Limits to genetic bottlenecks and founder events imposed by the Allee effect

The Allee effect can result in a negative population growth rate at low population density. Consequently, populations below a minimum (critical) density are unlikely to persist. A lower limit on population size should constrain the loss of genetic variability due to genetic drift during population bottlenecks or founder events. We explored this phenomenon by modeling changes in genetic variability and differentiation during simulated bottlenecks of the alpine copepod, Hesperodiaptomus shoshone. Lake surveys, whole-lake re-introduction experiments and model calculations all indicate that H. shoshone should be unlikely to establish or persist at densities less than 0.5–5 individuals m⁻³. We estimated the corresponding range in minimum effective population size using the distribution of habitat (lake) sizes in nature and used these values to model the expected heterozygosity, allelic richness and genetic differentiation resulting from population bottlenecks. We found that during realistic bottlenecks or founder events, >90% of H. shoshone populations in the Sierra Nevada may be resistant to significant changes in heterozygosity or genetic distance, and 70–75% of populations may lose <10% of allelic richness. We suggest that ecological constraints on minimum population size be considered when using genetic markers to estimate historical population dynamics.     

New Analytic Results for Speciation Times in Neutral Models

In this paper, we investigate the standard Yule model, and a recently studied model of speciation and extinction, the “critical branching process.” We develop an analytic way—as opposed to the common simulation approach—for calculating the speciation times in a reconstructed phylogenetic tree. Simple expressions for the density and the moments of the speciation times are obtained. Methods for dating a speciation event become valuable, if for the reconstructed phylogenetic trees, no time scale is available. A missing time scale could be due to supertree methods, morphological data, or molecular data which violates the molecular clock. Our analytic approach is, in particular, useful for the model with extinction, since simulations of birth-death processes which are conditioned on obtaining n extant species today are quite delicate. Further, simulations are very time consuming for big n under both models.     

Property control of sophorolipids: influence of fatty acid substrate and blending

Sophorolipids (SLs) were synthesized by fed-batch fermentation of Candida bombicola on glucose and either palmitic acid (SL-p), stearic acid (SL-s), oleic acid (SL-o) or linoleic acid (SL-l) and the structural distribution accurately determined by atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). The surfactant properties, including critical micelle concentration (CMC), minimum surface tension (min.ST) and oil-water interfacial tension (IFT) were measured by tensiometry. Minimum STs of 35–36 mN/m were obtained regardless of the substrate while IFTs ranged from 3–5 mN/m with the exception of SL-l, which had an IFT of 7 mN/m. The largest disparity occurred in the CMC values, which ranged from 35 ppm for SL-s to 250 ppm for SL-l. By manually mixing these four SLs in different ratios, it was possible to better control the CMC values without affecting the min.ST or IFT, which will prove beneficial as new applications for SLs are established. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Imaginal discs regulate developmental timing in Drosophila melanogaster

The regulation of body size in animals involves mechanisms that terminate growth. In holometabolous insects growth ends at the onset of metamorphosis and is contingent on their reaching a critical size in the final larval instar. Despite the importance of critical size in regulating final body size, the developmental mechanisms regulating critical size are poorly understood. Here we demonstrate that the developing adult organs, called imaginal discs, are a regulator of critical size in larval Drosophila. We show that damage to, or slow growth of, the imaginal discs is sufficient to retard metamorphosis both by increasing critical size and extending the period between attainment of critical size and metamorphosis. Nevertheless, larvae with damaged and slow growing discs metamorphose at the same size as wild-type larvae. In contrast, complete removal of all imaginal tissue has no effect on critical size. These data indicate that both attainment of critical size and the timely onset of metamorphosis are regulated by the imaginal discs in Drosophila, and suggest that the termination of growth is coordinated among growing tissues to ensure that all organs attain a characteristic final size.     

Evolutionarily conserved thermal biology across continents: The North American lizard Plestiodon gilberti (Scincidae) compared to Asian Plestiodon

1.

The lizard genus Plestiodon (Scincidae; formerly Eumeces) is widespread in North America and Asia, but the thermal biology of only a few species has been studied.     

