According to researchers at University College London (UCL), UK and Albert Einstein College of Medicine (USA), there is a direct relation between how male and female worms behave and the differences in brain development and structure in areas involved in higher order processing. Researchers found through their study that the genetic and developmental differences in the brain of male and female worms causes structural differences in the brain during sexual maturation.
This is what causes the difference in behavior as far as sex is concerned. Brain of males tend to remember previous sexual encounters and when given an option, opt for sex over other choices.
Researchers further identified that this behavioral change is a direct result of previously unidentified cells. Researchers say that these two neurons are born from cells calls glial cells, which are companion and support cells of neurons.
Researchers have named the two newly identified neurons as ‘mystery cells of the male’ or ‘MCMs’. These cells bring about behavioral differences between the two sexes by changing a brain circuit common to both. Whether the neurons are born or not depends on the genetic sex of the glial cells from which they arise and not on the sex of the animal or on hormones. The MCM neurons are only made from glial cells that have male chromosomes.
“Our findings suggest that differences in learning and perception depend not just on the sex of the animal but also on the sex of the individual neural progenitor cells”, says co-senior author Dr Richard Poole, UCL Cell & Developmental Biology. “This means that different aspects of an animal’s behavior may well develop independently of each other in some circumstances, instead of through the co-ordinated action of hormones.”
The effect of the cells on the worms’ (males and hermaphrodites) behaviour was tested using classic conditioning behavioural assays in which worms learn to associate aversive or pleasant experiences (such as starvation or mates) with another stimulus (salt) and change their behavioural responses to that stimulus. Worms that were previously starved in the presence of salt, learned to move away from areas with high concentrations of salt when placed in a new environment that had various different salt concentrations. This indicated that worms had learned to perceive salt as a sign for the absence of food.
Both males and hermaphrodites perform this type of learning. In contrast, when males were starved in the presence of salt and mates (i.e. sexual partners), and then placed in a new environment that had different salt concentrations, males sought areas of high concentrations of salt. This indicated that the association of salt with sex was stronger than and preferred over the association of salt with lack of food. This change in behaviour does not occur in hermaphrodites. Importantly, it also does not occur in males whose MCM neurons were surgically removed – demonstrating that these neurons are required for sex-based differences in learning.
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