Northward invasion of the parasitic deer ked ( Lipoptena cervi), is there geographical variation in pupal size and development duration?

The deer ked (Lipoptena cervi) is a common ectoparasite of cervids. During the last decades the species has rapidly invaded in northern Europe, especially in Finland, towards the north and increased its prevalence on the moose population. Consequently, during this rapid invasion the deer ked has faced more severe climatic conditions. We studied whether pupal size (measured as pupal weight) and pupal development duration of the deer ked varies along historical invasion zones and temperature zones towards north in Finland. Moreover, we explored possible size- and gender-dependent variation in pupal development duration. We divided wild-collected pupae in respect to their origin in two ways: (1) temperature zones (from south-west to colder north-east) and (2) invasion history (from early to late establishment). We reared pupae in the controlled laboratory conditions in identical temperature and light conditions. Pupal size decreased towards north and the smaller pupae developed faster. However, the results do not show differences in pupal size or developmental characteristics between the invasion zones. This supports the idea of rapid developmental plasticity of the deer ked and that not the invasion history but the current temperature regime determines the life history of the deer ked when invading towards a colder environment.     

Host‐specific variation in off‐host performance of a temperate ectoparasite

Antagonistic host–parasite interactions are rarely considered from an ecological perspective of the parasite. We used a blood‐feeding ectoparasite of boreal cervids, the deer ked (Lipoptena cervi L., Hippoboscidae), to study host‐dependent variation in a parasite's ability to cope with an abiotic environment during the free‐living stage(s) in two allopatric Fennoscandian populations. We found that a strongly host‐specific deer ked population in eastern Fennoscandia, exploiting only moose (Alces alces), produced the largest offspring that were the most cold‐tolerant and emerged the earliest as adults, when compared with the western Fennoscandian population that exploited two hosts efficiently. Within the western population, however, offspring produced on roe deer (Capreolus capreolus) were significantly larger, more cold‐tolerant, and had higher survival than those produced on moose in the same area. We discuss potential causes for both host‐specific and geographical differences in off‐host performance: (1) maternal host directly affects the offspring survival prospects; (2) divergent co‐evolution with local main host(s) has shaped the parasite's life history; and/or (3) off‐host performance is shaped by adaptation to the local abiotic environment. In conclusion, this study increases our understanding of the evolution of host–parasite interactions by demonstrating how geographical differences in host exploitation may result in differences in survival prospects outside the host.     

Freezing tolerance and low molecular weight cryoprotectants in an invasive parasitic fly, the deer ked (Lipoptena cervi)

Insect cold hardiness is often mediated by low molecular weight cryoprotectants, such as sugars, polyols, and amino acids (AA). While many free-living northern insects must cope with extended periods of freezing ambient temperatures (Ta), the ectoparasitic deer ked Lipoptena cervi imago can encounter subfreezing Ta only during a short autumnal period between hatching and host location. Subsequently, it benefits from the body temperature of the cervid host for survival in winter. This study investigated the cold tolerance of the species by determining its lower lethal temperature (100% mortality, LLT100) during faster and slower cold acclimation, by determining the supercooling point (SCP) and by measuring the concentrations of potential low molecular weight cryoprotectants. The LLT100 of the deer ked was approximately -16 ° C, which would enable it to survive freezing nighttime Ta not only in its current area of distribution but also further north. The SCP was -7.8 ° C, clearly higher than the LLT100 , indicating that the deer ked displays freezing tolerance. The concentrations of free AA, especially nonessential AA, were higher in the cold-acclimated deer keds similar to several other insects. The concentrations of proline increased together with γ-aminobutyrate, arginine, asparagine, cystine, glutamate, glutamine, hydroxylysine, sarcosine, serine, and taurine. AA could be hypothesized to act as cryoprotectants by, e.g., protecting enzymes and lipid membranes from damage caused by cold.     

