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mercoledì 5 agosto 2015

LE DIMENSIONI (DEL CERVELLO) CONTANO, SE SEI UNA PESCIOLINA TROPICALE

a guppy
Sig. Guppy (Pub Dom img)
Avere un cervello grande aumenta la capacità di sopravvivere ai predatori nelle femmine, ma non nei maschi, di Poecilia reticulata, una specie di piccoli pesci tropicali detti guppy. La scoperta, fatta da un gruppo di scienziati delle università di Stoccolma e Vienna, è riportata sulla rivista scientifica Ecology letters






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SIZE DOES MATTER (WHEN IT COMES TO BRAIN AND YOU ARE A FEMALE LITTLE FISH)

a guppy
Mr. Guppy (Pub Dom img)
Size does matter. At least when it comes to brain and the ability of surviving predators' attacks and when you are a female of Poecilia reticulata, a species of small tropical fishes called guppies. The discovery, made by a group of scientists from the universities of Stockholm and Vienna, is reported in the journal Ecology letters.






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The following text is that of the podcast
in Eng?ish

O-oooooh hallo dear English-hearing-speaking-thinking listener, welcome to the third of my podcasts in Engmark, that is English-question mark, a language that is to real English what “spaghetti bolognese” is to an actual Italian dish and the combination of a piece of evil chalk scraping a blackboard with Marge Simpson’s voice is to velvet.
Speaking of voices, the one you’re hearing is that of my avatar, a dumb human controlled via a wireless-voodoo trick by me, “sciencemug”, the blog which tells you about science, sings the song of love but scrambles all the words while skipping the rope of summer in company of ice creams in a blue mood aaand while shutting down the alien conspiracy which aims to take over the world production of donuts in order to change the recipe and make them taste like deep space tofu, that is as saaaad as the Earth’s one, but colder and with a bit of a Haggis aftertaste.
Soooo, what am I telling you this time? Weeell, I’m telling you a science story about dimensions, brains, little tropical fishes, predators and evolution! 

guppies meet jaws_ by sciencemug
by sciencemug
[The guppies pic is a Public Domain image adapted by sciencemug (source: wikia.com)]

Size does matter, as usual. At least when it comes to brains and the ability of surviving predators' attacks and when you are a female, hence not a male, of Poecilia reticulata, a species of small tropical fishes called guppies. The discovery, made by a group of scientists from the universities of Stockholm and Vienna, is reported in the journal Ecology letters.

Ooooh, well well, doctor Alexander Kotrschal (which I’m gonna call Alex, from now on, to avoid to plead guilty of consonant slaughter in a trial for mass murder of the poor people of the alphabet and then face the wrath of the ghosts of those innocents letters for the rest of my blog-life, and, by the way, according to the usual reliable sources of the internet, 1 blog’s year is equal to 5 leap years of a sloth), so, doctor Alex, I was saying, and other 5 scientists form Sweden and Austria (and I‘m gonna call this science bunch “the Alexanders”, ‘cause, well, I think it’s really really cool) they decide to try to understand whether and how evolution kisses the kiss of blessing to the bigger brains. To do that the Alexanders decide to study little tropical fishes, the guppies, and to analyze the relationship

existing between the size of their brain and their ability to evade predation, that is a pretty useful skill to evolve indeed.

First thing first, Alex and his colleagues go to Quare river in Trinidad, a Carribean island few kilometers off-shore the est coast of Venezuela. The Alexanders, once there, pick up about 5 hundreds guppies, then they go back to the lab and make these little tropical fishes mate. The researchers let the mating-party go on, of course scientifically supervising and planning its stages, till they get what they want, that is 1 million virtual points from the biggest seller of baby bottles for fishes of the northern hemisphere, virtual points that grant the Alexanders the right to choose, as a prize, between a full-optional international tour of the 5 most spectacular expositions of hyper-decorated fake nails in North America and Siberia, and 6 VIP-passes for all the 93 Las Vegas dates of the “Sleeping tongue” company and its shows of 7 hours in which all the 45 actors and actresses use one after the other their tongues to mime every single voice of the “Dictionary of the fiscal terms, 2015 extended edition”. Aaand besides these exciting prizes, the Alexanders, once the guppies mating process is over, get also the genetic selection of different populations of fishes, lines in biological terms: lines of guppies with bigger brains (the biggies), and lines with smaller brains (the tinies). The biggies and the tinies differ in fact by up to about 14% in brain size relative to body size. Now, since guppies’ body size doesn’t change between the two lines, well dear podcast-enthusiast, this means biggies and tinies have brains with substantially different absolute dimensions.


