A Dichotomy Theorem for Homomorphism Polynomials

In the present paper we show a dichotomy theorem for the complexity of polynomial evaluation. We associate to each graph H a polynomial that encodes all graphs of a fixed size homomorphic to H. We show that this family is computable by arithmetic circuits in constant depth if H has a loop or no edge and that it is hard otherwise (i.e., complete for VNP, the arithmetic class related to #P). We also demonstrate the hardness over the rational field of cut eliminator, a polynomial defined by B\"urgisser which is known to be neither VP nor VNP-complete in the field of two elements, if VP is not equal to VNP (VP is the class of polynomials computable by arithmetic circuit of polynomial size)

Pond canopy cover: a resource gradient for anuran larvae

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72395/1/j.1365-2427.2005.01497.x.pd

Ecological and evolutionary functional genomics - How can it contribute to the risk assessment of chemicals?

Ecological and evolutionary functional genomics has progressed enormously over the last 10 years. One of the developments most relevant for environmental science is genome-wide gene expression profiling, using microarrays and RNAseq, of organisms exposed to toxic chemicals. In this way, the action spectrum of chemicals can be characterized on the basis of an extremely large number of endpoints. In this paper we identify a number of formidable problems for the use of transcription profiling in risk assessment. We raise four issues (1) Is it possible at all to assess environmental quality based on transcriptomes (mRNA abundance)? (2) Does gene expression classify treatments according to exposure or effect? (3) Do gene expressions allow identification of chemicals in mixtures? (4) Is it possible to discriminate fitness-neutral gene expressions from those associated with adverse outcomes? We call for the generation of more background data under normal, clean conditions. A close connection between traditional ecotoxicology and genomics seems to be particularly fruitful. Only in this way can transcriptome data be connected to endpoints accepted in risk assessment schemes. © 2011 American Chemical Society

Can artificially selected phenotypes influence a component of field fitness? Thermal selection and fly performance under thermal extremes

Artificially selected lines are widely used to investigate the genetic basis of quantitative traits and make inferences about evolutionary trajectories. Yet, the relevance of selected traits to field fitness is rarely tested. Here, we assess the relevance of thermal stress resistance artificially selected in the laboratory to one component of field fitness by investigating the likelihood of adult Drosophila melanogaster reaching food bait under different temperatures. Lines resistant to heat reached the bait more often than controls under hot and cold conditions, but less often at intermediate temperatures, suggesting a fitness cost of increased heat resistance but not at temperature extremes. Cold-resistant lines were more common at baits than controls under cold as well as hot field conditions, and there was no cost at intermediate temperatures. One of the replicate heat-resistant lines was caught less often than the others under hot conditions. Direct and correlated patterns of responses in laboratory tests did not fully predict the low performance of the heat selected lines at intermediate temperatures, nor the high performance of the cold selected lines under hot conditions. Therefore, lines selected artificially not only behaved partly as expected based on laboratory assays but also evolved patterns only evident in the field releases