http://www.extento.hawaii.edu/kbase/Crop/Type/b_phoeni.htm
and here is a picture
Posted on 08/10/2004 10:16:36 PM PDT by SunkenCiv
The false spider mite has been revealed as the first known animal to make do with only one set of chromosomes, challenging traditional theories of evolution... Using standard sequencing techniques, Weeks's team found the mites' chromosomes to be very different. As far as the researchers could tell, none of the mites carried two identical copies of any particular gene. They conclude that the species is exclusively haploid. Weeks thinks being exclusively haploid might give the animals an evolutionary advantage... This genetic state may be rare simply because diploidy was "frozen" early in evolution and other animals haven't had the opportunity to make the transition.
(Excerpt) Read more at newscientist.com ...
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Here is the text
The false spider mite has been revealed as the first known animal to make do with only one set of chromosomes, challenging traditional theories of evolution.
The cells of most multicellular animals are "diploid" - they carry two copies of each chromosome. This makes evolutionary sense: if a mutation strikes a gene on one chromosome, a flawless version on the other can compensate. But no one has ever found an animal where both sexes are "haploid" - carrying a single set of unpaired chromosomes.
Until now, that is. A team led by Andrew Weeks of the University of Amsterdam in the Netherlands has shown that the false spider mite Brevipalpus phoenicis, a pest of crops such as citrus fruits, tea and palms, fits the bill. "It seems that in biology there are exceptions to every rule," says Weeks.
"Never before has a female from the animal kingdom been found to be exclusively haploid," he says. Almost all the mites are female and produce only female offspring from unfertilised eggs.
"This is quite a surprise - it goes against the dogma I was taught," says Sarah Otto, an evolutionary biologist at the University of British Columbia in Vancouver. Because no all-haploid species had been discovered, biologists assumed that the strategy couldn't work.
Evolutionary advantage
The adult cells of false spider mites contain two chromosomes. But before Weeks's study, no one knew whether these chromosomes were similar, suggesting a diploid state, or unrelated, suggesting a haploid state.
Using standard sequencing techniques, Weeks's team found the mites' chromosomes to be very different. As far as the researchers could tell, none of the mites carried two identical copies of any particular gene. They conclude that the species is exclusively haploid.
Weeks thinks being exclusively haploid might give the animals an evolutionary advantage. In the long term, their lack of chromosome copies to compensate for harmful mutations might help the species by ensuring that dangerous mutations kill the individuals carrying them rather than spreading down the generations.
This genetic state may be rare simply because diploidy was "frozen" early in evolution and other animals haven't had the opportunity to make the transition.
Weeks believes the mites once consisted of diploid females and haploid males. But he has shown that infection by an as yet unclassified bacterium feminised any rare males in the wild, possibly by blocking the secretion of a crucial male hormone.
The offspring of these infected mites would eventually develop into haploid females, leaving few males for the diploid females to mate with.
hmmmm. nothing yet. but I do hear a rumbling off in the distance.
The V.P. should be credited with the discovery that Leahy is haploid, and merely simplified his hypotheses to layman terms.
and here is a paper report by S Subramanian
http://genomebiology.com/2001/2/9/reports/0029
Significance and context
Haplodiploidy, a state where males are haploid and females are diploid, is seen in many insect species, but so far no organism has been found to exist exclusively in the haploid state. Weeks and colleagues report that females of a mite species exist exclusively in a haploid state. Brevipalpus phoenicis, a minute phytophagous mite found in tropical and subtropical regions, is considered to be one of the major pests of many economically important crops such as citrus, coffee and tea. The false spider mite B. phoenicis and its close relatives B. obovatus and B. californicus reproduce by parthenogenesis. In the field, B. phoenicis is found almost exclusively in the female state. Both the eggs and adult cells of these female mites contain two chromosomes, but it has been difficult to unravel whether this represents a haploid or diploid state. Weeks et al. have shown that these two chromosomes are genetically distinct and that the female mites are haploid.
Key results
Weeks et al. used cytological and genetic studies to show that B. phoenicis is a haploid female parthenogen. They found that only one of the two chromosomes contains a nuclear-organizing region (NOR). If the two chromosomes were homologous, they would carry copies of the same genes in the same locations, thus, the presence of only one NOR suggests that the chromosomes are distinct and B. phoenicis is haploid. In addition, Weeks et al. used fluorescent in situ hybridization to locate the ribosomal DNA (rDNA) in the metaphase chromosomes. The B. phoenicis 18S rDNA probe hybridizes at the tip of both sister chromatids of one chromosome in a metaphase mitotic division and no hybridization signal was seen on the second chromosome. The results showed only one carries an 18S ribosomal DNA gene. The authors also screened 45 clonal lines of B. phoenicis for genetic variation at seven polymorphic microsatellite loci and found no differences at any locus.
During the investigation large numbers of endosymbiotic bacteria were found to be associated with these mites. Weeks et al. attempted to discover whether these bacteria were involved in female haploid parthenogenesis. By sequencing bacterial 16S rDNA amplified from mites, the bacterium was identified as an endosymbiote that is also found in the tick Ixodes scapularis. To establish whether the bacteria are involved in causing parthenogenesis, B. phoenicis females were treated with the antibiotic tetracycline, which eliminated the bacteria, and were then allowed to lay eggs. Significantly more male offspring were produced after tetracycline treatment than without, suggesting that female haploid parthenogenesis is caused by bacterial infection which results in feminization of genetic males.
Conclusions
Brevipalpus phoenicis exist only as females in the haploid state. The two chromosomes of this species are genetically distinct. Feminization of haploid genetic males results from infection by an endosymbiotic bacterium.
Reporter's comments
This is the first report that feminization by an extra-chromosomal factor has been found outside of heterogametic reproductive systems. Weeks et al. have shown that feminization can involve bacteria other than Wolbachia - a bacterium that is known to induce feminization by blocking the formation of the androgenic gland. Studying the possible infection mechanism by which these bacteria induce feminization will shed more light on the sex-determination process of these mites.
Thanks for those (other than the photo, that was pretty creepy).
The mite's populations would once have included males with one set of chromosomes and females with two. This condition has evolved many times in mites and insects, such as ants.
http://www.nature.com/NSU/010705/010705-1.html
Ya'll got enough popcorn over behind them thar feed bags? If not, I'll trade you some of mine for a soda, from over here behind the hay bales.
Hope it's a good show. If not, then I'll sneak out watch Perseids, if the clouds have left.
Nice pic. Thanks for the ping. I don't know what to make of this thread. If it gathers steam I may ping the evo list.
I thought that Darwinian dogma excluded goals.
There is, of course, an assumed selection gradient here, which would function over time as a "goal". Assuming the assumed gradient actually exists.
Yes, that was the best of the pictures on the Web. But, no trace of any Intelligent Designer, not even a sober one.
Assume2
Assuming the assumed gradient actually exists.
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