Global assessment of marine plastic exposure risk for oceanic birds

Plastic pollution is distributed patchily around the world's oceans. Likewise, marine organisms that are vulnerable to plastic ingestion or entanglement have uneven distributions. Understanding where wildlife encounters plastic is crucial for targeting research and mitigation. Oceanic seabirds, particularly petrels, frequently ingest plastic, are highly threatened, and cover vast distances during foraging and migration. However, the spatial overlap between petrels and plastics is poorly understood. Here we combine marine plastic density estimates with individual movement data for 7137 birds of 77 petrel species to estimate relative exposure risk. We identify high exposure risk areas in the Mediterranean and Black seas, and the northeast Pacific, northwest Pacific, South Atlantic and southwest Indian oceans. Plastic exposure risk varies greatly among species and populations, and between breeding and non-breeding seasons. Exposure risk is disproportionately high for Threatened species. Outside the Mediterranean and Black seas, exposure risk is highest in the high seas and Exclusive Economic Zones (EEZs) of the USA, Japan, and the UK. Birds generally had higher plastic exposure risk outside the EEZ of the country where they breed. We identify conservation and research priorities, and highlight that international collaboration is key to addressing the impacts of marine plastic on wide-ranging species.

Factors influencing mercury levels in Leach's storm-petrels at northwest Atlantic colonies

Mercury (Hg) is a globally distributed heavy metal, with negative effects on wildlife. Its most toxic form, methylmercury (MeHg), predominates in aquatic systems. Levels of MeHg in marine predators can vary widely among individuals and populations. Leach's storm-petrels (Hydrobates leucorhous) have elevated levels of Hg but the role of Hg in storm-petrel population declines is unknown. In this study, we used egg and blood samples to study variation in Hg exposure among several northwest Atlantic colonies during breeding seasons, thereby evaluating relative toxicity risk within and among colonies. Total mercury (THg) concentrations were higher with increasing colony latitude, and were more pronounced in blood than in eggs. THg concentrations in blood were mostly associated with low toxicity risk in birds from the southern colonies and moderate risks in birds from the northern colonies; however, those values did not affect hatching or fledging success. THg concentrations in both eggs and blood were positively correlated with δ³⁴S, emphasizing the role of sulfate-reducing bacteria in methylation of THg acquired through marine food webs, which is consistent with enriched δ³⁴S profiles. By associating tracking data from foraging trips with THg from blood, we determined that blood THg levels were higher when storm-petrel's intensive search locations were over deeper waters. We conclude that spatial variation in THg concentrations in Leach's storm-petrels is attributable to differences in ocean depth at foraging locations, both at individual and colony levels. Differences in diet among colonies observed previously are the most likely cause for observed blood THg differences. As one of the few pelagic seabird species breeding in Atlantic Canada, with limited overlap in core foraging areas among colonies, Leach's storm-petrels can be used as biomonitors for less sampled offshore pelagic regions. The global trend in Hg emissions combined with legacy levels warrant continued monitoring for toxicity effects in seabirds.

New geographic records for Echinococcus canadensis in coyotes and moose from Nova Scotia, Canada

Echinococcus spp. tapeworms can cause serious diseases in mammals, including humans. Within the E. granulosus species complex, metacestodes produce unilocular cysts that are responsible for cystic echinococcosis in animal intermediate hosts. Canids are definitive hosts, harbouring adult cestodes in their intestines. Adult E. canadensis were recovered from the small intestine of 1 of 262 coyotes (Canis latrans) from Nova Scotia, Canada. Subsequently, we found unilocular cysts in lungs and livers of 4 of 8 sympatric moose (Alces alces) from Cape Breton Island. DNA was extracted from three cysts using the Qiagen DNeasy Blood and Tissue kit and assayed by polymerase chain reaction (PCR) with primers (cest4 and cest5) for a 117-bp region of the small subunit of ribosomal RNA of E. granulosus sensu lato, and further validated as E. canadensis G8 using primers targeting nicotinamide adenosine dinucleotide dehydrogenase subunit 1 (ND1) and cytochrome c oxidase subunit 1 (CO1) mitochondrial genes. These are the first records of E. canadensis in any of the three Maritime provinces, which include Nova Scotia, New Brunswick, and Prince Edward Island. The parasite was thought to be absent in this region due to extirpation of wolves (Canis spp.) in the 1800s. These findings suggest that further wildlife surveillance and risk assessment is warranted.

