Sex‐specific reproductive investment of summer spawners of Illex argentinus in the southwest Atlantic

Energy investment in reproduction and somatic growth was investigated for summer spawners of the Argentinean shortfin squid Illex argentinus in the southwest Atlantic Ocean. Sampled squids were examined for morphometry and intensity of feeding behavior associated with reproductive maturation. Residuals generated from length‐weight relationships were analyzed to determine patterns of energy allocation between somatic and reproductive growth. Both females and males showed similar rates of increase for eviscerated body mass and digestive gland mass relative to mantle length, but the rate of increase for total reproductive organ weight relative to mantle length in females was three times that of males. For females, condition of somatic tissues deteriorated until the mature stage, but somatic condition improved after the onset of maturity. In males, there was no correlation between somatic condition and phases of reproductive maturity. Reproductive investment decreased as sexual maturation progressed for both females and males, with the lowest investment occurring at the functionally mature stage. Residual analysis indicated that female reproductive development was at the expense of body muscle growth during the immature and maturing stages, but energy invested in reproduction after onset of maturity was probably met by food intake. However, in males both reproductive maturation and somatic growth proceeded concurrently so that energy allocated to reproduction was related to food intake throughout the process of maturation. For both males and females, there was little evidence of trade‐offs between the digestive gland and reproductive growth, as no significant correlation was found between dorsal mantle length‐digestive gland weight residuals. The role of the digestive gland as an energy reserve for gonadal growth should be reconsidered. Additionally, feeding intensity by both males and females decreased after the onset of sexual maturity, but feeding never stopped completely, even during spawning.     

Seasonal variation of xanthine oxidoreductase activity in the digestive gland cells of the mussel Mytilus galloprovincialis: a biochemical, histochemical and immunochemical study

The activity and the tissue distribution of the oxygen radical producing enzyme xanthine oxidoreductase (XOR) were measured in the digestive gland of the common marine mussel Mytilus galloprovincialis Lmk along an annual cycle. No xanthine oxidase (XOX) activity could be measured, the enzyme only displaying xanthine dehydrogenase (XDH) activity in all the cases. This is interpreted as a mechanism to avoid the harmful effects of the oxygen radicals that would be produced by XOX during periods following anoxic conditions at low tide. The highest XDH activities coincided with the late spring/early summer months, the activity maxima being recorded from May to July. Histochemically XOR activity was very pronounced in duct and stomach epithelial cells as well as in the surrounding connective tissue and hemolymph vessels, the activity increasing towards the summer months. These seasonal variations in XDH or XOR activities are possibly linked to hormonal changes governing the reproductive cycle and to changes in food availability. The localization of the protein in the connective tissue lining the hemolymph vessels was confirmed immunohistochemically using a polyclonal antibody against rat liver protein that cross-reacted specifically with a polypeptide of 150 kDa of molecular mass in homogenates of the digestive gland. This polypeptide was linked to cytosolic fractions isolated by differential centrifugation from mussel digestive glands. In paraffin sections the antibody labeled the digestive cells of digestive tubules, as well as the connective tissue surrounding the hemolymph vessels, gonadal follicles, digestive epithelia and certain protozoan parasites. Taken together our results suggest that in the digestive gland of bivalve molluscs XOR is involved in the metabolism of purines and in the scavenging of oxygen free radicals.     

Variation of lipid classes among organs of the Northern krill Meganyctiphanes norvegica, with respect to reproduction.

