To understand the fundamental conflict between males and females, Martyna turns her attention to the learning roundworm (Caenorhabditis remanei). These roundworms (like humans) have male worms and female worms. Male worms have to chase after female worms by following the trails of sex pheromones female worms secrete.
The conflict between male and female learning roundworms
The battle of the sexes has many faces. In one of its versions, males and females are limited in how different they can evolve because they share most of their genomes.
In these roundworms, male worms invest much of their energy into finding females and mating with them. Learning comes in handy to accomplish such tasks. Female worms, on the other hand, have to invest most of their energy into producing as many babies as possible.
“With a few hundred neurons and hundreds of babies to produce, you don’t want to waste energy on something that you don’t need.” – Martyna summed up why there can be an on-going battle of sexes in these microscopic roundworms.
To test for the conflict and to see its consequences, Martyna conducted a selection experiment where she carefully picked the best and the worst female learners and let them produce babies. She continued with this selection process for 13 generations. This sounds like a very long time, but it took less than three months. If this experiment was done on humans, it would take approximately 325 years!
What is good for the females is not necessarily good for the males
Because males and females share so much of their genomes, their fate is intertwined (in the more technical term, this is called intersexual genetic correlations). In Martyna’s selection experiment males were forced to follow females to become better or worse learners because of the genetic correlation.
What Martyna’s experiment found was that when males were forced to become poor learners (by selecting on poorly learning females), they were really bad at making babies. Whereas females that became bad learners produced as many babies as their smarter counterparts!
However, the intertwined fate of males and females will make it more difficult for male worms to become better learners even though that’s what’s best for them. This ‘what’s best for me is not necessarily best for you’ battle can happen like forever in the evolution of the roundworms or any animal with separate sexes!
Take home message
“Learning things that don’t increase your evolutionary success (in female roundworms) isn’t smart, so not learning something doesn’t actually make you stupid!” – Martyna summed up the lesson learnt from her battle of the sexes experiment.
Source: Zwoinska MK, Lind MI, Cortazar-Chinarro M, Ramsden M, Maklakov AA (2016) Selection on learning performance results in the correlated evolution of sexual dimorphism in life history. Evolution 70: 342-357.