Breeding Phase Research Articles

Transplacental Exposure to the DNA Demethylating Agent, 5-AZA-CdR, Affects the Sexual Behavior of CD-1 Male Mice

Intrauterine exposure to 5-AZA-2′-deoxycytidine (5-AZA-CdR) alters gene expression causing malformations, abnormal post-natal growth and altered reproductive capacity. To elucidate whether the phenomenon observed in 5-AZA-CdR in utero exposed male mice was a behavioral alteration, at gestation day (GD) 10, CD-1 pregnant mice were administered 1 mg/kg i.p. of 5-AZA-CdR or saline solution. After parturition, the number and sex of pups were recorded. While litter size was not affected, the ratio of male to female offspring was altered in treated mice. To determine whether the phenotypic observation of male gender corresponded to the appropriate genotype, presence of Sry gene in 5-AZA-CdR F1 males was determined. At 3 months of age, the male sexual behavior test outlined by Chubb was conducted. Presence of vaginal plug and pregnancy were determined in the natural breeding phase. Mount latency and number of mounts per mouse were assessed in the behavioral test phase. In utero exposed male mice resulted in diminished mating behavior (as measured by vaginal plug presence, mount latency and number of mounts) and reduced sexual interest while exposed to a receptive female. While normal presence of Sry gene was observed, mating behavior was altered in exposed males suggesting that the reproductive alteration could be attributed to a behavioral phenomenon.

Breeding ecology of birds

One of the most fascinating aspects in the life of birds is their breeding phase, which is intimately tied to the distribution and abundance of food resources in their environment. However, food is not evenly distributed in space and time, and this is thought to have been one of the factors affecting the evolution nesting strategies. To understand how birds have evolved different types of nesting patterns ornithologists have used a variety of approaches, the most useful of which have been to build simple models based on optimality principles.

A Random Sampling of Salt Marsh Harvest Mice in a Muted Tidal Marsh

Successful conservation of an endangered species, such as the salt marsh harvest mouse (SMHM; Reithrodontomys raviventris), requires detailed knowledge of the species' habitat and microhabitat associations. Identifying critical habitat features, however; can be problematic. We designed and implemented a randomized sampling regime with a large sample size of sites (n = 40) to identify potential microhabitat requirements or habitat constraints affecting the localized distribution of the southern subspecies of SMHM (R. r. raviventris) We used the random trapping technique to determine SMHM distribution across a muted-tidal, predominantly pickleweed (Salicornia virginica) marsh at the Dot Edwards San Francisco Bay National Wildlife Refuge, California, USA. We tested the null hypothesis that this species' distribution is not associated with pickleweed salinity, sympatric rodent species, or the site location (peripheral vs. interior). We found SMHM throughout the marsh and detected no association with interior versus peripheral sites. We detected no associations between SMHM and sympatric rodent species. Pickleweed salinities ranged between 200 and 899 mmol/kg Cl - . In the prebreeding phase. SMHM were randomly dispersed. However, in the breeding and postbreeding phases, the population was clumped and associated with sites having mid-range (500-699 mmol/kg Cl - ) salinities in pickleweed. Managers and biologists attempting to conserve SMHM in managed marshes need to be concerned with maintaining this mid-range salinity level in pickleweed. We found that SMHM were absent from areas of low salinity (200-499 mmol/kg Cl - ) and were rare in hypersaline areas (699 mmol/kg Cl - ). Mid-range pickleweed salinities can be created and maintained in managed SMHM habitat only via fresh infusions of sea water on a natural tidal basis.

Enhancing Salt Tolerance in Crops Through Molecular Breeding: A New Strategy

SUMMARY Salinity limits crop production in many rainfed ecosystems and is an increasing problem in irrigated areas. Developing and developed countries alike need more efficient methods of enhancing salt tolerance in crops. The traditional breeding approach consists of (i) screening germplasm collections for donors of salt tolerance, (ii) crossing a donor with an elite line and advancing the F1 hybrid to about the F7 or F8 generation while selecting for elite traits, and concurrently (iii) selecting for salt tolerance starting at about the F4 generation. The low efficiency of this pedigree approach is due principally to the difficulty of recovering elite genotypes with salt tolerance traits, the genetic complexity of salt tolerance, and the strength of genotype × environment interactions (GEI). Advances in genomics are making possible an alternative approach in which a pre-breeding phase is used to pyramid several known genes and finely mapped major QTLs for complementary aspects of salt tolerance. The known genes can include transgenes modified by deliberate mutation or promoter switching. DNA-based selection protocols that are used to pyramid these genes are again employed during the breeding phase to transfer the entire set of genes for salt tolerance into any elite line by backcrossing. Breeding efficiency is increased because (i) elite traits are more easily recovered by backcrossing than by the pedigree approach, (ii) the genetic complexity of salt tolerance is reduced to a small set of well-defined genes and loci of large effect, (iii) the confounding effects of GEI are eliminated from the breeding phase, and (iv) the investment in gene discovery and QTL mapping can be recouped by transferring the same set of genes to a range of recipient lines that require salt tolerance. Efficiency will increase over time as more genes are added to the gene set and as QTL are replaced by the corresponding gene. Here we summarize the scientific advances underlying this new strategy, which should be applicable to other complex traits such as drought tolerance, durable resistance to pests and diseases, yield potential and product quality.

