Gonad Mass Research Articles

BREEDING RESOURCE DISTRIBUTION AFFECTS SELECTION GRADIENTS ON MALE PHENOTYPIC TRAITS: EXPERIMENTAL STUDY ON LIFETIME REPRODUCTIVE SUCCESS IN THE BITTERLING FISH (RHODEUS AMARUS)

The spatial distribution of breeding resources can have pronounced demographic and evolutionary consequences. We used 20 experimental groups of the bitterling (Rhodeus amarus), an annual fish with a promiscuous, resource-based mating system, and extended breeding season to investigate how the spatial distribution (clumped or regular) of bitterling oviposition sites (live freshwater mussels) affected offspring production, variation in reproductive success, and directional selection on phenotypic traits over their entire reproductive lifetime. We did not detect any effect of resource distribution on offspring production or variation in reproductive success among individual fish, although variation between replicates was higher with a clumped distribution. This finding is discussed with regard to the incidence of alternative mating behaviors (sneaking) within the limitations imposed by our experimental design. Breeding resource distribution had a significant effect on selection on male phenotypic traits. Stronger directional selection on traits associated with intrasexual competition for fertilizations, gonad mass (an indicator of sperm competition), and the extent of red, carotenoid-based pigment in the iris (an index of dominance status), was detected with a clumped resource distribution. With a regular resource distribution, a stronger positive selection on male body size was detected. We discuss the implications of our results for natural populations.

Energetic trade‐off between maintenance costs and flight capacity in the sand cricket (Gryllus firmus)

Summary 1Energetic trade-offs are those compromises that appear when the energy budget of an individual's life history closely matches or exceeds the net available energy in the environment in a given moment. In these situations, two or more functions can compete and organisms face physiological decisions in order to survive and reproduce. 2In insects, one of the most costly investments is flight capacity, which increases dispersal capacity but is energetically expensive. Adult sand crickets (Gryllus firmus) can vary drastically in this capacity, being macropterous or micropterous depending on whether they exhibit flight-capable wings. However, this binary phenotype has a continuous subjacent determinant in the macropterous morph which is the mass of the muscles that power flight, the dorso-longitudinal muscles (DLM). 3Using respirometric measurements, we studied a potential trade-off between body parts, the mass of the DLM and energy metabolism (including both maximum and average metabolism). By recording the metabolic rate of c. 180 crickets and then dissecting and weighing their body parts, we took advantage of the correlational structure to infer associations between energetic and morphological variables. We found that the residual mass of the DLM shows a quadratic relationship with residual resting and average metabolism: at low DLM mass there is a negative relationship, which becomes positive at higher DLM mass. 4We suggest that this pattern of covariance is a consequence of the negative correlation between DLM mass and gonad mass, and the relative contribution of functional vs. non-functional DLM. Then, by using energetics and a combination of multivariate and correlational statistics we were able to show how two important life-history functions (i.e. Dispersal and fecundity) compete for the same resources in an insect species.

Size‐independent age effects on reproductive effort in a small, short‐lived fish

Summary1. Age‐related changes in reproductive effort have been predicted by theoretical models and observed in a wide range of organisms. However, for indeterminate growers such as fish, an allometric relationship linking gonad weight to body size is commonly observed. There is often a positive linear relationship when these variables are log‐transformed, which by implication reduces the influence of age on reproductive effort.2. Contrasting with this usual pattern, we report a nonlinear relationship between gonad weight and fish size (after log‐transformation) in mosquitofish (Gambusia holbrooki), clearly resulting from age changes. The declining rate of increase of gonad mass as a function of body size revealed a higher reproductive effort for younger individuals relative to size.3. This size‐independent age effect on reproductive effort was predicted based on previous studies of mosquitofish and is certainly related to their particular life‐history strategy, combining an early maturation and short lifespan with the physiological costs of reproduction and over‐wintering. Our findings probably apply to other small, short‐lived species with similar life history.

