Stephanie A. Foré

Genetic structure of Helianthus occidentalis (Asteraceae) in a preserve withfragmented habitat.

We examined the spatial genetic structure of Helianthus occidentalis Riddell ssp. occidentalis Riddell (western sunflower) to determine whether this species is highly clonal and whether the distance between prairie patches influences genetic differentiation. In the Edge of Appalachia Preserve System, Ohio, this species is restricted to prairie patches that have a clumped distribution in the forest matrix. Data from this insect-pollinated forb with gravity-dispersed seed were compared to data from the same patches for Asclepias verticillata, an insect-pollinated species with wind-dispersed seed. Allozyme electrophoresis was used to collect genetic data from H. occidentalis samples from eight patches in four regions. Genetic data from three polymorphic loci indicted that this species is not highly clonal. Genetic differentiation was greater among patches within a region than among regions, suggesting that gene flow among patches is more limited in H. occidentalis than in A. verticillata. Founder effect may also have contributed to observed genetic differences among patches as some of these populations may have re-established after release from human use. As habitat fragmentation is increasing in the preserve, it is also likely that genetic differentiation may be increasing. Therefore, monitoring of genetic structure is necessary to further assess the effect of fragmentation.

Modeling the Influence of Peromyscus leucopus Body Mass, Sex, and Habitat on Immature Dermacentor variabilis Burden

ABSTRACT: Immature (larvae and nymph) tick burden on rodents is an important determinant of adult tick population size and understanding infectious disease dynamics. The objective of this research was to build a descriptive model for immature Dermacentor variabilis burden on Peromyscus leucopus. Mice were live-trapped on two permanent grids in an old field and an early successional forest every other month between April and October, 2006–2009. Negative binomial regression was used to examine the association between immature D. variabilis burden and the host related variables of host habitat, body mass, and/ or sex. The model containing all three variables had the lowest Akaikes Information Criterion (AIC), corrected AIC (AICc), and greatest AICc weight. Immature D. variabilis burden was positively associated with mice with higher body mass, male mice, and those captured in the field habitat. These data are consistent with studies from other tick-rodent systems and suggest that single factor models do not describe host burden. Variables other than those that are related to the host may also be important in describing the tick burden on rodents. The next step is to examine variables that affect tick development rate and questing behavior.

A Conceptual Model of the Amblyomma americanum Life Cycle in Northeast Missouri

ABSTRACT: The geographic distribution of Amblyomma americanum (the lone star tick) has increased as has its role as a pathogen vector. The objectives of this study were to determine seasonal activity patterns of each life stage of A. americanum in the northwestern part of the species range and the relationship of these activity patterns among life stages and degree days. Tick activity was monitored over four years since 2007 in a forest and old field habitat located in northeast Missouri. Every other week from February to December, ticks were collected using bait and drag methods. Autocorrelations demonstrated yearly seasonal patterns in each life stage and cross-correlations between life stages depicted a relationship between activity at a life stage and the previous stages activity. Cross-correlations indicated that degree days were related to activity. These data indicated that A. americanum generally complete their life cycle in a minimum of two years in northeast Missouri, with overwintering occurring predominantly in the nymphal and adult stages. These data provide a baseline to compare the life cycle of A. americanum in northeast Missouri to populations in different parts of the species range or at different times in the region.

Chemical attraction of Dermacentor variabilis ticks parasitic to Peromyscus leucopus based on host body mass and sex

Macroparasites are commonly aggregated on a small subset of a host population. Previous explanations for this aggregation relate to differences in immunocompetence or the degree to which hosts encounter parasites. We propose active tick host choice through chemical attraction as a potential mechanism leading to aggregated tick burdens. We test this hypothesis using a Y-maze olfactometer, comparing chemical attraction responses of larval and nymphal Dermacentor variabilis ticks parasitic to the white-footed mouse, Peromyscus leucopus, as a function of host sex and host body mass. We hypothesized that larger hosts and male hosts would be most attractive to searching ticks, as these hosts commonly have higher tick burdens in the field. Chemical attraction trials were run in the presence and absence of a known tick attractant, host-produced carbon dioxide (CO2). Male hosts and larger hosts were preferred by nymphal D. variabilis in the presence and absence of CO2, whereas larvae had no detectable host preference. The current study suggests that host-produced chemical cues may promote aggregated tick burdens among hosts of a single species based on host body mass and sex.