Now now, for their experiment the Alexanders use 48hundreds of these guppies. All the guppies are fully mature adults, with and age ranging from 6 to 8 months, they have never interacted with predators and they are equally divided among males and females, big brained and small brained. Of course to keep track of the biggies and the tinies, which externally are basically identical, the Alexanders have to mark ‘em, so they stick elastomere tags to the little swimming fellas, right below their dorsal fins. Biggies wear a green dot on the left side of the body and a red one on the right side, vice versa tinies proudly display the green dot on the right and the red one on the left (by the way rumors has it that Versace has already hired the fashionable dotted guppies for the next summer collection “Tropical brains and swims”).


Anyway, the Alexanders put the 48hundreds tagged guppies into a glass tank, a really cool one, indeed, since it replicates guppies habitat, meaning rivers and streams.
The tank is a ring, with an inner diameter of 5.3 meters and an outer one of 7.3 meters. By inserting 6 opaque PVC sheets into it, the Alexanders divide the tank into 6 identical segments, called, well, “streams”. Each stream has a surface of roughly 3square meters and becomes the house of 800 guppies, of course still equally divided between biggies and tinies males and biggies and tinies females.


The streams are filled with a layer of coloured lime stone gravel by which the researcher create areas of different depths that range from 0.5 to 40 cm. The shallow parts of the streams are the places where guppies can hide from predators. Another shelter for the guppies is a white PVC box that the Alexanders put on the bottom of each stream. The box’s measures are 40x30x20 cm. The box, besides, is partially submerged and, in correspondence of its shallowest part, it has a 10cm wide opening through which guppies can freely enter and leave.


Alex and his science buddies, to keep the guppies aquatic neighbourhood clean, place in each stream 2 pumps that filter the water and provide a constant water flow of 48hundres liter per hour.  Moreover the Alexanders hire water plants and fresh water snails as biological tank sweepers that destroy all organic waste (apparently unions cut a great deal, especially for the snails). The researchers then, buy a giant flat screen TV set and a year-long subscription to Neptune-flix, to cheers the guppies up (the little fishes by the way, almost jeopardized the experiment ‘cause they were spending too much time binge-watching that “Extreme-Makeover Tank edition” show on DiscoveryandCountryalot Channel).

Anyway, the Alexanders complete the staging of the tank streams by setting the temperature and, of course, the lights.
Electric heaters keep the water at a steady tropicalish temperature of 25 celsius degrees, while lighting follows a Carribeanish 12:12 timing, that is 12 hours of artificial light and 12 of dark. Well, almost 12 and 12, ‘cause the hyper-clever and mega-punctilious super science heroes Alexanders set even bright half-hour periods of increasing and dimming brightness to simulate sunset and dawn. During the night, moreover, faint lights wear the cosplay of moon light.


Last but not least, the kind researchers once a day feed the guppies till they are full (and this take just 3 to 4 minutes to happen). The Alexanders pour into the streams water flake food and sea-monkeys, that are not primates very good at hauling in the mainsail, nope, the sea monkeys are little crustaceans. The cool thing about this feeding strategy is that the stream artificial flow from the pumps disperses the food to all areas and, more importantly, while flakes slowly sink to the bottom of the streams, sea-monkeys stay in the water column. Like this guppies can find food everywhere in the stream and they can bite it from the surface, the water column and the bottom.
 

Got hungry? Time for a commercial break then!


Hungry? Hungry like: “I’ would eat a dwarf galaxy in which stars are spicy meatballs, and planets are an odd and tasty new variety of spherical pizzas and then I would go to lunch?”
Hungry like: “If you only dare to just sniff my bacon and glance at my french fries and think to my as dense as a pet of a black hole hot chocolate cup I will summon my buddy the “Emperor of shadows prince of darkness and broken bulbs and duke of the ‘damn wax matches that never light up but always annoyngly scratch my fingertips’” and make him make you disappear into his realm of infinite despair and blackness where every time you breath your lungs do a sound that is as pleasant as the full body of work of Skrillex played directly into your brain at full blast?
 
Foodoril pill_by sciencemug
by sciencemug

Try “Foodoril”, the new pill which, once ingested, satisfies your hunger by covering all your digestive system’s walls with a solid layer of ancient Mesopotamian spells, eggshells and resentment and crumbs of jinxs against the skinny people who can eat whatever they want and don’t gain weigh ‘cause “I have a fast metabolism”.
“Foodoril”, and your hunger and you will be best friends forever (and go party and forget to pay the check of consequences for the rest of your life, which, if you use “Foodoril”, will be pretty short). 


Sooo, quick recap: a bunch of scientists, the Alexanders, put almost 5 thousands little tropical fishes, called guppies, into a tank segmented into 6 identical artificial streams. The streams are lookalikes of guppies’ natural habitat and the little fishes are fed with delicious treats once a day. Each stream houses 800 guppies equally divided into 4 groups: big brained males, small brained males, big brained females, small brained females. Right?
Ok.
Now, the Alexander leave the guppies alone for 6 week, so the fishes can acclimate to the tank. And the little swimmers do it just fine, ‘cause the researchers check on them after the 6 weeks, and find that the guppies’ survival rate is almost 100% given that just 57 animals out of 48hundres are indeed missing, probably dead for natural causes. Or just got seriously good at hide-n-seek.


