The Grants in the Galápagos and their hybrid species

August 13, 2014 • 6:02 am

Peter and Rosemary Grant, known to all evolutionists as simply “The Grants,” have just come out with a new (April, 2014) book on their long-term field work, 40 Years of Evolution: Darwin’s Finches on Daphne Island (marginally cheaper at Amazon). I haven’t yet read it, but I know the work well, for the Grants do much of their research in my own field, speciation.

And, nine days ago, Jon Weiner wrote about the Grants’ book and work in a New York Times article called ‘In Darwin’s footsteps.” Weiner, as you may know, wrote a book about the Grants’ work two decades ago, The Beak of the Finch, which won a Pulitzer Prize for nonfiction. His new article updates the old one, although by necessity it leaves out many of the gazillion findings the Grants have made since then.

The Grants’ research program on the Galapagos began in the mid 1970s; for the first ten years it was carried out by students and postdocs (like my colleague Trevor Price; see below), and the Grants began working on the island themselves around 1985. 

Nearly all of the Grants’ work, by the way, takes place on a tiny and godawfully desolate volcanic cone in the Galápagos: the island of Daphne Major, which has only a few trees (genus Bursera) and no fresh water (all supplies, including water for long field seasons, is brought in by boat and carried up the hill). It’s about 5 km², and so is tiny. But it has finches:

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(Times caption): aphne Major, foreground, a volcanic cinder cone island in the Galápagos, has served as a natural laboratory for two British biologists for the past 40 years. Credit D. Parer and E. Parer-Cook

One of the Grants’ findings is singled out by Weiner: a possible new “hybrid species” formed after hybridization between existing species twenty-odd years ago. It was itself founded by a probable hybrid male formed by interbreeding between two of the archipelago’s 14 finch species, and the male then mated with a member of one of its parental species (a “backcross”). That created (over a decade later) a population that interbreeds only among itself, and, if you employ the Biological Species Concept, its reproductive isolation from other species and interbreeding among itself means that we have seen, in just a few years, the creation of a new species. Biologists find such speciation exciting because the possibility of new species forming by hybridization between others is not only fast, but something we can study, as the Grants have in real time. It belies the creationists’ claim that we’ve never seen new species form. (I deal with that issue in both WEIT and my book Speciation with Allen Orr, showing that we already know of several “polyploid” plant species that have formed in historical times.)

The interesting thing about this hybrid finch “species” is that the isolating barrier between it and other species is based almost entirely on song. The males inherit their song culturally, by hearing and imitating their father, and females mate with the song they hear when they’re nestings. That means that since the original hybrid male (a descendant of the populations’s hybrid founder,”Big Bird”) had an unusual song, his descendants would sing only that song (if male) and mate only with males singing that song (if female). The lineage would be interbreeding but isolated from others. And while there are some genetic differences between the new hybrid species and any other finch species, the isolating barrier itself could be based on culture, not genes.

My own view is that there are some good cases of hybrid species, but that the phenomenon is probably not ubiquitous. The Grants are wary of calling this new population a “species,” though for the time being it’s certainly acting like one. My colleague Trevor Price at Chicago, who got his Ph.D. working with the Grants on Daphne, isn’t inclined to call it a species because, he feels, it may eventually fuse with another species via hybridization. (He points out that two well-demarcated species on Daphne, the cactus finch and the medium ground finch, are hybridizing fairly extensively, and my one day fuse.)

But I consider species concepts to operate in the here and now, not prospectively. Who knows whether this new isolated lineage will persist? Whether it does is a matter of waiting. Do we decide, for instance, that we’ll call it a new species only if it is still distinct in 2090? Nevertheless, my own view, like Trevor’s, is that the existence of this “species” is precarious. But so long as it lasts as a population for at least a while, and doesn’t mate with other species, we can provisionally say we’ve seen The Origin of A Species.

I got to know Peter and Rosemary when I did part of a sabbatical in Princeton, and I called them “The World’s Nicest Scientists.” I meant that, because they’re simply wonderful and generous folks.  And they’re tenacious: I, for one, couldn’t maroon myself on a desolate island for several months every year to study the birds onsite. I love my Chinese food and urban attractions too much. But the Grants have persisted for four decades. They’re both 77, and, as Weiner says, they know they can’t keep it up forever. But it’s still the longest-running and most fruitful field work on evolutionary genetics and ecology that I know of, and the Grants deserve the many honors they’ve accrued. Here they are on Daphne, working away:

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(From the Times): Peter and Rosemary Grant on Daphne Major, capturing and measuring finches. Their work documented the evolution of finches in the genus Geospiza in real time. Credit K.T. Grant

25 thoughts on “The Grants in the Galápagos and their hybrid species

  1. I’ve read their 2011 book “How and Why Species Multiply:The Radiation of Darwin’s Finches”, which I enjoyed and recommend. Can anyone comment on how this new book compares or adds to that one? (I’m asking as a non-biologist general reader.)

  2. I could tolerate & even enjoy the isolation & rockiness but the absence of rain & the aridity would frustrate me.

    Are birds particulary susceptible to hybridising more than mammals or reptiles? I am thinking that they disperse more readily perhaps, so can bounce back & colonise areas distant from their parents…

    An interesting bird family for looking at specieation is the genus Motacilla -pied wagtails. They seem confusing as species/subspecies…
    http://www.bioone.org/doi/abs/10.1650/0010-5422%282002%29104%5B0725%3ASAHBOW%5D2.0.CO%3B2

  3. Urban pleasures, indeed. I can only be away from New York City for so long before I start pining to return.

    “Forty Years of Evolution” has been duly Wish Listed on Amazon.