Modeling the biotic and abiotic factors that describe the number of active off‐host Amblyomma americanum larvae

ABSTRACT: Amblyomma americanum (L.) is a three-host tick that spends most of its life off-host and is an important vector of pathogens in the eastern United States. Our objectives were to develop a predictive statistical model that describes the number of active, off-host larvae from 2007 to 2011 and to determine the environmental variables associated with this pattern. Data used in this study came from monitoring conducted in northeast Missouri in which off-host ticks were collected from a permanent plot in a forest and an old field habitat every other week from approximately February to December. Variables examined were day length, degree days, total precipitation prior to sampling, wind speed, saturation deficit, number of adults prior to sampling, and collection site. Of the four regression models tested, the negative binomial model was selected. Fitted candidate models were compared relative to one another using values of eight model selection criteria and model averaging was used to develop a predictive model. The residual plots indicated that the weighted average model performs well in describing the number of larvae. Of the variables considered, the number of larvae was most strongly associated with increasing degree days, the number of active adults prior to sampling, and the forested site.

Model selection criteria for overdispersed data and their application to the characterization of a host-parasite relationship

In the statistical modeling of a biological or ecological phenomenon, selecting an optimal model among a collection of candidates is a critical issue. To identify an optimal candidate model, a number of model selection criteria have been developed and investigated based on estimating Kullback’s (Information theory and statistics. Dover, Mineola, 1968) directed or symmetric divergence. Criteria that target the directed divergence include the Akaike (2nd international symposium on information theory. Akadémia Kiadó, Budapest, Hungary, pp 267–281, 1973, IEEE Trans Autom Control AC 19:716–723, 1974) information criterion, AIC, and the “corrected” Akaike information criterion (Hurvich and Tsai in Biometrika 76:297–307, 1989), AICc; criteria that target the symmetric divergence include the Kullback information criterion, KIC, and the “corrected” Kullback information criterion, KICc (Cavanaugh in Stat Probab Lett 42:333–343, 1999; Aust N Z J Stat 46:257–274, 2004). For overdispersed count data, simple modifications of AIC and AICc have been increasingly utilized: specifically, the quasi Akaike information criterion, QAIC, and its corrected version, QAICc (Lebreton et al. in Ecol Monogr 62(1):67–118 1992). In this paper, we propose analogues of QAIC and QAICc based on estimating the symmetric as opposed to the directed divergence: QKIC and QKICc. We evaluate the selection performance of AIC, AICc, QAIC, QAICc, KIC, KICc, QKIC, and QKICc in a simulation study, and illustrate their practical utility in an ecological application. In our application, we use the criteria to formulate statistical models of the tick (Dermacentor variabilis) load on a white-footed mouse (Peromyscus leucopus) in northern Missouri.

Potential role of pollinators in microhabitat structure within a large population of Echinacea laevigata (Asteraceae)1

Abstract Understanding the linkages among population spatial, demographic, and genetic structure is a priority for threatened or endangered species, particularly when the physical or biotic landscape influences key processes such as pollinator behavior or plant establishment, growth, and flowering. We investigated spatial, demographic, and genetic structure, and followed activity of insect visitors within a large population of a federally endangered herb, Echinacea laevigata (C.L.Boynton & Beadle) S.F.Blake, distributed among microhabitats from an open powerline right-of-way across a narrow dirt road and into adjacent forest. Population and genetic structure differed among the microhabitats, but these differences were not due to clonal growth. Most genetic variation was within rather than among microhabitats. Plants differed in size (number of leaves) and the percentage of flowering plants among microhabitats, with smaller plants and lower flowering in the edge, larger plants and intermediate flowering in the forest and powerline, and smaller plants, but higher flowering, along the open road. Observations of insect visitors suggest activity of potential pollinators can interact with demographic structure contribute to, or reinforce, genetic structure in the population. Collectively, results of this research indicate that microhabitat effects on population structure and pollinator activity should be considered in species management plans for E. laevigata.

Macrogeographic allozyme variation in Passiflora incarnata

the southern United States and common in old fields and roadsides. This herbaceous, perennial vine has hermaphroditic flowers yet is self-incompatible. Large bees pollinate these flowers that produce fruits that may be eaten by mammals. Although the mode of sexual reproduction suggests the potential for long distance dispersal of genes, this species also displays extensive vegetative reproduction from rhizomes. Vegetative reproduction may reduce the amount of genetic variation within a population and increase differentiation among populations. We report on the macrogeographic allozymic variation within P. incarnata. Plants were collected from three regions in South Carolina (SC) and Georgia (GA). Genetic data were collected from nine polymorphic loci with starch gel electrophoresis of allozymes. In our sample of 168 plants from SC and GA, we observed 82 different multilocus genotypes. Plants with the same multilocus genotype were collected within and among regions. Genetic data indicated that there was little genetic differentiation among regions. These data suggest that there is extensive long distance transport of genes and that the species may rely heavily on sexual reproduction to establish new habitat.