Batty bigamy and worse

Normally, inbreeding isn’t such a good thing

The idea that three generations of related females might share the same mate is, frankly, abhorrent and strange to us humans, but among bats, this tactic may be a fairly common phenomenon.

Generally, animals avoid inbreeding with one another because doing so results in the development of “inbreeding depression” in a population. This depression refers to falling rates of reproduction and survival that result when relatives interbreed. An example of what happens with inbreeding can be found among the royal houses of Europe in previous centuries. The members of these families would often receive papal dispensations to ignore the rules about consanguinity—close relatedness—to be allowed to marry another royal personage. There just weren’t that many eligible royal folk wandering around Europe and inbreeding was the ultimate result.

Hidden disorders emerge

Because of this inbreeding, often with third or second cousins marrying through several generations, the royal families would manifest disorders that normally would remain hidden. Some of these disorders required the inheritance of two alleles, both carrying mutations, for them to manifest. If the royal families had not constantly been intermarrying, the two recessive alleles would have been much less likely to come together in a single person. As it was, many royal households had children who were sickly, who could not reproduce successfully, or who manifested mental illness or retardation. One particularly notable trait that arose through several families was the “Hapsburg jaw,” a severe underbite and jutting jawbone that traced its way through the European royal chessboard. One potentate had a jaw deformity so severe that he could not chew his food.

Horseshoe bats don’t care

But the greater horseshoe bat appears to be untroubled by such issues of consanguinity, at least in the sense that related females from several generations will mate with the same male. In the world of the horseshoe bat, it pays to be a male bat who attracts a female. If the male attracts the daughter, he has a good chance of also mating with the mother and the grandmother, too. And he may be set for his relatively long bat-life; greater horseshoe bats can live up to 30 years, and females will consistently select the same male for the annual bat mating ritual, which results in a single offspring per female each year.

In spite of this inbreeding and polygyny, in which several females mate with the same male, the females apparently are quite adept at avoiding mating with their own fathers. A female will only mate with her mother’s partner if her mother has switched partners and is no longer mating with the daughter’s father.

Beat that, Belgium

This complex mating web results in a bat family tree that is more confusing than that of all the royal houses of Europe combined. It is possible for a female bat and her maternal half-aunt to be half-sisters on their father’s side.

How did researchers unravel this remarkable complexity? They identified a colony of female bats—who spend most of the year living in single-sex groups—in an old mansion in Great Britain. DNA analysis showed that the several hundred females lived in about 20 groups of related females who shared mates. The females met up with the males, who lived in a permanent stag party condition in a nearby cave, only once a year. Researchers speculate that females use smell to avoid mating with their fathers.

What benefit this interbreeding?

Why risk interbreeding in the first place? Actually, many species exhibit tactics that lead to closer kinship among individuals. Researchers speculate that closer kinships result in better teamwork to protect the genetic investment. In the world of team-playing ants, for example, female siblings can be 75% related, rather than the 50% most sexually producing species share genetically with their siblings. Experts believe that this extra genetic relatedness enhances the teamwork atmosphere of an ant colony. In much the same way, the related groups of female bats work together to raise the young. Researchers believe that this horseshoe bat tactic may extend beyond the greater horseshoe to other bat species.


Inbreeding in the Darwin dynasty?

Darwin and his wife were first cousins

Charles Darwin married his first cousin, Emma Wedgwood, and his own mother was the product of a marriage between third cousins. Given his insights into the relationship among variation, nature’s choices, and adaptation and his observations of weakening in inbred plants, it is no surprise that Darwin worried about his own family’s consanguinity. Did the inbreeding in the Darwin/Wedgwood families show up in his children?

Is marrying your first cousin really so bad?

Had the Darwin/Wedgwoods only engaged in the first-cousin marriage between Charles and Emma, the outcome would likely not have been serious. A 2002 study reported by the National Society of Genetic Counselors found that having first cousins as parents raises the risk of having a significant genetic defect from 3-4% up to about 4-7%. The group concluded that first cousins planning to reproduce require no more intense genetic counseling than unrelated couples.

