A Comparison of Field and Molecular Techniques for Sexing Beavers

Abstract: The traditional method of sex identification in beavers (Castor canadensis) by external palpation can be inaccurate. We tested 2 genetic methods for determining sex in beavers, the zinc-finger DNA marker and the Y chromosome-specific sex determining region (SRY) marker. The SRY marker identified sex correctly in 57 of 67 (85%) beavers, whereas the zinc-finger technique was successful less often in only 48 of 67 (72%) animals. Sex was correctly assigned by palpation for 21 of 27 beavers (78%). Beaver studies in which accurate sex identification is critical may benefit by verifying the sex of individuals using one or both of these molecular markers.     

Parasite genetic differentiation by habitat type and host species: molecular epidemiology of Schistosoma japonicum in hilly and marshland areas of Anhui Province, China

Schistosoma japonicum , a parasite of significant public health importance in parts of China and Southeast Asia, is a true generalist pathogen with over 40 species of mammals suspected as definitive host reservoirs. In order to characterize levels of parasite gene flow across host species and identify the most important zoonotic reservoirs, S. japonicum larvae (miracidia) were sampled from a range of definitive host species in two contrasting habitat types within Anhui Province, China: a low-lying marshland region, and a hilly region, where animal reservoir populations may be predicted to differ substantially. Miracidia samples were genotyped using seven multiplexed microsatellite markers. Hierarchical F -statistics and clustering analyses revealed substantial geographical structuring of S. japonicum populations within Anhui, with strong parasite genetic differentiation between habitat types. Within most villages, there was very little or no parasite genetic differentiation among host species, suggesting frequent S. japonicum gene flow, and thus also transmission, across species. Moreover, the data provide novel molecular evidence that rodents and dogs are potentially very important infection reservoirs in hilly regions, in contrast to bovines in the marshland regions. The parasite genetic differentiation between habitat types might therefore be associated with contrasting host reservoirs. The high levels of parasite gene flow observed across host species in sympatric areas have important implications for S. japonicum control, particularly in hilly regions where control of infection among wild rodent populations could be challenging.     

Genome‐wide single nucleotide polymorphisms reveal population history and adaptive divergence in wild guppies

Adaptation of guppies (Poecilia reticulata) to contrasting upland and lowland habitats has been extensively studied with respect to behaviour, morphology and life history traits. Yet population history has not been studied at the whole‐genome level. Although single nucleotide polymorphisms (SNPs) are the most abundant form of variation in many genomes and consequently very informative for a genome‐wide picture of standing natural variation in populations, genome‐wide SNP data are rarely available for wild vertebrates. Here we use genetically mapped SNP markers to comprehensively survey genetic variation within and among naturally occurring guppy populations from a wide geographic range in Trinidad and Venezuela. Results from three different clustering methods, Neighbor‐net, principal component analysis (PCA) and Bayesian analysis show that the population substructure agrees with geographic separation and largely with previously hypothesized patterns of historical colonization. Within major drainages (Caroni, Oropouche and Northern), populations are genetically similar, but those in different geographic regions are highly divergent from one another, with some indications of ancient shared polymorphisms. Clear genomic signatures of a previous introduction experiment were seen, and we detected additional potential admixture events. Headwater populations were significantly less heterozygous than downstream populations. Pairwise F_ST values revealed marked differences in allele frequencies among populations from different regions, and also among populations within the same region. F_ST outlier methods indicated some regions of the genome as being under directional selection. Overall, this study demonstrates the power of a genome‐wide SNP data set to inform for studies on natural variation, adaptation and evolution of wild populations     

Responses of soil respiration to elevated CO2, air warming, and changing soil water availability in a model old-field grassland

Responses of soil respiration to atmospheric and climatic change will have profound impacts on ecosystem and global carbon (C) cycling in the future. This study was conducted to examine effects on soil respiration of the concurrent driving factors of elevated atmospheric CO₂ concentration, air warming, and changing precipitation in a constructed old‐field grassland in eastern Tennessee, USA. Model ecosystems of seven old‐field species were established in open‐top chambers and treated with factorial combinations of ambient or elevated (+300 ppm) CO₂ concentration, ambient or elevated (+3 °C) air temperature, and high or low soil moisture content. During the 19‐month experimental period from June 2003 to December 2004, higher CO₂ concentration and soil water availability significantly increased mean soil respiration by 35.8% and 15.7%, respectively. The effects of air warming on soil respiration varied seasonally from small reductions to significant increases to no response, and there was no significant main effect. In the wet side of elevated CO₂ chambers, air warming consistently caused increases in soil respiration, whereas in the other three combinations of CO₂ and water treatments, warming tended to decrease soil respiration over the growing season but increase it over the winter. There were no interactive effects on soil respiration among any two or three treatment factors irrespective of time period. Treatment‐induced changes in soil temperature and moisture together explained 49%, 44%, and 56% of the seasonal variations of soil respiration responses to elevated CO₂, air warming, and changing precipitation, respectively. Additional indirect effects of seasonal dynamics and responses of plant growth on C substrate supply were indicated. Given the importance of indirect effects of the forcing factors and plant community dynamics on soil temperature, moisture, and C substrate, soil respiration response to climatic warming should not be represented in models as a simple temperature response function, and a more mechanistic representation including vegetation dynamics and substrate supply is needed.     

