Laying characteristics of one- and two-year old pheasants (Phasianus colchicus, L.)

The aim ofthe study was to assess laying traits, the weight of eggs and characters ofthe laying rhythm of pheasants in the first and second years of reproduction. Pheasants (10 cockerels and 50 hens) were kept in aviaries. Daily, individual control of laying was performed beginning with the day of the first laying and ending with the last egg. The following parameters were evaluated: age at first laying, length of the laying period, number of laid eggs and the average weight of the egg in the 8th week of laying. The laying rhythm was also assessed and comprised: the number of egg clutches, the number of eggs in a clutch, the number of eggs in the longest clutch, the number of intervals, the length of intervals and the longest interval between clutches. During the first period of reproduction, in comparison with the second, pheasants laid slightly more eggs of similar average weight. The first laying period was longer than the second and was characterised by a greater number of egg clutches and greater number of intervals between clutches. The greatest number of eggs was laid in 10-egg and longer clutches, although the l-egg clutches were the most numerous. A positive correlation was found between the number of eggs and the number of clutches, the greatest number of eggs in a clutch and the number of intervals between clutches. The similar values of the reproductive characters of one- and two-year old pheasants point to the possibility of longer utilization of these birds than only for one laying period. On the other hand, the considerable variability between the experimental hens with regard to the number and the length of egg clutches, as well as the intervals between them, indicate the possibility to carry out selection taking into account traits characterising the laying rhythm.     

Negative effects of elevated testosterone on female fecundity in zebra finches

Although factors influencing androgen deposition in the avian egg and its effects on nestling fitness are recently receiving considerable attention, little is known about the potential costs of high testosterone levels in the females. Our study aimed at determining the effect of injections of testosterone (T) in female zebra finches (Taeniopygia guttata), on clutch size, egg mass, yolk mass, and yolk androgen content. Females were given a single bolus injection of T in a range of doses after laying the first egg. Results show that administration of T negatively affected clutch size; the strength of this effect increased with increasing doses of T. Females injected with the highest testosterone dose showed suppressed oviposition of the third and the fourth eggs. Interestingly, testosterone administration made females produce eggs with relatively large yolks, suggesting that T may mediate the trade-off between number and size of eggs. Testosterone injection resulted in elevated levels of androgen in the eggs, in contrast to control clutches, which showed a decreasing pattern of androgen concentration along the laying sequence. We conclude that high androgen investment in eggs may be limited by physiological requirements of the ovulatory process.     

Egg formation and the pre-laying period of the Common guillemot Una aalge

The patterns of colony attendance of male and female Common guillemots, relative to calendar date and relative to the female's laying date during the three weeks prior to egg laying, are presented. The probability of a male being at the colony was consistently higher than that for females. Male attendance peaked in the three days before his mate laid: female attendance was lowest at this time. Examination of the yolk showed that the egg was formed over 14–15 days, with yolk deposition (of first eggs) taking 11–5 days, and a lag period (between the end of yolk deposition and laying) of 3–4 days. Yolk deposition occurred over a shorter period (9–3 days) in replacement eggs, and followed a different pattern from first eggs.     

Maternal resource variation across the laying sequence in Canada geese Branta canadensis maxima

Variation in maternal investments to offspring presumably reflects an optimization of resource allocation such that a female's fitness is maximized. In birds, both egg size and yolk constituents are examples of resources that can vary among offspring within a clutch. Egg size and maternally-derived steroid hormone concentrations present in yolk have been characterized for many species that lay small clutches or have altricial young, but little information is available for species that lay moderate to large clutches of precocial young. In this study, we recorded laying position, measured fresh egg mass and determined maternally-derived testosterone and estradiol concentrations present in yolks for whole clutches of free-living Canada geese Branta canadensis maxima to assess variation in maternal resources within clutches. We found that egg size varied non-linearly across the laying sequence such that first laid eggs were small, the largest eggs in the clutch occurred in the second and third positions, and size declined in eggs laid in subsequent positions. Concentration of testosterone in the yolk followed a pattern in which the first and second laid eggs have the highest concentrations within a clutch and declining concentrations in subsequently laid eggs. In contrast, maternally-derived yolk estradiol concentrations (measured in a subset of clutches) did not change across the laying sequence.     

Geographical variation in reproductive traits and trade‐offs between size and number of eggs in the king ratsnake,Elaphe carinata

We collected gravid king ratsnakes (Elaphe carinata) from three geographically separated populations in Chenzhou (CZ), Lishui (LS) and Dinghai (DH) of China to study the geographical variation in female reproductive traits and trade‐offs between the size and number of eggs. Not all reproductive traits varied among the three populations. Of the traits examined, five (egg‐laying date, post‐oviposition body mass, clutch size, egg mass and egg width) differed among the three populations. The egg‐laying date, ranging from late June to early August, varied among populations in a geographically continuous trend, with females at the most northern latitude (DH) laying eggs latest, and females at the most southern latitude (CZ) laying eggs earliest. Such a trend was less evident or even absent in the other traits that differed among the three populations. CZ and DH females, although separated by a distance of approximately 1100 km as the crow flies, were similar to each other in most traits examined. LS females were distinguished from CZ and DH females by the fact that they laid a greater number of eggs, but these were smaller. The egg size–number trade‐off was evident in each of the three populations and, at a given level of relative fecundity, egg mass was significantly greater in the DH population than in the LS population. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 701–709.     

