March 11, 2011

Dolphin mtDNA phylogeny

Tursiops truncatus brain size
Left to right: pig, dolphin and human brains
There is hardly any more iconic animal than the dolphin but there is also hardly any animal closer to us in a key identity element: intelligence. Lacking hands and living in water, dolphins have never developed some of the technological landmarks that we associate with human-like intelligence: fire management and tool creation, however their brains are, in comparison to body mass, very much our size, they demonstrate once and again to be very intelligent beings with some abilities (notably sonar perception and communication) rather beyond our comprehension. For instance only recently have we begun to understand that dolphin language is not framed in the mere two dimensions ours is but is actually tridimensional.

A few weeks ago, it came out in a discussion on "Neanderthals and us" whether dolphins, with their many different species, many of them (if not all) showing striking intelligence, could be a model to understand the relations between the various species of the genus Homo in the past. A problem, at least for me, is that we really do not know so much about dolphins either anyhow. Most documentaries are about the successful common bottlenose dolphin Tursiops truncatus or the also very successful and impressively bright orcas. But there are dozens of dolphin species.

In this sense it is very interesting to take a look at this new paper establishing a mitochondrial phylogeny on these sea mammals:

Particularly illustrative is the proposed phylogeny of figure 1:


It is notable that there are cases of hybridization (fertile hybrids!) in the wild as in captivity, of such different species as Turiops truncatus and Pseudorca crassidens, which would have diverged some 8.5 million years ago, roughly the (true) distance between chimpanzees (and bonobos) and us.

This really challenges the concept of species as defined in classical terms (absolute possibility of production of fertile hybrids) and reinforces the modern revised concept (normal reproduction in the wild).


Common dolphin noaaThe closest equivalent (always assuming all age estimates are correct) of "Neanderthal and us" (i.e. Homo ergaster and derived species by most accounts) in the tree above would be the relation between the long-beaked common dolphin (D. capensis) and the Indo-pacific bottlenose dolphin (T. aduncus). Just a little bit upstream and we get to the equivalent of all the Homo genus, while the overall dolphin relationships are in the range, as already mentioned of "Chimpanzees and us". 

Probably this phylogeny will not be of much use for comparison, more so as the various intelligence levels and other cognitive, linguistic or social adaptions of dolphins are ill understood at the moment, but it is still better than nothing and hence I felt it was an interesting reference to have in mind.

23 comments:

  1. Maju very interesting reflection.

    Very good comparing between the phylogeny of dolphins and the genus Homo, hopefully in the future know more about the dolphins to help us understand the different aspects of intelligence.

    When I have more time I think about this idea and investigate more on dolphins, elephants ...:)

    Greetings and thank you for this great idea that sure makes us think.

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  2. Great interesting post Maju.

    "It is notable that there are cases of hybridization (fertile hybrids!) in the wild as in captivity, of such different species as Turiops truncatus and Pseudorca crassidens, which would have diverged some 8.5 million years ago, roughly the (true) distance between chimpanzees (and bonobos) and us".

    That's an even greater diversification than even I would have though hybrids were possible. Bears out what I've consistently claimed though.

    "This really challenges the concept of species as defined in classical terms (absolute possibility of production of fertile hybrids) and reinforces the modern revised concept (normal reproduction in the wild)".

    But using 'normal reproduction in the wild' as a criterium is no guide. Many species would be quite capable of forming fertile hybrids but never have the opportunity to meet 'in thw wild'.

    I'm not sure if you read mt essay on 'Species' when I first posted it. If not here;'s a link:

    http://humanevolutionontrial.blogspot.com/2009/06/human-evolution-on-trial-species.html

    You may find it interesting.

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  3. We have to understand that there are two ways to speciation: sympatric and allopatric.

    When two related species diverge in geography it is an allopatric speciation and, even if they might exchange genes now and then in the process, geography alone keeps them separated and will make them be eventually unable to breed with each other (what is a gradual and not absolute process).

    Instead when two related species diverge in ecological niche within the same geography, it is a sympatric speciation. In these cases evolving patterns that prevent interbreeding is part of the speciation process and will probably be more intense because the specialized species require specialization, so outbreeding in this case may be more harmful than beneficial.

    There are intermediate variants (peripatric, parapatric) but this dychotomy pretty much sums it up.

