edoc

Sexual selection mechanisms in a simultaneously hermaphroditic flatworm

Santhosh, Santhosh. Sexual selection mechanisms in a simultaneously hermaphroditic flatworm. 2024, Doctoral Thesis, University of Basel, Faculty of Science.

[img]
Preview
PDF
Available under License CC BY-NC-ND (Attribution-NonCommercial-NoDerivatives).

2211Kb

Official URL: https://edoc.unibas.ch/96586/

Downloads: Statistics Overview

Abstract

Male and female animals often display striking differences in shape, behaviour, or reproductive strategies. For the most part, this was attributed to evolution under sexual selection where males and females are thought to be under different selection regimes. Although initially described to occur mainly through contests between males for mates and mate choice by females, sexual selection is now widely accepted to occur after copulations through sperm competition and/or cryptic female choice. However, studying these post-copulatory processes proved to be challenging because they occur internally and are often difficult to observe and measure. Therefore, advancements in understanding post-copulatory sexual selection greatly depend on the development of techniques that facilitate the observation of internal processes. Moreover, measuring the reproductive success of individuals under competitive conditions hinges on techniques that allow easy identification of the parentage of offspring.
During my PhD project, I used the simultaneously hermaphroditic flatworm Macrostomum lignano to study aspects of pre- and postcopulatory sexual selection. The establishment of a transgenic line of worms expressing a green fluorescent protein (GFP) in all cells provides a unique opportunity to differentiate and track sperm under competitive scenarios within the female reproductive tract in vivo. Additionally, a suite of transgenic lines (NL lines), each expressing fluorescent proteins localized to specific tissues of the body or nuclei of cells, provide distinct inheritable markers that enable efficient identification of parentage in offspring from mating crosses. I tested and validated the reliability of the NL lines, mating crosses between lines, and other GFP techniques, which I could then effectively use to study central aspects of sexual selection in M. lignano.
The NL lines were instrumental in my experiment designed to measure the strength of sexual selection in the male and female sex functions in M. lignano. The difference in the strength of sexual selection between the sexes, i.e., stronger sexual selection in males than in females, has been attributed to the difference in costs of producing male and female gametes (i.e., anisogamy). Therefore, theoretical considerations of simultaneous hermaphrodites that also exhibit anisogamy predict stronger sexual selection in the male compared to the female sex function. M. lignano exhibits a reciprocal mating system (i.e., worms donate and receive sperm simultaneously), where the copulations in the male and female sex functions are strictly linked. My measurements of standardised selection metrics in M. lignano revealed substantial scope for sexual selection in both male and female sex functions with no significant difference between the same. My findings thus suggest that although anisogamy may lead to a difference in the reproductive interests of the male and female sex functions, the actual strength of sexual selection may be influenced by other factors, such as the mating system.
Previous studies in M. lignano have shown that sexual selection predominantly occurs in post-copulatory episodes. My investigation into the role of sperm size in a post-copulatory episode of selection revealed a non-linear association with a competitive advantage for intermediate sperm size. I speculate that the observed selection for intermediate size may arise due to the trade-off between sperm size and the number of sperm produced. That is, an increase in sperm size may be associated with fewer sperm produced and transferred to the partner, leading to fewer sperm represented in sperm competition. Therefore, the selective forces for more competitive larger sperm and that for numerous but smaller sperm may reach a balance at an intermediate optimum.
In conclusion, I took advantage of several features and powerful techniques established in M. lignano to obtain novel insights into the operation of sexual selection. My PhD works further signify the importance of sexual selection as an evolutionary agent in simultaneous hermaphrodites.
Advisors:Ebert, Dieter
Committee Members:Affolter, Markus and Lüpold, Stefan
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Growth & Development > Cell Biology (Affolter)
05 Faculty of Science > Departement Umweltwissenschaften > Integrative Biologie > Evolutionary Biology (Ebert)
UniBasel Contributors:Ebert, Dieter and Affolter, Markus
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:15423
Thesis status:Complete
Number of Pages:iv, 105
Language:English
Identification Number:
  • urn: urn:nbn:ch:bel-bau-diss154233
edoc DOI:
Last Modified:26 Jul 2024 04:30
Deposited On:25 Jul 2024 08:58

Repository Staff Only: item control page