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Saturday, May 23, 2015

The Damselfly and Phylogenetic Relationships

Yesterday I came across a beautiful insect in the grass. At first, I thought it was a dragonfly. But on closer inspection I was not really sure. Something about it was like no other dragonfly I had seen.


I got in as close as I could, and I tried to film it, but it was hard to focus on something so small  for too long.


Later, I posted the photo below and asked my friends on Facebook to tell me what this insect was called. Some thought it was a dragonfly just as I had initially believed. But my friend Arle identified it as a damselfly, a close relative of the dragonfly.



Somebody else asked: "Are damselflies like  mayflies?" I answered that they were quite different, as mayflies are in the order Ephemeropteroida, because they are short-lived, but damselflies, like dragonflies,  are in the Odonata order. Arle agreed, He also noted: "They are about as closely related as I am to a rhinoceros." This was a startlingly vivid way to consider phylogenetic relationships, and I think it's a mental exercise well worth the effort.



Every once in a while, someone I know will exclaim that we cannot be more closely related to Bow than Bow is to a monkey, because Bow "looks like a monkey", and we don't. In fact, Bow does not look any more like a monkey than we do, but there is a psychological effect in place that makes us always view ourselves as unique, and anyone who is different from us as more similar to all the others who are different from us. I don't know what this effect is called, but it should have a name.


 All living things on earth are related. Somewhere in the tree of life, you will find our kinship with the ox-eye daisy.

Source: https://upload.wikimedia.org/wikipedia/commons/thumb/1/12/CollapsedtreeLabels-simplified.svg/800px-CollapsedtreeLabels-simplified.svg.png


 But the relationship to the daisy is so very distant, that we might as well not be related at all. On the other hand, the damselfly, the mayfly, the rhinoceros, the chimpanzee and man are all more closely related to each other than each of us is to a daisy. This kinship is formalized by biologists by saying that we all belong to the Kingdom animalia. whereas the daisy belongs to a different Kingdom, Plantae. We're all animals, and the daisy is a plant. So far, so good. Most people can recognize the difference between a plant and an animal, without ever having studied biology.

Can you tell which is the plant and which the animal in this picture?

Most people will also  agree that insects, (Kingdom: Animalia, Phylum: Anthropoda, Class: Insecta) are more closely related to each other than to any vertebrate (Kingdom: Animalia, Phylum Chordata. Clade: Craniata, Subphylum: Vertebrata). We have an almost instinctive sense of how those differences break down, which is why when I saw the damselfly I knew at once it was an insect. I had no need to look that up. Where it gets trickier is assessing relatedness between and among beings very different from ourselves, and maintaining objectivity regarding beings very similar to ourselves.

So the rhinoceros is classified phylogenetically like this:

DomainEukaryota • RegnumAnimalia • PhylumChordata • SubphylumVertebrata • InfraphylumGnathostomata • SuperclassisTetrapoda • ClassisMammalia • SubclassisTheria • InfraclassisEutheria • OrdoPerissodactyla • SuperfamiliaRhinocerotoidea • FamiliaRhinocerotidae • Genus: Rhinoceros
And my friend Arle is phylogenetically classified like this:

DomainEukaryota • RegnumAnimalia • PhylumChordata • SubphylumVertebrata • InfraphylumGnathostomata • SuperclassisTetrapoda • ClassisMammalia • SubclassisTheria • InfraclassisEutheria • OrdoPrimates • SubordoHaplorrhini • InfraordoSimiiformes • ParvordoCatarrhini • SuperfamiliaHominoidea • FamiliaHominidae • GenusHomo • Species: Homo sapiens 
It's all exactly the same until you get to the order! And the mayfly and the damselfly also share everything until you get down to the order, which is where they diverge. They are both insects and so very different from us, but when you look at it from their perspective, they are about as different as a rhinoceros is from a man.

So much for differences. Now let's compare similarities. The dragonfly and the damselfly share an order, Odonata, but they diverge at the suborder. The dragonfly is from suborder Anisoptera, whereas the damselfly is suborder Zygotoptera.

Family Tree of the Order Primates from Wikipedia


But humans and chimpanzees are much more closely related to each other than the damselfly is to the dragonfly, because we do not simply share an order, Primates, but we also share a family, Hominidae  (Great Apes) and a subfamily, Homininae, and a tribe, Hominini. The only thing we do not share is a genus. So yes, we are different species. But much more closely related than a dragonfly to a damselfly.

Family Tree of Odonaraptera from Wikipedia

Most phylogenetic classification presupposes binary bifurcations as you can see in the trees above. But real life can actually get much more messy. The other day I met a man who told me a long story about how his family tree crossed-over several times, along the lines of the popular song, "I am my own grandpa."  This involved marriage and in-laws, but it can also happen with plain genetic relationships. In reality, after humans and chimpanzees split into two groups, it is also known that they continued to interbreed for a period of time, so they may be even more closely related than a simple phylogenetic bifurcating tree can show.

 If dragonflies and damselflies are less closely related than chimpanzees are to humans, why is it so hard for us to tell the difference between the two, whereas we see the physical difference between humans and chimps so clearly?



I think it's the same reason that we tend to think we look very different from all our family members, but an outsider can spot the family relationship very clearly just by looking at us.  I have had complete strangers tell me I look just like my mother, and my daughter has had the same experience when people compared her to me, but we do not think we look anything alike. The differences are what we notice, not the similarities. To see how closely we resemble chimpanzees, we should ask an outsider, someone very different from us, like the damselfly,  how hard it is to tell us apart.

To a damselfly, humans and chimps probably look the same

4 comments:

  1. Familiarity certainly plays a role, as does similarity to self. I once heard a man from India who was in the U.S. for graduate school talking about how he tried to fit in culturally, so he asked an Anglo-American girl on a date. He went to confirm details with her later and found he simply could not tell her from any of the other girls around and he didn't know which one he had asked out. Of course he'd never had this trouble with Indian women he knew.

    While I've never had that sort of experience, I think of the experience of being exposed to a sort of music one has never heard before and the ways in which it can be baffling because it isn't like what we're used to: we simply don't know what to hear or how to hear it. I bought a CD of Tibetan music once and found I simply could not listen to the religious processional music: it sounded like random noise to me. I tried a few times to listen to it but I never got past the perception of noise.

    Similarly, if you went to most people and showed them different kinds of bagpipes, they might notice some superficial features, but they would have no basis for differentiating between them in a meaningful way. I specialize in bagpipes, however, so I can look at some types and tell you where they came from within a 20-km radius and even, in some instances, tell who the maker is.

    But if I turn to a saxophone, I could tell you absolutely nothing, even though a kid who went to junior high band class could probably tell you far more. I am simply unfamiliar with saxophones (other than considering them the mullet of the music world).

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    1. You bring up an interesting side issue in the investigation of phylogenetic relationships: that if we don't know anything about the salient features to look for, we might actually have trouble seeing that an individual member of a species is related to himself. Not being able to recognize someone you have seen before because she appears to look like everybody else is that kind of problem.

      The music example is like the language problem. It is hard to get someone to transcribe a language he's never heard before, because he doesn't know which sounds are the same and which are different.

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  2. Also, consider that for the daisy, if it were cognizant of creatures around it, the relevant difference between damselfly and the human might only be one of size, since what would be cognitively relevant is how likely one of them is to smash the daisy…

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    1. The daisy might also be interested in which of us are better pollinators.

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