Demographical and morphological differences among coyotes (Canis latrans) relative to sampling method

Collection methods can be biased, leading to misperceptions of population composition. We tested if collection method (footholds, snares, and shooting) gave different perceptions of demography or morphology of 3539 eastern coyotes (Canis latrans Say, 1823). We found no differences in sex ratios of animals among methods, but did find some evidence that younger, lighter, and smaller animals were more likely to be collected by footholds than with snares. Female reproductive histories (placental scars) did not differ among methods. In a subsample of 232 animals, we found no evidence of differences in helminth parasitism relative to collection method. Overall, our large sample for the non-parasite analyses facilitated finding statistical significance; the biological implications hinge on the precision required in estimating population composition and the focal characteristics being compared. For example, mass was 5.3% lower for coyotes caught with footholds versus snares and 10.4% lower for coyotes caught with footholds versus being shot, whereas linear trait measurements of coyotes caught with footholds were generally smaller by at most 4.5% compared with other methods (broadly consistent with linear versus volumetric measurements). Our study provides important baseline information for making inferences about populations of coyotes (and other species) sampled using only a single collection method.

Electrotarsogram responses to synthetic odorants by Varroa destructor, a primary parasite of western honey bees (Apis mellifera)

Olfaction is a key sensory modality for many arthropods and could be used as a tool in pest management through manipulation of pest behavior. Management of Varroa destructor, important parasitic mites of honey bees, could be improved through better understanding of the chemical ecology of this host-parasite relationship. We refined techniques of mounting mites to obtain electrophysiological recordings (electrotarsograms) of their responses to synthetic odor stimuli. Results of 271 electrotarsogram recordings from V. destructor revealed responses to 10 odorants relative to solvent controls. Electrotarsogram responses to methyl palmitate, ethyl palmitate, and 2-heptanol were highest at the lowest stimulus loading (10 ng) we tested, suggesting that V. destructor may have acute sensitivity to low concentrations of some odors. Results suggest that odorant origin (e.g., methyl oleate from honey bee larvae, geraniol from adult honey bee alarm pheromone, and α-terpineol, a plant secondary metabolite) can influence the degree of electrophysiological response. Varroa destructor tended to be more responsive to known attractants and repellents relative to previously unexplored odorants and some repellent terpenes. Electrotarsograms offer the potential for screening odors to determine their importance in V. destructor host detection.

Varroa destructor mite electrophysiological responses to honey bee (Apis mellifera) colony volatiles

Detection and interpretation of chemical cues is essential for Varroa destructor Anderson and Trueman, an important parasite of honey bees (Apis mellifera L.), to complete its life cycle. We collected volatiles from honey bee brood at various developmental stages and screened for V. destructor electrophysiological responses to these with gas chromatography-linked electrotarsal detection. Volatile collections contained several methyl-alkanes that evoked electrophysiological responses from V. destructor. Moreover, odors in honey bee colonies that regulate honey bee colony structure and function were also detected by V. destructor. Collections from mid- to late-stage larvae had detectable levels of low-volatility odors identified as components of the honey bee brood pheromone and branched alkanes likely originating from brood cuticle. Among these, several mid- to heavy-molecular weight compounds elicited high proportional electrophysiological responses by V. destructor relative to their abundance but could not be identified using chemical standards of previously documented honey bee brood odors. We suggest further investigation of these unknown volatiles and future behavioral assays to determine attractiveness/repellency (valence) of those identified through chemical standards.

A range-wide domino effect and resetting of the annual cycle in a migratory songbird

Latitudinal differences in timing of breeding are well documented but how such differences carry over to influence timing of events in the annual cycle of migratory birds is not well understood. We examined geographical variation in timing of events throughout the year using light-level geolocator tracking data from 133 migratory tree swallows ( Tachycineta bicolor) originating from 12 North American breeding populations. A swallow's breeding latitude influenced timing of breeding, which then carried over to affect breeding ground departure. This resulted in subsequent effects on the arrival and departure schedules at autumn stopover locations and timing of arrival at non-breeding locations. This 'domino effect' between timing events was no longer apparent by the time individuals departed for spring migration. Our range-wide analysis demonstrates the lasting impact breeding latitude can have on migration schedules but also highlights how such timing relationships can reset when individuals reside at non-breeding sites for extended periods of time.