Rofecoxib impairs adipose tissue development in a murine model of nutritionally induced obesity

The effect of rofecoxib (Vioxx), a cyclooxygenase (COX)-2 inhibitor, on adipose tissue development was studied in a murine model of diet-induced obesity. Oral administration of Vioxx for six weeks (34 mg/kg/day) to C57Bl/6 mice kept on high-fat diet (n = 19) resulted in a significant reduction in total body weight (p < 0.01) and of subcutaneous (p < 0.05) and gonadal (p < 0.01) adipose tissue mass, as compared to placebo-treated animals (n = 21). There was no significant difference in food intake between both groups (2.8 +/- 0.09 vs. 3.0 +/- 0.10 g/day; p = 0.20). Administration of Vioxx resulted in reduced total cholesterol and high-density lipoprotein (HDL) cholesterol levels (p < 0.0001) and in enhanced levels of liver enzymes, as compared to place-bo. In the gonadal but not in the subcutaneous adipose tissue, adipocytes were smaller after Vioxx treatment (p < 0.05). The macrophage content was significantly lower in gonadal adipose tissues of Vioxx-treated mice (p < 0.05), but not in the subcutaneous adipose tissues. This was, however, not associated with differences in adipose tissue levels of the pro-inflammatory tumor necrosis factor (TNF)-alpha. Blood vessel size or density in either fat pad were not affected by Vioxx treatment. Thus, in a nutritionally induced murine obesity model, oral administration of Vioxx, as compared to placebo, resulted in reduced adipose tissue development, associated with lower feeding efficiency and smaller adipocytes.

Assessment of magnesium chloride as an anaesthetic for adult sea urchins (Paracentrotus lividus): incidence on mortality and spawning

During this study different concentrations of magnesium chloride (MgCl2) were tested on adult wild-caught sea urchins (Paracentrotus lividus) immediately after their collection in the field in order to assess whether MgCl2 can act as an anaesthetic during their transport and prevent unplanned spawning. Such accidental spawning is a stress response associated with transport of this species. The mortality and gonadal indices were recorded after a 1-h submersion in different strength solutions of MgCl2 (5, 20, 40, 80 and 100 mmol L−1 MgCl2), followed by 5 h of dry transport under two different temperatures (19 and 25 °C). The effective concentration of MgCl2 was defined as one that does not induce mortality and gonad mass loss following sea urchin transport and laboratory conditioning. Treatment of sea urchins with 5 mmol L−1 MgCl2 prevented mortality and unplanned spawning; however, elevated concentrations of magnesium (40, 80 and 100 mM) were toxic to sea urchins, inducing a massive mortality and gonad mass decrease during the acclimatization period, essentially when sea urchins were transported under an elevated temperature (25 °C). It is concluded that MgCl2 is a suitable non-toxic anaesthetic, easily available for adult sea urchins (P. lividus) when it is used at its optimal anaesthetizing concentration.

The link between migration, the reproductive cycle and condition of Sardinella aurita off Mauritania, north‐west Africa

The annual migration pattern of round sardinella Sardinella aurita up and down the north‐western African coast between 12° N (Senegal) and 22° N (western Sahara) was shown to be associated with spawning activity and a distinct seasonality in fish condition, based on monthly sampling from commercial catches (2000–2003). Some S. aurita were found to spawn throughout the entire year, but a peak in spawning existed during the summer (June to September). The spawning cycle is apparent from seasonality in maturity stages, but is also demonstrated by the increase in gonad mass and fat content of the fish in springtime, the period preceding spawning. During the months after spawning, although feeding is maintained, the physical condition of the fish collapses, and fat content rapidly declines.

Breeding biology of Phyllomedusa azurea Cope, 1862 and P. sauvagii Boulenger, 1882 (Anura) from the Cerrado, Central Brazil

Phyllomedusa azurea and P. sauvagii are treefrogs from seasonal dry environments of Central Brazil. We report on reproductive and other natural history features of these species. The study was carried out in Serra da Bodoquena, Mato Grosso do Sul, Brazil. The reproductive period was determined by the presence of vocalizing males, amplectant pair or presence of tadpoles. The reproductive effort was measured as the ratio of gonad mass in relation to body mass (BM). The reproduction of both species was correlated with the rainy season. Female P. sauvagii produced more eggs and their eggs were larger than those of P. azurea. Both species showed sexual dimorphism in relation to the snout–vent length (SVL) and BM. The mating behaviour of both species was similar. Males in both species showed similar reproductive efforts, but females of P. azurea invested more in gonads compared to the males of P. sauvagii. Phyllomedusa azurea showed a significant relation between SVL versus number of the mature eggs (NME), and P. sauvagii between SVL versus NME and BM versus ovarian mass.

