Testes size, testosterone production and reproductive behaviour in a natural mammalian mating system

1. Testosterone (T) is a key mediator in the expression of numerous morphological and behavioural traits in mammals, but the factors underlying individual variation in circulating T levels are poorly understood. 2. The intimate structural integration of sperm and T production within the testes, alongside the dependency of sperm production on high levels of T, suggests that T requirements for spermatogenesis could be an important driver of individual differences in T. 3. To test this hypothesis, we examine how male capacity for sperm production (as indicated by their testes size) is associated with T levels in a feral population of Soay sheep, resident on St. Kilda, Scotland, during their rutting season. 4. We found a strong positive relationship between an individual's testes size (as measured before their seasonal enlargement) and the levels of circulating T during their rut, suggesting that T requirements for spermatogenesis has a prominent influence on the production of this androgen. 5. In contrast, body condition and competitive ability did not independently predict T levels, findings that are inconsistent with conventional 'condition-dependent' and 'challenge' hypotheses of T production. 6. This influence of male's capacity for sperm production on T appeared to be substantial enough to be biologically relevant, as testes size also predicted male aggression and mate-seeking behaviour. 7. Our results suggest that a male's inherent capacity for sperm and T production is tightly phenotypically integrated, with potential consequences for a wide range of other T-mediated reproductive traits.     

Genome-Wide Linkage Analysis Identifies Loci for Testicle and Ovary Traits in Chickens

Development of testes or ovaries is critical to chicken breeders. Understanding the genetic mechanisms influencing the development of the testes and ovaries could enhance selection efforts which target reproductive traits. The linkage analysis was conducted within an F2 population derived from Beijing-You chickens and a commercial broiler line. The results have identified one quantitative trait loci (QTL, designated T1) for bilateral testicular weight (TW) and the percentage of TW to carcass weight, and five QTLs (designated O1–O5) for ovary weight (follicle-free, OW) and the percentage of OW to carcass weight. For the testes traits, QTL T1 is located between 6.55 and 8.56 Mb on GGA13. Especially, the gene gamma-amino butyric acid A receptor, alpha 1 (GABRA1) located near the T1 peak. For ovarian traits, QTL O2 was located at 29.31 Mb on GGA7. G protein-coupled receptor 39 (GPR39) present at the O2 peak was expressed at higher levels within the reproductive tract. It is also involved in the regulation of several reproductive functions. Other QTL peaks and the genes’ function in the ovary and testes need to be evaluated. The QTLs and the genes identified in this study could provide valuable information for establishing reproductive traits in chickens, and need further investigation.     

Differing amounts of genetic polymorphism in testes and male accessory glands ofDrosophila melanogaster andDrosophila simulans

We surveyed genetic polymorphism by two-dimensional gel electrophoresis of male reproductive tract proteins in 20 isofemale lines each ofDrosophila melanogaster andDrosophila simulans. After classifying 244 such proteins ofDrosophila melanogaster and 271 ofDrosophila simulans by their distribution between testes and accessory glands within the reproductive tract, significant correlations were found between genetic polymorphism and tissue distribution. In both species, gland-specific proteins were significantly more polymorphic than testis-specific proteins, as well as those found in both testes and glands. Simultaneously, inDrosophila simulans, proteins found in roughly equivalent relative abundance in both testes and glands were significantly less variable than gland-specific and testis-specific proteins, as well as those with a quantitative difference in relative abundance between testes and glands. These correlations may reflect general differences in variability between extracellular and intracellular proteins and between proteins with broad as opposed to tissue-specific distributions.We thank the Natural Sciences and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).     

