Genetic differentiation in natural populations of a Keystone Bunchgrass (<Emphasis Type="Italic">Aristida stricta</Emphasis>) across its native range

Aristida stricta Michx. (Poaceae) is a perennial bunchgrass native to the Southeastern Coastal Plain of North America where it is a keystone species in the longleaf pine savannas and slash pine flatwoods from southeastern North Carolina to Florida, and westward to the coast of Mississippi. We examined genetic relationships within and among ten populations of A. stricta by using eight inter-simple sequence repeat (ISSR) markers to generate band frequency data for 32 individuals from each sampled population. An analysis of molecular variance showed that 38% of the variation resided among populations while 62% was attributable to variation within populations. Grouping the populations by habitat or by geographic location did not show significant differentiation between the groups. Overall, pair-wise geographic and genetic distances were not correlated. Data indicate that while individuals within each population are genetically diverse, there seemingly are barriers to gene flow across populations leading to their divergence. Each population contains several exclusive loci suggesting that limited gene flow and/or genetic drift are likely leading to this pattern of localization. Our results, coupled with those of the previous studies that presented evidence for local adaptation and phenotypic differences among populations, suggest that there is sufficient differentiation among populations of this species to warrant: (1) maintenance of the existing genetic diversity at individual sites, and (2) use of local seed and plant sources for conservation projects.     

Structure of a dimeric fungal α-type carbonic anhydrase

The crystal structure of Aspergillus oryzae carbonic anhydrase (AoCA) was determined at 2.7 Å resolution and it revealed a dimer, which only has precedents in the α class in two membrane and cancer-associated enzymes. α carbonic anhydrases are underrepresented in fungi compared to the β class, this being the first structural representative. The overall fold and zinc binding site resemble other well studied carbonic anhydrases. A major difference is that the histidine, thought to be the major proton shuttle residue in most mammalian enzymes, is replaced by a phenylalanine in AoCA. This finding poses intriguing questions as to the biological functions of fungal α carbonic anhydrases, which are promising candidates for biotechnological applications.Structured summaryAoCA binds to AoCA by molecular sieving (View interaction)AoCA binds to AoCA X-ray crystallography (View interaction)     

A hierarchy of signals regulates entry of membrane proteins into the ciliary membrane domain in epithelial cells

The membrane of the primary cilium is continuous with the plasma membrane but compositionally distinct. Although some membrane proteins concentrate in the cilium, others such as podocalyxin/gp135 are excluded. We found that exclusion reflects a saturable selective retention mechanism. Podocalyxin is immobilized by its PDZ interaction motif binding to NHERF1 and thereby to the apical actin network via ERM family members. The retention signal was dominant, autonomous, and transferable to membrane proteins not normally excluded from the cilium. The NHERF1-binding domains of cystic fibrosis transmembrane conductance regulator and Csk-binding protein were also found to act as transferable retention signals. Addition of a retention signal could inhibit the ciliary localization of proteins (e.g., Smoothened) containing signals that normally facilitate concentration in the ciliary membrane. Proteins without a retention signal (e.g., green fluorescent protein-glycosylphosphatidylinositol) were found in the cilium, suggesting entry was not impeded by a diffusion barrier or lipid microdomain. Thus, a hierarchy of interactions controls the composition of the ciliary membrane, including selective retention, selective inclusion, and passive diffusion.     

Home range,habitat use,and activity patterns of free-roaming domestic cats

We used radio-telemetry and collar-mounted activity sensors to compare home range size, habitat use, and activity patterns of owned and unowned free-roaming cats on the outskirts of Champaign-Urbana, Illinois, USA. Owned cats (3 M, 8 F) had smaller home ranges than unowned cats (6 M, 10 F), but we failed to detect consistent differences in home range size between the sexes or among seasons. Home ranges of unowned cats included more grassland and urban area than predicted based on availability in all seasons, and farmsteads were selected in fall and winter. Within home ranges, unowned cats shifted their use of habitats among seasons in ways that likely reflected prey availability, predation risk, and environmental stress, whereas habitat use within home ranges by owned cats did not differ from random. Unowned cats were more nocturnal and showed higher overall levels of activity than owned cats. Space use and behavioral differences between owned and unowned cats supported the hypothesis that the care a cat owner provides influences the impact a cat has on its environment, information that is important for making decisions on controlling cat populations. © 2011 The Wildlife Society.     

