The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Masanori Kohda - One of the best experts on this subject based on the ideXlab platform.
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Parker’s sneak-guard model revisited: why do reproductively parasitic males heavily invest in Testes?
Naturwissenschaften, 2011Co-Authors: Kazutaka Ota, Masanori Kohda, Michio Hori, Tetsu SatoAbstract:Alternative reproductive tactics are widespread in males and may cause intraspecific differences in Testes investment. Parker’s sneak-guard model predicts that sneaker males, who mate under sperm competition risk, invest in Testes relatively more than bourgeois conspecifics that have lower risk. Given that sneakers are much smaller than bourgeois males, sneakers may increase Testes investment to overcome their limited sperm productivity because of their small body sizes. In this study, we examined the mechanism that mediates differential Testes investment across tactics in the Lake Tanganyika cichlid fish Lamprologus callipterus . In the Rumonge population of Burundi, bourgeois males are small compared with those in other populations and have a body size close to sneaky dwarf males. Therefore, if differences in relative testis investment depend on sperm competition, the rank order of relative testis investment should be dwarf males > bourgeois males in Rumonge = bourgeois males in the other populations. If differences in relative testis investment depend on body size, the rank order of relative Testes investment should be dwarf males > bourgeois males in Rumonge > bourgeois males in the other populations. Comparisons of relative testis investment among the three male groups supported the role of sperm competition, as predicted by the sneak-guard model. Nevertheless, the effects of absolute body size on Testes investment should be considered to understand the mechanisms underlying intraspecific variation in Testes investment caused by alternative reproductive tactics.
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Cooperatively breeding cichlid fish adjust their testis size but not sperm traits in relation to sperm competition risk
Behavioral Ecology and Sociobiology, 2008Co-Authors: Satoshi Awata, Tomohiro Takeyama, Yoshimi Makino, Yuko Kitamura, Masanori KohdaAbstract:Theoretical models predict that in external fertilisers, sperm competition risk selects for larger Testes and larger sperm with higher velocity, at the expense of sperm longevity. Although several empirical studies have tested this prediction within a fish species, there has been little evidence that an individual male can adjust his testis size and sperm traits according to the risk of sperm competition. Using the cooperatively breeding cichlid Julidochromis transcriptus , we examined testis size and sperm traits (sperm size, velocity and longevity) of males that were assigned to monogamous pairs (without risk of sperm competition) or cooperatively polyandrous trios composed of two males and one female (with risk); the groups were reared for breeding for 2 or more months. Our experiments showed that the polyandrous males, both siring eggs in a clutch, had larger relative testis mass than the monogamous males. However, sperm traits were unrelated to sperm competition. These results suggest that individual males of J. transcriptus can adjust their testis size but not sperm traits in response to sperm competition risk. We also examined the effect of testis investment on growth rate and the somatic condition of males. Increased investment in Testes slowed growth rates, whereas testis investment did not affect somatic condition, indicating a trade-off between investment in Testes and growth. We conclude that testis investment, in response to perceived sperm competition risks, occurs at the expense of growth and may be a conditional reproductive strategy that is determined by the social status (monogamous or polyandrous) of each J. transcriptus male.
T R Birkhead - One of the best experts on this subject based on the ideXlab platform.
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sperm competition selects beyond relative Testes size in birds
Evolution, 2009Co-Authors: Stefan Lupold, George M Linz, James W Rivers, David F Westneat, T R BirkheadAbstract:Sperm morphology varies considerably across taxa, and postcopulatory sexual selection is thought to be one of the main forces responsible for this diversity. Several studies have investigated the effects of the variation in sperm design on sperm function, but the consequences of variation in sperm design on testis morphology have been overlooked. Testes size or architecture may determine the size of the sperm they produce, and selection for longer sperm may require concomitant adaptations in the Testes. Relative Testes size differs greatly between species and is often used as an index of sperm competition, but little is known about whether larger Testes have more sperm-producing tissue or produce sperm at a faster rate. Using a comparative approach in New World Blackbirds (Icteridae), we found (1) a strong link between testis histology and sperm length, suggesting selection on testis architecture through selection on sperm size, and (2) that species under intense sperm competition had a greater proportion of sperm-producing tissue within their Testes. These results support the prediction that sperm competition fosters adaptations in reproductive organs that extend beyond Testes size, and raise questions about the trade-offs influencing reproductive investment.
