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Topic: Sperm competition

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Sperm

Spermatozoon

Evolutionarily stable strategy

Semen

Testicle

Oral genital stimulation

2 (number)

Ovum

Anatomical position

X chromosome

Urethra

Primate

Corpora cavernosa

Masturbation

Mitochondria

	Sperm Competition in Nematodes
		The effects of sperm competition are varied and spectacular, ranging from post-copulatory mate guarding (many insects) and incredibly high sperm counts (birds and humans) to penises fashioned with brushes and hooks that function to remove rival sperm from the female reproductive tract (dragonflies).
		These data show that hermaphrodite sperm have become smaller, and that male sperm are largest in male/female species where the incidence of sperm competition is greatest.
		Thus, sperm competition appears to have driven the evolution of sperm size in nematodes.
	www.mcb.arizona.edu /wardlab/spermcomp.html (395 words)

	Female remating, sperm competition and sexual selection in Drosophila
		Sperm competition should therefore exert a strong evolutionary pressure on characteristics that allow males to pre-empt the sperm stored by females from previous matings, and/or to avoid sperm pre-emption by males that encounter the female after mating.
		Sperm competition arises mainly because of the elaborate capacity for sperm storage within the female, because of the highly efficient use of stored sperm at fertilization, and because of the high probability of remating (Parker, 1970).
		Sperm precedence is simply the non-random utilization of sperm from one of the two males to mate with a female.
	funpecrp.com.br /GMR/year2002/vol3-1/gmr0034_full_text.htm (16477 words)

	Sperm Wars
		He found that the volume of sperm a man ejaculates while having sex with his partner is unrelated to how long it has been since he last had an ejaculation; the important variable is the length of time that has passed since he last had sex with his wife.
		The volume of sperm may be as much as three times that of normal if the man has been separated from his wife for a long period of time.
		Advocates of the sperm competition theory argue that a longer penis provides sperm delivery closer to the cervix and gives sperm a head start in their competition with rivals.
	www.ulm.edu /~palmer/SpermWars.htm (805 words)

	Sperm competition in fish
		Sperm numbers in stripped ejaculates were also higher in species where sperm competition was more likely to occur1.
		Indeed, a positive correlation between sperm length and ovum number25 suggests that speed is of paramount importance when egg numbers increase, but that sperm longevity, which correlates negatively with sperm length1, is of minor importance.
		[3] Parker G.A. Sperm competition and its evolutionary consequences in the insects.
	cas.bellarmine.edu /tietjen/Ecology/sperm_competition_in_fish.htm (5156 words)

	Monarchs in the Classroom
		Sperm precedence, or nonrandom fertilization success among a female’s mates, is often an important determinant of male fitness.
		Sperm are transferred last, and shortly after mating ends they begin to move through the ductus seminalis, and into the spermatheca (see sperm movement).
		It is possible that relative amounts of sperm and other materials in the ampules of these male types vary, but differences were not apparent when we looked at their contents; all were essentially full of sperm.
	www.monarchlab.umn.edu /Research/Rep/sperm.html (4014 words)

	Sperm heteromorphism - Wikipedia, the free encyclopedia
		Sperm heteromorphism is the simultaneous production of two or more distinguishable types of sperm by a single male.
		Non-fertile sperm delay or prevent the female mating again, thus allowing the male producing the non-fertile sperm a greater share of the paternity of her offspring (because the male avoids Sperm competition).
		Alternatively, the sperm may transfer chemicals similar to sex peptide, a chemical which is carried on the sperm of Drosophila melanogaster that makes females less likely to accept mates (i.e.
	en.wikipedia.org /wiki/Sperm_heteromorphism (640 words)

	Researchers Watch Worm Sperm Evolve In A Petri Dish
		Then, by simply looking at sperm from males and hermaphrodites side by side under a microscope, he found that the males' sperm were larger than the hermaphrodites'.
		LaMunyon sampled sperm (don't ask) from nineteen different species, took them back to his microscope, and found that, indeed, sperm from the male-female species were all significantly larger than sperm from the hermaphroditic species.
		The sperm from the hermaphroditic colony, where there was no sperm competition, remained the same size throughout the experiment.
	unisci.com /stories/20022/0604022.htm (872 words)

	Sperm Competition in the Absence of Fertilization in Caenorhabditis elegans -- Singson et al. 152 (1): 201 -- Genetics
		Sperm Competition in the Absence of Fertilization in Caenorhabditis elegans -- Singson et al.
		Sperm Competition in the Absence of Fertilization in Caenorhabditis elegans
		causes sperm competition to occur in the absence of fertilization.
	www.genetics.org /cgi/content/full/152/1/201 (3858 words)

	CRES Projects: Testosterone Levels and Sperm Competition in Primates
		Relationships between circulating testosterone, sexual behavior, mate competition, and aggressiveness in male mammals are complex.
		Findings confirm that larger testes and occurrences of sperm competition among primates are associated wtih elevated testosterone levels in adult males.
		Rather, it appears that competition between males for access to females in multimale-multifemale mating systems is associated with higher circulating testosterone in a number of primates.
	cres.sandiegozoo.org /projects/pd_sperm_competition.html (219 words)

