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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
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Home | Pregnancy Timeline | News Alerts | News Archive July 24, 2013

 

Microbiome tree of life

The tree of life made out of Nasonia microbes. (Image credit: Robert Brucker/Vanderbilt.









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We are the microbes we carry

You are not just yourself. You are also the thousands of microbes that you carry. In fact, they represent an invisible majority that may be more you than you realize.

These microscopic fellow travelers are collectively called our microbiome. Realization that every species of plant and animal is accompanied by a distinctive microbiome is old news. But evidence of the impact that these microbes have on their hosts continues to grow rapidly in areas ranging from brain development to digestion to defense against infection to producing bodily odors.

Now, contrary to current scientific understanding, it also appears that our microbial companions play an important role in evolution. A new study, published online on July 18 by the journal Science, has provided direct evidence that these microbes can contribute to the origin of new species by reducing the survival of hybrids produced between males and females of different species.


This study provides the strongest evidence to date for the controversial hologenomic theory of evolution, which proposes that the object of Darwin's natural selection is not just the individual organism as he proposed, but the organism plus its associated microbial community. (The hologenome includes the genome of the host and the genomes of all of its microbes.)


"It was a high-risk proposition. The expectation in the field was that the origin of species is principally driven by genetic changes in the nucleus. Our study demonstrates that both the nuclear genome and the microbiome must be considered in a unified framework of speciation," said Associate Professor of Biological Sciences Seth Bordenstein who performed the study with post-doctoral fellow Robert Brucker.

They conducted their research using three species of the jewel wasp Nasonia. These tiny, match-head sized wasps parasitize blowflies and other pest flies, which make them useful for biological control.

"The wasps have a microbiome of 96 different groups of microorganisms," said Brucker. Two of the species they used (N. giraulti and N. longicornis) only diverged about 400,000 years ago so they are closely related genetically. This closeness is also reflected in their microbiomes, which are quite similar. The third species (N. vitripennis), on the other hand, diverged about a million years ago so there are greater differences in both its genome and microbiome, he explained.

The mortality of hybrid offspring from the two closely related species was relatively low, about 8 percent, while the mortality rate of hybrid offspring between either of them and N. vitripennis was quite high, better than 90 percent, the researchers established.

"The microbiomes of viable hybrids looked extremely similar to those of their parents, but the microbiomes of those that did not survive looked chaotic and totally different," Brucker reported.

The researchers showed that the incompatibilities that were killing the hybrids had a microbial basis by raising the wasps in a microbe-free environment. They were surprised to find that the germ-free hybrids survived just as well as purebred larvae. But when they gave the germ-free hybrids gut microbes from regular hybrids, their survival rate plummeted.

"Our results move the controversy of hologenomic evolution from an idea to an observed phenomenon," said Bordenstein. "The question is no longer whether the hologenome exists, but how common it is?"

This research was supported by award DEB 1046149 from the National Science Foundation's Dimensions of Biodiversity program.

Further information can be found at the Bordenstein Lab, the author's blogs at Symbionticism and Live In Symbiosis, and the author's twitter feeds @Symbionticism and @LiveInSymbiosis.

Original press release:http://www.eurekalert.org/pub_releases/2013-07/vu-mci071613.php