Sunday, February 12, 2012


1. It just gets better as you get older. A scanning electron microscope photo of a 600,000,000 year old  4 cell embryo from China. Embryo is .65 mm in diameter (0.02559055 inches)

Evolution has only four basic requirements; an organism needs to reproduce, the offspring need to be different from one another, the differences need to be inheritable, and differential survival among the offspring is due to those inherited differences. In celebration of Valentine’s Day, let’s see what the fossil record can tell us about the first of these.

Paleontology is full of the flotsam and jetsam of reproduction.  Dinosaur eggs and nests, fossil female rhinos and whales with preserved skeletons of fetuses preserved within their rib cages, morphological sexual dimorphism (where the males and females look quite different), PreCambrian single cell organisms preserved in the act of dividing, microscopic multicellular marine invertebrate embryos, and pollen and spores are just a few examples. However, what is really rare are fossil organisms preserved in copulito (the technical term for “doing it”).  But under the right conditions even such a transient behavior can be preserved.

2. Love's eternal embrace.  A mating pair of black scavenger gnats in 25,000,000 year old Dominican amber.

Amber is fossilized plant resin or “sap”.  The sap is exuded by the plant to seal external injuries and keep infectious organisms out.  Huge amounts of resin pour from entire forests trees when there is large scale damage from fires, storms, outbreaks of boring insects, etc. The resin is sticky when exuded and hardens slowly, sometimes taking thousands of years after burial to become amber. Amber is known as far back as the Carboniferous, some 300 million years ago.  The bulk of fossil amber dates from the Triassic and most of that is from conifers (such as pines) although a few large Cenozoic amber deposits come from broad leafed trees. Humans have known of amber and used it for jewelry and decoration for some 13,000 years. 

3. Two fossilized copulating  gnats in  amber.

Resin preservation is spectacular, showing exquisite details such as sensory hairs, color patterns, even small parasitic mites attached to larger insects and bacteria in insect guts. Even more impressive is the preservation of cellular and subcellular details such as muscle and nerve cells and even mitochondria!!

4. Two unidentified  amber entombed wasps copulating. The smaller individual on the left is the male.

5. Don't you guys ever get tired of looking at that stuff? A pair of mites (Glaesacarus rhombeus) in amber go at it for eternity.

Well how did our ancient lovers of today’s post come to be?  It’s when the resin is most sticky that is of interest to us.  At this stage it can flow over and envelop slowing moving animals or entrap anything that lands on its surface. Insects and other arthropods are abundant in forests and so, not surprisingly, are the most common type of amber inclusion. 

6. The fearsome "penis" of a male seed beetle.  The frightful array of spines sometimes punctures the genital tract of the female during copulation.

Male insects can have remarkably complex "penises", wonderfully twisted, contorted, bedecked in a coat of fearsome spines, and looking more like a scifi movie monster than a reproductive organ.  These complex penises fit tightly into the reproductive tracts in the female, a lock and key type of mechanism that helps insure that mating only occurs between members of the same species.  Females play the field and often copulate with multiple partners, so its in the male’s interest to try and stay attached as long as possible to the female to ensure that’s it’s his sperm that fertilize the eggs.  The complexity of the reproductive organs helps keep then attached.  It’s not true love, but it works. It also gets you trapped in amber. 

For those of you interested in exploring the truly astounding diversity of animal reproductive behavior and the evolutionary reasons for such, one can do no better than Olivia Judson’s delightful book Dr. Tatiana’s Sex Advice to All Creation. Judson is an Oxford Ph.D., an outstanding writer, and quite adept at making the technical side of evolutionary biology understandable.  She is damn wickedly clever too.  The book is set up as a series of love advice columns of a fictitious Dr. Tatiana, with each chapter containing letters from concerned organisms about his or her mate.  One of my favorites is from Chapter 1 A Sketch of the Battlefield:

“Dear Dr. Tatiana,

My name is twiggy and I’m a stick insect.  It’s with great embarrassment that I write to you while copulating, but my mate and I have been copulating for ten weeks already.  I’m bored out of my skull, yet he shows no sign of lagging. He says it’s because he’s madly in love with me, but I think he’s just plain mad.  How can I get him to quit?”

Some years ago the book was made into a two part miniseries for the BBC, but I haven’t yet found it in a format I can play in the US.

For a more technical discussion, see Thornhill and Alcock’s The Evolution of Insect Mating Systems. Although a detailed scientific work, it is not without some humor, such as the photograph of a male burpestid beetle trying to copulate with a discarded brown beer bottle some 5 times his size.  Presumably the bottle has some key visual properties that reminded him of conspecific females and triggered the mating attempt. 

7. Lust in the Australian desert.  Passionate male burpestid beetles will die from the heat as they try unsuccessfully to mate with a "Big Momma" beer bottle. Note genitalia projecting from the tip of the abdomen.

Finally, for those of you interested in movie trivia, the opening of the first Jurassic Park movie shows a mosquito being overwhelmed and trapped in resin (actually honey).  A friend who is an entomologist and works on dipterans (flies, mosquitos, and their ilk) pointed out to me that the dipteran in the scene is a tipulid (crane fly) and not a mosquito.  Adult tipulids feed on pollen, not blood.  However, they are quite large and thus easy to film. 

1. Grimaldi, D. and Engel, M.S. 2005. Evolution of the Insects. Cambridge University Press: 755 pp.

2. Judson, O. 2002.  Dr. Tatiana’s Sex Advice to All Creation. The Definitive Guide to the Evolutionary Biology of Sex.  Henry Holt and Co.: 308 pp.

3. Poinar, G. 1992. Life in Amber. Stanford University Press, Stanford: xii + 350 pp.

4. Poinar, G. and Poinar, R.  1994. The Quest for life in Amber.  Helix Books, Reading:  xiii + 219 pp.

5. Thornhill, R. and Alcock, J. 1983.  The Evolution of Insect Mating Systems. Harvard University Press, Cambridge: 547. 

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