	Semen Displacement as a Sperm Competition Strategy in Humans by Gordon G. Gallup, Jr. and Rebecca L. Burch
		Keywords: penis morphology, semen displacement, sperm competition, sperm retention, premature ejaculation, double mating, circumcision, penile hypersensitivity, refractory period, fertilization by proxy, last male precedence, infertility, self-semen displacement, semen coagulation, wife rape.
		From the standpoint of sperm competition, another benefit of extended periods of copulation would be more effective displacement of rival semen from the female reproductive tract.
		The effectiveness of sperm competition strategies in general, and semen displacement in particular, is time dependent (i.e., related to the elapsed time since the extra-pair copulation).
	human-nature.com /ep/articles/ep021223.html (4704 words)

	APS Staff Research Interests Professor Tim Birkhead
		The aim of this study is to determine the functional significance of sperm phenotype; to determine the factors that maintain the variance in sperm phenotype and to understand the evolution of sperm phenotypes.
		There is increasing evidence that post-copulatory sexual selection in the form of sperm competition and cryptic female choice can result in divergence in male reproductive traits and the coevolution of interacting male and female traits.
		We predict that sperm morphology, which we have shown to be unique in the bullfinch, makes bullfinch¹s sperm less likely to be transported and/or accepted by the female canary reproductive tract than are canary sperm into the bullfinch female reproductive tract.
	www.shef.ac.uk /aps/tim.html (1680 words)

	Australian Museum - Sperm Attacks
		This means that sperm from one species can come into contact with an egg from another for which it is not intended.
		As soon as a sperm meets an egg, the egg releases an enzyme called glycosidase that prevents the binding of all sperm but the first.
		However, if the sperm happens to be from a different seasquirt species, the same mechanism is still triggered, rendering that egg useless.
	www.amonline.net.au /archive.cfm?id=197 (279 words)

	BioMed Central \| Full text \| Highly variable sperm precedence in the stalk-eyed fly, Teleopsis dalmanni
		Such post-copulatory sexual selection can be a potent evolutionary force, as is evidenced by the numerous male behavioral, physiological, and morphological adaptations that influence sperm competition, such as mate guarding, increased copulation duration, seminal fluid induced reluctance of female re-mating, and the mechanical removal of sperm [1-3].
		Sperm precedence was not the only mode of sperm utilization, since the null model of random sperm mixing (i.e.
		Simmons LW: Sperm competition and its evolutionary consequences in the insects.
	www.biomedcentral.com /1471-2148/6/53 (5176 words)

	ScienceDaily: When It Comes To Sperm Competition, Size Can MatterIt's The Female Who Holds The Aces
		Science Daily — When it comes to mating and determining whose sperm reaches the elusive egg, females control both the playing field and the rules of the game, according to a new study on male sperm competition vs. female choice to be published in the Nov. 8 issue of Science.
		Most people are familiar with the elaborate competitions that occur between males before mating, such as the ritualistic clash of horns of Big Horn Sheep or the bloody battles between male elephant seals.
		Sexual Competition Drives Evolution Of A Sex-related Gene (November 11, 2004) -- In what could be termed a truly seminal discovery, researchers have shown that when females are more promiscuous, males have to work harder -- at the genetic level, that is. More specifically, they...
	www.sciencedaily.com /releases/2002/11/021108071925.htm (2162 words)

	LiveScience.com - Longest Known Sperm Create Paradox of Nature
		If there was a prize for biggest sperm in nature, it would go to Drosophila bifurca, a tiny fruit fly whose coiled sperm would measure more than 2 inches long if straightened out.
		In many species, the number of sperm produced by males far outnumbers the amount of eggs produced by females.
		That's because the female bodies of many species are not passive arenas within which sperm compete, but more like obstacle courses, with hurdles and defenses in place to weed out weakling sperm.
	www.livescience.com /animalworld/060616_big_sperm.html (600 words)

	Researchers Discover the 'Big Sperm Paradox'
		This leads to the “big sperm paradox” because the idea that postcopulatory sexual selection could favor the evolution of giant sperm clashes with traditional sexual selection theory, which predicts that the most successful sperm competitors will be the males that produce many, tiny sperm.
		Their results show that, once females evolve a preference for longer sperm, intense sperm competition can actually reverse the trajectory of sperm evolution so that the most successful males are those with the most female-like strategy of producing very few, large gametes.
		In essence, sperm competition is attributed with the evolutionary maintenance of anisogamy.
	www.physorg.com /news68999588.html (1116 words)

	Untitled Document (Site not responding. Last check: 2007-09-10)
		Male transfer sperm to the female that are relatively cheap to produce.
		This competition will not only be for access to those females but also to fertilise the eggs of the females they mate with.
		Sperm competition occurs when there is the potential for ejaculates from more than one male to overlap in the female's reproductive tract.
	www.shef.ac.uk /aps/mbiolsci/katie-hartnup/sperm-competition.html (255 words)

