Host control over infection and proliferation of a cheater symbiont

Host control mechanisms are thought to be critical for selecting against cheater mutants in symbiont populations. Here, we provide the first experimental test of a legume host’s ability to constrain the infection and proliferation of a native‐occurring rhizobial cheater. Lotus strigosus hosts were experimentally inoculated with pairs of Bradyrhizobium strains that naturally vary in symbiotic benefit, including a cheater strain that proliferates in the roots of singly infected hosts, yet provides zero growth benefits. Within co‐infected hosts, the cheater exhibited lower infection rates than competing beneficial strains and grew to smaller population sizes within those nodules. In vitro assays revealed that infection‐rate differences among competing strains were not caused by variation in rhizobial growth rate or interstrain toxicity. These results can explain how a rapidly growing cheater symbiont – that exhibits a massive fitness advantage in single infections – can be prevented from sweeping through a beneficial population of symbionts.     

Historical DNA from museum type specimens clarifies diversity of Asian leaf turtles (Cyclemys)

Species boundaries in Asian leaf turtles of the genus Cyclemys are difficult to define on the basis of morphology, primarily because many populations exhibit considerable ontogenetic variation in shell and head coloration. Two recent molecular phylogenetic hypotheses of Cyclemys species relationships, based largely on market and pet-trade samples of uncertain provenance, were highly incongruent. We used historical DNA methods to sequence fragments of the mitochondrial cytochrome  b gene from eight type specimens of Cyclemys (including one collected by Alfred Russel Wallace), and phylogenetically placed these type sequences into the context of published cytochrome  b variation. Our phylogenetic hypothesis supports the recognition of four named species ( Cyclemys atripons , Cyclemys dentata , Cyclemys oldhamii , and C. pulchristriata ), as well as a fifth species of unknown geographical provenance obtained from the Hong Kong pet trade. The type sequences show that previous molecular phylogenetic studies were hampered by misidentifications, supporting the notion that Cyclemys of unknown provenance are not reliably identified to species solely on the basis of morphology.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 131–141.     

Isolation and characterization of microsatellite markers in Phytophthora ramorum,the causal agent of sudden oak death

We describe specific primers and conditions to amplify two dinucleotide and five trinucleotide microsatellite DNA loci isolated from the oomycete Phytophthora ramorum, the causal agent of sudden oak death. The primer sets were tested on 14–30 isolates from North America and Europe. Seven of 14 loci differentiated between A1 and A2 mating types. All seven loci successfully amplified DNA isolated from infected plant tissue. Four loci may be useful for the diagnosis of P. ramorum because they do not amplify closely related Phytophthora species.     

The Growth Physiology of Coleoptiles in Continuous-Record Vessels: Anomalous Kinetics of Cycloheximide Action on Auxin-Controlled Growth

The interacting effects of auxin and cycloheximide upon the growth of Triticum coleoptiles depends upon the incubation conditions. In the growth vessel developed by Evans and Ray (1969) the action of cycloheximide is severe and the growth kinetics show a rapid nullification of auxin action by the inhibitor; hormone action is also totally prevented by a relatively short period of pre-treatment with cycloheximide. The kinetics of response to the two substances are quite different when coleoptiles are floating on the test solutions; here, cycloheximide is much less severe in its action. These differences are due to a heightened sensitivity to cycloheximide induced by exclusion of the air bubble from the coleoptile cylinder in the Evans and Ray chamber. The outer surface of the coleoptile wall is a less efficient respiratory surface than the inner one. When coleoptiles are filled with a stagnant solution insufficient oxygen can be taken up through the inner surface and the tissue therefore suffers oxygen deprivation. This exacerbates the action of cycloheximide as a potent respiratory inhibitor. The results raise questions concerning the use of conditions in which coleoptile sections are filled and submerged, which is a feature of recently introduced continuous-record growth vessels. In particular, interpretation of the interactions between cycloheximide and auxin under such conditions must be made cautiously.