Continuous mantle melt supply beneath an overlapping spreading center on the East Pacific Rise

Tomographic images of upper mantle velocity structure beneath an overlapping spreading center (OSC) on the East Pacific Rise indicate that this ridge axis discontinuity is underlain by a continuous region of low P-wave velocities. The anomalous structure can be explained by an approximately 16-kilometer-wide region of high temperatures and melt fractions of a few percent by volume. Our results show that OSCs are not necessarily associated with a discontinuity in melt supply and that both OSC limbs are supplied with melt from a mantle source located beneath the OSC. We conclude that tectonic segmentation of the ridge by OSCs is not the direct result of magmatic segmentation at mantle depths.     

Species coextinctions and the biodiversity crisis

To assess the coextinction of species (the loss of a species upon the loss of another), we present a probabilistic model, scaled with empirical data. The model examines the relationship between coextinction levels (proportion of species extinct) of affiliates and their hosts across a wide range of coevolved interspecific systems: pollinating Ficus wasps and Ficus, parasites and their hosts, butterflies and their larval host plants, and ant butterflies and their host ants. Applying a nomographic method based on mean host specificity (number of host species per affiliate species), we estimate that 6300 affiliate species are "coendangered" with host species currently listed as endangered. Current extinction estimates need to be recalibrated by taking species coextinctions into account.     

Radiological assessment of severity of canine nasal tumours and relationship with survival

A radiological assessment of 35 canine nasal tumours using an objective scoring system was carried out and related to patient survival. The scoring system demonstrated significant increases in disease-free interval and survival for dogs with scores of less than 12 compared to those with scores of 1 2 or above.     

Effects of bark girdling on carbohydrate supply and resistance of loblolly pine to southern pine beetle (Dendroctonus frontalis Zimm.) attack

Importance of current photosynthate in the regulation of tree defense against the southern pine beetle (SPB),Dendroctonus frontalis Zimm. (Coleoptera: Scolytidae) was investigated in loblolly pine,Pinus taeda L. Downward translocation of carbohydrate was blocked by removing a ring of bark (girdle) at 3.5 m above ground. Beetle colonization success and tree defensive responses measured as resin flow and induced lesion formation to inoculations with the beetle-associated fungus,Ophiostoma minus (Hedge.) H. and P. Sydow., were assessed above and below girdles. We hypothesized that a decrease in a available carbohydrate would lead to a decrease in tree defense and an increase in SPB colonization success below girdles. At 2 weeks, post-girdling carbohydrates were already reduced by 50% below girdles, but no significant differences in beetle colonization success or defensive responses were measured. At 8 weeks, post-girdling starch was reduced by 93%, sucrose by 44% and resin flow by 44% below girdles. Southern pine beetle adults were more successful in colonizing areas below than above girdles. However, no significant differences were detected in the size of the lesions that formed in response to inoculated fungi. This suggests that the size of the induced lesion may not be a reliable indicator of tree resistance to bark beetle attack as previously believed, and that lesion development is not entirely dependent on available carbohydrate or related to tree defense against beetles. Cambial growth was reduced below girdles with no latewood formed below and 25 rows of latewood formed above girdles. Latewood contains much higher densities of resin ducts than earlywood. This may explain why resin flow was lower and beetles were more successful in colonizing areas of the tree below girdles. Therefore, tree defense against bark beetles may be more complex than a simple supply-and-demand relationship for carbohydrate, and changes in source-sink relationships, as influenced by the environment, may be more important than supply.