Testes Mass,but Not Sperm Length,Increases with Higher Levels of Polyandry in an Ancient Sex Model

There is strong evidence that polyandrous taxa have evolved relatively larger testes than monogamous relatives. Sperm size may either increase or decrease across species with the risk or intensity of sperm competition. Scorpions represent an ancient direct mode with spermatophore-mediated sperm transfer and are particularly well suited for studies in sperm competition. This work aims to analyze for the first time the variables affecting testes mass, ejaculate volume and sperm length, according with their levels of polyandry, in species belonging to the Neotropical family Bothriuridae. Variables influencing testes mass and sperm length were obtained by model selection analysis using corrected Akaike Information Criterion. Testes mass varied greatly among the seven species analyzed, ranging from 1.6±1.1 mg in Timogenes dorbignyi to 16.3±4.5 mg in Brachistosternus pentheri with an average of 8.4±5.0 mg in all the species. The relationship between testes mass and body mass was not significant. Body allocation in testes mass, taken as Gonadosomatic Index, was high in Bothriurus cordubensis and Brachistosternus ferrugineus and low in Timogenes species. The best-fitting model for testes mass considered only polyandry as predictor with a positive influence. Model selection showed that body mass influenced sperm length negatively but after correcting for body mass, none of the variables analyzed explained sperm length. Both body mass and testes mass influenced spermatophore volume positively. There was a strong phylogenetic effect on the model containing testes mass. As predicted by the sperm competition theory and according to what happens in other arthropods, testes mass increased in species with higher levels of sperm competition, and influenced positively spermatophore volume, but data was not conclusive for sperm length.     

The relationship between body mass and relative investment in testes mass in cetaceans: Implications for inferring interspecific variations in the extent of sperm competition

Based on sperm competition theory, percentage testes mass (% of total body mass) has been used to infer variations in the extent of sperm competition within mating systems of cetaceans. However, in most amniote taxa, including mammals, there is an underlying negative relationship between body mass and relative investment in testes mass, which must first be taken into account. Here, I identify a very strong nonlinear, negative relationship between body mass in cetaceans and relative investment in testes mass based on data from 31 species. As a result, if percentage testes mass alone is used to infer the relative extent of sperm competition in cetaceans, its importance in mating systems of smaller species is likely to be overestimated, whereas its role in larger species is likely to be underestimated. Similarly, there will also be systematic biases if this relationship is assumed to be linear when it is not. Therefore, it is essential that the underlying, nonlinear body mass–testes mass relationship is correctly taken into account when using relative investment in testes mass to estimate the relative levels of sperm competition in cetaceans. This is particularly important if such inferences are used to inform conservation strategies for endangered cetacean species.     

Rapid decreases in relative testes mass among monogamous birds but not in other vertebrates

Larger testes produce more sperm and therefore improve reproductive success in the face of sperm competition. Adaptation to social mating systems with relatively high and low sperm competition are therefore likely to have driven changes in relative testes size in opposing directions. Here, we combine the largest vertebrate testes mass dataset ever collected with phylogenetic approaches for measuring rates of morphological evolution to provide the first quantitative evidence for how relative testes mass has changed over time. We detect explosive radiations of testes mass diversity distributed throughout the vertebrate tree of life: bursts of rapid change have been frequent during vertebrate evolutionary history. In socially monogamous birds, there have been repeated rapid reductions in relative testes mass. We see no such pattern in other monogamous vertebrates; the prevalence of monogamy in birds may have increased opportunities for investment in alternative behaviours and physiologies allowing reduced investment in expensive testes.     

Adult nutrition,but not inbreeding,affects male primary sexual traits in the leaf‐footed cactus bug Narnia femorata (Hemiptera: Coreidae)

Adverse conditions may be the norm rather than the exception in natural populations. Many populations experience poor nutrition on a seasonal basis. Further, brief interludes of inbreeding can be common as population density fluctuates and because of habitat fragmentation. Here, we investigated the effects of poor nutrition and inbreeding on traits that can be very important to reproductive success and fitness in males: testes mass, sperm concentration, and sperm viability. Our study species was Narnia femorata, a species introduced to north‐central Florida in the 1950s. This species encounters regular, seasonal changes in diet that can have profound phenotypic effects on morphology and behavior. We generated inbred and outbred individuals through a single generation of full‐sibling mating or outcrossing, respectively. All juveniles were provided a natural, high‐quality diet of Opuntia humifusa cactus cladode with fruit until they reached adulthood. New adult males were put on a high‐ or low‐quality diet for at least 21 days before measurements were taken. As expected, the low‐quality diet led to significantly decreased testes mass in both inbred and outbred males, although there were surprisingly no detectable effects on sperm traits. We did not find evidence that inbreeding affected testes mass, sperm concentration, and sperm viability. Our results highlight the immediate and overwhelming effects of nutrition on testes mass, while suggesting that a single generation of inbreeding might not be detrimental for primary sexual traits in this particular population.     