Oviductal sperm storage structure and their changes during the seasonal (dissociated) reproductive cycle in the soft-shelled turtle Lissemys punctata punctata.

The oviduct of the Indian fresh water soft-shelled turtle Lissemys punctata punctata was examined throughout the year under light and scanning electron microscopes to determine the location, histomorphological characteristics, and function of sperm storage structure, as well as their changes at different phases of the seasonal reproductive cycle. Sperm storage structures in the form of tubules were observed in the wall of isthmus throughout the year. These tubules developed either by folding or fusion of the oviductal mucosal folds and were lined by both ciliated and nonciliated epithelial cells. The height and secretory activities of the epithelia were markedly high during the breeding phase (August to September) but low in the nonbreeding phase (October to June). A few short tubules lined by cuboidal epithelium appear in the wall of infundibulum only during the breeding phase. Following mating (May), inseminated sperm were stored within the tubules of isthmus up to the pre-ovulatory stage (August). Thereafter, sperm associated with PAS-positive materials secreted from the epithelium (referred to as a carrier matrix) moved forward to the infundibulum and were stored within the storage tubules of the infundibulum for a short time. Subsequently, sperm evacuated the storage tubules and entered the oviductal lumen to fertilize the subsequently ovulated eggs during or prior to ovulation. The isthmus-tubules become shorter and narrower in the regressive phase (October to November) and remained so until the early preparatory phase (April). Sperm release might have been stimulated by estrogen secreted from the ovarian follicles of pre-ovulatory turtles. Stored sperm not utilized for fertilization remained viable not less than six months in the present turtle species.

Differential effects of melatonin on plasma levels of thyroxine and triiodothyronine levels in the air-breathing fish, Clarias gariepinus, during breeding and quiescent periods

Effects of morning and evening injections of three doses of melatonin were studied on the plasma levels of thyroxine (T 4) and triiodothyronine (T 3) in an air-breathing fish Clarias gariepinus during its quiescent phase and breeding phase. Depending on seasons and time of administration, melatonin increased, decreased or had no effects on the plasma levels of T 4 and T 3. Present findings strongly suggest that melatonin is involved in the regulation of thyroid hormones in C. gariepinus, and differentially influences T 4 and T 3 level.

Members of opposite sex mutually regulate gonadal recrudescence in the lizardCalotes versicolor (Agamidae)

Adult males and females of the seasonally breeding lizard Calotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17b-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in the C. versicolor.

Optimum selection age for wood density in loblolly pine

Genetic and phenotypic parameters for core wood density of Pinus taeda L. were estimated for ages ranging from 5 to 25 years at two sites in southern United States. Heritability estimates on an individual-tree basis for core density were lower than expected (0.20–0.31). Age–age genetic correlations were higher than phenotypic correlations, particularly those involving young ages. Age–age genetic correlations were high, being greater than 0.75. Age–age genetic correlations had a moderately linear relationship, while age–age phenotypic correlations had a strong linear relationship with natural logarithm of age ratio. Optimum selection age for core density was estimated to be 5 years when calculations were based on both genetic and phenotypic correlations. However, age 5 was the youngest examined in this study and optimum selection age may be younger than 5. Generally, the optimum selection age was robust to changes in breeding phase and assumptions concerning age-related variation in heritability estimates. Early selection for core density would result in a correlated increase in earlywood density but little progress in latewood density or latewood proportion at maturity.

Water temperature and pH influence olfactory sensitivity to pre-ovulatory and post-ovulatory ovarian pheromones in male Barilius bendelisis.

