Human Oestrus

Iris and I are reading Jared Diamond's book on the evolution of human sexuality, "Why is sex fun?" An interesting read, and in many ways a good introduction to the science of behavioral ecology, except that Diamond falls into his usual habit of making the same point many times and many ways, as if to beat you into agreeing with him. Since I generally start out agreeing with him, this gets tiring. The chapter we were reading last night was primarily his speculations on the evolutionary basis of the lack of obvious oestrus in humans. I was therefore very interested when this evening, browsing the table of contents of ProcRoySoc B, I cam across an article titled "Human Oestrus"

Here is the abstract:

For several decades, scholars of human sexuality have almost uniformly assumed that women evolutionarily lost oestrus—a phase of female sexuality occurring near ovulation and distinct from other phases of the ovarian cycle in terms of female sexual motivations and attractivity. In fact, we argue, this long-standing assumption is wrong. We review evidence that women's fertile-phase sexuality differs in a variety of ways from their sexuality during infertile phases of their cycles. In particular, when fertile in their cycles, women are particularly sexually attracted to a variety of features that likely are (or, ancestrally, were) indicators of genetic quality. As women's fertile-phase sexuality shares with other vertebrate females' fertile-phase sexuality a variety of functional and physiological features, we propose that the term oestrus appropriately applies to this phase in women. We discuss the function of women's non-fertile or extended sexuality and, based on empirical findings, suggest ways that fertile-phase sexuality in women has been shaped to partly function in the context of extra-pair mating. Men are particularly attracted to some features of fertile-phase women, but probably based on by-products of physiological changes males have been selected to detect, not because women signal their cycle-based fertility status.

Art of Science!

My department every year has an Art and Science show (This year it is the 4th Annual IB Art & Science Show, April 25, 2008. 5PM in VLSB. Open to the public, food and drink provided.)

Submissions are supposed to be artworks inspired by, related to, or otherwise modified by science.

I was thinking about what to submit when someone (alias Plastic Devil Ducky) posted a bag of Legos on Freecycle. So my submission will be a Lego rotifer (with egg). The difficult part was finding pieces from a pirate ship and a space station that could be made to look like cilia.

Dream of Science!

I dreamed there was a news paper article with the headline, "The Nutroavailabitizer!"

Below the headline, there was a picture of a long skinny fish with a big weird bumpy appendage, almost as massive as the main fish, sticking up from its tail. The article was quoting a scientist who had concluded that the function of this big appendage was to take nutrients in the water in the stream where it lived, and convert them to a form that would be easier for the trees around the stream to use. In the dream, Iris asked me what I thought of that, and I said that it didn't make very much sense from an evolutionary perspective, because the fish would be putting enormous energy and resources into building and operating the filter thing, and it would make the fish much less streamlined, and in the end the only benefit the fish gets is healthier trees around the stream. I argued that if there was a mutation for not having that appendage, the mutant fish would still get the benefit of the healthier trees, because of the other fish still having the filters, but would not have to support the costs of having a filter itself. Likewise, if there were no fish with that filter, and one had a mutation that caused it, or an earlier version of it, only it would bear the costs but all would get the benefits, so it would be at a disadvantage again. Iris asked why I thought the fish did have it, and then my cellphone rang with a 7AM automated sales call.

Public warned that lead bullets make meat toxic

In an extremely important, despite being obvious, revelation, the government of North Dakota has ordered the destruction of tons of venison, after being presented with evidence that deer shot with high velocity lead bullets are not fit for eating because of microscopic lead fragments spread throughout the body of the deer.

While the science is not new, the difference this time is that the study was done by a hunter from North Dakota, rather than by the Peregrine Fund.

Note to hunters: If you shot a deer with a lead bullet and you are planning on feeding it to your family, you are poisoning them. Throw that meat out, buy some copper bullets, go shoot another deer.