Mouse Genital Ridges in Organ Culture: The Effects of Temperature on Maturation and Experimental Induction of Teratocarcinogenesis

Abstract. Testicular teratomas can be induced experimentally by grafting genital ridges from male mouse fetuses to the testes of adults. A high incidence of teratomas occurs in genital ridges grafted to scrotal testes, but not in genital ridges grafted to testes maintained at body temperature. Genital ridges were cultured at 32° C or 37° C prior to grafting to the testes to determine the effect of temperature on the incidence of teratomas. Genital ridges cultured at 32° C for two or three days produced a high incidence of teratomas when grafted to the testes, in contrast to genital ridges cultured at 37° C for two or three days which produced a low incidence. Histologically, genital ridges cultured at 32° C contained disorganized testicular tubules and were retarded in development. Genital ridges continued to develop in vitro at 37° C, but were histologically different from genital ridges maturing in the fetus. Genital ridges cultured at 32° C for 10 to 12 days did not develop teratomas in vitro or after grafting to the testes. Further characterization of temperature effects in vitro may lead to a better understanding of teratocarcinogenesis in vivo.     

Differential alteration of the reproductive axis by testosterone and estrogen in peripubertal and adult male Siberian hamsters (Phodopus sungorus)

In male Siberian hamsters, administration of adult physiological levels of testosterone (T) and estrogen (E2) to juveniles inhibited pubertal onset by distinct pathways. It is presently unclear if T and E2 also exert an inhibitory effect on the reproductive function of sexually mature and sexually maturing hamsters. This study aims to determine if there is an age-dependent decline in the sensitivity of the hypothalamic-pituitary-gonadal (HPG) axis to these inhibitory steroids and if their actions remain distinct. Peripubertal and adult male Siberian hamsters were implanted with a silastic capsule containing T, E2, or cholesterol (Ch, control). Testosterone treatment significantly reduced testes mass and length and impaired spermatogenesis in both ages. In contrast, E2 treatment reduced testes mass only in peripubertal, but not adult, animals. In fact, E2 treatment significantly increased testes mass in adults without altering spermatogenesis. In addition, circulating E2 is very high immediately prior to pubertal onset and declines thereafter. Our results showed the inhibitory effects of T persist into adulthood whereas those of E2 subside as the animals become sexually mature. The decreased sensitivity of the HPG axis to the inhibitory effects of E2 in adult animals and the high level of circulating E2 immediately prior to pubertal onset suggest E2 may play an important role in the regulation of puberty in this species.     

Correlates of testis mass in capybaras (Hydrochaeris hydrochaeris): dominance assurance or sperm production?

To infer possible functions for the low gonadosomatic index and the high proportion of non-spermatogenic tissue of capybara testes, we analysed the relationship between testes mass and the size and ratio of the testes compartments and, indirectly, their activities. We found that the testes mass of the capybara is closely associated with the size of androgen-dependent scent glands and to the proportion of non-spermatogenic tissue in the testis. We further investigated the associations between variables related to dominance and to sexual characters. The results suggest that dominance in capybaras is more associated with androgen-dependent scent glands than with sperm production. We suggest that male capybaras compete for dominance with chemical and visual status signalling.     

Effect of surgical restriction of growth of the testicular artery on testis size and histology in bulls.

The growth of the testicular artery was restricted on one side in young bulls and subsequent testicular development was monitored. After the animals had been killed, the testes were studied histologically and compared with testes from hypoplastic bulls. The growth rate of testes from the experimental side was significantly lower than that of testes from the sham-operated side over a period of 578 days. At death, the experimental testes had a mean (+/- SD) mass of 76 (+/- 41) g compared with 220 (+/- 31) g for the control testes. The sham-operated testes accounted for 0.071 (+/- 0.008)% of live body mass compared with 0.025 (+/- 0.014)% for the experimental testes. The seminiferous tubules in the sham-operated testes had a mean diameter (+/- SD) of 211 (+/- 25) microns, whereas those of the artery-restricted testes and hypoplastic testes were significantly smaller (152 (+/- 37) and 145 (+/- 45) microns, respectively). In the artery-restricted and hypoplastic testes, the interstitial tissue accounted for a significantly greater proportion of the testicular tissue than in the sham-operated testes and spermatogenesis was either totally absent or present in only a small proportion of tubules. It is suggested that the artery-restricted testes could be used as a model for testicular hypoplasia.     

