Several factors are involved in determining the outcome of sperm competition. In addition to sperm number, sperm quality and male phenotype, insemination order is often associated with skewed paternity share. Patterns of sperm precedence can be produced by the mechanics of sperm storage and fertilisation, or by active processes under male or female control. However, as males and females always interact during copulation, it is difficult to identify the responsible mechanism. The Trinidadian guppy, Poecilia reticulata, is a polyandric species characterised by last male sperm precedence in natural matings. During such matings, females allow attractive males to inseminate more sperm by controlling the duration of the copulation. We used artificial insemination to clarify the extent to which female control on sperm transfer influences the observed pattern of sperm precedence in this species. This technique allowed us to experimentally manipulate the number of sperm transferred and the timing of insemination. Contrary to the pattern of sperm precedence observed after natural copulations, we found a significant first male fertilisation advantage. This advantage, however, declined as the time between insemination and parturition increased. Our results suggest that the last male precedence detected in natural copulations is caused by female mediated processes, rather than by insemination order per se. Presumably, the anatomy and the physiology of the female genital tract favour egg fertilisation by the first ejaculate inseminated; whereas sperm mixing is likely to be responsible for the reduction of first male advantage associated with longer insemination-parturition intervals. As patterns of sperm precedence have large consequences on male reproductive strategies (for example mate guarding and male mate choice copying), unravelling their dynamics represents an important contribution to understanding the sexual behaviour of this model species.

Artificial insemination unveils a first-male fertilisation advantage in the guppy

MAGRIS, MARTINA;PILASTRO, ANDREA AUGUSTO
2017

Abstract

Several factors are involved in determining the outcome of sperm competition. In addition to sperm number, sperm quality and male phenotype, insemination order is often associated with skewed paternity share. Patterns of sperm precedence can be produced by the mechanics of sperm storage and fertilisation, or by active processes under male or female control. However, as males and females always interact during copulation, it is difficult to identify the responsible mechanism. The Trinidadian guppy, Poecilia reticulata, is a polyandric species characterised by last male sperm precedence in natural matings. During such matings, females allow attractive males to inseminate more sperm by controlling the duration of the copulation. We used artificial insemination to clarify the extent to which female control on sperm transfer influences the observed pattern of sperm precedence in this species. This technique allowed us to experimentally manipulate the number of sperm transferred and the timing of insemination. Contrary to the pattern of sperm precedence observed after natural copulations, we found a significant first male fertilisation advantage. This advantage, however, declined as the time between insemination and parturition increased. Our results suggest that the last male precedence detected in natural copulations is caused by female mediated processes, rather than by insemination order per se. Presumably, the anatomy and the physiology of the female genital tract favour egg fertilisation by the first ejaculate inseminated; whereas sperm mixing is likely to be responsible for the reduction of first male advantage associated with longer insemination-parturition intervals. As patterns of sperm precedence have large consequences on male reproductive strategies (for example mate guarding and male mate choice copying), unravelling their dynamics represents an important contribution to understanding the sexual behaviour of this model species.
2017
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3236123
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