Hormonal evidence for induced ovulation in Monodelphis domestica.

Breeding activity in the South American grey opossum, Monodelphis domestica, is stimulated by the presence of males. This study presents the first analysis of changes in concentrations of plasma progesterone during pregnant and nonpregnant cycles. In Expt 1, females were paired with either intact or vasectomized males to stimulate a reproductive cycle, or were isolated from males. Within 4-8 days of pairing, females showed marked changes in the size of the urogenital opening (vulva), which were paralleled by similar changes in body weight (11.4 +/- 2%; mean +/- SEM; n = 13). There was a second increase and decrease in body weight (21.7 +/- 3.3%; n = 13) in pregnant and nonpregnant cycles during the luteal phase of the cycle. Changes in concentrations of plasma progesterone, determined from samples collected three times a week, were similar in pregnant and nonpregnant cycles. Plasma progesterone concentration, which was increased for 15-18 days, showed two distinct peaks. The first peak, 3-4.5 ng ml-1, occurred immediately after the decrease in vulval swelling, and the second peak (1-2 ng ml-1) occurred 8-12 days later. Concentrations of plasma progesterone were low before parturition occurred. Females isolated from males for 35 days showed no changes in body weight or vulval swelling and concentrations of plasma progesterone remained undetectable. In Expt 2, concentrations of luteinizing hormone (LH) in plasma were determined twice a day for the first few days after pairing. In three of five females an LH peak was detected coincident with the maximal swelling of the vulva.     

Development and application of a monoclonal antibody-based sandwich ELISA for quantification of Japanese medaka (Oryzias latipes) vitellogenin

Vitellogenin (Vtg) was purified from ascitic fluid of a 17beta-estradiol (E2)-treated female Japanese medaka by anion-exchange chromatography. The molecular mass of medaka Vtg by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), corresponding to the Vtg monomer, was 200 kDa. BALB/c mice were immunized with purified-Vtg and two hybridoma clones producing specific antibodies against medaka Vtg were selected. The specificity of these monoclonal antibodies (mAbs) was evaluated by Western blot analysis of the plasma proteins separated on SDS-PAGE, and no cross-reactivity was observed with plasma proteins from control males. A sandwich enzyme-linked immunosorbent assay (ELISA) for quantification of medaka Vtg was developed using these mAbs. The assay range was between 1 and 100 ng/ml, and the intra- and inter-assay variations determined from plasma samples were within 7.7 and 8.5%, respectively. Recovery of medaka Vtg added to plasma was 92-111%. In a plasma dilution test, plots of Vtg concentration gave a straight line. After exposure of male medaka to E2 (10 ng/l), Vtg appeared in liver and plasma on the first day and reached a maximum on the 3rd to 5th day. The sandwich ELISA could be useful for the detection of estrogenic properties, and the medaka Vtg bioassay could be a very sensitive and good tool for screening of endocrine disrupting compounds.     

Does Breeding Ornamentation Signal Genetic Quality in Arctic charr, <Emphasis Type="Italic">Salvelinus alpinus</Emphasis>?

Genetic theories of sexual selection predict that most ornamental secondary sexual traits provide reliable indication of the genetic quality of their bearers. Accordingly, also the offspring of mates with elaborate mating display should perform better than those of less conspicuous counterparts. In this study, we used Arctic charr (Salvelinus alpinus) as a model species to investigate whether the variation in a carotenoid-based red breeding coloration (a sexually dichromatic trait) in different sexes would reflect differences in individual genetic variability, one measure of individual quality, and/or indirectly, be manifested in variation in the offspring’s early viability and growth. We created maternal half-sibling families by artificially fertilizing the eggs with milt from bright- and pale-coloured males and then held the resulting progenies under identical hatchery conditions. The expression of red coloration among parental fish was not associated with their genetic diversity estimates in either sex nor did offspring sired by bright males consistently differ in terms of embryo survival or endogenous growth efficiency from offspring sired by pale males. By contrast, maternal effects were notably strong and, additionally, the degree of female coloration was negatively linked to their reproductive potential. The more intensely coloured females had a smaller relative fecundity and they also produced offspring of lower viability, implying a significant trade-off in resource allocation between ornamentation and offspring. Our results indicate that the red breeding ornamentation of Arctic charr is likely to be informative rather among females than males when the reproductive quality is predicted on grounds of the number of offspring produced. Nevertheless, this study does not support the direct selection hypothesis in explaining the evolution of female ornamentation, but rather suggests that the less intense coloration of female charr compared to males may reflect inter-sexual differences in the trade-off between natural and sexual selection.     

