Energetic cost of spawning in male and female Atlantic salmon (Salmo salar L.)

Energetic expenditure during spawning of male and female 1 -sea-winter Atlantic salmon, Salmo salar L., was measured. Before spawning, the somatic energy content per unit weight did not differ between the sexes. The testes content offat was 0.24, of carbohydrate 8.89, of water 1.21 and of ash 1.61 times as high as that of the ovaries. Just prior to spawning, mean gonadosomatic index (GSI; wet weight, %) in males was 4.36 and in females 20.26, and expressed as energy ratios (kJ, %) 4.47 and 27.75, respectively. During spawning the energy loss of male soma was higher (35.57%) than that of females (25.00%). This was a result of higher loss of fat in males than in females. Total energy cost of spawning in males and females was on average 51.8 and 51.4%, respectively.     

Allocation of resources in an European cyprinid during maturation period as measured by nucleic acids

Changes in the nucleic acid levels of different tissues during a regular gonadal maturation were used to investigate the sex-related size differences in Iberian barbel, Barbus sclateri. Gonadal DNA concentration was associated with gonadal development in both sexes. There was a decline in DNA when ovaries were ripe. In contrast, the maximum size of the testes was related with highest gonadal DNA concentrations. Gonadal growth was not related with liver RNA : DNA ratios of male, while it was with female ratios. White muscle DNA concentrations indicate that somatic cell volume decreased during gonadal growth in both sexes. This suggests the translocation of several elements toward the gonad. Moreover, during gonadal maturation period adult barbel showed no change in their somatic growth. However, males apparently were in poorer metabolic condition (lower muscle RNA : DNA ratio) than females. Females may have allocated additional energy to self-maintenance rather than to breeding effort and it might influenced the cumulative annual growth. One might reasonably assume that there is a trade-off between investment in current versus future reproductive success in female. This result was not seen in males.     

Reproductive cycle and gonadal development of the Atlantic sea urchin Arbacia punctulata in the Gulf of Mexico: changes in nutritive phagocytes in relation to gametogenesis

ABSTRACT

The annual reproductive cycle comprises steady gametogenic activities that synchronize gonadal maturation and spawning rhythms, which are important for aquatic organisms including marine echinoderms (Echinodermata, Echinoidea). In this study, we report the annual reproductive cycle, gonadal development, and changes in nutritive phagocytes (NPs, which accumulate nutrients in germ cells) in relation to gametogenesis of the Atlantic sea urchin (Arbacia punctulata, an edible echinoid) in the Gulf of Mexico. Monthly changes in gonadal development and maturation were observed morphologically and histologically. We calculated gonadosomatic index (GSI) and compared the stages of gonadal development in order to determine the NPs index, and characteristics of germ cells (eggs and sperm) during the annual reproductive cycle. According to GSI and histological analyses, gametogenic activities were classified into four stages of both sexes: mature (June–August), spent (September–November), recovery (December–March), and growing (April–May). The GSI values in both sexes were high during summer months. In males, testicular lobules were densely packed with sperm from June to August. In females, however, mature eggs first appeared in some ovaries in May, numerically increased from June to July, and decreased in August. During gametogenesis, on the other hand, NPs in both testes and ovaries were depleted from June to August. Collectively, our results suggest that the Atlantic sea urchin spawns during summer months in the Gulf of Mexico. This is the first report, to the best of our knowledge, on gonadal development and changes in NPs during the annual reproductive cycle of any Arbacia species in the Gulf of Mexico.     

