in sea level, premature seawater (SW) acclimation may co-occur with increased temperatures on pre-smolt juveniles. To evaluate the interactive effects of salinity and temperature on juvenile life stages of salmonids, rainbow trout alevin (3 days post-hatching) were exposed to 13, 16.4 and 19°C for 10 days and then challenged for 24 h to 18 parts per thousand SW. Similarly, fry (4 weeks post-hatching) were exposed to 13, 16.4 and 19°C for 2 weeks (14 days) and then challenged to SW. Estradiol-17β (E2 ), cortisol, triiodothyronine (T3 ) and thyroxine (T4 ) were measured in whole animal homogenates and muscle tissue using enzyme-linked immunosorbent assays. Transcripts of gill Na+ /K+ ATPase β (NKAα1b), brain growth hormone I (gh1) and brain gonadotropin-releasing hormone receptor 2 (gnrh2) were also measured. Alevin exhibited a significant temperature-dependent decrease in survival, and fry showed a temperature-dependent decrease in condition factor. The gene expression of NKAα1b, gh1 and gnrh2 significantly decreased in all SW-challenged alevin, and a significant decrease in gnrh2 expression was observed in fry with temperature. Alevin T3 and T4 concentrations significantly increased with increasing temperature. There was a temperature-dependent increase in E2 of fry but not of alevin. The results of this study demonstrate that increasing temperature and SW exposure may adversely affect the survival and SW acclimation of alevin and fry stages of salmonids and that the tolerances of younger juvenile stages should be considered when assessing the response of salmonid populations to climate change stressors.

Thermal Tolerance May Slow, But Not Prevent, the Spread of Sargassum horneri (Phaeophyceae) along the California, USA and Baja California, MEX Coastline.

Biological invasions have become increasingly prevalent in marine ecosystems, modifying biodiversity and altering the way ecosystems function. Understanding how variation in environmental factors influences the success of non-native species, especially their early life stages, can be a crucial step in identifying habitats that are under threat of invasion, and in predicting how rapidly and far these species may spread once they arrive in novel habitats. The invasive marine macroalga Sargassum horneri was first observed in Long Beach Harbor, CA, USA in 2003, and has since spread throughout the Southern California Bight and along the Baja California Peninsula, MEX where it now forms dense stands on subtidal rocky reefs and displaces native habitat-forming macroalgae. We examined how variation in temperature, nutrients, and irradiance affect survival, growth, and development in S. horneri early life stages over a three-week period. Our experimental treatments consisted of orthogonally crossed temperatures (10, 15, 20, and 25°C), nutrient concentrations (ambient and nutrient-enriched seawater), and irradiances (50 and 500µmol photons · m-2 · s-1 ). Overall, temperature exerted the greatest influence on S.horneri's germling and juvenile life stages, with moderate temperatures facilitating their greatest survival, growth, and development. In contrast, fewer germlings developed fully under the lowest or highest temperatures, and juvenile survival and growth were reduced, especially when combined with low irradiances. Together, our data suggest that ocean temperatures of or below 10˚C and of or above 25°C may slow, but likely not stop, S. horneri's northward and southward expansion along the California and Baja California coasts.

Predicting the Distribution of Penaeid Shrimp Reveals Linkages Between Estuarine and Offshore Marine Habitats

Marine fish and shrimp species are often dependent on estuarine habitats for juvenile or other early life stages, yet the effect of estuarine habitat availability has rarely been linked to the offshore, marine distribution of species. Penaeid shrimp are an estuary-dependent taxa that have global economic importance and are frequently cited as prey of fish. Species distribution models were developed for three penaeid species in the northern Gulf of Mexico, USA, with the objectives of modeling the distribution of species and testing the influ ence of multiscale predictor variables depicting oceanography, geography, geomorphology, and area of nearby estuaries and coastal wetlands. Fishery-independent trawl survey data of brown shrimp (Penaeus aztecus), white shrimp (Penaeus setiferus), and pink shrimp (Penaeus duorarum) were analyzed with boosted regression tree statistics. Species distribution models of catch per unit effort explained 30–45% of model deviance for brown shrimp and white shrimp; the presence/absence model of pink shrimp had an area under the curve statistic of 0.85 and overall accuracy of 83% correct. Oceanographic predictors had the greatest influence in each of the models, and the spatial distribution of each species was distinct based on these conditions. The marine distribution of all three penaeids was associated with nearby wetland area, and white shrimp were additionally associated with nearby estuary area. Geomorphology predictors were retained less often and were of low relative influence. Our findings demonstrate the importance of considering multiple spatial scales when identifying species-habitat relationships, including the influence of adjacent or nearby environments.

