Open Access Publications

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Open access publications by faculty, staff, postdocs, and graduate students in the Department of Entomology and Wildlife Ecology.

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Moths are less attracted to light traps than they used to be
(Journal of Insect Conservation, 2024-04-19) Battles, Ian; Burkness, Eric; Crossley, Michael S.; Edwards, Collin B.; Holmstrom, Kristian; Hutchison, William; Ingerson-Mahar, Joseph; Owens, David; Owens, Avalon C.S.
As evidence of global insect declines continues to mount, insect conservationists are becoming increasingly interested in modeling the demographic history of at-risk species from long-term survey data. However, certain entomological survey methods may be susceptible to temporal biases that will complicate these efforts. Entomological light traps, in particular, may catch fewer insects today than they once did due solely to increases in anthropogenic light pollution. Here we investigate this possibility by comparing the demographic histories of corn earworm moths (Helicoverpa zea) estimated from pairs of blacklight and pheromone traps monitored at the same farms. We find a stark decline in blacklight trap efficacy over 25 years of monitoring in Delaware, USA, mirrored over 10 years of monitoring in New Jersey, USA. While the precise causes of this decline remain a subject for discussion, the practical consequences are clear: insect conservationists cannot fully rely on long-term trends from entomological light traps.
Diversity and host specificity of Borrelia burgdorferi’s outer surface protein C (ospC) alleles in synanthropic mammals, with a notable ospC allele U absence from mixed infections
(Infection and Immunity, 2023-12-15) Shifflett, Scarlet A.; Ferreira, Francisco C.; González, Julia; Toledo, Alvaro; Fonseca, Dina M.; Ellis, Vincenzo A.
Interactions among pathogen genotypes that vary in host specificity may affect overall transmission dynamics in multi-host systems. Borrelia burgdorferi, a bacterium that causes Lyme disease, is typically transmitted among wildlife by Ixodes ticks. Despite the existence of many alleles of B. burgdorferi’s sensu stricto outer surface protein C (ospC) gene, most human infections are caused by a small number of ospC alleles [“human infectious alleles” (HIAs)], suggesting variation in host specificity associated with ospC. To characterize the wildlife host association of B. burgdorferi’s ospC alleles, we used metagenomics to sequence ospC alleles from 68 infected individuals belonging to eight mammalian species trapped at three sites in suburban New Brunswick, New Jersey (USA). We found that multiple allele (“mixed”) infections were common. HIAs were most common in mice (Peromyscus spp.) and only one HIA was detected at a site where mice were rarely captured. ospC allele U was exclusively found in chipmunks (Tamias striatus), and although a significant number of different alleles were observed in chipmunks, including HIAs, allele U never co-occurred with other alleles in mixed infections. Our results suggest that allele U may be excluding other alleles, thereby reducing the capacity of chipmunks to act as reservoirs for HIAs.
Biology and Management of Lesser Mealworm Alphitobius diaperinus (Coleoptera: Tenebrionidae) in Broiler Houses
(Journal of Integrated Pest Management, 2023-01-30) Sammarco, Ben C.; Hinkle, Nancy C.; Crossley, Michael S.
Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), the lesser mealworm, is a ubiquitous generalist  pest of poultry broiler and layer facilities, originating in southern Africa and now found worldwide. They spend their full life cycle within the litter and manure of poultry, causing structural damage to poultry houses, injuring birds, and acting as a reservoir for several avian pathogens, notably Salmonella spp. and Escherichia coli. Management commonly consists of spraying walls and floors of poultry houses with organophosphates, pyrethroids, neonicotinoids, or spinosyns between flocks, and periodic removal and replacement of litter. Populations have been observed to become resistant to specific insecticides after ca. 10 yr of consistent use and exhibit cross resistance to insecticides of the same mode of action. Alternative cultural and biological control methods have been identified but are not currently implemented. More research is needed regarding the economic impact of A. diaperinus, the mechanisms of its insecticide resistance, and patterns and mechanisms of colonization for effective integrated pest management programs to be devised and implemented.
Artificial light at night is a top predictor of bird migration stopover density
(Nature Communications, 2023-12-04) Horton, Kyle G.; Buler, Jeffrey J.; Anderson, Sharolyn J.; Burt, Carolyn S.; Collins, Amy C.; Dokter, Adriaan M.; Guo, Fengyi; Sheldon, Daniel; Tomaszewska, Monika Anna; Henebry, Geoffrey M.