Lipid content and class in the Northern krill Meganyctiphanes norvegica (digestive gland, stomach, gonad, fat body, abdomen) was investigated and correlated with sex and reproductive stage. Ready to spawn females, have high lipid content in ovaries, while in males and spent females, the major site of lipid deposits was the digestive gland, followed by the fat body. These differences among spawning and spent females are indicative of strong interactions between the ovary and digestive gland and the ovary and fat body during vitellogenesis. Triacylglycerols (TAG) were the major neutral lipid class with high levels in the digestive gland. The major phospholipid was phosphatidylcholine (PC) particularly in the muscular tissue of the abdomen. Phosphatidyl-ethanolamine (PE) and -serine-inositol (PS-PI), were present at intermediate levels. Reproductive males were depleted in TAG and diacylglycerols (DAG) in the digestive gland, gonad and fat body, and had 4 times lower cholesterol in the gonad than ready to spawn females. Furthermore, ready to spawn females had in the ovary higher amounts of TAG, DAG and phospholipids (PC, PE, PS-PI) than spent females. Linear relationships between lipid content and main lipid class (TAG, PC, PE, PS-PI) in different fractions of males and ready to spawn females showed that: (1). TAG was stored for both sexes in all cephalothorax fractions with highest values in the digestive gland and ovary fluid; (2). PC was accumulated for both sexes in the fat body and the gonad with a higher slope for females, with the highest values in the ovary fluid and in the abdomen of males and that (3). PS-PI was stored only in the ovary and abdomen of mature females. These results are discussed in terms of the strategy developed by Meganyctiphanes norvegica to allocate lipids to the next generation for optimised embryogenesis.     

Lack of gonadal control of the dorsal gland and sandbathing in male and female bannertail kangaroo rats (Dipodomys spectabilis)

Previous studies have demonstrated gonadal control of mammalian scent glands; castration leads to reduced scent-marking rates and smaller gland sizes. I investigated whether gonadal hormones control the size of the dorsal gland (a specialized sebaceous gland) and sandbathing as a scent-marking behavior in adult male and female bannertail kangaroo rats (Dipodomys spectabilis). Gland sizes of males and females were similar in all age classes, except adult males with larger body weights had proportionately larger glands than females. Male gland sizes declined 18% following castration but were not significantly smaller than those of intact males; females showed no change in dorsal gland size either as a result of ovariectomy or after estradiol benzoate implants. Sandbathing rates also did not decline as a result of gonadectomy. Rather, castrated males and overiectomized females sandbathed at higher frequencies than intact males and ovariectomized females with estradiol benzoate implants, respectively. Gonadal hormones apparently have little influence on the function of a specialized scent gland and may inhibit sandbathing as a scent-marking behavior in adult D. spectabilis.     

厚壳贻贝两种新型防御素的分子鉴定

贻贝是全球范围内具有重要经济价值和生态价值的双壳贝类。贻贝抗菌肽具有极强的分子多样性,也是当前抗菌肽研究的重要对象。防御素是贻贝抗菌肽的重要成员, 从厚壳贻贝中鉴定到2种新型防御素, 但其分子特性和免疫机制尚不清楚。为此, 对厚壳贻贝体内新发现的2种防御素开展研究。序列分析结果表明,2种新型防御素均具有节肢动物防御素结构特征,因而被命名为arthropod like defensin (ALD)。利用荧光定量PCR研究了2种防御素在贻贝不同组织及不同发育阶段的表达量差异。进一步分析了2种防御素在3种不同微生物诱导下的表达量时间曲线。利用固相化学合成技术对2种防御素的成熟肽区进行合成并开展了功能验证。研究结果表明, 2种ALD 主要表达部位在外套膜和消化腺, 且ALD-1具有雄性特异表达特征。此外, ALD-1和ALD-2在贻贝幼虫阶段均未表达; 在不同微生物刺激下, 2种ALD表现出不同的免疫反应模式, 显示出2种防御素具有不同的免疫调节机制。化学合成的2种ALD均具有抑菌活性, 其对不同微生物的抑制率在20%~80%之间。上述研究为深入了解贻贝免疫防御的分子机制,以及贻贝抗菌肽的免疫功能和后续的分子资源开发奠定了基础。     

Climate-driven impacts of prey abundance on the population structure of a tropical aquatic predator

