Intrapopulation variation in reproduction by female eastern kingbirds Tyrannus tyrannus: the impacts of age, individual performance, and breeding site

I used data from a 13-year study of eastern kingbirds Tyrannus tyrannus from central New York, USA, to evaluate the relative impact of female age and body size on reproduction. I also calculated repeatabilities of reproductive traits for both females and the sites where they bred in an attempt to evaluate the relative contribution of each to intrapopulation variation in reproduction. Female age had a strong influence on timing of breeding (breeding date advanced by one day for each year of life), but was not a significant source of variation for clutch size, egg mass, number of young to hatch or fledge, or total seasonal production. Repeatabilities of breeding date for females and sites were both significant (0.284 and 0.181, respectively), but the only other significant repeatabilities were for female clutch size (0.282) and female egg mass (0.746). Among-year repeatabilities of breeding date for females who bred at two or more sites over their lifetime were as high as those for females that were site faithful. Thus, breeding date was probably affected independently by the female and site. No measure of productivity exhibited a repeatable pattern in comparisons made among females or sites. All reproductive traits were entered as dependent variables in a series of stepwise multiple regression analyses in an attempt to identify female properties (size, lifespan and condition) that might be linked proximately to differences in breeding statistics. I found that (a) large birds tended to breed the earliest, (b) clutch size was independent of female size, condition and lifespan, (c) female body size and egg size were correlated positively, but (d) production of young was independent of all measured female properties. Reproduction appears to be linked more closely to the female than to the site. Body size accounts for a portion of the repeatable portion of breeding date and egg mass, but most of the intrapopulation variation in these and other traits remained unexplained.     

Photoperiod as a reproductive cue in the marsupial genus Antechinus: ecological and evolutionary consequences

Species in the Australian marsupial genus Antechinus exhibit a short annual mating period which is concluded by the abrupt death of all males. The timing of the annual rut within each of the ten described species varies little from year to year at any given locality, but for some species can differ by up to four months between locations. To determine the influence of photoperiod in regulating the precise interannual synchrony of mating and ovulation, we first investigated populations of each species at over 300 localities throughout their geographical ranges to identify the time of reproduction. We then compared the absolute photoperiod and the rate of change of photoperiod prevailing at the time of reproduction in all population localities. A different, and characteristic, rate of change of photoperiod was correlated strongly with the reproductive timing of four species; there was probably a correlation with reproduction in four more species, but sample sizes were small. For two species, there was no obvious photoperiodic correlation with time of reproduction. There was no evidence that absolute photoperiod or ambient temperature explained the synchrony or narrow timespan of reproduction among any species of Antechinus . Different species-specific ovulatory responses to photoperiod appear to separate the timing of reproduction in sympatric species, with the larger member of species pairs usually breeding first. We suggest that photoperiodic cues (1) allow females to produce young during seasons when food is most reliable and abundant and their energetic demands are maximal; (2) facilitate allochronic isolation between sympatric congeners, and (3) maximize body size differences and hence ecological separation between species.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 365–379.     

Expression of vitellogenin receptor in the ovarian follicles during the reproductive cycle of the spotted ray Torpedo marmorata Risso 1880

The aim of this investigation was to identify the encoding sequence of vitellogenin receptor gene (vtgr), and its expression during the oogenesis in the spotted ray, Torpedo marmorata, in different phases of reproductive cycle. From an ovarian cDNA of vitellogenic female, we obtained a fragment of 581?bp, which corresponds to a partial sequence encoding the vitellogenin receptor (VTGR) in Torpedo (accession number: gi/193244760). This sequence shows a high identity with the VTGR of other vertebrates, particularly Leucoraja erinacea (89% identity) and Squalus acanthias (84% identity). We also showed that vtgr mRNA expression in the ovary modifies during the oogenesis and throughout the reproductive cycle. Indeed, in immature females, whose ovary contains only previtellogenic follicles, vtgr mRNA occurred in the oocyte cortex as well as within intermediate and pyriform cells. In mature females, whose ovary contains pre- and vitellogenic follicles, vtgr mRNA was detectable not only in the oocyte cortex and in intermediate and pyriform cells but also in small follicle cells present in the follicular epithelium of vitellogenic follicles. In ovulating females, that, as pregnant ones, show pre-and vitellogenic follicles, vtgr mRNA was evident in the oocyte cortex only, whereas in pregnant females, no vtgr mRNA was evident. The role of VTGR in the control of Torpedo vitellogenesis is discussed.     

