Overwinter Mortality Research Articles

Reduced density and visually complex apiaries reduce parasite load and promote honey production and overwintering survival in honey bees.

Managed honey bee (Apis mellifera) colonies are kept at much greater densities than naturally occurring feral or wild colonies, which may have detrimental effects on colony health and survival, disease spread, and drifting behavior (bee movement between natal and non-natal colonies). We assessed the effects of a straightforward apiary management intervention (altering the density and visual appearance of colonies) on colony health. Specifically, we established three “high density / high drift” (“HD”) and three “low density / low drift” (“LD”) apiary configurations, each consisting of eight bee colonies. Hives in the HD apiary configuration were of the same color and placed 1m apart in a single linear array, while hives in the LD apiary configuration were placed 10m apart at different heights, facing outwards in a circle, and made visually distinctive with colors and symbols to reduce accidental drift between colonies. We investigated disease transmission and dynamics between the apiary configurations by clearing all colonies of the parasitic mite Varroa destructor, and subsequently inoculating two randomly-chosen colonies per apiary with controlled mite doses. We monitored the colonies for two years and found that the LD apiary configuration had significantly greater honey production and reduced overwinter mortality. Inoculation and apiary management intervention interacted to affect brood mite levels, with the highest levels in the inoculated colonies in the HD configuration. Finally, foragers were more than three times more likely to drift in the HD apiary configurations. Our results suggest that a relatively straightforward management change–placing colonies in low-density visually complex circles rather than high-density visually similar linear arrays–can provide meaningful benefits to the health and productivity of managed honey bee colonies.

Latitudinal Growth Variation in Young Tautogs: A Field, Laboratory, and Growing Degree‐Day Assessment of Potential Intrinsic Differences in Growth Responses to Temperature

AbstractA difference in size at age of young Tautogs Tautoga onitis has been reported from two sites in the Mid‐Atlantic Bight, USA, whereby southern fish (Virginia [VA]) reach a twofold greater size than northern fish (Rhode Island [RI]) by age 1 but grow at similar size‐dependent annual rates thereafter. We investigated the basis for this difference by using a coordinated field, laboratory, and growing degree‐day (GDD) approach. Age‐0 Tautogs were sampled from three locations (Chesapeake Bay, VA; Delaware Bay, Delaware [DE]; and Narragansett Bay, RI) and showed a clinal relationship of decreasing fish size and growth rate with increasing latitude. Otolith‐based estimates of larval stage duration and growth rate showed no significant clinal relationship. Young Tautogs from these locations were reared in common‐garden experiments (at 5, 15, and 25°C) to determine whether there were intrinsic postsettlement growth differences related to temperature. None of the location‐specific groups of age‐0 Tautogs exhibited growth that was consistently faster than that of Tautogs from the other locations over all temperatures examined. These data and the results of a GDD assessment between VA and RI indicate that latitudinal differences in temperature regime and growing season length are the major factors determining latitudinal growth differences in age‐0 fish. However, age‐1 RI fish of equivalent size grew significantly faster than age‐0 RI and DE fish and similar to age‐0 VA fish at 15°C and grew 40% faster than all age‐0 fish at 25°C, suggesting countergradient growth variation in age‐1 and older northern Tautogs. Size‐selective overwinter mortality of age‐0 northern fish—whereby smaller individuals are most susceptible to low temperature—is proposed as the likely underlying mechanism leading to faster growth of older northern fish at temperature. Such a mechanism would at least partially compensate for the lower temperature and shorter growing season at higher latitudes.

