Fins improve the swimming performance of fish sperm: A hydrodynamic analysis of the Siberian sturgeon Acipenser baerii

Abstract

The flagella of sturgeon sperm have an ultrastructure comprising paddle-like fins extending along most of their length. These fins are seen in several other marine and freshwater fish. The sperm of these fish are fast swimmers and are relatively short lived: it is therefore tempting to think of these fins as having evolved for hydrodynamic advantage, but the actual advantage they impart, at such a small length scale and slow speed, is unclear. The phrase "the fins improve hydrodynamic efficiency" is commonly found in biological literature, yet little hydrodynamic analysis has previously been used to support such conjectures. In this paper, we examine various hydrodynamic models of sturgeon sperm and investigate both swimming velocity and energy expenditure. All of the models indicate a modest hydrodynamic advantage of finned sperm, in both straight line swimming speed and a hydrodynamic efficiency measure. We find a hydrodynamic advantage for a flagellum with fins, over one without fins, of the order of 15-20% in straight line propulsive velocity and 10-15% in a hydrodynamic efficiency measure.

Variability in sperm form and function in the context of sperm competition risk in two Tupinambis lizards

“…Selection is expected to act on sperm form and function, but the evidence supporting this assumption remains controversial (Simmons and Fitzpatrick ; Gillies et al. ; Simpson et al. ).…”

“…Sperm velocity is an important determinant of male fertility in noncompetitive (Malo et al 2005;Gomendio et al 2007;Gomendio and Roldan 2008) and competitive contexts (Birkhead et al 1999;Gage et al 2004;Gomendio and Roldan 2008;Pizzari and Parker 2009). Selection is expected to act on sperm form and function, but the evidence supporting this assumption remains controversial (Simmons and Fitzpatrick 2012;Gillies et al 2013;Simpson et al 2013).…”

Biophysics of Fish Sperm Flagellar Movement: Present Knowledge and Original Directions

“…In addition, variations in the constitutive morphology of individual spermatozoa within the species also influence their velocity in viscous media [118]. As already mentioned, the viscosity effects are enhanced in case of the ribbon-shaped flagella like those in fish spermatozoa possessing fins, the latter greatly increasing the surface of viscous interaction with the surrounding medium [37].…”

“…Often, the plasma membrane also forms one or two fin-like ridges along the fish sperm flagellar tail, which are oriented along the horizontal axis defined by the central microtubules [34][35][36][37]. The ribbon shape instead of the usual cylindrical shape of the flagellum makes it brighter when observed by dark-field microscopy and allows to better visualization and recording of wave shapes [6].…”

“…The ribbon shape instead of the usual cylindrical shape of the flagellum makes it brighter when observed by dark-field microscopy and allows to better visualization and recording of wave shapes [6]. This feature of the flagellar membrane has been documented among species belonging to many fish families: Poeciliidae, Jenysiidae, Pantodontidae and Embiotocidae [17,[38][39][40] and was shown to potentially contribute to improve the swimming efficiency [37].…”