Isolation and characterization of 20 polymorphic microsatellite loci in the migratory freshwater fish Leporinus obtusidens (Characiformes: Anostomidae) using 454 shotgun pyrosequencing

Twenty polymorphic microsatellite markers were developed for the Neotropical fish Leporinus obtusidens using a next generation sequencing approach and tested in two other characifomes species, Schizodon platae and Prochilodus lineatus. Microsatellite loci alleles in L. obtusidens ranged between 2 and 20 alleles per locus (mean = 5·7), with expected heterozygosity values ranging from 0·097 to 0·956 (mean = 0·578) and observed heterozygosity values ranging from 0·000 to 0·800 (mean = 0·400) in a sample of 20 specimens from the lower Paraná River (Argentina). Most of these markers will be a valuable tool for captive breeding and stocking programmes, as well as for analyses of population connectivity and genetic structure in this broadly distributed Neotropical migratory fish.     

Inter-sexual combat and resource allocation into body parts in the spider, Stegodyphus lineatus

Abstract.  1. Sexual conflict, which results from the divergence of genetic interests between males and females, is predicted to affect multiple behavioural, physiological, and morphological traits.
2. Sexual conflict over mating may interact with population density to produce predictable changes in resource allocation into inter-sexual armament.
3. In the spider Stegodyphus lineatus , males fight with females over re-mating. The outcome of the fight is influenced by the cephalothorax size of the contestants. The investment in armament – the cephalothorax, may be traded-off against investment in abdomen, which is a trait that affects survival and fecundity. Pay-offs may depend on population density. Both sexes are expected to adjust resource allocation into different body parts accordingly.
4. Males had increased cephalothorax/body size ratio in low densities where probability of finding another receptive female is low and females had increased cephalothorax/body size ratio in high densities where cumulative costs of multiple mating are high.
5. The results support the theoretical conjecture that population density affects resource allocation into inter-sexual armament and call for further research on the interaction between sexual selection and population density.     

Large scale Agriotes spp. click beetle (Coleoptera: Elateridae) invasion of crop land from field margin reservoirs

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Distribution and microhabitat use by flatfishes in a Louisiana estuary

We used a 1 m beam trawl to characterize microhabitat use of flatfishes in monthly samples collected in Barataria Bay, Louisiana. Six strata were established along a salinity gradient from the nearshore zone along the Gulf of Mexico to approximately 30 km inland. Randomized sampling within strata characterized flatfish distributions and environmental conditions throughout the bay. Microhabitats were characterized by salinity, temperature, dissolved oxygen, depth, distance from shore, and substrate type. In 594 short-duration, beam-trawl samples collected from October 1992 through September 1994, we identified seven flatfish species from 7046 specimens, most of which were juveniles. Four species accounted for 98.3% of all flatfishes. The two most abundant, offshore tonguefish and bay whiff, were euryhaline and widely distributed over the salinity gradient; however, offshore tonguefish were concentrated in the lowermost stratum where bay whiff were uncommon. The third species, fringed flounder, was more abundant in middle and lower bay strata at higher salinities. The fourth species, blackcheek tonguefish, was most common in middle and upper bay strata and declined in abundance in coastal strata. A rotated factor analysis resolved six environmental variables into three major axes that explained 69 percent of the variance and were characterized as seasonal, depth-distance, and substrate-salinity axes. Separation of species and life history intervals in three-dimensional factor space reflected temporal and spatial segregation. Within the four common flatfishes, 14 of 24 variable comparisons showed clear ontogenetic trends in which at least two size-class means differed significantly. Among the common species, temporal differences were reflected by mean temperatures and dissolved oxygen concentrations and spatial differences were reflected by other environmental variables, including depth, distance, substrate, and salinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Occupancy Models of Nesting-Season Habitat Associations of Red-Shouldered Hawks in Central Minnesota