Residual life

Most of us take for granted that we will live for a long time after we stop having kids (for those of us who will have kids). The standard picture for Americans these days is to stop at 40 or so, hope to live to twice that age. And this doesn't seem unrealistic. But when viewed evolutionarily, it seems a bit bizarre. Most organisms do not have a post-reproductive lifespan, human females very clearly do. I've previously written about the most common hypothesis to explain this fact, is the "Grandmother Hypothesis."

On Tuesday I was giving a talk on my research to Berkeley's Primate Research Group, including my experimental examination of the Grandmother Hypothesis. After the talk, I got a lot of good feedback, including an interesting question. How certain are we that females of other species of primates wouldn't live as long post-menopause as humans if they lived as cushy lives as we do?

The only answer I could give them is that I haven't seen any data suggesting otherwise. But then, on my way home, it occurred to me that I already have probably the world's best data set for answering exactly that question.

Primates in well run zoos tend to greatly outlive their wild cousins. Medical care, reliable food supplies, no predators and few pathogens. Not to say the life of a captive primate is perfect, or that there isn't significant variation in the quality of care, but for many species maximum longevity in captivity is much greater than in the wild. And it just so happens that I have life tables, including age specific reproductive rates and mortality rates, for 120 species of primates. These come from ISIS data, meaning data from relatively well run zoos, and I will need permission from ISIS to use them in this way, but I doubt they will have any major objections.

The idea of writing a paper based on data I already have is exciting to me. Usually I spend years between having an idea and having assembled the data to address it. I have almost all the data I need to address this question safely on several computers. I'll get the hang of this science thing yet.

Scrounge of Science

I don't have a grant for my current rotifer experiments. The professor who pays for my Graduate Student Research stipend pays for minor research expenses out of the same grant. Even so, I am not lacking in equipment. In my lab space I have 5 (soon to be six) microscopes of various descriptions, a several thousand dollar refrigerated incubator, a refrigerator, an 8-channel multipipettor and a panoply of smaller bits. I have my own wireless network, desks, chairs, office supplies and so-forth. In all, probably $15K worth of equipment, almost all of it borrowed, traded, scrounged, temporarily absconded with or pulled out of the trash.

The incubator is a perfect example. The temperature in the room varied too much for my rotifers. So I decided I needed an incubator. I went to the incredibly helpful people in my department's instructional support office and asked if they had an incubator they weren't using. They did, but they weren't sure it worked. We pulled it out and I cleaned it up and got it working, so they lent it to me. But there was a problem. This incubator would heat up if the room got cold, but it didn't cool when the room got too hot. I could set a lower bound, but not an upper bound, and I need both. I went wandering the various labs I have access to, and observed that the MVZ molecular genetics lab had a big fancy refrigerated incubator with all the bells and whistles, and it had a piece of paper taped to it that said "always keep at 37C."

I guessed that in order to stay at 37C, it didn't need the refrigeration function. So I talked the super helpful lab manager into letting me temporarily trade the incubator I had borrowed from instructional support for the fancy refrigerated one.

My latest quest is to borrow a compound microscope with digital camera attachment, so I can take known magnification pictures of, and thereby measure, rotifer eggs. It took several days and emailing various friends within the department, but I now know where there is an unused microscope with camera fitting, and I'm working on getting permission to borrow it. I've already borrowed a camera that will work with it.

The thing that is amazing to me, once I stop patting myself on the back for my scrounging prowess, is how much scroungable stuff there is around here. Chairs and desks get thrown away because the professor who used them moved to another university. There are cabinets full of rarely used microscopes everywhere. People have 40 years of equipment piled in their labs and are eager to see it put to use.

When my rotifer experiments are done, I'm going to have an awful lot of borrowed stuff to give back. I hope I remember where I got everything.

Arthur C. Clarke passes into the Monolith

Aides report Clarke planned post-life tour of whole solar system, except Europa.

