Differential susceptibility of tree species to oviposition by periodical cicadas

Abstract 1. Periodical cicadas occur widely in deciduous forests of eastern North America and represent the largest insect emergences in the world. Their effects on forest community dynamics, via oviposition damage and root feeding, are potentially great but not well understood. If tree species vary in their susceptibility to cicada oviposition and root colonization, then periodical cicadas may affect ecological interactions among tree species and forest composition. 2. We measured oviposition damage on 63 tree species at 52 sites in southern Indiana, U.S.A. for two broods of periodical cicadas. We compared oviposition damage among different sites, habitats, and tree species. We also measured cicada emergence rates in mature and successional forest habitats and from beneath different tree species. 3. Certain tree species received significantly more oviposition damage than others, and the most and least damaged species were consistent between the two broods. For some species, oviposition damage varied between mature and successional sites. Despite the differences in oviposition rates among species, there was no difference in emergence rates from beneath different tree species, suggesting that initial differences in cicada density among tree species are not maintained through the nymphal life cycle. 4. Cicadas oviposited more at successional sites, but emerged more in mature forest stands, suggesting that successive generations of cicadas represent a shifting mosaic between forests of different ages. As tree species consistently vary in their susceptibility to oviposition damage, periodical cicadas could alter local competitive interactions and therefore affect forest dynamics.     

Bias and variance in model results associated with spatial scaling of measurements for parameterization in regional assessments

Models are central to global change analyses, but they are often parameterized using data that represent only a portion of heterogeneity in a region. This creates uncertainty in the results and constrains the reliability of model inferences. Our objective was to evaluate the uncertainty associated with differential scaling of parameterization data to model soil organic carbon stock changes as a function of US agricultural land use and management. Specifically, we compared analyses in which model parameters were derived from field experimental data that were scaled to the entire US vs. the same data scaled to climate regions within the country. We evaluated the effect of differential scaling on both bias and variance in model results. Model results had less variance by scaling data to the entire country because of a larger sample size for deriving individual parameter values, although there was a relatively large bias associated with this parameterization, estimated at 2.7 Tg C yr^?1. Even with the large bias, resulting confidence intervals from the two parameterizations had considerable overlap for the estimated national rate of SOC change (i.e. 77% overlap in those intervals). Consequently, the results were relatively similar when focusing on the uncertainty rather than solely on the mean estimate. In contrast, large biases created less overlap in confidence intervals for the change rates within individual climate regions, compared with the national estimates. For example, the overlap in resulting intervals from the two parameterizations was only 32% for the warm temperate moist region, with a corresponding bias of 3.1 Tg C yr^?1. These findings demonstrate that there is a greater risk of making erroneous inferences because of large biases if models are parameterized with broader scale information, such as an entire country, and then used to address impacts at a finer spatial scale, such as sub‐regions within a country. In addition, the study demonstrates a trade‐off between variance and bias in model results that depends on the scaling of data for model parameterization.     

Patterns of parasitism in monarch butterflies during the breeding season in eastern North America

1. Migratory behaviour can result in reduced prevalence of pathogens in host populations. Two hypotheses have been proposed to explain this relationship: (i) ‘migratory escape’, where migrants benefit from escaping pathogen accumulation in contaminated environments; and (ii) ‘migratory culling’, where the selective removal of infected individuals occurs during migration. 2. In the host–parasite system between the monarch butterfly (Danaus plexippus Linn.) and its obligate protozoan parasite Ophryocystis elektroscirrha (OE), there is evidence to support both hypotheses, particularly during the monarchs' autumn migration. However, these processes can operate simultaneously and could vary throughout the monarchs' annual migratory cycle. Assessing the relative strength for each hypothesis has not previously been done. 3. To evaluate both hypotheses, parasite infection prevalence was examined in monarchs sampled in eastern North America during April–September, and stable isotopes (δ²H, δ¹³C) were used to estimate natal origin and infer migration distance. There was stronger support for the migratory escape hypothesis, wherein infection prevalence increased over the breeding season and was higher at southern latitudes, where the breeding season tends to be longer compared with northern latitudes. Little support was found for the migratory culling hypothesis, as infection prevalence was similar whether monarchs travelled shorter or longer distances. 4. These results suggest that migration allows individuals to escape parasites not only during the autumn, as shown in previous work, but during the monarchs' spring and summer movements when they recolonise the breeding range. These results imply a potential fitness advantage to monarchs that migrate further north to exploit parasite‐free habitats.     

