Variation In Reproductive Performance Research Articles

Variation in Reproductive Performance and Egg Quality Between Wild and Pond-Reared Indian White Shrimp, Fenneropenaeus indicus, Broodstock

ABSTRACT The shrimp hatchery industry worldwide has placed immense interest on the production of closed-life cycle broodstock from farm stock. Unfortunately, majority of the studies have proven that pond-reared broodstock are inferior to their wild counterparts in terms of reproductive performance, spawn quality and post-hatching performance. In the present study, reproductive performance, egg, and nauplii quality of wild and pond-reared Indian white shrimp, Fenneropenaeus indicus, broodstock were analyzed. Biochemical analyses were done with egg and nauplii from both the sources, in an attempt to explain the difference in their performance. Results indicated better reproductive performance by wild females compared to pond-reared ones. The wild eggs contained higher total lipid, and vital HUFAs namely EPA (Eicosapentaenoic acid), DHA (Docosahexaenoic acid) and ARA (Arachidonic acid). However, one of the dominant PUFA, 18:2 (n-6) was high in pond broodstock eggs. Biochemical analysis also indicated that glucose, carotenoids, and triacylglycerol content were significantly higher (P < 0.001) in wild eggs. But, egg protein and triacylglycerol content did not record significant difference between the egg samples. The percentage viable nauplii, nauplii length and triacylglycerol content were all significantly higher (P < 0.05) with wild nauplii. This study proves the better nutritional profile of wild eggs and nauplii in terms of analyzed biochemical components. But, as our knowledge on specific nutrient requirement for successful reproductive performance and offspring quality is limited, the better performance of wild eggs could not be attributed to any single nutrient. Meanwhile, it could be presumed that all the deficient nutrients collectively contributed to the poor reproductive performance and spawn quality.

The stickleback–Schistocephalus host–parasite system as a model for understanding the effect of a macroparasite on host reproduction

Summary Reproductive life history traits are closely linked to fitness. Thus, changes in host reproductive traits associated with parasitic infection are of keen interest to the study of the evolutionary ecology of host‐parasite systems. Alterations of host reproductive function may reflect defensive host adaptations to mitigate the effect of parasitism, adaptive parasitic manipulations to promote pathogen reproduction and transmission, or non-adaptive side effects of infection. Parasitic infection often results in reduced host fitness through decreased reproductive performance representing parasite virulence. The pathology of Schistocephalus on reproduction in threespine stickleback (Gasterosteus aculeatus) classically has been viewed as largely resulting in the inability of infected host fish within a population to produce gametes and spawn. We show, however, that this model does not apply to stickleback populations world-wide. Several Alaskan populations of stickleback do not fit the classical model because a large fraction of individuals in each population may produce gametes, engage in reproductive behaviour, and spawn in the face of substantial infection. The significance of inter-population variation in reproductive performance of host stickleback is considered. Using the trophically transmitted Schistocephalus as a model, the suite of traits expressed in hosts of trophically transmitted parasites should be systematically investigated. Beyond the genetic constitutions of host and parasite, environmental conditions appear to play a major role in the manifestations of infection and must be considered more broadly in developing a complete understanding of the system.

Environmental and senescent related variations in Weddell seal body mass: implications for age‐specific reproductive performance

Recent studies have found age‐specific variations in reproductive performance amongst Weddell seals, Leptonychotes weddellii, and we hypothesized age‐related variations in maternal body mass as a mechanism linking maternal age and the observed patterns of reproductive performance. We evaluated the effects of maternal traits such as age and reproductive experience and the effects of environmental variations on maternal body mass at parturition. Maternal body mass at parturition showed substantial age‐ and environmental‐related variations. Maternal body mass increased with age through the young and middle ages, and evidence of senescent declines in body mass was found amongst the oldest ages. Additionally, body mass at parturition was strongly influenced by environmental variations during the pregnancy period, specifically sea‐ice extent and the state of the El‐Niño Southern Oscillation. Patterns of age‐specific variations in body mass were consistent with age‐specific patterns of offspring survival probability, which supported our hypothesis that changes in body mass link maternal age and reproductive performance in the Weddell seal. Further, environmental conditions during pregnancy may be an important component of Weddell seal reproductive performance.

Habitat-related variation in reproductive endocrine condition in the coral reef damselfish Acanthochromis polyacanthus

Spiny damselfish Acanthochromis polyacanthus are brood protectors with no larval dispersal stage, with the result that characteristics of local populations are likely to reflect local habitat conditions. In order to assess the possible effect of habitat on reproductive characteristics, spiny damselfish were captured by divers in 1999 and 2001 from reefs around Lizard Island in the northern section of Australia’s Great Barrier Reef, chosen to represent a range of coral cover characteristics. Fish were bled underwater immediately after capture, then blood and fish were placed on ice at the end of the dive for transport to the laboratory where plasma was separated for subsequent measurement of testosterone (T) and 11-ketotestosterone (11KT) in males, and T and 17β-estradiol (E 2) in females. Ovaries from fish captured in 2001 were dispersed to isolate vitellogenic follicles, fecundity and follicle size were determined, then follicles were incubated in Leibowitz L15 medium alone or with human chorionic gonadotropin (hCG), to assess steroidogenic capacity. In 1999 there were significant site to site variations in plasma T and E 2 levels in females, and in 2001, in E 2 in females, and in T and 11KT in males. Highest hormone levels were recorded from sites of both low and high coral cover (a measure of presumptive habitat quality), but there was consistently low steroid production in fish from a site of high coral cover and fish density. An initial expectation that poor reproductive condition might be associated with degraded coral sites was not met. Vitellogenic follicles from fish captured in 2001 showed increased in vitro production of E 2 and to a lesser extent, T, with increasing follicle size, and this was further augmented by treatment with hCG. Comparison of regression slopes of log E 2 production versus follicle size showed that fish from sites where there were generally low levels of plasma steroids also had impaired in vitro steroidogenic capacity, and that this effect partially disappeared when follicles were stimulated with hCG. Reduced steroidogenic capacity was strongly associated with low fecundity, indicating that low in vitro and in vivo E 2 production were reflected in reduced reproductive capacity. As the effect was most consistent at a site where fish density (and subsequent competition for planktonic food) was high, it is suggested that nutritional status associated with habitat characteristics may regulate reproductive endocrine condition in spiny damselfish. It is clear that local factors other than coral cover can generate site variation in reproductive performance.

Characterization and comparison of variations in reproductive performance of Chitralada strain Nile tilapia, Oreochromis niloticus (L.)

In an attempt to better understand and characterize the variability in the female reproduction of individual Thai-Chitralada strains of Nile tilapia, Oreochromis niloticus (L.), tagged mature females (n 5 68) from a single population were monitored in a hapa-in-pond system over a 12-month experimental period. Spawn female 1 , eggs female 1 day 1 , eggs kg female 1 day 1 , day spawn 1 and weight (g) at ¢rst spawning of individual females were determined from the regular weekly sampling of weight (g) and eggs per spawn. For analysis, the females were grouped into two, high spawning (HSF) and low spawning frequency (LSF) classes based on their spawning frequency (SF) record. Moreover, nested under these two classes were two groups each based on growth rate, i.e., high frequency ^ large size (HL), high frequency ^ small size (HS), low frequency ^ large size (LL) and low frequency ^ small size (LS). There was no diierence in eggs spawn 1 among all females. The HSF group produced 68% and 361% more eggs female 1 day 1 than the population mean and LSF group respectively. Eggs female 1 day 1 and spawn female 1 remained high in the HSF group and low in the LSF group throughout the 12-month experimental period. This suggests that individual female spawning activity is consistent within a population in a common environment. The inter-spawn interval increased with age in all four groups, and day spawn 1 was shorter by 130% in HSF females compared with day spawn 1 in LSF. The HSF group also spawned more successively ( 3), while the LSF group of females had fewer successive spawns ( 2). Body weight (g) had no in£uence on the number of eggs produced. The study indicates that separating frequently spawning females could be used as an important strategy to improve commercial seed production of Nile tilapia.

Comparison of estradiol, testosterone, vitellogenin and cathepsin profiles among young adult channel catfish ( Ictalurus punctatus) females from four selectively bred strains

Potential variation in reproductive performance as young broodfish among four selectively bred strains of channel catfish was evaluated by comparing profiles of plasma estradiol, testosterone, and vitellogenin, and activities of cathepsin D, L, and B in follicle-enclosed oocytes during vitellogenesis in 2- to 3-yr-old females. No differences among the four strains were detected for any of the parameters measured. Plasma steroid concentrations demonstrated temporal differences, with testosterone levels peaking in January and estradiol levels peaking in April. Monthly changes in circulating vitellogenin concentrations coincided with oocyte growth. Average oocyte size in May, the typical time of spawning, was smaller (1624 μm) than that considered normal for mature oocytes (approx. 3000 μm) in this species. Furthermore, only 9% of the females in this study spawned, and no significant correlations could be determined between the reproductive indices and spawning success. Activities of cathepsin D, L, and B were also similar between the four strains of catfish. Cathepsin L activity was highest in March, and cathepsin D activity was highest in March and May. Cathepsin B activity was generally lower than the activities of either cathepsin L or D, with the highest levels occurring in November, December, and March. This is the first report of cathepsin activities and their relationships to other reproductive parameters in channel catfish.

Fertility in South Australian commercial Merino flocks: aspects of management

Wide variation in reproductive performance of commercial Merino flocks in south central Australia is the result of genetic and environmental influences that are both amenable to change through decisions of management. Relationships of reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival, and lambs weaned) with variables that graziers can change or modify (strain of Merino, day or month of exposure of ewes to rams, ram effect or teasing, length of the mating period, ram percentage, days between weaning and next mating, stocking density and flock size at lambing, ewe liveweight, and condition) are reported in this paper, the third in a series. Small differences were observed between medium and strong-wool South Australian Merino strains for reproductive traits. Choosing the time of year that ewes are exposed to rams, between late spring to autumn, may result in reduced ovulation rate during early summer (December) giving a potentially smaller net reproductive efficiency (lambs weaned). The ram effect or teasing, used by about 50% of graziers to synchronise lambing, could be effectively employed to the end of January. The technique was not reproductively advantageous when compared with flocks that were not teased. The percentage of rams mated to ewes varied widely (approximately 1–3%) and did not alter flock fertility, suggesting that a substantial proportion of graziers could safely reduce the number of rams purchased. A positive relationship between incidence of estrus during the first 14 d of the cycle and the number of days from weaning to next mating and a negative relationship of returns to service with the same variable indicates that managers should consider increasing the time allowed for recovery of liveweight and body condition by adjusting age at weaning, length of the mating period, or both. Lamb survival was curvilinearly related to flock size and not stocking intensity, with the optimum size at about 400 ewes. The number of lambs weaned per 100 ewes exposed to rams increased by 1.0 kg −1 increase in liveweight at mating. We concluded that the major factor controlling net reproductive efficiency is nutritional in origin through its effects on ewe liveweight and condition, and is a factor that can be largely manipulated through management.

Exploring individual quality: basal metabolic rate and reproductive performance in storm-petrels

Despite evidence that some individuals achieve both superior reproductive performance and high survivorship, the factors underlying variation in individual quality are not well understood. The compensation and increased-intake hypotheses predict that basal metabolic rate (BMR) influences reproductive performance; if so, variation in BMR may be related to differences in individual quality. We evaluated whether BMR measured during the incubation period provides a proximate explanation for variation in individual quality by measuring the BMRs and reproductive performance of Leach's storm-petrels (Oceanodroma leucorhoa) breeding on Kent Island, New Brunswick, Canada, during 2000 and 2001. We statistically controlled for internal (body mass, breeding age, sex) and external (year, date, time of day) effects on BMR. We found that males with relatively low BMRs hatched their eggs earlier in the season and that their chicks' wing growth rates were faster compared to males with relatively high BMRs. Conversely, BMR was not related to egg volume, hatching date, or chick growth rate for females or to lifetime (≤23 years) hatching success for either sex. Thus, for males but not for females, our results support the compensation hypothesis. This hypothesis predicts that animals with low BMRs will achieve better reproductive performance than animals with high BMRs because they have lower self-maintenance costs and therefore can apportion more energy to reproduction. These results provide evidence that intraspecific variation in reproductive performance is related to BMR and suggest that BMR may influence individual quality in males. Copyright 2005.

Reproductive output of female mouflon (Ovis gmelini musimon×Ovis sp.): a comparative analysis

AbstractAlthough many mouflon Ovis gmelini musimon populations have been introduced to continental southern and central Europe, little is known about their reproductive output. Based on post‐mortem analysis of 344 harvested females, the variation in reproductive performance was investigated in three wild populations: two located in the French Alps and one in the south of France. Examination of tracts indicated a high pregnancy rate (&gt; 80%) for females ≥ years old. We found that a significant proportion of female lambs were pregnant in the Alps, c. 1 year earlier than generally reported for first reproduction in the mouflon, whereas female lambs did not conceive in the southern France population. Pregnant female lambs and yearling females always bore a single foetus. Among pregnant females ≥ years old, twinning occurred less often in southern France (2.5%) than in the Alps (10.8% and 20.7%). The data required to relate body mass and reproductive output of ewes at individual level were lacking, but female lamb–ewe body mass ratio was used to test that the population with high reproductive output should have the highest ratio. As expected, the index was higher in the Alps than in southern France, suggesting between‐population differences in the quality of the local environment. Differences in growth pattern and birth timing of lambs, or different tactics of maternal care could also have influenced the female lamb–ewe body mass ratio. Crossings between wild and domestic sheep during the recent history of these populations and differences in environmental conditions might have interplayed to shape age at first reproduction and twinning rates.

Ecological and social effects on reproduction and local recruitment in the red-backed shrike

Numerous hypotheses have been proposed to explain variation in reproductive performance and local recruitment of animals. While most studies have examined the influence of one or a few social and ecological factors on fitness traits, comprehensive analyses jointly testing the relative importance of each of many factors are rare. We investigated how a multitude of environmental and social conditions simultaneously affected reproductive performance and local recruitment of the red-backed shrike Lanius collurio (L.). Specifically, we tested hypotheses relating to timing of breeding, parental quality, nest predation, nest site selection, territory quality, intraspecific density and weather. Using model selection procedures, predictions of each hypothesis were first analysed separately, before a full model was constructed including variables selected in the single-hypothesis tests. From 1988 to 1992, 50% of 332 first clutches produced at least one fledgling, while 38.7% of 111 replacement clutches were successful. Timing of breeding, nest site selection, predation pressure, territory quality and intraspecific density influenced nest success in the single-hypothesis tests. The full model revealed that nest success was negatively associated with laying date, intraspecific density, and year, while nest success increased with nest concealment. Number of fledglings per successful nest was only influenced by nest concealment: better-camouflaged nests produced more fledglings. Probability of local recruitment was related to timing of breeding, parental quality and territory quality in the single-hypothesis tests. The full models confirmed the important role of territory quality for recruitment probability. Our results suggest that reproductive performance, and particularly nest success, of the red-backed shrike is primarily affected by timing of breeding, nest site selection, and intraspecific density. This study highlights the importance of considering many factors at the same time, when trying to evaluate their relative contributions to fitness and life history evolution.

Health state and reproductive output in Magellanic penguins (Spheniscus magellanicus)

Health status has been proposed as an important factor affecting individual variation in reproductive performance in birds. We studied individual variation in haematological variables indicating health status (haematocrit, white blood cell count (WBC), heterophil/lymphocyte ratio) in breeding Magellanic penguins Spheniscus magellanicus and their association with reproductive variables like egg size and fledging success. Haematological measures were taken for both males and females shortly after the hatching of their young, while the parents' condition was measured at laying. Sex had a significant effect on WBC, with males showing lower values. Females with more leucocytes in peripheral blood, and assumed, therefore, to be in poorer health, layed smaller eggs and raised fewer chicks to fledging. Both effects were linked to variation in lymphocyte but not heterophil number. Haematological measures together with condition may be used to predict the reproductive output of breeders without resorting to long-term population studies.

Clutch size versus clutch interval: life history strategies in the colour-polymorphic pygmy grasshopper Tetrix subulata.

Theory posits that reproduction carries a cost in terms either of future fecundity, growth or survival. Different life history strategies may evolve in response to different external sources of mortality. In ectothermic organisms, such as insects and reptiles, reproductive characteristics may also vary due to effects of differences in body temperature on activity and physiological performance. In this study, female pygmy grasshoppers [Tetrix subulata (L.) Orthoptera: Tetrigidae] belonging to four different colour morphs were maintained under two different temperatures, and data on reproductive life history traits were used to test for costs of reproduction, plasticity of reproductive characteristics in response to temperature and variation among colour morphs in reproductive strategies. The results revealed that average clutch size decreased progressively from the first to third clutch, and that females producing relatively large clutches displayed a greater reduction (in both absolute and relative terms) in the number of eggs to the following clutch, as expected from the hypothesis that present reproduction negatively affects future fecundity. Great expenditure on present reproduction also negatively influenced the time to next clutch:the decrease in mean clutch size with clutch number was associated with a reduction in inter-clutch interval, and clutch interval increased with clutch size across individuals within colour morphs. Females maintained in a warm environment were more likely to oviposit, laid their first clutch earlier, produced more clutches and had shorter intervals between sequential clutchesthan females in a cold environment, suggesting that differences in body temperature may contribute to variation in reproductive performance within and among natural populations. A comparison among colour morphs maintained under identical conditions suggested that females belonging to certain morphs produce relatively large clutches at the expense of fewer clutches per unit time. However, experimental data revealed no difference in relative fat content between dark and pale individuals maintained either in sun-exposed outdoor enclosures (where they were unable to increase their body temperature by basking) or in shaded enclosures. This suggest that the divergence in life history strategies among colour morphs may reflect a response to morph-specific differences in adult survival imposed by visually searching predators, rather than being due to the effects of differences in body temperature.

High genetic merit and high-producing dairy cows in commercial Australian herds don't have substantially worse reproductive performance

AbstractThe National Dairy Herd Fertility Project (renamed the InCalf Project) consists of two large, prospective observational studies conducted in commercial dairy herds from 4 Australian states. The project aims to identify factors associated with variation in reproductive performance between cows and herds. The larger of the two studies included over 33,000 cows and 168 herds. The database has undergone extensive error checking and correction resulting in high quality data. Large variations in reproductive performance were observed between cows and herds, indicating that there are important risk factors for reproductive performance and that cows and herds are exposed to varying combinations of these risk factors. Models for several reproductive outcomes were constructed using multivariable stepwise logistic regression. No significant associations were detected between any measures of cow genetic merit and 6 week in-calf rate. Neither milk volume nor protein yield were significantly associated with 6 week in-calf rate. A weak negative association was detected between fat yield in the first 120 days of lactation and 6 week in-calf rate. However, differences in estimated 6-week in-calf rate between moderate and high producing groups (2 to 5 percentage points) were small when contrasted against the 63 percentage point range in performance observed between herds (23% to 86%).

The use of multilevel models to evaluate sources of variation in reproductive performance in dairy cattle in Reunion Island

Sources of variation in measures of reproductive performance in dairy cattle were evaluated using data collected from 3207 lactations in 1570 cows in 50 herds from five geographic regions of Reunion Island (located off the east coast of Madagascar). Three continuously distributed reproductive parameters (intervals from calving-to-conception, calving-to-first-service and first-service-to-conception) were considered, along with one Binomial outcome (first-service-conception risk). Multilevel models which take into account the hierarchical nature of the data were used to fit all models. For the overall measure of calving-to-conception interval, 86% of the variation resided at the lactation level with only 7, 6 and 2% at the cow, herd and regional levels, respectively. The proportion of variance at the herd and cow levels were slightly higher for the calving-to-first-service interval (12 and 9%, respectively) — but for the other two parameters (first-service-conception risk and first-service-to-conception interval), >90% of the variation resided at the lactation level. For the three continuous dependent variables, comparison of results between models based on log-transformed data and Box–Cox-transformed data suggested that minor departures from the assumption of normality did not have a substantial effect on the variance estimates. For the Binomial dependent variable, five different estimation procedures (penalised quasi-likelihood, Markov-Chain Monte Carlo, parametric and non-parametric bootstrap estimates and maximum-likelihood) yielded substantially different results for the estimate of the cow-level variance.

Factors affecting breeding success of Peregrine and Lanner Falcons in South Africa

Jenkins, A.R. 2000. Factors affecting breeding success of Peregrine and Lonner Falcons in South Africa. Ostrich 71 (384): 385-392.Breeding success was recorded for three Peregrine Falcon, Falco peregrinus, populations in South Africa over nine years, and for Peregrine and Lanner Falcon, Ebiarmicus, populations in an area of sympatry over three years. The objectives of the study were to measure geographic and interspecific variation in reproductive performance, and determine environmental correlates of productivity. Territory occupancy, the frequency of breeding per occupied territory and clutch size did not vary significantly between the three Peregrine populations. However, Peregrine breeding success was generally lower on the Cape Peninsula (1. 11 young fledged per territorial poir), higher in the Soutpansberg (1.36) and highest on the Orange River (1.70). Overall, fledging rates of Soutpansberg Peregrines and Lanners were not significantly different, although annual productivity of the Lonner population was consistently higher. Neither species' breeding success was significantly depressed by the presence of close neighbouring pairs of the other, suggesting that they were not active competitors. Breeding performance of Peregrines on the Cape Peninsula correlated strongly with spring weather conditions: egg and hatchling survival was lower in wet years, and fledging rates were higher in warm years. Annual productivity of Orange River Peregrines correlated positively with the height of the river at the onset of breeding, and productivity of Soutpansberg Peregrines was higher in seasons following years of high rainfall. Elements of the physical structure of the nesting habitat (exposure of the nest ledge, height of the nest cliff) correlated positively with Peregrine breeding performance. Breeding success of Soutpansberg Lanners was largely unaffected by any of the environmental variables considered. Overall, it is proposed that Peregrine productivity reflected variation in the physical environment and its affect on prey availability.

Optimization of Dairy Heifer Management Decisions Based on Production Conditions of Pennsylvania

We used a dynamic programming model to determine optimum rearing decisions of dairy replacements. Heifers were described in the model by age, season, body weight, pregnancy state, and prepubertal growth rate. Prices and parameters were chosen to represent the dairy population of Pennsylvania. We calculated monthly costs and revenues from calf value, feed costs, veterinary costs, semen costs, carcass value, and fullgrown heifer value. The model considered a stochastic variation in the onset of puberty, conception, involuntary disposal, and a seasonal variation in the prices of calves, heifers, and feed.Based on a critical prepubertal average daily gain of 0.9 kg/d and a maximum achievable postpubertal growth rate of 1.1 kg/d, the optimum practice resulted in an average age at first calving of 20.5 mo at a body weight of 563kg. Discounted net returns equaled $107 per heifer per year. The optimum rearing practice was not sensitive to seasonal variation in prices. Nevertheless, the economic results per season of birth varied considerably; the highest income per heifer was obtained from heifers born in December ($142/yr), whereas those born in May yielded the lowest ($100/yr).Sensitivity analyses demonstrated a considerable influence of growth rate restrictions and variation in reproductive performance on both the optimal rearing practices as the expected net returns.Key words: heifer rearing, dynamic programming, optimization, Pennsylvania

Reproductive Phenology of a Tropical Canopy Tree, Spondias mombin1

We studied the reproductive phenology of isolated populations of Spondias mombin to determine the degree of flowering and fruiting synchrony among populations and to examine spatial and temporal variability in fruit production. The study was conducted on six small islands (1.8–3.5 ha) in the Panama Canal. All individuals (10 cm in diameter at breast height (DBH) were marked in 1991 and censused each year through 1994 to record recruits and deaths. All marked trees were censused monthly for flowering and fruiting activity from April 1992 through December 1995. Spondias mombin was seasonal and highly synchronous in flower and fruit production among islands and across years. Proportions of individuals fruiting varied among islands, years, and tree size classes. There was a positive relationship between probability of fruit production and tree size. Synchronous reproductive activity in S. mombin probably was due to responses to proximate environmental cues such as fluctuations in irradiance, but other factors must have been responsible for temporal and spatial variation in reproductive performance. We suggest that this variation may have been due partly to temporal and spatial differences in pollinator abundance.

Age-Specific Reproduction in Three Species of European Ducks

We tested the effects of female age on reproductive performance of Northern Shovelers (Anas clypeata), Tufted Ducks (Aythya fuligula), and Common Pochards (A. ferina) based on a long-term study (1958 to 1995) at Engure Marsh, Latvia. Yearling females initiated nests later than older (&2 years) females in each species, but female age explained little of the remaining variation in reproductive performance. Clutch size and brood size of all species declined seasonally. Age-specific increases in reproductive performance were most consistent between 1 and 2 years of age and were more apparent in the diving ducks than in Northern Shovelers. Clutch size, brood size, and duckling mass of yearling Tufted Ducks, and brood size and duckling mass of yearling Common Pochards, were smaller than those of older females. In Northern Shovelers, only duckling mass increased with age of the female. Nesting and hatching success did not vary by age for any species. Among 2-year-old females with and without previous breeding experience, experienced females nested five to six days earlier than inexperienced females in all species. Experienced, 2-year-old Tufted Ducks also had larger clutches and broods than inexperienced females. Effects of breeding experience generally lasted for only a single breeding season. Nesting date and duckling mass of yearling Northern Shovelers did not differ from that of inexperienced 2-year-olds. However, inexperienced 2-year-old Tufted Ducks and Common Pochards nested earlier and produced larger ducklings than did yearling females. Brood size of inexperienced, 2-year-old Common Pochards also was larger than that of yearlings. We found no evidence that age-specific increases in reproductive performance were related to differential survival of good breeders. Reproductive performance was constrained by past breeding experience in Northern Shovelers and by age and experience in Tufted Ducks and Common Pochards.

Environmental and seasonal influences on the return-to-oestrus after weaning in primiparous sows: a review

The domestic pig is not a true seasonal breeder but manifests variations in reproductive performance throughout the year. For instance, the weaning-to-oestrus interval is longer in sows weaned in summer and early fall. These variations are more pronounced in primiparous than in multiparous sows. Long light duration and more obviously high ambient temperature play a role in this prolonged anoestrus. The neuroendocrine mechanisms mediating the effects of photoperiod and temperature on the hypothalamo-pituitary-ovarian axis are poorly understood in the pig. In seasonal breeders, photoperiod regulates reproduction through diurnal variations in melatonin secretion by the pineal gland and subsequent modifications in gonadotrophin secretion. In domestic pigs, diurnal patterns of melatonin are confusing and a nocturnal increase is not always observed. Light duration does not seem to influence gonadotrophin secretion in primiparous sows. Under high ambient temperature, pulsatility of the luteinizing hormone and circulating concentrations of cortisol are decreased whereas those of growth hormone are increased. Since lactating sows and particularly primiparous sows reduce their food intake under high ambient temperature, it can be suggested that delayed oestrus in summer is, at least in part, due to nutritional deficiency.

Nest Architecture and Reproductive Performance in Tree Swallows (Tachycineta bicolor)

ABSTMACT.-Nests are an important component of parental effort in birds. From 1988 to 1990, I compared the architecture of nests built by subadult and adult female Tree Swallows (Tachycineta bicolor) in boxes in southeastern Michigan in order to determine if there were age-related differences in nest architecture and if these differences were associated with agerelated differences in reproductive performance. Nests built by Tree Swallows were composed of a mat of dry grasses and a nest cup lined with feathers. On average, nest material filled approximately 30% of a nest box. I observed few age-related differences in nest architecture. However, nests built by subadult females were significantly less well feathered than nests built by adult females, but feather score was not correlated with the production of nestlings or fledglings. There were age-related and within-season variations in reproductive performance associated with variations in nest architecture, especially later in the season. Among subadult females that bred later in the season (i.e. after the population median date of clutch initiation), those females that built larger nests (as indicated by total nest volume, depth of material beneath the nest cup, and percentage of nest box filled with material) hatched more eggs per clutch. In 1990, subadult females that bred later in the season and built larger nests (as indicated by depth of material beneath nest cup and percentage of nest box filled with material) produced significantly more hatchlings but significantly fewer fledglings. Among adult females that bred later in the season, those females that built nests that filled a larger percentage of the nest box hatched fewer eggs. Adult females with nests having larger cups produced significantly more fledglings, but those with cups crowded with nestlings (as indicated by a cup index [total egg volume/nest cup volume]) produced significantly fewer fledglings. In 1990, adult females that bred later in the season and built larger nests (as indicated by depth of nest material, total nest volume, percentage of nest box filled with material) and had more-crowded nest cups produced fewer hatchlings and fledged a significantly smaller proportion of hatchlings. These results suggest that nestling hyperthermia in well-insulated nests may affect the reproductive performance of Tree Swallows that breed late in the season. Received 11 January 1993, accepted 1 July 1993.