ABSTRACT Red-shouldered hawks (Buteo lineatus) are a species of special conservation concern in much of the Great Lakes region, and apparent population declines are thought to be primarily due to habitat loss and alteration. To evaluate red-shouldered hawk-habitat associations during the nesting season and at the landscape scale, we conducted repeated call-broadcast surveys in central Minnesota, USA, across 3 landscapes that represented a range of landscape conditions as a result of differing management practices. In 2004, we conducted repeated call-broadcast surveys at 131 locations in 2 study areas, and in 2005, we surveyed 238 locations in 3 study areas. We developed models relating habitat characteristics at 2 spatial scales to red-shouldered hawk occupancy and assessed support for these models in an information-theoretic framework. Overall, a small proportion of nonforest (grass, clear-cut area, forest <5 yr old), and a large proportion of mature deciduous forest (>40 yr old), had the strongest association with red-shouldered hawk occupancy (proportion of sites occupied) at both spatial scales. The landscape conditions we examined appeared to contain a habitat transition important to red-shouldered hawks. We found, in predominately forest landscapes, the amount of open habitat was most strongly associated with red-shouldered hawk occupancy, but in landscapes that included slightly less mature forest and more extensive open habitats, the extent of mature deciduous forest was most strongly associated with red-shouldered hawk occupancy. Our results suggested that relatively small (<5 ha) patches of open habitat (clear-cuts) in otherwise forested landscapes did not appear to influence red-shouldered hawk occupancy. Whereas, in an otherwise similar landscape, with smaller amounts of mature deciduous forest and larger (>15 ha) patches of open habitat, red-shouldered hawk occupancy decreased, suggesting a threshold in landscape composition, based on both the amount of mature forest and open area, is important in managing forest landscapes for red-shouldered hawks. Our results show that during the nesting season, red-shouldered hawks in central Minnesota occupy at similar rates landscapes with different habitat compositions resulting from different management strategies and that management strategies that create small openings may not negatively affect red-shouldered hawk occupancy.     

Patch Connectivity and Genetic Variation in Two Congeneric Grasshopper Species with Different Habitat Preferences

Two congeneric species of grasshopper, Stenobothrus lineatus and S. stigmaticus, are compared in an analysis of genetic structure relative to their observed mobility, and to the spatial structure of their habitat networks. The species differ in their habitat requirements, the latter being rarer and more restricted to isolated patches. We tested for different patch connectivity between the two species in an analysis of genetic variance (based on allozymes) under the assumption that, besides isolation, rarity influences the genetic parameters. Between the species we found no differences in genetic structure as estimated by F_ST; i.e., no isolation effects and no apparent differences between the species in the potential to move between habitat fragments on either a local or regional scale were found. However, the amount of genetic variation in the more widely distributed and less xerothermic S. lineatus was significantly higher than in S. stigmaticus. Some consistency with observed philopatry within patches was found (F_IS > 0), but we consider regular dispersal events of medium and especially long distance to cause the habitat linking. We conclude that the connectivity between occupied patches inferred by genetic analyses can seldom be derived from low observed life-time movements recorded by conventional marking studies. Consequences of applying observed relative to indirect dispersal estimates for the examination of grasshopper metapopulations are discussed.     

Carabid populations in field beans and their effect on the population dynamics of Sitona lineatus (L.)

The abundance and diversity of potential carabid predators of Sitona lineatus (L.) in field beans were monitored between 1980 and 1983. The absolute abundance of the large predatory species was determined in mark-recapture experiments and a radio-labelling technique was used to estimate the level of predation in the field. Using previously published population data for S. lineatus, the importance of predation in the population dynamics of the weevil was estimated. The mortality of weevil larvae due to predation varied from 0.6%– 10.5% while that of adult weevils varied from 2.6%– 23.8%. It appeared that carabids played a significant role in the population dynamics of S. lineatus and, in years when abundant, could reduce the population of larvae and overwintering adults by more than 30%.     