    It's not so important what exactly is an species as how far the process of speciation has reached and why it happened.

    Are you planning to continue your 2009 archive blog?

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  10. This conversation is being seriously moderated a posteriory. Neither I nor my readers need to read that humankind was created by ETs.

    To be fair I have also deleted my own replies. No more of that junk, thanks.

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  11. I wanted to test your reaction. Now I can see you act as a "conventional" scientist on your own field while at the same time you're a hopeless dilettante at historical linguistics.

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  12. I do not have any fiedl. I am amateur in all fields.

    I do not think you have any right to "test" me in any case.

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  13. "geography alone keeps them separated and will make them be eventually unable to breed with each other"

    Note: 'eventually'. Many populations defined as being separate species are simply regional variations, and when they have the opportunity to meet up are quite capabale of forming fertile hybrids. This happens often through human agency, but also occurrs often enough naturally.

    "Instead when two related species diverge in ecological niche within the same geography, it is a sympatric speciation".

    My feeling is that sympatric speciation is much less common than is allopatric speciation. When two species are divided by ecology it is more often than not the result of species having first diversified through geographic speciation been able to meet up again, but over the period of separation been able to develop into separate species.

    "so outbreeding in this case may be more harmful than beneficial".

    There are few examples of similar species occupying separate ecological niches within the same geography being able to successfully interbreed.

    "There are intermediate variants (peripatric, parapatric) but this dychotomy pretty much sums it up".

    Those intermediates are usully geographically intermediate as well and they form part of a cline.

    "Are you planning to continue your 2009 archive blog?"

    I wouldn't mind, but I think it would take up a lot of time. I might seek your advice some time.

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  14. To me the false orca and the bottlenose dolphin do not seem the same species. The false orca has evolved a body like that of a catfish (without the whiskers) and is much larger than a bottlenose dolphin. They have diverged for more than 8 million years also.

    You have to push things a lot in order to argue that they are the same species only because they can produce fertile hybrids.

    It just comes to show how the classical working definition of species is not too valid.

    "There are few examples of similar species occupying separate ecological niches within the same geography being able to successfully interbreed".

    Maybe but evolution always favors inbreeding over outbreeding in such cases: the diverging species develop different mating times, different pheromones, different colors... there are accidents but exceptions do not a rule make, and therefore not a species either.

    As for your blog, I ask because if I'm going to link it from the sidebar, I'd like it to be a live blog that updates at least now and then.

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  15. "To me the false orca and the bottlenose dolphin do not seem the same species".

    Agreed. But I see from the link that the hybrid was barely fertile. The calves usually died. So they are easily calssified as imperfectly fertile, so are different species.

    "As for your blog, I ask because if I'm going to link it from the sidebar, I'd like it to be a live blog that updates at least now and then".

    I'll see how things develop. Perhaps a local can show me the best way to do it.

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  16. There is at least one surviving calf, what is worse as what I just watched yesterday at TV about a local couple unlucky enough to share a mysterious gene of degenerative death. This couple, suffering not from excessive genetic distance but, it seems, excessive genetic coincidence were losing all their children to rare genetic disease and their only hope of having a healthy child was through in vitro techniques (not too clear if the father was still the biological father of the third and only healthy son).

    We are talking after all of two species as distant in time as chimpanzees and us.

    What about polar and brown bears, who hybridize on occasion in the wild? Are polar bears less of a separate species for that? They have different hibernation patterns, different proportions, specializations... they are as strictly separate as any two interfertile species living side by side can be. But they hybridize now and then, with some success it seems.

    For most biologists they remain distinct species and it is our concept of species and not polar bears who have to adapt.

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  17. "This couple, suffering not from excessive genetic distance but, it seems, excessive genetic coincidence"

    Interestingly the effect is much the same in the two extremes. I mentioned as much in this essay on 'Hybrid Vigour and Inbreeding':

    http://humanevolutionontrial.blogspot.com/2009/06/human-evolution-on-trial-hybrid-vigour.html

    You may find it interesting.

    "We are talking after all of two species as distant in time as chimpanzees and us".

    I don't think many would consider the false orca and the bottlenose dolphin to be the same species even though 'there is at least one surviving calf'. Even Charles Darwin could say, 'For all practical purposes it is most difficult to say where perfect fertility ends and sterility begins'. Imperfect fertility can be a product of either excessive genetic distance or excessive relatedness.