Parasitism of the deer ked,Lipoptena cervi,on the moose,Alces alces,in eastern Finland

The deer ked, Lipoptena cervi L. (Diptera: Hippoboscidae), is an ectoparasitic fly that spread to Finland in the early 1960s from the southeast across the Soviet border. It is currently a common parasite of the moose, Alces alces (Artiodactyla: Cervidae), in the southern part of the country and its area of distribution is gradually spreading to Finnish Lapland, where it will come into contact with another potential cervid host, the semi‐domesticated reindeer, Rangifer tarandus tarandus. The aim of this study was to determine the intensity of deer ked parasitism on the moose in eastern Finland. Whole skins of 23 moose were examined for the presence of deer keds, which were extracted and their total numbers estimated. The intensity of deer ked parasitism was correlated to the age, sex, skin area and anatomical region of the host. Bulls had the highest total number of keds (10616 ± 1375) and the highest deer ked density (35.7 ± 4.4 keds/dm² of skin). Cows had a higher total number of keds than calves (3549 ± 587 vs. 1730 ± 191), but ked densities on cows and calves were roughly equal (11.8 ± 1.7 vs. 9.4 ± 1.1 keds/dm² of skin). The density of keds was highest on the anterior back, followed by the posterior back, front limbs, abdomen, head and hind limbs. The sex ratio of deer keds was close to equal (male : female, 1.0 : 1.1). After they had consumed blood, male keds were heavier than females. As the total numbers and densities of deer keds were higher than reported previously on moose or for any other louse fly species, the effects of parasitism on the health of the host species should be determined.     

Geographical variation in host use of a blood-feeding ectoparasitic fly: implications for population invasiveness

Invasive generalist ectoparasites provide a tool to study factors affecting expansion rates. An increase in the number of host species may facilitate geographic range expansion by increasing the number of suitable habitats and by affecting local extinction and colonization rates. A geographic perspective on parasite host specificity and its implications on range expansion are, however, insufficiently understood. We conducted a field study to explore if divergent host specificity could explain the observed variation in expansion rates between Fennoscandian populations of the deer ked (Lipoptena cervi), which is a blood-feeding ectoparasitic fly of cervids. We found that the rapidly expanding eastern population in Finland appears to specialize on moose, whereas the slowly expanding western population in Norway breeds successfully on both moose and roe deer. The eastern population was also found to utilize the wild forest reindeer as an auxiliary host, but this species is apparently of low value for L. cervi in terms of adult maintenance, reproductive output and offspring quality. Abundant numbers of roe deer and white-tailed deer were observed to be apparently uninfected in Finland, suggesting that host use is not a plastic response to host availability, but rather a consequence of population-level evolutionary changes. Locally compatible hosts were found to be the ones sharing a long history with the deer ked in the area. Cervids that sustained adult deer keds also allowed successful reproduction. Thus, host use is probably determined by the ability of the adult to exploit particular host species. We conclude that a wide host range alone does not account for the high expansion rate or wide geographic distribution of the deer ked, although loose ecological requirements would increase habitat availability.     

Quantitative genetic approach for assessing invasiveness: geographic and genetic variation in life-history traits

Predicting the spread of invasive species is a challenge for modern ecology. Although many invasive species undergo genetic bottlenecks during introduction to new areas resulting in a loss of genetic diversity, successful invaders manage to flourish in novel environments either because of pre-adaptations or because important traits contain adaptive variation enabling rapid adaptation to changing conditions. To predict and understand invasion success, it is crucial to analyse these features. We assessed the potential of a well-known invader, the Colorado potato beetle (Leptinotarsa decemlineata), to expand north of its current range in Europe. A short growing season and harsh overwintering conditions are apparent limiting factors for this species’ range. By rearing full-sib families from four geographically distinct populations (Russia, Estonia, Poland, Italy) at two fluctuating temperature regimes, we investigated (a) possible differences in survival, development time, and body size among populations and (b) the amount of adaptive variation within populations in these traits. All populations were able to complete their development in cooler conditions than in their current range. A significant genotype–environment interaction for development time and body size suggests the presence of adaptive genetic variation, indicating potential to adapt to cooler conditions. The northernmost population had the highest survival rates and fastest development times on both temperature regimes, suggesting pre-adaptation to cooler temperatures. Other populations had minor differences in development times. Interestingly, this species lacks the classical trade-off between body size and development time which could have contributed to its invasion potential. This study demonstrates the importance of considering both ecological and evolutionary aspects when assessing invasion risk.     