Soil pH influences embryonic survival in Pseudophryne bibronii (Anura: Myobatrachidae)

Abstract: There has been limited research examining the role that terrestrial habitat characteristics play in influencing persistence of amphibian populations. In this study we investigated the influence of a terrestrial habitat attribute on the distribution of the terrestrial egg‐laying toadlet, Pseudophryne bibronii. Eggs of this species are deposited in depressions, or under leaf litter, and develop to a stage where they can hatch to free swimming tadpoles when water covers breeding sites or embryos are washed into water. Because rainfall can be intermittent, eggs may sit for extended periods in terrestrial nests before sufficient rainfall initiates hatching. Appropriate egg‐laying sites must be chosen by both males and females to ensure embryos survive these periods. A study of 20 sites found that soil pH at sites where P. bibronii were recorded as present was significantly lower than pH at sites where P. bibronii were recorded as absent. To determine whether soil pH influenced the hatching success in P. bibronii, experiments were conducted in which batches of eggs were translocated to local areas with different soil pH. Survival rate of eggs was significantly influenced by relatively small changes in pH, with hatching success higher at lower pH. In a laboratory trial survival of eggs raised on sterilized soil was not affected by soil pH. Fungal infection of eggs was observed in the field and laboratory suggesting that hatching success might be affected via a complex interaction between soil pH, fungi and other soil biota. Choice trials using P. bibronii metamorphs indicated that individuals were capable of distinguishing between small differences in pH. Therefore, distribution of P. bibronii may be influenced by either differential mortality of embryos, or habitat choice by post metamorphic individuals, and further experiments are required to determine the relative importance of these factors.     

Predictability of Silurian Fossil-Konservat-Lagerstatten in North America

Fossil-Konservat-Lagerstätten from a limited time frame can be classified in a way that provides predictive value, demonstrating that it is possible to prospect for additional deposits of exceptionally preserved fossils. Q-mode cluster analysis reveals that eight Silurian Lagerstätten in North America are divisible into two groups on the basis of biotic components and sedimentary features: eurypterid-phyllocarid-dominated (EP) biotas (Williamsville, Syracuse, Pointe-aux-Chenes, Kokomo, Waubakee) and dendroid-graptolite-characterized (DG) biotas (Brandon Bridge, Lecthaylus , Mississinewa). AU fossil deposits are characterized by fine-grained, laminated, carbonate sediment bearing evidence of anoxic depositional conditions. The EP biotas were deposited in hypersaline peritidal lagoons limited stratigraphically to Upper Silurian strata surrounding the Michigan Basin, similar Lagerstätten maybe predicted for this type of setting in North America and elsewhere in strata of like age. DG biotas are taxonomically, ecologically, stratigraphically, and areally more diverse than EP biotas, and these Lagerstunen are less easily predicted. OFOSSIL-KONSERVAT-LACERSTÄTTEN, Silurian, cluster analysis, prediction.     

Water-Stress-Induced Changes in the Pattern of Protein Synthesis in Maize Seedling Mesocotyls: A Comparison with the Effects of Heat Shock

Cut segments from the growing and non-growing regions of 4-d-oldmaize seedling mesocotyls exhibit reduced protein synthesiswhen subjected to water-stress imposed directly by incubationin solutions of polyethylene glycol. Growing mesocotyl tissuecan recover full protein synthesis upon return to a fully-hydratedcondition following stress to –0.5 MPa, while non-growingtissue recovers well from greater stresses (–0.75 to –1.0MPa), and in lesser time. Using two-dimensional electrophoresisand fluorography of de novo synthesized proteins in vivo itwas possible to follow changes in protein synthesis in the non-growingtissue under water-stress and upon subsequent recovery. Thesynthesis of several proteins was reduced by stress, althoughthat of others intensified. Those proteins exhibiting reducedsynthesis under stress were synthesized at control levels (i.e. the same levels as in unstressed tissue) when the stresswas relieved. Some proteins whose synthesis was intensifiedunder stress retained this intensification upon return to fullhydration. No unique proteins were synthesized in response towater-stress, in contrast to the ‘heat-shock’ proteinsinduced when the mesocotyls were subjected to high temperature.Hence water-stress induces quantitative rather than qualitativechanges in the pattern of protein synthesis. Key words: Zea mays, Water-stress, Pattern of protein synthesis     

Sex,snails, and schistosomes: the influence of compatibility genotype on reproductive strategy

Summary

The impact of current parasitic infection status on mate choice and reproductive strategies has been widely reported, particularly amongst vertebrate host-parasite systems. However, evidence is lacking as to whether animals discriminate between mates on the basis of their potential infection status, in terms of host resistance or susceptibility genotype (i.e., compatibility). In a series of experiments, Biomphalaria glabrata snail strains were artificially selected for either resistance or susceptibility to Schistosoma mansoni infection. Individual snails from each line were then paired with a partner of matched compatibility status and the proportion of outcrossed to selfed offspring produced identified by RAPD-PCR. Individual unselected snails, either infected or uninfected, were then given a choice of partners artificially selected for either resistance or susceptibility to infection, and their behaviour analysed. The results demonstrate that compatibility genotype can influence reproductive strategy and are discussed in terms of their implications regarding the maintenance of sex and the evolution of recognition systems.