紫翅猪毛菜、钠猪毛菜不同个体大小繁殖分配差异及随海拔的变化

以新疆准噶尔盆地藜科猪毛菜属植物紫翅猪毛菜(Salsola affinis C.A.Mey)、钠猪毛菜(Salsola nitraria Pall)为研究对象,用繁殖分配比例的方法对比分析了两种猪毛菜不同海拔同一种群内不同个体大小繁殖分配的特点,并用异速生长模型分析了不同海拔繁殖生物量与营养生物量之间分配与个体大小的依赖关系。结果发现:1)不同海拔繁殖生物量(R)与营养生物量(V)呈不同程度的异速生长。紫翅猪毛菜随海拔的升高R-V的异速生长斜率显著升高,截距随海拔的升高没有显著增加;而钠猪毛菜的斜率随海拔升高显著降低,截距则显著升高。2)紫翅猪毛菜在较低海拔个体大小与繁殖分配呈负相关,在较高海拔呈正相关;钠猪毛菜在较低海拔个体大小与繁殖分配呈正相关,在较高海拔呈负相关;两种猪毛菜繁殖分配的适应对策相反。3)将同一种群个体大小分成大、中、小3种类型,多重比较发现紫翅猪毛菜在较低海拔,中小个体的繁殖分配显著高于大个体的繁殖分配;在较高海拔,大个体的繁殖分配显著高于中小个体的繁殖分配。钠猪毛菜在较低海拔,大个体的繁殖分配显著高于中、小个体的繁殖分配;在较高海拔,小个体的繁殖分配显著高于大、中个体的繁殖分配。综合分析认为:两个物种随海拔变化产生不同的繁殖分配策略,除遗传效应外,环境和个体大小对钠猪毛菜繁殖分配的变化均产生重要影响,而紫翅猪毛菜繁殖分配的变化主要由海拔差异导致。由于微生境对同一种群的个体大小产生影响,进而产生不同的繁殖分配模式,所以在干旱区更应重视个体大小对繁殖分配的影响。     

Characterization and Social Correlates of Fecal Testosterone and Cortisol Excretion in Wild Male <Emphasis Type="Italic">Saguinus mystax</Emphasis>

Reproductive success in male primates can be influenced by testosterone (T) and cortisol (C). We examined them in wild Saguinus mystax via fecal hormone analysis. Firstly, we wanted to characterize male hormonal status over the course of the year. Further we tested the influence of the reproductive status of the breeding female, social instability, and intergroup encounter rates on T levels, comparing the results with predictions of the challenge hypothesis (Wingfield et al., 1990). We also tested for interindividual differences in hormonal levels, possibly related to social or breeding status. We collected data during a 12-mo study on 2 groups of moustached tamarins at the Estación Biológica Quebrada Blanco in northeastern Peru. We found fairly similar T and C levels over the course of the year for all males. Yet an elevation of T shortly after the birth of infants, during the phase of ovarian inactivity of the groups breeding female, was evident. Hormonal levels were not significantly elevated during a phase of social instability, did not correlate with intergroup encounter rates, and did not differ between breeding and nonbreeding males. Our results confirm the challenge hypothesis (Wingfield et al., 1990). The data suggest that reproductive competition in moustached tamarins is not based on endocrinological, but instead on behavioral mechanisms, possibly combined with sperm competition.     

Testosterone, testes size, and mating success in birds: a comparative study

Reproductive behaviors of vertebrates are often underpinned by temporal patterns of hormone secretion. We investigated interspecific patterns of circulating testosterone in male birds to test the hypothesis that testosterone plays a crucial role in sexual selection as determined by degree of polygyny and extra-pair paternity. We predicted that the evolution of increased levels of polygyny and extra-pair paternity would have resulted in the evolution of increased levels of testosterone to allow males more efficiently to compete for mates. This hypothesis was tested in comparative analyses of 116 species of birds using Generalized Least Squares Models. We assessed the importance of latitudinal distribution, because this can confound the relationship between testosterone and mating success. There were weak positive phylogenetic correlations between measures of testosterone and estimates of mating success at the social level, but this association appeared to be confounded by latitudinal distribution, a significant correlate of testosterone titers. However, we found a significantly positive relationship between peak and residual peak testosterone (which is the peak testosterone level that is controlled for the baseline level) and extra-pair paternity independent of latitude. These results suggest that selection pressures arising from social and sexual mating differently affected testosterone levels with the former being mediated by factors associated with latitudinal distribution. An analysis of residual testes size revealed a positive association between peak and residual testosterone and testes size relative to body size. In a path analysis, we show that relative testis size primarily evolved in association with intense sperm competition and thus high sperm production, and these mechanisms had a secondary impact on blood testosterone levels at a phylogenetic scale. Our results suggest that sperm competition has played an important role in the evolution of reproductive mechanisms in birds.     

