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Male sexual ornament size is positively associated with reproductive morphology and enhanced fertility in the stalk-eyed fly Teleopsis dalmanni.

Rogers DW, Denniff M, Chapman T, Fowler K, Pomiankowski A - BMC Evol. Biol. (2008)

Bottom Line: Although "good genes" arguments are typically invoked to explain this phenomenon, a simpler alternative is possible if variation in male reproductive quality (e.g. sperm number, ejaculate content, mating rate) is an important determinant of female reproductive success.If eyespan indicates male reproductive quality, females could directly increase their reproductive success by mating with males with large eyespan.Fertility enhancement may have arisen because males with larger eyespan mated more often and/or because they transferred more sperm or other substances per ejaculate.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Galton Laboratory, Research Department of Genetics, Evolution and Environment, University College London, 4 Stephenson Way, London, NW1 2HE, UK. d.rogers@imperial.ac.uk

ABSTRACT

Background: Exaggerated male ornaments and displays often evolve in species where males only provide females with ejaculates during reproduction. Although "good genes" arguments are typically invoked to explain this phenomenon, a simpler alternative is possible if variation in male reproductive quality (e.g. sperm number, ejaculate content, mating rate) is an important determinant of female reproductive success. The "phenotype-linked fertility hypothesis" states that female preference for male ornaments or displays has been selected to ensure higher levels of fertility and has driven the evolution of exaggerated male traits. Females of the stalk-eyed fly Teleopsis dalmanni must mate frequently to maintain high levels of fertility and prefer to mate with males exhibiting large eyespan, a condition-dependent sexual ornament. If eyespan indicates male reproductive quality, females could directly increase their reproductive success by mating with males with large eyespan. Here we investigate whether male eyespan indicates accessory gland and testis length, and then ask whether mating with large eyespan males affects female fertility.

Results: Male eyespan was a better predictor of two key male reproductive traits--accessory gland and testis length--than was body size alone. This positive relationship held true over three levels of increasing environmental stress during the maturation of the adult accessory glands and testes. Furthermore, females housed with a large eyespan male exhibited higher levels of fertility than those with small eyespan males.

Conclusion: Male eyespan in stalk-eyed flies is subject to strong directional mate preference and is a reliable indicator of male reproductive quality--both because males with larger eyespan have bigger accessory glands and testes, and also as they confer higher fertility on females. Fertility enhancement may have arisen because males with larger eyespan mated more often and/or because they transferred more sperm or other substances per ejaculate. The need to ensure high levels of fertility could thus have been an important selective force in the coevolution of female preference and male eyespan in stalk-eyed flies. Our results support the phenotype-linked fertility hypothesis and suggest that it might be of general importance in explaining the evolution of exaggerated male ornaments and displays in species where males only provide females with ejaculates during reproduction.

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The effect of male eyespan on fertility. Least squares means ± s.e. number of fertile eggs laid in 32-day period following mating (at average levels of fecundity) by large residual eyespan and small residual eyespan males.
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Figure 2: The effect of male eyespan on fertility. Least squares means ± s.e. number of fertile eggs laid in 32-day period following mating (at average levels of fecundity) by large residual eyespan and small residual eyespan males.

Mentions: The number of fertile eggs laid by groups of 8 females mated to a single male for 24 hours was assessed over the subsequent 32 days. Both female fecundity (F1,71 = 107.21, p < 0.001) and male thorax length (F1,71 = 15.96, p = 0.002) predicted the number of fertile eggs laid. Adding male eyespan (as a categorical variable) to this model significantly improved the fit (F1,71 = 6.80, p = 0.011, Fig. 2). Females mated to large residual eyespan males laid significantly more fertile eggs than did females mated to small residual eyespan males (large = 199.83 ± 7.44, small = 172.07 ± 7.54, least squares mean ± s.e.). Thus, male eyespan predicted significantly more variance in fertility than body size alone. Adding absolute values of male eyespan (instead of eyespan category) to the basic model of body size and fecundity produced qualitatively similar results; eyespan significantly improved the fit of the model (F1,71 = 7.95, p = 0.006). Estimating the regression coefficient (b ± s.e.) of the number of fertile eggs on eyespan indicated that females laid 15.38 ± 4.25 more fertile eggs per mm increase in male absolute eyespan (eyespan range: 3.96 – 9.21 mm) – equivalent to roughly an 8% increase in female fertility per mm increase in male absolute eyespan.