PCB disruption of the hypothalamus-pituitary-interrenal axis involves brain glucocorticoid receptor downregulation in anadromous Arctic charr

We examined whether brain glucocorticoid receptor (GR) modulation by polychlorinated biphenyls (PCBs) was involved in the abnormal cortisol response to stress seen in anadromous Arctic charr (Salvelinus alpinus). Fish treated with Aroclor 1254 (0, 1, 10, and 100 mg/kg body mass) were maintained for 5 mo without feeding in the winter to mimic their seasonal fasting cycle, whereas a fed group with 0 and 100 mg/kg Aroclor was maintained for comparison. Fasting elevated plasma cortisol levels and brain GR content but depressed heat shock protein 90 (hsp90) and interrenal cortisol production capacity. Exposure of fasted fish to Aroclor 1254 resulted in a dose-dependent increase in brain total PCB content. This accumulation in fish with high PCB dose was threefold higher in fasted fish compared with fed fish. PCBs depressed plasma cortisol levels but did not affect in vitro interrenal cortisol production capacity in fasted charr. At high PCB dose, the brain GR content was significantly lower in the fasted fish and this corresponded with a lower brain hsp70 and hsp90 content. The elevation of plasma cortisol levels and upregulation of brain GR content may be an important adaptation to extended fasting in anadromous Arctic charr, and this response was disrupted by PCBs. Taken together, the hypothalamus-pituitary-interrenal axis is a target for PCB impact during winter emaciation in anadromous Arctic charr.     

Mature males of Arctic charr,Salvelinus alpinus,release F-type prostaglandins to attract conspecific mature females and stimulate their spawning behaviour

Synopsis We examined the behavioural and biological functions of prostaglandins (PG) of F-type as a chemosensory signal during spawning in Arctic charr. Immunoassay revealed F-type PGs in water inhabited by ripe charr of both sexes performing spawning-related acts. High concentrations of immunoreactive PGFs seemed to coincide with male spawning activity. Ripe isolated males were more odorous to other charr (as assayed by EOG) than either females or immature charr. When these males received chemical cues from ovulated females, they increased their release of odorants, including F-type PGs, into the water. PGF_2α at concentrations of 0.1 nM attracted ovulated females and ripe males. It also stimulated digging behaviour in mature females. It is concluded that F-type PGs or their derivatives are released by ripe males on the spawning grounds to attract females and elicit their spawning behaviour.     

Effects of fasting on temporal changes in plasma concentrations of sex steroids, growth hormone and insulin‐like growth factor I, and reproductive investment in Arctic charr

Proportions of maturing fish and reproductive output [egg size, relative fecundity, spermatocrit and gonado‐somatic index ( I _G)] were studied in repeat‐spawning (+4 year old) male and female Arctic charr Salvelinus alpinus , subjected to periods of fasting. Groups of individually tagged Arctic charr were fasted for c . 3, 6, 7 and 9 months, from November 1998. In the period February to November 1999, size (fork length and mass), specific growth rate ( G ), condition factor ( K ) and plasma concentrations of growth hormone (GH), insulin‐like growth factor I (IGF‐I), oestradiol‐17β(E₂; females) and 11‐ketotestosterone (11KT; males), were monitored monthly. Maturing fish in each group started to gain mass soon after food was made available, and both sexes reached the highest K and G c . 2 months after the onset of feeding. The fasting regimes resulted in different growth patterns during spring and summer when energy stores are normally replenished in Arctic charr, and K prior to the breeding season was significantly higher in the groups fasted for 3 and 6 months compared to the groups fasted for 7 and 9 months. There were significant positive correlations between K during the period prior to the breeding season and reproductive output in terms of the I _G, spermatocrit and relative fecundity. There was, however, no clear relationship between the length of starvation and the proportion of maturing fish. Likewise, no clear relationships were found between reproductive development and plasma levels of GH and IGF‐I, although both showed marked seasonal changes, being 'down‐regulated' during winter months and 'up‐regulated' throughout summer months.     