Bioenergetics of age-related versus size-related reproductive tactics in female Viviparus georgianus

Individual Viviparus georgianus from a New York population are iteroparous, maturing in their second year. Ovoviviparous females have a maximum lifespan 1 year longer than that of males (4 + versus 3+ years), though individuals of both sexes can be reproductively active for three consecutive years. Embryophores are carried over winter and released each spring. Female survivorship is positively size related, as is incremental growth within any year. Reproductive effort is age related, increasing from 5.3% for modal 2-year females to 79.7% for modal 4-year females. Reproduction is size limited in 2-year females, no females below 16 mm shell length were found containing broods. The lack of observable survivorship penalties related to reproduction may result from reproductive females have greater biomass and hence greater survivorship. Spat size is positively correlated with female age irrespective of female size, though brood numbers increase with maternal size and growth rates. Caged experiments have shown spat born early to older females grow fastest. Data presented indicate that the young of older females have greater expected lifetime fecundity and fitness. In this population, 3-year females produce approximately 50.0% of each new cohort, with 2-year and 4-year females producing 21.0% and 26.0% respectively. Matrix models of the natural population and modified hypothetical populations emphasize the importance of survivorship and early reproduction in such stable, age-structured populations.     

Re-evaluation of reproductive cycle and fecundity of finetooth sharks Carcharhinus isodon (Valenciennes 1839) from the Northwest Atlantic Ocean,with new observations on ovarian cycle and reproductive endocrinology of biennially reproducing sharks

To provide updated information on life history for improved fishery management, the reproductive cycle of the finetooth shark Carcharhinus isodon from Northwest Atlantic (NWA) populations was investigated by examining temporal changes in morphology and histology of reproductive organs. Changes in plasma concentrations of gonadal sex hormones in relation to reproductive stage were also examined. Increases in testis width, epididymis head width, plasma testosterone concentrations and occurrence of mature spermatozoa were observed in male sharks between December and April, suggesting a seasonal pattern in reproduction that culminates with copulatory activity in May. Increases in maximum follicular diameter, oviducal gland width, plasma 17β-estradiol concentrations and occurrence of vitellogenic follicles were observed in non-pregnant female sharks during the same time period along with the occurrence of newly pregnant females in May, demonstrating strong synchronicity between male and female reproductive cycles. Pregnant females bearing full-term embryos were also observed in May, indicating that parturition occurs between mid-May and early June and gestation requires 12 months. Only transient temporal changes in follicle size and oviducal gland width were observed in pregnant females, indicating that reproductive periodicity is biennial; nonetheless, a single female exhibiting signs of concurrent vitellogenesis and pregnancy was observed. Mean brood size ± S.D. was 3.9 ± 0.9 offspring/female. Fecundity was not significantly correlated with female size, in part due to an unexpectedly high rate of early embryo mortality, which occurred in 11% of pregnant females, and was more common in larger individuals. Changes in ovarian activity during mid-pregnancy were observed, suggesting possible roles for the ovary in regulating some aspects of early to mid-gestation. This study confirms that earlier characterizations of the reproductive cycle and fecundity in NWA finetooth sharks remain valid for use in fishery management. This study also highlights unusual features of finetooth shark pregnancy (e.g., early embryo death, mid-pregnancy changes in ovarian function) that may have broader relevance to understanding elasmobranch reproduction.     