The energy costs of sexual dimorphism in mole-rats are morphological not behavioural

Different reproductive strategies of males and females may lead to the evolution of differences in their energetic costs of reproduction, overall energetic requirements and physiological performances. Sexual dimorphism is often associated with costly behaviours (e.g. large males might have a competitive advantage in fighting, which is energetically expensive). However, few studies of mammals have directly compared the energy costs of reproductive activities between sexes. We compared the daily energy expenditure (DEE) and resting metabolic rate (RMR) of males and females of two species of mole-rat, Bathyergus janetta and Georychus capensis (the former is sexually dimorphic in body size and the latter is not) during a period of intense digging when males seek females. We hypothesized that large body size might be indicative of greater digging or fighting capabilities, and hence greater mass-independent DEE values in males of the sexually dimorphic species. In contrast to this prediction, although absolute values of DEE were greater in B. janetta males, mass-independent values were not. No differences were apparent between sexes in G. capensis. By comparison, although RMR values were greater in B. janetta than G. capensis, no differences were apparent between the sexes for either species. The energy cost of dimorphism is most likely to be the cost of maintenance of a large body size, and not the cost of behaviours performed when an individual is large.     

Reproductive effort and costs of reproduction do not explain female-biased sex ratios in the moss Pseudocalliergon trifarium (Amblystegiaceae)

A fundamental assumption in life-history theory is that reproduction is costly. Higher reproductive investment for fruits than for flowers may result in larger costs of reproduction in females than in males, which is often used to explain male-skewed sex ratios in unisexual seed plants. In contrast, bryophytes have predominantly female-biased sex ratios, suggested to be a product of a higher average cost of sexual reproduction in males. Empirical evidence to support this notion is largely lacking. We investigated sex-specific reproductive effort and costs in the unisexual moss Pseudocalliergon trifarium that has a female-dominated expressed sex ratio and rarely produces sporophytes. Annual vegetative segment mass did not differ among male, female, and non-expressing individuals, indicating that there was no threshold-size for sex expression. Mean and annual mass of sexual branches were higher in females than in males, but branch number per segment did not differ between sexes. Prefertilization reproductive effort for females was significantly greater (11.2%) than for males (8.6%). No cost for sexual branch production in terms of reduced relative vegetative growth or decreased investment in reproductive structures in consecutive years was detected. A higher realized reproductive cost in males cannot explain the unbalanced sex ratio in the study species.     

The cost of sex: quantifying energetic investment in gamete production by males and females

The relative energetic investment in reproduction between the sexes forms the basis of sexual selection and life history theories in evolutionary biology. It is often assumed that males invest considerably less in gametes than females, but quantifying the energetic cost of gamete production in both sexes has remained a difficult challenge. For a broad diversity of species (invertebrates, reptiles, amphibians, fishes, birds, and mammals), we compared the cost of gamete production between the sexes in terms of the investment in gonad tissue and the rate of gamete biomass production. Investment in gonad biomass was nearly proportional to body mass in both sexes, but gamete biomass production rate was approximately two to four orders of magnitude higher in females. In both males and females, gamete biomass production rate increased with organism mass as a power law, much like individual metabolic rate. This suggests that whole-organism energetics may act as a primary constraint on gamete production among species. Residual variation in sperm production rate was positively correlated with relative testes size. Together, these results suggest that understanding the heterogeneity in rates of gamete production among species requires joint consideration of the effects of gonad mass and metabolism.     

Physiological costs of reproduction in the Sydney rock oyster<Emphasis Type="Italic"> Saccostrea glomerata</Emphasis>

In this study, triploid Sydney rock oysters Saccostrea glomerata, which do not reproduce and have only limited gonadal development, were used to calculate the cost of producing and maintaining somatic tissues. The consumption of oxygen was measured and converted to units of energy expended. The consumption of oxygen of diploid oysters, in different stages of the reproductive cycle, was also measured. Knowing the costs of producing and maintaining somatic tissues (obtained from the triploid oysters), it was possible to calculate the energy demand of somatic and reproductive tissues of diploid oysters. The focus of this study was to test whether this method would work, to investigate if this method would give results in accordance with modern life-history theory and to test hypotheses about costs of reproduction in oysters. It was found that in diploid oysters, 27% of the consumed oxygen was needed for reproductive processes. It was also found that the costs of production and maintenance of reproductive tissues were on average 84% of those of somatic tissues. Costs for the production and maintenance of somatic tissues decreased over time. Costs for reproduction also decreased, but were dependent on the stage of gonadal development. If the relative mass of gametes in the gonads was large, the costs were relatively small; if the mass was relatively small, the costs were large. Differences between traits of males and females were never significant, suggesting that reproductive effort and costs were similar in males and females. It was estimated that if diploid oysters did not reproduce, they could gain 64% more somatic ash-free dry mass. Thus, in terms of growth, reproduction is an expensive activity.     