The mechanism of action of adrenaline in the induction of sexual reproduction (encystation) in Opalina sudafricana parasitic in Bufo regularis

El Mofty M. M. and Sadek I. A. 1973. The mechanism of action of adrenaline in the induction of sexual reproduction (encystation) in Opalina sudafricana parasitic in Bufo regularis. International Journal for Parasitology3: 425–431. Adrenaline injections induced encystation in the opalinids of normal, hypophysectomized, and gonadectomized toads in the pre-breeding and post-breeding seasons. In normal and gonadectomized male and female toads, adrenaline injections may stimulate the release of ACTH of the anterior pituitary which in turn induces the secretion of androgenic steroids from the interrenal tissue. It is speculated that the breakdown products of these androgenic steroids cause the encystation of the parasites. In hypophysectomized male and female hosts, the injected adrenaline may stimulate the interstitial tissue of the testes and ovaries to secrete androgens, the breakdown products of which induce encystation of the opalinids. Adrenaline or ACTH gave negative results in vitro. Urine of male or female toad injected with adrenaline, ACTH, or testosterone propionate induced encystation in Opalina sudafricana m vitro.     

Population density mediates the interaction between pre‐ and postmating sexual selection

When females mate with more than one male, sexual selection acts both before and after mating. The interaction between pre‐ and postmating episodes of selection is expected to be context dependent, but few studies have investigated how total sexual selection changes under different ecological conditions. We examined how population density mediates the interaction between pre‐ and postmating sexual selection by establishing replicate populations of the horned dung beetle Onthophagus taurus at low, medium, and high densities, and then using microsatellite‐based parentage analyses to measure male fitness. We found that mating success and fertilization success were positively correlated at all three densities, but the strength of the correlation decreased with increasing density. We also found a shift from negative to positive linear selection on testes mass as density increased, and opposing selection on weapons and testes at high densities. These patterns suggest that the importance of postmating processes increases with increasing population density, which reduces the selective advantage of weapons for premating contest competition, and increases the selective advantage of large ejaculates for postmating sperm competition. We expect that density‐dependent selection on testes mass has contributed to the phenotypic variation observed between natural populations of O. taurus that differ in density.     

Histology of the normal and retained equine testis

Abdominal, inguinal and scrotal testes of horses were examined grossly and by light microscopy. An average of 1.5, 2.3 and 4.6 layers of spermatogenic cells, and mean seminiferous tubule diameters of approximately 66.2, 83.6 and 146.6 micron in the abdominal, inguinal and scrotal testes, respectively, were recorded. The interstitial spaces and the number of interstitial cells (of Leydig) seemed to be increased while spermatogenesis appeared to be arrested in the retained testes. Early spermatocytes were the most mature stages of the spermatogenic cells in the retained testes. An extensive vacuolation of spermatogenic cells was evident in these testes. The changes may result due to a high temperature of the abdominal environment in concert with the altered production of androgens.     

Alpha and beta adrenergic control of contraction force of perch heart (Perca fluviatilis) in vitro

Noradrenaline showed a negative inotropic effect on the isolated electrically triggered atrium of the perch. The effect was stronger at lower temperature and was antagonized by an alpha adrenergic blocker, phentolamine. The inotropic effect of adrenaline was dependent on incubation temperature. The effect was negative at 15 C but biphasic at 24 C, where with increasing adrenaline concentration a positive inotropic effect was followed by negative inotropy. Phentolamine not only antagonized the negative inotropic effect of adrenaline at 15 degrees C but changed it to positive. This positive inotropic effect was antagonized by a beta adrenergic blocker, propranolol. On the triggered ventricular strip adrenaline had no effect at 6 or 15 C, but increased contraction force at 24 C. It can be suggested that in the perch heart atrium there is an activity balance of alpha and beta receptors, which mediate the negative and positive inotropic control, respectively. As in higher vertebrates, alpha adrenergic activation decreases and beta activation increases by agonists in the following order: noradrenaline, adrenaline and isoprenaline. The balance changes towards increased beta activity when temperature rises.     