Application of a robust design occupancy model for assessing fish recruitment

Fish recruitment is complex, regulated by environmental factors that induce high mortality early in life. Additionally, age-0 fish can be difficult to sample, making recruitment difficult to detect. We used a robust design occupancy model to evaluate the effects of biotic (age-0 and adult common carp (Cyprinus carpio), bluegill (Lepomis macrochirus), walleye (Sander vitreus), and northern pike (Esox lucius) relative abundance, prey availability, age-0 carp length) and abiotic (water level, temperature) factors on age-0 carp occupancy, detection, and extinction in 13 lakes in South Dakota, USA, for July–April 2008–2010. Age-0 carp occupancy decreased with increasing adult carp abundance and increased with increasing water levels. Age-0 carp detection probability was high during summer (>0.75) but decreased in fall and spring (0.34). Most lakes were occupied in July but overwinter extinction probability was high (59%), resulting in 51% occupancy probability by April. Other environmental factors were not supported, suggesting they had little effect on reproduction and survival. Our results indicate reproduction was universally successful but difficult to detect and that overwinter mortality often resulted in recruitment failure.

Impacts of freshwater aquaculture on fish communities: A whole‐ecosystem experimental approach

Abstract Aquaculture is a growing global industry; freshwater aquaculture has significant potential for expansion in Canada, but growth of the freshwater sector has been slow due to concerns over potential environmental impacts and a lack of information on potential impacts to native fish communities. To provide guidelines and target variables for evaluating aquaculture impacts on freshwater fish communities, we operated an experimental aquaculture farm as a whole‐lake experiment where 10,000 rainbow trout (Oncorhynchus mykiss) were raised annually from 2003 to 2007. Impacts were assessed using up to 8 years of pre‐impact and 8–10 years of post‐impact data. Prey fish abundance increased dramatically during aquaculture but declined sharply following the experiment. High abundance of littoral minnows in autumn was not observed during spring and, combined with size distribution data, suggests high overwinter mortality of adult minnows. White sucker (Catostomus commersonii) abundance and body condition declined during and after aquaculture, with evidence of overwinter juvenile recruitment failure in the last 2 years of operation, although size‐at‐age increased. The adult abundance of lake trout (Salvelinus namaycush) doubled during aquaculture, due to a combination of (a) increased growth rates of young trout and (b) earlier age and larger sizes at maturation. Within 2 years following aquaculture, lake trout abundance declined by nearly 50% to background levels, suggesting a large increase in lake trout mortality once operations ceased. These changes were not observed in nearby reference lakes. While aquaculture appeared to benefit some species (slimy sculpin [Cottus cognatus], minnows, lake trout), prolonged declines in white sucker abundance and condition and continued depression of Mysis densities and optimal oxythermal habitat availability nearly a decade following operations suggest potentially long‐term impacts at this magnitude. Importantly, this experiment highlights important indicator species and life history traits for monitoring of freshwater aquaculture impacts on native fish communities.

Nutritional correlates of the overwintering and seaward migratory decisions and long-term survival of post-spawning Atlantic salmon.

Despite the importance of iteroparity (i.e. repeated spawning) for the viability of Atlantic salmon populations, little is known about the factors influencing the migratory behaviour and survival prospect of post-spawned individuals (kelts). To test the hypothesis that post-spawning nutritional condition underlies differences in spatiotemporal aspects of the habitat use and survival of migrating Atlantic salmon kelts, we physiologically sampled and acoustically tagged 25 individuals from the Middle River, Nova Scotia in autumn 2015. Kelts were subsequently tracked within their natal river during the winter months, and as far as 650 km away along known migration pathways towards the Labrador Sea and Greenland. Some kelts were detected nearly 2 years later, upon their return to the natal river for repeat spawning. Overall, kelts in poor or depleted post-spawning nutritional state (i.e. low body condition index or plasma triglyceride level): (i) initiated down-river migration earlier than higher condition kelts; (ii) experienced higher overwinter mortality in the natal river; (iii) tended to spend greater time in the estuary before moving to sea and (iv) did not progress as far in the marine environment, with a reduced probability of future, repeat spawning. Our findings suggest that initial differences in post-spawning condition are carried through subsequent migratory stages, which can ultimately affect repeat-spawning potential. These results point to the importance of lipid storage and mobilisation in Atlantic salmon kelts for mediating post-spawning migratory behaviour and survival.

