Monthly Archives: September 2012

Few news from Mars, but there is a disappointing study on Earth

Two weeks ago I wrote in this blog (Is there life on Mars?) on the Mars Science Laboratory mission of NASA with the famous Curiosity rover, which its main aim is finding possible signs of past life in the red planet.

Well, as expected, until now there are no spectacular news, as in all scientific studies, things take time. The Curiosity has been taking photos (see one here) and taking samples and analyzing them. Today there are 40 days since the landing and it has walked about 150 meters. As stated in the last NASA chronicle, Curiosity continues its work “in good health”. So keep waiting.

martian landscapeOne of the photos taken by Curiosity at Gale crater with a 34 mm Mastcam camera. The mountains (far 15 km) are called Mount Sharp. Image: NASA/JPL-Caltech/MSSS

But today I want to comment some disappointing news regarding the possibilities that there had been life on Mars. It turns out that a recent study of French and American researchers (Meunier et al, 2012) provides evidences that Martian clays could have a direct magmatic origin and therefore they would not have made by contact of the basaltic crust with liquid water, as hypothesized until now. And so, the less likely the existence of liquid water on Mars in the past, less likelihood of living beings there.

Clays are hydrous silicates (of phyllosilicates group), mainly of aluminium (Al2O3 · 2 SiO2 · 2 H2O). They are minerals with granular structure, which originate on Earth mainly by decomposition of magmatic rocks containing silicate minerals such as the feldspar by the action of liquid water (this may contain carbonic acid and other compounds). Clays have been identified on Mars some years ago with the spectrometers of the OMEGA observatory carried by the Mars Express spacecraft of the European Agency, which is orbiting Mars (Bibring et al, 2006). It was believed until now that these clay minerals, abundant in Mars surface, would have been formed for a long time by interaction of liquid water with basaltic crust, decomposing the magmatic rocks, but early in Mars history, 3700 million years ago, at the same time that Earth life was beginning. The presence of liquid water would be a sign of warmer and wetter conditions on early Mars, and therefore more likely to carry life.

martian claysClay minerals (in red) exposed in the old crust of pyroxene (metallic silicates) of Mars at Mawrth Vallis, looking south. Image © Joseph Michalski

But the recent published work of Meunier et al. suggests a different mechanism that does not require prolonged reaction of rocks with water. Interestingly, evidence has been found on Earth, studying clays of Mururoa Atoll in French Polynesia, which are similar to Martians phyllosilicate clays. Using petrographic techniques (study of the mineral structures at the microscopic level), microanalysis of elements, and isotope ratio analysis, these researchers have found that the Mururoa clays, rich in Fe and Mg, are much richer in rare earth elements (lanthanides and other), and microscopic structures are very different from other more abundant clay on Earth, originated from aqueous weathering. The characteristics of the Mururoa clays assert that were originated by short pulses of degassing magma in the interstices of basalt, and the water contained in clays would be only of magmatic origin.

Meunier et al. have also studied clays of Martian meteorites and have found that some of them have similar characteristics as those of Mururoa. Especially the ratio of the isotopes carbon-13 and deuterium in Lafayette meteorite shows that their clay was formed by direct precipitation of magmatic fluid containing water, by degassing magma.

Therefore, if martian clays, very similar to those of Mururoa (at least in their spectra), are proved to be formed also by magmatic degassing, then the presence of liquid water in early Mars would be more difficult to prove, and this planet would not have had easy conditions of habitability, at the same early period when life began to flourish on Earth.

The place where Curiosity is walking around, the Gale Crater, is known to contain phyllosilicates, i.e. clays. So, we must therefore wait that this rover could find clays and analyze them, and wait for some news a little more optimistic.