Seasonal variability in the diet of juvenile European catfish, Silurus glanis, in the Arno River (Italy) in Florence

Abstract While approaches for assessing the impact of invasive species are advancing, fundamental autoecological information such as feeding preferences is often unavailable for many invasive species. The European catfish, Silurus glanis, is a well-known, high-impact invasive predator; however, there remain considerable gaps in knowledge about its feeding preferences and biotic interactions that limit ecological impact predictions for this predator. This study is an investigation of seasonal variability in this predator’s diet during the juvenile life stage using the Arno River, Italy as a model system. This study identified significant differences across seasons, provided further information on the dietary spectrum of this species, and raised important questions for further study.

Fertility and mortality impacts of thermal stress from experimental heatwaves on different life stages and their recovery in a model insect.

With climate change creating a more volatile atmosphere, heatwaves that create thermal stress for living systems will become stronger and more frequent. Using the flour beetle Tribolium castaneum, we measure the impacts of thermal stress from experimental heatwaves in the laboratory on reproduction and survival across different insect life stages, and the extent and pace of any recovery. We exposed larvae, pupae, juvenile and mature adult male beetles to 5-day periods of heat stress where temperatures were maintained at either 40°C or 42°C, a few degrees above the 35°C optimum for this species' population productivity, and then measured survival and reproduction compared with controls at 30°C. Mortality due to thermal stress was greatest among juvenile life stages. Male reproductive function was specifically damaged by high temperatures, especially if experienced through pupal or immature life stages when complete sterility was shown at reproductive maturity; larval exposure did not damage adult male fertility. High temperatures impaired testis development and the production of viable sperm, with damage being strongest when experienced during pupal or juvenile adult stages. Despite this disruption, males recovered from heat stress and, depending on the stage of exposure, testis size, sperm production and fertility returned to normal 15–28 days after exposure. Our experiments reveal how thermal stress from heatwave conditions could impact on insect survival and reproduction across different life stages, and the potential and timescales of recovery.

Regional variations and relationships among cytokine profiles, white blood cell counts, and blood mercury concentrations in Steller sea lion (Eumetopias jubatus) pups

The Steller sea lion (SSL) population west of 144°W longitude experienced a significant population decline. While there appears to be a stable or increasing population trend in rookeries in the Gulf of Alaska (GOA) and Southeast Alaska (SEA), some rookeries within the Aleutian Islands (AI) have failed to recover. Previous studies found regional differences in whole blood total mercury concentrations ([THg]) showing more than 20% of AI pups had [THg] above critical thresholds for increased risk of immunological effects and other adverse outcomes. Measurements of immune cell-signaling proteins can be used to evaluate the immune status of marine mammals in relation to [THg]. We compared serum cytokine and chemokine concentrations in pups among regions (AI, eastern GOA, SEA), and examined associations among cytokines, chemokines, white blood cell (WBC) counts, and [THg]. Considering liver is an important target organ for mercury and immune protein synthesis we additionally examined the relationship of [THg] with liver-related enzymes serum aspartate (AST) and alanine aminotransferase (ALT). We observed regional differences in cytokine and chemokine measurements and immune protein associations. There was a positive association between total WBC counts and [THg] in AI pups, whereas a negative association between lymphocytes and [THg] in SEA pups. These findings may indicate regional variation in proliferation and differentiation of hematopoietic cells, differences in immune system development, and/or a difference in antigenic stimuli. No associations between [THg] and cytokines, chemokines, AST or ALT were found. Observed regional differences in cytokine and chemokine milieu during gestational and early development in SSL pups could lead to an imbalance in cell differentiation that could impact immunological resiliency in juvenile and adult life stages. We report concentration ranges of a suite of cytokines and chemokines which may prove to be a useful metric for ecotoxicology and risk assessment studies in SSLs and other wildlife.

