Evolution of gene expression in fire ants: the effects of developmental stage, caste, and species.

Ants provide remarkable examples of equivalent genotypes developing into divergent and discrete phenotypes. Diploid eggs can develop either into queens, which specialize in reproduction, or workers, which participate in cooperative tasks such as building the nest, collecting food, and rearing the young. In contrast, the differentiation between males and females generally depends upon whether eggs are fertilized, with fertilized (diploid) eggs giving rise to females and unfertilized (haploid) eggs giving rise to males. To obtain a comprehensive picture of the relative contributions of gender (sex), caste, developmental stage, and species divergence to gene expression evolution, we investigated gene expression patterns in pupal and adult queens, workers, and males of two species of fire ants, Solenopsis invicta and S. richteri. Microarray hybridizations revealed that variation in gene expression profiles is influenced more by developmental stage than by caste membership, sex, or species identity. The second major contributor to variation in gene expression was the combination of sex and caste. Although workers and queens share equivalent diploid nuclear genomes, they have highly distinctive patterns of gene expression in both the pupal and the adult stages, as might be expected given their extraordinary level of phenotypic differentiation. Overall, the difference in the proportion of differentially expressed genes was greater between workers and males than between workers and queens or queens and males, consistent with the fact that workers and males share neither gender nor reproductive capability. Moreover, between-species comparisons revealed that the greatest difference in gene expression patterns occurred in adult workers, a finding consistent with the fact that adult workers most directly experience the distinct external environments characterizing the different habitats occupied by the two species. Thus, much of the evolution of gene expression in ants may occur in the worker caste, despite the fact that these individuals are largely or completely sterile. Analyses of gene expression evolution revealed a combination of positive selection and relaxation of stabilizing selection as important factors driving the evolution of such genes.

The relationship between Lamb weather types and long-term changes in flood frequency, River Eden, UK

Research has found that both flood magnitude and frequency in the UK may have increased over the last five decades. However, evaluating whether or not this is a systematic trend is difficult because of the lack of longer records. Here we compile and consider an extreme flood record that extends back to 1770. Since 1770, there have been 137 recorded extreme floods. However, over this period, there is not a unidirectional trend of rising extreme flood risk over time. Instead, there are clear flood-rich and flood-poor periods. Three main flood-rich periods were identified: 18731904, 19231933, and 1994 onwards. To provide a first analysis of what is driving these periods, and given the paucity of more sophisticated datasets that extend back to the 18th century, objective Lamb weather types were used. Of the 27 objective Lamb weather types, only 11 could be associated with the extreme floods during the gauged period, and only 5 of these accounted for > 80% of recorded extreme floods The importance of these five weather types over a longer timescale for flood risk in Carlisle was assessed, through calculating the proportion of each hydrological year classified as being associated with these flood-generating weather types. Two periods clearly had more than the average proportions of the year classified as one of the flood causing weather types; 19001940 and 19832007; and these two periods both contained flood-rich hydrological records. Thus, the analysis suggests that systematic organisation of the North Atlantic climate system may be manifest as periods of elevated and reduced flood risk, an observation that has major implications for analyses that assume that climatic drivers of flood risk can be either statistically stationary or are following a simple trend. Copyright (c) 2011 Royal Meteorological Society

Roadway Lighting on Secondary Roads in Iowa, HR-251, 1984

There are approximately 800 installations of destination lighting at secondary road intersections in Iowa. Approximately 90% of these have only a single luminaire. The other installations have two luminaires. No warrants currently exist for justifying the use of this type of lighting. Previous research has examined the safety benefits from full lighting of rural intersections that generally serve substantially higher traffic volumes than secondary road intersections in Iowa. However, the safety benefit of destination lighting at intersections carrying relatively low volumes has not been the subject of previous research. The research reported here, sponsored by the Iowa Department of Transportation, was undertaken to identify locations where destination lighting could be expected to improve highway safety. If destination lighting were shown to reduce accident frequency, warrants for its use on secondary roads could be developed. An inventory of secondary road lighting installations in Iowa was assembled. From this inventory, two samples were constituted that would permit two separate comparisons of the accident experience with and without destination lighting. Before and after comparisons were made for the same locations if accident records were available for at least one full year both preceding and following the installation of destination lighting. Accident records for this purpose were available from a statewide computerized record system covering the period from 1977 through 1982. The accident experience at locations having destination lighting installed before 1978 was compared with a sample of comparable locations not having destination lighting. The sample of secondary road intersections used for the before and after comparison included 91 locations. The sample of continuously lighted locations included 102 intersections. Accident experience at these locations was compared with the experience at 102 intersections that were not lighted. The intersections included in these samples averaged only 0.31 accidents per year. The accident rate at secondary road intersections that had destination lighting did not differ significantly from the accident rate at intersections that were not lighted. This conclusion was derived from both comparisons, the before and after experience and the comparison of experience at intersections that were continuously lighted with that at unlighted locations. Furthermore, no significant differences were noted between lighted and unlighted locations in the proportion of accidents that occurred at night. The distribution of accidents by type also did not differ between unlighted intersections and those having destination lighting. It was not possible to formulate warrants for destination lighting since analyses directed toward identifying specific characteristics of an intersection that could be correlated with highway safety did not yield any useful relationships. However, it was noted that the average damages for night accidents that occurred at lighted intersections were lower than for accidents at unlighted intersections. Even in the absence of a more definitive demonstration of beneficial effects, destination lighting is perceived by officials in most of the counties having such installations as yielding desirable effects and is recognized as helpful to motorists in performing the guidance function in driving. Given this benefit and a relatively low cost (an average of $74 per year for one luminaire), and given that the subjective criteria that have been used in the past to justify the installation of destination lighting have led to a high degree of public acceptance and satisfaction, it is recommended that the same subjective criteria continue to be used in lieu of definitive warrants.