Sperm competition risk drives plasticity in seminal fluid composition.
BACKGROUND
Ejaculates contain a diverse mixture of sperm and seminal fluid proteins, the combination of which is crucial to male reproductive success under competitive conditions. Males should therefore tailor the production of different ejaculate components according to their social environment, with particular sensitivity to cues of sperm competition risk (i.e. how likely it is that females will mate promiscuously). Here we test this hypothesis using an established vertebrate model system, the house mouse (Mus musculus domesticus), combining experimental data with a quantitative proteomics analysis of seminal fluid composition. Our study tests for the first time how both sperm and seminal fluid components of the ejaculate are tailored to the social environment.


RESULTS
Our quantitative proteomics analysis reveals that the relative production of different proteins found in seminal fluid--i.e. seminal fluid proteome composition--differs significantly according to cues of sperm competition risk. Using a conservative analytical approach to identify differential expression of individual seminal fluid components, at least seven of 31 secreted seminal fluid proteins examined showed consistent differences in relative abundance under high versus low sperm competition conditions. Notably three important proteins with potential roles in sperm competition--SVS 6, SVS 5 and CEACAM 10--were more abundant in the high competition treatment groups. Total investment in both sperm and seminal fluid production also increased with cues of heightened sperm competition risk in the social environment. By contrast, relative investment in different ejaculate components was unaffected by cues of mating opportunities.


CONCLUSIONS
Our study reveals significant plasticity in different ejaculate components, with the production of both sperm and non-sperm fractions of the ejaculate strongly influenced by the social environment. Sperm competition risk is thus shown to be a key factor in male ejaculate production decisions, including driving plasticity in seminal fluid composition.
Mammalian Behaviour and Evolution Group, Institute of Integrative Biology, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK. steven.ramm@uni-bielefeld.de.|Evolutionary Biology, Bielefeld University, Morgenbreede 45, 33615, Bielefeld, Germany. steven.ramm@uni-bielefeld.de.
Steven A
SA
Ramm
Mammalian Behaviour and Evolution Group, Institute of Integrative Biology, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK. D.Edward@liverpool.ac.uk.
Dominic A
DA
Edward
Mammalian Behaviour and Evolution Group, Institute of Integrative Biology, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK. amyjclaydon44@gmail.com.|Centre for Proteome Research, Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK. amyjclaydon44@gmail.com.
Amy J
AJ
Claydon
Centre for Proteome Research, Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK. D.E.Hammond@liverpool.ac.uk.
Dean E
DE
Hammond
Centre for Proteome Research, Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK. P.Brownridge@liverpool.ac.uk.
Philip
P
Brownridge
Mammalian Behaviour and Evolution Group, Institute of Integrative Biology, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK. J.Hurst@liverpool.ac.uk.
Jane L
JL
Hurst
Centre for Proteome Research, Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK. R.Beynon@liverpool.ac.uk.
Robert J
RJ
Beynon
Mammalian Behaviour and Evolution Group, Institute of Integrative Biology, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK. P.Stockley@liverpool.ac.uk.
Paula
P
Stockley
D000818:Animals; D003163:Competitive Behavior; D008297:Male; D051379:Mice / Q000502:physiology*; D020543:Proteome; D012661:Semen / Q000502:physiology*; D012726:Sexual Behavior, Animal; D012931:Social Environment; D013094:Spermatozoa / Q000502:physiology*
D020543:Proteome