Foraging areas, offshore habitat use, and colony overlap by incubating Leach's storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic

Despite their importance in marine food webs, much has yet to be learned about the spatial ecology of small seabirds. This includes the Leach’s storm-petrel Oceanodroma leucorhoa, a species that is declining throughout its Northwest Atlantic breeding range. In 2013 and 2014, we used global location sensors to track foraging movements of incubating storm-petrels from 7 eastern Canadian breeding colonies. We determined and compared the foraging trip and at-sea habitat characteristics, analysed spatial overlap among colonies, and determined whether colony foraging ranges intersected with offshore oil and gas operations. Individuals tracked during the incubation period made 4.0 ± 1.4 day foraging trips, travelling to highly pelagic waters over and beyond continental slopes which ranged, on average, 400 to 830 km from colonies. Cumulative travel distances ranged from ~900 to 2,100 km among colonies. While colony size did not influence foraging trip characteristics or the size of areas used at sea, foraging distances tended to be shorter for individuals breeding at the southern end of the range. Core areas did not overlap considerably among colonies, and individuals from all sites except Kent Island in the Bay of Fundy foraged over waters with median depths > 1,950 m and average chlorophyll a concentrations ≤ 0.6 mg/m³. Sea surface temperatures within colony core areas varied considerably (11–23°C), coincident with the birds’ use of cold waters of the Labrador Current or warmer waters of the Gulf Stream Current. Offshore oil and gas operations intersected with the foraging ranges of 5 of 7 colonies. Three of these, including Baccalieu Island, Newfoundland, which supports the species’ largest population, have experienced substantial declines in the last few decades. Future work should prioritize modelling efforts to incorporate information on relative predation risk at colonies, spatially explicit risks at-sea on the breeding and wintering grounds, effects of climate and marine ecosystem change, as well as lethal and sub-lethal effects of environmental contaminants, to better understand drivers of Leach’s storm-petrel populations trends in Atlantic Canada.

Honey bee-collected pollen in agro-ecosystems reveals diet diversity, diet quality, and pesticide exposure

European honey bees Apis mellifera are important commercial pollinators that have suffered greater than normal overwintering losses since 2007 in North America and Europe. Contributing factors likely include a combination of parasites, pesticides, and poor nutrition. We examined diet diversity, diet nutritional quality, and pesticides in honey bee-collected pollen from commercial colonies in the Canadian Maritime Provinces in spring and summer 2011. We sampled pollen collected by honey bees at colonies in four site types: apple orchards, blueberry fields, cranberry bogs, and fallow fields. Proportion of honey bee-collected pollen from crop versus noncrop flowers was high in apple, very low in blueberry, and low in cranberry sites. Pollen nutritional value tended to be relatively good from apple and cranberry sites and poor from blueberry and fallow sites. Floral surveys ranked, from highest to lowest in diversity, fallow, cranberry, apple, and blueberry sites. Pesticide diversity in honey bee-collected pollen was high from apple and blueberry sites and low from cranberry and fallow sites. Four different neonicotinoid pesticides were detected, but neither these nor any other pesticides were at or above LD₅₀ levels. Pollen hazard quotients were highest in apple and blueberry sites and lowest in fallow sites. Pollen hazard quotients were also negatively correlated with the number of flower taxa detected in surveys. Results reveal differences among site types in diet diversity, diet quality, and pesticide exposure that are informative for improving honey bee and land agro-ecosystem management.

Lesser snow goose helminths show recurring and positive parasite infection-diversity relations

The patterns and mechanisms by which biological diversity is associated with parasite infection risk are important to study because of their potential implications for wildlife population's conservation and management. Almost all research in this area has focused on host species diversity and has neglected parasite diversity, despite evidence that parasites are important drivers of community structure and ecosystem processes. Here, we assessed whether presence or abundance of each of nine helminth species parasitizing lesser snow geese (Chen caerulescens) was associated with indices of parasite diversity (i.e. species richness and Shannon's Diversity Index). We found repeated instances of focal parasite presence and abundance having significant positive co-variation with diversity measures of other parasites. These results occurred both within individual samples and for combinations of all samples. Whereas host condition and parasite facilitation could be drivers of the patterns we observed, other host- or parasite-level effects, such as age or sex class of host or taxon of parasite, were discounted as explanatory variables. Our findings of recurring and positive associations between focal parasite abundance and diversity underscore the importance of moving beyond pairwise species interactions and contexts, and of including the oft-neglected parasite species diversity in infection-diversity studies.

Relationships between blood mercury levels, reproduction, and return rate in a small seabird

Mercury (Hg) is a ubiquitous heavy metal that occurs naturally in the environment, but its levels have been supplemented for decades by a variety of human activities. Mercury can have serious deleterious effects on a variety of organisms, with top predators being particularly susceptible because methylmercury bioaccumulates and biomagnifies in food webs. Among birds, seabirds can have especially high levels of Hg contamination and Leach's storm-petrels (Oceanodroma leucorhoa), in particular, have amongst the highest known levels. Several populations of Leach's storm-petrels have declined recently in the Northwest Atlantic. The causes of these declines remain uncertain, but the toxic effects of Hg could be a potential factor in this decline. Here, we tested for relationships between adult blood total Hg (THg) concentration and several offspring development parameters, and adult return rate of Leach's storm-petrels breeding on Bon Portage Island (43° 28' N, 65° 44' W), Nova Scotia, Canada, between 2011 and 2015 (blood samples n = 20, 36, 6, 15, and 13 for each year, respectively). Overall, THg levels were elevated (0.78 ± 0.43 μg/g wet wt.) compared to other species of seabirds in this region, and varied significantly among years. However, we found no associations between THg levels and reproductive parameters or adult return rate. Our results indicate that levels of mercury observed in Leach's storm-petrel blood, although elevated, appear not to adversely affect their offspring development or adult return rate on Bon Portage Island.