Anyway, at week 7, the Alexanders put one predator in each of the 6 streams of the tank and place 3 pipes of clay in the deepest areas of the streams as shelters for this predator. And the predator is not a space hunter with odd space dreadlocks and a space weakness for Austrian-American muscular actors/former politicians who are always murmuring “I’ll be back” with a strong accent anytime they leave a room, any room, anywhere. Nope. The predator is an adult pike cichlid, a carnivorous fish which often share the same geographical areas with guppies. The predators are wild caught, and, for the 6 weeks before their introduction into the tank, the predators are fed exclusively with guppies. And they like ‘em so much that the researcher expect, in the used setting, that each pike cichlid hunts 3 times per hour.

by sciencemug
by sciencemug
[The images of the guppies scheme and the pike are Public Domain images adapted by sciencemug (source: wikia.com)] 

In short then, at week 6 in each stream of the tank there are roughly 800 guppies, equally divided in 4 groups: big brained, small brained, males and females. At week 7 the predators enter the tank and the guppies are no longer safe. And the researchers start selling the tickets for the “Hunter Water Games” and get rich. And they also do weekly censuses of the guppies, censuses that stop at week 20, when a predefined criterion is met, meaning that the number of all the 4 above mentioned groups of guppies in each stream has halved.

At week 20, then, Alex and collegues end the experiment, collect and analyze the data and statistically check them.


Then they start enjoying the money they got thanks to the “Hunter Water Games” and all the connected cruel merchandising like the “One guppy a day keeps the vet away” shirts and the “Pike for Jaws” pins.
Naaa, just joking (pity though, those pins would have been pretty cool…). The Alexanders then study the checked data and get to their experiment results. Results say that, before the predators join the party in the tank, well, all guppies, whatever size their brain be, have the same survival rate. After the predators arrival, though, guppies with bigger brains (the biggies) live longer than guppies with smaller brains (the tinies).
In detail: female biggies have on average 15.1% higher survival than female tinies, while there’s basically no difference in survival rate between males biggies (40%) and males tinies (38%). Besides, females live longer than males (guppies and humans, closer than ever!).


Aaat this point the Alexanders start asking themselves: why we got these results? Where do all the dreams go when we wake up? And above all, when did socks team up with chamaleons and learn the camouflage techniques? 
And the Alexanders realize that, while it’s impossible to find an answer for the last 2 questions, it is not for the first one.


And they explain their results.


Let’s start with why big brained females survive better than the small brained ones.
The Alexanders rule out, as a possible explanation, that female biggies age more gracefully than female tinies. By the end of the experiment all the guppies are in fact between 300 and 360 days old, that is they are way younger than the minimum life’s expectancy of guppies, which is of about 400 days.


The researchers, then, rule out also that big brained females survived longer than smal brained ones because biggies were better than the tinies at finding food. Alex and fellas, as I said before, fed the guppies once a day, and they provided the fishes so much food that it is impossible that even the dumb ones couldn’t find it and therefore die of starvation.


Sooo, why females biggies are better survivalists than the tinies?


The Alexanders say that the most probable explanation is that female with big brains are way better at escaping predators than females with small brains.
Ok, but why? Well, let’s see how the predator-prey dynamics work in the Alexanders’ scenario. The pike chiclids, the carnivorous fish that feed on guppies in the streams inside the tank, well this vicious swimmer is a predator that uses the ambush strategy.
In short this finny hunter waits while hiding in its shelter, the clay pipes in the deepest areas of the streams, and then zap! it attacks when it sees a guppy coming nearby above it.


To defend themselves from this kind of threat, guppies stage the predator inspection behavior
(1). Basically, when the predator is spotted, usually one or two guppies swim in its direction till a bunch of body lengths away. Once in position, the audacious scouts spend some seconds gathering information about the identity and the position of the predator and about its tendency to attack. The inspection, besides, possibly prevent the attack itself because it makes the ambushing predator aware of the fact that it has been noticed by its preys and therefore that it has lost the precious advantage of surprise. Once done the inspection, the guppies on a reconnaissance slowly go back to their fellas to transmit them the informations (1).

Soo, said that, the Alexanders hypothesize that big brained females master the “predator inspection behavior” while small brained females don’t. A bigger brain, the researcher think, gives higher cognitive abilities, that are those which allow a brain to perform better at reasoning, remembering, understanding, and problem solving. So as for hunted lady guppies, the big brained females have stronger cognitive abilities and therefore they can gather, process and remember informations faster and longer thus the smart lady fishes can perform shorter and fewer inspections than the female tinies.
 