Genetic variation in growth and development time under two selection regimes in Leptinotarsa decemlineata

It is possible to predict the potential range of a species on the basis of its ecological characteristics and those of the invaded ecosystem. The existence of genetic variation indicates a species’ potential to respond to new environmental conditions, thus facilitating its success as an invader. Accordingly, evolutionary and ecological approaches are needed to identify the factors explaining both species’ range and their potential to invade new areas. We combined these two approaches and studied whether genetic variation in life‐history traits under abiotic (temperature) and biotic (host plant) selection pressures contributes to the potential range expansion of Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae). We reared full‐sib families of L. decemlineata from the current northernmost European population at 15 °C (temperature below that in the current range) and 25 °C (optimal temperature) and on three potato varieties. We monitored development time, adult weight and larval‐to‐adult survival, and estimated the amount of heritable variance. The development time and adult weight of progenies were more variable between than within families. Thus, there was genetic variability in traits relevant to the ability to adapt to a colder environment (i.e., accelerate development and become heavier) allowing range expansion further north in Europe, even though low temperature increased beetle mortality. Temperature strongly affected all traits measured. Potato variety, in turn, did not strongly affect beetles’ performance. Beetle ability to adapt to a cool environment was further enhanced by the fact that size was not constrained by fast development. The results showed that beetle populations possess genetic variation allowing a response to temperature and thus have the evolutionary potential to adapt and spread beyond their current range.     

Salt licks do not increase local densities of the deer ked,Lipoptena cervi,an abundant ectoparasite of cervids

The deer ked, Lipoptena cervi (Diptera: Hippoboscidae), is a common ectoparasite of the moose, Alces alces (Artiodactyla: Cervidae). Salt licks are widely used to manipulate moose movements to prevent damage to saplings and traffic accidents. They may cause moose to gather in small areas, which could create aggregates of deer ked pupae as the parasite is a short‐distance flyer and its dispersion depends on its hosts. We investigated whether the population density of flying deer keds could be influenced by manipulating salt licks and how environmental variables affect parasite density. Densities were estimated in 40 experimental sites with four treatments (no salt licks, introduced salt licks, removed salt licks, permanent salt licks) in September during 2007–2010. Forest edges, mixed forests on mineral soil and coniferous forests on peat soil were the habitats with high numbers of parasites. The manipulation of salt licks seemed to be ineffective in reducing the density of deer keds as the only factor to show statistical significance with parasite numbers in the mixed‐model analysis was year of determination. Annual deer ked densities correlated with the abundance of moose in the region. Moreover, high spring and summer temperatures seemed to increase the numbers of flying imagos.     

Anisotropic spread of hemlock woolly adelgid in the eastern United States

Simple population models predict that the spread of an invading species through a homogenous habitat should be equal in all directions, but geographic variation in the habitat that affects either reproduction or movement could result in variable rates of spread. We analyse records of the historical range expansion of the hemlock woolly adelgid (HWA) (Adelges tsugae Annand) in the eastern United States from 1951 to 2006 to document that this species has spread in an anisotropic fashion. Furthermore, the magnitude and direction of this anisotropy has varied through time. We explore the extent to which this spatial and temporal variation in spread can be explained by geographical variation in climate and by the abundance of hosts, eastern hemlock (Tsuga canadensis L.) and Carolina hemlock (Tsuga caroliniana Engelm.). We found that a significant component of the spatial anisotropy in HWA spread rate can be explained by the geographical distribution of host trees. January temperatures were negatively associated with spread rates but this may be an artifact of the association between hemlock and cold climates. The current distribution of the adelgid in eastern N. America may be approaching the extent of its potential range to the south and west determined by availability of host hemlock and to the north determined by lethal cold winter temperatures.     