Plastics and other anthropogenic debris in freshwater birds from Canada

Plastics in marine environments are a global environmental issue. Plastic ingestion is associated with a variety of deleterious health effects in marine wildlife, and is a focus of much international research and monitoring. However, little research has focused on ramifications of plastic debris for freshwater organisms, despite marine and freshwater environments often having comparable plastic concentrations. We quantified plastic and other anthropogenic debris in 350 individuals of 17 freshwater and one marine bird species collected across Canada. We determined freshwater birds' anthropogenic debris ingestion rates to be 11.1% across all species studied. This work establishes that plastics and other anthropogenic debris are a genuine concern for management of the health of freshwater ecosystems, and provides a baseline for the prevalence of plastic and other anthropogenic debris ingestion in freshwater birds in Canada, with relevance for many other locations.

Neonicotinoid pesticides severely affect honey bee queens

Queen health is crucial to colony survival of social bees. Recently, queen failure has been proposed to be a major driver of managed honey bee colony losses, yet few data exist concerning effects of environmental stressors on queens. Here we demonstrate for the first time that exposure to field-realistic concentrations of neonicotinoid pesticides during development can severely affect queens of western honey bees (Apis mellifera). In pesticide-exposed queens, reproductive anatomy (ovaries) and physiology (spermathecal-stored sperm quality and quantity), rather than flight behaviour, were compromised and likely corresponded to reduced queen success (alive and producing worker offspring). This study highlights the detriments of neonicotinoids to queens of environmentally and economically important social bees, and further strengthens the need for stringent risk assessments to safeguard biodiversity and ecosystem services that are vulnerable to these substances.

Leucocyte profiles of Arctic marine birds: correlates of migration and breeding phenology

Most Arctic marine birds are migratory, wintering south of the limit of annual pack ice and returning north each year for the physiologically stressful breeding season. The Arctic environment is changing rapidly due to global warming and anthropogenic activities, which may influence the timing of breeding in relation to arrival times following migration, as well as providing additional stressors (e.g. disturbance from ships) to which birds may respond. During stressful parts of their annual cycle, such as breeding, birds may reallocate resources so that they have increased heterophil-to-lymphocyte ratios in their white blood cell (leucocyte) profiles. We analysed leucocyte profiles of nine species of marine birds to establish reference ranges for these species in advance of future Arctic change. Leucocyte profiles tended to cluster among taxonomic groups across studies, suggesting that reference values for a particular group can be established, and within species there was evidence that birds from colonies that had to migrate farther had higher heterophil-to-lymphocyte ratios during incubation than those that did not have to travel as far, particularly for species with high wing loading.

Trace elements and ingested plastic debris in wintering dovekies (Alle alle)

We provide the first report on winter concentrations of 32 trace metals from dovekies (Alle alle), a small, Arctic seabird that has a seasonal shift in diet from small zooplankton in the breeding season to larger zooplankton and small fish in the non-breeding season. Concentrations of selected trace elements, as well as stable carbon (δ(13)C) and nitrogen (δ(15)N) isotope concentrations for a sample of 25 dovekies, were similar between adult males and females, and there was evidence that dovekies feeding at higher trophic levels had higher hepatic Hg. We also found plastic debris in nine of 65 (14%) gizzards examined. Our study helps provide a more complete picture of the foraging ecology and contaminant profile of dovekies, an important species in Arctic marine food webs.

Nematode parasites and leukocyte profiles of Northern Leopard Frogs, Rana pipiens: location, location, location

Globally, amphibians face a variety of anthropogenic stresses that include exposure to contaminants such as agricultural pesticides. Pesticides may negatively affect amphibian immune systems, concomitantly increasing susceptibility to parasitism. We quantified nematodes and evaluated leukocyte profiles of Northern Leopard Frogs (Rana pipiens Schreber, 1782) collected from five wetlands in southwestern Quebec, Canada, that spanned a gradient of pesticide exposure. Three taxa of nematode parasites (Rhabdias ranae Walton, 1929, genus Oswaldocruzia Travassos, 1917, and genus Strongyloides Grassi, 1879) were sufficiently numerous for detailed evaluation. When all frogs were pooled, frog size was negatively correlated with nematode species richness, abundances of each of the three nematode species, and densities of three different leukocytes. When all frogs were pooled, there was strong evidence of both negative and positive associations between pairs of parasite species. However, none of the previous relationships was significant within wetlands. Our results reveal strong spatial organization of amphibian–parasite communities and illustrate the importance of controlling for sampling locale in evaluating host–parasite associations. Finally, although several response variables varied significantly among wetlands, causes of this variation did not appear to be related to variation in nematode parasitism or pesticide exposure.