Reassessment of the environmental model of developmental polyphenism in spadefoot toad tadpoles

Polyphenism is the expression of multiple, discrete phenotypes from one genotype, and understanding the environmental factors that trigger development of alternative phenotypes is a critical step toward understanding the evolution of polyphenism and its developmental control. While much is known about the ecology of the well-known carnivore/omnivore polyphenism in spadefoot toad tadpoles, the environmental cues for the development of the specialized carnivore phenotype are not completely clear. We examined 27 different experimental treatments in two spadefoot toad species and used over 1,000 tadpoles in an attempt to elucidate those cues. While only 44 carnivores developed in these treatments, they were concentrated at cooler water temperatures and a diet that included fairy shrimp. However, while a diet of fairy shrimp promoted carnivore development, it was not necessary for inducing carnivore development at lower and intermediate water temperatures. Evidence also suggested a role for social inhibition that limited the proportion of interacting tadpoles that become carnivores. Tadpoles of Spea multiplicata grew larger at cooler temperatures and larger when their diets included fairy shrimp, whereas tadpoles of S. bombifrons grew larger at warmer temperatures and when their diets did not include fairy shrimp. These results indicate that carnivore induction can occur through different cues and that our current model for carnivore development is too limited. Finally, we argue that the carnivore/omnivore spadefoot system is neither a polyphenism nor a polymorphism but is a continuously distributed plasticity.     

Evolutionary criteria outperform operational approaches in producing ecologically relevant fungal species inventories

Analyses of the structure and function of microbial communities are highly constrained by the diversity of organisms present within most environmental samples. A common approach is to rely almost entirely on DNA sequence data for estimates of microbial diversity, but to date there is no objective method of clustering sequences into groups that is grounded in evolutionary theory of what constitutes a biological lineage. The general mixed Yule-coalescent (GMYC) model uses a likelihood-based approach to distinguish population-level processes within lineages from processes associated with speciation and extinction, thus identifying a distinct point where extant lineages became independent. Using two independent surveys of DNA sequences associated with a group of ubiquitous plant-symbiotic fungi, we compared estimates of species richness derived using the GMYC model to those based on operational taxonomic units (OTUs) defined by fixed levels of sequence similarity. The model predicted lower species richness in these surveys than did traditional methods of sequence similarity. Here, we show for the first time that groups delineated by the GMYC model better explained variation in the distribution of fungi in relation to putative niche-based variables associated with host species identity, edaphic factors, and aspects of how the sampled ecosystems were managed. Our results suggest the coalescent-based GMYC model successfully groups environmental sequences of fungi into clusters that are ecologically more meaningful than more arbitrary approaches for estimating species richness.     

Waxy bloom in peas influences the performance and behavior of Aphidius ervi, a parasitoid of the pea aphid

Leaf surface waxy bloom can influence the predator–prey interactions that take place on peas. We tested whether the interaction between the pea aphid Acyrthosiphon pisum Harris (Homoptera: Aphidae) and a parasitoid, Aphidius ervi Haliday (Hymenoptera: Aphidiidae), is affected by reduced wax. We performed greenhouse experiments comparing aphid parasitism by individual A. ervi on two varieties of reduced wax peas to two normal wax sister varieties. We also observed the behavior of individual A. ervi in the greenhouse and measured field parasitism in small plots of reduced wax and normal wax peas. In the greenhouse, individual A. ervi parasitized more aphids on the reduced wax varieties than on their normal wax counterparts. Wasps spent more time actively foraging on reduced wax pea plants, which may contribute to the higher parasitism observed on those varieties. The greenhouse results suggested that the improved performance of individual A. ervi on reduced wax peas might contribute to a higher parasitism on reduced wax peas in the field. Field parasitism was significantly higher in reduced wax pea plots during 2000. Overall parasitism was higher in 2000 than in 2001 and 2002. In the latter years, parasitism was higher on reduced wax plants, but not significantly different from normal wax plants. Improved foraging by individual A. ervi resembles improved foraging by other carnivorous insects on reduced wax peas. The advantages of reduced wax for biological control of the pea aphid may hold when any of several different natural enemies is abundant.     

The line of action in the tibia during axial compression of the leg

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions. For each test, the location and angle of the line of action were calculated at the tibial midshaft. The line of action was extended to the bone ends in order to determine the locations of the effective centers of pressure on the tibial plafond and tibial plateau. The effective center of pressure on the tibial plafond consistently migrated anteriorly in dorsiflexion, laterally in eversion, posteriorly in plantarflexion, and medially in inversion. An opposite pattern was observed on the tibial plateau. When the knee was flexed, the effective center of pressure was generally isolated to a small area in the posterior portion of the medial tibial condyle. The percentage of the axial load borne by the fibula varied from -8% to 19%, and was related to the inversion/eversion angle of the ankle (p<0.02), as well as the distance between the fibula and the axial load path at the midshaft (p<0.001). The line of action through the tibia appeared to follow the external load path to the extent allowed by the available joint contact surfaces.