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Does sex-specific selection change mating behaviour in a hermaphrodite?Martin MajvallMartin Majvall

Majvall, Martin (2020) BIOK01 20201
Degree Projects in Biology
Popular Abstract
Experimental Evolution: From hermaphrodite to two sexes!

When one hears the word evolution most of us think of Charles Darwin and his theory of natural selection. He once said, ”It is not the strongest of species that survive, nor the most intelligent, but the one most responsive to change”. We will get back to that, but a very important thing here is that the timeframe he is talking about is millions of years. However, what if we could, using experiments, see the effects of evolution in just a few years instead?

We wanted to look at how sex chromosomes, which in humans are the X & Y chromosomes, evolve from a hermaphroditic ancestor. To do this we subjected the simultaneous hermaphroditic flatworm Macrostomum lignano to sex-limited... (More)
Experimental Evolution: From hermaphrodite to two sexes!

When one hears the word evolution most of us think of Charles Darwin and his theory of natural selection. He once said, ”It is not the strongest of species that survive, nor the most intelligent, but the one most responsive to change”. We will get back to that, but a very important thing here is that the timeframe he is talking about is millions of years. However, what if we could, using experiments, see the effects of evolution in just a few years instead?

We wanted to look at how sex chromosomes, which in humans are the X & Y chromosomes, evolve from a hermaphroditic ancestor. To do this we subjected the simultaneous hermaphroditic flatworm Macrostomum lignano to sex-limited treatments, the agent of change. This means that some of them are only allowed to reproduce through eggs, and others only through sperm, but they still have the capacity to produce both. We then wanted to see how they react both physically and behaviourally.

So, what did we find?

The experiment has gone on for 6 years now, and halfway through by generation 25 we could already see responsive adaptations to the change. Male-selected worms became better at reproducing through sperm while the female-selected became better at reproducing through eggs. The worms also showed minor morphology changes with changed testes-, ovary- and body size. This is according to theory how it would all begin, as these changes mean they put energy and resources into that which brings them beneficial gains.

The experiment is up to generation 44 and what we wanted to look at now is whether their mating behaviour has changed. These worms perform a behaviour after mating in which they put their mouth over their female genital opening and orally extract sperm (as seen in the image). Therefore, we recorded how often the experimental worm and their partner performed this suck behaviour when they receive new potential partners, both in the first five matings, and the total in a 2-hour time period. We also looked at the duration of mating and how often they mate.

What we found is that although the male-selected worms mate more often and longer than female-selected, they do not seem to suck more. We expected this to mean their partners suck less because we found that all worms sucked less when mating for longer durations. Contrary to our expectations however, the partners sucked the most when mating with male-selected and the least with female-selected. Therefore, we believe the sucking to be a female-benefit behaviour to remove the excess or poor-quality sperm, though this must be further looked into as we did not focus on sperm quantities. Our results are indicative of changes that, in time, can lead to more defined sexually dimorphic traits and diverging sex chromosomes. This will occur when the sexual conflict leads to greater genetic differences and requirements to suppress antagonistic genes.

Examensarbete för kandidatexamen i Biologi 15 hp, VT 2020
Biologiska institutionen, Lunds Universitet
Handledare: Aivars Cīrulis, Jessica Abbott
Department of Biology, Section for Evolutionary Ecology, Abbott Laboratory (Less)
Please use this url to cite or link to this publication:
author
Majvall, Martin
supervisor
organization
course
BIOK01 20201
year
type
M2 - Bachelor Degree
subject
language
English
id
9018235
date added to LUP
2020-06-15 12:01:30
date last changed
2020-06-15 12:01:30
@misc{9018235,
  author       = {{Majvall, Martin}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Does sex-specific selection change mating behaviour in a hermaphrodite?Martin MajvallMartin Majvall}},
  year         = {{2020}},
}