The attractive response and sexual activity elicited by pre-ovulatory steroid sulphate and post-ovulatory 15K-PGF pheromones are greater in wild caught tubercular males and immature males which express breeding tubercles on the snout (at 12-13 days post androgen implant) than in non-tubercular and non-androgen implanted males of freshwater fish Barilius bendelisis. This shows that circulatory androgens exert an activational effect on olfactory receptors of male fish. Wild caught tubercular males and androgen implanted juvenile males exhibit a high responsiveness to steroid sulphate at the water temperature and pH which fish experience during the pre-spawning phase. The male's sensitivity to 15K-PGF is almost equally high at the water temperature and pH which they experience in wild during the both pre-spawning and spawning periods. This suggests that the differential olfactory sensitivity to the two classes of pheromones in androgen implanted males is due to the varied temperature and pH of water, and that during the breeding season the male's olfactory sensitivity to PGF pheromone is more widespread than to the steroidal pheromone. An increased and decreased olfactory sensitivity in mature males to sex pheromones and L-alanine respectively during the breeding phase is in agreement with the hypothesis that pheromonal stimuli dominate over feeding stimuli to promote spawning success.

Ukraine: Prosyanoye — kaolin

This study combines observational data with a two-dimensional numerical model results to determine the fate of fish eggs released in the Gulf of Kachchh (GoK), a semi enclosed basin on the west coast of India. Fish eggs were treated as passive particles in the model, and were released from probable spawning sites identified from the field surveys. Areas with retention of larvae above 30% have been demarcated as nursery areas. Most of these nursery areas fall in ecologically significant sites which are rich in mangroves and reefs. We find that about 80% of the particles are retained in the basin for all the three prominent seasons prevailing in the GoK. Complete retention of particles in the southern Gulf region and small quantity of flushing out in the northern boundary of the Gulf could be a major reason for sustaining an abundance of larvae in the southern Gulf. Trawler catch data at various sampling points also suggest abundance of fish in the southern GoK region. Model simulation of fish larval transport in the GoK reiterates the fact that fish larval aggregation occurs in the southern GoK during active breeding phase with varying dispersal patterns from spawning sites. Marine protected areas in the Gulf demarcated based on the ecological significance of sites reasonably corroborate with the areas of likelihood of retention of fish larvae differentiated by the model.

Change in body mass in relation to breeding phase in bull‐headed shrikes

Changes in body mass of both sexes of the bull‐headed shrike, Lanius bucephalus, were investigated over the six breeding phases of this species. Standardized body mass (SBM), which was defined as body mass divided by the length of the tarsus, of the males was relatively constant over the phrases, while the SBM of the females changed drastically. In the females, the SBM during egg‐laying was higher than the SBM in all the other breeding phases. The SBM of the females did not differ between the incubation and early‐nestling phases, and was lowest during the fledgling phase. Mass loss in bull‐headed shrikes did not correspond to an adaptive adjustment of body mass to permit a reduction in the power required for flight in the nestling period. It is likely that incubating females constantly maintain their body mass to invest in parental efforts from the incubating to nestling periods.

Remote-sensing systems and seabirds: their use, abuse and potential for measuring marine environmental variables

We examined how seabirds might be used to study marine environmental variables, which necessitates knowing location and the value of the variable to be studied. Five systems can potentially be used for determination of location: VHF (Very High Frequency) telemetry, PTT (Platform Terminal Transmitters) telemetry, GLS (Global Location Service) geolocation methods, dead reckoning and GPS (Global Positioning System), each with its own advantages with respect to accuracy, potential number of fixes and size. Temperature and light were used to illustrate potential difficulties in recording environmental variables. Systems currently used on seabirds for measurement of temperature respond slowly to environmental changes; thus, they may not measure sea surface temperature adequately when contact periods with water bodies are too short. Light can be easily measured for light extinction studies, but sensor orientation plays a large role in determining recorded values. Both problems can be corrected. The foraging behaviour of seabirds was also examined in order to identify those features which would be useful for determination of marine environmental variables at a variety of spatial and temporal scales. Area coverage by birds is highly dependent on breeding phase and tends to be concentrated in areas where prey acquisition is particularly enhanced. The identification of these sites may be of particular interest to marine biologists. 'Plungers' and 'divers' are potentially most useful for assessment of variables deeper within the water column, with some divers spending up to 90% of their time sub-surface. Few seabirds exploit the water column deeper than 20 m, although some divers regularly exceed 50 m (primarily penguins and auks), while 2 species dive in excess of 300 m. The wide-ranging behaviour of seabirds coupled, in many instances, with their substantial body size makes them potentially excellent carriers of sophisticated environmental measuring technology; however, the ethical question of how much the well-being of birds can, and should, be compromised by such an approach needs to be carefully considered.