Experimental evidence for paternal effects on offspring growth rate in Arctic charr (Salvelinus alpinus)

Sexual selection theory predicts that females should choose males that signal viability and quality. However, few studies have found fitness benefits among females mating with highly ornamented males. Here, we use Arctic charr (Salvelinus alpinus), a teleost fish with no parental care, to investigate whether females could gain fitness benefits by mating with highly ornamented and large-sized males. Carotenoid-based coloration signalled by males during spawning is believed to be an indicator of good genes for this species. Paternal effects on offspring size (body length and dry body mass) were examined experimentally by crossing eggs and sperm in vitro from 12 females and 24 males in a split-brood design and raising larvae to 30 days past hatching. We clearly demonstrated that there was a relationship between offspring size and paternal coloration. However, a negative interaction between paternal length and coloration was evident for offspring length, indicating that positive effects of paternal coloration were only present for smaller males. Thus, the red spawning coloration of the male Arctic charr seems to be an indicator of good genes, but the effect of paternal coloration on offspring length, an indicator of 'offspring quality', is size dependent.     

Induction of vitellogenesis by estradiol-17beta and development of enzyme-linked immunosorbant assays to quantify plasma vitellogenin levels in green turtles (Chelonia mydas)

Treatment of juvenile green turtles (Chelonia mydas) with estradiol-17beta resulted in the induction of a 200 kDa plasma protein, consistent with vitellogenin (Vtg). The N-terminal 15 amino acids of the anion exchange purified protein shared sequence homologies with vitellogenins of several vertebrate species. Rabbit antiserum raised against purified Vtg recognized the plasma protein as well as several yolk proteins. Monoclonal antibody (Mab) HL1248, produced by inoculating mice with turtle yolk granules, showed specificity for plasma Vtg as well as a set of yolk proteins 120, 82, 43 and 32 kDa in size. The N-terminal 22 amino acids of the 43 kDa yolk protein was similar to the lipovitellin I subunit of Vtg of several vertebrate species. The peptide mass map of the 82 kDa yolk protein shared enough ions with that of purified plasma Vtg to support the conclusion that this protein was derived from plasma Vtg. Taken together, these results validate the specificity of Mab HL1248 for Vtg. Using purified Vtg concentration standards, competition and antigen capture enzyme-linked immunosorbant assays (ELISAs) were shown to quantitatively detect Vtg in green turtle plasma. Pre-induced plasma of juvenile turtles had Vtg levels of 2-4 micrograms/ml whereas post-estradiol exposure samples had 38-40 mg/ml. The plasma Vtg concentration of a nesting female turtle was 4.6 mg/ml, approximately 20-fold higher than that of a non-nesting adult female. The antigen capture ELISA will be useful in population studies of this endangered species, to detect vitellogenesis in females that will nest in a given year and to detect inappropriate Vtg levels in turtles exposed to xenoestrogens.     

Ascorbic acid status in high-mountain charr,Salvelinus alpinus,in relation to the reproductive cycle

Synopsis Concentrations of total and dehydroascorbic acids and of glutathione were determined in tissues of male and female Arctic charr at different stages of the reproductive cycle. In fish inhabiting an Alpine lake (2344 m above sea level) the ascorbic acid concentrations were significantly higher in the ovary (344 g g^–1 in August) than in the testis (62.6 g g^–1). The ascorbate concentration was significantly higher in liver and kidney of males than in females in the period prior to spawning. This suggests that there was an intensive investment of body ascorbate reserves in the ovary and the results indicated that females deposited approximately 10 times the amount of vitamin C in ovaries than males deposited in testes. However, the endogenous stores cannot account for all ascorbate deposited in ovaries and the remainder must come from food consumed in summer. Since the resident charr of the high-mountain lake had the ascorbate concentration in ovary by one order of magnitude higher than in cultured salmonids it is plausible to speculate that the change in ascorbic acid metabolism reflects the adaptation to the harsh environmental conditions.     

Evidence from plasma progesterone concentrations for male-induced ovulation in the brush-tailed bettong, Bettongia penicillata.

Female brush-tailed bettongs, Bettongia penicillata, were housed with either an intact or vasectomized male or isolated from males in the peripartum period. Development of the quiescent corpus luteum formed at the post partum oestrus was initiated by removing the pouch young. Blood samples for analysis of plasma progesterone were collected from the females 2 days before removal of pouch young, daily for 5 or 6 days and then 2-3 times each week until 19 days after removal of pouch young. Plasma progesterone profiles were similar in pregnant and nonpregnant cycles. There was an early progesterone peak (1206 +/- 121 pg ml-1, mean +/- SEM; n = 16) between days 2 and 5 after removal of pouch young, and a second period of high concentrations (greater than 800 pg ml-1) before birth on day 17.4 +/- 0.2 (n = 16). The interval between the early peak and birth was 14 or 15 days. On five of 34 occasions, no increases in plasma progesterone concentrations occurred after removal of pouch young. On 12 of 15 occasions for 13 females that had been isolated from males post partum, plasma progesterone concentrations also remained low (less than 100 pg ml-1) and did not change after removal of pouch young. Females that showed no increases in plasma progesterone concentration after removal of pouch young had significantly lower (P less than 0.001) plasma progesterone concentrations while lactating than those females that did undergo a cycle after removal of pouch young (60 +/- 4 pg ml-1, n = 17 and 225 +/- 23 pg ml-1, n = 30, respectively). Females isolated from males post partum, and monitored until day 12 after removal of the pouch young, and that showed no increases in progesterone in this period, had ovaries that contained no corpus luteum, only corpora albicantia and numerous atretic or developing follicles. We conclude that brush-tailed bettongs are induced ovulators, a characteristic described for only one other marsupial, Monodelphis domestica, from South America.     

Gonadal differentiation and hormonal sex reversal in Arctic charr (Salvelinus alpinus)

The purpose of this study was to develop a practical protocol for the production of female populations of Arctic charr (Salvelinus alpinus). Achieving this required knowledge of the timing of gonadal differentiation. Undifferentiated gonads were observed microscopically to be present by 194 degrees C-days post-hatch and definitive germ cells by 346 degrees C-days post-hatch, where " degrees C-days" denote acquired thermal units calculated as the product of temperature and days. Some of the gonads had developed a lumen by 510 degrees C-days post-hatch, and by 681 degrees C-days post-hatch anatomical divergence into two types of gonads was clear. Two protocols (immersion and feeding) were tested for hormonal sex reversal of genotypic females using the synthetic androgen 17alpha-methyldihydrotestosterone (MDHT). Six-hour MDHT immersions (0.5, 1, 3, 5 and 10 mg/L) were carried out weekly from hatch to first feeding (140 degrees C-days post-hatch), whereas daily feeding treatments (0.5 mg/kg) went from 140 to 600 degrees C-days post-hatch. The sex ratios of all immersion experimental groups were significantly different from the control, with the proportion of presumptive males increasing as MDHT concentration increased. The highest immersion treatment, 10 mg/L, yielded a population of 90% presumptive males and 10% with atypical gonads. However, the most effective treatment, yielding a population of 90% presumptive males and no fish with atypical gonads, was the feeding treatment. Given that female salmonid fishes are homogametic, sex-reversed (masculinized) genotypic females produced in this way can serve as broodstock for the creation of all-female charr populations for aquaculture.     

