Insects constitute nearly 80% of species on earth and are among the most diverse group of organisms in the history of life, giving them considerable potential to provide insight into evolutionary mechanisms. Insects, with their large number of species, their biomass, diversity of adaptation, and ecological impact, support the structure and function of ecosystem and biodiveristy on the lands of the earth. Numerous crops rely on insects for pollination, with the importance of insects extending into other agricultural and human health concerns. Insects have been in existence for at least 400 million years, making them among the earliest land animals. Though nearly one million insect species have been classified and named, their actual number is believed to be between 2.5 and 10 million. It is widely accepted that insects diverged as members of one of the largest subphyla in arthropods more than 390 million years ago. During this time, insects experienced rapid evolution and a radiation that is considered faster than any other group , migrating into nearly all available environmental niches except the benthic zone . Mitochondrial DNA strongly supports an insect-crustacean clade as a sister group, which excludes the other arthropod subphyla collectively known as the myriapods . The insects are a monophyletic group, a universally held view supported by morphological and molecular features.
The structure of an organism is an outgrowth of development tailored to meet functional demands in an idiosyncratic evolutionary history. Like other segmented animals, insects are composed of a series of repeated units called metameres. Extant arthropods share many taxonomical characteristics, such as an exoskeleton, jointed appendages, and reduced coeloms and hemocoels. The segments of the insect body are organized into three major tagmata unique to this subclass: the head, thorax, and abdomen . The thorax has three pair of legs, and in pterygotes, the wings. In the abdomen, we find the presence of an ovipositor in females. In addition to the macro-scale features mentioned above, other defining features of the Insecta include: the loss of musculature and the presence of the Johnsonton's organ in the antenna, loss of articulations between the coxae and the sterna, sub-segmentation of the tarsus into units called tarsomeres, articulation of the pretarsal claws with the apical-most tarsomere , and the presence, at least primitively, of a long terminal filament . Insects are one of only four lineages of animals with powered flight, the others being pterosaurs, birds, and bats. Wings refine insect design, vastly improving mobility, dispersal, and complex behaviors to adapt to environmental challenges. It is widely held that insects evolved flight just once, at least 100 million years before pterosaurs, perhaps 170 million years ago . Other noteworthy features include the development of the posterior tentorium into a tranverse bar, and metamorphism and segmentation of metameres [7,8].
It is likely that the specialized features of the Insecta clade are based on components specific to its proteome. Characterization of this protein set should improve understanding of the molecular basis for the diversification of insects and their extensive success in ecological niches. Toward elucidating this molecular basis, we have characterized the eukaryote and insect proteomes. The large number of eukaryote genome sequences now available, including various insect genomes, makes it possible to characterize proteomes computationally. In this work, we utilized the insect genome sequences of fruit fly, mosquito, silk worm, beetle, honeybee, locust ESTs, and the non-insect eukaryote genomes of nematode, human, and yeast. (The insect-species in our study coverholometabolousandhemimetabolousdevelopment.) Since our approach utilizes genome sequence for approximating the proteome, the resolution of the proteome characterization improves as more genomes become available. This rapid characterization of proteomes through computation facilitates rational hypothesis generation and experiment design in applied research in many areas, such as biodiversity, agriculture and human health.