As billions of nocturnal avian migrants traverse North America, twice a year they must contend with landscape changes driven by natural and anthropogenic forces, including the rapid growth of the artificial glow of the night sky. While airspaces facilitate migrant passage, terrestrial landscapes serve as essential areas to restore energy reserves and often act as refugia—making it critical to holistically identify stopover locations and understand drivers of use. Here, we leverage over 10 million remote sensing observations to develop seasonal contiguous United States layers of bird migrant stopover density. In over 70% of our models, we identify skyglow as a highly influential and consistently positive predictor of bird migration stopover density across the United States. This finding points to the potential of an expanding threat to avian migrants: peri-urban illuminated areas may act as ecological traps at macroscales that increase the mortality of birds during migration.
Seasonal patterns and protection status of stopover hotspots for migratory landbirds in the eastern United States
(Current Biology, 2024-01-22) Guo, Fengyi; Buler, Jeffrey J.; Smolinsky, Jaclyn A.; Wilcove, David S.
Summary Migratory landbirds in North America are experiencing dramatic population declines. Although considerable research and conservation attention have been directed toward these birds’ breeding and wintering grounds, far less is known about the areas used as stopover sites during migration. To address this knowledge gap, we used 5 years of weather surveillance radar data to map seasonal stopover densities of landbirds across the eastern United States during spring and autumn migration. We identified stopover hotspots covering 2.47 million ha that consistently support high densities of migratory landbirds in spring or autumn. However, only 16.7% of these sites are hotspots in both seasons. The distribution of hotspots is shifted eastward in autumn compared with spring. Deciduous forest is the most important habitat type in both seasons, with deciduous forest fragments embedded in broadly deforested regions having the highest probability of being hotspots. The concentration of birds in these forest fragments is stronger in spring, especially in the agricultural Midwest. We found generally higher stopover densities in protected areas than in unprotected areas in both seasons. Nonetheless, only one-third of identified stopover hotspots have some sort of protected status, and more than half of these protected hotspots are subject to extractive uses. A well-distributed network of well-protected stopover areas, complementing conservation efforts on the breeding and wintering grounds, is essential to sustaining healthy populations of migratory landbirds in North America.
New extralimital breeding records of saltmarsh sparrows (Ammospiza caudacuta) and Nelson's sparrows (Ammospiza nelsoni) and their implications
(Ecology and Evolution, 2023-09-19) Ruskin, Katharine J.; Clark, Jonathan D.; Hotopp, Alice; Kovach, Adrienne I.; Guido, Nicole A.; Hernandez, Dean L.; Peña, Colin; Webb, Samantha N.; Shriver, W. Gregory
Saltmarsh (Ammospiza caudacuta) and Nelson's (A. nelsoni) sparrows are sister taxa that breed in tidal marshes along the coast of the Northeastern United States and Canada. The Saltmarsh Sparrow breeds from mid-coast Maine south to Virginia, while the Acadian Nelson's Sparrow breeds from the Canadian maritime provinces south to northern Massachusetts. Here, we present three extralimital observations of breeding Saltmarsh (n = 2) and Nelson's (n = 1) sparrows. In 2021 and 2022, we observed Saltmarsh Sparrow females attending nests at Mendall Marsh, ME, and Milbridge, ME, respectively, approximately 60 and 110 km beyond the documented northern extent of the Saltmarsh Sparrow breeding range. In 2022, we observed a breeding-condition male Nelson's sparrow singing in the upriver portion of a marsh on Cape Cod, Massachusetts, approximately 115 km beyond the previously documented southern extent of the Nelson's Sparrow breeding range. We confirmed morphological species identification using a panel of microsatellite DNA loci. Due to both the well-documented population declines of these species in the region and the intensity of sampling effort undertaken in recent years, we suggest that these observations likely are not indicative of range expansion. However, they do indicate that these 2 taxa have the capacity to use and successfully reproduce in marshes well beyond their established breeding limits. Our findings provide novel insight into the potential for these taxa to occur and successfully breed outside their documented breeding ranges. Given increased interest in their conservation, these results support the idea that management actions aimed at creating or maintaining nesting habitat across both species ranges could benefit both taxa.