Habitat related growth and reproductive investment in estuarine waters, illustrated for the tellinid bivalve Macoma balthica (L.) in the western Dutch Wadden Sea

In estuarine areas, bivalve species can be found in a variety of environments, where they experience large differences in environmental conditions. In the present paper, the importance of different habitats (intertidal, subtidal and adjacent coastal waters) for the persistence of the population was evaluated for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea estuary. Intra-specific variation in growth and reproductive output were followed during the year and related to local abiotic conditions. Significant differences in growth and reproductive investment were found between locations. Young individuals were mostly found in the intertidal area, where growth in terms of somatic mass was good. These areas were not favourable for adult individuals, since growth in shell length was low and many individuals did not reproduce. In the subtidal, where the highest densities were found, somatic and gonadal mass indices were low. Coastal areas had the lowest densities and showed high growth in terms of shell length and body mass. The habitat with the highest reproductive effort per individual was not the most important habitat in terms of reproductive output due to differences in density and in size of the habitat type. For M. balthica, the subtidal habitat contributed the most to the reproductive output of the western Dutch Wadden Sea population although the highest reproductive output per individual was in the coastal area.

Life history variation of invasive mosquitofish ( Gambusia holbrooki) along a salinity gradient

The mosquitofish ( Gambusia holbrooki) is among the most invasive fish worldwide, with well documented ecological impacts on ecosystem functioning and several native taxa. Although it has been suggested that salinity limits the invasive success of mosquitofish, there are few studies on how salinity affects its ecology. We examined differences in life history traits of mosquitofish at 19 sampling sites from fresh (438 μS/cm; ca. 0.2‰ of salinity) to polysaline waters (35.1 mS/cm; ca. 23‰). Salinity affected the density and life history traits of both male and female mosquitofish; density showed a unimodal response to salinity, stronger for females and thus affecting the sex ratio. On the other hand, the endemic Aphanius iberus was only present in polysaline and eusaline waters, where mosquitofish were generally absent. Mosquitofish increased reproductive investment (higher gonadal mass) in oligosaline waters, at the cost of somatic condition in females. The increase in reproductive investment also implied an increase in total mass in contrast to somatic mass, demonstrating that the latter is a better indicator of condition. Females from higher salinity waters presented more embryos in advanced developmental stages, indicating earlier reproduction than in fresh water. After correction for brood and fish sizes, females from saltier environments presented heavier embryos (independently of maturation state). In summary, salinity mainly affected mosquitofish females which, despite presenting earlier maturation and higher reproductive investment, reduced their condition and density, hence supporting the hypothesis that salinity limits mosquitofish invasive success.

Altered development and reproduction in mosquitofish exposed to pulp and paper mill effluent in the Fenholloway River, Florida USA

Female mosquitofish exposed to pulp and paper mill effluent (PME) in the Fenholloway River, Florida, USA have masculinized secondary sex characteristics and altered aromatase enzyme activity. We and others have shown that the Fenholloway River PME contains androgenic and progestogenic substance(s). The present study was designed to test the hypothesis that the development and reproductive health of PME-exposed Fenholloway River mosquitofish are altered compared to mosquitofish living in Econfina River, which is the reference site. Fish were collected on a single day from both sites in June and August 1999 and January and June 2000. We compared standard length, anal fin length and segment number; body, liver, and gonad mass; and number of eggs and embryos from Fenholloway and Econfina River mosquitofish. The data were analyzed collectively for generalized site effect, for site effects during reproductive and nonreproductive seasons, and for repeatability of site effects between years. Mosquitofish exposed to PME in the Fenholloway River were generally smaller in length and mass, anal fin segment number was greater, and the number of embryos, but not oocytes, was significantly decreased compared to the reference site fish. Anal fin length and segment number and liver and testis masses were generally greater in Fenholloway compared to the Econfina River males. The importance of this study is that we have documented masculinized development and decreased embryo production in PME-exposed mosquitofish and that these site effects are generally consistent across seasons and between years.