References

Bibring, J-P. et al (2006) Global mineralogical and aqueous Mars histoy derived from OMEGA/Mars Express Data. Science 312, 5772, 400-404

Hynek, B. (2012) Planetary science: Unhabitable martian clays ? Nature Geoscience, News and Views, online 9 sept 2012: http://dx.doi.org/10.1038/ngeo1560

Meunier, A. et al (2012) Magmatic precipitation as a possible origin of Noachian clays on Mars. Nature Geoscience, online 9 sept 2012: http://dx.doi.org/10.1038/ngeo1572

http://en.wikipedia.org/wiki/Clay

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Hyenas communicate by scent through symbiotic bacteria

The spotted hyena (Crocuta crocuta), also known as laughing hyena, is the best known and greatest species of hyena, living in Sub-Saharan Africa. Although not considered in immediate danger of extinction, their numbers have been increasingly shrinking, like all other large African mammals and their total number is estimated at about 40,000. Most of them live in national parks of the East Africa, especially in the Serengeti in Tanzania. In the rest of western and southern Africa, populations in many cases are lower than 1000 individuals in each country, and isolated from each other, so in real danger of extinction.

The spotted hyena (Crocuta crocuta). Photo: Tophat21 (animalswikia.com)

It is the carnivorous mammal with more complexity of social behaviour, similar to the cercopithecine primates (baboons and macaques), and because of this, his intelligence is comparable to those primates and in some respects even to the chimpanzees.

They live in communities, clans, of about 40 to 80 individuals and these societies are matriarchal: females, larger than males, are dominant, with even the lowest ranking females being dominant over the highest ranking males. Maybe they could be caught by the radical feminists as a symbol, right?

Social relationships among hyenas may have to do with maintaining the hierarchy, or to find food (hunting or scavenging), or reproduce, or control of the territory against other clans, and are based on communication systems that manifest with multiple sensory modalities, both body language and vocalizations. Of these, a wide range of sounds (about 12 different) have been registered, the best known of which are a howl and a kind of laughing where the nickname comes from. Body language is also quite complex, with different attitudes and positions of the ears, tail, etc., sometimes similar to wolves.

Like primates, spotted hyenas recognize individual conspecifics, are conscious that some clan-mates may be more reliable than others, recognize foreign family groups and rank relationships among clan-mates, and adaptively use this knowledge during social decision making.

Creamy secretion of anal scent glands, and olfactory communication

The title of this blog post refers to a particular form of communication, but very common among these hyenas: a chemical signal, olfactively detectable. It is an odorous marking, with a smelly white creamy secretion, called paste, produced by a pair of anal sebaceous glands. This secretion is composed of lipid-rich sebum and desquamated epithelial cells. The paste is deposited on grass stalks, and produces a powerful soapy odour, which even humans can detect. They do it on several occasions, as when lions are present, or the males do it near the dens, and most often in their territory limits. Often, after the pasting, they scratch the ground with their front legs, which adds even more flavours that come from the secretions of their interdigital glands. Clans mark their territories by either pasting or pawing in special latrines located on clan range boundaries.

In addition, this odorous secretion is also part of usual greetings among members of the clan. So, two of the individuals are placed in parallel and in opposite directions from one another, lifting one leg back and smelling each other anogenital areas [1].

Spotted hyenas greeting one another. Photo: Tony Camacho, Science Photo Library

The scent of paste secretion

The major volatile constituents of paste are fatty acids, esters, hydrocarbons, alcohols and aldehydes. Collectively, they give paste a pungent, sour mulch odour that persists, detectable by the human nose, for more than a month after paste is deposited on grass stalks.

It has been shown that odour of spotted hyena paste varies based on the individual identity, sex and group membership of the scent donor. Hyenas’ group-specific odours, in particular, are due to underlying variation in the structure of short-chain fatty acid (mainly acetic, propionic and butyric acids) and ester profiles of paste.

These odorants are well-documented products of bacterial fermentation. These scent glands are warm, moist, organic-rich and largely anaerobic, and thus appear highly conducive to the proliferation of fermentative symbiotic bacteria.