Range expansion ofLymantria dispar dispar(L.) (Lepidoptera: Erebidae) along its north‐western margin in North America despite low predicted climatic suitability

AbstractAimThe European gypsy moth,Lymantria dispar dispar(L.), (Lepidoptera: Erebidae) is an invasive defoliator that has been expanding its range in North America following its introduction in 1869. Here, we investigate recent range expansion into a region previously predicted to be climatically unsuitable. We examine whether winter severity is correlated with summer trap captures of male moths at the landscape scale, and quantify overwintering egg survivorship along a northern boundary of the invasion edge.LocationNorthern Minnesota,USA.MethodsSeveral winter severity metrics were defined using daily temperature data from 17 weather stations across the study area. These metrics were used to explore associations with male gypsy moth monitoring data (2004–2014). Laboratory‐reared egg masses were deployed to field locations each fall for 2 years in a 2 × 2 factorial design (north/south aspect × below/above snow line) to reflect microclimate variation. Rates of successful egg hatch were assessed the following springs.ResultsReductions in summer male moth captures are associated with several metrics of winter severity, such as minimum temperatures. Most egg masses suffered >95% mortality each winter. However, hatching success reached up to 80% in egg masses that had overwintered below the snow line (e.g., <30 cm from the ground).Main ConclusionsOur findings that cold winter temperatures are associated with reduced summer trap captures of European gypsy moth, likely due to increased overwintering mortality of exposed egg masses, are consistent with previous predictions of thermal range boundaries for this species. However, high survival in egg masses deposited close to the ground are consistent with thermal escape in subnivean environs (i.e., below snow cover), and suggest that further northward range expansion will be likely in areas that receive measurable annual snowfall.

Exploring the Influence of Food and Temperature on North Sea Sandeels Using a New Dynamic Energy Budget Model

The zooplanktivorous schooling fish sandeels A. marinus comprise a quarter of North Sea fish biomass and are essential food for a number of marine mammals and birds. However, in recent decades there has been a decline in the abundance of older sandeels, with increased overwinter mortality proposed as a contributor. To survive winter animals require a minimum energy reserve which is determined by temperature, prey abundance, and possibly prey size. Here a new dynamic energy budget model is created to determine the influence of food and temperature on sandeel energy dynamics. The model hindcasts changes in energy and survival between 2000 and 2008, a period of pronounced stock decline in the northwestern North Sea. Overwinter starvation mortality was a large contributor towards a recent decline in sandeels in northern UK waters. Highest over-winter mortality rates were recorded for juveniles and not individuals aged 1 or over due to the effect of weight-specific metabolism. However, a sensitivity analysis of the model suggests that mortality rates are more sensitive to changes in copepod abundance in the build up to overwintering rather than temperature during overwintering. Further, projections show that temperature rises are negated by increases in large, but not small copepods. The conclusion is that food-driven size-selective starvation mortality contributed to the northwestern North Sea stock decline and that indirect food web effects of climate change are greater than direct physiological effects on sandeels.

Overwinter survival and post-release movements of translocated water voles: implications for current mitigation guidance