Regulation of Yolk-Androgen Concentrations by Plasma Prolactin in the American Kestrel

The concentrations of maternally derived androgens in the yolks of avian eggs vary within and among clutches, but a mechanistic basis for this variation has not been elucidated. We investigated in the American kestrel, Falco sparverius, whether changes in plasma-prolactin concentrations induced by changes in photoperiod and food supply affect yolk-androgen concentrations. Over the course of a photoinduced breeding period in the laboratory, we measured concentrations of plasma immunoreactive prolactin (ir-prolactin) in female kestrels with ad libitum food availability (control) or food availability that was reduced during the early breeding period. In a second laboratory study, we administered via osmotic mini-pumps ovine prolactin (o-prolactin) to females beginning on the day they laid their first egg of a clutch (egg-day 1) to determine the effects of high prolactin concentrations on yolk-androgen concentrations. In both this study and one on free-living kestrels, we quantified changes in yolk-androgen concentrations with date of clutch initiation. Concentrations of ir-prolactin in nonlaying females rose with date, irrespective of food treatment. Egg-day 1 ir-prolactin concentrations were higher in control females laying late during the breeding phase than in those laying early. This increase was absent in food-reduced females. Yolk-androgen concentrations in eggs 3 and 4 but not eggs 1 and 2 of the clutch were higher in clutches initiated late than in clutches initiated early in the breeding phase in both the field and laboratory. o-Prolactin treatment elevated yolk-testosterone but not androstenedione concentrations. These findings suggest that, in American kestrels, seasonal and laying-associated increases in plasma-prolactin concentrations elevate yolk-testosterone concentrations. Food availability and other factors may interact with date to regulate the effects of prolactin on yolk-testosterone deposition.

The resting metabolic cost of egg laying and nestling feeding in great tits.

To estimate the metabolic costs of regrowth of reproductive organs and formation of eggs, we compared the resting metabolic rate (RMR) of female great tits (Parus major) during the periods of ovarian recrudescence, egg laying, nestling feeding and during winter. We found RMR of individual females, as measured in an open circuit respirometer during night, to be significantly higher during all the breeding phases when compared to measurements during the winter. Females had a 12% increase in RMR during the nest-building phase, an increase of 27% during egg production and an increase of 20% during the chick feeding phase compared to RMR during winter. However, we found no significant difference in energy expenditure during the night between females producing eggs and females feeding chicks. A causal link between RMR and egg production was further confirmed by females producing large eggs having a higher RMR than females producing small eggs. Mass-specific RMR increased steadily from the winter throughout the breeding season, being highest when females were feeding their nestlings. Thus, even though females did not produce ovary-oviduct tissue or eggs during chick feeding, they had a very high RMR. We conclude that the biosynthetic cost of egg formation will probably not limit clutch size but may well, together with the cost of ovary-oviduct recrudescence, influence the timing of reproduction. We suggest that the high RMR of females feeding nestlings, probably is due to an increase in size and efficiency of the alimentary tract, needed to sustain a high rate of energy turnover during this period.

A REPRODUCTIVE PHASE-DEPENDENT EFFECT OF DIETARY L-TRYPTOPHAN ON PINEAL GLAND AND GONAD OF A NOCTURNAL BIRD, INDIAN SPOTTED OWLET ATHENE BRAMA

Unlike other temperate owls, Indian spotted owlet Athene brama possesses a well-developed pineal gland that secrets moderate amount of hydroxy- (serotonin) and methoxy- (melatonin) indoles in circulation. However, in this study, we have reported the response of this endocrine gland to exogenous L-Tryptophan (precursor of the above indoles), and also its effect on gonads of this nocturnal bird. During breeding phase or pineal inactive phase (March), oral treatment of L-Trp (0.5 mg/100 g Bwt/day) significantly increased the pineal gland wt and plasma melatonin (MEL) level, while decreased the gonadal wt and plasma sex steroids levels (estradiol and progesterone in female and testosterone in male). Interestingly, during reproductively quiescent phase or pineal active phase (August), similar amount of L-Trp significantly decreased the plasma MEL level, while increased the above sex steroid levels in plasma. Finally, the results show a clear reproductive phase-dependent inverse effect of L-Trp on pineal gland and gonads for both sexes of the spotted owlets, and suggest that the therapeutic use of this amino acid would be a great advantage for controlling the reproduction of these economically important birds.

