"Lesbian nematodes"

Scientists have created ‘lesbian worms' in a new development that some are suggesting could shed light on the nature vs nurture debate over sexuality, according to a number of licentious news sources (Sidney Morning Herald for example). University of Utah researchers tweaked nematode worms to make them attracted to worms of the same sex and appear to have demonstrated that sexual orientation is hard wired, at least in nematodes (abstract, pdf). "The conclusion is that sexual attraction is wired into brain circuits common to both sexes of worms, and is not caused solely by extra nerve cells added to the male or female brain," says biologist Erik Jorgensen (press release).

The ‘lesbian worms' line is a bit of red herring. There aren't true females in the C. elegans nematodes used, only hermaphrodites and (rare) true males. "A hermaphrodite makes both eggs and sperm," says Jorgensen. "... Most of the time, the hermaphrodites do not mate. But if they mate, instead of having 200 progeny, they can have 1,200 progeny."

As attraction in the worms is based on smell Jorgensen and co monkeyed around with male worms to find out whether their attraction to hermaphrodites was influenced by core nerve cells, accessory nerve cells, or a combination of the two. The answer was both. They also took hermaphrodite worms and turned on the genes that determine maleness, these then became the famous ‘lesbian worms', chasing after other hermaphrodites. (The Daily Utah Chronicle notes that Jorgensen calls hermaphrodites "females" because they reproduce independently.)

The Salt Lake Tribune is one of those taking on whether this means human sexuality is hard wired. Basically the answer is only "maybe", but it adds some credence to the idea.

Image: hermaphrodite (top) and male (bottom) pair of worms / Jamie White

Posted by Daniel Cressey on October 26, 2007

http://blogs.nature.com/news/thegreatbeyond/2007/10/lesbian_nematodes.html 

Hervé This - créateur de la gastronomie moléculaire, est physico-chimiste INRA au Laboratoire de chimie du Collège de France et au Laboratoire de chimie d'AgroParisTech. Directeur scientifique de la Fondation Science & Culture Alimentaire (Académie des sciences), il est aussi conseiller scientifique de la revue Pour la science, où il tient la rubrique "Science et gastronomie".

devient dur quand l'eau contenue dans la mie est vaporisée par des ondes trop intenses.

Extrait :
Quand le climat mondial semble se réchauffer, n'est-il pas étonnant que les millions de foyers qui cuisinent chaque jour gaspillent jusqu'à 80 pour cent de l'énergie qu'ils utilisent pour chauffer leurs aliments ? Sauf en hiver, il semble déraisonnable de chauffer la cuisine plutôt que les aliments. Quelles solutions la technologie propose-t-elle ? Les chauffages par induction et les fours à micro-ondes semblent s'imposer, car leurs rendements énergétiques sont très bons.
Hélas, dans un four à micro-ondes, le pain réchauffé prend une consistance dure, un peu comme du cuir. Pourquoi ? Michael Uzzan et ses collègues de l'Université de Haïfa, en Israël, viennent d'élucider ce durcissement du pain. Simultanément, ils ont déterminé pourquoi la mie du pain excessivement chauffée par des micro-ondes prend un aspect crayeux. [...]

http://www.pourlascience.com/index.php?ids=TKbFZtMQVEmvZnXonclh&Menu=Pls&Action=3&idn3=6127# 

 

M. Philippe Ciofi est neuroanatomiste à l'Institut François Magendie, INSERM U378, à Bordeaux.

Pourquoi certaines femmes ont-elles des orgasmes, et d'autres non ? Dans un livre récent, la biologiste Elisabeth Lloyd défend une thèse controversée : comme les femmes n'ont pas besoin d'éprouver du plaisir pour avoir des enfants, cette capacité, qui n'est pas indispensable à la survie de l'espèce, se serait raréfiée chez elles.

Extrait :
Pourquoi les hommes et les femmes sont-ils inégaux face à l'orgasme ? Tous les hommes, peu ou prou, connaissent cette sensation de plaisir culminant, alors  que certaines femmes n'y goûtent jamais. Pourquoi la nature aurait-elle distribué les cartes de façon si inégale ?
La question est moins anodine qu'il n'y paraît. La fonction de reproduction occupe une place centrale dans l'évolution des espèces, dont elle est à la fois le substrat et le moteur. Le substrat, car la vision classique de Darwin propose que les individus les plus aptes à se reproduire ont une plus grande descendance, descendance sur laquelle s'exerce la sélection naturelle. Le moteur aussi, car, pour être transmises de parents à enfants, les mutations génétiques aléatoires, qui introduisent les légères variations interindividuelles porteuses d'avantages adaptatifs, doivent toucher les ovules et les spermatozoïdes. [...]

http://www.pourlascience.com/index.php?ids=TKbFZtMQVEmvZnXonclh&Menu=Cp&Action=2&idn3=550# 

L'insomnie du poisson zèbre peut-elle expliquer notre sommeil ?