Reproductive tactics and development of sexually dimorphic structures in a stream-dwelling characid fish (Deuterodon stigmaturus) from Atlantic Forest

The reproductive tactics of Deuterodon stigmaturus were investigated in this study, testing whether the species presents a seasonal or opportunistic life-history strategy in a high latitude Atlantic Forest stream in Brazil. The relation between the development of anal-fin spinelets (sexually dimorphic structures in characids) and the reproductive period of D. stigmaturus was also investigated. The species displayed a seasonal life-history strategy, with the reproductive period occurring between austral spring and summer. The reproductive period was related to increase in temperature and photoperiod, corroborating several studies that suggest positive relation between seasonal reproduction and abiotic predictability. The data indicated total spawning occurring in January, coinciding with the month of greatest rainfall (historical and in the study year). However, the observation of postovulatory follicles in previous months suggests small spawning before January. The development of spinelets on the anal-fin was the only sexual dimorphic trait between males and females. Contrasting with several other studies, seasonal development of anal-fin spinelets was observed in adult males, following the reproductive period and regressing afterwards. Thus, some characid species probably retain this structure throughout the year and others do not, which may be related to life-history strategy differences.     

External factors determining seasonal breeding in a subtropical population of the shore crab Pachygrapsus transversus (Gibbes, 1850) (Brachyura,Grapsidae)

Summary

Monthly samples of the shore crab Pachygrapsus transversus from two distinct annual periods showed that ovigerous females are present throughout the year in the population. However, the relative ovigerous abundance of specimens among sexually mature changes from less than 10% during the winter months to almost 80% in summer. Linear correlations for each year revealed that both temperature and photoperiod were positively associated with relative abundance of ovigerous females. Multiple regression analyses suggested that photoperiod was the main factor affecting breeding in this species. Timing of observed reproductive pattern may enhance larval survival because of particular oceanographic conditions in the study region and favor early juvenile development due to certain species-specific growth features.     

Density-dependence vs. density-independence - linking reproductive allocation to population abundance and vegetation greenness

1. Recent studies have shown that optimal reproductive allocation depends on both climatic conditions and population density. We tested this hypothesis using six years of demographic data from eight reindeer (Rangifer tarandus) populations coupled with data on population abundance and vegetation greenness [measured using the Enhanced Vegetation Index (EVI)]. 2. Female spring body mass positively affected summer body mass gain, and lactating females were unable to compensate for harsh winters as efficiently as barren ones. Female spring body mass was highly sensitive to changes in population abundance and vegetation greenness and less dependent on previous autumn body mass and reproductive status. Lactating females were larger than barren females in the spring. Moreover, female autumn body mass was positively related to female autumn body mass and reproductive success and was not very sensitive to changes in vegetation greenness and population abundance. 3. Offspring autumn body mass was positively related to both maternal spring and autumn body mass, and as predicted from theory, offspring were more sensitive to changes in vegetation greenness and population abundance than adult females. A lagged cost of reproduction was present as larger females who were barren, the previous year produced larger offspring than equally sized females that successfully reproduced the previous year. 4. Reproductive success was negatively related to female autumn body mass and positively related to female spring body mass. Moreover, females who successfully reproduced the previous year experienced the highest reproductive success. The fact that negative density-dependence was only present for females that had successfully reproduced the previous year further support the hypothesis that reproduction is costly. 5. This study shows that female reindeer buffer their reproductive allocation according to expected winter conditions and that their buffering abilities were limited by population abundance and a lagged cost of reproduction and enhanced by vegetation greenness.     

Reproductive biology of Philodryas patagoniensis (Snakes: Dipsadidae) in south Brazil: Female reproductive cycle

In this study, we describe the female reproductive cycle of Philodryas patagoniensis in south Brazil, which was described through morpho‐anatomical and histological analyses. The peak of secondary vitellogenesis occurred during winter–spring (July–December), ovulation in spring (October–December), mating and fertilization in spring–summer (October–February), oviposition in spring–autumn (October–May) and births from late spring to autumn (December–July). The diameter of vitellogenic follicles/eggs was larger in winter–spring than in other seasons. The diameter of the shell glands was also larger in winter–spring. In spite of the clear reproductive peak, gonads only showed reduced activity in the autumn. Therefore, at the individual level, females have a discontinuous cyclical reproduction; in the populational level, the reproductive cycle is seasonal semisynchronous. We support the hypothesis that P. patagoniensis have the ability to produce multiple clutches with long‐term stored sperm. Sexual dimorphism in body size was evident, and females are significantly larger and heavier than males. Larger females were able to produce follicles and eggs in larger amount and size. The maternal body size was positively related to the reproductive effort and fecundity. To conclude, we deliberated about the proximal and distal causes that influence the reproductive traits and patterns of P. patagoniensis.     