COVARIATION OF CLUTCH SIZE, LAYING DATE, AND INCUBATION TENDENCY IN THE AMERICAN KESTREL

Seasonal decline in clutch size is common in birds, but the proximate mechanisms for this phenomenon have not been elucidated. The most credible model to date posits that late-laying females lay fewer eggs due to a seasonal increase in the tendency to incubate during laying, which inhibits egg production. We tested this model with free-living and laboratory American Kestrels (Falco sparverius) by quantifying changes in clutch size and incubation tendency during laying over the course of the breeding phase. Consistent with the model, clutch size in free-living kestrels decreased while incubation increased with progress of the 74-day breeding phase. Inconsistent with the model, variation in incubation tendency during laying was not associated with clutch size in either the field or the laboratory. In the laboratory, incubation increased but clutch size did not decrease over the course of the 77-day breeding phase. In the laboratory, females that nested early in one breeding phase renested more quickly and nested in a second breeding phase more quickly than females nesting late in the first breeding phase. This indicates that timing of laying is, in part, a property of individual females, independent of environmental factors. Together, our findings suggest that both clutch size and timing of laying are inherent, correlated properties of particular females. Although incubation tendency may influence clutch size, other factors appear to override its influence. Covariación del Tamaño de la Nidada, la Fecha de Postura y la Tendencia de Incubación en Falco sparverius Resumen. Aunque la disminución estacional en el tamaño de la nidada es común entre las aves, los mecanismos proximales para este fenómeno no han sido elucidados. El modelo de mayor credibilidad propuesto hasta el momento sugiere que las hembras que ovipositan tarde ponen menos huevos debido a un aumento estacional en la tendencia a incubar durante la postura que inhibe la producción de huevos. Pusimos a prueba este modelo con individuos de Falco sparverius en condiciones naturales y en cautiverio, cuantificando los cambios en el tamaño de la nidada y la tendencia a incubar durante la postura a lo largo de la época reproductiva. Tal como el modelo plantea, el tamaño de la nidada en individuos silvestres de F. sparverius disminuyó mientras que la incubación aumentó a medida que transcurrían los 74 días de la época de reproducción. Mientras tanto, en contraste con el modelo, la variación en la tendencia a incubar durante la postura no estuvo asociada con el tamaño de la nidada ni en el campo ni en el laboratorio. En el laboratorio, la incubación aumentó pero el tamaño de la nidada no disminuyó en el transcurso de la época reproductiva (77 días). En condiciones de laboratorio, las hembras que anidaron temprano en una fase reproductiva volvieron a anidar más rápidamente en una segunda fase que las hembras que anidaron tarde en la primera. Esto indica que el tiempo en que se hace la postura es en parte una propiedad de cada hembra y es independiente de factores ambientales. En conjunto, nuestros hallazgos sugieren que tanto el tamaño de la nidada como el momento de la postura son propiedades correlacionadas de cada hembra en particular. Aunque la tendencia a incubar podría influenciar el tamaño de la nidada, otros factores parecen anular su influencia.

The use of incubation behavior to adjust avian reproductive costs after egg laying

Reproduction in birds requires the input of time and energy during discrete breeding phases leading to investment trade-offs between laying date, clutch size, body mass, and incubation constancy. We investigated costs during incubation by experimentally enlarging 25 clutches of white-tailed ptarmigan Lagopus leucurus. The experiment was conducted in 2 years, one with harsh weather that forced a natural delay in reproduction. When forced to delay egg-laying, females began incubation with poorer body condition and foraged more during incubation. Rates of mass loss during incubation were not affected by clutch enlargement, and did not differ between harsh and benign years; however, females that were heavier at the start of incubation lost more mass than lighter females. Clutch-enlarged females had reduced nest attendance compared to control birds in both years and incubation periods increased by up to 2 days relative to controls. In the harsh year, there was a trend for clutch-enlarged females to have lower nest success, but there was no effect on overwinter survival. Different behavioral responses by females in the 2 years showed that incubation costs may depend on other factors such as female quality, food supply, or weather conditions. Incubation is a dynamic period during which birds may adjust energy balances by varying body condition and food intake.