	Sperm competition
		That means lots of sperm from different individuals all competing to be the first one to reach the egg.
		I know what you're wondering, and the answer is: humans fall right on the line, suggesting that sperm competition has played a minor role in the evolution of our sexual anatomy and behavior.
		The influence of females' behavior and sexual anatomy on those of males is a fertile field for study of sperm competition and its role in evolution.
	www.anthro.ucdavis.edu /faculty/stewart/stpballs.htm (752 words)

	Gene Expression: "Sperm competition"
		Postcopulatory sperm competition is a key aspect of sexual selection and is believed to drive the rapid evolution of both reproductive physiology and reproduction-related genes1, 2, 3, 4.
		It is well-established that mating behavior determines the intensity of sperm competition, with polyandry (i.e., female promiscuity) leading to fiercer sperm competition than monandry1, 2, 3.
		Studies in mammals, particularly primates, showed that, owing to greater sperm competition, polyandrous taxa generally have physiological traits that make them better adapted for fertilization than monandrous species, including bigger testes, larger seminal vesicles, higher sperm counts, richer mitochondrial loading in sperm and more prominent semen coagulation2, 5, 6, 7, 8.
	www.gnxp.com /MT2/archives/003062.html (707 words)

	Promiscuity (Tim Birkhead) - book review
		Promiscuity is a tour of animal sexuality, exploring the effects of sperm competition and sex-based selective pressures on reproductive biology and behaviour.
		This is followed by a chapter on sperm, ejaculates and ova —; mostly on sperm size and number and the role of seminal fluid.
		At one point he writes: "because [sperm competition] dealt directly with variation in reproductive success its evolutionary significance was much more immediate than that of other behaviours, such as foraging".
	dannyreviews.com /h/Promiscuity.html (898 words)

	Concepts in sperm heterogeneity, sperm selection and sperm competition as biological foundations for laboratory tests ...
		Sperm samples were video-recorded and their motion analysed using a Hobson sperm tracker.
		After 24 h, sperm were activated in water and motility analysed using computer-assisted sperm analysis on a Hobson sperm tracker (for more detailed method see Van Look and Kime 2003), points represent individual spermatozoa.
		Parker GA 1970 Sperm competition and its evolutionary consequences in the insects.
	www.reproduction-online.org /cgi/content/full/127/5/527 (5530 words)

	Male sperm expenditure under sperm competition risk and intensity in quacking frogs -- Byrne 15 (5): 857 -- Behavioral ...
		Male sperm expenditure under sperm competition risk and intensity in quacking frogs -- Byrne 15 (5): 857 -- Behavioral Ecology
		Male sperm expenditure under sperm competition risk and intensity in quacking frogs
		sperm number irrespective of whether a mating involved one,
	beheco.oxfordjournals.org /cgi/content/abstract/15/5/857 (337 words)

	Sperm Competition (Site not responding. Last check: 2007-09-10)
		An analysis of quantitative genetic experiments (Hughes 1997) indicates that just a few loci that reside on chromosome III have large effects on sperm competitive ability.
		By using special balancer stocks of mutant flies in a series of crosses, it is possible to generate different lines of flies that have different third chromosomes.
		Males from these lines have wild type body color, and they are used in sperm competition experiments to determine which lines have a high sperm competitive ability and which ones a low ability.
	www.life.uiuc.edu /kahughes/sperm_competition.htm (327 words)

	SCARE: Sperm Competition and Remating Estimates (Site not responding. Last check: 2007-09-10)
		SCARE is a C++ program designed for inferences on a model of remating and sperm displacement.
		The details of the model and the algorithm SCARE uses can be found in Jones and Clark 2002, "Bayesian Sperm Competition Estimates".
		The model has 2 parameters: alpha, the remating parameter (questions about alpha?), and beta, the parameter governing sperm displacement.
	www.massey.ac.nz /~mbjones/research/content_local/scare.html (529 words)

	Of mice and sperm -- Pizzari 103 (41): 14983 -- Proceedings of the National Academy of Sciences
		Of mice and sperm -- Pizzari 103 (41): 14983 -- Proceedings of the National Academy of Sciences
		determinants of the outcome of sperm competition is the relative
		are also expected to evolve in response to sperm competition.
	www.pnas.org /cgi/content/short/103/41/14983?rss=1 (290 words)

	Promiscuity: An Evolutionary History of Sperm Competition
		Or the Samoans who have a celebrated a festival annually for centuries which centers on the spawning of the Palolo worm and gorging themselves on the sperm and egg discharges the worms' reproduction entails.
		From sexual selection, paternity, protection, genitalia, insemination, sperm, and sperm competition to polyandry, ova, copulation, and sperm choice.
		Female promiscuity and male sperm competition are rife in the animal kingdom.
	www.2think.org /promiscuity.shtml (1035 words)

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