Bath, UK (SPX) Oct 30, 2006
The family tree covering almost half the animal species on the planet has been re-drawn following a genetic analysis which has revealed new relationships between four major groups of insects. Scientists have found that flies and moths are most closely related to beetles and more distantly related to bees and wasps, contrary to previous theory.
The findings are published in the special Honey bee Genome issue of the journal Genome Research which coincides with Nature's publication of the honey bee genome sequence (also Thursday 26 October 2006).
The results are based on an analysis of the same 185 genes found in the genomes of eight different insect families, which together represent 45 per cent of all known animal species.
This enabled the international group of scientists to work out the evolutionary relationships between the insects based on changes and mutations within those genes.
Previously scientists had assumed that flies and moths were most closely related to bees and wasps, with beetles more distantly related to these groups.
This new family arrangement also brings the different species of social insects, such as termites and bees, closer together - suggesting that the ability of insects to cooperate in social groupings may have evolved just once, rather than independently in several different species.
"About half of all animal species belong to just four groups of insects but, surprisingly, we never knew for sure how they are related to each other," said Dr Martin Lercher from the University of Bath, who lead the research.
"While there was never unequivocal evidence for it, scientists believed for a long time that, based on morphology, flies and moths were most closely related to bees, with beetles more distantly related to these three groups.
"By comparing genetic information from 185 genes that were sequenced in species from all of these groups, we found that in fact flies and moths are most closely related to beetles, and more distantly related to bees.
"This sheds new light on a large number of evolutionary questions, as a correct understanding of the evolutionary relationships is fundamental to any interpretation of similarities or differences among species.
"For example, social colonies are common among bees and wasps and their relatives, ants, as well as among more distantly related insects, such as termites and aphids.
"That beetles don't show this tendency, known as eusociality, has been interpreted as a sign that eusociality has evolved several times independently.
"Now that we know that bees, wasps and ants are in fact the closest relatives to the more distantly related (or 'basal') species, it appears more likely that the genetic basis for eusociality may have evolved only once, and was lost in the common ancestor of beetles, moths, and flies."
The researchers used the genomes of six different insects from the holometabolous group of insects (insects which undergo complete metamorphosis): fruit fly (Drosophila melanogaster), mosquito (Anopheles gambiae), silk moth (Bombyx mori), flour beetle (Tribolium castaneum), honey bee (Apis mellifera) and sibling parasitic wasp species (Nasonia vitripennis and Nasonia giraulti).
These insects represent the four major orders of holometabolous insects, beetles (Coleoptera), moths (Lepidoptera), flies (Diptera) and bees and wasps (Hymenoptera), which together represent 45 per cent of the animal species on earth.
They also included one orthopteran (the grasshopper Locusta migratoria) and one hemipteran (the pea aphid Acyrthosiphon pisum), both of which are uncontested out-groups to the holometabolous insects.
The researchers are from the University of Cologne (Germany), Baylor College of Medicine (USA), University of Rochester (USA), the Institute for Genomic Research (USA), the University of Bath (UK) and the European Molecular Biology Laboratory (Germany).
The research was funded by the Human Frontier Science Program Organization, the Deutsche Forschungsgemeinschaft (DFG), the Royal Society and the 21st Century Research and Technology Fund.
The research of Zachary Huang, MSU associate professor in the Department of Entomology, and his colleagues will be featured in the Oct. 26 edition of the journal Genome Research.
"This research gives us a better understanding of the sex-determining system of honey bees, as well as the age and evolutionary history of the csd (complementary sex determination) gene," Huang said. "The various versions of the csd genes are shared among honey bees. They evolved before they became different species."
In addition, the findings also will allow breeders to design better and more efficient mating systems. Breeders more easily will be able to raise new queens to lead hives.
This research is supported by grants from the National Institutes of Health, Office of Vice President for Research of the University of Michigan, the University of Kansas General Research Fund and the Michigan Agricultural Experiment Station.
The csd gene determines the difference between a male and female honey bee, according to Huang. His research shows this method of sex determination first appeared in a shared ancestor of the European and three Asian honey bee species.
In humans, sex is determined by the combination of sex-determining chromosomes one has. In females, both sex-determining chromosomes are the same - XX; for males the two chromosomes are different - XY.
Honey bees do things a bit differently. Specific combinations of the csd gene regulate the gender and social roles of each honey bee.
In the past, scientists thought the sex determination of offspring was left purely up to the queen, Huang said. Scientists believed that after a queen bee returned to her hive from a mating flight she had a choice of laying fertilized or unfertilized eggs. The unfertilized eggs would develop into male drones. The fertilized eggs develop into female honey bees. But there's more to the story.
Alleles are different versions of the same gene. In humans, they dictate characteristics like eye and hair color.
If the bee has two different alleles, the csd gene will be female. If it has only a single version of the gene, it will become a normal, fertile male. Finally, if the bee has two identical csd types it will become a diploid male, which is infertile, Huang explained. The unlucky infertile males will never successfully reproduce so they are eaten by other members of the hive to save resources.
Aside from determining life and death, csd mechanism is important to the overall function of the hive.
There's a big difference between the duties of a fertile male honey bee and those of a female. The males lead a life of luxury - their duties include eating, resting and mating.
After hatching a female's life can take one of two directions. Fed a diet of royal jelly, the female hatchling will develop into a queen bee. If not, she will become one of the 20,000 to 60,000 worker bees tending to the needs of the hive, the drones, her queen and the next generation.
Ultimately the csd system shared by all honey bee species means increased genetic diversity and a better chance for their genes to carry over to the next generation.
"This is a matter of gene transmission," Huang said. "It is an evolutionary strategy to maximize gene transmission to the next generation."
University of Bath
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