A Review of the Planthoppers (Hemiptera: Fulgoroidea) of the United States: Supplement 1
(Transactions of the American Entomological Society, 2023-04-28) Bartlett, Charles R.; Wilson, Stephen W.
Here we review changes to the planthopper (Hemiptera: Fulgoroidea) fauna north of Mexico since the publication of “A review of the planthoppers (Hemiptera: Fulgoroidea) of the United States” (Bartlett et al. 2014). There are 12 species in 4 families added to the fauna and 50 changes in the generic assignment in 4 families. The most significant faunal addition is the spotted lanternfly (Lycorma delicatula (White)), with populations reported in 14 states and vagrants in 3 more. We review some nomenclatural and taxonomic issues and provide a list of anomalous records that may represent unreported or undescribed species that require further investigation. All told, these additions and changes (excluding anomalous records) give totals of 175 genera and 924 species in 13 families of planthoppers, a net addition of 1 family, 8 genera, and 10 species to the tally provided in 2014.
A high-quality de novo genome assembly for clapper rail (Rallus crepitans)
(G3 Genes|Genomes|Genetics, 2023-05-02) Elizondo, Elisa C.; Faircloth, Brant C.; Brumfield, Robb T.; Shakya, Subir B.; Ellis, Vincenzo A.; Schmidt, Carl J.; Kovach, Adrienne I.; Shriver, W. Gregory
The clapper rail (Rallus crepitans), of the family Rallidae, is a secretive marsh bird species that is adapted for high salinity habitats. They are very similar in appearance to the closely related king rail (R. elegans), but while king rails are limited primarily to freshwater marshes, clapper rails are highly adapted to tolerate salt marshes. Both species can be found in brackish marshes where they freely hybridize, but the distribution of their respective habitats precludes the formation of a continuous hybrid zone and secondary contact can occur repeatedly. This system, thus, provides unique opportunities to investigate the underlying mechanisms driving their differential salinity tolerance as well as the maintenance of the species boundary between the 2 species. To facilitate these studies, we assembled a de novo reference genome assembly for a female clapper rail. Chicago and HiC libraries were prepared as input for the Dovetail HiRise pipeline to scaffold the genome. The pipeline, however, did not recover the Z chromosome so a custom script was used to assemble the Z chromosome. We generated a near chromosome level assembly with a total length of 994.8 Mb comprising 13,226 scaffolds. The assembly had a scaffold N50 was 82.7 Mb, L50 of four, and had a BUSCO completeness score of 92%. This assembly is among the most contiguous genomes among the species in the family Rallidae. It will serve as an important tool in future studies on avian salinity tolerance, interspecific hybridization, and speciation.
Relating weather radar data to migrating waterfowl abundance in the Rainwater Basin of Nebraska
(The Journal of Wildlife Management, 2023-06-01) Liu, Boyan; Kemink, Kaylan; Sieges, Mason; Smolinsky, Jaclyn; Varner, Dana; Buler, Jeffrey
Waterfowl migrations are large-scale events that involve millions of birds moving over broad geographic extents, which make them difficult to quantify and study. Historically, wildlife managers have relied mostly on field surveys, such as visual counts from the ground or air that sample at small spatial or temporal extents, or both. Combining field surveys with remote sensing data comprehensively collected over large spatial extents at high temporal frequency may improve the study of migrating waterfowl distributions. We tested the strength of the relationship between broad-scale weather surveillance radar data and fine-scale field surveys of waterfowl abundance at wetlands within the Rainwater Basin of Nebraska, USA, from 2017–2019. Radar reflectivity of waterfowl at the peak exodus of evening flights was positively correlated with diurnal waterfowl count data, although there was unexplained variation in the relationship. The association was also very similar across various time scales ranging from daily to monthly averages of waterfowl abundance. We suggest that human-based ground surveys can calibrate and leverage more comprehensive remote sensing data to get a broad understanding of waterfowl distributions during migration. Several confounding factors, such as spatial displacement between radar and survey observation, individual variation in orientation and body size, and identification of avian species sampled by radar, remain on the path to improving radar-based waterfowl estimates.