Consistent consanguinity, on the other hand

But that study didn’t address serial consanguinity of the kind seen in some European royal houses or in the Darwin/Wedgwood families. And a new analysis reported in BioScience avers that the Darwin offspring did experience the repercussions of such inbreeding. Applying an inbreeding coefficient to calculate whether childhood mortality in the Darwin/Wedgwood family across several generations was related to inbreeding, the authors indeed found an association.

Three of the Darwins’ ten children died at age 10 or younger, one of tuberculosis, one of scarlet fever, and one of an unidentified disease. Studies suggest an association between childhood mortality from bacterial infection and consanguinity, and the Darwin family seems to bear that out. In addition, three of the Darwin children who did live to adulthood experienced lengthy marriages without any children, and such infertility may be another manifestation of homozygous states that interfere with reproduction. A photograph of the youngest Darwin child, Charles, who died in toddlerhood, suggests that the baby had some congenital disorder, although the nature of it remains unclear. Emma Darwin was 48 years old when she gave birth to Charles, so Down Syndrome is one likely explanation.

Successful Darwins

In spite of some of the sad facts of the Darwin family story, a few of his children experienced successes of different kinds. Three of his sons were members of the Royal Society, a long-time Darwin family tradition that skipped over the most famous member of the tribe, Charles himself. And Darwin by any measure of fitness did pretty well: in spite of the loss of three children and the infertility of three children, he nevertheless had several grandchildren.

Did Darwin himself suffer from the effects of inbreeding?

Charles Darwin experienced a variety of chronic health conditions, but they do not necessarily seem to have been related to his family’s consanguineous status. Several theories abound to explain his symptoms, which included digestive and skin problems, but no one knows for certain what afflicted the great naturalist. One of the foremost hypotheses is that he had Chagas disease, occurring after a bug bite on one of his voyages transferred an infectious protozoan that may have permanently damaged the scientist’s gut. Stress seems to have exacerbated the problem, whatever its etiology.

Mosquito nose transplanted to frogs, flies

To combat malaria, we must understand the mosquito’s nose

Malaria affects several hundred million people worldwide every year, and each year, more than one million people–mostly children–die of the disease.  The vectors for transferring the plasmodium that causes malaria to humans are female mosquitoes from the Anopheles genus. To combat these mosquitoes and this deadly disease, we must first understand the mosquito nose.

The mosquito sense of smell is localized to the animal’s antennae. There, nerve cells sense various odors (all smells are particulate!) via molecules of protein called receptors (because they “receive” the input). Scientists have reasoned that if they can understand which odors trigger these receptors–and thus, the mosquito’s interest–they may be able to develop odorants (smells) that distract the mosquito from people, thus reducing transmission of malaria.

Fruit flies and frogs with mosquito noses

While using the actual animal might seem to be the way to go, scientists turn to more standard laboratory models for such work. Fruit flies and frog eggs are long-time, well-characterized standbys in the lab environment, and specific manipulations allow researchers to introduce genes from other organisms into these species. Because fruit flies and frogs are such prolific animals, reproducing by the hundreds, the proteins that these introduced genes encode can be produced in the context of the whole organism in large numbers. In science and industry, a process that allows big production outputs like this is called “high throughput.”

The labs of Dr. John Carlson of Yale and Dr. Lawrence Zweibel of Vanderbilt have respectively co-opted the fruit fly (Drosophila melanogaster) and a frog (species not specified) as their method of high-throughput production of these mosquito nose proteins. The fly approach is a bit slower, involving painstaking insertion of the mosquito genes into flies one at a time. The flies express the proteins in their own antennae, a replacement for their own receptors that have been knocked out.

