Quantitative analysis of sperm plane circular movement in the blue mussels Mytilus edulis, M. trossulus and their hybrids

Abstract

Fertilization success of free spawning organisms such as Mytilus species depends on gamete interactions. Therefore, gamete traits such as sperm movement are important for determining fertilization success in free spawning organisms. Since little is known about sperm movement pattern in Mytilus species, the purpose of this study was to investigate sperm movement pattern of blue mussel M. edulis, M. trossulus and their hybrids using computer-assisted sperm movement video analysis. Sperm of all genotypes were found to conduct circular movement in a two-dimensional plane. Furthermore, new sperm movement parameters, real time radius (R), angle change rate (θ) and the center of circular track (O(t)) were developed to verify and quantitatively describe the plane circular movement pattern using software (Image-J) that may be widely applied to sperm movement study in other organisms. Angle change rate was positively correlated to fertilization success. However, no correlation between fertilization and real time radius was detected. Although no interspecific differences were found in the radius, the F¹ (first generation) hybrid sperm had a lower angle change rate than M. edulis and M. trossulus. Published studies have shown that sperm circular movement is more prevalent in aquatic broadcast spawning species than in species with mating behavior or internal fertilization. Therefore, a two-dimensional circular movement pattern in sperm may represent a trait that increases fertilization success for broadcast spawning species by either increasing gamete interaction rate at a small scale and/or avoiding swimming further away from the eggs before sperm detects the chemoattractant gradient.

CASA in invertebrates

“…CASA-Mot analysis of five species in two invertebrate phyla of so-called broadcast spawners show helical sperm tracks similar to those described by many investigators (Levitan 1993(Levitan , 1995(Levitan , 1998Au et al 2001;Farley 2002;Riffell and Zimmer 2007;Fitzpatrick et al 2010;Liu et al 2011;Suquet et al 2013;Fabbrocini et al 2016) or at least analysed by CASAMot or objective sperm motility analysis using alternative methods (Basti et al 2013;Lymbery et al 2016). There are few detailed descriptions of the nature of the patterns of these tracks, except for Liu et al (2011) and Vogel et al (1982), who referred to the helical tracks as 'Don Giovanni' and the forward moving tracks as 'Don Ottavio'.…”

“…There are few detailed descriptions of the nature of the patterns of these tracks, except for Liu et al (2011) and Vogel et al (1982), who referred to the helical tracks as 'Don Giovanni' and the forward moving tracks as 'Don Ottavio'. The implication is that theoretically there will be a bigger oocyte hit rate with helical swimming presumably because of the larger search area per volume.…”

Contribution of the CASA system, based on open source software, to the assessment of sperm characteristics: informetric and usage-based approaches

“…Computer-assisted sperm analysis supports numerous options for default values, making it possible to apply the analysis to virtually all fish species as well as to other taxa, as observed in mammals (Lemaitre et al, 2012;El-Sherry et al, 2014;Fisher et al, 2014;Jaiswal et al, 2014;Simpson et al, 2014), birds (Helfenstein et al, 2010a(Helfenstein et al, , 2010bLosdat et al, 2011;Simpson et al, 2014), and marine invertebrates (Fitzpatrick et al, 2010;Liu et al, 2011b;Sasson et al, 2012;Suquet et al, 2012;Simpson et al, 2014). As a result, fish sperm from 23 species from diverse environments has been studied to date.…”

Caspase 3 in molluscan tissues: Localization and possible function

“…This hypothesis is supported by the fact that Callista spermatozoa, negative for caspase when in the testis, become positive after activation in sea water. The difference observed in timing of caspase production may be related to the type of fertilization as Bivalves are free spawning (Liu et al, ) with gametes released into the water while the two Gastropods release sperms in the female genital tract at mating (Gomot, ).…”