Sperm design and sperm function

Abstract

Spermatozoa vary enormously in their form and dimensions, both between and within species, yet how this variation translates into fertilizing efficiency is not known. Sperm swimming velocity is a key determinant of male fertilization success, but previous efforts to identity which sperm phenotypic traits are associated with swimming velocity have been unsuccessful. Here, we examine the relationship between the size of several sperm components and sperm swimming velocity in natural populations of red deer (Cervus elaphus hispanicus) where selective pressures to enhance male reproductive success are expected to be strong. Our results show that there is little within-male and considerable between-male variation in sperm dimensions. Spermatozoa with longer midpieces swim more slowly, a finding which does not support the hypothesis that the size of the midpiece determines the amount of energy which is translated into swimming speed. In contrast, spermatozoa with elongated heads, and those in which the relative length of the rest of the flagellum is longer, swim faster. Thus, the hydrodynamic shape of the head and the forces generated by the relative size of the rest of the flagellum seem to be the key determinants of sperm swimming velocity.

Effect of sperm concentration in an ejaculate on morphometric traits of spermatozoa in Duroc boars

“…Spermatozoa with elongated heads are faster than those with round heads (Malo et al 2006). Research in dogs by Rijsselaere et al (2004) has shown that sperm concentration influences sperm dimensions.…”

Sperm competition differentially affects swimming velocity and size of spermatozoa from closely related muroid rodents: head first

“…Changes in head dimensions may affect hydrodynamic resistance, therefore resulting in a more hydrodynamically efficient sperm design (Malo et al 2006, Gillies et al 2009). Furthermore, the increase in sperm HA is associated with the appearance of a hook.…”

“…Besides methodological issues, different hypotheses have been proposed to explain which are the first evolutionary steps that lead to early increases in sperm swimming velocity. An intraspecific study on red deer showed that an elongation of the sperm head was associated with an increase in sperm swimming speed, suggesting that elongated sperm heads experience a reduction in drag and make sperm more hydrodynamically efficient (Malo et al 2006). Alternatively, a comparative study on a closely related group of cichlid fish found an evolutionary disassociation between increases in sperm swimming speed in response to sperm competition and the size of the sperm, and postulated that the first steps may involve increases in energy production which precede any changes in sperm dimensions (Fitzpatrick et al 2009).…”

“…Modifications in the dimensions of the sperm head may also lead to an increase in head elongation (i.e. increase in HL/HW ratio) that could reduce drag and lead to a more efficient propulsion (Malo et al 2006, Gillies et al 2009, Tourmente et al 2011a. Sperm heads may also bear modifications either in the apical or in the basal region, particularly in rodents, in which hooks or post-nuclear appendices have been described, and which may be related to more efficient swimming (reviewed in Roldan et al (1992)).…”

Patterns of genetic variation and covariation in ejaculate traits reveal potential evolutionary constraints in guppies

“…For example, Malo et al (2006) reported a negative phenotypic correlation between midpiece length and VAP in red deer, whereas Mossman et al (2009) have recently reported a negative genetic correlation between midpiece length and sperm velocity in zebra finches. Similarly, Firman and Simmons (2008) showed that in house mice sperm length (including the midpiece) was negatively associated with competitive fertilization success, although in that species midpiece length appears to be positively associated with sperm swimming velocity (Firman and Simmons, 2010).…”