Symbiotic bacterial communities that produce social odour of hyenas

The bacteria use protein and lipid of glands as substrates, producing odoriferous metabolites, which are used by their mammal guests as chemical signals. The bacterial communities differ according to the hyena individuals and especially to the clans, according to symbiotic microbial communities are slightly different among clans, they are group-specific. Bacterial communities arise from the contact between the hyenas of the same clan, as they share the same space and common areas where they deposit the paste secretion. Spotted hyenas frequently scent mark the same grass stalks as their clan-mates (i.e. overmarking), and they often do so in rapid succession to one another. Therefore, overmarking appears to be a viable pathway for the transmission of bacterial communities among members of hyena clans. Although average genetic relatedness within hyena clans is low, it is higher within than among clans.

This mechanism to explain the social scent specific for group has also been proposed for some other mammals such as bats (Eptesicus fuscus, Myotis bechsteinii) and badger (Meles meles), but precisely in the spotted hyena it has been well demonstrated recently in an article published by scientists from Michigan (USA) [2].

These authors have worked with anal scent secretions of female hyenas from Masai Mara reserve in Kenya. They have shown by electron microscopy the presence of bacteria in the paste.

bacteria in pasteBacilli- and cocci-shaped bacteria surrounded by the paste secretion, with lipid droplets (asterisk) [2].

Bacterial DNA was extracted from samples of paste secretion and 16S rRNA genes were amplified and sequenced. Comparing the obtained sequences with data from GenBank ® (public database of genetic sequences, http://www.ncbi.nlm.nih.gov), different bacteria were identified. The genera found were some of the groups of gram-positive Actinobacteria (Corynebacterium and Propionibacterium) and Firmicutes (Anaerococcus and others), and some of the gram-negative group of bacteroides. While the types found were more or less the same in the different clans of hyenas, the proportions of bacterial types were significantly different according to the clan.

Propionibacterium, coloured electron microscopy image: Dennis Kunkel Microscopy, Inc./Visuals Unlimited, Inc. Other species of this bacterial genus producing propionic acid are involved in the production of Emmental cheese types.

So, using the latest molecular techniques, culture independent techniques and sequencing, this work [2] shows that symbiotic bacteria may be helpful to their animal guests, by increasing diversity of odoriferous signals available, with variability among hyenas’ clans.

Importance of symbiosis

This is a quite peculiar symbiosis of bacteria with mammals. But, as you know, most mammals, including us the humans, live with millions of bacteria inside, many of which are beneficial, like most that inhabit the digestive tract or other body parts, which constitute the so-called “microbiome”. The probiotics we eat with some fermented dairy products contribute to maintaining populations of these symbiotic bacteria.

More and more data on the importance of symbiosis in multiple aspects of living beings is being known, as well as symbiosis is a key factor in evolution. Just remember that the most likely hypothesis for the origin of the first eukaryotic cells (about 2000 million years), is that it was due to a combination of the two types of prokaryotes, bacteria and archaea. Some millions of years later, the two well known endosymbiosis took place in the eukaryotic cell: bacteria carrying aerobic respiration that gave rise to mitochondria, and photosynthetic oxygenogenic cyanobacteria that were the origin of chloroplasts in algae and plants.

Other important evolutionary symbiosis were the establishment of mycorrhizae between fungi and plants, which led to the colonization of land by these, or nitrogen-fixing bacteria (Rhizobium) with legume plants, or a group of organisms, lichens, which are symbiosis of fungi with some algae or cyanobacteria, and live in many very different and hostile environments. And many other cases of symbiosis between distinct species getting benefits because live together.

So, symbiosis is a good lesson from biological evolution: by cooperation, benefits for both participants are always obtained.

References

[1] Mills, G., H. Hofer (1998). Hyaenas: status survey and conservation action plan. IUCN/SSC Hyena Specialist Group.

[2] Theis, K.R., T.M. Schmidt, K.E. Holekamp (2012) Evidence for a bacterial mechanism for group-specific social odors among hyenas. Nature Scientific Reports 2, 615

[  ]  http://en.wikipedia.org/wiki/Spotted_hyena

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