Translocation is currently used as a last resort mitigation strategy for water voles (Arvicola amphibius) in the UK (Dean et al. 2016), where populations have undergone widespread declines during the past century. To increase the chances of success, current guidance suggests translocation of voles during autumn should not be carried out as individuals may be at higher risk of overwinter mortality, and instead should be overwintered in captivity for release the following spring. To verify this guidance, we carried out a mark recapture and radiotracking study of an autumn translocated and resident population in lowland England. Whilst we found translocated voles undertook longer exploratory movements than residents and those previously recorded in spring, there was no evidence from our study that translocated voles suffered higher mortality rates compared to the resident individuals. The turnover in both populations was high with 25% and 8% of the translocated and resident individuals being recaptured in spring. Younger voles that were not collared had a significantly higher chance of being recaptured in spring and their survival and settlement on the receptor channel is considered important as this is the age class that will produce most of the following years’ young. Mean weekly distances moved by collared voles showed no pattern of stabilisation, in either sex, over the 10-week monitoring period and combined dispersal from both study populations accounted for 26% of those that were not recaptured in spring. However, due to low sample size, we were unable to distinguish between the effects of dispersal and mortality. We conclude that where individuals or populations will be negatively impacted by planned development, autumn translocations in lowland England may offer a feasible alternative to housing animals in captivity, given the high financial cost and additional health and welfare risks associated with a captive environment. The receptor site and adjacent habitat (> 1 km) would need to support a seasonal abundance of food and cover, be connected to existing populations and be part of a wider landscape that is mink free and under an effective mink control programme to help secure long-term population viability. We advise, however, that due to our small sample size, further studies are undertaken to confirm our findings.

Natural and sexual selection drive multivariate phenotypic divergence along climatic gradients in an invasive fish

Invasive species that rapidly spread throughout novel distribution ranges are prime models to investigate climate-driven phenotypic diversification on a contemporary scale. Previous studies on adaptive diversification along latitudinal gradients in fish have mainly considered body size and reported either increased or decreased body size towards higher latitudes (i.e. Bergmann’s rule). Our study is the first to investigate phenotypic divergence in multiple traits, including sexually selected traits (size and shape of the male copulatory organ, the gonopodium) of invasive Gambusia affinis in China. We studied body size, life history traits and morphological variation across populations spanning 17 degrees of latitude and 16 degrees of longitude. Even though we found phenotypic variation along climatic gradients to be strongest in naturally selected traits, some sexually selected traits also showed systematic gradual divergence. For example, males from southern populations possessed wider gonopodia with increased armament. Generally, males and females diverged in response to different components of climatic gradients (latitudinal or longitudinal variation) and in different trait suites. We discuss that not only temperature regimes, but also indirect effects of increased resource and mate competition (as a function of different extrinsic overwinter mortality rates) alter the selective landscape along climatic gradients.

American Pika (Ochotona princeps) Population Survival in Winters with Low or No Snowpack

A prediction that has gained considerable traction in the American pika (Ochotona princeps) literature is that because of climate change, high mortality is likely to occur in winters of low or early snowmelt and cause extirpation of local populations. The basis for this prediction is the perception that the absence of an insulative layer of snow to protect pikas from severe winter cold temperatures may cause animals to utilize metabolic reserves through excessive thermoregulation before the spring emergence of fresh vegetation, or die directly from exposure to extreme winter temperatures. The Sierra Nevada of east central California experienced its lowest snowfall in recorded history during the winter of 2014/2015. We observed patch occupancy as a proxy for overwinter survivorship of American pikas in the Sierra Nevada during summer 2015 in comparison to baseline populations at the same sites during summer 2014. In summer 2015, pika presence was documented at 36 of 37 sites where pikas had been observed in summer 2014. Contrary to the low snowfall-high mortality prediction, there was no evidence that the nearly total lack of snow caused unusual overwinter mortality in Sierra Nevada pikas.

Transcriptional response to low temperature in the yellow drum (Nibea albiflora) and identification of genes related to cold stress