Annual reproductive cycle of a bitterling, Tanakia tanago, reared in an outdoor tank

From June 2000 to September 2001, we investigated the presence of eggs spawned in Margaritifera laevis and the seasonal changes in the gonads of Tanakia tanago. Eggs were observed from mid-March to mid-September. In females with a shrunken ovipositor, as the GSI gradually increased, most ovaries were in the prespawning phase (Oct-Mar). As the GSI increased further, most ovaries were in the early spawning phase (Mar-Jun). As the GSI gradually deceased, ovaries in the late spawning phase appeared (Jun-Sep). When the GSI was very low, most ovaries were in the postspawning phase (Sep-Oct). In males, when the GSI was low, most testes were in the early prespawning phase from Oct-Dec. As the GSI gradually increased, most testes were in the late prespawning phase (Dec-Jan). As the GSI increased further, testes were in the early spawning phase (Jan-Jun). As the GSI gradually decreased, amost testes were in the late spawning phase (Jun-Sep). When the GSI was very low, most testes were in the postspawning phase (Sep-Oct). These results indicate that T. tanago has a distinct annual reproductive cycle and is a spring-autumn spawner. Based on the relationship between reproductive activity and environmental factors, the spawning season of T. tanago appears to be initiated by increasing temperature and / or longer days in spring and to be terminated by shorter days in autumn.     

Costs of reproduction in a population of European adders

Eleven years of data on a small population of adders (Vipera berus) in southern Sweden provide quantitative information on the nature and degree of costs faced by reproducing animals. Reproduction imposes both an energy cost (measured by loss in body mass) and a mortality cost on adders of both sexes. The extent of the energy cost is broadly independent of levels of reproductive activity in males, but mortality costs are highest for large males, perhaps because they are more obvious to predators. In females, energy costs include a high ‘fixed’ (fecundity-independent) component, such that a large litter may cost little more to produce than would a small litter. Energy costs and mortality costs are separate in males, but inter-related in females. Mortality of reproducing females is high (40% per year), primarily because post-parturient females are emaciated and must forage actively, hence increasing their vulnerability to predators. Females producing relatively large litters (high Relative Clutch Mass) lose more body mass, and are less likely to survive after reproducing. The observed low reproductive frequencies of female adders may result from the presence of high fecundity-independent costs of reproduction.     

Both sexes suffer increased parasitism and reduced energy storage as costs of reproduction in the brown anole,Anolis sagrei

Sexual selection theory proposes that males suffer reduced immune function and increased parasitism as costs of expressing sexual signals. Life‐history theory proposes that females suffer the same costs because of inherent trade‐offs between reproduction and self‐maintenance. Mechanistically, each theory invokes an energetic trade‐off, although few experiments have directly compared these costs of reproduction between the sexes as a result of fundamental sex differences in the nature of reproductive investment and a tendency for each theory to focus on a single sex. To test whether males and females experience comparable costs of reproduction in terms of energetics, immune function, and parasitism, we used gonadectomy to eliminate most aspects of reproductive investment in wild brown anole lizards (Anolis sagrei) of both sexes. We compared these nonreproductive males and females with intact, reproductive controls with respect to stored energy (fat bodies), immune function (swelling response to phytohemagglutinin), and the prevalence and intensity of infection by four types of parasite (gastric nematodes, intestinal nematodes, faecal coccidia, and ectoparasitic mites). Gonadectomized anoles experienced dramatic increases in fat storage that were accompanied by decreases in the prevalence of intestinal nematodes and in the intensity of coccidia infection. These costs of reproduction were comparable between males and females, although neither sex exhibited the predicted increase in immune function after gonadectomy. Our results suggest that, despite fundamental sex differences in the nature of reproductive investment, both male and female anoles experience similar costs of reproduction with respect to energy storage and some aspects of parasitism.     

