Sperm competition, whereby sperm from multiple males compete to fertilize an egg, selects for adaptations that increase fertilization success. Because fertilization success is related to sperm number, size, and quality, both interspecific and intraspecific variation in these traits are predicted to correlate with the level of sperm competition. Specifically, species and individuals that experie...

Female sperm storage is an essential component of reproduction in many animals. In insects, female sperm storage affects fecundity, sperm competition/preference and receptivity to re-mating. Female sperm storage consists of several stages, including sperm entry into the sperm storage organs (SSOs), maintenance within the SSOs and exit from the SSOs. The Drosophila melanogaster male seminal prot...

Damselflies (Odonata: Zygoptera) have a more complex sperm transfer system than other internally ejaculating insects. Males translocate sperm from the internal reproductive organs to the specific sperm vesicles, a small cavity on the body surface, and then transfer them into the female. To examine how the additional steps of sperm transfer contribute to decreases in sperm quality, we assessed s...

Sperm competition, when sperm from different males compete to fertilize a female's ova, is a widespread and fundamental force in the evolution of animal reproduction. The earliest prediction of sperm competition theory was that sperm competition selected for the evolution of numerous, tiny sperm, and that this force maintained anisogamy. Here, we empirically test this prediction directly by usi...

Post-copulatory sexual selection, in the form sperm competition, has influenced the evolution of several male reproductive traits. However, theory predicts that sperm competition would lead to trade-offs between numbers and size of spermatozoa because increased costs per cell would result in a reduction of sperm number if both traits share the same energetic budget. Theoretical models have prop...

OBJECTIVE To examine the relationship among sperm apoptosis, sperm chromatin status, and DNA ploidy in different sperm fractions. DESIGN Prospective study. SETTING Reproductive research center in a tertiary care hospital. INTERVENTION(S) Sperm prepared by density gradient were evaluated for sperm count, motility, apoptosis, and sperm chromatin assessment. MAIN OUTCOME MEASURE(S) Sperm c...

Sperm competition is now recognised as a potent selective force shaping many male reproductive traits. While the influence of sperm competition on sperm number is widely accepted, its effects upon sperm size remain controversial. It had been traditionally assumed that there is a trade-off between sperm number and sperm size, so that an increase in sperm number would result in a decrease in sper...

Sperm competition has classically been thought to maintain anisogamy (large eggs and smaller sperm) because males are thought to maximize their chance of winning fertilizations by trading sperm size for number. More recently it has been recognized that sperm quality (e.g., size, velocity) can also influence sperm competition, although studies have yielded conflicting results. Because sex evolve...

It is often questioned whether sperm parameters, including whether retrieved or ejaculated, have any effect on intracytoplasmic sperm injection (ICSI) results. Do severe spermatogenic defects affect embryo quality or pregnancy rate? Further, does it matter in azoospermic patients whether the sperm source is testicular or epididymal? Our studies show there is no significant difference in results...

A new instrument for assessing mammalian semen attributes, the Sperm Quality Analyzer, was evaluated as a potential tool for determining rooster sperm quality. The Sperm Quality Analyzer measures the “activity” of sperm in a semen sample as the sperm motility index (SMI). The SMI is defined as the number and amplitude of deflections in a light path per second as a result of sperm movement wit...