Tag: Hybridization

Don't hate the hybrid!

By Razib Khan | November 21, 2011 4:44 am

There is a specter haunting the intersection of conservation biology and public policy, the specter of the biological species concept. Coyote-Wolf Hybrids Have Spread Across U.S. East:

Scientists already knew that some coyotes, which have been gradually expanding their range eastward, mated with wolves in the Great Lakes (map) region. The pairings created viable hybrid offspring—identified by their DNA and skulls—that have been found in mid-Atlantic states such as New York and Pennsylvania.

Now, new DNA analysis of coyote poop shows for the first time that some coyotes in the state of Virginia are also part wolf. Scientists think these animals are coyote-wolf hybrids that traveled south from New England along the Appalachian Mountains.

Most of the wolf ancestry in the lower 48 states might be in “coyotes!”

MORE ABOUT: Hybridization

Neanderthal-human mating, months later….

By Razib Khan | July 18, 2011 3:27 pm

Image credit:ICHTO

Recently something popped up into my Google news feed in regards to “Neanderthal-human mating.” If you are a regular reader you know that I’m wild for this particular combination of the “wild thing.” But a quick perusal of the press release told me that this was a paper I had already reviewed when it was published online in January. I even used the results in the paper to confirm Neanderthal admixture in my own family (we’ve all been genotyped). One of my siblings is in fact a hemizygote for the Neanderthal alleles on the locus in question! I guess it shows the power of press releases upon the media. I would offer up the explanation that this just shows that the more respectable press doesn’t want to touch papers which aren’t in print, but that’s not a good explanation when they are willing to hype up stuff which is presented at conferences at even an earlier stage.

A second aspect I noted is that except for Ron Bailey at Reason all the articles which use a color headshot use a brunette reconstruction, like the one here which is from the Smithsonian. But the most recent research (dating to 2007) seems to suggest that the Neanderthals may have been highly depigmented. This shouldn’t be too surprising when one considers that they were resident in northern climes for hundreds of thousands of years.

But there are some new tidbits, from researchers in the field of study:

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Neandertal hybridization & Haldane's rule

By Razib Khan | April 27, 2011 11:35 pm

Mr. James Winters at A Replicated Typo pointed me to a short hypothesis paper, Neanderthal-human Hybrids. This paper argues that selective mating of Neandertal males with females of human populations which had left Africa more recently, combined with Haldane’s rule, explains three facts:

- The lack of Neandertal Y chromosomal lineages in modern humans.

- The lack of Neandertal mtDNA lineages in modern humans.

- The probable existence of Neandertal autosomal ancestry in modern humans.

If you don’t know, Haldane’s rule basically suggests that there’s going to be some sort of breakdown in the heterogametic sex. In humans females are homogametic, XX, and males are heterogametic, XY. The breakdown need not be death (or spontaneous abortion). It could be sterility (e.g., some mutation or genetic incompatibility which results in the malfunctioning of the flagella of sperm would do it).

So you have a scenario where only Neandertal males are interbreeding with the intrusive groups from the south. The hybrids from these pairings would then lack Neandertal mtDNA, since mtDNA is passed only from mothers. But the male offspring would have Neandertal Y chromosomes. This is where Haldane’s rule kicks in: these males in their turn would not reproduce. Therefore only the female hybrids would pass on their genes. These females obviously don’t pass on a Y chromosome. And, they would pass on their non-Neandertal mother’s mtDNA.

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CATEGORIZED UNDER: Evolution, Genetics, Genomics

Hybridization is like sex

By Razib Khan | August 12, 2010 5:30 pm

480px-Olivia_MunnOne of the major issues which has loomed at the heart of biology since The Origin of Species is why species exist, as well as how species come about. Why isn’t there a perfect replicator which performs all the conversion of energy and matter into biomass on this planet? If there is a God the tree of life almost seems to be a testament to his riotous aesthetic sense, with numerous branches which lead to convergences, and a inordinate fascination with variants on the basic morph of beetles. From the outside the outcomes of evolutionary biology look a patent mess, a sprawling expanse of experiments and misfires.

A similar issue has vexed biologists in relation to sex. Why is it that the vast majority of complex organisms take upon themselves the costs of sex? The existence of a non-offspring bearing form within a species reduces the potential natural increase by a factor of two before the game has even begun. Not only that, but the existence of two sexes who must seek each other out expends crucial energy in a Malthusian world (selfing hermaphrodites obviously don’t have this problem, but for highly complex organisms they aren’t so common). Why bother? (I mean in an ultimate, not proximate, sense)

It seems likely that part of the answer to both these questions on the grande scale is that the perfect is the enemy of long term survival. Sexual reproduction confers upon a lineage a genetic variability which may reduce fitness by shifting populations away from the adaptive peak in the short term, but the fitness landscape itself is a constant bubbling flux, and perfectly engineered asexual lineages may all too often fall off the cliff of what was once their mountain top. The only inevitability seems to be that the times change. Similarly, the natural history of life on earth tells us that all greatness comes to an end, and extinction is the lot of life. The universe is an unpredictable place and the mighty invariably fall, as the branches of life’s tree are always pruned by the gardeners red in tooth and claw.

ResearchBlogging.orgBut it is one thing to describe reality in broad verbal brushes. How about a more rigorous empirical and theoretical understanding of how organisms and the genetic material through which they gain immortality play out in the universe? A new paper which uses plant models explores the costs and benefits of admixture between lineages, and how those two dynamics operate in a heterogeneous and homogeneous world. Population admixture, biological invasions and the balance between local adaptation and inbreeding depression:

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CATEGORIZED UNDER: Evolution, Genetics, Genomics

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

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