Autumn stopover hotspots and multiscale habitat associations of migratory landbirds in the eastern United States
(Proceedings of the National Academy of Sciences, 2023-01-09) Guo, Fengyi; Buler, Jeffrey J.; Smolinsky, Jaclyn A.; Wilcove, David S.
Significance: Understanding the en route habitat requirements of migratory birds is critical for conservation but difficult to know at a large scale. We mapped stopover density of landbirds during autumn migration for the eastern United States using radar data. At a coarse scale, we found that birds migrate across a relatively broad front, underscoring the importance of widespread, locally based conservation efforts. At finer scales, we identified stopover hotspots that consistently support high densities of migrants. We demonstrate that forests provide the most important habitats for autumn migrants and that deciduous forest fragments in heavily deforested regions support especially high densities of migrants. We also present evidence that the now-agriculture-dominated Midwest constitutes an inland migration barrier for forest birds. Abstract: Halting the global decline of migratory birds requires a better understanding of migration ecology. Stopover sites are a crucial yet understudied aspect of bird conservation, mostly due to challenges associated with understanding broad-scale patterns of transient habitat use. Here, we use a national network of weather radar stations to identify stopover hotspots and assess multiscale habitat associations of migratory landbirds across the eastern United States during autumn migration. We mapped seasonal bird densities over 5 y (2015 to 2019) from 60 radar stations covering 63.2 million hectares. At a coarse scale, we found that landbirds migrate across a broad front with small differences in migrant density between radar domains. However, relatively more birds concentrate along the Mississippi River and Appalachian Mountains. At a finer scale, we identified radar pixels that consistently harbored high densities of migrants for all 5 y, which we classify as stopover hotspots. Hotspot probability increased with percent cover of all forest types and decreased with percent cover of pasture and cultivated crops. Moreover, we found strong concentrating effects of deciduous forest patches within deforested regions. We also found that the prairie biome in the Midwest (now mostly cropland) is likely a migration barrier, with large concentrations of migrants at the prairie–forest boundary after crossing the agricultural Midwest. Overall, the broad-front migration pattern highlights the importance of locally based conservation efforts to protect stopover habitats. Such efforts should target forests, especially deciduous forests in highly altered landscapes. These findings demonstrate the value of multiscale habitat assessments for the conservation of migratory landbirds.
Impact of heat waves on egg survival and biological performance across life stages in the Asian corn borer
(Entomologia Experimentalis et Applicata, 2023-01-02) Quan, Yudong; Mason, Charles E.; He, Kanglai; Wang, Zhenying; Wei, Hongyi
One of the many extreme events as a result of climate change is the frequent appearance of extraordinarily daily high temperatures that can directly drive an insect's adaptive response. Insects have complex life cycles that may uncouple temperature's effects in one stage from the physiology in the next. In this study we focused on the Asian corn borer (ACB), Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae), one of the most important pests of maize (corn) in Asia, investigated the consequences of eggs exposed to ecologically relevant heat shock regimes, simulating heat waves at extreme high temperature. This consisted of five 90-min heat treatments separated by two degrees that ranged from 37 to 45°C for three consecutive days compared to a constant temperature of 25°C. Temperature that triggered mortality was between 39 and 41°C. Egg hatching significantly declined when temperature was 41°C or higher. There was no egg hatching at 45°C. Developmental times were significantly prolonged and the larval growth rate became slower in treatments of 41 and 43°C. There were no significant differences in pupal mass, fecundity, and sex ratio among treatments. Life table parameters showed significant adverse effects at treatments of 41 and 43°C. Depending on the fitness response of the ACB, environmental heat waves can be classified into three categories based on temperature criteria, i.e., adaptable (35–39°C), critical (39–45°C), and fatal (≥45°C). The findings of the present study will serve as an important reference for forecasting the population dynamics of the ACB.
First record of the family Issidae (Hemiptera, Auchenorrhyncha, Fulgoroidea) from the Hawaiian Islands
(Biodiversity Data Journal, 2022-03-22) Gnezdilov, Vladimir; Bartlett, Charles R.