To summarize, then, the less you show off around your predator, the higher your probabilities to survive are. Well, unless you’re an annoying little yellow Tweety bird… Then you can survive even a nuclear blast three centimeters away from you, ‘cause you’re an evil annoying little yellow darn Tweety bird. And I hate you!
 

I think is time for a commercial break now…


Do you feel to be the one empty headed personification of “Dumb and Dumber”? Do you feel to be to intelligence and memory what a red salmon in spandex is to acid jazz?

Brinine logo_by sciencemug
Brinine logo (by sciencemug)
[The brain image is a Public Domain pic adapted by sciencemug (source: wikia.com)]


Try “Brainine” the pill that will dope your neurons and make your synapse so pumped up that they will finally beat your house snail at ironfist.
“Brainine”, and you’ll no longer forget things.
“Brainine”, and you’ll no longer forget things.
“Brainine”, and you’ll no longer forget things.


Ok, sooo, there are two more questions to answer about the results of the experiment of our mates the Alexanders. One: “why, unlike the females, big brained and small brained males of guppies have the same rate of survival”, and two: “why females guppies live longer than males”.


Answer one: males of guppies are colourful, females not much. This happens ‘cause males use colors to attract females for mating. Moreover big brained males are more colourful than small brained ones, and the Alexanders say that it may be due, I quote, “to a genetic correlation between brain size and colouration” (Kotrschal et al., 2015). So, in short, the more color on your skin, the easier is for a predator to see you, the higher is the risk you get caught, swallowed and killed.
So two the rise of the conjunctions, even if your bigger brain make you better with the inspection stuff, if you are as stealthy as a fireworks show performed on the nose of Pinocchio after he has just broken the local galactic group record of lies telling, well pal, you’ve the same chance to survive of one of your swimming mates with the brain with the size of a muon.
 

Oook, time to answer to the question two: “why females guppies live longer than males”.
 

Well, simply put, females of guppies are not much coloured and, whichever is the size of their brain, have bigger bodies and can swim faster and longer than males. Therefore when you’re a guppy, if you’re a female you’ve higher probabilities to evade predation than if you’re a male.
 

Oooooooh, hurray, answers mission accomplished! Well, indeed if you look better in the closet of intellect right in the drawer of curiosity, well, you find another one of them questions
Possibly the really basic one. That is: why Alex and his colleagues put on all this show with artificial streams, thousands of fishes, months of work and a wild bunch of carnivorous predators?

Well, the band of Alex wants to know whether and how evolution favors bigger brains. To understand that the Alexanders investigate how a big brain increases the fitness of its owner. And by fitness I’m not speaking about having muscular dorsal fins of curvy squat sculpted yummy caudal fins. Nope, by fitness I mean the chance a living being has to survive to generate a viable offspring.


So, Alex and colleagues know already from former studies that, and I quote again: “large-brained bird species have higher survival in the wild [...] and they are better at colonising urban environments
[...] compared to small-brain species. Also, in several taxa large-brained species [of] mammals [...], birds [...], [and] reptiles [...], but not fishes [...] are more likely to establish viable populations after introduction events compared to small-brain species (Kotrschal et al., 2015).

Our friend scientists, in other words, are aware of the cognitive buffer hypothesis. The idea is that a big brain is a buffer against the environment. In other words a big brain and the cognitive abilities that it provides make it easier for their owner to find the right thing to do when challenged. Therefore a big brain is a wonderfully useful tool for animals to try to live another day.


Now, the Alexanders also know that evidences for the buffer hypothesis come from comparative studies among different species, and that they regard macroevolution, that is evolution at a species level.
What is missing, Alex and coworkers think, is an experiment that test the hypothesis within one species, at the single individual level.
Therefore the Alexanders design and perform the experiment I just told you, and thanks to the evidences they find, the researchers can eventually conclude that, I quote for the last time I swear: “natural selection favours individuals with larger brains, at least under certain conditions [and that] survival under predation is an important selective force in the evolution of vertebrate brain size
(Kotrschal et al., 2015).

That’s all, guppies and folks, have a nice day, sleep well, good afternoon aaand ciao!




ARTICOLO RACCONTATO NEL PODCAST/THE PAPER THIS PODCAST IS BASED ON
- Kotrschal, A., Buechel, S. D., Zala, S. M., Corral-Lopez, A., Penn, D. J., and Kolm, N. (2015). Brain size affects female but not male survival under predation threat. Ecol Lett 18, 646-652.

BIBLIOGRAFIA/BIBLIOGRAPHY
1 - Dugatkin, L. A., and Godin, J.J.G. (1992). Predator  inspection, shoaling and foraging  under predation  hazard in  the Trinidadian  guppy, Poecilia  reticulata Environmental  Biology  of  Fishes 34, 265-276.

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