In the present study we explore how annual variation in climate (late wet-season rainfall) affects population demography in a gape-limited obligate piscivorous predator, the Arafura filesnake Acrochordus arafurae in the Australian tropics. These aquatic snakes display extreme sexual dimorphism, with body sizes and relative head sizes of females much larger than those of males. Two consecutive years with low rainfall during the late wet season reduced the abundance of small but not large sized fish. Although snake residual body mass (RBM, calculated from a general linear regression of ln-transformed mass to ln-SVL) decreased after the first year with low prey availability, it was not until the second year that reduced prey abundance caused a dramatic decline in filesnake survival, and hence in population numbers. Thus, our results suggest that most snakes survived the first year of reduced prey abundance, but a successive year with low prey availability proved fatal for many animals. However, the effects of prey scarcity on RBM and survival fell disproportionately on some size classes of snakes. Medium-sized animals (large males and intermediate-sized females) were affected more dramatically than were small or large snakes. We attribute the higher survival of small snakes to their lower energy needs compared to medium-sized individuals, and the higher survival of large snakes to the continued abundance of large prey (mainly large catfish). Two successive years with low abundance of smaller sized prey thus massively modified the size-structure of the filesnake population, virtually eliminating large males and intermediate-sized females. Our field data provide a clear demonstration of the ways in which stochastic variation in climatic conditions can have dramatic effects on predator population demography, mediated via effects on prey availability.     

Sex differences in diurnal rhythms of food intake in mice caused by gonadal hormones and complement of sex chromosomes

We measured diurnal rhythms of food intake, as well as body weight and composition, while varying three major classes of sex-biasing factors: activational and organizational effects of gonadal hormones, and sex chromosome complement (SCC). Four Core Genotypes (FCG) mice, comprising XX and XY gonadal males and XX and XY gonadal females, were either gonad-intact or gonadectomized (GDX) as adults (2.5 months); food intake was measured second-by-second for 7 days starting 5 weeks later, and body weight and composition were measured for 22 weeks thereafter. Gonadal males weighed more than females. GDX increased body weight/fat of gonadal females, but increased body fat and reduced body weight of males. After GDX, XX mice had greater body weight and more fat than XY mice. In gonad-intact mice, males had greater total food intake and more meals than females during the dark phase, but females had more food intake and meals and larger meals than males during the light phase. GDX reduced overall food intake irrespective of gonad type or SCC, and eliminated differences in feeding between groups with different gonads. Diurnal phase of feeding was influenced by all three sex-biasing variables. Gonad-intact females had earlier onset and acrophase (peak) of feeding relative to males. GDX caused a phase-advance of feeding, especially in XX mice, leading to an earlier onset of feeding in GDX XX vs. XY mice, but earlier acrophase in GDX males relative to females. Gonadal hormones and SCC interact in the control of diurnal rhythms of food intake.     

Isolation and biochemical characterization of the microsomal fraction from the digestive gland of mussel Mytilus galloprovincialis Lam

A procedure to prepare microsomes from the mussel digestive gland is proposed. The data concerning the biochemical characterization of this subcellular fraction shows a typical RNA:protein ratio, but the presence of hydrolytic enzymes was also found; therefore a mixture of hydrolase inhibitors to study the different biochemical characteristics was used. The biochemical data demonstrate that glucose-6-phosphatase activity (G6Pase), a typical microsomal marker in mammalian cells, is not present in mussel digestive gland microsomes but a high non-specific phosphatase activity was detected. Benzo[a]pyrene hydroxylase activity was found to be present although in a minimal amount. The evaluation of the molecular weight of the rRNA demonstrates that the larger ribosomal subunit contains RNA of Mr 1.40 X 10(-6) (approximately 26S) and the smaller subunit is composed of RNA of Mr 0.65 X 10(-6) (18S). The data from mussel digestive gland microsomes was compared with that experimentally obtained from rat liver microsomes and discussed from a functional or an evolutionary point of view.     

