Sperm chemotaxis promotes individual fertilization success in sea urchins

Abstract

Reproductive success fundamentally shapes an organism's ecology and evolution, and gamete traits mediate fertilization, which is a critical juncture in reproduction. Individual male fertilization success is dependent on the ability of sperm from one male to outcompete the sperm of other males when searching for a conspecific egg. Sperm chemotaxis, the ability of sperm to navigate towards eggs using chemical signals, has been studied for over a century, but such studies have long assumed that this phenomenon improves individual male fitness without explicit evidence to support this claim. Here, we assessed fertilization changes in the presence of a chemoattractantdigesting peptidase and used a microfluidic device coupled with a fertilization assay to determine the effect of sperm chemotaxis on individual male fertilization success in the sea urchin Lytechinus pictus. We show that removing chemoattractant from the gametic environment decreases fertilization success. We further found that individual male differences in chemotaxis to a well-defined gradient of attractant correlate with individual male differences in fertilization success. These results demonstrate that sperm chemotaxis is an important contributor to individual reproductive success.

Observations of Simultaneous Sperm Release and Larval Planulation Suggest Reproductive Assurance in the Coral Pocillopora acuta

“…We propose that when sperm is absent, P. acuta produces parthenogenic offspring through automixis, diploidization of oocytes, or restitutional meiosis (Figure 1); alternately, when sperm is present, P. acuta is able to reproduce sexually (Figure 3) -a strategy consistent with the reproductive assurance hypothesis. Indeed, eggs of some coral species contain sperm attractant molecules, and this could explain why sexual reproduction is favored in the presence of sperm (Coll et al, 1994;Hussain et al, 2016). Our hypothesis would explain why Combosch and Vollmer (2013) observed a greater proportion of sexually produced larvae at the beginning of the planulation event -colonies were isolated the day prior to planulation, and thus eggs may have already been fertilized by other colonies in the aquaria.…”

“…In low population densities, a mixed-mode of reproduction would be expected to reinforce the benefits of the strategy: reproductive success would still be possible, thus allowing the species to colonize new habitats or rebound from catastrophic events even in the absence of conspecifics (Tsounis and Edmunds, 2016). However, when mates are within the sperm dispersal range, P. acuta may potentially use chemical cues such as sperm chemotaxis to attract non-self sperm (Coll et al, 1994;Hussain et al, 2016), and may thus benefit from the advantages of sexual reproduction. The modular nature of corals may also allow for multiple paternity per colony: when in close proximity to multiple mates, each polyp in a colony may be fertilized by a different father.…”

Advances in Microfluidics‐Based Assisted Reproductive Technology: From Sperm Sorter to Reproductive System‐on‐a‐Chip

“…Using a microfluidic chemotaxis sorter coupled with IVF, Hussain et al recently showed that chemotactic sperms subsequently increased the fertility rate in sea urchin . Zhang et al devised a hexagonal shape microchamber connected to six microchannels to simultaneously study the effect of sperm chemotaxis at three concentration gradients of progesterone .…”

Effects of CXCL12/CXCR4/CXCR7 axis on human sperm motility and chemotaxis

“…Chemotaxis is one of the most important factors in sperm guidance during fertilization among marine invertebrates, which provides a good inspiration to study the fertilization of human (De Lisa et al, 2013; Hussain et al, 2016). The sperm-attracting substances secreted by female genital tract are called chemoattractant.…”