Age and rearing environment interact in the retention of early olfactory memories in honeybees

Due to the changing behavioral contexts at which social insects are exposed during the adult lifespan, they are ideal models to analyze the effect of particular sensory stimuli during young adulthood on later behavior. Specifically, our goal is to understand early influences on later foraging behavior. For that, olfactory memories were established by worker honeybees to different pre-foraging ages using either (1) classical conditioning in the proboscis extension response (PER) paradigm or (2) the offering of scented-sugar solution under different rearing conditions. By testing long-term memories (LTM) through a single PER test in workers of foraging ages (17-25 days), we found that retention of the early olfactory memories in honey bees is age-dependent and not time-dependent. Independently of the environmental conditions in which they were reared (laboratory cages or hives), bees were able to retain food-odor association from 5 days after emergence, but rarely before. In most experiments we observed a bi-modal pattern of response: bees exposed to scented-food at 5-8 and 13-16 days showed better retention than those exposed at 9-12 days. These differences disappeared for bees reared in hives. Retrieval of LTMs depending on the timing and the continuous inputs of appropriate sensory stimuli are discussed.     

Ultrasonic communication in concave-eared torrent frogs (Amolops tormotus)

The concave-eared torrent frogs (Amolops tormotus) have highly unusual ear morphology--in males the eardrums are embedded deep inside ear cavities. In collaboration with our colleagues we investigated the functional significance of this morphological feature in hearing. Sound recordings in the field showed that males of A. tormotus produce diverse bird-like melodic calls with pronounced frequency modulations and non-linear phenomena (e.g., frequency jumps, different orders of subharmonics, and chaos) that often contain spectral energy in the ultrasonic range. The audible as well as the ultrasonic components of the species call could effectively evoke males' vocal responses, demonstrating that they can hear and respond to ultrasound. Electrophysiological recordings from the auditory midbrain confirmed the ultrasonic hearing capacity of these frogs. The recessed tympana and extremely thin tympanic membranes are adaptations for hearing ultrasound--this sensitivity may have evolved in response to the intense, predominately low-frequency ambient noise from local streams. Finally, results from the isolated laryngeal preparation in euthanized frogs revealed that the origin of call complexity and diversity lies with having a vocal system with nonlinear properties.     

血液灌流救治危重型毒蛇咬伤的临床护理

目的探讨血液灌流(HP)救治重型毒蛇咬伤的临床治疗和护理方法.方法采用德国生产的型号为Adsorda300C的血液灌流器、CVVH导管为重症毒蛇咬伤病人行HP救治,护士配合医生,认真做好HP术前、术中、术后的观察与护理工作.结果5例患者行HP时间为4h,均为一次性炭肾治疗成功,痊愈出院.结论HP能及时有效的清除血中毒物,治疗效果确切,疗效快.在行HP技术时,护士应充分做好准备,掌握娴熟的专科操作技术,密切观察病情变化,保持各种管道通畅,保护好穿刺部位,及时处理各种并发症,才能保证HP的顺利进行.     

Sodium—A Functional Plant Nutrient

Plant scientists usually classify plant mineral nutrients based on the concept of “essentiality” defined by Arnon and Stout as those elements necessary to complete the life cycle of a plant. Certain other elements such as Na have a ubiquitous presence in soils and waters and are widely taken up and utilized by plants, but are not considered as plant nutrients because they do not meet the strict definition of “essentiality.” Sodium has a very specific function in the concentration of carbon dioxide in a limited number of C₄ plants and thus is essential to these plants, but this in itself is insufficient to generalize that Na is essential for higher plants. The unique set of roles that Na can play in plant metabolism suggests that the basic concept of what comprises a plant nutrient should be reexamined. We contend that the class of plant mineral nutrients should be comprised not only of those elements necessary for completing the life cycle, but also those elements which promote maximal biomass yield and/or which reduce the requirement (critical level) of an essential element. We suggest that nutrients functioning in this latter manner should be termed “functional nutrients.” Thus plant mineral nutrients would be comprised of two major groups, “essential nutrients” and “functional nutrients.” We present an array of evidence and arguments to support the classification of Na as a “functional nutrient,” including its requirement for maximal biomass growth for many plants and its demonstrated ability to replace K in a number of ways, such as being an osmoticium for cell enlargement and as an accompanying cation for long-distance transport. Although in this paper we have only attempted to make the case for Na being a “functional nutrient,” other elements such as Si and Se may also confirm to the proposed category of “functional nutrients.”     

Habitat edges and predator-prey interactions: effects on critical patch size.

We use partial differential equation models to examine the effects of cross-edge incursions by a predator on the persistence or extinction of a patch-resident prey species. For each of two predator-incursion profiles (namely, a constant incursion distance and a constant loss rate for predators during incursions), we examine the conditions under which the predator can (and cannot) influence the critical patch size of a prey species.