Post-plasmogamic pre-karyogamic sexual selection: mate choice inside an egg cell

Abstract

Intersexual selection is often categorized as precopulatory or post-copulatory mate choice by individuals of one sex over showy individuals of the other sex. We extend the framework of post-copulatory choice to include post-plasmogamic pre-karyogamic sexual selection. That is, selection of haploid nuclei within the microcosm of a single fertilized egg cell after sperm has entered an egg cell but before fusion of their nuclear membranes, in which an egg nucleus chooses a sperm nucleus with which to fuse. The role of sexual selection at this nuclear level is probably small in monospermic out-crossers, but large in polyspermic outcrossers. Post-plasmogamic pre-karyogamic sexual selection may also explain how the sperm nucleus is rejected in gynogens, and how the egg nucleus is rejected in androgens. We propose that male and female nuclei behave independently within an egg cell, and that post-plasmogamic pre-karyogamic mate choice is largely based on either (1) a pre-existing sensory bias for certain characteristics of the sperm pronuclear membrane, or (2) detection of good genes through signal (mRNA) detection.

Physiological factors influencing female fertility in birds

“…While multiple sperm can penetrate the PVL in birds, only one male pronucleus typically fuses with the female pronucleus in the germinal disc during syngamy. This provides additional potential for the female pronucleus itself to be selective [ 206 ], although the exact mechanisms of avian syngamy remain unknown [ 28 ]. In the comb jelly ( Beroe ovata ), where fertilization is also polyspermic, the female pronucleus migrates within the egg cell prior to syngamy, moving between different immobile male pronuclei before finally fusing with just one [ 206 , 207 ].…”

“…This provides additional potential for the female pronucleus itself to be selective [ 206 ], although the exact mechanisms of avian syngamy remain unknown [ 28 ]. In the comb jelly ( Beroe ovata ), where fertilization is also polyspermic, the female pronucleus migrates within the egg cell prior to syngamy, moving between different immobile male pronuclei before finally fusing with just one [ 206 , 207 ]. Whether sexual selection occurs at the point of syngamy in birds remains to be seen, but could present an additional opportunity for females to influence the outcome of fertilization by discriminating between males, for example, based on male genotype, or on the integrity of the male's DNA [ 155 , 206 ].…”

Micropyle number is associated with elevated female promiscuity in Lepidoptera

“…Why physiological polyspermy occurs only in some taxa is unclear, although a recent study by Hemmings & Birkhead [24] indicates that polyspermy is essential for early embryonic development in both domestic fowl and the zebra finch (Taeniopygia guttata). Physiological polyspermy enables the intriguing possibility of mate choice within an egg cell [25]. In the polyspermic ctenophore (Beroe ovata), the female pronucleus migrates among male pronuclei within the egg before fusing with one [26].…”

“…Micropyles allow sperm entry into the egg; hence more micropyles should aid sperm entry in to the egg, reducing the likelihood of infertility, while at the same time increasing the likelihood of physiological polyspermy. Whether physiological polyspermy benefits early embryogenesis in insects as it appears to do in birds [24] and/or offers an alternative site for cryptic female choice [25] requires further study.…”

The evolution and diversification of sex : from sex to the sexes

“…"Y" signifies that gynogens or parthenogens exist in these taxa. Appendix B: Gorelick, Derraugh, Carpinone, Bertram (2011). Post-plasmogamic, pre-karyogamic sexual selection: Mate choice inside an egg cell.…”