Infra-population and -community dynamics of the parasites Nosema apis and Nosema ceranae, and consequences for honey bee (Apis mellifera) hosts

Nosema spp. fungal gut parasites are among myriad possible explanations for contemporary increased mortality of western honey bees (Apis mellifera, hereafter honey bee) in many regions of the world. Invasive Nosema ceranae is particularly worrisome because some evidence suggests it has greater virulence than its congener N. apis. N. ceranae appears to have recently switched hosts from Asian honey bees (Apis cerana) and now has a nearly global distribution in honey bees, apparently displacing N. apis. We examined parasite reproduction and effects of N. apis, N. ceranae, and mixed Nosema infections on honey bee hosts in laboratory experiments. Both infection intensity and honey bee mortality were significantly greater for N. ceranae than for N. apis or mixed infections; mixed infection resulted in mortality similar to N. apis parasitism and reduced spore intensity, possibly due to inter-specific competition. This is the first long-term laboratory study to demonstrate lethal consequences of N. apis and N. ceranae and mixed Nosema parasitism in honey bees, and suggests that differences in reproduction and intra-host competition may explain apparent heterogeneous exclusion of the historic parasite by the invasive species.

Honey bee Apis mellifera parasites in the absence of Nosema ceranae fungi and Varroa destructor mites

Few areas of the world have western honey bee (Apis mellifera) colonies that are free of invasive parasites Nosema ceranae (fungi) and Varroa destructor (mites). Particularly detrimental is V. destructor; in addition to feeding on host haemolymph, these mites are important vectors of several viruses that are further implicated as contributors to honey bee mortality around the world. Thus, the biogeography and attendant consequences of viral communities in the absence of V. destructor are of significant interest. The island of Newfoundland, Province of Newfoundland and Labrador, Canada, is free of V. destructor; the absence of N. ceranae has not been confirmed. Of 55 Newfoundland colonies inspected visually for their strength and six signs of disease, only K-wing had prevalence above 5% (40/55 colonies = 72.7%). Similar to an earlier study, screenings again confirmed the absence of V. destructor, small hive beetles Aethina tumida (Murray), tracheal mites Acarapis woodi (Rennie), and Tropilaelaps spp. ectoparasitic mites. Of a subset of 23 colonies screened molecularly for viruses, none had Israeli acute paralysis virus, Kashmir bee virus, or sacbrood virus. Sixteen of 23 colonies (70.0%) were positive for black queen cell virus, and 21 (91.3%) had some evidence for deformed wing virus. No N. ceranae was detected in molecular screens of 55 colonies, although it is possible extremely low intensity infections exist; the more familiar N. apis was found in 53 colonies (96.4%). Under these conditions, K-wing was associated (positively) with colony strength; however, viruses and N. apis were not. Furthermore, black queen cell virus was positively and negatively associated with K-wing and deformed wing virus, respectively. Newfoundland honey bee colonies are thus free of several invasive parasites that plague operations in other parts of the world, and they provide a unique research arena to study independent pathology of the parasites that are present.

Effects of fluvalinate on honey bee learning, memory, responsiveness to sucrose, and survival

Contaminants can affect organisms' behaviour and, as a consequence, survival. Tau-fluvalinate (hereafter fluvalinate) is the active ingredient in a pesticide commonly used in North America to control Varroa destructor mites in honey bee (Apis mellifera) colonies. Fluvalinate's effects on honey bees are not well known. Honey bee cognitive and neural function can be assessed using the proboscis extension reflex (PER), which applies Pavlovian conditioning techniques. This study used PER to evaluate effects of fluvalinate on honey bee acquisition learning, (long-term) memory recall, responsiveness to sucrose, and mortality. We also evaluated how exclusion criteria for honey bees that did not exhibit PER during training and memory trials affected interpretation of results. Fluvalinate was administered both orally and dermally at high and low doses to mimic routes by which honey bees are exposed. We found negative effects of fluvalinate on honey bee learning, memory, responsiveness to sucrose, and survival, especially in high oral doses. We also found significant consequences to interpretation of results using different exclusion criteria. For example, almost 50% of individuals that failed to show evidence of learning subsequently showed evidence of memory. The latter results have important implications regarding traditional assessment of PER-based learning and memory; the former results suggest that evaluation of honey bee exposure to fluvalinate and attendant consequences warrants further investigation.