The frog egg approach is more truly high throughput, as the engineered frog eggs express an abundance of the mosquito nose proteins. The smell-sensitive egg then can be tested using a system that measures nerve signals: Whenever a specific odorant dissolved in the buffer solution surrounding the egg sets off the nose protein receptor, the system registers the electrical response.

The flies are good for testing compounds that volatilize in air, showing by their behavior whether or not the odor attracts, while the frog eggs allow for a more truly high-throughput analysis. Together, they make quite a team when it comes to testing the mosquito’s sense of smell.

Frogs and flies, working together

The two labs tested each system using 72 receptors from the Anopheles “nose” and a panel of 110 odorants. The mosquito-nosed frog eggs and mosquito-nosed flies yielded results that pretty much matched: Some receptors are generalist types, reacting to just about any smell, but a special few focus more on specific odors. As it turns out, 27 of these receptors are fine-tuned to respond to the odorants in human sweat. The results from these studies are reported simultaneously in two papers, one in Nature and one soon to appear in the Proceedings of the National Academy of Sciences.

A decoy smell for the mosquito

Why go to all the trouble to make mosquito noses in flies and frogs? The hope is to use these high-throughput methods to identify compounds that can serve as decoys for the mosquitoes by deceiving these “nose” receptors. If researchers can identify an eau d’ sweat that distracts the mosquito away from a human target or an odorant combination that repels the mosquito from people, the outcome could be a decrease in transmission rates of malaria.

UPDATE: Malaria does not distinguish between kings and commoners: News reports indicate that the microscopic plasmodium may have felled King Tut himself.

Ideas for questions

Why do scientists focus on species like fruit flies or frogs (e.g, Xenopus laevis) when they do research like this? Why not use the species being studies instead?

Do some research on the relationship between the malarial plasmodium and the mosquito. Do all species of mosquito transmit this pathogen? What distinguishes species that transmit malaria?

The article references measuring electrical activity in the frog eggs in response to odorants. Look up “voltage clamp.” How is that used to measure electrical activity?

World/public health question: What has been done in the past to combat malaria? How effective were these efforts? What is being done today? Some efforts are high-tech, like the studies described above. Some are low-tech. Can you identify a few examples of each?

Turkey taming happened twice

The taming of the turkey

It’s not unusual for our domesticated familiars to have gone through several cycles of domestication. In the Old World, pigs and sheep and cows submitted to the process several times. But the New World has only a few examples of its own homegrown domesticates, and now, thanks to some fossilized poop, we can trace the taming of the turkey.

Mitochondria and coprolites

Using coprolites–that’s the poop–and mitochondrial DNA, researchers describe in a study published in PNAS having nailed down the domestication of the turkey in the American Southwest. The previous idea was that the turkey was like beans, maize, and squash–it made its domesticated way to the Southwest by way of trade routes from southern Mexico. Indeed, in southern Mexico, indigenous peoples had domesticated their own version of the bird.

But the southwesterners had their own version, too, and mitochondrial DNA–which passes from mother to offspring and accumulates mutations at a slow, predictable rate–shows that their turkeys came from a different species.

Modern turkeys are imports

You might think that the turkeys around today came from one or the other of these turkey lines, so carefully bred 2000 years ago. Nope. Europeans showed up, took some turkeys back to Europe. There, other Europeans produced some deeply inbred turkeys that then made their way via import back to the Americas. The turkeys we eat today, the ones that make the centerpiece around a Thanksgiving table or in a Sarah Palin interview, may trace back to southern Mexico, but they’re now really inbred European imports. Good thing Ben Franklin didn’t get his way when he allegedly proposed the turkey as the national bird for his fledgling nation.

Ideas for questions

Why do you think mitochondrial DNA accumulates mutations more slowly than, say, nuclear DNA?

Explain why mitochondrial DNA passes only from mother to offspring.

How do you think the researchers could tell whether or not turkeys were inbred?

Coprolites are trace fossils, while fossilized bones are body fossils. What are other examples of trace fossils? What can these trace fossils tell us in the absence of body fossil information?

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