Evolution and developmental plasticity of lung structure in high-altitude deer mice.

Hypoxia at high altitudes can constrain the ability of endotherms to maintain sufficient rates of pulmonary O2 transport to support exercise and thermogenesis. Hypoxia can also impede lung development during early post-natal life in some mammals, and could thus accentuate constraints on O2 transport at high altitude. We examined how these challenges are overcome in deer mice (Peromyscus maniculatus) native to high altitude. Lung structure was examined in highland and lowland populations of deer mice and lowland populations of white-footed mice (P. leucopus; a congener restricted to low altitude) that were bred in captivity. Among mice that were born and raised to adulthood in normoxia, highland deer mice had higher alveolar surface density and more densely packed alveoli. The increased alveolar surface density in highlanders became fully apparent at juvenile life stages at post-natal day 30 (P30), after the early developmental period of intense alveolus formation before P21. Alveolar surface density was maintained in highlanders that were conceived, born, and raised in hypoxia (~ 12kPa O2), suggesting that lung development was not impaired by post-natal hypoxia as it is in many other lowland mammals. However, developmental hypoxia increased lung volume and thus augmented total alveolar surface area from P14. Overall, our findings suggest that evolutionary adaptation and developmental plasticity lead to changes in lung morphology that should improve pulmonary O2 uptake in deer mice native to high altitude.

Modeling schistosomiasis transmission: the importance of snail population structure

BackgroundSchistosomiasis is a neglected tropical disease endemic in 54 countries. A major Schistosoma species, Schistosoma mansoni, is sustained via a life cycle that includes both human and snail hosts. Mathematical models of S. mansoni transmission, used to elucidate the complexities of the transmission cycle and estimate the impact of intervention efforts, often focus primarily on the human host. However, S. mansoni incurs physiological costs in snails that vary with the age of the snail when first infected. Snail demography and the age of snail infection could thus affect the force of infection experienced by humans, which is frequently used to predict the impact of various control strategies.MethodsTo address how these snail host and parasite interactions influence model predictions, we developed deterministic models of schistosomiasis transmission that include varying complexity in the snail population age structure. Specifically, we examined how model outputs, such as schistosome prevalence in human and snail populations, respond to the inclusion of snail age structure.ResultsOur models suggest that snail population age structure modifies the force of infection experienced by humans and the relationship between snail infection prevalence and corresponding human infection prevalence. There are significant differences in estimated snail infection, cercarial density and mean worm burden between models without snail population dynamics and those with snail populations, and between models with a homogeneous snail population and those with age stratification. The variation between finely age-stratified snail populations and those grouped into only juvenile and adult life stages is, however, minimal.ConclusionsThese results indicate that including snails and snail age structure in a schistosomiasis transmission model alters the relationship between snail and human infection prevalence. This highlights the importance of accounting for a heterogeneous intermediate host population in models of schistosomiasis transmission where the impact of proposed control measures is being considered.Graphical

Dietary and reproductive biomarkers in a generalist apex predator reveal differences in nutritional ecology across life stages

Knowledge of the nutritional requirements of apex predators is key for determining ecological interactions. However, an understanding of how diet is influenced by reproduction, and the consequences of foraging variation on the nutritional status of a predator, is limited. Here, we used short-term dietary markers (plasma and whole-blood fatty acids) integrated with reproductive hormones (17β-estradiol and testosterone) and ultrasonography as a non-lethal approach to investigate the effect of life stage on nutritional status and trophic dynamics of female tiger sharks Galeocerdo cuvier. Despite their generalist feeding behavior, female tiger sharks fed on different food sources and/or modulated their fatty acid metabolism depending on the reproductive context. This suggests some adjustment in their nutritional requirements associated with changes in their reproductive state. Plasma and whole-blood fatty acids indicated distinct dietary sources across life stages, with a high dependence on coastal/benthic food resources during juvenile life stages, and on pelagic/oceanic and reef-associated food resources during adult life stages. Higher percentages of highly unsaturated omega-3 fatty acids found in females during their reproductive cycles suggest the dependency on these fatty acids as a source of metabolic energy during reproduction. A high percentage of arachidonic acid (ARA) found in plasma of gravid females suggests the possibility of a selective diet of ARA-rich prey species and/or selective mobilization of ARA from stored energy during gestation. Based on our findings, we propose a conceptual model of expected changes in nutritional and trophic markers across life stages of female tiger sharks.

The lampricide 3-trifluoromethyl-4-nitrophenol causes temporary metabolic disturbances in juvenile lake sturgeon (Acipenser fulvescens): implications for sea lamprey control and fish conservation.

The pesticide 3-trifluoromethyl-4-nitrophenol (TFM) is applied to rivers and streams draining into the Laurentian Great Lakes to control populations of invasive sea lamprey (Petromyzon marinus), which are ongoing threats to fisheries during the lamprey’s hematophagous, parasitic juvenile life stage. While TFM targets larval sea lamprey during treatments, threatened populations of juvenile lake sturgeon (Acipenser fulvescens), particularly young-of-the-year (<100 mm in length), may be adversely affected by TFM when their habitats overlap with larval sea lamprey. Exposure to TFM causes marked reductions in tissue glycogen and high energy phosphagens in lamprey and rainbow trout (Oncorhynchus mykiss) by interfering with oxidative ATP production in the mitochondria. To test that environmentally relevant concentrations of TFM would similarly affect juvenile lake sturgeon, we exposed them to the larval sea lamprey minimum lethal concentration (9-h LC99.9), which mimicked concentrations of a typical lampricide application and quantified energy stores and metabolites in the carcass, liver and brain. Exposure to TFM reduced brain ATP, PCr and glycogen by 50–60%, while lactate increased by 45–50% at 6 and 9 h. A rapid and sustained depletion of liver glucose and glycogen of more than 50% was also observed, whereas the respective concentrations of ATP and glycogen were reduced by 60% and 80% after 9 h, along with higher lactate and a slight metabolic acidosis (~0.1 pH unit). We conclude that exposure to environmentally relevant concentrations of TFM causes metabolic disturbances in lake sturgeon that can lead to impaired physiological performance and, in some cases, mortality. Our observations support practices such as delaying TFM treatments to late summer/fall or using alternative TFM application strategies to mitigate non-target effects in waters where lake sturgeon are present. These actions would help to conserve this historically and culturally significant species in the Great Lakes.

Opposing life stage-specific effects of ocean warming at source and sink populations of range-shifting coral-reef fishes.

Climate change is altering the latitudinal distributions of species, with their capacity to keep pace with a shifting climate depending on the stochastic expression of population growth rates, and the influence of compensatory density feedback on age-specific survival rates. We use population-abundance time series at the leading edge of an expanding species' range to quantify the contribution of stochastic environmental drivers and density feedbacks to the dynamics of life stage-specific population growth. Using a tropical, range-shifting Indo-Pacific damselfish (Abudefduf vaigiensis) as a model organism, we applied variants of the phenomenological Gompertz-logistic model to a 14-year dataset to quantify the relative importance of density feedback and stochastic environmental drivers on the separate and aggregated population growth rates of settler and juvenile life stages. The top-ranked models indicated that density feedback negatively affected the growth of tropical settlers and juveniles. Rates of settlement were negatively linked to temperatures experienced by parents at potential source populations in the tropics, but their subsequent survival and that of juveniles increased with the temperatures experienced at the temperate sink. Including these stochastic effects doubled the deviance explained by the models, corroborating an important role of temperature. By incorporating sea-surface temperature projections for the remainder of this century into these models, we anticipate improved conditions for the population growth of juvenile coral-reef fishes, but not for settlers in temperate ecosystems. Previous research has highlighted the association between temperature and the redistribution of species. Our analyses reveal the contrasting roles of different life stages in the dynamics of range-shifting species responding to climate change, as they transition from vagrancy to residency in their novel ranges.

Resilience of the temperate coral Oculina arbuscula to ocean acidification extends to the physiological level

Both juvenile and adult life stages of the temperate scleractinian coral Oculina arbuscula are resilient to the effects of moderate ocean acidification (OA) in contrast to many tropical corals in which growth and calcification rates are suppressed. Here, potential mechanisms of resilience to OA related to photosynthetic physiology and inorganic carbon processing were studied in adult O. arbuscula colonies. After exposing colonies to ambient and elevated carbon dioxide (CO2) treatments for 7 weeks, photosynthetic performance was characterized using photosynthesis versus irradiance experiments, chlorophyll fluorescence kinetics, and algal pigment content. Inorganic carbon-processing capabilities were assessed by measurement of internal and external carbonic anhydrase activity of the coral host, internal carbonic anhydrase activity of symbiotic algae, and the reliance of photosynthesis on external carbonic anhydrase. Photosynthetic physiology was unaffected by OA ruling out the possibility that resilience was mediated by increased photosynthetic energy supply. Carbonic anhydrase activities were maintained at elevated CO2 suggesting no major rearrangements of the inorganic carbon-processing machinery, but this could be a sign of resilience since tropical corals often down-regulate carbonic anhydrases at high CO2. The general lack of effect of ocean acidification on these physiological traits suggests other characteristics, such as maintenance of calcifying fluid pH and ability to acquire energy from heterotrophy, may be more important for the resilience of O. arbuscula to OA.

Experimental Quantification of Piscivore Density and Habitat Effects on Survival of Juvenile Chinook Salmon in a Tidal Freshwater Estuary

Introduction of non-native piscivores has been implicated in the decline of native Chinook Salmon Oncorhynchus tshawytscha via predation during juvenile life stages. However, isolating effects of predation on Chinook Salmon survival is complicated by changes in physical habitat that are often concomitant with non-native piscivore establishment. We performed two field experiments with enclosures deployed in tidal freshwater habitat to quantify effects of non-native Largemouth Bass Micropterus salmoides density and habitat type on the survival and movement behavior of juvenile Chinook Salmon. In experiment one, bass densities were doubled and quadrupled across treatment levels with a baseline value of field-observed densities. In experiment two, three habitat types (dock, submerged aquatic vegetation (SAV), and open water) were tested while bass density was held at the medium (doubled) value. Juvenile Chinook Salmon implanted with passive integrated transponders were released into the enclosures to assess their survival and movement through the treatments over multiple trials. Mark-recapture models indicated that the survival of juvenile Chinook Salmon was reduced in the medium bass density, but not the high-density treatment, when compared to the lowest density value suggesting relationships may be non-linear. The SAV treatment had a well-supported negative effect on juvenile Chinook Salmon survival relative to a dock or open water. Residence time was positively related to bass density. Relationships with a habitat were not consistently different. These results suggest that restoration strategies targeting non-native SAV control could reduce predation on juvenile Chinook Salmon by Largemouth Bass. However, piscivore density manipulation may only be effective over a narrow range of densities.

Factors Influencing Capture and Retention of Razorback Sucker in Light Traps

AbstractLight trap captures of larval, endangered Razorback Sucker Xyrauchen texanus are used to guide flow release timing from reservoirs and measure Razorback Sucker annual reproductive success in the Green River, Utah. However, little is known regarding efficacy of light traps to capture or retain larvae under variable and field‐relevant environmental conditions. We conducted laboratory experiments to investigate the effects of light trap set time, fish release distance from trap, light presence, turbidity, fish density, and cover on capture and retention probabilities of five early life stages of Razorback Sucker. Mean capture probability of protolarvae prior to swim bladder development (7–9 mm TL) was 0.40 (range = 0.28–0.55) over various treatments but rose to 0.76 (0.73–0.80) after swim bladder development in later protolarvae (9–10 mm TL). Mesolarvae (11–17 mm TL), the most common life stage captured in field sampling, had a similar mean capture probability (0.86; 0.82–0.90) as later protolarvae. Capture probabilities of metalarval (mean = 0.42, range = 0.21–0.63; 15–24 mm TL) and juvenile (mean = 0.24, range = 0.20–0.28; 22–37 mm TL) life stages were lower. Larvae retention probabilities were generally &gt; 0.75 and increased to 0.97 for juveniles. Longer set times positively influenced capture probabilities, though capture probabilities were similar in 1‐, 3‐, and 5‐m release distances and relatively high (&gt;0.75) for most the commonly sampled life stages in standard conditions. Light presence in traps greatly increased capture and retention of larvae compared with unlit traps. Our results confirm that light traps may be useful to detect first presence of Razorback Sucker larvae in Green River backwaters each spring, which triggers Flaming Gorge Reservoir releases to inundate floodplain wetlands and for annual monitoring of reproductive success. We also provide recommendations for gear set up, deployment, and techniques to increase capture and retention probabilities of Razorback Sucker larvae.

Urban manta rays: potential manta ray nursery habitat along a highly developed Florida coastline

The giant oceanic manta rayMobula birostriswas listed in the US Endangered Species Act as a threatened species in 2018, yet insufficient data exist on manta populations throughout US waters to designate critical habitat. Taxonomic and genetic evidence suggests that manta rays in the Western Atlantic are a separate species (M.cf.birostris) and little is understood about the ecology and life history of this putative species. The juvenile life stage of bothM. birostrisandM.cf.birostrisis particularly understudied. Here, we are the first to describe the characteristics of a manta ray population along a highly developed coastline in southeastern Florida using boat-based surveys and photo identification of individuals. Fifty-nine manta individuals were identified between 2016 and 2019. All males were sexually immature based on clasper development, and 96% of females were classified as immature based on size and absence of mating scars or visible pregnancies. Twenty-five (42%) individuals were observed more than once during the study period and 8 individuals were sighted over multiple years. The occurrence of juveniles, high site fidelity and extended use of the study area by juvenile manta rays suggest that southeastern Florida may serve as a nursery habitat. High occurrence of fishing line entanglement (27% of individuals) and vessel strike injury were documented, and rapid wound healing was observed. Future research and conservation efforts will focus on identifying the physical and biological features of the potential nursery habitat and on mitigation of anthropogenic impacts.

Evidence of genetic determination in the growth habit of Nothofagus pumilio (Poepp. & Endl.) Krasser at the extremes of an elevation gradient

ABSTRACT In temperate mountainous regions, altitudinal clines in tree size and growth habit develop from a gradual adjustment of multiple traits to tolerate harshening conditions with altitude. We perform a common garden trial with seedlings from two stands of Nothofagus pumilio: low altitude, tall forest (1200 m a.s.l) vs. high altitude, shrubby forest (1560 m a.s.l), to determine whether the contrasting growth habits observed in the forest have a genetic basis, which expresses in the juvenile tree life stage. Growth habit syndrome was assessed including size, phenology, growth rhythm and architecture traits. Shrubby archetypes, i.e. small densely-branched plants with codominant axes, were more frequent between plants from higher altitude. Instead, large single-stemmed, slender morphotypes prevailed between plants from the lower stand. These contrasting frequencies between both extremes of the elevation gradient could be explained by differences in cumulative effects in multiple underlying traits, giving clues that there could be genetic determination in the growth habit of N. pumilio. Based on our findings, we recommend that the sampling strategy of future study systems of N. pumilio genetic variation, should encompass multiple elevation gradients along its distribution. Meanwhile, altitudinal zoning seems a precautionary advice for ongoing restoration plans.

Pre- to post-fledging carryover effects and the adaptive significance of variation in wing development for juvenile songbirds.

Evolutionary ecologists have long been interested in the adaptive significance of morphological traits across stages of animal life. In some cases, traits that are not adaptive in one life stage may be adaptive in a subsequent stage. As such, morphological traits may generate important carryover effects, whereby conditions experienced during one life-history stage influence fitness during subsequent stages. Carryover effects are particularly relevant in young animals, as early life stages are thought to be critical with respect to animal life-history evolution and population dynamics. In songbirds, pre- to post-fledging carryover effects operating within species may be critical for survival and shape life histories among species, but remain poorly understood. Among potential songbird traits, wing development and its associated flight ability may be the most important for post-fledging survival. Thus, to assess the adaptive significance of wing development for juvenile songbirds under Arnold's (Integrative and Comparative Biology, 23, 1983, 347) classic performance-morphology-fitness paradigm, we tested for pre- to post-fledging carryover effects among 20 coexisting species (nine focal species) of an avian community in east-central Illinois, USA. We found evidence for pre- to post-fledging carryover effects of wing development in all species, by which individuals with less developed wings exhibited poorer flight ability and experienced higher rates of mortality after fledging. Furthermore, our findings suggest that carryover effects operating at the species level ultimately help shape patterns of life-history variation among species. Specifically, we found that species with higher rates of nest predation had shorter nestling periods, fledged young with less developed wings and exhibited higher rates of post-fledging mortality. Our results highlight the adaptive significance of wing development as a key factor generating pre- to post-fledging carryover effects among songbirds, and demonstrate how morphological traits, locomotor performance, and age-specific survival may trade-off and interact across juvenile life stages to shape animal life histories.

Evaluation of a Deepwater Release Method for Hatchery‐Reared Lake Sturgeon

AbstractHatchery rearing and stocking of young Lake Sturgeon Acipenser fulvescens have become key management and species recovery tools in many jurisdictions, yet there has been relatively little investigation into the optimization of release methods. Based on the contemporary understanding of the species’ ecology in Boreal Shield rivers, it was hypothesized that poststocking survival and/or within‐reach retention could be improved via release of hatchery‐reared fish directly into the deepwater habitats that are preferred by juvenile and subadult life stages. Acoustic telemetry and mark–recapture methods were used to evaluate this hypothesis. In total, 390 PIT‐tagged age‐1 Lake Sturgeon (mean ± SD of length measured 1 week prior to stocking = 242 ± 29 mm FL) were released during spring 2015 from shore at the base of a set of falls on the Nelson River, Manitoba (mimicking the status quo stocking procedure for the reach), and 391 PIT‐tagged individuals (240 ± 27 mm FL) were released approximately 4.2 river kilometers downstream of the shore release location into an approximately 750‐m‐long patch of deepwater habitat (maximum depth = 15 m) using the deepwater release method. Of the released fish, 30 (15 per stocking method) were implanted with acoustic transmitters. In total, 23% and 22% of the stocked fish were recaptured in gill‐net surveys conducted during fall 2015 and 2016, respectively. Recapture proportions associated with the two release types were not significantly different. Acoustic telemetry revealed considerable variation among individuals and offered general insight into poststocking behavior but provided no direct support for the primary hypothesis. Despite the null results of the current study, optimization of release methods for Lake Sturgeon may warrant further investigation.

Evaluation of commercial and experimental grower diets for use in intensive burbot (Lota lota maculosa) culture

Burbot (Lota lota maculosa) are the only true freshwater gadiforms (cod-like fish) and are a promising new species for cold water aquaculture. This “freshwater cod” produces a delicate white flesh fillet, the liver and roe are considered delicacies, and the skin can be manufactured into leather. Furthermore, burbot grow-out requires similar water quality parameters as trout production, and burbot have been found to be relatively refractory to most primary salmonid pathogens. Burbot could be reared at existing trout production facilities and represent a means of diversifying production in already established cold water aquaculture operations. For commercial burbot culture to succeed, optimal diet selection for grow-out must be determined. To address this, two feeding trials were conducted to evaluate the effect of different dietary formulations on the growth of juvenile and subadult burbot. Four dietary treatments at fixed rations were evaluated, Europa (commercial), Oncor (commercial), a formulated marine-like reference diet (Burbot 1; B1), and a formulated trout-like reference diet (Burbot 2; B2). Juvenile growth results indicated a difference in relative growth (RG; P < .001) and biomass gain (BG; P < .001) among the marine blend dietary treatments, with the fish fed B1 and Europa showing better growth than the Oncor and B2 diets in these cases. This is indicative of a preference for marine-type diets during the juvenile life stage of burbot. Growth results also indicate a difference in protein efficiency ratio (PER; P = .008) among the diets, with the fish fed Europa exhibiting the lowest protein utilization rate. Subadult growth results indicate no differences in RG (P = .771), SGR (P = .804), BG (P = .727) for fish fed any of the diets. Thus, it appears that the subadult burbot grow and perform equally well on trout-like formulations at this life stage. While additional studies are needed, results from this work are important and indicate general dietary preference of burbot at juvenile and grow-out stages. Such information can be used to guide feed related decisions for current or future producers interested in commercial burbot production.