Today in Science: GLV Daily Digest for August 19, 2014

Today in science, a molecular mechanism responsible for sex determination has been identified in fruit flies, and it is essential for fertility and properly differentiating females and males. New genetic evidence indicates that the so-called 'pygmy' build evolved more than once among populations of hunter-gatherers living in sub-Saharan Africa's rainforests, and there seem to be compelling reasons for it.

Experiments with genetically modified pig hearts transplanted into the abdomens of baboons have produced some remarkable successes, and this science is expected to help many patients currently on the wait list for a heart. Finally, a parasitic fungus and its ant hosts are locked in a competitive struggle, and science has provided new insights on their relationship. Welcome to the Guardian Liberty Voice Science Daily Digest for Aug. 19, 2014.

Sex Determination Mechanism Discovered in Fruit Flies

Male and female fruit flies owe their sexual identity to molecular mechanisms called microRNAs (miRNAs), which have been discovered to play a vital role in determining sex in these insects. These miRNAs play a crucial role in suppressing the function of some genes that code for proteins, allowing others to code more freely.

Scientists with Cold Spring Harbor Laboratory (CSHL) in New York found that differences in the miRNAs carried by female and male fruit flies were crucial to ensuring proper differentiation of the sexes and fertility. The miRNAs regulate the development of germ-line cells, responsible for producing sperm in males and eggs in females. When one type of miRNA was removed from adult flies, whether female or male, the flies became infertile and started to develop male and female sex determinants simultaneously.

Pygmy Build Evolved More Than Once in Humans

So-called 'pygmy' peoples seem to have evolved their short stature on more than one occasion, according to a new study that found different genetics underpinning the short stature of the Batwa people of Uganda and the Baka people of west-central Africa. The short stature of these and other pygmy peoples in sub-Saharan Africa, Southeast Asia and the Philippines may be an adaptation to lifestyles as rainforest hunter-gatherers.

The scientists responsible for the study compared the genetics of the Batwa, a culture of hunter-gatherers living in the rainforests of Uganda, with their neighbors the Bakiga, a non-pygmy people who farm the land. They identified changes at 16 different genetic locations responsible for the short stature of the Batwa people, among whom women are about four feet eight inches and men are about five feet. The differences between the two groups indicated that short stature in the Batwa is an evolutionary adaptation produced by a number of different genes.

Similar comparisons of the pygmy Baka people, hunter-gatherers in the rainforests of west-central Africa, with the neighboring non-pygmy Nzebi and Nzime farming peoples yielded parallel results. The science indicated that like the Batwa of Uganda, the Baka of west-central Africa have evolved short stature as an evolutionary adaptation influenced by multiple genes. However, the genetic changes the researchers found in the Baka were different from those they found in the Batwa, indicating that the two peoples evolved their short stature independently.

The scientists hold that both the Batwa and the Baka, as well as other pygmy peoples in Africa and elsewhere, quite likely evolved their short stature as an adaptation to their lifestyles as hunter-gatherers in hot, humid tropical rainforests. Food is not as abundant in rainforests as intuition might suggest, and smaller bodies that require less food should be adaptive for that very reason.

Smaller bodies are also less prone to overheating, another advantage in a hot and humid rainforest. Additionally, people who are shorter in stature enjoy advantages of mobility in overgrown rainforests, finding it easier to traverse landscapes that are thick with tangled vegetation and to climb trees to access food sources there.

Genetically Modified Pig Hearts Survive in Baboons

Transplanted hearts from genetically modified pigs have been kept alive in the abdomens of baboons for up to a year and counting, in a new breakthrough expected to help cardiac patients on the waiting list. The genomes of the pigs were genetically modified to suppress certain genes known to cause immune reactions in humans, and certain human genes were added to increase compatibility. The hearts were implanted into the abdomens of baboons so that they could be tested without jeopardizing the baboons' own lives in the event that they were rejected.

Different genetic modifications were introduced into different experimental groups of pigs, allowing the scientists to identify the genetic modifications that made for the most successful transplantations. The study also used very specific immunosuppression efforts, limiting the risk that the hearts would be rejected without suppressing the immune system as a whole.

The group of genetically modified pig hearts that performed the best expressed a human gene that helped to prevent problems with microvascular clotting, a common issue in organ transplantation. For the five hearts in this group median survival time was over 200 days. Moreover, three of the five are still going strong, and the longest-running has broken the one-year mark.

In the U.S. alone, the waiting list for a heart stands at about 3,000 people, and the supply of donor hearts stands at a mere 2,000 per year. Given the limited number of human hearts available, as well as the shortcomings of mechanical devices, so-called xenotransplantation may offer many people with end stage heart failure a new lease on life.

New Insights Into Competition Between Parasitic Fungus and Ant Hosts

Scientists have gained new insights into the competition betweenthe parasitic fungus Ophiocordyceps camponoti-rufipedis, more colorfully known as the 'zombie ant fungus,' and the carpenter ants ( Camponotus rufipes) that it infects. While the parasitic fungus adroitly manipulates its ant hosts to die near their own colonies in order to increase the fungus's chance of infecting new hosts, the ants are anything but defenseless, and have in fact evolved powerful social immunities.

When the fungus infects an ant, it takes over the ant's behavior, manipulating it into climbing up vegetation near the colony and biting onto a leaf before dying. This is perfect for the fungus, which can then grow a spore-boring structure called the ascoma, perched on a long stalk called the stroma. The spores can then disperse to infect new hosts. Out of 17 ant colonies observed by the researchers in Brazil, all of them had cadavers of ants killed by the fungus nearby.

However, the mere fact that the fungus must carry out its lifecycle outside of the ant colony is testament to a vigorous response from the ants themselves, a kind of social immunity that keeps the rate of fungal infections down. The researchers who carried out the study placed the carcasses of ants that had been recently killed by the fungus into one of two nests, an occupied nest and an unoccupied one. In all cases the fungus was unable to develop properly, even in the completely empty nest, and in the occupied nest the ants rid themselves of nine of the carcasses.

The fact that the fungus was not able to develop properly inside an occupied ant colony is easy enough to explain in terms of the ants' own fastidiousness in keeping their nests clean. The fact that it was unable to complete its development even in an unoccupied, empty nest points to a role for other factors, such as the limited physical space inside ant colonies and the influence of their microclimates. These findings provide new insights into the characteristics of the competitive relationship between the ants and the fungi that parasitize them.

Commentary by Michael Schultheiss, Science Editor