DNA stability in the anabiotic fourth-stage juveniles of Ditylenchus dipsaci (Nematoda)

Water plays an important role in DNA structure and desiccation of microorganisms has been correlated with breaks in their DNA. The fourth-stage juveniles of the anabiotic nematode Ditylenchus dipsaci can lose up to 90% of their body water and survive in a dehydrated state for long periods of time; however, there was no increase in the frequency of breaks in DNA isolated from anabiotic as opposed to hydrated juveniles. Desiccation of the non-anabiotic nematode Panagrellus redivivus similarly did not lead to an increased frequency of DNA breaks, nor did the polyol glycerol significantly effect DNA stability. The stability of DNA during tissue desiccation, like the stability of proteins, seems to be a general feature of biological material and not a unique property of anabiotic organisms.     

Physical and Serologic Properties of an Antigen Prepared from Erythrocytes of Horses with Acute Babesiosis*

SYNOPSIS. By means of precipitation with protamine sulfate, a soluble antigen (PS) was obtained from erythrocytes of horses with acute babesiosis due to Babesia caballi and B. equi. This antigen reacted in gel diffusion tests with sera from horses recovered from acute babesiosis. The PS antigen was found to be muco-protein, susceptible to destruction by trypsin and taka-diastase. Analysis of the antigen by paper electrophoresis revealed 2 components which were not present in similar preparations made from erythrocytes of Babesia-free horses. When the PS antigen was heated in boiling water for 30 minutes, a serologically inactive precipitate was formed; however, the supernate remained serologically active and was termed boiled PS (BPS) antigen. This antigen was polysaccharide in nature; its serologic activity was destroyed by taka-diastase. In gel diffusion tests with sera of recovered horses, the PS antigen formed 2 lines of precipitation which coalesced in a single line formed between these sera and the BPS antigen. Both PS and BPS antigens reacted with sera of horses recovered from acute babesiosis in the gel-diffusion test, but not with sera of dogs and rats recovered from acute infection with Babesia canis and Babesia rodhaini, respectively. The serologic specificity of these antigens suggests that they might have application in the serodiagnosis of inapparent Babesia infections of equine animals.     

Variation in Outcrossing Rates in Eichhornia paniculata: Temporal Changes in Populations of Contrasting Style Morph Structure

Abstract Surveys of mating-system parameters in populations of the annual, self-compatible, tristylous, emergent aquatic, Eichhornia paniculata (Pontederiaceae) from N.E. Brazil and Jamaica have indicated that the species exhibits a wide range of outcrossing rates. To investigate whether temporal variation in outcrossing rate was also a feature of populations, open-pollinated families were sampled from five populations of contrasting style morph structure from N.E. Brazil over three consecutive years (1987–1989). Multilocus estimates of outcrossing rate ( t ) were obtained from assays of isozyme polymorphisms using starch gel electrophoresis. There was significant variation both among populations and between years in the frequency of outcrossing. Outcrossing in three tristylous populations was high ( t > 0.80), with relatively small fluctuations occurring over the three-year sampling period. In contrast, in a dimorphic and monomorphic population considerable self-fertilization occurred and the frequency of outcrossing declined significantly from 1987 to 1989 in both populations. In the dimorphic population, increased selfing was associated with a marked reduction in population size and an increase in the frequency of selfing variants of the mid-styled morph. The significance of temporal variation in outcrossing frequency in plant populations is discussed in relation to its effect on population genetic structure and recent models of mating-system evolution.     

The development of eight microsatellite loci in the wild daffodil Narcissus triandrus (Amaryllidaceae)

We report microsatellite primer pairs for the wild tristylous daffodil, Narcissus triandrus (Amaryllidaceae). From enriched libraries, we identified 58 unique microsatellite loci. We designed primer pairs for 27 of these loci and screened genomic DNA from 38 to 40 adults from a single population. For eight polymorphic loci, the number of alleles per locus ranged from five to 17. As six primers also amplified loci in three other Narcissus species, including two horticultural varieties, we expect that some of these markers will be transferable to other Narcissus species.     

Growth patterns of a stream vertebrate differ between urban and forested catchments

1. Urban development results in the decline of amphibian density and species richness. A logical next step towards understanding why urbanisation negatively impacts amphibians is to track species‐specific demographic responses to urbanisation. 2. We monitored growth of two‐lined salamander (Eurycea cirrigera Green) larvae over two complete cohorts (2006 and 2007) in nine western Georgia, U.S.A. streams. 3. We found that salamanders in streams surrounded by urbanised and developing catchments hatched at the same size as their reference‐stream counterparts, but achieved larger sizes within the first few months of growth. We evaluated the effect of four variables that correlate with the urban‐forest gradient and found that elevated temperatures in the urban environment, coupled with decreased intraspecific competition because of lower survivorship in these same habitats, were two of the most likely explanations for increased growth rates. 4. Such an increase in growth of surviving larvae may maintain population viability in urban areas where it has been shown survival is difficult because of increased in‐channel flow during flood events. Because larvae that do survive in urban streams undergo metamorphosis at large sizes, they may recoup a component of fitness (i.e. increased adult survivorship and reproduction) through growth.     