Persistent Positron Emission Tomography–Positive Liver Lesions After Successful Chemotherapy in Mediastinal Seminoma

Persistent Positron Emission Tomography–Positive Liver Lesions After Successful Chemotherapy in Mediastinal Seminoma

Reproductive seasonality in a swamp‐locked African cichlid

Abstract – This study quantified the seasonal pattern of reproduction in a swamp‐dwelling population of the African cichlid Pseudocrenilabrus multicolor victoriae. In the hypoxic waters of the Lwamunda Swamp, Uganda, P. multicolor was reproductively active throughout the year, even during the peak of the dry seasons. However, the degree of activity was seasonal, with rainfall providing a predictor of the percentage of ripe, mature females. There was no correlation between aquatic oxygen availability dissolved oxygen (DO) and either adjusted mean gonad mass or percentage of mature females, suggesting that DO is not limiting reproductive activity in this system. Reproductively mature females were larger during drier periods and may maximise their lifetime reproductive success by producing young throughout the year; but with a lower brooding efficiency. A comparison with Welcomme’s (1969) study of a river‐swamp system feeding Lake Victoria suggests that reproductive patterning is variable among populations of P. multicolor and may reflect adaptive response to chronically hypoxic conditions in the Lwamunda Swamp.

Life History of the Warrior Darter (Etheostoma bellator) and Comparison with the Endangered Vermilion Darter (Etheostoma chermocki)

ABSTRACT The Warrior darter (Etheostoma bellator) is endemic to the Black Warrior River drainage (Mobile Basin) above the Fall Line in Alabama. Etheostoma bellator is a species complex, with the nominal form common and widespread, and includes a population in Gurley Creek in the lower Locust Fork in Blount County and Jefferson County, Alabama. Based on morphology and genetics, this population of Warrior darters has been identified as a potential surrogate for the federally endangered vermilion darter (E. chermocki), which is restricted to Turkey Creek, which is adjacent to Gurley Creek. Fresh collections of Warrior darters from November 2004 to June 2006 and museum collections were evaluated to determine life history characteristics. Standard length was significantly correlated with body mass and gonad mass. Males were larger than females, and the sex ratio (2:1) was in favor of females. Length frequency distribution and enumeration of otolith annuli revealed four age classes (0+ to 3+). Warrior darters matured at the end of the first year of life. Gonadosomatic index indicated reproduction occurred from March to June. Mean clutch size was 71 oocytes per female. The Warrior darter is an opportunistic benthic invertivore, predominantly consuming larval chironomids, tipulids, baetid mayflies, and glossosomatid and hydropsychid caddisflies. Diet breadth was greatest during warmer months and least during colder months. Based on current information, the Warrior darter appears to be the ideal surrogate for the endangered vermilion darter because both species share similar life history characteristics.

Prey resources before spawning influence gonadal investment of female, but not male, white crappie

In this study, an outdoor pool experiment was used to evaluate the effect of prey resources during 4 months before spawning on the gonadal investments of male and female white crappie Pomoxis annularis, a popular freshwater sportfish that exhibits erratic recruitment. Fish were assigned one of three feeding treatments: starved, fed once every 5 days (intermediate) or fed daily (high). All measurements of male testes (i.e. wet mass, energy density and spermatocrit) were similar across treatments. Conversely, high‐fed females produced larger ovaries than those of intermediate‐fed and starved fish, and invested more energy in their ovaries than starved fish. Compared to pre‐experiment fish, starved and intermediate‐fed females appeared to increase their ovary size by relying on liver energy stores (‘capital’ spawning). Conversely, high‐fed females increased liver and gonad mass, implying an ‘income’‐spawning strategy (where gonads are built from recently acquired energy). Fecundity did not differ among treatments, but high‐fed fish built larger eggs than those starved. Females rarely ‘skipped’ spawning opportunities when prey resources were low, as only 8% of starved females and 8% of intermediate‐fed females lacked vitellogenic eggs. These results suggest that limited prey resources during the months before spawning can limit ovary production, which, in turn, can limit reproductive success of white crappies.

Swimming stimulates oocyte development in European eel

In this study, we subjected eels from Lake Balaton (Hungary) to a swimming period of 1 week and 2 or 6 weeks. Most eels were silver and were 13–21 years old. Time dependent changes in morphometrical parameters and developmental characteristics of the oocytes were determined. Already after 1 week of swimming, the gonadal mass increased and oocytes became larger, filled with large numbers of lipid droplets. After 2 and 6 weeks of swimming we found in addition a significant enlargement of the eyes, which is a sign of sexual maturation. In contrast to the resting eels, that had oocytes in the primary growth phase (stage 1–2); the swimming eels had oocytes in stage 3; the cortical alveolus or lipid droplet stage. The results indicate that lipid mobilisation induced by swimming is a requirement for the natural incorporation of lipid droplets in the oocytes, a crucial step in oocyte maturation. As the Balaton eels responded stronger to swimming than young farmed eels, it is suggested that older eels are more sensitive for maturation triggers.