Forest fragmentation and plant reproductive success: a case study in four perennial herbs

We assessed the effects of habitat fragmentation on reproductive success in natural populations of four forest herbs with differing life-history traits and whose distribution patterns appeared to be negatively affected by decreased habitat size and/or increased isolation: Carex sylvatica, Galium odoratum, Sanicula europaea and Veronica montana. Our aims were to test (1) whether habitat size and isolation are positively correlated with population size and isolation, respectively, (2) whether plant reproductive success, a major component of plant fitness, is reduced in small and/or isolated populations when also accounting for differences in habitat quality (edaphic conditions, light intensity) and the effects of plant size, and (3) whether species with different life histories are affected differently. There were significant positive relationships between habitat and population size and between habitat and population isolation in some, but not all of the species. We mostly found no negative effects of small population size or isolation on reproduction. However, reproductive success was reduced in small populations of Sanicula, and this effect was independent of differences in plant size and environmental conditions. The reduced fecundity in small populations may be a consequence of the Allee-effect, a possible mechanism being pollen limitation. Furthermore, the proportion of flowering ramets was reduced in small and isolated populations of Galium, which may have been caused by changes in population structure. Lastly, we found some evidence for largely outcrossing, non-clonal species to be more sensitive to reductions in population size, at least in terms of their reproductive success.     

青藏高原不同生境下湿生扁蕾(Gentianopsis paludosa)个体大小依赖的繁殖分配

植物对资源的投资和分配是生态学中的重要问题,它反映了植物应对环境变化时的生活史策略。选择青藏高原东缘同一海拔下的嵩草草甸(Kobresia sp.meadow)、金露梅灌丛(Potentilla fruticosa shrub meadow)以及草甸-灌丛交错带3种生境类型,并以3种生境下的湿生扁蕾(Gentianopsis paludosa)为对象,研究了其繁殖分配特征。结果发现:(1)在种群水平上,在生境从草甸经交错带到灌丛的变化中,湿生扁蕾个体大小和繁殖分配比例逐渐增加;3个种群湿生扁蕾的总花数目没有显著差异,但草甸生境湿生扁蕾的蕾期花数目显著高于灌丛生境,而果期花数目则显著低于灌丛生境;(2)在个体水平上,湿生扁蕾的繁殖绝对投入与个体大小显著正相关,且各种群植株都存在繁殖所需的个体大小阈值,而繁殖阈值在生境从草甸经交错带到灌丛的过渡中逐渐减小;湿生扁蕾的繁殖相对投入与个体大小负相关,但相关系数随着生境从草甸经交错带到灌丛的过渡中逐渐减小;各种群花数目与湿生扁蕾植株个体大小显著正相关。研究表明,湿生扁蕾的繁殖投资存在大小依赖效应,但生境差异会对其繁殖投资和生活史策略造成显著影响,而这种影响主要是由不同生境下自然条件的不同造成的。同时,资源分配也与湿生扁蕾的遗传特性和延迟自交的繁育系统特征有关。湿生扁蕾这种不同生境下个体大小依赖的繁殖投资差异是湿生扁蕾与其生境长期适应和进化(生境选择)的结果。     

On noninvasive assessment of the reproductive status of male Campbell’s dwarf hamsters (<Emphasis Type="Italic">Phodopus campbelli</Emphasis>) using digital images

The possibility of estimating the reproductive status of males using computer analysis of the contours of testes and midventral gland (MVG) in digital images was tested in Campbell’s dwarf hamsters (Phodopus campbelli). Relationships between the anogenital distance (AGD) and the diameters of testes and MVG were analyzed. The Pearson coefficient of correlation between the actual size of testes and that estimated from their visible contours proved to depend on the amount of white fat and varied from 0.9 in low-fat to 0.67 in high-fat hamsters. A strong correlation was revealed between the AGD and the diameter of testes in digital images. Both these parameters proved to be significantly greater in the reproductive period than in the non-reproductive (winter) period, while the diameter of MVG remained unchanged. These results agree with data on the winter ecology of Campbell dwarf hamsters and confirm that the above method can be used for assessing seasonal changes in the reproductive status of males.     