Cougar Kill Rate and Prey Composition in a Multiprey System

Abstract: Assessing the impact of large carnivores on ungulate prey has been challenging in part because even basic components of predation are difficult to measure. For cougars (Puma concolor), limited field data are available concerning fundamental aspects of predation, such as kill rate, or the influence of season, cougar demography, or prey vulnerability on predation, leading to uncertainty over how best to predict or interpret cougar-ungulate dynamics. Global Positioning System (GPS) telemetry used to locate predation events in the field is an efficient way to monitor large numbers of cougars over long periods in all seasons. We applied GPS telemetry techniques combined with occasional snow-tracking to locate 1,509 predation events for 53 marked and an unknown number of unmarked cougars and amassed 9,543 days of continuous predation monitoring for a subset of 42 GPS-collared cougars in west-central Alberta, Canada. Cougars killed ungulates at rates near the upper end of the previously recorded range, and demography substantially influenced annual kill rate in terms of both number of ungulates (subad F [SAF] = 24, subad M [SAM] = 31, ad M = 35, ad F = 42, ad F with kittens <6 months = 47, ad F with kittens <6 months = 67) and kg of prey (SAF = 1,441, SAM = 2,051, ad M = 4,708, ad F = 2,423, ad F with kittens <6 months = 2,794, ad F with kittens >6 months = 4,280). Demography also influenced prey composition; adult females subsisted primarily on deer (Odocoileus spp.), whereas adult males killed more large ungulates (e.g., moose [Alces alces]), and subadults incorporated the highest proportion of nonungulate prey. Predation patterns varied by season and cougars killed ungulates 1.5 times more frequently in summer when juveniles dominated the diet. Higher kill rate in summer appeared to be driven primarily by greater vulnerability of juvenile prey and secondarily by reduced handling time for smaller prey. Moreover, in accordance with predictions of the reproductive vulnerability hypothesis, female ungulates made up a higher proportion of cougar diet in spring just prior to and during the birthing period, whereas the proportion of males increased dramatically in autumn during the rut, supporting the notion that prey vulnerability influences cougar predation. Our results have implications for the impact cougars have on ungulate populations and have application for using cougar harvest to manage ungulates.     

Rapid Homogenization of Multiple Sources: Genetic Structure of a Recolonizing Population of Fishers

Abstract: Fishers (Martes pennanti) were extirpated from much of southern Ontario, Canada, prior to the 1950s. We hypothesised that the recent recolonization of this area originated from an expansion of the population in Algonquin Provincial Park, which historically served as a refuge for fishers. To test this hypothesis, we created a sampling lattice to encompass Algonquin and the surrounding area, and we collected contemporaneous DNA samples. We sampled fishers from each of 35 sites and genotyped them at 16 microsatellite loci. Using a Bayesian assignment approach, with no a priori geographic information, we inferred 5 discrete genetic populations and used genetic population assignment as a means to cluster sites together. We concluded that the Algonquin Park fisher population has not been a substantial source for recolonization and expansion, which has instead occurred from a number of remnant populations within Ontario, Quebec, and most recently from the Adirondacks in New York, USA. The genetic structure among sampling sites across the entire area revealed a pattern of isolation-by-distance (IBD). However, an examination of the distribution of genetic structure (F_ST/1^- F_ST) at different distances showed higher rates of gene flow than predicted under a strict IBD model at small distances (40 km) within clusters and at larger distances up to 100 km among clusters. This pattern of genetic structure suggests increased migration and gene flow among expanding reproductive fronts.     

Climate‐driven increases in storm frequency simplify kelp forest food webs

Climate models predict a dramatic increase in the annual frequency and severity of extreme weather events during the next century. Here we show that increases in the annual frequency of severe storms lead to a decrease in the diversity and complexity of food webs of giant kelp forests, one of the most productive habitats on Earth. We demonstrate this by linking natural variation in storms with measured changes in kelp forest food web structure in the Santa Barbara Channel using structural equation modeling (SEM). We then match predictions from statistical models to results from a multiyear kelp removal experiment designed to simulate frequent large storms. Both SEM models and experiments agree: if large storms remain at their current annual frequency (roughly one major kelp‐removing storm every 3.5 years), periodic storms help maintain the complexity of kelp forest food webs. However, if large storms increase in annual frequency and begin to occur year after year, kelp forest food webs become less diverse and complex as species go locally extinct. The loss of complexity occurs primarily due to decreases in the diversity and complexity of higher trophic levels. Our findings demonstrate that shifts in climate‐driven disturbances that affect foundation species are likely to have impacts that cascade through entire ecosystems.     

产自中国云南下禄丰组(下侏罗统)的爬行动物不完美硕鳄的再研究(英文)

一般认为植龙类在三叠纪末期灭绝,但有研究显示它们可能在欧洲和亚洲延续到了侏罗纪最早期。来自亚洲的证据是产自中国云南下禄丰组(?赫唐阶-锡内穆阶)的不完美硕鳄(Pachysuchus imperfectus)。重新研究显示不完美硕鳄正型标本和植龙类存在许多不同点,它可能属于一个保存较差的、分类位置无法确定的蜥脚型类恐龙头骨。这一属种的归入标本也无法明确归入某一类群,因此亚洲没有可靠的晚于三叠纪的植龙类化石记录。欧洲的侏罗纪植龙类化石也存在着同样的问题。因而认为,植龙类的化石记录仅限于三叠纪晚期。