Gender Biased applicants

In the time I have worked on the rotifers, I have had the following assistants:

Lauren
Myfanwy
Rose
Laurel
Chris
Phoebe
Polina
Christina
Nicole
Deanna
Willard
Vincent
Catherine

That makes 3 males and 10 females. Hardly 50/50.

I was wondering why this was, if I was in some way unconsciously discriminating against male applicants, or practicing affirmative action. So I counted how many male and female applicants I have had in the last two rounds of hiring. The most recent I had 2 male and 8 female applicants. The previous time, I had 3 male and 13 female applicants. So if anything, I'm over-hiring males as compared to their representation in the applicant pool.

What I am wondering about now is why so many more females than males apply. The biology classes in my department have a slight majority of females, but not nearly that big. My guess is that because the project specifically investigates the evolutionary basis of menopause, and women tend to be more interested in (and comfortable with the topic of) menopause, fewer males are interested.

Rotifers, sex and locomotion: fast males, slow females

A while back I saw a male rotifer and for the first time knew that it was a male rotifer I was seeing. Three things immediately struck me:
1. Oh! so that's what I've been seeing all this time.
2. Damn they're so tiny compared to the females
3. Golly-gee-willackers they move fast.

To give you a sense of this, observe the following Youtube video I came across. The little bizarrely fast ones are the males.



The males are short-lived, have no digestive system or foot (meaning they can't eat or anchor in one place). They hatch from an unfertilized egg, carry their mothers' genes to other females, and die.

I was discussing this with a friend of mine, who asked, "what good are the males anyway?"

"They're just swimming sperm packets." I replied. But then I thought about it more, and realized the question could be viewed another way. There are plenty of invertebrates that are hermaphroditic. A single individual has both ovaries and testes. I fertelize you while you fertilize me. No need to build a whole separate individual to deliver the sperm. So why go to all the expense of pumping out fleets of males?

Maybe, I thought, it was that speed. The smaller a rotifer is, the faster it can swim. This is the result of the fluid dynamics of how they swim. I don't know a thing about fluid dynamics, so I won't try to explain that, but the data show that swimming speed is predicted with great accuracy by size.

Having fast moving sperm deliverers could have two benefits that immediately occur to me. First, one can spread one's genes much further by producing small, fast males and sending them off in all directions, than by having one big slow female swim around. Especially considering that the female's immediate neighbors have a good chance of being clones of herself, to make sexual reproduction worthwhile, she needs to get get her sperm far away. That may require speed.

Second, maybe being fast is useful in the competition for mating. If the females are not just willing to mate with every rotifer that wanders along, perhaps being fast increases the chance of fertilizing her eggs.

These are all just hypotheses, but they are testable ones, and perhaps some day I will get to testing them.

Research website

I've put up a somewhat expanded research website: dlevitis.org
In addition to an abbreviated CV, it has:

A page on my teaching philosophy and student feedback.

A section on undergraduate mentoring which includes pages on useful resources for my students to use in finding and tracking scientific literature, and advice for students applying for research positions.
I'd particularly appreciate feedback on this advice from others who have interviewed many undergrads for research positions.

There is also, of course, the obligate links list.

Nesting Season

The time of year has come when it is hard for bird lovers to concentrate on almost anything. Sit down and try to type, and there are ravens making absurd hooting noises in the pine tree over the house. Go out in the backyard and there are Red-shouldered Hawks screaming at each other up the hill, scrub-jays carrying twigs and sparrows pulling grass. The male wrens are dancing on the fencetops and the male hummingbirds are doing their shooting-star routine. Everyone is nesting, breeding displaying. And of course it isn't just the birds. Frogs incessantly sing their one-line resumes. Squirrels chitter with more vim than usual. Young women prance around campus in too little clothing for the still chilly air. Plum and cherries trees engage in shock-and-awe advertising war against a billion other flowers in the fight for the affection of bees.

It is hard to sit inside and type.