Biology essay on sperm competition

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Biology essay on sperm competition

Sneaker males usually face a number of disadvantages, including reduced access to females and the higher likelihood that upon ejaculation, their sperm face competition from other males. Nevertheless, sneaker males represent an evolutionarily stable strategy under a wide range of conditions.

Biology essay on sperm competition

Interestingly, the direction and magnitude of this skew in paternity shifted according to individual female egg donors, suggesting cryptic female choice could moderate the outcomes of sperm competition in this externally fertilizing species.

Hooknose, jack, salmon, sexual selection, sneaker male, sperm competition Introduction Evolutionary processes have produced a stunning variety of characteristics that appear adaptive for male reproductive success, including morphological weaponry, genitalic, and sperm features, and alternative mating strategies Andersson Sneaker males usually encounter numerous obstacles to fertilization, including reduced access to females, and the virtual guarantee that their sperm will be competing with sperm from other males.

Nevertheless, sneaking represents an evolutionarily stable strategy under many conditions. How sneaker males compensate for their apparent reproductive disadvantages is a subject of much interest.

Finite resources create a fundamental trade-off between development of precopulatory i. In general, dominant males invest in weaponry that can be used to monopolize access to females, while sneaker males invest in ejaculates to win fertilizations through sperm competition.

A fair raffle implies that sperm competition outcomes are determined by the relative quantity of competing sperm, and selection favors sneaker males that produce more sperm per unit body mass than dominants. Consistent with this prediction, sneaker males in many different species have larger testes relative to their body mass compared with dominant males Stockley and Purvis ; Gage et al.

Under a loaded raffle, selection favors sneaker males that produce higher quality sperm compared with dominant males Parker a. Differences in sperm quality can also arise from a male's behavioral adaptations, such as better-timed sperm release close to eggs.

Most direct studies of sperm competition among dominant and sneaker males have been unable to distinguish the fair and loaded raffle models.

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Stoltz and Neff estimated that sneaker male sperm was nearly twice as competitive as dominant male sperm, but sneaker male sperm were released closer to the female's eggs to mimic natural conditions. Other sperm competition experiments controlled sperm count and distance to female gametes, but competing males were chosen randomly instead of explicitly testing a dominant versus sneaker male Evans et al.

Using a combination of maximum likelihood, logistic regression, and independent subsampling, we reject the fair raffle in favor of the loaded raffle model, demonstrating that sneaker jack males make competitively superior sperm to dominant males. Although jack males outcompeted hooknoses overall, the magnitude and even the direction of their competitive superiority shifted with individual female egg donor, suggesting females influence the outcomes of sperm competition.

Materials and Methods Study system Chinook salmon offer an ideal study species for asking whether a sneak-guard system follows the fair or loaded raffle. Young fry leave their natal stream during the smolt and spend the next few years in the open ocean Healey Instead, jacks take on cryptic coloration and occupy the peripheral edges of rivers, where they wait for hooknose males to begin spawning with females, then dart in and around the spawning pair to release their sperm while avoiding aggressive interactions with dominant males Heath et al.

Because dominant males vigorously defend nesting females, they are expected to outcompete jack males for access to ova Rutter ; Ginzburg ; Gile and Ferguson ; Perchec et al. In combination with the high heritability of jacking Heath et al.

Biology Essay on Sperm Competition - Sample Essays

Fish selection and gamete collection Our experimental design represents a trade-off between testing numerous fully independent parents versus multiple observations from the same gamete combinations.

We increased the number of observations per sperm-egg combination in order to test for sperm-by-egg interactions. We account for the non-independence of this approach using a variety of statistical methods and subsampling as described below.

A total of five females, five jack males, and five dominant hooknose males Appendix S1 were collected at the Big Creek Hatchery weir Oregon Department of Fish and Wildlife in northwestern Oregon during early October of the spawning season. Jack males were distinguished from hooknose males based on their smaller size, lack of defensive hump, lack of kype, smaller teeth, and cryptic coloration resembling a female.

Biology essay on sperm competition

Only sexually mature fish in good physical condition — without injuries, fungus, and fin wear — were selected. Prior to gamete collection, fish were wiped dry with paper towels to preclude contamination with water and mucus.

Sperm are quiescent at this stage and do not become active until exposure to water Kime et al.Biology: Biology, study of living things and their vital processes that deals with all the physicochemical aspects of life. Modern principles of other fields, such as chemistry, medicine, and physics, for example, are integrated with those of biology in areas such as biochemistry, biomedicine, and biophysics.

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