Kepler-424 b: A "lonely" hot Jupiter that found a companion

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The origin of the parrotfish species Scarus compressus in the Tropical Eastern Pacific: region-wide hybridization between ancient species pairs

BACKGROUND: In the Tropical Eastern Pacific (TEP), four species of parrotfishes with complex phylogeographic histories co-occur in sympatry on rocky reefs from Baja California to Ecuador: Scarus compressus, S. ghobban, S. perrico, and S. rubroviolaceus. The most divergent, S. perrico, separated from a Central Indo-Pacific ancestor in the late Miocene (6.6 Ma). We tested the hypothesis that S. compressus was the result of ongoing hybridization among the other three species by sequencing four nuclear markers and a mitochondrial locus in samples spanning 2/3 of the latitudinal extent of the TEP. RESULTS: A Structure model indicated that K = 3 fit the nuclear data and that S. compressus individuals had admixed genomes. Our data could correctly detect and assign pure adults and F1 hybrids with > 0.90 probability, and correct assignment of F2s was also high in some cases. NewHybrids models revealed that 89.8% (n = 59) of the S. compressus samples were F1 hybrids between either S. perrico × S. ghobban or S. perrico × S. rubroviolaceus. Similarly, the most recently diverged S. ghobban and S. rubroviolaceus were hybridizing in small numbers, with half of the admixed individuals assigned to F1 hybrids and the remainder likely > F1 hybrids. We observed strong mito-nuclear discordance in all hybrid pairs. Migrate models favored gene flow between S. perrico and S. ghobban, but not other species pairs. CONCLUSIONS: Mating between divergent species is giving rise to a region-wide, multispecies hybrid complex, characterized by a high frequency of parental and F1 genotypes but a low frequency of > F1 hybrids. Trimodal structure, and evidence for fertility of both male and female F1 hybrids, suggest that fitness declines sharply in later generation hybrids. In contrast, the hybrid population of the two more recently diverged species had similar frequencies of F1 and > F1 hybrids, suggesting accelerating post-mating incompatibility with time. Mitochondrial genotypes in hybrids suggest that indiscriminate mating by male S. perrico is driving pre-zygotic breakdown, which may reflect isolation of this endemic species for millions of years resulting in weak selection for conspecific mate recognition. Despite overlapping habitat use and high rates of hybridization, species boundaries are maintained by a combination of pre- and post-mating processes in this complex

A Comparison Study of Eleven Static Heuristics for Mapping a Class of Independent Tasks onto Ileterogeneous Distributed Computing Systems

ABSTRACT Il\u27lixed-machine heterogeneous computing (HC) environments utilize a distributed suite of different high-performance machines, interconnected with high-speed links to perform different computationally intensive applications that have diverse comput ational requirements. HC environments are well suited to meet thl: computational dell-tands of large, diverse groups of tasks. The problem of mapping (defined as matching and scheduling) these tasks onto the machines of a distributed HC environment has been shown, in general, to be NP-complete, requiring the development of heuristic techniques. Selecting the best heuristic to use in a given enviroi~menth, owever, remains a difficult problem, because comparisons are often clouded by different underlying assumptions in the original studies of each heuristic. There~fore; a collection of eleven heuristics from the literature has been selected: a,dapted, in~plementeda, nd anaiyzed under one set of common assumptions. It is assumed that the heuristics derive a, mapping statically (i.e., off-line). It is also assumed that a meta-task (i.e., a set of independent, non-communicating tasks) is being mapped, and that the goal is to minimize the total execution time of the metla-task. The eleven heuristics examined are Opportunistic Load Balancing, Minimum Execution Time, MininLlum Clompletion Time, Min-min, hllax-min, Duplex? Genetic i-Ilgorithm, Simulated Annealing, Genetic Simulat.ed .Annealing, Tabu, and Ax. This study provides one even basis for comparisor] and insights into circumstances where one technique will out perform another. The evaluation procedure is specified, the heuristics are defined, and then comparison results are discussed. It is shown that for the ca.ses studied here, the relat,ively simple Min-min heuristic performs well in comparison to the other techniques

Syntactic processing as a marker for cognitive impairment in amyotrophic lateral sclerosis

Despite recent interest in cognitive changes in patients with amyotrophic lateral sclerosis (ALS), investigations of language function looking at the level of word, sentence and discourse processing are relatively scarce. Data were obtained from 26 patients with sporadic ALS and 26 healthy controls matched for age, education, gender, anxiety, depression and executive function performance. Standardized language tasks included confrontation naming, semantic access, and syntactic comprehension. Quantitative production analysis (QPA) was used to analyse connected speech samples of the Cookie Theft picture description task. Results showed that the ALS patients were impaired on standardized measures of grammatical comprehension and action/verb semantics. At the level of discourse, ALS patients were impaired on measures of syntactic complexity and fluency; however, the latter could be better explained by disease related factors. Discriminant analysis revealed that syntactic measures differentiated ALS patients from controls. In conclusion, patients with ALS exhibit deficits in receptive and expressive language on tasks of comprehension and connected speech production, respectively. Our findings suggest that syntactic processing deficits seem to be the predominant feature of language impairment in ALS and that these deficits can be detected by relatively simple language tests