Background: Euroxenus vayssieresi (Bonfils, Attie & Reynaud, 2001) (Issinae, Sarimini) was described (in the genus Borbonissus Bonfils, Attie & Reynaud, 2001) from Réunion Island, in the Indian Ocean and, previous to this report, has not been recorded elsewhere. Euroxenus vayssieresi is here illustrated and re-described to improved taxonomic diagnosis. New information: Euroxenus vayssieresi is recorded for the first time from the Island of Hawaii in the Hawaiian Archipelago. This is first record of the family Issidae from the Hawaiian Archipelago.
Past and recent farming degrades aquatic insect genetic diversity
(Molecular Ecology, 2022-06-30) Crossley, Michael S.; Latimer, Christopher E.; Kennedy, Christina M.; Snyder, William E.
Recent declines in once-common species are triggering concern that an environmental crisis point has been reached. Yet, the lack of long abundance time series data for most species can make it difficult to attribute these changes to anthropogenic causes, and to separate them from normal cycles. Genetic diversity, on the other hand, is sensitive to past and recent environmental changes, and reflects a measure of a populations' potential to adapt to future stressors. Here, we consider whether patterns of genetic diversity among aquatic insects can be linked to historical and recent patterns of land use change. We collated mitochondrial cytochrome c oxidase subunit I (COI) variation for >700 aquatic insect species across the United States, where patterns of agricultural expansion and intensification have been documented since the 1800s. We found that genetic diversity was lowest in regions where cropland was historically (pre-1950) most extensive, suggesting a legacy of past environmental harm. Genetic diversity further declined where cropland has since expanded, even after accounting for climate and sampling effects. Notably though, genetic diversity also appeared to rebound where cropland has diminished. Our study suggests that genetic diversity at the community level can be a powerful tool to infer potential population declines and rebounds over longer time spans than is typically possible with ecological data. For the aquatic insects that we considered, patterns of land use many decades ago appear to have left long-lasting damage to genetic diversity that could threaten evolutionary responses to rapid global change.
Opposing global change drivers counterbalance trends in breeding North American monarch butterflies
(Global Change Biology, 2022-06-10) Crossley, Michael S.; Meehan, Timothy D.; Moran, Matthew D.; Glassberg, Jeffrey; Snyder, William E.; Davis, Andrew K.
Many insects are in clear decline, with monarch butterflies (Danaus plexippus) drawing particular attention as a flagship species. It is well documented that, among migratory populations, numbers of overwintering monarchs have been falling across several decades, but trends among breeding monarchs are less clear. Here, we compile >135,000 monarch observations between 1993 and 2018 from the North American Butterfly Association's annual butterfly count to examine spatiotemporal patterns and potential drivers of adult monarch relative abundance trends across the entire breeding range in eastern and western North America. While the data revealed declines at some sites, particularly the US Northeast and parts of the Midwest, numbers in other areas, notably the US Southeast and Northwest, were unchanged or increasing, yielding a slightly positive overall trend across the species range. Negative impacts of agricultural glyphosate use appeared to be counterbalanced by positive effects of annual temperature, particularly in the US Midwest. Overall, our results suggest that population growth in summer is compensating for losses during the winter and that changing environmental variables have offsetting effects on mortality and/or reproduction. We suggest that density-dependent reproductive compensation when lower numbers arrive each spring is currently able to maintain relatively stable breeding monarch numbers. However, we caution against complacency since accelerating climate change may bring growing threats. In addition, increases of summer monarchs in some regions, especially in California and in the south, may reflect replacement of migratory with resident populations. Nonetheless, it is perhaps reassuring that ubiquitous downward trends in summer monarch abundance are not evident.
Using weather radar to help minimize wind energy impacts on nocturnally migrating birds
(Conservation Letters, 2022-05-02) Cohen, Emily B.; Buler, Jeffrey J.; Horton, Kyle G.; Lodd, Scott R.; Cabrera-Cruz, Sergio A.; Smolinsky, Jaclyn A.; Marra, Peter P.
As wind energy rapidly expands worldwide, information to minimize impacts of this development on biodiversity is urgently needed. Here we demonstrate how data collected by weather radar networks can inform placement and operation of wind facilities to reduce collisions and minimize habitat-related impacts on nocturnally migrating birds. We found over a third of nocturnal migrants flew through altitudes within the rotor-swept zone surrounding the North American Great Lakes, a continentally important migration corridor. Migrating birds concentrated in terrestrial stopover habitats within 20-km from shorelines, a distance well beyond the current guidelines for construction of new land-based facilities, and their distributions varied seasonally and at local and regional scales, creating predictable opportunities to minimize impacts from wind energy development and operation. Networked radar data are available across the United States and other countries and broad application of this approach could provide information critical to bird-friendly expansion of this globally important energy source.