Gametogenesis and gonad mass cycles in the common circumpolar Antarctic echinoid Sterechinus neumayeri

Polar conditions (low and stable seawater temperature coupled with highly seasonal primary productivity) constrain reproduction in benthic invertebrates. The reproductive cycle of the common Antarctic sea urchin Sterechinus neumayeri was investigated at monthly intervals over a 2 yr period in relation to seasonality of chlorophyll standing stock and ability to feed. Competence to spawn increased gradually throughout the austral winter to peaks in September to November. Gonad mass varied strongly, both seasonally and among 3 geographically close sites. Spawning occurred between October and January at each site, and was strongest in November of both years. Spawning was not always accompanied by a reduction in gonad mass because of simultaneous feeding and deposition of nutritive tissue for the forthcoming winter. Spawning was annual but there was also strong evidence for longer, multi-year periodicity in reproductive output. Histological analysis indicated an 18 to 24 mo vitellogenic cycle, with oocytes developing from 20 to 50 μm in the first winter, and from 50 to 120 μm in the second winter. Of total oocyte volume increase (vitellogenesis), 93% occurred within the last 12 mo. Spermatogenesis took 12 mo. S. neumayeri does not feed during the austral winter, and vitellogenesis is therefore predominantly decoupled from energy intake. Much of the cost of reproductive synthesis is met at a time of severe energy limitation.

Mass dynamics of wintering Pacific Black Brant: body, adipose tissue, organ, and muscle masses vary with location

We compared body size and mass of the whole body, organs, adipose tissue, and muscles of adult Pacific Black Brant ( Branta bernicla nigricans (Lawrence, 1846)) collected concurrently in Alaska and Baja California during the fall, winter, and spring of 2002–2003. Head and tarsal lengths of males were similar between sites and slightly larger for females in Alaska than in Baja California. Brant appear to operate under similar physiological bounds, but patterns of nutrient allocation differ between sites. Birds wintering in Alaska lost similar amounts of adipose tissue during early winter as birds in Baja California gained during late winter before migration. Masses of the body, adipose tissue, and flight muscles during mid-winter were similar between sites. Seasonal adipose tissue deposition may, therefore, equally favor winter residency or long-distance migration. Gonad and liver masses increased in late winter for birds in Alaska but not for those in Baja California, suggesting birds wintering in Baja may delay reproductive development in favor of allocating reserves needed for migration. Phenotypic flexibility allows Brant to use widely divergent wintering sites. The wintering location of Brant likely depends more upon changes in environmental conditions and food availability, than upon physiological differences between the two wintering populations.

Growth and reproduction of the bivalve Spisula subtruncata (da Costa) in Dutch coastal waters

The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm 3. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns.

RELATION OF SEASONAL CHANGES IN THE MASS OF THE GONAD AND SOMATIC TISSUES OF THE ZEBRA ARK SHELL ARCA ZEBRA TO ENVIRONMENTAL FACTORS

Over the period from June 2002 to June 2003, we examined the relationship of seasonal changes in the mass of the gonad and somatic tissues to environmental factors for four size groups of the zebra ark shell Arca zebra at Chacopata, in northeastern Venezuela. The gonads of A. zebra began to increase in size when individuals attained 18–20 mm in shell length, but maximum gonad mass relative to somatic mass was only attained at 55–60 mm in length. Large individuals (>50 mm) showed a distinct annual reproductive cycle with a marked increase in gonad mass from July to late September 2002, coinciding with the increase in temperatures related to stratification of the water column. A decrease in gonad size occurred during October 2002 through January 2003 and coincided with a temperature decline related to renewed upwelling. The mass of somatic tissues was highest between late August to late December 2002, coinciding with the reproductive period and elevated temperatures. Other environmental factors showed little seasonal variation, although chlorophyll a concentration was lowest during the major period of increase in the gonad and somatic tissues (July to late September 2002), suggesting that the animals were not limited by the abundance of phytoplankton food. A. zebra seemed to be well adapted to the high loads of inorganic seston found in the Chacopata region.

Spatial variability in growth and reproduction of the Pacific oyster Crassostrea gigas (Thunberg, 1793) along the west European coast

The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion.