Molecular diet analysis reveals predator-prey community dynamics and environmental factors affecting predation of larval lake sturgeon Acipenser fulvescens in a natural system.

This study utilized molecular tools to quantify the prevalence of predation during the vulnerable drifting larval life-history stage of lake sturgeon Acipenser fulvescens. How predators, the co-distributed prey community and abiotic environmental conditions (e.g., stream substrata) affected predation levels was quantified. Nightly D-frame drift net surveys were used to estimate the biomass of A. fulvescens and co-distributed prey. Gastrointestinal diet samples (n = 1,140) from 28 species of potential fish predators were collected during electrofishing surveys. Sampling was conducted for 17 days across 2015 and 2016. Based on DNA barcode analysis using sturgeon-specific mtDNA cytochrome oxidase I primers, A. fulvescens DNA was detected in 73 of 1,140 diet samples (6.40%) from 16 of the 28 predator species examined. A logistic regression model was used to analyse the effects of biotic and abiotic variables associated with the likelihood a predator had consumed larval A. fulvescens. Increasing lunar illumination and biomass of larval A. fulvescens increased predation rates on larval A. fulvescens. Higher discharge and greater biomass and proportions of alternative prey decreased predation rates of larval A. fulvescens. Predation rates were slightly higher in habitats with sand substrata. Most predator species preyed upon larval A. fulvescens at similar rates. The study revealed considerably higher incidence of predation on larval A. fulvescens than previous studies had documented using traditional morphological diet analysis. Co-distributed prey and abiotic environmental variables that affected the predation rates of a species of regional conservation concern can inform future management actions.

Interannual variation in effective number of breeders and estimation of effective population size in long-lived iteroparous lake sturgeon (Acipenser fulvescens).

Quantifying interannual variation in effective adult breeding number (N(b)) and relationships between N(b), effective population size (N(e)), adult census size (N) and population demographic characteristics are important to predict genetic changes in populations of conservation concern. Such relationships are rarely available for long-lived iteroparous species like lake sturgeon (Acipenser fulvescens). We estimated annual N(b) and generational N(e) using genotypes from 12 microsatellite loci for lake sturgeon adults (n = 796) captured during ten spawning seasons and offspring (n = 3925) collected during larval dispersal in a closed population over 8 years. Inbreeding and variance N(b) estimated using mean and variance in individual reproductive success derived from genetically identified parentage and using linkage disequilibrium (LD) were similar within and among years (interannual range of N(b) across estimators: 41-205). Variance in reproductive success and unequal sex ratios reduced N(b) relative to N on average 36.8% and 16.3%, respectively. Interannual variation in N(b)/N ratios (0.27-0.86) resulted from stable N and low standardized variance in reproductive success due to high proportions of adults breeding and the species' polygamous mating system, despite a 40-fold difference in annual larval production across years (437-16 417). Results indicated environmental conditions and features of the species' reproductive ecology interact to affect demographic parameters and N(b)/N. Estimates of N(e) based on three single-sample estimators, including LD, approximate Bayesian computation and sibship assignment, were similar to annual estimates of N(b). Findings have important implications concerning applications of genetic monitoring in conservation planning for lake sturgeon and other species with similar life histories and mating systems.

Individual-based analyses reveal effects of behavioral and demographic variables associated with multi-annual reproductive success of male and female lake sturgeon.

Quantifying effects of individual attributes and population demographic characteristics that affect inter- and intrasexual interactions and adult reproductive success, and the spatial and temporal contexts in which they are expressed is important to effective species management. Multi-year individual-based analyses using genetically determined parentage allowed the examination of variables associated with the reproductive success of male and female lake sturgeon (Acipenser fulvescens) in the well-studied population in Black Lake, Michigan, USA. Spawning lake sturgeon (a total of 599 individuals where many were captured more than once based on 1024 total captures) and larvae (N = 3436) were genotyped during each of seven consecutive years (2001-2007). Factors associated with individual reproductive success differed between sexes and varied among spawning groups within a year and among years depending on spawning date (higher reproductive success earlier in the season for females) and spawning locations (higher reproductive success in upstream spawning zones for females). Female reproductive success increased nonlinearly with increasing body size. Male reproductive success increased with increasing residence time in spawning areas and, to a modest degree, with increasing body size in a nonlinear fashion. Fixed effects of repeatability in spawn timing and location across years led to consistently higher or lower reproductive success for females. Results identified factors, including time spent at spawning areas by males and intersexual encounters and mate number, that contributed to higher interindividual variance in reproductive success and affected population levels of recruitment, the degree of subpopulation genetic structure (lack of isolation by time), and effective population size.

Behavioral evidence of olfactory imprinting during embryonic and larval stages in lake sturgeon.