Potential Effect of Low-Rise, Downcast Artificial Lights on Nocturnally Migrating Land Birds
(Integrative and Comparative Biology, 2021-07-08) Cabrera-Cruz, Sergio A.; Larkin, Ronald P.; Gimpel, Maren E.; Gruber, James G.; Zenzal, Theodore J. Jr; Buler, Jeffrey J.
Artificial light at night (ALAN) on tall or upward-pointed lighting installations affects the flight behavior of night-migrating birds. We hypothesized that common low-rise lights pointing downward also affect the movement of nocturnal migrants. We predicted that birds in flight will react close to low-rise lights, and be attracted and grounded near light sources, with a stronger effect on juveniles during their autumn migration. We conducted a controlled longitudinal experiment with light-emitting diode floodlights and considered nearby structures that turn on lights at night. We analyzed 1501 high-resolution 3D nocturnal flight paths of free-flying migrants and diurnally captured 758–2009 birds around experimental lights during spring and autumn 2016, and spring 2017. We identified change points along flight paths where birds turned horizontally or vertically, and we considered these indicative of reactions. Flight paths with and without reactions were generally closer to our experimental site in spring than in autumn when the lights were on. Reactions were up to 40% more likely to occur in autumn than in spring depending on the threshold magnitude of turning angle. Reactions in spring were up to ∼60% more likely to occur at ∼35 m from the lights than at >1.5 km. In autumn, some vertical reactions were ∼40% more likely to occur at ∼50 m from the lights than at >2.2 km. Interactions between distance to lights and visibility or cloud cover were consistent with known effects of ALAN on nocturnal migrants. Under poor visibility, reactions were up to 50% more likely to occur farthest from structures in spring, but up to 60% more likely to occur closest to lights in autumn. Thus, the effects of ALAN on night-migrating land birds are not limited to bright lights pointing upward or lights on tall structures in urban areas. Diurnal capture rates of birds were not different when lights were on or off for either season. To our knowledge, this is the first study to show that low-rise lights pointing downward affect night-migrating birds. Although the interpreted reactions constitute subtle modifications in the linearity of flight paths, we discuss future work that could verify whether the protection of nocturnal migrants with lights-out programs would have greater impact if implemented beyond urban areas and include management of low-rise lights.
The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
(Wiley-Blackwell, 2016-12-16) Hudson, Lawrence N.; Newbold, Tim; Contu, Sara; Hill, Samantha L. L.; Lysenko, Igor; De Palma, Adriana; Phillips, Helen R. P.; McCarthy, Jennifer L.; McCarthy, Kyle P.; McCarthy, Jennifer L.; McCarthy, Kyle P.
The PREDICTS project—Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)—has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
Scale-dependent effects of nonnative plant invasion on host-seeking tick abundance
(Wiley-Blackwell, 3/25/16) Adalsteinsson,Solny A.; D'Amico,Vincent; Shriver,W. Gregory; Brisson,Dustin; Buler,Jeffrey J.; Solny A. Adalsteinsson,1,� Vincent D�Amico,2 W. Gregory Shriver,1 Dustin Brisson,3 and Jeffrey J. Buler1; Shriver, W G.;Buler, Jeffrey John
Nonnative, invasive shrubs can affect human disease risk through direct and indirect effects on vector populations. Multiflora rose (Rosa multiflora) is a common invader within eastern deciduous forests where tick-borne disease (e.g., Lyme disease) rates are high. We tested whether R.multiflora invasion affects blacklegged tick (Ixodes scapularis) abundance and at what scale. We sampled host-seeking ticks at two spatial scales: fine scale, within R.multiflora-invaded forest fragments; and patch scale, among R.multiflora-invaded and R.multiflora-free forest fragments. At a fine scale, we trapped 2.3 times more ticks under R.multiflora compared with paired traps 25m away from R.multiflora. At the patch scale, we trapped 3.2 times as many ticks in R.multiflora-free forests compared with R.multiflora-invaded forests. Thus, ticks are concentrated beneath R.multiflora within invaded forests, but uninvaded forests support significantly more ticks. Among all covariates tested, leaf litter volume was the best predictor of tick abundance; at the patch scale, R.multiflora-invaded forests had less leaf litter than uninvaded forests. We suggest that leaf litter availability at the patch scale plays a greater role in constraining tick abundance than the fine-scale, positive effect of invasive shrubs.