Detection of Lyme disease and anaplasmosis pathogens via PCR in Pennsylvania deer ked

Borrelia burgdorferi and Anaplasma phagocytophilum are obligate intracellular parasites that maintain their life cycles in enzoonotic vector‐host cycles with Ixodes scapularis as a vector. In addition to ticks, the hosts are commonly infested with insects from the Hippoboscidae family. This study confirms the presence of B. burgdorferi and A. phagocytophilum in deer keds (Lipoptena cervi) removed from white‐tailed deer using PCR. Detection of these pathogens in deer ked represents a potential novel susceptibility of wildlife and also suggests the risk of transmission of these pathogens to humans and animals alike through the bite of an infected ectoparasite. This study represents the first instance in the U.S. of detection of tick‐borne pathogens in a member of the Hippoboscid family.     

Morphological variation between populations of the expanding ectoparasitic deer ked Lipoptena cervi (Diptera: Hippoboscidae) in Fennoscandia

We examined morphological and genetic differences among Fennoscandian deer ked (Lipoptena cervi L, Hippoboscidae) populations with varying expansion history: the eastern population (Finland) has expanded rapidly, whereas the western population is divided into an old and relatively stationary sub‐population in Sweden and a newly established and more expansive sub‐population in Norway. The genetic analysis suggests that the distinct populations represent a single species. Individuals from expansive populations were characterized by a large body size, relatively large and robust thorax shape, and wing shape with an exaggerated basal posterior margin. Yet, there was no among population variation in relative wing size or its elongated shape after variation in overall size was controlled for. Although certain size and shape variables showed thermal sensitivity, the degree of plasticity did not differ between the populations. In general, we observed that shape is more sensitive to external thermal conditions at the pupal stage than size per se, with the thermal sensitivity of the latter depending on the trait under examination. We conclude that the possible adaptive value of morphological differences relies on variation in survival during the off‐host life stages or short‐distance flight to reach a susceptible host instead of long‐distance dispersal ability.     

Climate change is the primary driver of white‐tailed deer (Odocoileus virginianus) range expansion at the northern extent of its range; land use is secondary

Quantifying the relative influence of multiple mechanisms driving recent range expansion of non‐native species is essential for predicting future changes and for informing adaptation and management plans to protect native species. White‐tailed deer (Odocoileus virginianus) have been expanding their range into the North American boreal forest over the last half of the 20th century. This has already altered predator–prey dynamics in Alberta, Canada, where the distribution likely reaches the northern extent of its continuous range. Although current white‐tailed deer distribution is explained by both climate and human land use, the influence each factor had on the observed range expansion would depend on the spatial and temporal pattern of these changes. Our objective was to quantify the relative importance of land use and climate change as drivers of white‐tailed deer range expansion and to predict decadal changes in white‐tailed deer distribution in northern Alberta for the first half of the 21st century. An existing species distribution model was used to predict past decadal distributions of white‐tailed deer which were validated using independent data. The effects of climate and land use change were isolated by comparing predictions under theoretical “no‐change between decades” scenarios, for each factor, to predictions under observed climate and land use change. Climate changes led to more than 88%, by area, of the increases in probability of white‐tailed deer presence across all decades. The distribution is predicted to extend 100 km further north across the northeastern Alberta boreal forest as climate continues to change over the first half of the 21st century.     

Host use patterns of Culicoides spp. biting midges at a big game preserve in Florida,U.S.A., and implications for the transmission of orbiviruses