Seasonal changes in reproductive development in male spiny mice (Acomys spinosissimus) from South Africa

Seasonal reproduction is a common characteristic of many small mammals which inhabit seasonal environments in temperate regions, the sub-tropics as well as the tropics. It is important for an animal to reproduce during the most favourable time of the year to ensure the survival of the young and maximize reproductive success. In southern Africa, female spiny mice (Acomys spinosissimus) breed during the warm and wet spring and summer months, whereas the reproductive pattern of males is unknown although an opportunistic breeding pattern has been implicated. We investigated testes mass and volume, seminiferous tubule diameter, spermatogenesis and plasma testosterone concentrations in a South African population of male spiny mice on a 2-monthly basis over one year. Testes mass and volume started to increase in July/August and was high from September until December. Seminiferous tubule diameter and spermatogenesis increased during the same months. Plasma testosterone concentration was elevated from July/August to November/December. Development of the reproductive characteristics of male spiny mice was correlated with high rainfall and high ambient temperatures, but reproductive development had already started during the dry season and the coldest months. This shows that reproductive development in males may not be dependent on climatic conditions, and other factors, such as photoperiod, may trigger the onset of reproduction. The data, however, suggest that A. spinosissimus is a true seasonal breeder with reproduction confined to the spring and summer months in southern Africa.     

Constraints on, and determinants of, the annual number of breeding attempts in the multi-brooded Black Redstart Phoenicurus ochruros

With reference to models predicting patterns of reproduction in multi-brooded species, I analysed some of the factors potentially affecting the number of breeding attempts per season made by female Black Redstarts Phoenicurus ochruros in the central Swiss Alps. The maximum number of successful broods per female per season was three, the median two. The proportion of females initiating only a single clutch per season varied from 16 to 58% over 10 years. Variation in the frequency of single brooding between years was positively related to the date of the onset of breeding. Egg-laying started after a temperature-related threshold value was crossed in April. Females frequently re-nested before fledglings of the previous brood were independent. Short interbrood intervals were associated with triple brooding. The interbrood interval shortened during the breeding season. Intra-individual variation in the number of breeding attempts per season was partitioned according to female age, laying date of the season's first egg (standardized in relation to the median date of first laying within a year) and the occurrence of breeding failures before the ultimate nesting attempt. However, mortality during the season often terminated breeding early, in particular among novice breeder females. Seasonal reproductive success increased linearly with each additional breeding attempt. The productivity of a breeding attempt was independent of the time in the season. Increased reproductive effort affected neither current or future survival nor reproduction of females. The reproductive patterns and trade-offs in multi-brooded Black Redstarts contrast in many aspects with those found in single-brooded species. They are in accordance with models predicting that multi-brooded species are selected to start breeding as early as possible, continue breeding for as long as conditions are suitable, and save time by overlapping broods.     

Interspawning interval of wild female three-spined stickleback Gasterosteus aculeatus in Alaska

The interspawning interval, or spawning frequency, of wild three-spined stickleback, Gasterosteus aculeatus , was estimated using histological examination of postovulatory follicles (POF). Females in Alaskan lakes appeared to have as much as a 48 h delay between ovulation and ovoposition, yet the POF method could still be used to estimate the interspawning interval. In two Alaskan lakes the interspawning interval was estimated to range from 2·2 to 7·8 days among individual female G. aculeatus . These estimates were consistent with the range (2·5 to 5 days) of previous estimates among individual females from laboratory observations of spawning G. aculeatus , as well as anecdotal accounts of spawning intervals reported from wild populations in Canada (5–10 days). The interspawning interval of females increased during the course of the spawning season in Alaska, showing that the majority of female spawning activity occurred during the earliest portion of the approximate 6-week reproductive season. The increased interspawning interval appears to be related to a previously reported decrease in body condition in reproductive females during the breeding season. Thus, female G. aculeatus may be unable to sustain the initial rate of reproduction as energy stores that support the rapid growth of vitellogenic oocytes are depleted.     