Thermal and hydric implications of diurnal activity by a small tropical frog during the dry season

Amphibians are typically intolerant of high temperatures and dehydrating conditions, and small species are particularly susceptible to desiccation. The rockhole frog, Litoria meiriana (Hylidae), is diurnal and is often observed on rocks in the sun near streams in tropical Australia. These hot, desiccating conditions are avoided by most frog species. We measured the microclimate in the areas used by frogs and the activity, body temperatures and hydric state of free‐ranging individuals of this small frog. We also used plaster models to further explore the dynamic nature of hydric state by combining estimates of water loss and water uptake with behavioural observations of activity and microhabitat selection. Both direct measures and estimates of dynamic hydric state indicated that free‐ranging frogs generally maintained a hydric state above 95% of full hydration, but occasionally, particularly during the afternoon, frogs allowed their hydric state to fall as low as 85%. Body temperatures of frogs remained below the critical thermal maximum (CT_max) even when the frogs were in the sun, because this species has no cutaneous resistance to evaporative water loss and so they cool by evaporation. However, during the hotter part of the day, on dry sunny substrates, the hydric state of the frogs could fall to near lethal hydration states (approximately 70% of full hydration) within a short period (approximately 20 min). Thus, the threat of desiccation appears to be more limiting than the threat of overheating. These diurnal frogs rely on frequent bouts of rehydration to support their ability to venture onto hot, dry rocks during the day.     

Distribution and Broadscale Habitat Relations of the Wolverine in the Contiguous United States

ABSTRACT Conservation of the wolverine (Gulo gulo) at the southern extent of its North American range requires reliable understandings of past and present distribution patterns and broad-scale habitat relations. We compiled 820 verifiable and documented records of wolverine occurrence (specimens, DNA detections, photos, and accounts of wolverines being killed or captured) in the contiguous United States from museums, the literature, and institutional archives. We spatially referenced 729 records with areal precision ≤1 township (93.2 km²) and temporal precision ≤10 years. Historical records (1827–1960) were located primarily in the western mountains and Great Lakes region. However, our data suggest that the historical distribution of wolverines in the Cascade Range and Sierra Nevada was disjunct, contradicting previous interpretations. Our results indicate that wolverine range in the contiguous United States had contracted substantially by the mid-1900s. Current records (1995–2005) are limited to north-central Washington, northern and central Idaho, western Montana, and northwestern Wyoming. We investigated potential relations between wolverines and alpine vegetation, cold temperatures, and spring snow cover by comparing the distribution of historical wolverine records with Kuchler's potential natural vegetation types, Holdridge's climatic life zones, and EASE snow-cover maps during the latter portion of the wolverine denning period (15 Apr-14 May). In the western mountains, historical wolverine records generally occurred in or near alpine vegetation and climatic conditions, especially at the limits of their distribution in the Cascade Range, Sierra Nevada, and southern Rocky Mountains. However, the only habitat layer that fully accounted for historical distribution patterns was spring snow cover. Causal factors for the extirpation of wolverines from the southern portions of their range in the contiguous United States are unknown, but are likely related to high levels of human-caused mortality and low to nonexistent immigration rates.     

Isolation and characterization of di‐ and tetranucleotide microsatellite loci in the yellow‐spotted night lizard Lepidophyma flavimaculatum (Squamata: Xantusiidae)

We report the development of 17 di‐ and tetranucleotide microsatellite markers in the Yellow‐Spotted Night Lizard Lepidophyma flavimaculatum. Levels of heterozygosity ranged from 0 to 100%. Several loci also amplify in other Lepidophyma species and several species of the sister genus Xantusia. High levels of variation at some loci indicate that they will be useful for parentage assessment and population genetic studies, whereas the 15 loci that amplify across multiple Lepidophyma species suggest these will be useful in determining the origin of parthenogenetic populations.     