Culicoides spp. biting midges (Diptera: Ceratopogonidae) are vectors of pathogens that have a significant economic impact on the livestock industry. White‐tailed deer (Odocoileus virginianus), a farmed species in the U.S.A., are susceptible to two Culicoides spp. borne orbiviruses: bluetongue virus and epizootic haemorrhagic disease virus. Elucidating host–vector interactions is an integral step in studying disease transmission. This study investigated the host range of Culicoides spp. present on a big game preserve in Florida on which a variety of Cervidae and Bovidae freely roam. Culicoides were captured with Centers for Disease Control and Prevention (CDC) miniature light traps run twice weekly on the preserve for 18 consecutive months (July 2015–December 2016). Host preference was quantified through forage ratios, based upon PCR‐based bloodmeal analysis of Culicoides spp. and overall animal relative abundance on the preserve. Culicoides stellifer preferentially fed on Cervus spp. and fallow deer (Dama dama) and displayed a relative avoidance of Bovidae and white‐tailed deer. Culicoides debilipalpis preferred white‐tailed deer and avoided all Bovidae. Culicoides pallidicornis and Culicoides biguttatus showed preferences for white‐tailed deer and Père David's deer (Elaphurus davidianus), respectively. These results add to current knowledge of preferred hosts of Florida Culicoides spp. and have implications for the spread of orbiviruses. Copyright © 2018 John Wiley & Sons, Ltd.     

Unexpected population genetic structure of European roe deer in Poland: an invasion of the mtDNA genome from Siberian roe deer

Introgressive hybridization is a widespread evolutionary phenomenon which may lead to increased allelic variation at selective neutral loci and to transfer of fitness‐related traits to introgressed lineages. We inferred the population genetic structure of the European roe deer (Capreolus capreolus) in Poland from mitochondrial (CR and cyt b) and sex‐linked markers (ZFX, SRY, DBY4 and DBY8). Analyses of CR mtDNA sequences from 452 individuals indicated widespread introgression of Siberian roe deer (C. pygargus) mtDNA in the European roe deer genome, 2000 km from the current distribution range of C. pygargus. Introgressed individuals constituted 16.6% of the deer studied. Nearly 75% of them possessed haplotypes belonging to the group which arose 23 kyr ago and have not been detected within the natural range of Siberian roe deer, indicating that majority of present introgression has ancient origin. Unlike the mtDNA results, sex‐specific markers did not show signs of introgression. Species distribution modelling analyses suggested that C. pygargus could have extended its range as far west as Central Europe after last glacial maximum. The main hybridization event was probably associated with range expansion of the most abundant European roe deer lineage from western refugia and took place in Central Europe after the Younger Dryas (10.8–10.0 ka BP). Initially, introgressed mtDNA variants could have spread out on the wave of expansion through the mechanism of gene surfing, reaching high frequencies in European roe deer populations and leading to observed asymmetrical gene flow. Human‐mediated introductions of C. pygargus had minimal effect on the extent of mtDNA introgression.     

Bartonella Infections in Deer Keds (Lipoptena cervi) and Moose (Alces alces) in Norway

Infections with Bartonella spp. have been recognized as emerging zoonotic diseases in humans. Large knowledge gaps exist, however, relating to reservoirs, vectors, and transmission of these bacteria. We describe identification by culture, PCR, and housekeeping gene sequencing of Bartonella spp. in fed, wingless deer keds (Lipoptena cervi), deer ked pupae, and blood samples collected from moose, Alces alces, sampled within the deer ked distribution range in Norway. Direct sequencing from moose blood sampled in a deer ked-free area also indicated Bartonella infection but at a much lower prevalence. The sequencing data suggested the presence of mixed infections involving two species of Bartonella within the deer ked range, while moose outside the range appeared to be infected with a single species. Bartonella were not detected or cultured from unfed winged deer keds. The results may indicate that long-term bacteremia in the moose represents a reservoir of infection and that L. cervi acts as a vector for the spread of infection of Bartonella spp. Further research is needed to evaluate the role of L. cervi in the transmission of Bartonella to animals and humans and the possible pathogenicity of these bacteria for humans and animals.     

Thirty‐four polymorphic microsatellites for European roe deer

The European roe deer (Capreolus capreolus) is an interesting model for molecular ecology studies because of its abundance and adaptability across a range of environments (including human‐modified habitats), and because of its increasing impacts on agricultural crops and on regenerating forests. We identify polymorphic microsatellites in two managed populations of roe deer in France by using cross‐species amplification of primers from other Cervids and from Bovids. Of the 62 primer pairs tested, 45 amplified microsatellites in roe deer, and 34 were polymorphic. Eleven primer pairs were selected for multiplex gel‐loading for routine genotyping of the studied populations.     