The yellow drum (Nibea albiflora) is an economically important maricultured fish in China, but the aquaculture of this species is severely affected by overwinter mortality associated with cold stress. Characterization of the molecular mechanisms underlying the susceptibility of the yellow drum to cold might increase our understanding of how this fish adapts to environmental challenges. Here, the transcriptional response of the yellow drum to cold stress (7.5 °C) was investigated with RNA-Seq analysis. We compared brain and muscle transcriptomes among cold-tolerant (Tol) fish that survived the cold treatment, cold-sensitive (Sen) fish that were killed by the cold treatment, and control (Con) fish that were not subjected to cold. Our analysis recovered 233,245 unigenes. The genes (DEGs) differentially expressed in the brain and muscle of the Tol versus Con group, the Sen versus Con group, and the Tol versus Sen group had tissue-specific expression patterns. Gene ontology, enrichment, and pathway analyses indicated the most highly enriched pathways in the DEGs were signaling molecules and interaction, signal transduction, carbohydrate metabolism, lipid metabolism, digestive system, and endocrine system pathways. These pathways were all associated with biological functions relevant to cold adaptation in the yellow drum, including transduction of stress signals, energy metabolism, and stress-induced cell membrane changes. We identified genes likely to be involved in cold-susceptibility and -tolerance as those differentially expressed in the Tol group as compared to the Sen group. Further investigation and characterization of these candidate genes might improve our understanding of the mechanisms underlying cold adaptation in the yellow drum.

Consequences of catch-and-release angling on the physiology, behaviour and survival of wild steelhead Oncorhynchus mykiss in the Bulkley River, British Columbia

Steelhead, the anadromous form of rainbow trout (Oncorhynchus mykiss), is one of the most coveted recreationally targeted salmonids worldwide, and catch-and-release (C&R) is commonly used as a conservation strategy to protect wild stocks. Nevertheless, little research has examined how wild steelhead respond to capture and handling. During a summer-run recreational fishery on the Bulkley River in British Columbia, we used non-lethal blood sampling and radio telemetry to assess the physiological stress response, post-release behaviour, and survival of wild steelhead exposed to either 0 s, 10 s, or 30 s of air exposure, over a range of water temperatures, fight times, and landing methods. Steelhead that were air exposed following landing had greater reflex impairment and moved further downstream immediately following release than fish kept in the water, though there was no observed difference in movement two weeks after capture. Overall, angled fish had significantly greater blood lactate levels than baseline levels (obtained from a subsample of fish dip netted from the river) suggesting a general stress response to angling and handling. Regardless of air exposure treatment, water temperature was positively associated with blood lactate and negatively associated with blood pH. Other variables such as fish body size (mm) and fight time (s) had little influence on any of the physiological or behavioural variables. Estimated 3-day survival of steelhead was 95.5%, with deep-hooking as the primary source of mortality. Over-winter mortality of caught-and-released fish was estimated at 10.5%, with an estimated total pre-spawn mortality of 15.0%. This study is the first to evaluate the factors that influence C&R outcomes in wild steelhead in a recreational fishery. Findings suggest that steelhead anglers should limit air exposure to less than 10 s, and that anglers should be cautious (minimize handling and air exposure) when water temperatures are warmer.

Incorporating estimates of capture probability and river network covariance in novel habitat – abundance models: Assessing the effects of conservation stocking on catchment-scale production of juvenile Atlantic salmon (Salmo salar) from a long-term electrofishing dataset

There are increasing calls for “conservation stocking” to counter declines in Atlantic salmon (Salmo salar) populations, the assumption being that stocking can bypass population bottlenecks and increase recruitment over natural processes. However, there are too few quantitative studies with sufficient data to assess the efficacy of conservation stocking. The Girnock Burn is a unique long-term monitoring site where adult and juvenile salmon numbers have been monitored for over 50 years, including 11 years with conservation stocking. Adults were monitored at a fixed trap and juveniles were monitored by electrofishing. In stocked years, ova were incubated in surface water to reduce density-independent over-winter mortality. In eight years, eyed ova were stocked at uniform densities to reduce local density-dependence. In three years, stocking replicated natural spatial variability in ova deposition removing any potential benefits of reduced local density-dependence. Juvenile production was estimated by summing the product of reach-scale density estimates and river area obtained from a novel spatial statistical river network model that incorporated the effects of capture probability, habitat and stock level. Capture probability varied with life-stage (age 0+ fry or ≥1+ parr), electrofishing pass and day of the year, but importantly also exhibited a positive temporal trend across years. Survival from ova to fry was density-independent and higher under uniform stocking than natural spawning or simulated natural spawning. Under uniform stocking, fry densities varied smoothly with altitude, while under natural spawning and simulated natural spawning, fry exhibited a more patchy distribution. Increased fry production did not translate to increased parr production, which was strongly density-dependent. This likely reflected the inability of fry to move between stocked locations and suitable overwintering habitat, decreasing survival between fry and parr life-stages. Consequently, there was no overall benefit of stocking. The modelling framework used in this study provides a valuable approach for interpreting long-term datasets where site locations, equipment and staffing vary over time. The long-term Girnock dataset was valuable in separating management action from natural population regulation and permitting understanding of ecological processes. The study indicates that conservation stocking can be ineffective, even where implemented to best scientific standards. It is therefore recommended that a detailed understanding of local population dynamics is obtained, and a realistic appraisal of the expected benefits of stocking is undertaken, before management actions are considered.