Long-term dynamics in local host-parasite interactions linked to regional population trends
(Wiley-Blackwell, 8/18/16) Ladin,Zachary S.; D'Amico,Vincent; Baetens,Jan M.; Roth,Roland R.; Shriver,W. Gregory; Zachary S. Ladin, Vincent D�Amico, Jan M. Baetens, Roland R. Roth, and W. Gregory Shriver; Shriver, W G.;Roth, Roland Ray
Temporal changes in the relative abundances of host-parasite populations can influence the magnitude of the effects of corresponding interspecific interactions. When parasite populations are at relatively low abundance, the negative effects on host populations may be insignificant, but when parasite abundance increases beyond critical thresholds, they can have population limiting effects on the host. Here, we used data from a 40-yr demographic study on breeding Wood Thrushes (Hylocichla mustelina) and avian brood parasitic Brown-headed Cowbirds (Molothrus ater) in the mid-Atlantic United States to disentangle host-parasite interactions. The relative abundance for these two species has changed both locally and regionally over this time period with a reduction in host abundance coincident with an increase in the parasite population. We detected a fivefold increase in Brown-headed Cowbird parasitism rates of Wood Thrushes over the 40-yr time period leading to a reduction in Wood Thrush fitness (i.e.,adult survival, fecundity, and recruitment). After accounting for the effects of Wood Thrush age, individual, and annual and within-season variation in reproduction, we found that Wood Thrushes exhibited increased reproductive effort (produced more nests per year) as nest parasitism rates increased. Additionally, we found that as parasitism rates increased, both Wood Thrush clutch size and fecundity declined. In conjunction with widespread habitat loss and land use change on both wintering and breeding ranges, increasing rates of Brown-headed Cowbird parasitism are reducing Wood Thrush fitness, and are likely contributing to observed regional Wood Thrush population declines. Coordinated local and regional efforts to reduce Brown-headed Cowbird populations, particularly in fragmented landscapes, may help reduce the decline for Wood Thrushes, and likely other parasitized Neotropical migratory species.
Differential introgression and the maintenance of species boundaries in an advanced generation avian hybrid zone
(Biomed Central Ltd, 3/22/16) Walsh,Jennifer; Shriver,W. Gregory; Olsen,Brian J.; Kovach,Adrienne I.; Jennifer Walsh, W. Gregory Shriver, Brian J. Olsen and Adrienne I. Kovach; Shriver, W G.
Background: Evolutionary processes, including selection and differential fitness, shape the introgression of genetic material across a hybrid zone, resulting in the exchange of some genes but not others. Differential introgression of molecular or phenotypic markers can thus provide insight into factors contributing to reproductive isolation. We characterized patterns of genetic variation across a hybrid zone between two tidal marsh birds, Saltmarsh (Ammodramus caudacutus) and Nelson's (A. nelsoni) sparrows (n = 286), and compared patterns of introgression among multiple genetic markers and phenotypic traits. Results: Geographic and genomic cline analyses revealed variable patterns of introgression among marker types. Most markers exhibited gradual clines and indicated that introgression exceeds the spatial extent of the previously documented hybrid zone. We found steeper clines, indicating strong selection for loci associated with traits related to tidal marsh adaptations, including for a marker linked to a gene region associated with metabolic functions, including an osmotic regulatory pathway, as well as for a marker related to melanin-based pigmentation, supporting an adaptive role of darker plumage (salt marsh melanism) in tidal marshes. Narrow clines at mitochondrial and sex-linked markers also offer support for Haldane's rule. We detected patterns of asymmetrical introgression toward A. caudacutus, which may be driven by differences in mating strategy or differences in population density between the two species. Conclusions: Our findings offer insight into the dynamics of a hybrid zone traversing a unique environmental gradient and provide evidence for a role of ecological divergence in the maintenance of pure species boundaries despite ongoing gene flow.

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