Tuesday, July 30, 2013

The puzzle of monogamy

This article from Discovery News compares two recent studies that try to understand the evolution of The first one from Opie, et al. at University College in London looked at the primate family tree and used statistical models to show that appearance of monogamy coincided frequently with the appearance of infanticide. In this case, infanticide refers to the practice of males who kill the offspring of females that they have not mated with. This strategy evolved because females of many species will immediately become fertile if the young they are caring for are killed. Thus, the males create a mating opportunity for themselves and eliminate the offspring of a rival male. Of course a male that engages in infanticide runs the risk of losing his own offspring to another male, so monogamy may have evolved as a way for fathers to protect their children from other males.

The second study by Lukas and Clutton-Brock from the University of Cambridge is similar but it looked at monogamy across all mammalian species. But they did not find a correlation between monogamy and infanticide. Instead, their analysis suggested that monogamy evolved as a consequence of females living in solitary territories. Males in this situation have to defend a large area if they want to mate with multiple females and prevent other males from mating with their partners. Presumably then monogamy evolved because it was more efficient to only defend one female against rival suitors.

Monogamy is an interesting puzzle in evolutionary biology, because on the surface it seems like a bad idea. If the name of the game is to get your genes copied into the next generation then you would want to mate with as many partners as possible. This only applies to males though because females are usually limited by the number of eggs they can produce or the number of offspring they can gestate at one time in the case of mammals. Many hypotheses have been proposed over the years to try explain the phenomenon. For example, it was once assumed that monogamy evolved for the benefit of the offspring. Having two adults looking after you has obvious benefits for survival over just one. However, even though these two studies do not agree on what was the original function of monogamy, they both failed to support the paternal care hypothesis. They showed that fathers started actively caring for their offspring after monogamy evolved which suggests that paternal care may have appeared as a side benefit of a strategy that originally only benefited the fathers.

Thursday, July 25, 2013

False memories implanted in mouse brains

'Total Recall' for Mice | Science/AAAS | News

A very cool study out of MIT showing that it is possible to create false memories in a mouse brain. They first put the mice in a chamber and let them form a memory of that location. Then they put the mice in a different chamber and gave them painful electric shocks while simultaneously stimulating the same neurons in the brain that had been activated in the first chamber. Then, when the mice were put back into the first chamber, they froze as if they were recalling the memory of the electrical shock. They way they identified the neurons associated with the memory and reactivated them later is an impressive technological feat in and of itself. The mice were genetically modified to express a protein called channelrhodopsin-2 which was only expressed in active neurons. Essentially , this protein acted as a tag for activated neurons which means it labels the neurons that are involved in storing the initial memory. This protein is also light-sensitive and it causes the neuron it is expressed in to become active when exposed to certain colors of light. So, before being placed in the shock chamber, they put a fiber optic cable into the brains of the mice which would shine light onto the parts of the brain where the memory was stored and activated them. This is an example of a new field called optogenetics which is allowing lots of exciting new questions to be asked about brain activity. The Science article discusses the possibility of understanding how false memories are formed in the human brain, but the ability to create and manipulate memories in the brain may someday be a way to treat lots of psychological problems such as PTSD.

Wednesday, July 24, 2013

Yes, dogs can see in color.

Dogs See the World in Living Color - D-brief | DiscoverMagazine.com
This study from the Russian Academy of Sciences should put to rest the old myth that dogs can only see in black and white. Scientists already knew this because dogs have two different kinds of cone receptors in their retinas which means they can differentiate between at least two wavelengths of light. Humans, of course, have three kinds of cones, so dogs are not as good as us at color vision, but we are well behind some other animals like the mantis shrimp for example which has up to 16 kinds of cones. So dogs essentially have about the same degree of color vision as a colorblind human. The term 'colorblind' is probably the reason why people misunderstand this condition. It does not mean the inability to see any color; it is just means an insensitivity to certain colors. In the case of dogs, they cannot see red or orange parts of the spectrum. They have no problem with green, blue, and yellow, however. The study described in the article above shows that dogs not only are capable of discerning color but actually use color cues when making decisions; even more so than other cues like brightness. The study design ingeniously simple: the dogs were trained to associate a reward with a cue that differed from non-reward cue in both color and brightness (dark yellow vs. light blue, or light yellow vs. dark blue). Then the cues were switched: if the dog had learned that dark yellow was the rewarded cue, for example, it was given the choice between light yellow and dark blue. If brightness were a more salient feature, the dog would look for a reward next to the dark blue cue even though it had associated a reward with dark yellow previously. However, 70% of the time, the dogs chose the cue that matched the color that they had seen before (i.e. if they had learned that dark yellow was associated with reward in the training trials, they chose light yellow in the test trials). Of course it is no surprise that dogs are not as good color vision as much as humans. Dogs rely on other senses such as scent much more than humans.