Circannual vitellogenin levels in Chinese loach <Emphasis Type="Italic">(Misgurnus anguillicaudatus)</Emphasis>

To improve the use of the Chinese loach, Misgurnus anguillicaudatus, as a sentinel species for environmental investigations, normal ranges of plasma vitellogenin (Vtg) was studied. Male and female loaches were collected every 2 months from November 2004 to September 2005, and a specific and sensitive competitive enzyme-linked immunosorbent assay (ELISA) was used to determine plasma Vtg levels. Our data indicated that the average maximum Vtg level of female loaches (757 ± 356 μg mL⁻¹) appeared in March, approximately 1 month before spawning. Female plasma Vtg significantly correlated with gonadosomatic index (GSI) which indicated that female plasma Vtg can be used as an indicator of the reproductive stages of the ovary. Low detectable plasma Vtg levels was detected in a number of male loaches, and the highest average plasma Vtg concentration attained to the level of μg mL⁻¹; after exposure to estrogenic compounds by waterborne, injection or oral food, Vtg can be induced in male fish, so the presence of Vtg in male loaches might be attributed to the ingestion of estrogenic substances in food, the contamination of estrogenic compounds from the living environment, or the estrogen used by the local fish breeders to accelerate the rate of growth during artificial culture. The results indicate that Vtg levels in male and female Chinese loaches will be very helpful in field studies which use Chinese loach as a sentinel species.     

Annual variability in the life-history characteristics of brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) in a subalpine Norwegian lake

The annual variability in growth and life history traits of brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.)) in Lake Atnsjøen, a Norwegian subalpine lake, was studied over a period of 13 years (1985–1997). The extent to which life-history characteristics recorded on one occasion can be regarded as representative for the population was explored. We found inter-cohort variation in growth for both species; estimates of asymptotic length (L _∞) in ten cohorts ranged between 225–305 mm (CV = 10.5%) for brown trout and 273–301 mm (CV = 4.1%) for Arctic charr. However, this variation was much lower than inter-population variation for brown trout based on single samples from 169 populations (CV = 24.6%). In Lake Atnsjøen, annual growth increment correlated highly with the number of days warmer than 7?°C (R ²=0.60–0.89) for brown trout, and days warmer than 10?°C (R ²=0.40–0.58) for Arctic charr. Females of Arctic charr were younger at sexual maturity than males, while no such difference was found in brown trout. Generally speaking, early maturing individuals of both species grew faster, particularly from age-2 and onwards, than immature individuals. Early maturing individuals, however, were smaller at maturity than those maturing one year older. Age and size at maturity were significantly correlated with asymptotic lengths only in Arctic charr females.     

In vitro antifilarial activity of extracts of the medicinal plant Cardiospermum halicacabum against Brugia pahangi

The in vitro effects of ethanol and aqueous extracts of the medicinal plant Cardiospermum halicacabum on adult worms and microfilariae of Brugia pahangi were investigated. With or without the plant extracts in culture medium, the motility of adult worms, microfilariae and microfilarial release from female worms were monitored daily. After 7 days of culture, viability or tissue damage of adult worms was assessed using the MTT assay. At > 500 microg ml-1, the aqueous extract significantly reduced motility of adult females after 24 h of exposure and adult males after 3 days. The aqueous extract, at > 500 microg ml-1, also significantly reduced microfilarial release from female worms, starting on day 2. The reduction in the motility of adult worms and the pattern of microfilarial release from female worms were concentration and time dependent. The MTT assay results revealed that adult worms cultured in the presence of aqueous extracts at > 500 microg ml-1 were damaged. However, the aqueous extract did not affect the motility of microfilariae with the exception of those in higher concentration extracts. Higher concentrations of ethanol extracts (2 mg ml-1) inhibited both the motility of adult worms and the release of microfilariae from females. Little effect of ethanol extracts was detected by the MTT assay, as only slight damage was caused to worms exposed only to the highest concentration (2 mg ml-1). However, ethanol extract at 500 microg ml-1 rapidly reduced the motility of microfilariae on day 2. The present study revealed that an aqueous extract of C. halicacabum has mild but definite direct macrofilaricidal action on B. pahangi.     

