Monday, June 28, 2010

Dissertations: His, Hers, and Ours

In the 1970s, when we were young and thought we were immortal, Erika and I pursued our doctoral research in the eastern lowland Ecuadorian jungle. I studied antbirds, a widespread tropical American family of birds that follow army ant swarms and feed off the arthropods fleeing from the ants.  The Ornate Antwren, below, is an example of an antbird.
I wondered if the antbirds (26 species inhabited my study area) obeyed Gause's Rule, that no two species can occupy the same niche.  What I found, briefly, was that these birds do divide up their resources so that no two species exploit the environment in exactly the same fashion.  In the jungle, we suffered through 15 feet of rain a year.  As we were on the equator, there was no dry season, which is when tropical birds often nest.  I was surprised to find that the antbird species appeared to breed all year.

Meanwhile, Erika studied the effects of intercontinental migration on the trematode fauna of Solitary and Pectoral Sandpipers.  These sandpipers breed in Canada and winter in South America.  The bird below is a Solitary Sandpiper.
Trematodes are internal parasites of many vertebrates.  There are many trematode species and some even inhabit humans.  They are found in many organs of their hosts. They are fascinating and beautiful creatures, as you can see in the photo below, which shows an hermaphrodite, the normal condition for a trematode, with both an ovary and two testes in the same individual.  Trematodes just sit there and fertilize thousands of eggs.  The trematode life cycle goes through several intermediate hosts, (always in evolutionary order!), before reinfecting their vertebrate host.
Erika discovered that Pectoral and Solitary Sandpipers have relatively few trematode parasites, and that the few they do have, hold on really tight.  The most amazing of these trematodes live in the birds' air sacs, which are extensions of birds' lungs.

Being of boundless energy, Erika and I also collected trematodes from my antbirds.  In effect, this study amounted to our doing a third dissertation!  There are two different feeding strategies among the antbirds, those that feed in the bushes, and those that always feed while walking on the ground, like the Striated Ant-thrush you see here:
We found that, despite some overlap, the ground walkers and the bush feeders harbor different trematodes.  Organisms that have close common ancestry often have the same parasites (ostriches and emus, for example).  Perhaps these two types of antbirds are not closely related.  Indeed, geneticists discovered that the DNA of the two groups of antbirds are not closely related.  Most ornithologists now place them in completely different families, Thamnophilidae for the bush inhabitants, and Formicariidae for the ground walkers.  In 1990, Erika and I presented this research at the International Ornithological Congress in Christchurch, New Zealand.

3 comments:

  1. Cool how technology proves you right way after the fact sometimes. Neat story.
    In the 1970s, when we were young and intrepid, we moved to SD from NY, sight unseen... a salute to you and Erika for your superior sense of adventure and purpose! =)

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  2. Very interesting! I haven't been to South or Central America, but I was born in Kenya and lived there until I was five -- I remember a lake full of flamingos, Lake Nakuru, and there's a family story of me and a small playmate being closely watched by a couple of large vultures in somebody's garden. My mother wrote several books of juvenile fiction and nonfiction about African wildlife, and her interest in birds, which I eventually caught, was born there I think.

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  3. I have several photos of birds at Lake Nakuru. Here are some of the flamingos there: http://picasaweb.google.com/danerika/Flamingos#5231139675330583634

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