Immunological sex differences in socially promiscuous African ground squirrels

Differences in how males and females respond to foreign antigens are common across taxa. Such sexual differences in the immune system are predicted to be greater in species with high promiscuity and sociality as these factors increase the likelihood of disease transmission. Intense sperm competition is thought to further this sexual dichotomy as increased investment in spermatogenesis likely incurs additional immunological costs. Xerus inauris, a ground squirrel found throughout southern Africa, is extremely social and promiscuous with one of the highest male reproductive investments among rodents. These life-history attributes suggest males and females should demonstrate a large dichotomy in immunity. Contrary to our prediction, we found no difference in spleen mass between the sexes. However, we did find significant biases in leukocyte types and red blood cell counts, possibly reflecting responses to parasite types. Among males, we predicted greater investments in spermatogenesis would result in reduced immunological investments. We found a negative association between testes and spleen size and a positive relationship between testes and number of lice suggesting trade-offs in reproductive investment possibly due to the costs associated with spermatogenesis and immunity. We suggest when measuring sexual differences in immunity it is important to consider the effects of reproductive pressures, parasite types, and life history costs.     

Targeted disruption of luteinizing hormone/human chorionic gonadotropin receptor gene

LH/hCG receptors were disrupted by gene targeting in embryonic stem cells. The disruption resulted in infertility in both sexes. The gonads contained no receptor mRNA or receptor protein. Serum LH levels were greatly elevated, and FSH levels were moderately elevated in both sexes; estradiol and progesterone levels decreased but were not totally suppressed in females; testosterone levels were dramatically decreased and estradiol levels moderately elevated in males. The external and internal genitalia were grossly underdeveloped in both sexes. Abnormalities included ambiguous vaginal opening, abdominal testes, micropenis, dramatically decreased weights of the gonads and reproductive tract, arrested follicular growth beyond antral stage, disarray of seminiferous tubules, diminished number and hypotrophy of Leydig cells, and spermatogenic arrest beyond the round spermatid stage. LH/hCG receptor gene disruption had no effect on FSH receptor mRNA levels in ovaries and testes, progesterone receptor (PR) levels in ovaries and androgen receptor (AR) levels in testes. However, it caused a dramatic decrease in StAR and estrogen receptor-alpha (ERalpha) mRNA levels and an increase in ERbeta mRNA levels in both ovaries and testes. Estradiol and progesterone replacement therapy in females and testosterone replacement in males, to determine whether phenotype and biochemical changes were a consequence of decreased gonadal steroid levels or due to a loss of LH signaling, revealed complete restoration of some and partial restoration of others. Nevertheless, the animals remained infertile. It is anticipated that the LH receptor knockout animals will increase our current understanding of gonadal and nongonadal actions of LH and hCG.     

Seasonal gonadal development and age-related maturity patterns of introduced pumpkinseed (Lepomis gibbosus Linnaeus, 1758) in a heated thermal reservoir and an adjacent river reach