  4. Someone should tell those finches to broaden their taste in music. Audio-Fascists trying to branch off completely ignoring all the wonderful genes at their disposal.

    Some sexy mellow jazz might do the trick.

    1. I was with you right up until mellow jazz. Sketches of Spain and Naima, that’s some finch jazz right there.
      Or maybe some Skrillex, we’ll make the finches dance like zombies.

      1. 😀

        I think I could watch finches raving to skrillex for the rest of my days and be fairly content.

        But we must not forget to provide them with plenty of water which is a bit of a challenge given the location of the party.

        Give the damn birds some E, put on some skrillex, add water and watch the evolutionary fireworks!

  5. “The Grants are wary of calling this new population a “species,” though for the time being it’s certainly acting like one.”

    Typical humans vs nature. We like to fuss around with boundaries and distinctions, while nature just gets on with it. I don’t mind calling it a species for as long as it lasts. None of them last forever.

  6. I am looking forward to catching up on reading about finch evolution. I did not realize how much bird speciation could rely on learned behaviors. I think there are many cases of bird species / incipient species that seem maintained by males singing a song that is preferred by their females. The eastern and western meadowlarks are an example. So now I wonder to what degree other cases of speciation have depended on learned behaviors.

    1. Learned behaviour can be considered (in some respects) an extrinsic rather than instrinsic property of a species or individual, like its location in space (which is inherited because babies hatch more-or-less where the egg was laid) rather than its morphology or genotype. As such it comes under “conditions of existence” in Darwin’s terms, which have usually (since Darwin) been considered important causes of evolutionary change.

      It reminds me of another case, a hypothetical explanation for the ‘masculinised’ genitalia of female Spotted Hyenas. The morphology is affected by hormonal conditions in the mother during gestation, which happen to be very high in testosterone. This also affects the endocrine system of female pups and causes them to produce similar hormone levels when they grow up. So maybe (my theory, which is mine) the masculinised state is not really an expression of an underlying genotype ‘for’ the condition, but a historical vestige of elevated testosterone levels in an ancestral female that has been inherited somatically, and could have started with (e.g.) an endocrine tumour in a female ancestor, rather than a DNA mutation in the germ line. (Of course it would then impose selective pressure on genetic variants, acting like a culturally transmitted trait analogous to learned song or inherited nesting site…)

  7. The NY Times is about the only general interest newspaper that does any science coverage these days. It has an excellent podcast called Science Times. It comes out once a week and is usually 20 to 25 minutes. You can listen or subscribe to the podcast at:
    http://www.nytimes.com/pages/science/

    The show is hosted by David Corcoran and he talks to the writers (and sometimes the subject) of science stories in the Times. Last week, he spoke with Jonathan Weiner who wrote the piece on the Grants. It got my attention, I read the article and will probably get the book.

    This week, there is a great story on the African wild dog. It is very distinct from dogs and wolves. Jerry might even like them. There are also two supplemental podcasts this week dealing with issues in the news – ebola and depression. I heartily recommend both the podcast and the Times science section to keep up with developments in science.

    1. It’s a scoria cone. Well known in areas of fairly fluid lavas. They do look almost artificial, but when you look in detail, you can often detect asymmetries that would shame any Roman architect. For example, in many eruptions, there’s a preferred wind direction, resulting in a preferred orientation of tephra deposits and extent.
      I spent an afternoon mapping one on Tenerife a couple of years ago ; by the end of the afternoon (at the end of a week of volcanology) I’d barely “got my eye in” for recognising the different eruptions visible. Beats laying on a beach turning lobster-coloured though.
      If you ever fly into Tenerife on an easterly wind (or out of there on a westerly wind), you’ll fly over it.

  8. Loved Weiner’s book “The Beak Of The Finch” and have read it at least 3 times. Have to get the Grant’s version of events after Weiner diverged into guppies. Hope they write as well. And what a wonderful relationship they have – now that would be a great film (forget Noah and other such biblical nonsense :)).

  9. The power of song eh, the seduction of the fittest.
    Big ups to the Grant’s, what wonderful dedicated people.
    I could definitely bury myself in 40 years of research and I don’t even have to go into the back yard. What a wuss!
    Now where is my plectrum I feel a song coming on…

  10. I’ve read the Finch book several times, but even so I hadn’t realised just how bleak Daphne Major really is. To be still climbing around that island at 77 years of age shows a dedication to science that is truly extraordinary.

  11. My copy just arrived. Last one on Amazon UK apparently. It’s an expensive book…, but justified, well bound, lots of quality plates, a class production. I can’t give a review of the contents as I’ve only just navigated the prefix. But this is an exciting topic, not least because of the idea (mentioned in Wiener’s the “Beak Of The Finch) that the finches beak adaptations are only really adaptive in extreme conditions and in times of plenty they just nom (is this a WEIT specific term?) the same stuff as everyone else. That is such a great insight! Anyway, thanks to Jerry for this post, I doubt I would have noticed otherwise.

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