Osteology and myology of the cephalic region and pectoral girdle of Plotosus lineatus, with comments on Plotosidae (Teleostei: Siluriformes) autapomorphies

From comparisons of the cephalic and pectoral girdle structures of Plotosus lineatus with those of other plotosid as well as non-plotosid siluriforms, plotosid catfishes can be defined by at least six autapomorphies. These are: (1) the absence of the ventral division of the muscle arrector dorsalis; (2) the double articulation between the neurocranium and the anterior part of the suspensorium; (3) the greatly enlarged utricular otolith, which profoundly inflates the ventral surfaces of both the prootic and the pterotic; (4) the attachment of the muscle extensor tentaculi on the neurocranium lies further anteriorly than its insertion on the autopalatine; (5) the coronoid process of the mandible is linked to the maxillary by means of two thick, long ligaments; (6) the enlarged base of the maxillary barbel.     

Red-Shouldered Hawk Occupancy Surveys in Central Minnesota,USA

ABSTRACT Forest-dwelling raptors are often difficult to detect because many species occur at low density or are secretive. Broadcasting conspecific vocalizations can increase the probability of detecting forest-dwelling raptors and has been shown to be an effective method for locating raptors and assessing their relative abundance. Recent advances in statistical techniques based on presence—absence data use probabilistic arguments to derive probability of detection when it is < 1 and to provide a model and likelihood-based method for estimating proportion of sites occupied. We used these maximum-likelihood models with data from red-shouldered hawk (Buteo lineatus) call-broadcast surveys conducted in central Minnesota, USA, in 1994–1995 and 2004–2005. Our objectives were to obtain estimates of occupancy and detection probability 1) over multiple sampling seasons (yr), 2) incorporating within-season time-specific detection probabilities, 3) with call type and breeding stage included as covariates in models of probability of detection, and 4) with different sampling strategies. We visited individual survey locations 2–9 times per year, and estimates of both probability of detection (range = 0.28-0.54) and site occupancy (range = 0.81-0.97) varied among years. Detection probability was affected by inclusion of a within-season time-specific covariate, call type, and breeding stage. In 2004 and 2005 we used survey results to assess the effect that number of sample locations, double sampling, and discontinued sampling had on parameter estimates. We found that estimates of probability of detection and proportion of sites occupied were similar across different sampling strategies, and we suggest ways to reduce sampling effort in a monitoring program.     

Overwintering conditions affect cold hardiness,survival, and post-overwintering fitness of the pea leaf weevil

Overwintering conditions affect the physiological state of ectotherms, and therefore, their cold hardiness and survival. A measure of the lethal and sublethal impacts of overwintering conditions on pest populations is crucial to predict population dynamics and to manage pests the following spring. The impact of winter conditions can be most intense for invasive insects undergoing range expansion. Insect herbivores can display plastic host use behaviours that depend on their body condition following winter. The pea leaf weevil, Sitona lineatus L. (Coleoptera: Curculionidae), is an invasive pest of field peas, Pisum sativum L., and faba bean, Vicia faba L. (Fabaceae). Pea leaf weevil has expanded its range in North America to include the Prairie Provinces of Canada. This study investigated the effects of temperature and microhabitat on overwintering survival and cold hardiness of pea leaf weevil in its expanded range. Further, we investigated the sublethal effect of overwintering temperature and duration on post-overwintering survival, feeding, and oviposition of pea leaf weevil. We also investigated the role of juvenile hormone in modulating body condition of overwintering weevils. The overwintering survival of pea leaf weevil adults increased with soil temperature and varied with region and microhabitat. More weevils survived winters when positioned near tree shelterbelts compared to open alfalfa fields. The supercooling point of pea leaf weevil varied throughout its expanding range but did not differ for weevils held in the two microhabitats. The average threshold lethal temperature of pea leaf weevil at all three sites was −9.4 °C. Weevils that overwintered for a longer duration and at a higher temperature subsequently fed more on faba bean foliage and laid more eggs compared to those which overwintered for a shorter duration at a lower temperature. Our findings highlight that warm winters would increase overwintering survival and post-overwintering fitness, facilitating further pea leaf weevil invasion northward in the Prairie Provinces of Canada.