Effect of Seasonal Change on Testicular Protein Expression in White Roman Geese

The purpose of this study was to investigate the change in protein expression in the testes of ganders at various breeding stages. A total of nine 3-year-old male White Roman ganders were used. The blood and testis samples were collected at the nonbreeding, sexual reactivation, and breeding stages for sex hormone analysis and proteomic analysis, respectively. The testicular weight and serum testosterone observed for ganders at the breeding stage were higher than those for ganders at nonbreeding and sexual reactivation stages (P?<?0.05). There were 124 protein spots differentially expressed in the testes of ganders at various reproductive stages. A total of 107 protein spots of 74 proteins was identified through mass spectrometry. Most of the differentially expressed proteins were responsible for the molecular functions of protein binding (24%) and catalytic activity (16%). A functional pathway analysis suggested that proteins involved in steroidogenesis, metabolism, and spermatogenesis pathways changed in the White Roman geese at various reproductive stages. In conclusion, ganders at various reproductive stages exhibited different levels of testosterone and protein expression in the testes. The varied levels of the proteins might be essential and unique key factors in seasonal reproduction in ganders.     

三种同域分布喉毛花的繁殖分配

以青藏高原高寒草甸中三种同域分布的喉毛花为研究对象,通过比较三个种的植株性状和繁殖分配,探讨繁殖分配的种间差异及其与植株个体大小的关系。结果表明:(1)三个种的植株高度、顶花大小和单株花数目、繁殖分配均存在种间差异,这可能与其各自的交配系统和具体的生境以及相应的生活史对策有关;(2)在三种喉毛花中,投入到营养器官和繁殖器官的绝对资源量均呈显著正相关,未检测到植株生长和繁殖间的权衡关系;(3)三个种的个体大小与繁殖器官生物量均呈显著正相关,而与繁殖分配均呈显著负相关,这表明个体越大,繁殖投入越高,而繁殖分配越低,与以往研究结果一致,这可能是由于繁殖分配与个体大小之间存在异速关系。     

Effects of cocaine hydrochloride on the male reproductive system

The reproductive system effects of cocaine were studied in male rats. The analysis included measurements of circulating levels of luteinizing hormone (LH) and testosterone (T) by radioimmunoassay (RIA). The weights of the testes and sex accessory organs were also assessed and compared with control animals. Dosage level, duration of treatment, and interval between injection and sacrifice were the parameters examined. Following a single intraperitoneal (IP) injection, LH levels decreased over a 3-hour period. At a high dosage (40 mg/kg), cocaine caused a significant elevation in serum T followed by a significant depression of T for at least 2 hours. When administered chronically for 15 days, the low dose group (10 mg/kg) did not vary significantly from the vehicle controls. However, the high dose group had lower LH and T levels, as well as correspondingly lighter weight seminal vesicles and epididymis. No changes were noted in the weights of the ventral prostate or testes. This research suggests that cocaine acts primarily at the hypothalamic-hypophyseal axis with a possible secondary action at the gonadal level.     

Effects of Aluminum Exposure on Serum Sex Hormones and Androgen Receptor Expression in Male Rats

The effects of aluminum (Al) exposure on reproductive functions of male rats were investigated. Forty male Wistar rats (4?weeks old) weighing 75-95?g were randomly divided into four groups and orally exposed to 0 (control group GC), 64.18 (low-dose group GL), 128.36 (middle-dose group GM), and 256.72 (high-dose group GH) mg/kg aluminum trichloride in drinking water for 120?days. The levels of testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were determined by radioimmunoassay. The androgen receptor (AR) expressions in testes were detected respectively by immunohistochemistry and time quantitative PCR. Results showed that the levels of T and LH in GM and GH were lower than those in GC (P??0.05). AR protein expressions in GM and GH were lower than those in GC (P?相似文献   

Nonlinear continuum of egg size-number trade-offs in a snake: is egg-size variation fitness related?