Differential Activity of Stanniocalcin in Male and Female Fresh Water Teleost Mastacembelus armatus (Lacepede) during Gonadal Maturation

The present study was carried out to analyze the differences in the activity of hormone stanniocalcin (STC) between male and female fishes of Mastacembelus armatus during their gonadal cycle. A large variation in nuclear diameter of cells of corpuscles of Stannius (CS) were recorded in relation to testicular cycle as well as ovarian cycle which indicates that the cellular activity varied with different phases of reproductive cycle in both male and female fish. Similar changes in nuclear diameter of CS cells were also observed after 17alpha-methyltestosterone administration in males and 17 β-estradiol administrations in females. A positive correlation was observed between plasma STC levels, gonadosomatic index (GSI) and the sex steroids in both sexes, suggesting that STC has a role in the processes involved in gonadal development. In addition females showed remarkable changes in plasma calcium level during gonadal cycle while no such change for males were observed. In females the plasma calcium level estimated during different phases of reproductive cycle indicates positive correlation between plasma level of calcium and gonad growth. Thus hyperactivity of CS cells was noted in both male and female fishes during gonadal cycle along with the differences in the activity of STC as well. In female it may act as hypocalcemic factor and bring the level of calcium to normal which increases during preparatory and pre spawning phases to fulfill the increased demand of calcium for vitellogenesis. However data of male fishes indicated that plasma STC concentration varied widely during gonadal cycle but showed no consistent relationship to plasma calcium level.     

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: II. Responses to acute stress in the laboratory.

Circulating concentrations of plasma corticosterone and gonadal steroids were measured in intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season.     

Growth, maturation and reproductive investment in Arctic charr

Size and rates of growth in a cohort of 1 + Arctic charr housed in standard conditions were tracked over 12 months (December to December) and mature and immature males and females compared retrospectively. In both sexes, maturing fish were larger than non-maturing ones. In males, this size differential was the result of differences in growth in winter and early spring, but not in the remainder of the study period. In females, size differentials resulted mainly from growth rate differences immediately prior to breeding. In females but not in males, gonadosomatic index was predicted by growth rates in the months leading up to maturation, and among the females that matured, faster growing fish produced more eggs. Lipid reserves in July were correlated negatively with growth during the previous 7 months and, in females only, lipid reserves were significantly lower in maturing fish than in non-maturing fish, indicating that mobilization of lipid energy reserves in maturing fish had commenced by this time. Variation in investment in gonadal tissue, measured as gonadosomatic index, was not explained by variation in July lipid reserves for either males or females. However, July lipid reserves were negatively correlated with egg number, so females investing more in ova exhibited greater depletion of lipid reserves. These results are discussed in the context of the relationship between body condition and the onset of maturation in salmonids, relative investment in reproduction and sexual differences in the cost of reproduction.     

MODE OF SEXUAL SELECTION DETERMINED BY RESOURCE ABUNDANCE IN TWO SAND GOBY POPULATIONS

We used field observations and experiments to show that sexual selection in two populations of sand gobies, Pomatoschistus minutus (Pisces, Gobiidae), was affected by differences in resource availability. Male sand gobies rely on empty mussel shells for nest building and spawning. The two populations differed considerably in nest-site abundance and sexual-selection regimes. In one population nest sites were scarce, leading to stronger male-male competition over nests, a higher nest site colonization rate and reduced potential for female choice compared with the other population that had a surplus of nests. In the high-competition population, males were larger than females, perhaps as a response to selection, whereas the other population was not sexually size dimorphic. The results from the field were confirmed in a pool experiment that demonstrated the effect of nest abundance on nest occupancy and male reproductive success. Larger males were more successful in obtaining nest sites in both high and low nest availability treatments. Larger males were also favored by females as mating partners, but only in the treatment with surplus nest sites. Nest shortage was associated with an increased potential for intrasexual selection (measured as the coefficient of variation), whereas the potential for intersexual selection was increased when nests were common. In conclusion, nest-site abundance can influence the relative contribution of intrasexual competition and mate choice in a population. Hence, resource availability can contribute to within-species variation in mating patterns.     