To breed or not to breed: Physiological correlates of reproductive status in a facultatively biennial iguanid

It is unusual for seasonal breeders to frequently skip opportunities for reproduction. We investigated the relationship between physiological state and reproductive decision-making in Galápagos marine iguanas (Amblyrhynchus cristatus), a species in which females typically reproduce biennially, although the proportion of breeding individuals varies significantly across years. Nearly all adult-sized females initiated follicular development prior to the lekking period, but 38% of females resorbed all developing follicles 5-15 days before the start of copulations. Receptive and non-receptive females differed in reproductive hormones during the mate choice period. Testosterone peaked in receptive females immediately prior to copulation, indicating that testosterone or its derivative estradiol likely mediates female receptivity in Galápagos marine iguanas. Non-receptive females showed significant peaks in both testosterone and progesterone during follicular atresia, suggesting that these hormones may be involved in inhibiting vitellogenesis. Two to three weeks prior to the period of reproductive decision-making (and the onset of follicular atresia in non-receptive females) receptive females were in higher body condition, were developing larger follicles, and had lower levels of both baseline and stress-induced corticosterone. Reproduction is extremely costly in this long-lived species, and increases the likelihood of mortality in the year following breeding; females could therefore gain significant benefits from being attuned to indicators of reproductive success. We suggest that corticosterone may modulate reproductive decisions by altering individual sensitivity to both internal and external cues of the likelihood of successful reproduction.     

Effect of environmental temperature on growth- and reproduction-related hormones gene expression in the female blue gourami (Trichogaster trichopterus)

Fish are ectothermic vertebrates, and their gonadal development and spawning are affected by changes in environmental temperature. Recent global temperature changes have increased the importance of studying the effect of temperature on reproduction. The aim of this paper was to study the effect of temperature on oogenesis and hormone gene expression related to reproduction and growth in the blue gourami female maintained under non-reproductive and reproductive conditions. In females under non-reproductive conditions, vitellogenic oocytes, gonadotropin-releasing hormone 3 (GnRH3), β luteinizing hormone (βLH) and growth hormone (GH) mRNA levels were affected by temperature changes. In females maintained under reproductive conditions with non-reproductively active males, a percentage of females in the final oocyte maturation (FOM) stage, pituitary adenylyl cyclase activating polypeptide (PACAP and PRP-PACAP), gonadotropins and GH mRNA levels were affected due to temperature changes. In females maintained under reproductive conditions with reproductively active males, also GnRH3 and insulin-like growth factor 1 (IGF-1) were affected by temperature changes. In conclusion, in blue gourami females, changes in environmental temperature affect oogenesis through changes in brain and pituitary hormone mRNA levels.     

Fitness consequences of alternative life histories in water striders,Aquarius remigis (Heteroptera: Gerridae)

Using field and laboratory observations and experiments over 3 years, I investigated whether reproductive trade-offs shape individual life histories in two natural populations of the water strider, Aquarius remigis, in which univoltine and bivoltine life cycles coexist. Both later eclosion dates and food shortages, even after adult eclosion, induced diapause in females, thus deferring reproduction to the following spring. Adult body size was positively affected by food availability during juvenile development. Higher food levels also increased the reproductive output of females, but not their longevity or oviposition period. When compared to spring breeders (univoltine life cycle), direct (summer) breeders (bivoltine life cycle) experienced reduced lifetime egg numbers and longevity, as well as reduced survivorship of their second-summer-generation offspring; these reproductive costs offset, at least in part, the advantage in non-decreasing populations of having two generations per year. Fecundity was correlated with body size, and among summer-generation females direct breeders were larger than non-breeders. The time remaining before the onset of winter and/or the time since adult eclosion augmented cumulative energy uptake, and consequently the lipid reserves and winter survival probability of non-breeding (diapausing) summer adults approaching hibernation. Overwintered spring reproductives died at faster rates than non-reproductive summer individuals despite greater food availability in spring, indicating a mortality cost of reproduction. Body length correlated with absolute and not with proportional lipid content but showed no consistent relationship with survivorship in the field. These results are in agreement with current theory on the evolution of insect voltinism patterns, and further indicate high degrees of life history flexibility (phenotypic plasticity) in the study populations in response to variable environmental factors (notably photoperiod and food availability). This may be related to their location in a geographic transition zone from uni- to bivoltine life cycles.     