Fate of dermally applied miticides fluvalinate and amitraz within honey bee (Hymenoptera: Apidae) bodies

Varroa mites, Varroa destructor Anderson & Trueman, are economically important pests of honey bees. Varroa mites are principally controlled within honey bee colonies using miticides. However, despite their importance in managing mite populations for apiculture, potential effects of miticides on honey bees are poorly understood. Using gas chromatography-flame ionization detection, we investigated concentrations, over variable time frames and within different body regions, of two commonly used miticides, tau-fluvalinate and amitraz, after dermal exposure to honey bees. We also quantified mortality of honey bees exposed to each miticide at both a low and high dose. Significant differences were observed in distributions of miticides among body regions. Within honey bee body parts, tau-fluvalinate was more readily absorbed and decreased in concentration more rapidly than amitraz. Mortality increased with higher dosages of miticides, and at higher dosages mortality was greater from fluvalinate than from amitraz. For individual honey bees, our results for rate of breakdown suggest that fluvalinate may be the preferred miticide for apiculturists, whereas our mortality results suggest that amitraz may be preferable. Either choice must be weighed against geographic variation in varroa resistance to each pesticide and attendant costs of parasitism.

The proboscis extension reflex to evaluate learning and memory in honeybees (Apis mellifera): some caveats

The proboscis extension reflex (PER) is widely used in a classical conditioning (Pavlovian) context to evaluate learning and memory of a variety of insect species. The literature is particularly prodigious for honeybees (Apis mellifera) with more than a thousand publications. Imagination appears to be the only limit to the types of challenges to which researchers subject honeybees, including all the sensory modalities and a broad diversity of environmental treatments. Accordingly, some remarkable insights have been achieved using PER. However, there are several challenges to evaluating the PER literature that warrant a careful and thorough review. We assess here variation in methods that makes interpretation of studies, even those researching the same question, tenuous. We suggest that the numerous variables that might influence experimental outcomes from PER be thoroughly detailed by researchers. Moreover, the influence of individual variables on results needs to carefully evaluated, as well as among two or more variables. Our intent is to encourage investigation of the influence of numerous variables on PER results.

Effects of cold immobilization and recovery period on honeybee learning, memory, and responsiveness to sucrose

In addition to human error and variation in laboratory conditions, there are numerous factors that can complicate comparisons among studies. Furthermore, differences in how experimental methods are executed can make it difficult to distinguish between effects of focal versus extraneous variables. Insect neural function is commonly evaluated using Pavlovian conditioning techniques; learning and memory in many species can be assessed using the proboscis extension reflex (PER). However, there are significant inconsistencies in methods used to immobilize insects prior to PER tests. We compared responses of honeybees immobilized in a refrigerator, on ice, and in a freezer, and evaluated influence of recovery interval before testing. Ice-chilling weakly decreased learning (response to an originally neutral odor) more so than refrigeration or freezing, but not 24-h recall of odor. We found no significant differences in responsiveness to sucrose relative to cooling method, but responsiveness was significantly lower among honeybees left to recover for only 0.75h versus 1.5 or 3h. Finally, we observed increased responsiveness to sucrose and geraniol between June and August. Our results suggest that inconsistencies in cold immobilization methods could confound interpretation and comparison of results from a large body of work on honeybee learning and memory.

Correlates of mercury in female river otters (Lontra canadensis) from Nova Scotia, Canada

Mercury (Hg) can reach toxic concentrations in aquatic habitats, sometimes as a consequence of human activity. Mercury can have deleterious effects, particularly in piscivorous mammals in which it bioaccumulates. Furs from trapper-provided female otter (Lontra canadensis) carcasses in Nova Scotia were analyzed for total Hg. Concentrations of total Hg in fur samples averaged 25 µg/g dry weight, ranging from 1.4 to 137 µg/g; 20 µg/g is the fur concentration at which toxic effects are expected. Mercury concentrations were greater in otters from watersheds with bedrock substrates known to contain more available Hg, from otters trapped farther inland, and from otters trapped on watersheds with hydroelectric dams. Otter reproductive potential was measured by counting the number of blastocysts in reproductive tracts. Tooth annuli were used to age otters. Reproductive potential was not related to Hg concentration, nor was Hg concentration related to age. In a general linear model, 53% of variation in fur Hg was explained by underlying bedrock, distance from the coast at which otters were trapped, and presence/absence of a hydroelectric dam. The proportion of juveniles in a population did not differ relative to bedrock Hg concentration, but was lower on watersheds with hydroelectric dams. Because we found no evidence of reduced reproductive potential from greater Hg concentrations, the low proportion of juveniles suggests that Hg reduced juvenile survival, although our evidence is circumstantial.