Quand on les empêche de dormir la nuit, les Poisson zèbreEgalement nommé danio rerio, le poisson zèbre est un petit poisson populaire chez les aquariophiles, originaire des eaux tropicales de l\'Inde. Il mesure entre 2 et 5 centimètres de long, et arbore sur son corps des bandes horizontales bleues et argentées.');" onmouseout="killlink()">poissons zèbres ne récupèrent pas pendant le jour, comme le feraient la plupart des MammifèreClasse de vertébrés comprenant plus de 4000 espèces. Ils se caractérisent entre autres par :
- une température corporelle constante ;
- la possession de poils ;
- le fait d\'allaiter leurs petits ;
- la présence d\'une demi mâchoire inférieure formée d\'un seul os.
Les premiers mammifères...');" onmouseout="killlink()">mammifères. Cette étrange observation s'explique peut-être par une différence dans l'action d'un RécepteurProtéine, généralement située à la surface des cellules, capable de fixer une molécule informative (médiateurs chimiques, neurotransmetteurs, hormones...) et de convertir ce message extracellulaire en signal intracellulaire, entraînant une réponse de la part de la cellule.');" onmouseout="killlink()">récepteur du système nerveux, également impliqué dans la NarcolepsieLa narcolepsie est un trouble neurologique qui se caractérise par des envies rapides et irrépressibles de dormir, pouvant intervenir plusieurs fois dans une seule et même journée. La narcolepsie se manifeste souvent à l\'adolescence et touche deux fois plus d\'hommes que de femmes.');" onmouseout="killlink()">narcolepsie. Mais au fait, pourquoi dort-on ?

 http://www.futura-sciences.com/fr/sinformer/actualites/news/t/zoologie/d/linsomnie-du-poisson-zebre-peut-elle-expliquer-notre-sommeil_13271/

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 http://www.nature.com/news/2007/071016/full/news.2007.167.html

Fish insomnia sheds light on sleep

Studies across species could reveal how sleep evolved.

Emma Marris

Zebrafish won't be caught napping after a sleepless night.

Zebrafish don't nap more during daylight hours when sleep deprived, a new study shows. The work suggests that fish are better able to use light cues to stay awake during the day than mammals, hinting that evolution has produced different systems for regulating sleep in different groups of animals.

Every animal sleeps, but many do so in ways that humans would hardly recognize. Cows stand stock still on their four legs; dolphins take a separate nap in each hemisphere of their brains so they can keep swimming. Even fruitflies catch forty winks now and again in their short lives.

The way you can tell a zebrafish is asleep, says Emmanuel Mignot at Stanford University in Palo Alto, California, is that its tail droops, it hangs immobile at the bottom of the tank, and it requires more of a prod - a mild electric current will do - to get it swimming than when it is awake.

Mignot and his colleagues are keen to keep zebrafish awake to study how sleep - or the lack of it - affects this often-studied fish. No one really understands why people sleep; how sleep evolved is equally mysterious, says Mignot. "Sleep is one of the basic mysteries remaining, in terms of why it has been selected for." To understand that, he is studying sleep in animals from dogs to zebrafish. "It is better to understand how we sleep across evolution, and then we will understand the reason for sleep," he says.

Dodging the sleep debt

The team found that if you keep zebrafish awake all night and then leave the lights off, they will make up for lost snoozing time. But if you keep them awake and then flip on the lights, they won't nap more during the next day, as mammals would¹.

To find out what was causing this behaviour, Mignot and his colleagues looked at what happens when a mutation knocks out the only receptor for the sleep neuropeptide hypocretin (also known as orexin) in the zebrafish.

In mammals, such a gap in the hypocretin system causes narcolepsy, a syndrome featuring crushing daytime sleepiness and night-time insomnia as well as bouts of muscle collapse called cataplexy. But in the fish, this seems to cause only the night-time insomnia.

Mignot says he thinks that light and the hormone it triggers - melatonin - suppress sleep in the fish so strongly, they overrule any 'sleep debt' from the night before. Unlike mammals, they only need their hypocretin system to regulate sleep at night. Physiological studies support this theory. Some birds seem to behave the same way, Mignot adds, hinting that light and melatonin-dominated day regulation might span the non-mammalian animal family tree.

"I do believe the role of light and melatonin came to a kind of crossroads. At some point it became less effective, and animals had to develop a different way to promote wakefulness," says Mignot.

The finding contradicts previous work that has found that hypocretin increases wakefulness during the day as well as at night in zebrafish - though this was in larvae rather than adults. "Further analysis of hypocretin-receptor mutants is needed to resolve these discrepancies," says Alexander Schier of Harvard University in Cambridge, Massachusetts, one of the authors of the previous study.

Drowsy dogs

Mignot has been mapping the neurochemistry of sleep in humans, rodents, and a pack of narcoleptic dogs for years.

He says he would like to see much more work done across the animal kingdom, to create an evolutionary tree of sleep. He's going to stick with his zebrafish for now, he adds, but he would love to study the same system in an animal such as a platypus - from the most ancient and reptile-like family of mammals. "I would dream to do this in a monotreme, to find out if we could have a narcoleptic platypus."

The narcoleptic dogs, incidentally, are no longer an active area of research - the dogs have all been retired into private life. "We have one last dog, and he was just adopted," says Mignot. "He's now mine."

References

1. Yokogawa, T. et al. PLoS Biol. 5, e277 (2007).
2. Prober, D. A., Rihel, J., Onah, A. A., Sung, R.-J. & Schier, A. F. J. Neuroscience. 26, 13400-13410 (2006