Many migratory fishes are thought to navigate to natal streams using olfactory cues learned during early life stages. However, direct evidence for early-life olfactory imprinting is largely limited to Pacific salmon, and other species suspected to imprint show life history traits and reproductive strategies that raise uncertainty about the generality of the salmonid-based conceptual model of olfactory imprinting in fishes. Here, we studied early-life olfactory imprinting in lake sturgeon (Acipenser fulvescens), which have a life cycle notably different from Pacific salmon, but are nonetheless hypothesized to home via similar mechanisms. We tested one critical prediction of the hypothesis that early-life olfactory imprinting guides natal homing in lake sturgeon: that exposure to odorants during early-life stages results in increased activity when exposed to those odorants later in life. Lake sturgeon were exposed to artificial odorants (phenethyl alcohol and morpholine) during specific developmental windows and durations (limited to the egg, free-embryo, exogenous feeding larvae and juvenile stages), and later tested as juveniles for behavioral responses to the odorants that were demonstrative of olfactory memory. Experiments revealed that lake sturgeon reared in stream water mixed with artificial odorants for as little as 7 days responded to the odorants in behavioral assays over 50 days after the initial exposure, specifically implicating the free-embryo and larval stages as critical imprinting periods. Our study provides evidence for olfactory imprinting in a non-salmonid fish species, and supports further consideration of conservation tactics such as stream-side rearing facilities that are designed to encourage olfactory imprinting to targeted streams during early life stages. Continued research on lake sturgeon can contribute to a model of olfactory imprinting that is more generalizable across diverse fish species and will inform conservation actions for one of the world's most imperiled fish taxonomic groups.

Computational analysis of the enhancement of photoelectrolysis using transition metal dichalcogenide heterostructures.

Finding a material with all the desired properties for a photocatalytic water splitter is a challenge yet to be overcome, requiring both a surface with ideal energetics for all steps in the hydrogen and oxygen evolution reactions (HER and OER) and a bulk band gap large enough to mediate said steps. We have instead examined separating these challenges by investigating the energetic properties of two-dimensional transition metal dichalcogenides (TMDCs) that could be used as a surface coating to a material with a large enough bulk band gap. First we investigated the energetics of monolayer MoS2and PdSe2using density functional theory and then investigated how these energetics changed when they were combined into a heterostructure. Our results show that the surface properties were practically (<0.2 eV) unchanged when combined and the MoS2layer aligns well with the OER and HER. This work highlights the potential of TMDC monolayers as surface coatings for bulk materials that have sufficient band gaps for photocatalytic applications.

First Isolation of a Herpesvirus (Family Alloherpesviridae) from Great Lakes Lake Sturgeon (Acipenser fulvescens).

The lake sturgeon (Acipenser fulvescens; LST) is the only native sturgeon species in the Great Lakes (GL), but due to multiple factors, their current populations are estimated to be <1% of historical abundances. Little is known about infectious diseases affecting GL-LST in hatchery and wild settings. Therefore, a two-year disease surveillance study was undertaken, resulting in the detection and first in vitro isolation of a herpesvirus from grossly apparent cutaneous lesions in wild adult LST inhabiting two GL watersheds (Erie and Huron). Histological and ultrastructural examination of lesions revealed proliferative epidermitis associated with herpesvirus-like virions. A virus with identical ultrastructural characteristics was recovered from cells inoculated with lesion tissues. Partial DNA polymerase gene sequencing placed the virus within the Family Alloherpesviridae, with high similarity to a lake sturgeon herpesvirus (LSHV) from Wisconsin, USA. Genomic comparisons revealed ~84% Average Nucleotide Identity between the two isolates, leading to the proposed classification of LSHV-1 (Wisconsin) and LSHV-2 (Michigan) for the two viruses. When naïve juvenile LST were immersion-exposed to LSHV-2, severe disease and ~33% mortality occurred, with virus re-isolated from representative skin lesions, fulfilling Rivers' postulates. Results collectively show LSHV-2 is associated with epithelial changes in wild adult LST, disease and mortality in juvenile LST, and is a potential threat to GL-LST conservation.

Assessing impact of exogenous features on biotic phenomena in the presence of strong spatial dependence: A lake sturgeon case study in natural stream settings.

Modeling spatially explicit data provides a powerful approach to identify the effects of exogenous features associated with biological processes, including recruitment of stream fishes. However, the complex spatial and temporal dynamics of the stream and the species' reproductive and early life stage behaviors present challenges to drawing valid inference using traditional regression models. In these settings it is often difficult to ensure the spatial independence among model residuals-a key assumption that must be met to ensure valid inference. We present statistical models capable of capturing complex residual anisotropic patterns through the addition of spatial random effects within an inferential framework that acknowledges uncertainty in the data and parameters. Proposed models are used to explore the impact of environmental variables on Lake sturgeon (Acipenser fulvescens) reproduction, particularly questions about patterns in egg deposition. Our results demonstrate the need to apply valid statistical methods to identify relationships between response variables, e.g., egg counts, across locations, and environmental covariates in the presence of strong and anisotropic autocorrelation in stream systems. The models may be applied to other settings where gamete distribution or, more generally, other biotic phenomena may be associated with spatially dynamic and anisotropic processes.