Sexual selection: when to expect trade-offs

Empirical evidence is mixed for interspecific trade-offs in investment among sexually selected traits. One important reason may be the way resources are allocated among species. Consider a set of species that obtains the same fitness pay-off for investment in song or plumage. Simulations where resources were normally distributed among species revealed significant trade-offs between song and plumage ( ± s.d. of r = -0.54 ± 0.06). However, simulations where resources were distributed in a negative binomial fashion usually produced positive correlations (r = 0.11 ± 0.09). Repeating simulations on three published studies that concomitantly quantified elaboration of song and plumage indicated that trade-offs are likely, although these analyses make assumptions that require further evaluation. Moreover, there are currently too few empirical distributions to make generalizations about the likelihood of interspecific trade-offs in sexually selected traits.

Nest-site characteristics and breeding success of three species of boreal songbirds in western Newfoundland, Canada

Delineating habitat requirements and preferences of species is essential for conservation planning. We studied nest habitat use and effects of microsite vegetation characteristics on breeding success of yellow-rumped warblers ( Dendroica coronata (L., 1766)), blackpoll warblers ( Dendroica striata (J.R. Forster, 1772)), and white-throated sparrows ( Zonotrichia albicollis (Gmelin, 1789)) in an area with a low extent (<6% of available land) of forest harvest in northwestern Newfoundland. During 2004 and 2005, 99 nests were located and monitored, and the characteristics of nest sites measured. Vegetation at yellow-rumped and blackpoll warbler nest sites differed from random sites; however, within used sites, no vegetation characteristics were significantly associated with success. White-throated sparrow nest sites contained more downed wood and less ground vegetation than did random sites; however, successful nests were associated with different variables than those that distinguished them from random sites, including less canopy cover and less woody debris. Thus, whereas yellow-rumped and blackpoll warblers used specific nest-site characteristics and white-throated sparrows had higher nest success associated with certain characteristics, the nest characteristics these birds appeared to choose did not have demonstrable fitness benefits.

Time and recruitment costs as currencies in manipulation studies on the costs of reproduction

Life history theory predicts that parents will have lower Darwinian fitness if they tend clutches that are above or below the size they naturally produce. We experimentally tested for relationships between fitness and clutch size in Tree Swallow (Tachycineta bicolor) offspring and parents. Over 130 trios of nests initiated on the same day were randomly divided among reduce (-3 eggs), control (3 eggs picked up and replaced), or add (+3 eggs) manipulations. Pre-manipulation modal clutch size was six eggs (range before manipulations was 1-10; afterwards, it was 1-11). Hatching took longer in larger clutches, but the proportion of eggs hatching and fledging was similar for clutches from 4 to 10, so that clutches of 10 produced the maximum number of fledgling. Parental feeding rates were higher for larger broods, but per capita feeds to nestlings were fewer, and nestlings were smaller. Nonetheless, survival of both young and adults, based on recaptures in subsequent years, was not significantly affected by manipulations. Manipulations also had no significant effect on subsequent reproduction, including the number of fledglings produced by either local recruits or returning breeders. Collectively, our results failed to detect fitness costs associated with tending larger clutches for either parents or the offspring reared and suggested directional selection for larger clutch size. However, because clutches that hatch later produce fewer recruits, the extra days required to lay more eggs and to fledge extra young may eliminate a large part of the advantage that would accrue to parents producing enlarged clutches. For example, our data suggest that there may be less than a 16% benefit to producing nine instead of six eggs, rather than 50%, as is suggested by experimentally manipulated egg numbers alone. Thus, time, rather than costs of reproduction, may be the crucial constraint selecting against Tree Swallows laying larger clutches.

Does fumagillin control the recently detected invasive parasite Nosema ceranae in western honey bees (Apis mellifera)?

Western honey bee (Apis mellifera) colonies in Nova Scotia, Canada were sampled in spring and late summer 2007 to evaluate efficacy of fumagillin dicyclohexylammonium (hereafter, fumagillin) against Nosema ceranae. Colonies treated with fumagillin in September 2006 (n=94) had significantly lower Nosema intensity in spring 2007 than did colonies that received no treatment (n=51), but by late summer 2007 no difference existed between groups. Molecular sequencing of 15 infected colonies identified N. ceranae in 93.3% of cases, suggesting that fumagillin is successful at temporarily reducing this recent invasive parasite in western honey bees.