Status and trends of the Asian clam (Corbicula fluminea) in the lower Fox River and Green Bay

Abstract In the upper Great Lakes region, survival and population growth of the non-indigenous Asian clam Corbicula fluminea has been limited by cold climates that cause severe overwinter mortality. At these northern latitudes, Asian clam populations are often limited to thermal refugia – particularly warmwater discharges from industrial facilities. Several such facilities exist in the lower Fox River in Green Bay. Asian clams were first documented in the lower Fox River in 1999 and were extensively surveyed near the river mouth in 2011, but the few individuals found were restricted to the warmwater discharge from the Pulliam Power Plant. We performed a follow-up survey during 2017 to re-assess the population status of Asian clams in the lower Fox River at four industrial discharges, including the Pulliam Power Plant. We found more widespread evidence of Asian clams throughout the lower Fox River than previous surveys, but only one live individual was captured. We suspect that the back-to-back severe winters of 2013–2014 and 2014–2015 caused widespread overwinter mortality. Our investigation highlights the significant challenges for establishment of Asian clam populations in the upper Great Lakes region, and provides an example of a potential invasive species struggling to establish a viable population in a hostile climate.

Distribution and Habitat Use of the InvasiveCarcinus maenasL. (European Green Crab) and the NativeCancer irroratus(Say) (Rock Crab) in Intertidal Zones in the Upper Bay of Fundy, Canada

Carcinus maenas (European Green Crab) is an invasive marine portunid crab that has established populations globally outside of its native range and has been implicated in declines of benthic invertebrates in invaded ecosystems. Observations of Green Crab on intertidal mudflats in the upper Bay of Fundy have increased in recent years. We assessed the distribution and relative abundance of crab populations in Chignecto Bay, an arm of the upper Bay of Fundy, by trapping Green Crab and native Cancer irroratus (Say) (Rock Crab) at mudflats and in rocky intertidal zones in 2013 and 2014. Spatial distribution of Green Crabs indicated a preference for rocky intertidal habitats and greater abundance geographically lower in the Bay, which would correspond with an initial introduction at the mouth of the Bay and subsequent inward expansion. Abundance declined drastically from 2013 to 2014, suggesting that Green Crab may not yet be well established in Chignecto Bay. Carapace width indicated that crab age may be less variable further into the Bay, suggesting these sites may only be colonized in years with favorable environmental conditions. The population may be vulnerable under poorer conditions in other years, like 2014, when high overwintering mortality is a possible cause for the observed decline. There was not a corresponding decline in native Rock Crab. While Green Crab abundance is currently relatively low in Chignecto Bay, and their impact on mudflats likely minimal, prolonged favorable environmental conditions could lead to an increased presence.