Effects of Pinealectomy and Exogenous Melatonin on the Thyroid Gland Activity Varies in Relation to Reproductive Status of Male Spotted Munia (Lonchura punctulata; Aves, Passeriformes)

The purpose of this investigation was to explore whether the pineal organ and its hormone melatonin has any influence on the activity of thyroid glands, if so, how that relates to the reproductive status of a hitherto unstudied seasonally breeding wild bird. Accordingly, an identical experimental regimen was followed with adult male spotted munia (Lonchura punctulata; Passeriformes) during both its gametogenically active (August-September) and inactive (March-April) phases of the annual reproductive cycle. In either case, the levels of circulating thyroid hormones (both T3 and T4) and cellular characteristics of thyroid glands in groups of birds were studied following surgical removal of the pineal gland and/or daily afternoon administration of melatonin (10 μg/ 100 g body weight/ day for 30 days). The results of the same experimental schedule were found to be different depending on the sexual status of the concerned birds. During the breeding phase, pinealectomy (Px) induced significantly decreased values of T3 and increased for T4 along with hypertrophy of the thyroid follicular cells (TFC). The changes were reversed in melatonin treated Px birds. An increased amount of T3 and decreased concentration of serum T4 were also observed in melatonin injected intact birds. Conversely, the responses of TFC and of thyroid hormones in blood to either Px, or Px with melatonin, or to melatonin alone in intact munias during their inactive reproductive phase were just opposite to those noted during the breeding phase. The results of the present study suggest an influence of the pineal upon the thyroid in spotted munia. Moreover, it appears that this influence is carried out by melatonin, the action of which is reversible in relation with the gametogenic status of the concerned avian species.

Food consumption of tuna in the Equatorial Atlantic ocean: FAD-associated versus unassociated schools

Since 1991, fishing operations on tuna schools associated with drifting Fish Aggregating Devices (FADs) have become widespread in the purse seine fishery in the Gulf of Guinea. In the offshore South Sherbro area (0–5° N, 10–20° W), FAD-associated catches represent about 75 % of the total catch. This FAD fishery exploits concentrations of skipjack mixed with a smaller amount of bigeye and yellowfin tuna of similar size (46 cm), and some large yellowfin. Catches on unassociated tuna schools are mainly composed of large yellowfin in breeding phase and skipjack. Here we studied tuna diet in relation with the aggregation mode (FAD-associated or unassociated tuna schools), species, and size. The stomach contents of around 800 fish were analysed. Numerous empty stomachs were found, especially in fish caught under FADs. Diets were similar for all small-size tuna sharing the same aggregation type. Small tuna mainly feed on Vinciguerria nimbaria (Photichthyidae), a mesopelagic fish of the micronekton, whereas large tuna mainly feed on Scombridae, mixed with Cubiceps pauciradiatus (Nomeidae) when they were caught in unassociated schools. The feeding habits of tuna are discussed with emphasis on the behavior of V. nimbaria. Estimations of the daily ration of similarly sized tuna with the same aggregation mode were very close. The low estimated rations for small, FAD-associated tuna show that logs do not have a trophic function, but rather are a refuge. In contrast, FADs seem to influence the diet of large tuna because of the Scombridae prey that probably is associated to the FAD.

Melatonin Counteracts the Stimulatory Effects of Blinding or Exposure to Red Light on Reproduction in the Skipper Frog Rana cyanophlyctis

An earlier study reported that blinding or exposure to red light stimulates reproduction in R. cyanophlyctis. The present study investigates whether melatonin counteracted blinding- or red-light-induced ovarian stimulation. The study consisted of two experiments carried out during the prebreeding (March/April) and breeding phase (August/September) of the reproductive cycle of this species. In experiment 1, exposure to red light for 30 days increased (P<0.01) the gonadosomatic index (GSI) and oviductal weights, whereas exposure to continuous darkness for the same duration decreased (P<0.01) the GSI. Data on follicular kinetics revealed an increase in vitellogenic oocytes and decrease in previtellogenic oocyte numbers following exposure to red lights. Exposure to continuous dark on the other hand increased previtellogenic oocyte and decreased vitellogenic oocyte numbers. In experiment 2, the GSI and the number of vitellogenic oocytes increased in blinded and red-light-exposed frogs. However, treatment with melatonin (15 μg sc) for 30 days to both these groups of frogs reduced the GSI, oviductal weights, and the number of vitellogenic oocytes. The results both confirm earlier finding that blinding and exposure to red light stimulate ovarian growth and also demonstrate that melatonin counteracts blinding or red-light-induced stimulation of ovarian activity. This apart, the findings from experiment 1 demonstrate for the first time that exposure to continuous dark inhibits ovarian growth in this species. Ocular melatonin seems to play an important role in regulation of reproduction in this species.