Gonadal and hormonal characteristics of captive adult mourning doves during the nesting cycle

Paired mourning doves ($\text{Zenaida}$$\text{macroura}$) of a captive breeding colony were selected and sacrificed on specific day intervals postlaying and posthatching during 1976–1977. Blood plasma samples were analyzed for androgens, estradiol, and progestins using radioimmunoassays. Testes, ovary and oviduct weights, spermatozoan numbers, diameter of the three largest follicles in the ovary, the presence or absence of eggs in the reproductive tract, and crop gland characteristics also were recorded. Differences (P<0.05) existed between nonbreeding and breeding pairs in testes weights, spermatozoan numbers, and ovary and oviduct weights. No distinct cyclic pattern was observed in gonadal variables among breeding males and females during the nesting cycle, although trends were observed. No differences (P > 0.05) in androgen and progestin concentrations in males, or estradiol and progestin concentrations in females, between nonbreeding and breeding pairs, or among breeding pairs during different stages of the nesting cycle, were observed. Analysis of reproductive variables by stage of crop gland activity tended to indicate an inverse relationship between gonadal and crop gland activity in both male and female doves during the nesting cycle.     

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: I. Seasonal variation in the field.

In order to document sex differences in adrenal function and how this relates to gonadal function during the period of seasonal activity, blood samples from male and female six-lined racerunners, Cnemidophorus sexlineatus, were taken immediately after capture in the field for determination of plasma corticosterone and gonadal steroid concentrations. Plasma testosterone and dihydrotestosterone levels for males, and 17 beta-estradiol and progesterone levels for females, were measured. Trends in the concentration of plasma corticosterone differed significantly between males and females. In males the highest concentrations of corticosterone were measured in late spring and the lowest concentrations were measured in late summer. Whereas half of the variation in corticosterone levels among males could be explained as seasonal change, less than 1% of the variation among females could be explained as seasonal change. In males plasma corticosterone and androgens exhibited similar seasonal decreases. Corticosterone levels for females were not correlated with progesterone or 17 beta-estradiol levels. Sex differences in seasonal variation in plasma corticosterone concentrations suggest that corticosterone may be involved in the different reproductive strategies and energy requirements of males and females during the seasonal period of activity.     

Seasonal Variations in the Expression of the mRNA Encoding ß1-Adrenoceptor and AA-NAT Enzyme,and in the AA-NAT Activity in the Pineal Gland of Vizcacha (Lagostomus maximus maximus) – Correlation With Serum Melatonin

The vizcacha is a photoperiodic rodent living in the southern hemisphere. The adult males exhibit an annual reproductive cycle characterized by a gonadal regression period during winter with, in some animals, an almost complete loss of spermatogenesis. In this study, we investigated whether biochemical parameters involved in melatonin synthesis in the vizcacha pineal gland exhibited an annual rhythm in parallel with the annual reproductive cycle. By use of in situ hybridization, an annual variation of mRNA encoding ß 1 -adrenoceptor was shown, with a maximum during autumn and winter. In situ hybridization for mRNA encoding AA-NAT enzyme also exhibited an annual rhythm with the lowest and highest levels in May and August, respectively. Likewise, in August the activity of arylalkylamine N-acetyltransferase enzyme also reached a maximum. Finally, dertermination of the serum concentrations of melatonin by use of radioimmunoassay showed an increase during winter. Moreover, our results are in concordance with several biochemical and morphological parameters of the reproductive axis of the male vizcacha, which support the reproductive rhythmicity of this rodent. Thus, our data suggest that the pineal gland and melatonin, which is activated via the sympathetic system, could be involved in the photoperiodically dependent annual reproductive behavior of the vizcacha.