Jun-ichi Suto - One of the best experts on this subject based on the ideXlab platform.
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Genetic dissection of testis weight in mice: quantitative trait locus analysis using F_2 intercrosses between strains with extreme testis weight, and association study using Y-consomic strains
Mammalian Genome, 2011Co-Authors: Jun-ichi SutoAbstract:In the present study, dissection of genetic bases of testis weight in mice was performed. Autosomes and the X chromosome were searched using traditional quantitative trait locus (QTL) scans, and the Y chromosome was searched by association studies of Y-consomic strains. QTL analysis was performed in ♀DDD × ♂CBA F_2 mice; the inbred mouse DDD has the heaviest Testes, whereas the inbred mouse CBA has the lightest Testes. Two significant testis weight QTLs were identified on chromosomes 1 and X. A DDD allele was associated with increased and decreased testis weight at the locus on chromosomes 1 and X, respectively. In the reciprocal cross ♀CBA × ♂DDD F_2 mice, QTL on chromosome 1, and not on chromosome X, had a significant effect on testis weight. The DDD allele at the X-linked locus could not sustain testis weight in combination with the Y chromosome of the CBA strain. The Y chromosome per se had a significant effect on testis weight, i.e., DH-Chr Y^DDD had significantly heavier Testes than DH-Chr Y^CBA. On the basis of the results of Y-chromosome-wide association studies using 17 Y-consomic strains, variations in Uty , Usp9y , and Sry were significantly associated with testis weight. Thus, testis weight is a complex quantitative phenotype controlled by multiple genes on autosomes and sex chromosomes and their interactions.
Albrecht I Schultehostedde - One of the best experts on this subject based on the ideXlab platform.
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intraspecific variation of testis size and sperm length in the yellow pine chipmunk tamias amoenus implications for sperm competition and reproductive success
Behavioral Ecology and Sociobiology, 2004Co-Authors: Albrecht I Schultehostedde, John S MillarAbstract:Comparative analyses have found that relative testis size is a strong predictor of the prevalence of sperm competition for many taxa, including mammals, yet underlying this pattern is the assumption that intraspecific variation in testis size is related to individual fitness. Because intraspecific variation in ejaculate investment underlies interspecific patterns, it is critical to understand the causes and consequences of intraspecific variation in ejaculate investment. We examined relationships between ejaculate investment (testis size and sperm length) and reproductive success, body size and condition in the yellow-pine chipmunk (Tamias amoenus), a small ground squirrel in which sperm competition occurs. We examined genetic estimates of male reproductive success from a wild population of yellow-pine chipmunks and determined that males with large Testes had higher annual reproductive success than males with small Testes. This result provides empirical support for the numerous comparative studies that indicate testis size is associated with the intensity of sperm competition. In addition, males in good condition had relatively larger Testes than males in poor condition, but there was no evidence of sperm length being dependent on condition. Finally, contrary to many predictions, males that invested more in sperm production (relatively heavy Testes) produced shorter sperm, not longer sperm, than males that invested less.
John S Millar - One of the best experts on this subject based on the ideXlab platform.
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intraspecific variation of testis size and sperm length in the yellow pine chipmunk tamias amoenus implications for sperm competition and reproductive success
Behavioral Ecology and Sociobiology, 2004Co-Authors: Albrecht I Schultehostedde, John S MillarAbstract:Comparative analyses have found that relative testis size is a strong predictor of the prevalence of sperm competition for many taxa, including mammals, yet underlying this pattern is the assumption that intraspecific variation in testis size is related to individual fitness. Because intraspecific variation in ejaculate investment underlies interspecific patterns, it is critical to understand the causes and consequences of intraspecific variation in ejaculate investment. We examined relationships between ejaculate investment (testis size and sperm length) and reproductive success, body size and condition in the yellow-pine chipmunk (Tamias amoenus), a small ground squirrel in which sperm competition occurs. We examined genetic estimates of male reproductive success from a wild population of yellow-pine chipmunks and determined that males with large Testes had higher annual reproductive success than males with small Testes. This result provides empirical support for the numerous comparative studies that indicate testis size is associated with the intensity of sperm competition. In addition, males in good condition had relatively larger Testes than males in poor condition, but there was no evidence of sperm length being dependent on condition. Finally, contrary to many predictions, males that invested more in sperm production (relatively heavy Testes) produced shorter sperm, not longer sperm, than males that invested less.