Black rhinoceros (Diceros bicornis) in U.S. zoos: II. behavior,breeding success,and mortality in relation to housing facilities

The captive population of black rhinoceros (Diceros bicornis) is not self‐sustaining. The reasons for suboptimal reproduction and high mortality need to be investigated. This can only be achieved by cross‐institutional analyses of environments, behavior, and performance. In this study, we collected data on 23 zoos with black rhinoceros to compare zoo environments with reproductive success, mortality, and behavior. Institutional variation was characterized by enclosure area, percentage of walls around enclosure perimeter, percentage of public access along enclosure perimeter, climate, noise level, number of years zoo has maintained black rhinoceros, frequency of chlorine use, and number of male and female black rhinoceros at a zoo simultaneously. Birth and death rates for each institution were calculated from studbook records. We found that the breeding success of a zoo since 1973 correlated positively with enclosure area, and zoos with two or more females had a lower reproductive rate than zoos with only one female. Females residing during their pre‐reproductive years at a zoo with another reproductive female gave birth for the first time on average 3 years later than sole females. Mortality since 1973 correlated positively with percentage of public access. In Part I, we developed behavior profiles of 29.31 individual black rhinoceros from keeper ratings. Scores for males on the behavior trait Fear also correlated positively to percentage of public access, and we suggest that this aspect of black rhinoceros exhibits is a stressor for this species, especially the males. We found that different aspects of captive environments are associated with male and female black rhinoceros behavior. Male scores on the behavior trait dominant were higher in smaller enclosures, and female scores for a group of behaviors suggesting agitation (chasing/stereotypy/mouthing) were positively correlated with percentage of walls in their enclosure. These two behavior traits were found in Part I to be negatively correlated with the breeding success of an individual male or female. We re‐surveyed the behavior and husbandry of 29 black rhinoceros pairs in zoos 2 years after the original data were collected. The re‐survey confirmed that compatible black rhinoceros pairs are those with assertive females and submissive males, and that enclosure area and a low percentage of concrete walls around the enclosure are positive predictors of a pair's reproductive success. We conclude that temperament traits of individuals and characteristics of their captive environments both have an impact on a pair's breeding success. Our study demonstrates that cross‐institutional comparisons of zoo facilities, when integrated with behavioral assessments of individual animals, are a valuable tool for investigating potential causes of poor reproduction and well‐being in zoo animals. Zoo Biol 18:35–52, 1999. © 1999 Wiley‐Liss, Inc.     

Annual productivity and individual female reproductive success in a Great Bustard Otis tarda population

The reproductive success of Great Bustards Otis tarda in north-western Spain was studied between 1987 and 1998, both at the population ( c . 700 adult females breeding in our study area) and the individual level (sample of 32 marked females). Overall productivity was low, with a population mean of only 0.14 chicks reared per adult female, and an average breeding success of 0.15 chicks per year in the sample of marked females, but interannual variability was high (0.04–0.29). Population productivity was positively correlated with winter (October–March) precipitation prior to each breeding season, and negatively correlated with the number of days of rain during the hatching period. High annual productivity resulted from a high proportion of females rearing two chicks. Reproductive success was higher in females older than 6 years than in younger birds. The proportion of females in the marked sample that failed in breeding after having bred successfully the previous season was significantly higher than the proportion of those that did not. Finally, females with a higher than average breeding success tended to breed successfully in years of both low and high population productivity, whereas those with lower than average breeding success did so only in years of high productivity.     

