Sperm morphology and performance in relation to postmating prezygotic isolation in two recently diverged passerine species

Abstract

Divergence in sperm phenotype and female reproductive environment may be a common source of postmating prezygotic (PMPZ) isolation between species. However, compared to other reproductive barriers it has received much less attention. In this study, we examined sperm morphology and velocity in two hybridizing passerine species, the common nightingale (Luscinia megarhynchos) and thrush nightingale (L. luscinia). In addition, we for the first time characterized a passerine female reproductive tract fluid proteome. We demonstrate that spermatozoa of the common nightingale have significantly longer and wider midpiece (proximal part of the flagellum containing mitochondria) and longer tail compared to spermatozoa of thrush nightingale. On the other hand, they have significantly shorter and narrower acrosome. Importantly, these differences did not have any effect on sperm velocity. Furthermore, the fluid from the reproductive tract of common nightingale females did not differentially affect velocity of conspecific and heterospecific sperm. Our results indicate that the observed changes in the flagellum and acrosome size are unlikely to contribute to PMPZ isolation through differential sperm velocity of conspecific and heterospecific sperm in the female reproductive tract. However, they could affect other postcopulatory processes, which might be involved in PMPZ isolation, such as sperm storage, longevity or sperm-egg interaction.

Proteomic analysis reveals dynamic changes in cloacal fluid composition during the reproductive season in a sexually promiscuous passerine

“…the most abundant LYZ, LOC100224071 (ovostatin-like), LTF, SPINK5, ALB and ANXA1. Currently, the only one additional study, that has dealt with the composition of cloacal female uid in passerines, is available 19 , however, the study has a relatively small sample size, and the authors did not account for potential variation in cloacal uid composition associated with reproductive stages of females. Our study represents a signi cant advancement in rigorously testing and analyzing the changes of proteomic composition of the uids from the female reproductive tract during entire reproductive season.…”

“…Another option is to test the effect of uid from the female reproductive tract on sperm performance as female reproductive uids are supposed to interact with the ejaculate, mediate sperm migration, ensure sperm survival, and induce their modi cation 12 . Research on sperm-female uid interactions has so far mostly focused on externally fertilizing shes 11,13 but also on mammals 14,15 and, more recently, birds [16][17][18][19] . There is some evidence that female vaginal or cloacal uid can impact sperm traits such as motility 17,20,21 and/or longevity 17,22,23 .…”

“…The proteins and metabolites present in the female reproductive tract during sperm passage and storage probably in uence the survival of sperm 45,46 . In birds, some descriptions of uterine uid 47,48 , oviductal uid 49 and cloacal uid 19 proteomes are available. However, only the latter study focused on passerines.…”

Rapid gene content turnover on the germline-restricted chromosome in songbirds

“…We identified 57 genes inside species-specific regions on the two GRCs. This rapid gene turn-over represents a lot of opportunity for natural selection to act upon in creating reproductive isolation, both more generally among songbirds but also specifically in nightingales, where the two species are separated by female-limited hybrid sterility and divergence of sperm morphology 25 – 27 , 40 .…”

Comparative sperm proteomics in selected passerine birds reflects sperm morphology and mitochondrial metabolism

“…Functional categories of proteins that are associated with sexual reproduction, flagellar movement and metabolic processes, e.g. mitochondria-related ATP production, are enriched in spermatozoa across a wide range of vertebrate and invertebrate taxa (Bayram et al 2016, Whittington et al 2017, 2019, Rowe et al 2019, Garlovsky et al 2022, Poignet et al 2022). Moreover, the analysis of the whole seminal fluid proteome revealed that the fluids dataset is dominated by the ATP metabolic process (GO:0046034), which is linked to activated proteins (Fig.…”