Breach of the northern Rocky Mountain geoclimatic barrier: initiation of range expansion by the mountain pine beetle

Aim Our aim is to examine the historical breach of the geoclimatic barrier of the Rocky Mountains by the mountain pine beetle (Dendroctonus ponderosae Hopkins). This recent range expansion from west of the North American continental divide into the eastern boreal forest threatens to provide a conduit to naïve pine hosts in eastern North America. We examine the initial expansion events and determine potential mechanism(s) of spread by comparing spread patterns in consecutive years to various dispersal hypotheses such as: (1) meso‐scale atmospheric dispersal of insects from source populations south‐west of the Rocky Mountains in British Columbia (i.e. their historical range), (2) anthropogenic transport of infested plant material, and (3) spread of insect populations across adjacent stands via corridors of suitable habitat. Location British Columbia, Canada. Methods We explore potential mechanism(s) of invasion of the mountain pine beetle using spatial point process models for the initial 3 years of landscape‐level data collection, 2004–2006. Specifically, we examine observed patterns of infestation relative to covariates reflecting various dispersal hypotheses. We select the most parsimonious models for each of the initial 3 years of invasion using information criteria statistics. Results The initial range expansion and invasion of the beetle was characterized by aerial deposition along a strong north‐west to south‐east gradient, with additional aerial deposition and localized dispersal from persisting populations in following years. Main conclusions Following deposition of a wave front of mountain pine beetles parallel to the Rocky Mountains via meso‐scale atmospheric dispersal, the areas of highest intensity of infestations advanced up to 25 km north‐east towards jack pine (Pinus banksiana) habitat in a single year. There appeared to be no association between putative anthropogenic movement of infested materials and initial range expansion of the mountain pine beetle across the continental divide.     

Effects of temperature on the development,performance and fitness of the corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae): implications on its distribution under climate change

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Role of larval host plants in the climate-driven range expansion of the butterfly Polygonia c-album

1. Some species have expanded their ranges during recent climate warming and the availability of breeding habitat and species' dispersal ability are two important factors determining expansions. The exploitation of a wide range of larval host plants should increase an herbivorous insect species' ability to track climate by increasing habitat availability. Therefore we investigated whether the performance of a species on different host plants changed towards its range boundary, and under warmer temperatures. 2. We studied the polyphagous butterfly Polygonia c-album, which is currently expanding its range in Britain and apparently has altered its host plant preference from Humulus lupulus to include other hosts (particularly Ulmus glabra and Urtica dioica). We investigated insect performance (development time, larval growth rate, adult size, survival) and adult flight morphology on these host plants under four rearing temperatures (18-28.5 degrees C) in populations from core and range margin sites. 3. In general, differences between core and margin populations were small compared with effects of rearing temperature and host plant. In terms of insect performance, host plants were generally ranked U. glabra > or = U. dioica > H. lupulus at all temperatures. Adult P. c-album can either enter diapause or develop directly and higher temperatures resulted in more directly developing adults, but lower survival rates (particularly on the original host H. lupulus) and smaller adult size. 4. Adult flight morphology of wild-caught individuals from range margin populations appeared to be related to increased dispersal potential relative to core populations. However, there was no difference in laboratory reared individuals, and conflicting results were obtained for different measures of flight morphology in relation to larval host plant and temperature effects, making conclusions about dispersal potential difficult. 5. Current range expansion of P. c-album is associated with the exploitation of more widespread host plants on which performance is improved. This study demonstrates how polyphagy may enhance the ability of species to track climate change. Our findings suggest that observed differences in climate-driven range shifts of generalist vs. specialist species may increase in the future and are likely to lead to greatly altered community composition.     

Winter survival of Ceramica pisi (Lepidoptera: Noctuidae) in Iceland

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