Abstract
Postcopulatory sexual selection may select for male primary sexual characteristics like sperm morphology and sperm motility, through sperm competition or cryptic female choice. However, how such characteristics influence male fertilization success remains poorly understood. In this study, we investigate possible correlations between sperm characteristics and paternity success in the socially monogamous bluethroat (Luscinia svecica svecica), predicting that sperm length and sperm swimming speed is positively correlated with paternity success. In total, 25% (15/61) of broods contained extra-pair offspring and 10% (33/315) of the offspring were sired by extra-pair males. Paternity success did not correlate significantly with sperm morphology or any aspects of sperm motility. Furthermore, sperm morphology and sperm motility did not correlate significantly with male morphological characters that previously have been shown to be associated with paternity success. Thus, the sperm characteristics investigated here do not appear to be strong predictors of paternity success in bluethroats.
Highlights
In species where females copulate with two or more males, postcopulatory sexual selection may take place in the form of sperm competition [1] or cryptic female choice [2]
Postcopulatory sexual selection may select for male primary sexual characteristics like sperm morphology and sperm motility, through sperm competition or cryptic female choice
We investigate possible correlations between sperm characteristics and paternity success in the socially monogamous bluethroat (Luscinia svecica svecica), predicting that sperm length and sperm swimming speed is positively correlated with paternity success
Summary
In species where females copulate with two or more males, postcopulatory sexual selection may take place in the form of sperm competition [1] or cryptic female choice [2]. Cryptic female choice is the ability of females to control which male fertilizes their eggs after having copulated with several males [2]. Mechanisms of cryptic female choice include, for example, active ejection of less preferred sperm by the female [4] and differential chemical attraction between the sperm and egg, depending on the compatibility of their genotypes [5,6]. Cryptic female choice may counteract the effects of sperm competition, unless certain sperm traits are related to male qualities preferred by females [7,8]. While comparative studies give clear evidence that sperm traits differ among taxa according to the opportunity for postcopulatory sexual selection
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