Geomorphic dynamics of floodplains: ecological implications and a potential modelling strategy

1.  The dynamics of channel migration and floodplain renewal constitute an important control of the ecological diversity of river corridors. Restoration initiatives should therefore assess whether these dynamics must be reinstated in order to address the cause rather than the symptoms of floodplain biodiversity decline.
2.  Restoration of reach-scale dynamism in rivers where this is a natural behavioural process will restore smaller-scale geomorphological and sedimentological processes that encourage vegetation regeneration, but may require catchment-scale management of material flows.
3.  Channel dynamics depend on the style of river–floodplain interaction, and this may be summarised in qualitative, classificatory, sedimentological models of floodplain architecture that have been somewhat neglected in the ecological literature.
4.  One approach to the assessment of floodplain biodiversity and its restoration would be through the development of simulation models based on specified channel styles, and involving simplified hydrodynamics and successional changes. Such models, currently the subject of research as a spin-off from modelling studies of landscape evolution, would permit evaluation of the consequences for ecological diversity of implementing various management options that may affect the dynamics of channel migration.     

Photoperiod and Reproduction in Lobsters (Homarus)

SYNOPSIS. Photoperiodic control of lobster (Homarus) ovipositionranges from none in the European species (H. gammarus) to atwo-phase requirement in some populations of H. americanus.In the inshore population from Massachusetts two to three monthsof shortday photoperiod appear necessary to condition the ovaryfor final vitellogenesis following long-day onset (LDO). Thestimulus of LDO is only effective near the time of molt. Ifmolt follows LDO within 120 days, egg extrusion follows themolt in about 80 days. If LDO follows the molt, extrusion occursin about 125 days. Extrusion delayed in this way delays thefollowing molt, which is also delayed by the retention of eggson the pleopods. In lobsters from Prince Edward Island the photoperiodic responseseen at laboratory temperatures (ca. 14°C) appears to besubordinated to a response to other cues, probably temperature,when females are held on a near-natural temperature regime withwinter minimum of 2°C characteristic of inshore environments.H. americanus from the migratory outer continental shelf populationexperience winter temperatures rarely lower than 8°C andprobably require photoperiodic control to initiate migrationas well as vitellogenesis. The photoperiodic response may haveoriginated in offshore populations during the Pleistocene andspread to more northerly inshore areas as habitat opened afterthe retreat of the continental ice sheet.     

The Young Naturalists' Society and Natural History in the Northwest

SYNOPSIS. The beginnings of professional natural history inSeattle date from 1879. In this year a group of young men whowere completely untrained in the sciences formed the Young Naturalists'Society. The society quickly grew to eventually become a majorinstitution for natural history investigations in the PugetSound area at the end of the nineteenth century. The activitiesof the Young Naturalists included collecting a large and impressivecabinet, exchanging specimens with naturalists throughout theUnited States, organizing expeditions for marine investigations,and providing educational opportunities for the public throughlectures, public exhibits, newspaper reports, and summer Chautauqua.As the society became more professional in its work, it developedstrong ties to the University of Washington. In fact, by themid-1890s it was difficult to separate the natural history worksponsored by the University from the studies under the aegisof the Young Naturalists. Eventually the society disbanded andbecame absorbed by the various natural science departments ofthe University and by the Washington State Museum. The importanceof the Young Naturalists' was through its critical role in providingthe foundation for the development of a professional naturalhistory community in Seattle.     

The Conversion of 3-Indolylmethylglucosinolate to 3-Indolylacetonitrile by Myrosinase, and its Relevance to the Clubroot Disease of the Cruciferae

[Methylene-¹⁴C]-3-indolylmethylglucosinolate (¹⁴C-IMG) was convertedin vitro to [methylene-¹⁴Cl-3-indolylacetonitrile (¹⁴C-IAN)by myrosinase over a pH range of 4.0-6.0 and this conversionwas enhanced by ferrous ions. Other products of the reactionincluded 3-indolylmethanol, 3, 3'-diindolylmethane and ascorbigenA. Trace amounts of ¹⁴C-IAN were produced non-enzymically from¹⁴C-IMG in the presence of ferrous ion over a similar _pH range.Furthermore, swede tissues (Brassica napus cv. Danestone) infectedwith Plasmodiophora brassicae Woron. could convert ¹⁴C-IMG to¹⁴C-IAN. These results were consistent with the hypothesis thatthe overgrowth symptoms of the clubroot disease are caused bythe conversion of IMG to the auxin precursor IAN.