Testis and ovarian maturation status, maturity profile and gonado-somatic index (GSI) were assessed in pumpkinseed (Lepomis gibbosus) collected from Mirgenbach, a cooling-water reservoir associated with a nuclear power plant, and from the River Moselle 7 km downstream of the reservoir's thermal outflow. Histological investigation indicated that in both sexes, gonadal development of pumpkinseed in the heated reservoir was more advanced than in the cooler Moselle River throughout the breeding season. The histological maturity profile of reservoir males ranked by the advancement of sperm cells was highly correlated with its GSI (r_s=0.73, P<0.001). GSI of females in the reservoir increased with the stage at maturity, but GSI was not significantly correlated with total length, age or growth rate of the individual. All sampled individuals of both sexes were mature at age 1 in the heated reservoir, whereas 48% of age 1 males and 57% of age 1 females were not mature in the river. GSI patterns suggest that males in the reservoir adopted one of two reproductive strategies (nesters or cuckolders), whereas no small males with large enough testes to be considered cuckolders were apparent in the river. The warm thermal regime of Mirgenbach Reservoir led to precocial maturity, early season reproduction, and the greater prevalence of apparent cuckolder males than would normally occur in this climatic zone.     

Gonochorism and seasonal variations in the gonads of the labrid Symphodus (Crenilabrus) ocellatus (Forsskål)

A histological study of gonadal organization of 354 Symphodus ocellatus caught in the Bay of Naples from June 1985 to December 1986 demonstrated the absence of sexual inversion in this species. Four phases of gonadal development, related to the seasonal cycle, are described. During the reproductive period the ovaries showed the asynchrony in oocyte development that is typical of serial spawners. The testes of three types of males present in this species (territorial, satellite and sneaker males) were examined: the only difference found was in the gonadal growth pattern during the reproductive period.     

Reproductive biology of Astyanax fasciatus (Pisces: Characiformes) in a reservoir in southeastern Brazil

To study the reproductive biology of Astyanax fasciatus (Cuvier, 1819) in Furnas Reservoir, Minas Gerais, Brazil, a total of 1307 specimens were captured in bimonthly sampling from August 1993 to July 1994. The sex ratio showed a predominance of females, representing 65.2% of the total sample. The stages of gonadal maturation and spawning type were determined through macro- and microscopic analysis of the gonads as well as by variation in the gonadosomatic indices. A . fasciatus showed fractionated spawning and reproduction throughout the year, with spawning peaks influenced by water temperature and rainfall. Males and females initiated gonadal maturation at a mean standard length of 6.4 and 6.5 cm, respectively. During gonadal maturation, females showed a reduction in hepatosomatic index (from 1.06 to 0.83), suggesting that hepatic substances are transferred from the liver to the ovaries. In the reproductive period, A. fasciatus had lower stomach repletion and coelomic fat indices, indicating that this species ate less and consumed more fat reserves when reproduction had the maximum GSI (11.3 for females and 2.7 for males). Weight of the ovaries had a positive influence on the condition factor (K1), as the lowest K2 value (weight without gonads) were obtained during maturation, confirming the influence of the ovaries upon the physiological condition of the females. In weight–length relationship, parameter b was 3.02 for females and 2.23 for males, and the correlation coefficient ( r ²) was 0.84 and 0.66, respectively.     

Lipid dynamics in the common torpedo, Torpedo torpedo, from the south eastern Mediterranean

Liver stores the major part of lipids in both mature and immature Torpedo torpedo of both sexes. Fluctuations in the lipid contents of liver, muscles and gonads of immature fish followed the relative change in food intake throughout the year. Hepatic and muscular lipids in mature females diminished before ovulation and were intensively consumed in the last stages of gestation (in pregnant females). After parturition, the recovery of the lipid stores was very rapid due to intensive food uptake. Storing of hepatic lipids in mature males started a little before gonadal maturation and reached a maximum in January and February while gonadal lipids decreased in the same period. Gonadal lipid for both sexes fluctuated in parallel to fluctuations in the GSI. Water content showed significant inverse correlation with lipid content in both liver and gonad tissues, but no significant correlation was recorded in the muscle tissues.     