Reproductive traits of the small Patagonian octopus Octopus tehuelchus

This study evaluated the reproductive features of Octopus tehuelchus in three coastal environments of San Matías Gulf (Patagonia). Monthly samples of O. tehuelchus were used to estimate size at maturity, compare seasonal changes in oocyte size frequency distributions between sites as well as oocyte number and size between female maturity stage and sites. Females in Islote Lobos had a smaller size at maturity than females in San Antonio Bay and El Fuerte, probably as a consequence of a generally smaller body size. Males in San Antonio Bay were smaller at maturity than females. O. tehuelchus is a simultaneous terminal spawner. Fecundity (expressed as number of vitellogenic oocytes in ovary) was lower in Islote Lobos, and an increase in oocyte number in relation to female total weight was found. Females in San Antonio Bay had the largest oocytes, which may indicate higher energy reserves for the embryo and therefore higher juvenile survival. There was a close relationship between reproduction, growth and condition, represented as size at maturity, number and size of vitellogenic oocytes and period of maturity and spawning. Given the local variation in some reproductive features of O. tehuelchus, studies should focus on the environmental factors, which bring about this variation, and on how it affects the dynamics of local populations.     

Life history of the moose Alces alces: relationship between growth and reproduction

We studied the relationship between increase in body weight and reproductive performance in different populations of Norwegian moose to evaluate costs associated with early onset of reproduction, viz. whether early onset of reproduction was correlated with low adult body weight or reduced adult fecundity. The mean carcass weight of non-ovulating yearlings was significantly lower than for ovulating yearlings. However, those 2.5 yr old females that conceived as yearlings were lighter than non-reproducing females of the same age. Thus, to begin to reproduce as a yearling was assumed to be expensive because it reduces the possibilities for further growth. The cost associated with reproduction was further illustrated by the fact that the difference in mean carcass weight from age 2.5 to 3.5 yr of females that produced calves in both years, was less for the females from regions with lowest mean yearling weights, i.e. regions with probably the lowest resource availability. In populations with high mean yearling carcass weights, the proportion of cows with calf and the number of calves per pregnant female in the early reproductive phase (2.5 or 3.5 yr old) were higher than in populations in which the mean yearling weights were low. There was a negative correlation between growth rate in the population after 1.5 yr of age and the mean yearling carcass weight. Thus, low yearling weight was associated with a prolonged period of growth and thereby a reduced reproductive output during the first year of the female's life. For old females (≥ 9.5 yr old) the number of calves produced per pregnant female was highest in populations where yearling carcass weights were highest. Furthermore, mean yearling weight and the mean adult female weight were positively correlated in those regions. This relationship suggests that within this species early onset of reproduction is not related to retarded reproduction or lower weight later in life. We suggest that the moose has been selected for an early onset of reproduction.     

Effects of dietary astaxanthin supplementation on reproductive characteristics of rainbow trout (Oncorhynchus mykiss)

The effect of dietary astaxanthin supplementation on reproductive characteristics was investigated in five groups of female rainbow trout broodstock fed diets containing either 0.07, 12.46, 33.33, 65.06 or 92.91 mg astaxanthin kg^?1, respectively, and two groups of male rainbow trout broodstock fed diets supplemented with 0.07 and 33.33 mg astaxanthin kg^?1, respectively, for 6 months in an artificial photoperiod system until sexual maturation. The eggs from each group of female broodstock were divided into two equal batches. One batch was fertilized with homogenized sperm of four males fed diets with 0.07 mg astaxanthin kg^?1 and the other portion with sperm of four males fed diets with 33.3 mg astaxanthin kg^?1. The females produced eggs with astaxanthin concentrations ranging from 2.03 to 29.79 mg kg^?1. Dietary astaxanthin supplementation had positive effects on investigated reproductive traits. Significant differences in rate of fertilization, percentage of eyed and hatched eggs, and mortality of eyed eggs were found between treatments (P < 0.05), but no significant difference was found on percentage of mortality before hatching (P > 0.05). A significant difference (P < 0.05) in fertilization rate was found for male groups fed 0.07 and 33.3 mg astaxanthin kg^?1. The astaxanthin content in the eggs and fertilization rate, eyed‐egg percentage and percentage hatch were significantly correlated (P < 0.05). It is concluded that dietary supplements of astaxanthin are required for optimum reproduction in rainbow trout.