Testes size in birds: quality versus quantity—assumptions, errors, and estimates

Calhim, Sara; Birkhead, Tim R.

doi:10.1093/beheco/arl076

Cited by 72 publications

(72 citation statements)

References 36 publications

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“…Testis mass was determined from wet weight of previously frozen tissue (n = 3) or from formalin preserved tissue (n = 5). Calhim and Birkhead (2007) showed that formalinfixed testes do not change in mass, hence these two different measures are comparable. All measures are given using the mean ± standard deviation.…”

Section: Methodsmentioning

confidence: 95%

A single functional testis and long deferent duct papillae: the peculiar male reproductive tract of the classically polyandrous, sex-role reversed Black Coucal (Centropus grillii)

Frey

Goymann

2009

J Ornithol

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In many birds, the male reproductive tract is asymmetric with the left testis being larger than the right one. Coucals (Centropodidae) represent an exception as the asymmetry is typically reversed. Here, we describe the functional morphology of the reproductive tract of the African Black Coucal (Centropus grillii), a bird species with reversed sex-roles and a classical polyandrous mating system. In this species, the left testis has been reduced to a tiny, disk-like vestige that in almost all cases examined was not visible macroscopically. The vestigial left testis apparently does not participate in sperm production but has retained a vestigial left excurrent duct system. By contrast, the right deferent duct was engorged with sperm, suggesting a sperm storage function. Both deferent ducts opened on the tip of spectacularly long, erectile deferent duct papillae into the urodaeum of the male cloaca. Behavioural observations suggest that they may function as ''pseudophalli''. Testis mass represented 0.49% of body mass, less than half the size of other classical polyandrous bird species. Assuming moderate to high levels of sperm competition this represents a paradox. Heavy demands on the energy budget while caring for altricial young may have prevented males from maintaining two testes and large bilateral sperm storage devices. Reduced testis mass may be compensated for by frequent transfer of small amounts of sperm. Female Black Coucals have not evolved any corresponding cloacal specializations, but like all other birds have sperm storage tubules.

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Section: Methodsmentioning

confidence: 95%

A single functional testis and long deferent duct papillae: the peculiar male reproductive tract of the classically polyandrous, sex-role reversed Black Coucal (Centropus grillii)

Frey

Goymann

2009

J Ornithol

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“…So common is this view that many researchers, including the authors of this review (e.g. Fitzpatrick et al (2012aFitzpatrick et al ( , 2012bFitzpatrick et al ( , 2012c), commonly use relative testes size as a proxy measure for the strength of sperm competition in a given species, even in the absence of any information on a species mating behavior (Møller 1991, Briskie & Montgomerie 1992, Dunn et al 2001, Pitcher et al 2005, Calhim & Birkhead 2007). However, a degree of caution should be applied to accepting relative testes size as an absolute proxy for the level of sperm competition because testes can perform functions other than sperm production (Emerson 1997), and increased investment in testes mass could be favored in species where copulation occurs frequently (the male mating rate hypotheses) even in the absence of variation in the level of sperm competition (Crudgington et al 2009, Vahed & Parker 2012.…”

Section: Sperm: Solders In the Battle For Fertilizationmentioning

confidence: 98%

“…Indeed, several comparative studies in birds have found that sperm are morphologically less variable in species where the level of sperm competition is greater (Calhim et al 2007, Immler et al 2008, Kleven et al 2008, Lü pold et al 2009b. These studies provide support for the notion that sperm morphology is under strong selection from sperm competition.…”

Section: Variation In Sperm Morphologymentioning

confidence: 99%

Sperm wars and the evolution of male fertility

Simmons¹,

Fitzpatrick²

2012

Reproduction

300

343

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Females frequently mate with several males, whose sperm then compete to fertilize available ova. Sperm competition represents a potent selective force that is expected to shape male expenditure on the ejaculate. Here, we review empirical data that illustrate the evolutionary consequences of sperm competition. Sperm competition favors the evolution of increased testes size and sperm production. In some species, males appear capable of adjusting the number of sperm ejaculated, depending on the perceived levels of sperm competition. Selection is also expected to act on sperm form and function, although the evidence for this remains equivocal. Comparative studies suggest that sperm length and swimming speed may increase in response to selection from sperm competition. However, the mechanisms driving this pattern remain unclear. Evidence that sperm length influences sperm swimming speed is mixed and fertilization trials performed across a broad range of species demonstrate inconsistent relationships between sperm form and function. This ambiguity may in part reflect the important role that seminal fluid proteins (sfps) play in affecting sperm function. There is good evidence that sfps are subject to selection from sperm competition, and recent work is pointing to an ability of males to adjust their seminal fluid chemistry in response to sperm competition from rival males. We argue that future research must consider sperm and seminal fluid components of the ejaculate as a functional unity. Research at the genomic level will identify the genes that ultimately control male fertility.

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“…Relative testis size, a commonly used proxy for sperm competition in avian studies [6,17], was estimated by including both (ln-transformed) testes mass and body mass as independent variables in statistical models. Data on testes mass and body mass were obtained from museum sources, from published literature [39] or from males collected (under licence) during the breeding season. Data on sperm length variation were calculated from sperm as the between-male coefficient of variation (CV bm ¼ s.d./mean Â 100), adjusted for small sample size according to the formula adjusted CV bm ¼ (1 þ 1/4n) Â CV bm [40].…”

Section: (D) Index Of Sperm Competitionmentioning

confidence: 99%

Evolution of sperm structure and energetics in passerine birds

et al. 2013

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Spermatozoa exhibit considerable interspecific variability in size and shape. Our understanding of the adaptive significance of this diversity, however, remains limited. Determining how variation in sperm structure translates into variation in sperm performance will contribute to our understanding of the evolutionary diversification of sperm form. Here, using data from passerine birds, we test the hypothesis that longer sperm swim faster because they have more available energy. We found that sperm with longer midpieces have higher levels of intracellular adenosine triphosphate (ATP), but that greater energy reserves do not translate into faster-swimming sperm. Additionally, we found that interspecific variation in sperm ATP concentration is not associated with the level of sperm competition faced by males. Finally, using Bayesian methods, we compared the evolutionary trajectories of sperm morphology and ATP content, and show that both traits have undergone directional evolutionary change. However, in contrast to recent suggestions in other taxa, we show that changes in ATP are unlikely to have preceded changes in morphology in passerine sperm. These results suggest that variable selective pressures are likely to have driven the evolution of sperm traits in different taxa, and highlight fundamental biological differences between taxa with internal and external fertilization, as well as those with and without sperm storage.

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Testes size in birds: quality versus quantity—assumptions, errors, and estimates

Cited by 72 publications

References 36 publications

A single functional testis and long deferent duct papillae: the peculiar male reproductive tract of the classically polyandrous, sex-role reversed Black Coucal (Centropus grillii)

A single functional testis and long deferent duct papillae: the peculiar male reproductive tract of the classically polyandrous, sex-role reversed Black Coucal (Centropus grillii)

Sperm wars and the evolution of male fertility

Evolution of sperm structure and energetics in passerine birds

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