The relationship between offspring size and offspring number is crucial to life history evolution. To examine how these two life history variables are coupled and whether an altered balance between them will result in changes in maternal fitness, we manipulated clutch size of the Chinese cobra (Naja atra) by using the techniques of hormonal manipulation and follicle ablation. Females receiving exogenous follicle-stimulating hormone produced more but smaller eggs, and females undergoing follicle ablation produced fewer but larger eggs. Neither body size (body mass and snout-vent length) at hatching nor egg mass at oviposition had a role in determining hatchling survival and growth. Female hatchlings were more likely to die in early post-hatching days and grew more slowly than male hatchlings. Our data show that: (1) there is a nonlinear continuum of egg size-number trade-offs in N. atra within which there is a single inflexion where the rate at which egg size decreases with increasing clutch size, or clutch size increases with decreasing egg size, is maximized; (2) there is a fixed upper limit to egg size for a given-sized female, and the limit is not determined by her body volume; (3) egg size has no role in determining hatchling survival and growth; and (4) the extent to which females may enjoy reproductive benefits in a given reproductive episode depends on how well egg size and egg number are balanced.     

Female masculinization and reproductive life history in the western mosquitofish (<Emphasis Type="Italic">Gambusia affinis</Emphasis>)

In this study, we explored the relationship between female masculinization and various morphological and reproductive parameters of male and female western mosquitofish (Gambusia affinis), including body size, anal fin length, testes mass and female fecundity. We detected high levels of female masculinization in the Brazos and Little Brazos Rivers (Falls County, Texas) in March 2008, but not 2009. In both populations, masculinized females were smaller, possessed shorter anal fins, and had significantly lower total fecundity (collective number of eggs and embryos) compared to non-masculinized females. In addition, 2008 non-masculinized females were smaller and less fecund than 2009 non-masculinized females in both populations. Moreover, 2008 males were smaller, had shorter gonopodia, and smaller testes than 2009 males. Our results support the hypothesis that female masculinization can have a strong influence on reproductive life history and population dynamics of livebearing fishes.     

荒漠草原土壤相对湿度对猪毛蒿表型可塑性的影响

猪毛蒿(Artemisia scoparia)为菊科蒿属草本植物,是一种适应性较强的广幅种。研究荒漠草原不同土壤相对湿度条件下猪毛蒿的表型可塑性,对认识异质生境下猪毛蒿的生存适应策略具有重要的生态学意义。结果表明:株高、茎粗、根长、根重和单株生物量均表现出随土壤相对湿度的增大而增加的趋势,对异质生境具有较强的可塑性,而根冠比则表现出相对的稳定性。植株不同部位生物量大小排序为:上部中部下部,且植株下部显著大于上部生物量(P0.05)。土壤相对湿度40%生境下的头状花序数量和重量显著高于土壤相对湿度30%和30%—40%生境。繁殖器官绝对投入量(lg R)随着个体大小(lg V)的增大呈极显著的增加(P0.001),繁殖阈值介于1.868—2.006 g。随着土壤相对湿度的增加,繁殖分配比例极显著增大(P0.001)。营养器官和繁殖器官生物量、头状花序重量和数量、地下生物量和地上生物量均呈极显著线性正相关关系(P0.001),存在正向权衡。单个头状花序重量并不随个体大小和头状花序数量的增加而发生显著变化(P0.05),且在不同土壤相对湿度和不同部位间均无显著差异(P0.05)。由此可见,猪毛蒿在异质生境下产生的可塑性是其生存繁殖的重要反应机制之一。     

Daytime variations of serum testosterone and luteinizing hormone in captive thick-tailed bush babies (Galago garnetti)

Mean daytime serum levels of testosterone (T) and luteinizing hormone (LH) were determined in eight male thick-tailed bush babies at different times of the day by radioimmunoassay and leydig cell bioassay respectively. Blood samples were obtained twice a week from each animal at different times of the day between 08:30 and 16:00. This was carried out for a period of eight weeks. There was significantly higher mean serum T levels in the morning compared to evening hours (p<0.05). There was no significant variation in mean serum LH levels, and no significant correlation between serum T and LH levels.     