Evaluation of Potential Overwinter Mortality of Age-0 Walleye and Appropriate Age-1 Sampling Gear

AbstractPotential recruitment of age-0 Walleye Sander vitreus to adults is often indexed by the relative abundance of age-0 individuals during their first summer or fall. However, relationships between age-0 and adult Walleye abundance are often weak or nonsignificant in many waters. Overwinter mortality during the first year of life has been hypothesized as an important limitation to Walleye recruitment in lakes, but limited evidence of such mortality exists, likely due to difficulties in sampling age-1 Walleye during spring. The objectives of this study were to: 1) compare results from nighttime electrofishing to index relative abundance of age-1 Walleyes with relative abundance indices of minifyke nets in four eastern South Dakota lakes; 2) determine whether size-selective mortality was occurring in those four lakes; and 3) if size-selective mortality was occurring in these lakes, determine whether that mortality was attributed to body condition. We sampled four natural lakes in eastern South Dakota 2 wk after ice-off in 2013 and 2014. Precision of nighttime electrofishing (coefficient of variation = 216.6) was greater than that estimated for minifyke nets (coefficient of variation = 338.5) across both years. We detected no differences in length-frequency distributions of collected spring age-1 Walleye between the two gears. Age-0 fall relative abundance indices from electrofishing were significantly greater (P < 0.01) than spring age-1 nighttime electrofishing indices of relative abundance at three of the four study lakes, indicating that overwinter mortality may occur at a substantial rate during the first year of life for Walleye in these systems. Quantile–quantile regression plots showed evidence of size-selective mortality in three of four lakes sampled. However, body condition of age-0 Walleye appeared to have little to no influence on overwinter mortality. Instead, we suggest that smaller-sized walleye may be more vulnerable to overwinter predation. Collectively, these results provide evidence of previously hypothesized overwinter mortality within the first year for Walleye and indicate possibilities for indexing potential adult recruitment of Walleye just after this critical period.

The effects of epidermal fatty acid profiles, 1-oleoglycerol, and triacylglycerols on the susceptibility of hibernating bats to Pseudogymnoascus destructans.

White Nose Syndrome (WNS) greatly increases the over-winter mortality of little brown (Myotis lucifugus), Indiana (M. sodalis), northern (M. septentrionalis), and tricolored (Perimyotis subflavus) bats, and is caused by cutaneous infections with Pseudogymnoascus destructans (Pd). Big brown bats (Eptesicus fuscus) are highly resistant to Pd infections. Seven different fatty acids (myristic, pentadecanoic, palmitic, palmitoleic, oleic, and, linoleic acids) occur in the wing epidermis of both M. lucifugus and E. fuscus, 4 of which (myristic, palmitoleic, oleic, and, linoleic acids) inhibit Pd growth. The amounts of myristic and linoleic acids in the epidermis of M. lucifugus decrease during hibernation, thus we predicted that the epidermal fatty acid profile of M. lucifugus during hibernation has a reduced ability to inhibit Pd growth. Laboratory Pd growth experiments were conducted to test this hypothesis. The results demonstrated that the fatty acid profile of M. lucifugus wing epidermis during hibernation has a reduced ability to inhibit the growth of Pd. Additional Pd growth experiments revealed that: a) triacylglycerols composed of known anti-Pd fatty acids do not significantly affect growth, b) pentadecanoic acid inhibits Pd growth, and c) 1-oleoglycerol, which is found in the wing epidermis of E. fuscus, also inhibits the growth of this fungus. Analyses of white adipose from M. lucifugus also revealed the selective retention of oleic and linoleic acids in this tissue during hibernation.

The virulent, emerging genotype B of Deformed wing virus is closely linked to overwinter honeybee worker loss

