largest, yet most elusive, creatures inhabiting deep ocean waters. Adult sperm whales undertake long, deep dives (Watkins et al., 1993) into the darkness and high pressure of the mesoand bathypelagic depths. They do this to locate and catch approximately 1000 kg (Lockyer, 1981) of medium-sized squid and fish (Clarke et al., 1993) each day. The most prominent feature of the sperm whale physique ...

Prezygotic reproductive isolation and its importance in speciation is traditionally approached from the viewpoint of those events that occur before mating. However, recent interest in sperm competition theory has shown that prezygotic isolation can be affected by mechanisms that occur after mating but before fertilization. One neglected aspect of these studies is how the cost of sperm productio...

Sperm count evolution is driven by sexual selection, with an added role of selection on gamete resource allocation for hermaphrodite spermatogenesis. However, self-fertilization by hermaphrodites retards sexual selection and results in the evolution of reduced investment in sperm or pollen. In contrast to reproduction limited by female gametes (Bateman's Principle), self-fertilizing Caenorhabdi...

Recent evidence indicated that human sperm capacitation is associated with an increased production of superoxide anion (O2.-). To further study the role and importance of O2.- in capacitation, we investigated whether the O2.- generation is a general feature of capacitating spermatozoa, irrespective of the inducer used, and is correlated with capacitation levels and increased tyrosine phosphoryl...

Predetermination of sex in livestock offspring is in great demand and is of critical importance to providing for the most efficient production of the world's food supply. With the changes that have taken place in animal agriculture over the past generation the application of sex preselection to production systems becomes increasingly necessary. The current technology is based on the well-known ...

The relationships between testis size, hormone secretion and sperm production were studied during the spring (December) and autumn (May) in rams of two breeds with different breeding seasons and body weights (Corriedale and Australian Merino) maintained on native pastures and under natural photoperiods in Uruguay. Blood samples were collected at 20-min intervals during a 260-360-min period in 1...

Introduction: Varicocele disease is well-known cause of infertility in men. The presence of spermatic varices veins create a hostile environment to spermatogenesis. It results in reduced quality of the sperm production and in some cases can determine a total absence of sperm. The varicocelectomy procedure in patients with non-obstructive azoospermia (NOA) can raise the rates of sperm in the sem...

As sperm production is costly, males are expected to strategically allocate resources to sperm production according to mating opportunities. While sperm number adjustments have been reported in several taxa, only a few studies investigated whether sperm quality shows adaptive plasticity as well. We tested this prediction in the guppy, Poecilia reticulata. A total of 46 males were initially stri...

A major cause of male infertility, which includes 50 causes of infertility, is oxidative stress.  The aerobic respiration in the sperm cell is associated with the production of reactive oxygen species (ROS). Some reactions such as sperm capacitation and acrosome reactions require moderate levels of ROS. However, when the amount of ROS production surpasses the natural antioxidant defense of the ...

Sexual conflict can promote rapid evolution of male and female reproductive traits. Males of many polyandrous butterflies transfer nutrients at mating that enhances female fecundity, but generates sexual conflict over female remating due to sperm competition. Butterflies produce both normal fertilizing sperm and large numbers of non-fertile sperm. In the green-veined white butterfly, Pieris nap...