Male sexual ornament size is positively associated with reproductive morphology and enhanced fertility in the stalk-eyed fly Teleopsis dalmanni.

Rogers DW, Denniff M, Chapman T, Fowler K, Pomiankowski A - BMC Evol. Biol. (2008)

The effect of male eyespan on fertility. Least squares means ± s.e. number of fertile eggs laid in 32-day period following mating (at average levels of fecundity) by large residual eyespan and small residual eyespan males.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2562384&req=5

Figure 2: The effect of male eyespan on fertility. Least squares means ± s.e. number of fertile eggs laid in 32-day period following mating (at average levels of fecundity) by large residual eyespan and small residual eyespan males.
Mentions: The number of fertile eggs laid by groups of 8 females mated to a single male for 24 hours was assessed over the subsequent 32 days. Both female fecundity (F1,71 = 107.21, p < 0.001) and male thorax length (F1,71 = 15.96, p = 0.002) predicted the number of fertile eggs laid. Adding male eyespan (as a categorical variable) to this model significantly improved the fit (F1,71 = 6.80, p = 0.011, Fig. 2). Females mated to large residual eyespan males laid significantly more fertile eggs than did females mated to small residual eyespan males (large = 199.83 ± 7.44, small = 172.07 ± 7.54, least squares mean ± s.e.). Thus, male eyespan predicted significantly more variance in fertility than body size alone. Adding absolute values of male eyespan (instead of eyespan category) to the basic model of body size and fecundity produced qualitatively similar results; eyespan significantly improved the fit of the model (F1,71 = 7.95, p = 0.006). Estimating the regression coefficient (b ± s.e.) of the number of fertile eggs on eyespan indicated that females laid 15.38 ± 4.25 more fertile eggs per mm increase in male absolute eyespan (eyespan range: 3.96 – 9.21 mm) – equivalent to roughly an 8% increase in female fertility per mm increase in male absolute eyespan.

Bottom Line: Although "good genes" arguments are typically invoked to explain this phenomenon, a simpler alternative is possible if variation in male reproductive quality (e.g. sperm number, ejaculate content, mating rate) is an important determinant of female reproductive success.If eyespan indicates male reproductive quality, females could directly increase their reproductive success by mating with males with large eyespan.Fertility enhancement may have arisen because males with larger eyespan mated more often and/or because they transferred more sperm or other substances per ejaculate.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Galton Laboratory, Research Department of Genetics, Evolution and Environment, University College London, 4 Stephenson Way, London, NW1 2HE, UK. d.rogers@imperial.ac.uk

ABSTRACT

Background: Exaggerated male ornaments and displays often evolve in species where males only provide females with ejaculates during reproduction. Although "good genes" arguments are typically invoked to explain this phenomenon, a simpler alternative is possible if variation in male reproductive quality (e.g. sperm number, ejaculate content, mating rate) is an important determinant of female reproductive success. The "phenotype-linked fertility hypothesis" states that female preference for male ornaments or displays has been selected to ensure higher levels of fertility and has driven the evolution of exaggerated male traits. Females of the stalk-eyed fly Teleopsis dalmanni must mate frequently to maintain high levels of fertility and prefer to mate with males exhibiting large eyespan, a condition-dependent sexual ornament. If eyespan indicates male reproductive quality, females could directly increase their reproductive success by mating with males with large eyespan. Here we investigate whether male eyespan indicates accessory gland and testis length, and then ask whether mating with large eyespan males affects female fertility.

Results: Male eyespan was a better predictor of two key male reproductive traits--accessory gland and testis length--than was body size alone. This positive relationship held true over three levels of increasing environmental stress during the maturation of the adult accessory glands and testes. Furthermore, females housed with a large eyespan male exhibited higher levels of fertility than those with small eyespan males.

Conclusion: Male eyespan in stalk-eyed flies is subject to strong directional mate preference and is a reliable indicator of male reproductive quality--both because males with larger eyespan have bigger accessory glands and testes, and also as they confer higher fertility on females. Fertility enhancement may have arisen because males with larger eyespan mated more often and/or because they transferred more sperm or other substances per ejaculate. The need to ensure high levels of fertility could thus have been an important selective force in the coevolution of female preference and male eyespan in stalk-eyed flies. Our results support the phenotype-linked fertility hypothesis and suggest that it might be of general importance in explaining the evolution of exaggerated male ornaments and displays in species where males only provide females with ejaculates during reproduction.

Show MeSH
Related in: MedlinePlus