Genotype‐by‐environment interactions for seminal fluid expression and sperm competitive ability

Bahar Patlar,Steven A Ramm

doi:10.1111/jeb.13568

Abstract

Sperm competition commonly occurs whenever females mate multiply, leading to variation in male paternity success. This can be due to variation in the various traits that might affect sperm competitive ability, which itself depends on both genetic and environmental factors, as well as on genotype-by-environment interactions (GEI). Seminal fluid is a major component of the male ejaculate that is often expected to mediate sperm competition, where different genotypes can differ in their seminal fluid expression as a response to different levels of sperm competition (i.e. exhibit GEI). We therefore here focussed on testing for GEI in expression of two recently identified seminal fluid transcripts, suckless-1 and suckless-2, which potentially modulate sperm competitive ability in the simultaneously hermaphroditic flatworm Macrostomum lignano via their effects on manipulating post-mating partner behaviour and ultimately the fate of transferred ejaculates. In addition, we sought to test for GEI in sperm competitive ability in a standardized sperm competition (P1 and P2 ) assay, to investigate the relationship between natural variation in the expression of these seminal fluid transcripts generated through GEI and relative paternity success. We found GEI for the expression level of suckless-1 and suckless-2, as well as for sperm competitive ability. Moreover, we found a positive relation between the expression of suckless-1 and relative paternity success (P1 ). This suggests that natural variation in the expression of this seminal fluid transcript indeed can influence sperm competition outcomes in M.lignano.

Highlights

Sperm competition, that is the competition between the ejaculates of two or more males for the fertilization of a given set of ova (Parker, 1970), and cryptic female choice, in which females influence the outcome of sperm competition (Eberhard, 1996), are important evolutionary forces across a diverse range of taxa in which females mate multiply
We found evidence of genotype-by-environment interactions (GEI) for the expression level of two seminal fluid transcripts that were recently functionally characterized, suckless-1 and suckless-2 (Patlar et al, in press), and for relative paternity success, as well as evidence linking suckless-1 expression to sperm competitive ability
We already had some evidence of GEI for the expression of different seminal fluid transcripts from our previous study, where in total we showed significant GEI for 14 of 58 seminal fluid transcripts (Patlar et al, 2019), this did not include suckless-1 or suckless-2, and where we showed a lack of significant social group size effect for all 58 transcripts (Patlar et al, 2019; but see Ramm et al, 2019)

Summary

Introduction

That is the competition between the ejaculates of two or more males for the fertilization of a given set of ova (Parker, 1970), and cryptic female choice, in which females influence the outcome of sperm competition (Eberhard, 1996), are important evolutionary forces across a diverse range of taxa in which females mate multiply. KEYWORDS gene/transcript expression, Macrostomum lignano, paternity success, post-mating sexual selection, simultaneous hermaphrodites, social group size, sperm competition

Results

Conclusion