BACKGROUND: In many animals, the first few hours of life proceed with little or no transcription, and developmental regulation at these early stages is dependent on maternal cytoplasm rather than the zygotic nucleus. Translational control is critical for early Drosophila embryogenesis and is exerted mainly at the gene level. To understand post-transcriptional regulation during Drosophila early embryonic development, we used sucrose polysomal gradient analyses and GeneChip analysis to illustrate the translation profile of individual mRNAs. RESULTS: We determined ribosomal density and ribosomal occupancy of over 10,000 transcripts during the first ten hours after egg laying. CONCLUSION: We report the extent and general nature of gene regulation at the translational level during early Drosophila embryogenesis on a genome-wide basis. The diversity of the translation profiles indicates multiple mechanisms modulating transcript-specific translation. Cluster analyses suggest that the genes involved in some biological processes are co-regulated at the translational level at certain developmental stages.

Genetic studies of the targets of the Hox genes have revealed only the tip of the iceberg. Recent microarray studies that have identified hundreds more transcriptional responses to Hox genes in Drosophila will help elucidate the role of Hox genes in development and evolution.

Insect dispersal dimorphisms, in which both flight-capable and flightless individuals occur in the same species, are thought to reflect a balance between the benefits and costs of dispersal. Fitness costs and benefits associated with wing dimorphism were investigated in the male pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). In one-on-one mating competitions in small arenas between winged and wingless males, the winged aphids obtained most of the matings with virgin females. In contrast, during competition experiments in larger cages with multiple individuals of each morph, the winged males no longer had a clear mating advantage over wingless males. In the absence of competition, wingless males had marginally higher lifetime reproductive success than winged males, probably because mating winged males tended to die faster than wingless males. In the absence of females, winged males survived longer than wingless males and this difference disappeared under starvation conditions. Mating males of both morphs died significantly faster than males without access to females. There does not appear to be a direct tradeoff of dispersal ability with life history characteristics in pea aphid males, suggesting that the advantages of producing winged males may result from outbreeding.

What is the relationship between variation that segregates within natural populations and the differences that distinguish species? Many studies over the past century have demonstrated that most of the genetic variation within natural populations that contributes to quantitative traits causes relatively small phenotypic effects. In contrast, the genetic causes of quantitative differences between species are at least sometimes caused by few loci of relatively large effect. In addition, most of the results from evolutionary developmental biology are often discussed as though changes at just a few important 'molecular toolbox' genes provide the key clues to morphological evolution. On the face of it, these divergent results seem incompatible and call into question the neo-Darwinian view that differences between species emerge from precisely the same kinds of variants that segregate much of the time in natural populations. One prediction from the classical model is that many different genes can evolve to generate similar phenotypes. I discuss our studies that demonstrate that similar phenotypes have evolved in multiple lineages of Drosophila by evolution of the same gene, shavenbaby/ovo. This evidence for parallel evolution suggests that svb occupies a privileged position in the developmental network patterning larval trichomes that makes it a favourable target of evolutionary change.

Given a large collection of videos containing activities, we investigate the problem of organizing it in an unsupervised fashion into a hierarchy based on the similarity of actions embedded in the videos. We use spatio-temporal volumes of filtered motion vectors to compute appearance-invariant action similarity measures efficiently - and use these similarity measures in hierarchical agglomerative clustering to organize videos into a hierarchy such that neighboring nodes contain similar actions. This naturally leads to a simple automatic scheme for selecting videos of representative actions (exemplars) from the database and for efficiently indexing the whole database. We compute a performance metric on the hierarchical structure to evaluate goodness of the estimated hierarchy, and show that this metric has potential for predicting the clustering performance of various joining criteria used in building hierarchies. Our results show that perceptually meaningful hierarchies can be constructed based on action similarities with minimal user supervision, while providing favorable clustering performance and retrieval performance.