Female affiliative preference depends on reproductive state in the African cichlid fish, Astatotilapia burtoni

Hormones play a pivotal role in reproductive behavior and havebeen implicated in mediating mate choice decisions. Here weasked whether the differences in female reproductive state dependenton changes in hormone levels correspond to changes in femaleaffiliation with males. In the African cichlid fish, Astatotilapiaburtoni, males shift between reproductive (territorial; T) andnon-reproductive (non-territorial; NT) states depending on socialcontext while females alternate between gravid (egg bearing;G) and non-gravid (NG) reproductive states independent of socialconditions. Moreover, the brain-pituitary-gonadal axis controllingreproduction and reproductive hormones is substantially remodeledin both males and females depending on reproductive state. Tomeasure affiliative preference, gravid and non-gravid femaleswere given the choice of associating with T or NT males. Gravidfemales preferentially associated with T males, whereas non-gravidfemales showed no preference. To discover whether gravid femalesuse male size independent of dominance status as a cue for theirchoice, gravid females were given a choice between territorialmales of different sizes. Gravid females preferred the smallerof two T males, but the smaller T males were significantly moreactive. Our results show that associative change could be animportant behavioral mediator between hormonal cues and reproductivesuccess, and that females use a hierarchy of cues in decision-making,preferring to affiliate with T over NT males and, among T males,preferring more active animals.     

Effects of enhanced UV-B radiation on the hormonal content of vegetative and reproductive tissues of two tomato cultivars and their relationships with reproductive characteristics

The effects of enhanced UV-B radiation on hormone changes in vegetative and reproductive tissues of tomato (Lycopersicon esculentum Mill.) and their relationships with reproductive characteristics were studied. Two cultivars, TongHui (TH) and XiaGuang (XG), were grown in the field for one growing season under ambient (Control), ambient plus 2.54 kJ m^–2 d^–1 (T1) or ambient plus 4.25 kJ m^–2 d^–1 (T2) of supplemental ultraviolet-B (280–320 nm). The number of open flowers increased significantly in the TH cultivar under T2 while it declined in the XG cultivar under T1. Although pollen germination from both cultivars was inhibited by UV-B treatment, fruit number was enhanced in the TH cultivar at both UV-B doses and in the XG cultivar at the low dose. On the other hand, seed size (dry weight) was reduced in the XG cultivar by both UV-B doses and in the TH cultivar at the low UV-B dose. The final germination rates of seeds from control and UV-B treated plants of both cultivars showed no significant differences (p > 0.05), while germination was delayed in the TH cultivar at both doses of UV-B and in the XG cultivar only for T2. To determine the mechanism of UV-B's effects on developmental processes, hormone concentrations in leaves, pistils and seeds were analyzed using ELISA on partially purified extracts. The results suggested that enhanced UV-B radiation induced hormone changes in both vegetative and reproductive tissues. The alteration of flower number may be associated with the changes of ZR in leaves under enhanced UV-B radiation and the delayed germination may due to the changes in seed ABA and GAs.     

Seasonal variation in testes size in Polish Merino rams and its relationship to reproductive performance in spring

Observations relating testes size to body weight in growing and adult Polish Merino rams were performed during 3 consecutive years in a flock of 1700 pedigree ewes. October-born ram lambs were measured for testis diameter (TD), scrotal circumference (SC), and body weight (BW) at 100 (January), 150 (March), 180 (April), 240 (June), 365 (October), and 480 d (February) of age. In adult rams (n = 63 to 73 per year) BW and SC were measured in March, May (prior to breeding), August and October. Semen quality was evaluated before each breeding season, and the results of controlled reproductive performance (2 natural services to designated rams) were analyzed. Indices were applied to relate testis size to body weight: TD BW , SC BW and TW BW . Heritability estimates of testes indices in ram lambs at 100 to 240 d and at 480 d of age ranged from 0.21 to 0.36 (SE = 0.067 to 0.090). In adult rams SC measurements within months in consecutive years were repeatable (r = 0.55 to 0.68; P相似文献