8,380 research outputs found
Process rather than pattern: finding pine needles in the coevolutionary haystack
The geographic mosaic theory is fast becoming a unifying framework for coevolutionary studies. A recent experimental study of interactions between pines and mycorrhizal fungi in BMC Biology is the first to rigorously test geographical selection mosaics, one of the cornerstones of the theory
Reverse graded relaxed buffers for high Ge content SiGe virtual substrates
An innovative approach is proposed for epitaxial growth of high Ge content, relaxed Si1âxGex buffer layers on a Si(001) substrate. The advantages of the technique are demonstrated by growing such structures via chemical vapor deposition and their characterization. Relaxed Ge is first grown on the substrate followed by the reverse grading approach to reach a final buffer composition of 0.78. The optimized buffer structure is only 2.8 ”m thick and demonstrates a low surface threading dislocation density of 4Ă106 cmâ2, with a surface roughness of 2.6 nm. The buffers demonstrate a relaxation of up to 107%
An Evaluation of the Possible Protective Effects of Neonatal Striatal Transplants Against Kainic Acid-Induced Lesions
The present study examined the recent report
that transplantation of neonatal striatal tissue
into kainic acid (KA) lesioned striatum protected
the contralateral striatum from a subsequent KA
lesion. We did not find a significant difference in
the survival rate of animals that received
neonatal striatal transplants into a KA lesioned
striatum followed by a subsequent lesion of the
contralateral striatum compared to those
animals that received bilateral KA-induced
striatal lesions alone. The tissue transplants did
not protect against the degeneration of striatal
neurons induced by KA. Indeed, the survival
rate was very low (25%) in the transplant groups.
A second experiment was also performed to
examine whether a neonatal striatal transplant
might reduce the severe syndrome of aphagia
and adipsia associated with KA lesions of the
striatum. Animals that received the neonatal
striatal transplants showed increased aphagia
and adipsia compared to animals only receiving
the KA lesion. Again, the transplant group had a
very low survival rate (10%). The present study
was unable to confirm that neonatal striatal
transplants protect against KA lesions either by
themselves or in conjunction with a recent KA
lesion
Interaction specificity between leaf-cutting ants and vertically transmitted Pseudonocardia bacteria
BACKGROUND : The obligate mutualism between fungus-growing ants and microbial symbionts offers excellent
opportunities to study the specificity and stability of multi-species interactions. In addition to cultivating fungus
gardens, these ants have domesticated actinomycete bacteria to defend gardens against the fungal parasite Escovopsis
and possibly other pathogens. Panamanian Acromyrmex echinatior leaf-cutting ants primarily associate with
actinomycetes of the genus Pseudonocardia. Colonies are inoculated with one of two vertically transmitted
phylotypes (Ps1 or Ps2), and maintain the same phylotype over their lifetime. We performed a cross-fostering
experiment to test whether co-adaptations between ants and bacterial phylotypes have evolved, and how this
affects bacterial growth and ant prophylactic behavior after infection with Escovopsis.
RESULTS : We show that Pseudonocardia readily colonized ants irrespective of their colony of origin, but that the
Ps2 phylotype, which was previously shown to be better able to maintain its monocultural integrity after workers
became foragers than Ps1, reached a higher final cover when grown on its native host than on alternative hosts.
The frequencies of major grooming and weeding behaviors co-varied with symbiont/host combinations, showing
that ant behavior also was affected when cuticular actinomycete phylotypes were swapped.
CONCLUSION : These results show that the interactions between leaf-cutting ants and Pseudonocardia bear signatures of
mutual co-adaptation within a single ant population.http://www.biomedcentral.com/bmcevolbiolhb201
Sperm mixing in the polyandrous leaf-cutting ant Acromyrmex echinatior
The insemination of queens by sperm from multiple males (polyandry) has evolved in a number of eusocial insect lineages despite the likely costs of the behavior. The selective advantages in terms of colony fitness must therefore also be significant and there is now good evidence that polyandry increases genetic variation among workers, thereby improving the efficiency of division of labor, resistance against disease, and diluting the impact of genetically incompatible matings. However, these advantages will only be maximized if the sperm of initially discrete ejaculates are mixed when stored in queen spermathecae and used for egg fertilization in a âfair raffle.â Remarkably, however, very few studies have addressed the level of sperm mixing in social insects. Here we analyzed sperm use over time in the highly polyandrous leaf-cutting ant Acromyrmex echinatior. We genotyped cohorts of workers produced either 2 months apart or up to over a year apart, and batches of eggs laid up to over 2 years apart, and tested whether fluctuations in patriline distributions deviated from random. We show that the representation of father males in both egg and worker cohorts does not change over time, consistent with obligatorily polyandrous queens maximizing their fitness when workers are as genetically diverse as possible
Reconstructing eight decades of genetic variation in an isolated Danish population of the large blue butterfly Maculinea arion
<p>Abstract</p> <p>Background</p> <p>Fragmentation of terrestrial ecosystems has had detrimental effects on metapopulations of habitat specialists. <it>Maculinea </it>butterflies have been particularly affected because of their specialized lifecycles, requiring both specific food-plants and host-ants. However, the interaction between dispersal, effective population size, and long-term genetic erosion of these endangered butterflies remains unknown. Using non-destructive sampling, we investigated the genetic diversity of the last extant population of <it>M. arion </it>in Denmark, which experienced critically low numbers in the 1980s.</p> <p>Results</p> <p>Using nine microsatellite markers, we show that the population is genetically impoverished compared to nearby populations in Sweden, but less so than monitoring programs suggested. Ten additional short repeat microsatellites were used to reconstruct changes in genetic diversity and population structure over the last 77 years from museum specimens. We also tested amplification efficiency in such historical samples as a function of repeat length and sample age. Low population numbers in the 1980s did not affect genetic diversity, but considerable turnover of alleles has characterized this population throughout the time-span of our analysis.</p> <p>Conclusions</p> <p>Our results suggest that <it>M. arion </it>is less sensitive to genetic erosion via population bottlenecks than previously thought, and that managing clusters of high quality habitat may be key for long-term conservation.</p
Insights from the 2006 Disease Management Colloquium
This roundtable discussion emanates from the presentations given and issues raised at the 2006 Disease Management Colloquium, which was held May 10â12, 2006 in Philadelphia, Pennsylvania
Improving Health Care Quality through Value-Based Purchasing: What Can the Pioneers Teach Us?
The Department of Health Policy of Jefferson Medical College has been engaged in research on value-based purchasing (VBP) for the past five years. With support from The Commonwealth Fund, the Departmentâs research team has examined the potential of VBP to improve quality and cost-effectiveness of health care. This article summarizes this work
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