An enzyme-linked immunosorbent assay (ELISA) for measuring vitellogenin in English sole (Pleuronectes vetulus): development, validation and cross-reactivity with other pleuronectids

Vitellogenin (Vtg) is a yolk protein produced in the liver of oviparous animals in response to estrogen. Vitellogenesis is normally observed only in sexually mature females, but it can be induced in male and juvenile animals by exposure to exogenous estradiol (E₂) or substances that mimic estrogens. The abnormal production of Vtg by males can, therefore, be used as a biological indicator for exposure to xenoestrogens. In this study, an enzyme-linked immunosorbent assay (ELISA) for measuring Vtg in English sole (Pleuronectes vetulus) was developed and validated. Plasmatic Vtg was purified from E₂-injected male English sole using DEAE ion-exchange and Sepharose size-exclusion chromatography, and polyclonal antibodies against the purified Vtg protein were generated in rabbits. In this assay, a competition for the Vtg antibody was established between Vtg coated onto microtiter plate wells and free Vtg. Detection of adsorbed antigen–antibody complexes was achieved using a horseradish peroxidase conjugated anti-rabbit secondary antibody whose enzyme activity was revealed with 3,3′,5,5′-tetramethyl benzidine (TMB) substrate. Assay conditions provided a detectable Vtg range of 10–450 ng ml⁻¹ (85–20% of binding) of diluted sample. Plasma dilution curves from vitellogenic female and E₂-treated male English sole showed parallelism with the standard dilution curve. We are presently conducting field and laboratory studies to investigate estrogenic and anti-estrogenic activity resulting from exposure to contaminants.     

The Effect of Acute Stress and Temperature on Plasma Cortisol and ion Concentrations and Growth of Lake Inari Arctic Charr, Salvelinus Alpinus

One year old, individually tagged Lake Inari Arctic charr, Salvelinus alpinus, were reared at three constant temperatures, 10.3°C, 14.1°C and 18.1°C, over four weeks. Blood samples were collected from a group of unstressed fish after the cultivation period at the same time as another group of fish were subjected to acute handling stress treatment (2min netting in air and 40min (± 20min) recovery period in water). Plasma cortisol, calcium, sodium, potassium and chloride concentrations were measured on both groups. To study the effect of minor daily temperature fluctuations on the stress response of Arctic charr, two additional daily fluctuating temperature (14 ± 1°C, 18 ± 1°C) treatments were established. The samples were taken in the same manner as those in the constant temperature treatments. Growth was fastest at 10.3–14.1°C and clearly lower at 18.1°C. Pre-stress plasma cortisol levels were low but increased slightly with increasing temperature. After stressor treatment, the cortisol concentrations of Arctic charr were clearly higher in all temperature treatments but there were no significant differences in plasma cortisol concentrations among temperatures. Plasma calcium levels increased during the stress treatment but temperature did not modulate this effect. The plasma potassium concentrations declined at 14.1–18.1°C after acute stress but the response was not affected by temperature within this range. The concentrations of sodium and chloride were unaffected by acute stress. Temperatures of 10.3–18.1°C and fluctuating temperature treatments had no influence on any plasma ion concentrations. Arctic charr were able to maintain the plasma ion concentrations in fresh water at 10.3–18.1°C and after acute stress treatment. Results indicate that the optimum temperature for growth of Arctic charr has little to do with the plasma ion concentrations or the ability to maintain those concentrations after short-term stress. The plasma cortisol responses further indicate that the optimum temperature for growth of Arctic charr is not related to the suppressed ability to react to an acute handling stressor. Temperature fluctuations did not cause significant differences in cortisol levels when compared with constant temperatures.     