Reproductive seasonality of the detritivorous fish <Emphasis Type="Italic">Cyphocharax abramoides</Emphasis> (Kner, 1958) (Characiformes: Curimatidae) in flooded rivers of the eastern Amazon

The Lower Anapu River, Eastern Amazon, has a discrete flood pulse with narrow flooded areas due to the reduced influence of tides. In this environment, local precipitation might act as an important factor in the input of detritus, which can serve as a trigger for fish reproductive period. Therefore, this paper aims to determine the effects of local precipitation on the reproductive ecology of an abundant detritivorous fish in flooded rivers. Between May 2012 and April 2013, 886 specimens (471 females and 415 males) were captured monthly using gill nets. Individuals were measured, weighted, sexed, and the gonadal development stage was defined macroscopically and confirmed histologically. Sex ratio, length-weight relationship (LWR), condition factor (k), Gonadosomatic Index (GSI), relative frequency of maturity stages, and size at first gonadal maturity (L₅₀) were estimated and tested in relation to rainfall periods. There was no difference between the expected sex ratio (1:1), and both males and females showed polyphasic growth. The condition factor indicated higher values at the beginning of the rainy season and lower values during the dry season for both sexes. GSI and relative frequency of mature individuals indicated a long reproduction period with gonadal investment starting within the dry season until early in the rainy season for spawning within the rains. The L₅₀ value showed that males reach sexual maturity before females. Results indicated a reproductive pattern strongly influenced by rainfall, corroborating the importance of local precipitation for lacustrine environments.     

Comparison of Reproductive Indicators and Analysis of the Reproductive Seasonality of the Tinfoil Barb, Puntius schwanenfeldii, in the Perak River, Malaysia

The reproductive seasonality of Puntius schwanenfeldii from the Perak River, Malaysia was investigated over a 19 month period. Females greater than 160g had mature or rematuring ovaries, and males of all sizes had mature testes throughout the study period. Analysis of female reproductive condition was based upon the presence of post ovulatory follicles (POF), the gonadosomatic index (GSI) and the volume fraction of stage IV oocytes (IV%), and GSI and presence of tubercles for males. Recrudescence followed immediately after ovulation, which allowed the use of objective thresholds to identify recently spawned females during the GSI and IV% recovery period. GSI and IV% were the best indicators of reproductive patterns as a result of their recovery period being longer than for POF. Male tubercles and GSI showed some statistically significant variation, but no clear relation with observed changes in female indicators. Reproduction was apparently aseasonal, and this pattern is likely an effect of flow regulation by dams which have virtually eliminated the dominant flood period and most seasonal flow variation. Hypothesized shifts in the reproductive seasonality due to flow regulation are consistent with predictions based on life history theory under conditions of altered environmental seasonality.     

Biochemical content, energy composition and reproductive effort in the broadcasting sea star Asterias vulgaris over the spawning period

To assess sex differences in reproductive effort, we examined the biochemical composition and energetic content of the principal body components of the broadcast spawning sea star Asterias vulgaris in the Mingan Islands in the northern Gulf of St. Lawrence, eastern Canada. The body wall was the most stable body component, showing no variations in mass or in lipid and protein content (and total energetic content) between sexes or during spawning. Patterns in the gonads differed between sexes and with spawning. The lipid, protein and carbohydrate content of the ovary dropped during spawning, while only the protein content of the testis decreased significantly. Reproductive effort, expressed as loss of energy in the gonads during spawning for an individual weighing 10 g in underwater mass (8.2 cm in radius), was six times greater in females (49.5 kJ) than males (7.9 kJ). The energetic content of the pyloric caeca also decreased during spawning, by 17.7 kJ in females and 21.5 kJ in males, mainly due to a decrease in lipids. If this decrease is included as reproductive effort, it lessens the gender difference. The caecum decrease possibly represented expenditures due to formation of aggregations or the expulsion of gametes during spawning. Effectively, we observed aggregations during a massive spawning in this population. The sex ratio did not differ from 1:1 in all size classes sampled. This suggests that, unless males suffer higher mortality, females manage to allocate as much energy to somatic growth as males, possibly by feeding at higher rates to compensate for their higher reproductive effort. Stomach protein content tended to be higher in females than males and may indicate greater muscular development to facilitate digestion.