THE LIKELIHOOD OF SPERM COMPETITION IN MANATEES-EXPLAINING AN APPARENT PARADOX

Florida manatees ( Trichechus manatus latirostris ) are promiscuous, with multiple males mating with individual females. This suggests manatees are sperm competitors. Surprisingly, manatee testes are not relatively large. For adult males in non-winter, testicular size is approximately twice what is expected, based on allometry, for "typical" ( i. e. , non-sperm competitor) male mammals of similar size; for these manatees, combined testicular weight represents 0.19% of the body weight ( n = 27 manatees). Testicular weight was generally largest in manatees older than 7 yr in non-winter. Testicular size of some sperm competitors is as much as an order of magnitude (or more) larger than expected in a "typical" species. Perhaps in compensation for the testes not being remarkably large, the seminal vesicles of mature manatees may be larger than the testes. Production of notably large volumes of seminal fluid characterizes sperm competitor primate species and may have positive energy consequences for species such as the manatee that have extremely low metabolic rates. Another possible explanation for the observed relationship between testicular mass and body mass in manatees is that selection for a greatly expanded hindgut and extremely dense, heavy integument could make the body mass of manatees "artificially" high, and the relative testicular mass "artificially" low.     

Testicular migration, spermatogenesis, temperature regulation and environment of the sheath-tail bat, Taphozous georgianus

The testes of the common sheath-tail bat of tropical Australia undergo a seasonal migration between the abdomen and the scrotal pouches, while each cauda epididymidis is permanently maintained in the scrotal pouch. Straps of smooth muscle attach to both the cranial and caudal poles of the testes, and these extend cranially to the diaphragm and caudally to the cauda epididymidis. The testicular arteries are not coiled. Among the environmental factors investigated, maximum temperature correlated most significantly with testicular descent, and the number of spermatogonia per bat also correlated most significantly with maximum temperature. Body temperature of a captive bat ranged from 25 to 38 degrees C and this was closely related to body weight and ambient temperature. It seems likely that the scrotal pouch provides a temperature slightly below that of the body and so facilitates sperm storage in the permanently scrotal cauda epididymidis. Migration of the testes probably serves to ameliorate the seasonal temperature fluctuations to which they are exposed while the relatively high correlation between maximum environment temperature and spermatogonial numbers suggests that temperature may be a proximate influence on reproduction in the sheath-tail bat.     

Extreme variation in testes size in an insect is linked to recent mating activity

Ample sperm production is essential for successful male reproduction in many species. The amount of sperm a male can produce is typically constrained by the size of his testes, which can be energetically expensive to grow and maintain. Although the economics of ejaculate allocation has been the focus of much theoretical and empirical literature, relatively little attention has been paid to individual adult variation and plasticity at the source of sperm production, the testes themselves. We experimentally address this issue using the insect Narnia femorata Stål (Hemiptera: Coreidae). We established the metabolic cost of testicular tissue and then quantified variation in individual testes mass in response to multiple mate quality and quantity treatments. We uncovered extreme variation across individuals and considerable short‐term effects of mating activity on testes dry mass. Importantly, the observed variation in testes mass was associated with notable fitness consequences; females paired with males with larger testes had greater hatching success. Overall, pairing with a female resulted in a 11% reduction in dry testes mass. Despite this apparent considerable mating investment, we found no evidence of strategic allocation to higher quality females or longer‐term changes in testes mass. The dynamic nature of testes mass and its metabolic cost is vital to consider in the context of re‐mating rates, polyandry benefits and general mating system dynamics both in this species and more broadly.     

The Evolution of Large Testes: Sperm Competition or Male Mating Rate?

A positive relationship across species between the extent to which females mate with more than one male and relative testes mass has been demonstrated in a wide range of vertebrate taxa and certain insects. At least two hypotheses, which are not necessarily mutually exclusive, could account for this pattern: (1) the numerical sperm competition hypothesis, which assumes that larger testes enable the male to transfer more sperm to each female, giving the male an advantage in sperm competition and (2) the male mating rate hypothesis, which proposes that larger testes allow the male to produce a greater number of (potentially smaller) ejaculates to engage in frequent copulations with different females. Of these hypotheses, the former has won broad acceptance, while the latter has tended to be dismissed. Here, we argue that the lines of evidence commonly used to support the numerical sperm competition hypothesis in favour of the male mating rate hypothesis are not as clear cut or generally applicable as they are purported to be and that, consequently, the male mating rate hypothesis cannot be excluded with confidence on the basis of the current evidence. Furthermore, some evidence, such as the finding that ejaculate mass and/or sperm number is negatively correlated with testes mass across species in some insects and that larger testes in Drosophila can evolve in response to an increase in the number of females available for mating in the laboratory, provides support for the male mating rate hypothesis. Further work is needed to disentangle the relative effects of these selective pressures on the evolution of testes size.     