Synchronous female spawning and male mating behavior in a land-locked population of Japanese charr, Salvelinus leucomaenis japonicus

In resource-based promiscuous mating systems, synchronous spawning of females affects competition among males and variation in the reproductive success of males. We documented the mating behavior of Japanese charr (Salvelinus leucomaenis japonicus) through an annual breeding season to examine the relationship between female spawning synchrony and male mating behavior. Females spawned highly synchronously in the population studied, i.e., approximately half the spawning was finished within the first three days of the entire spawning season (11 days). The daily operational sex ratio (OSR) was nearly 1:1 through the spawning period. The number of males around a spawning female was very small (1.21+/-0.49 males per female) over the spawning ground and period, suggesting that a competitive male could effectively chase subordinate males away from a spawning female. A few males attempted to sneak near the oviposition site of females (16%; 9 of 57 breeding groups), while some males adopted sneaking tactics in the initial phase of females' spawning (24%). We did not observe any males to succeed in sneak fertilizations. We conclude that in this Japanese charr population, the synchronous spawning of females was related to the unbiased daily OSR, male aggregation around females, and consequently whether and how efficiently males engaged in sneak mating behavior.     

Reproductive Investment and Energy Allocation in an Alpine Arctic Charr, Salvelinus alpinus, Population

Reproductive investment was determined in a population of stunted Arctic charr, Salvelinus alpinus, living in an ultra-oligotrophic alpine lake (altitude 1100m) in central Norway (62°51W). No reductions in somatic energy content (carcass and intestines) were detected during the spawning period. Post-spawning somatic lipid, protein and total energy content did not differ between male spawners, female spawners and immatures. The recorded reproductive output consisted of gonad tissue equivalent to 13% of total pre-spawning energy in females and 4% in males, respectively. Mean stored somatic lipid reserves were as low as 2.8% and did not change significantly from pre- (30 June) to post-spawning (1% October) samples. Female fecundity varied between 41 and 84 (mean 60) eggs, with a corresponding body length varying between 110 to 160mm (mean 13%). Mean yearly survival rate after maturation was 70% for females and 64% for males, respectively. This particularly low reproductive investment is discussed in relation to environmental conditions and low resource availability.     

Spawning behavior of Arctic charr (Salvelinus alpinus): Spawning synchrony,vibrational communication,and mate guarding

A mismatch in synchrony between male and female gamete release in external fertilizers can result in reduced or failed fertilization, sperm competition, and reduced paternity. In Arctic charr (Salvelinus alpinus), males can adopt either a guard or sneak tactic resulting in both pre‐ and postcopulatory competition between males with alternative reproduction tactics. Here, spawning behavior of free‐living Arctic charr was video‐recorded, and their reproductive behavior was analyzed. From evaluating 157 spawning events, we observed that females mainly spawned with a guarding male and that the female and the guarding male synchronized timing of gamete release under sperm competition. Although sneakers spawned with higher synchrony than the guarding male in single‐male spawning events, the average sneaker released his milt less synchronized with the female than the guarding male under sperm competition. Approximately 50% of the recorded spawning events occurred under sperm competition, where each event included an average of 2.7 males. Additionally, sneakers were more exposed to sperm competition than guarding males. An influx of males, in close proximity to the female, occurred during the behavioral sequences leading up to egg release, but this influx seemed not dependent on egg release, suggesting that something else than gonadal product attracts sneaker males to the spawning female. Just before and during the actual release of gametes, the spawning couple vibrates their bodies in close contact and it seems likely that this vibrational communication between the spawning couple, which results in a larger amplitude sound wave than seen under regular courting, reveals time of gamete release to sneaker males. Thus, vibrational communication may enable synchrony between the guarding male and the female, and this might be traded against the cost of higher detectability from surrounding sneaker males, eavesdropping in close proximity.