Evolution of sperm structure and energetics in passerine birds

Abstract

Spermatozoa exhibit considerable interspecific variability in size and shape. Our understanding of the adaptive significance of this diversity, however, remains limited. Determining how variation in sperm structure translates into variation in sperm performance will contribute to our understanding of the evolutionary diversification of sperm form. Here, using data from passerine birds, we test the hypothesis that longer sperm swim faster because they have more available energy. We found that sperm with longer midpieces have higher levels of intracellular adenosine triphosphate (ATP), but that greater energy reserves do not translate into faster-swimming sperm. Additionally, we found that interspecific variation in sperm ATP concentration is not associated with the level of sperm competition faced by males. Finally, using Bayesian methods, we compared the evolutionary trajectories of sperm morphology and ATP content, and show that both traits have undergone directional evolutionary change. However, in contrast to recent suggestions in other taxa, we show that changes in ATP are unlikely to have preceded changes in morphology in passerine sperm. These results suggest that variable selective pressures are likely to have driven the evolution of sperm traits in different taxa, and highlight fundamental biological differences between taxa with internal and external fertilization, as well as those with and without sperm storage.

Low‐mobility sperm phenotype in the domestic turkey: Impact on sperm morphometry and early embryonic death

“…We thus find ourselves included in an extensive group of bird studies that have cumulatively yielded mixed results about the importance of midpiece size and flagellum length for sperm motility, velocity and function. Consistent with our results, a study in sparrows found no association between midpiece size and swimming velocity (Cramer et al, ), while a comparative study across 23 passerine birds found that, while midpiece length is positively correlated with ATP reserves, ATP is not correlated with velocity (Rowe et al, ). Another comparative analysis found significant but contrasting relationships between midpiece size and velocity among species belonging to two bird families (Immler & Birkhead, ).…”

Sperm morphology, adenosine triphosphate (ATP) concentration and swimming velocity: unexpected relationships in a passerine bird

“…[16]), raise the important question of why stored ATP content (and mitochondrial haplotype [33]) does not seem to be associated with swimming velocity in passerine sperm, despite the fact that sperm require a source of energy to swim. We propose three possible explanations: (i) energy for swimming could also be produced via another metabolic pathway e.g.…”

Mitogenomic data resolve basal relationships among passeriform and passeridan birds

“…One major group within passerines-the oscines (Passeri)-is characterized by a significant learning component in the development of their vocal repertoire, and several oscine species (especially the zebra finch, Taeniopygia guttata) have become models of vocal learning. Due to the impressive phenotypic variation in this species-rich group, many comparative studies of trait evolution have focused on passerines (Gohli et al, 2013;Ricklefs, 2012;Rowe et al, 2013;Sol et al, 2010), making an understanding of their phylogenetic relationships a priority for systematists and comparative biologists.…”