Bigger testes do work more: experimental evidence that testis size reflects testicular cell proliferation activity in the marine invertebrate, the free-living flatworm Macrostomum sp.

Schärer, Lukas; Ladurner, Peter; Rieger, Reinhard M.

doi:10.1007/s00265-004-0802-9

Cited by 74 publications

(87 citation statements)

References 46 publications

(57 reference statements)

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“…Comparative and experimental studies aimed at testing this prediction have generally used testis size as a measure of sperm production rate (see Schä rer et al 2004b for a list of parameters that have been used to estimate male allocation to sperm production). The choice of this parameter is largely guided by the relative ease with which it can be determined, but it has rarely been tested how testis size is related to sperm production rate; a linear relationship is usually just assumed.…”

Section: Introductionmentioning

confidence: 99%

“…First, testis size is a static measure, and therefore does not necessarily say much about the amount of resources that flow through it. We have previously discussed this issue (Schä rer et al 2004b) and we will therefore not further address it here. Second, testis size and sperm production rate may, at least to some degree, vary independently of each other.…”

Section: Introductionmentioning

confidence: 99%

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Phenotypic plasticity in sperm production rate: there’s more to it than testis size

Schärer

Vizoso

2006

Evol Ecol

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Evolutionary theory predicts that males should produce more sperm when sperm competition is high. Because sperm production rate is difficult to measure in most organisms, comparative and experimental studies have typically used testis size instead, while assuming a good correspondence between testis size and sperm production rate. Here we evaluate this common assumption using the marine flatworm Macrostomum lignano, in which we can estimate sperm production rate because the accumulation of produced sperm can be observed in vivo. In earlier studies we have shown that testis size is phenotypically plastic in M. lignano: worms can be induced to make larger testes by raising them in groups instead of pairs, and these larger testes have a higher cell proliferation activity (i.e. they are more energetically costly). Here we demonstrate that worms with such experimentally enlarged testes have a higher sperm production rate. Moreover, although testis size and sperm production rate were related linearly, worms with experimentally enlarged testes had a higher sperm production rate per unit testis size (i.e. a higher spermatogenic efficiency). We thus show that phenotypically plastic adjustment of sperm production rate includes a component that is independent of testis size. We discuss possible reasons for this novel finding, and suggest that the relationship between testis size and sperm production needs to be evaluated in other species as well.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phenotypic plasticity in sperm production rate: there’s more to it than testis size

Schärer

Vizoso

2006

Evol Ecol

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“…Typically, males that inseminate greater numbers of sperm achieve greater fertilization success (Martin et al 1974, Parker 1982. As the size of a males' testes predicts the proportion of the testes made up of sperm producing seminiferous tissue and the rate of sperm production (Willett & Ohms 1957, Parker 1982, Møller 1989, Marconato & Shapiro 1996, Scharer et al 2004, Lü pold et al 2009c, Ramm & Stockley 2010, Rowe & Pruett-Jones 2011, males with larger testes are expected to be competitively advantaged when engaging in sperm competition. Consequently, increases in the level of sperm competition are expected to select for increased investment in testicular tissue (Parker & Pizzari 2010).…”

Section: Sperm: Solders In the Battle For Fertilizationmentioning

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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“…Testes mass is accepted as a good proxy for sperm competition risk (Parker et al 1997;Parker & Ball 2005). However, the dynamics of sperm production can vary (Møller 1991;Schärer & Vizoso 2007;Vahed & Parker 2012) and thus sperm production is challenging to assess, mainly because the production rate of sperm is often hard to quantify (Schärer et al 2004).…”

mentioning

confidence: 99%

From storage to delivery: sperm volume and number of spermatozoa inside storage organs and ejaculates in males ofTimogenes elegans(Scorpiones: Bothriuridae)

Vrech

Olivero

Mattoni

et al. 2018

Journal of Arachnology

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Abstract. Sperm competition influences the evolution of many reproductive traits such as gonads, sperm or genitalia. Many sperm competition analyses concentrate in testes and ejaculates. Among arachnids, scorpions constitute an intriguing taxon for examining sperm production and usage. For example, in the family Bothriuridae the females of Timogenes elegans Mello-Leitão, 1931 accept more than one male per reproductive season and males produce spermatozoa continuously, storing them inside two elastic storage organs (i.e., two seminal vesicles plus two deferent ducts) before inseminating females, using a sclerotized spermatophore. In this study, we analyzed the sperm storage organs and the ejaculate volume transferred by T. elegans. We described the volume and number of spermatozoa at storage sites and in ejaculates, and investigated ejaculate volume and concentration in remating experiences. Storage organs varied in total size. Inside the spermatophore, the volume of the sperm drop represented 38% of the volume of both sperm storage sites. The remaining space around the sperm drop is filled with a gel-like substance. The ejaculate volume and spermatozoa number did not vary significantly between consecutive matings. Timogenes elegans stored abundant sperm inside the seminal vesicles. Available sperm was divided equally between both storage organs, and ejaculates were diluted in the spermatophore, presumably, with the gel stored in the trunk. There was no effect of body condition over any of the variables analyzed. Male sperm storage and ejaculate production are discussed considering the sperm depletion hypothesis and the sperm competition theory.

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Bigger testes do work more: experimental evidence that testis size reflects testicular cell proliferation activity in the marine invertebrate, the free-living flatworm Macrostomum sp.

Cited by 74 publications

References 46 publications

Phenotypic plasticity in sperm production rate: there’s more to it than testis size

Phenotypic plasticity in sperm production rate: there’s more to it than testis size

Sperm wars and the evolution of male fertility

From storage to delivery: sperm volume and number of spermatozoa inside storage organs and ejaculates in males ofTimogenes elegans(Scorpiones: Bothriuridae)

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