    "What about polar and brown bears, who hybridize on occasion in the wild? Are polar bears less of a separate species for that?"

    It is cerytainly possible to argue that they are in fact the same species.

    "For most biologists they remain distinct species and it is our concept of species and not polar bears who have to adapt".

    I agree. But humans like to see precise, well-defined categories. Nature is not actually like that and we should always keep that in the back of our minds.

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  18. "As for your blog, I ask because if I'm going to link it from the sidebar, I'd like it to be a live blog that updates at least now and then".

    You asked elsewhere if I was subtly asking for help in setting up. Any help you are prepared to offer would be gratefully accepted. Sorry for the late response to you question but I got sidetracked on that Tibetan blog.

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  19. "Any help you are prepared to offer would be gratefully accepted".

    Not sure what exactly this means. Help yourself to begin with - I'll become a follower and see if the Earth moves or not. But, meh, the last post has a date of 2009 and the blog is not even accessible from your profile.

    So, first get it movin' yourself, write because you want/feel to, make the blog easily accessible by adding it to your profile, and you'll see how things move on their own.

    The Sun does not shine for whoever may see it... it burns for its own quite nuclear reasons, and if, besides, we get warmth and a cheery mood from it, the better I guess. But the Sun does not shine for us, it does for its own personal motivations.

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  20. I've thought about it and for two main reasons I've decided not to bother. For one there is very little I would change in that series of essays, apart from perhaps abandoning the accused, prosecution and defence perspective. And for two I believe it is advantageous to concentrate the information. I believe there are already too many blogs around. I really only bother with yours and Dienekes' and you both link to particular subjects on other blogs anyway. I less often visit John Hawkes, Anthropology.net and averyremoteperiodindded.

    Besides which I've already convinced you of the truth of several of the conclusions I had come to by the time of the 2009 essays. I certainly invite you to blog concerning any aspects you still disagree with. You might like to start with the essay that comes before "Hybrid Vigour and Inbreeding". It is "Change":

    http://humanevolutionontrial.blogspot.com/2009/06/human-evolution-on-trial-change.html

    If you'd like some idea of what I look like here's a photograph of me playing fiddle at a local jazz festival:

    http://www.northernjazzsociety.com/index.php?option=com_rsgallery2&page=inline&id=153

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  21. A blog is a diary, a notebook. An open one maybe (not necessarily) but ultimately your notebook. That's why I began blogging, so I could concentrate my ideas in one (or few now) places and I could quickly share them with a single link, a single click, when necessary. It helps prevent unnecessary repetition of discussions, etc.

    Also, when yo write a blog entry, a small essay or article, you have to think on it a bit more normally, than when you just reply one-liners with other one-liners. "I do not think so" - "I do!"... what's the point?

    A blog post (article, mini-essay) is a self-contained item (plus links and discussion) that forces you to ponder the matter self-critically, not looking to persuade someone but looking to share information and discuss opinions with other people of similar interests.

    I helps to get your ideas focused, more or less clear for you and others...

    "I've already convinced you of the truth of several of the conclusions"...

    I really hate the preacher tone you have when you say that, it's like you believe you are some sort of carrier of the TRUTH (capitalized and absolutized) who is on a mission to persuade others, notably me (which sounds kinda psychopath stalker, mind you).

    You should make a self-criticism on this matter.

    "If you'd like some idea of what I look like here's a photograph of me playing fiddle at a local jazz festival"...

    He! That's nice. You look cool. :)

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  22. "He! That's nice. You look cool".

    Thanks. And thanks for sharing your thoughts on blogging.

    "I really hate the preacher tone you have when you say that, it's like you believe you are some sort of carrier of the TRUTH (capitalized and absolutized) who is on a mission to persuade others, notably me (which sounds kinda psychopath stalker, mind you)".

    I am alarmed at the likelihood of a resurgence of religious extremism, and I feel that the more of us who can show that humans have not been selected by God to have dominion over all other species the better we will all be in the long run. I also believe that the ecological damage we are committing cannot be reversed until we face up to the ecolgical damage we have already caused. Again, our survival depends on it.

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  23. I fail to see the connection of your reply to the quote. Sorry. :(

    Unless you imply that you are actually "on a mission". If so you should probably bring your mission to where is needed: religious forums. ;)

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