First detection of Nosema ceranae, a microsporidian parasite of European honey bees (Apis mellifera), in Canada and central USA

Nosema ceranae is an emerging microsporidian parasite of European honey bees, Apis mellifera, but its distribution is not well known. Six Nosema-positive samples (determined from light microscopy of spores) of adult worker bees from Canada (two each from Nova Scotia, New Brunswick, and Prince Edward Island) and two from USA (Minnesota) were tested to determine Nosema species using previously-developed PCR primers of the 16S rRNA gene. We detected for the first time N. ceranae in Canada and central USA. One haplotype of N. ceranae was identified; its virulence may differ from that of other haplotypes.

Rodent malaria parasites Plasmodium chabaudi and P. vinckei do not increase their rates of gametocytogenesis in response to mosquito probing

Several vector-borne infectious agents facultatively alter their life history strategies in response to local vector densities. Some evidence suggests that malaria parasites invest more heavily in transmission stage production (gametocytogenesis) when vectors are present. Such a strategy could rapidly increase malaria transmission rates, particularly when adult mosquitoes begin to appear after dry seasons. However, in contrast to a recent experiment with a rodent malaria (Plasmodium chabaudi), we found no change in gametocytogenesis in either P. chabaudi or in another rodent malaria, P. vinckei, when their mouse hosts were exposed to mosquitoes. Positive results in the earlier study may have been because mosquito-feeding caused anaemia in hosts, a known promoter of gametocytogenesis. The substantial evidence that malaria and a variety of other parasites facultatively alter transmission strategies in response to a variety of environmental influences makes our results surprising.

Haldane's rule and American black duck × mallard hybridization

Species ratios and rangewide distributions of American black ducks (Anas rubripes Brewster, 1902) and mallards (Anas platyrhynchos L., 1758) have undergone recent changes. Mechanisms behind these changes are not known with certainty, but recent investigations have focused on the possibility of competitive exclusion and the consequences of hybridization. Consequences of hybridization have been difficult to assess because of the difficulty in identifying hybrids beyond the F1generation and lack of means to quantify introgression in wild populations. We documented a postmating isolating mechanism between the two species that follows Haldane's rule in controlled, interspecific matings in captive populations. Hybridization reduces the proportion of F1females available to return to the breeding grounds in the subsequent year. This effect, although likely small in overall population consequences in any year, may be of local significance and may contribute to recent reports of range shifts in both American black ducks and mallards.

Tree swallow reproductive investment, stress, and parasites

We reduced or increased tree swallow, Tachycineta bicolor (Vieillot, 1808), clutch sizes by three eggs (50% of modal clutch size) to test experimentally for relationships between stress and parasite loads. In the first year of the study (1996), we enumerated two measures of stress (granulocyte to non-granulocyte ratios and heterophil to lymphocyte ratios), blood parasites, and ectoparasites living on birds (and not in nesting material). Stress indices increased for parents, but not for nestlings, associated with larger broods. Only one blood parasite (a trypanosome) was detected in blood smears from 221 different individuals. On individual birds, we found a median of 0 fleas, 0 lice, and 7 feather mites. In the second study (1998), we focused on parasites living in nesting material. Here, we found a median of 106 fleas and, of the parasites we observed, these probably had the greatest potential impact on the birds. Per capita flea loads were higher in nests that contained more young. However, despite higher stress to parents and higher per capita flea loads in enlarged broods, flea numbers were not associated with smaller nestlings or with reduced fledging success.

Ectoparasites, nestling growth, parental feeding rates, and begging intensity of tree swallows

Many studies fail to show relationships between ectoparasite loads and nestling growth rates. One explanation is that parent birds increase feeding rates to compensate for nestling energetic losses to ectoparasites. Nestling begging behaviours could signal need to parents. Accordingly, we tested whether higher flea and blow fly loads in tree swallow (Tachycineta bicolor) nests were associated with smaller nestlings, higher parental feeding rates, and increased nestling begging intensity. The study area was the Gaspereau Valley of Nova Scotia, Canada. When nestlings were 10 days old, parental feeding rates and nestling begging intensity were measured with tape recorders. At 13 days of age, nestlings were weighed and measured. Within 2 days of fledging, nest material was removed from nest boxes and enumerated for adult fleas and blow fly pupae. After including brood size and date of first egg as covariates in general linear models, no significant relationships were found between ectoparasite loads and nestling size, parental feeding rate, or nestling begging intensity. Our results suggest that nestling tree swallows were able to buffer the effects of naturally occurring ectoparasite loads without significant help from their parents. Low levels of virulence may have resulted from relatively benign weather during the study, low numbers of ectoparasites, selection on ectoparasites to avoid killing their hosts, and host defences.