Heritable testicular hypoplasia in Nguni (Bos indicus) bulls: vascular characteristics and testosterone production.

The biased unilateral occurrence of heritable gonadal hypoplasia was investigated by examining the gross- and microanatomy of the testicular artery and vein, testicular blood flow and testicular testosterone secretion in normal Nguni bulls and in Nguni bulls showing unilateral left, unilateral right and bilateral hypoplasia of the testis. A high incidence of branching of the testicular artery was found ipsilateral to hypoplastic testes. The branching occurs a short distance from the dorsal aorta: one branch proceeds to the testis, the other to the ipsilateral kidney. The association between arterial branching to the kidney and ipsilateral hypoplasia of the testis held for both unilaterally left and unilaterally right hypoplastic bulls. Variations in the anatomy of the testicular vein occurred in both normal and hypoplastic bulls but there was no specific association between the variations and ipsilateral hypoplasia. The lumen diameter of the testicular artery or branch correlated with testis mass. Wall thickness of the artery ipsilateral to hypoplastic testes was not different from that in normal bulls, discounting hyperplasia of the endothelium. Total blood flow to the testis correlated with testis mass. The secretion rate of testosterone from hypoplastic testes was lower than that of normal testes but there was no difference when compared on a unit mass basis.     

Seasonal and developmental changes of reproductive organs of male ringed seals (Phoca hispida) in the Svalbard area

The weights of testes, prostate gland and baculum of ringed seal males were related to age, season and differences in body size. There was a significant seasonal variation in testes and prostate gland size of sexually mature males, with a maximum occurring in early April. There were no seasonal changes in prostate weight of immature males, but some of the older immatures had elevated testes weights in April. Testes weight was significantly correlated with lean body mass. The increase in testes size with increasing body weight was greater for seals six years of age or older than for younger males. We suggest that some testicular growth and a seasonal cycle in testes growth occur before the testes become functional endocrinologically. We also believe that the primary event leading to puberty in ringed seals is an age-dependent shift in metabolic processes, directing a larger percentage of available energy towards the reproductive organs.     

Larger testes are associated with a higher level of polyandry, but a smaller ejaculate volume, across bushcricket species (Tettigoniidae)

While early models of ejaculate allocation predicted that both relative testes and ejaculate size should increase with sperm competition intensity across species, recent models predict that ejaculate size may actually decrease as testes size and sperm competition intensity increase, owing to the confounding effect of potential male mating rate. A recent study demonstrated that ejaculate volume decreased in relation to increased polyandry across bushcricket species, but testes mass was not measured. Here, we recorded testis mass for 21 bushcricket species, while ejaculate (ampulla) mass, nuptial gift mass, sperm number and polyandry data were largely obtained from the literature. Using phylogenetic-comparative analyses, we found that testis mass increased with the degree of polyandry, but decreased with increasing ejaculate mass. We found no significant relationship between testis mass and either sperm number or nuptial gift mass. While these results are consistent with recent models of ejaculate allocation, they could alternatively be driven by substances in the ejaculate that affect the degree of polyandry and/or by a trade-off between resources spent on testes mass versus non-sperm components of the ejaculate.     

Are secondary sex traits, parasites and immunity related to variation in primary sex traits in the Arctic charr?

Primary and secondary sex traits are influenced by the same sex hormones, and the expression of secondary sex traits may consequently signal males' capacity for sperm production. Sperm quality may also be influenced by immune activity, as sperm are non-self to the male. Parasite infections alter immune activity and may thus reduce ejaculate quality. In the Arctic charr (Salvelinus alpinus) the red abdominal colour is considered an ornament that signals important information in mate choice. We captured and individually caged sexually mature male Arctic charr during the spawning period. Afterwards we estimated abdominal colour, parasite infections, gonad mass and several spermatological and immunological variables. Intensity of abdominal colour was positively correlated to testes mass, milt mass and sperm cell numbers produced. Additionally, males with low parasite intensities had high testes mass and produced milt with high sperm density, indicating a trade-off between parasite resistance and development of primary sex traits. Our measures of immunity were, however, not related to primary sex traits. We conclude that females evaluating male abdominal coloration may obtain information about differences between males in fertilization potential and parasite resistance.