Bees are considered to be threatened globally, with severe overwinter losses of the most important commercial pollinator, the Western honeybee, a major concern in the Northern Hemisphere. Emerging infectious diseases have risen to prominence due to their temporal correlation with colony losses. Among these is Deformed wing virus (DWV), which has been frequently linked to colony mortality. We now provide evidence of a strong statistical association between overwintering colony decline in the field and the presence of DWV genotype-B (DWV-B), a genetic variant of DWV that has recently been shown to be more virulent than the original DWV genotype-A. We link the prevalence of DWV-B directly to a quantitative measure of overwinter decline (workforce mortality) of honeybee colonies in the field. We demonstrate that increased prevalence of virus infection in individual bees is associated with higher overwinter mortality. We also observed a substantial reduction of infected colonies in the spring, suggesting that virus-infected individuals had died during the winter. Our findings demonstrate that DWV-B, plus possible A/B recombinants exhibiting DWV-B at PCR primer binding sites, may be a major cause of elevated overwinter honeybee loss. Its potential emergence in naïve populations of bees may have far-reaching ecological and economic impacts.

Local demographic and epidemiological patterns in the Linum marginale–Melampsora lini association: a multi‐year study

Summary Many theoretical and empirical studies operate from an assumption that pathogens have a significant influence on the fecundity and life span of their host species. However, there are surprisingly little data investigating the long‐term fitness impacts and genetic consequences that arise from pathogen infection in natural populations. Here, we address this gap through the analysis of a dataset investigating the local population dynamics of a native host plant (Linum marginale) and an associated rust pathogen (Melampsora lini) across 12 years. To investigate patterns of disease prevalence and severity and track effects on host fecundity and demography, we conducted censuses on an annual basis at a single site. Annual M. lini infection prevalence ranged from 0% to 99%. Severe epidemics occurred in 3‐ to 4‐year cycles causing high overwintering mortality and subsequent changes in the relative abundance of different host phenotypes. Host population size oscillated in response to epidemics and declined towards the end of the observation period. Changes in host numbers were found to affect disease severity but not infection prevalence. Melampsora lini infection increased L. marginale fecundity; the infected plants produced threefold more seed capsules on average than uninfected plants (13·3 vs. 4·3 seed capsules per plant). To investigate how variation in environmental conditions affects epidemiology and host demography, we identified climatic factors affecting host growth, overwintering and disease severity. Winter (June) rainfall increased host overwintering success and summer (December) rainfall favoured host growth. The progress of M. lini disease epidemics benefited from optimal temperatures in February and suffered from rainfall in January. We further examined links between the genetic structure of the pathogen population and disease dynamics. There was a positive correlation between mean pathogen infectivity (as measured across a host differential set) and the severity of disease epidemics. Synthesis. Our results provide new insights into local drivers and consequences of pathogen epidemiology in natural populations. Melampsora lini infection can have profound consequences on the phenotype, demography and population structure of Linum marginale by increasing host fecundity, overwinter mortality and disease resistance.

Reliability and precision of pellet-group counts for estimating landscape-level deer density

This study provides hitherto unavailable methodology for reliably and precisely estimating deer density within forested landscapes, enabling quantitative rather than qualitative deer management. Reliability and precision of the deer pellet-group technique were evaluated in 1 small and 2 large forested landscapes. Density estimates, adjusted to reflect deer harvest and overwinter mortality, were compared with a drive count on the small landscape and with aerial counts using forward-looking infrared videography (FLIR) on the large landscapes. Estimates by 2 expert and 2 novice counters (range = 17.6 to 18.6 deer/km 2 ) on the small landscape were not different from each other and three of the four were not different from the drive count (17.4 deer/km 2 ). FLIR density estimates were approximately 30% lower than pellet-group estimates on the large landscapes (P < 0.04), an expected result. Precision on the small landscape was high; 95% confidence intervals for individual counters were <7.5% of mean estimates of density, and coefficients of variability were <10%. Precision on the larger landscapes was acceptable: 95% confidence intervals were 18.4 to 30.4% of mean estimates and coefficients of variability were <25%. The pellet-group technique produces reliable and precise estimates of deer density, is inexpensive, requires little training to implement, and is best suited to northern hardwood forests where snow and cold result in minimal deterioration of pellet groups. Unless corrected for hunter harvest and overwinter mortality, pellet-group counts represent average overwinter density and overestimate spring density.