Quantitative genetics of oviposition behaviour and interactions among oviposition traits in the sand cricket

We performed a quantitative genetic study of oviposition behaviours and oviposition traits in the sand cricket Gryllus firmus. Egg survival in crickets depends on the depth at which they are inserted into the soil with the ovipositor. We examined whether egg depth depends on ovipositor length alone, or on both morphological and behavioural traits associated with oviposition. Heritability estimates were high (h² >0.5) for ovipositor length and small (h²=0.2) for oviposition behaviours. Negative genetic correlations between ovipositor length and some behavioural traits (digging depth and the behavioural component of egg depth) indicated compensation between oviposition traits on egg depth. Because of behavioural compensation, females with different ovipositor lengths subject to stabilizing selection on egg depth could have equal fitnesses. Females laid their eggs deeper, and their eggs were marginally more evenly distributed in dry than in wet sand. This suggests adaptive phenotypic plasticity in laying behaviour, but may also result from physical constraints of the substrate on the insertion of the ovipositor. The absence of significant between-family variation in oviposition traits in response to sand moisture indicates low evolutionary potential for phenotypic plasticity in oviposition traits according to soil moisture. In highly unpredictable environments, females could spread the risk of desiccation by laying eggs at different depths independently of environmental conditions (bet hedging). Our results show significant additive genetic influences on the ability of a female to spread risks as measured by genetic variation in egg distribution, suggesting that a bet-hedging strategy of egg laying has the potential to evolve in this population. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Two eggs,two different constraints: a potential explanation for the puzzling intraclutch egg size dimorphism in Eudyptes penguins

Phenotypic plasticity and phenotypic stability are major components of the adaptive evolution of organisms to environmental variation. The invariant two-egg clutch size of Eudyptes penguins has recently been proposed to be a unique example of a maladaptive phenotypic stability, while their egg mass is a plastic trait. We tested whether this phenotypic plasticity during reproduction might result from constraints imposed by migration (migratory carry-over effect) and breeding (due to the depletion of female body reserves). For the first time, we examined whether these constraints differ between eggs within clutches and between egg components (yolk and albumen). The interval between colony return and clutch initiation positively influenced the yolk mass, the albumen mass, and the subsequent total egg mass of first-laid eggs. This time interval had only a slight negative influence on the yolk mass of second-laid eggs and no influence on their albumen and subsequent total masses. For both eggs, female body mass at laying positively influenced albumen and total egg masses. Female investment into the entire clutch was not related to the time in the colony before laying but increased with female body mass. These novel results suggest that the unique intraclutch egg size dimorphism exhibited in Eudyptes penguins, with first-laid eggs being consistently smaller than second-laid eggs, might be due to a combination of constraints: a migratory carry-over effect on the first-laid egg and a body reserve depletion effect on the second-laid egg. Both these constraints might explain why the timing of reproduction, especially egg formation, is narrow in migratory capital breeders.     

Eggshell coloration in relation to male ornamentation, female condition and egg quality in the collared flycatcher Ficedula albicollis

The blue-green eggshell pigment biliverdin is an efficient antioxidant, the deposition of which may be costly and act as a handicap to the female's antioxidant capacity. Thus, it is hypothesized that there exists a positive correlation between the degree of eggshell coloration and the condition and health state of the mother. In this study, we measured the blue-green chroma of collared flycatcher Ficedula albicollis eggs, and investigated the associations between egg colour and parental characteristics, laying date, clutch size and laying order. We also analysed the possible correlations between egg size, yolk carotenoid and antibody levels and eggshell pigmentation. Our results revealed no significant relationships between egg colour and female age, morphological and serological variables. Blue-green colour intensity of eggs increased throughout the breeding season, which could be the result of either a proximate constraint or an adaptive strategy. We found a positive association between egg colour saturation and yolk lutein concentration. This relationship could be the result of the seasonal improvement of caterpillar supply, which could influence the deposition of both components into the egg. Furthermore, we found that females mated to lower-quality males produced eggs with higher biliverdin pigmentation. It is possible that deposition of biliverdin is correlated to some unmeasured aspect of egg quality that could enhance the viability of offspring of lower-quality fathers. We found that intensity of blue-green coloration increased with laying order between the first and fifth eggs.     

Effects of Chromium Propionate on Egg Production,Egg Quality,Plasma Biochemical Parameters,and Egg Chromium Deposition in Late-Phase Laying Hens

This study was conducted to investigate the effects of chromium propionate on egg production, egg quality, plasma biochemical parameters and egg chromium deposition in late-phase laying hens. Four hundred thirty-two 60-weeks old laying hens were divided into four groups of 108 birds per group according to egg production. The dietary treatments consisted of the basal diet adding with 0, 200, 400, and 600 μg/kg chromium as chromium propionate. All laying hens were given feed and water ad libitum for 8 weeks. The addition of 400 μg/kg Cr as chromium propionate increased egg production (P?<?0.01) during the later 4 weeks, but decreased albumen height, yolk color score, and Haugh unit of eggs. Six hundred micrograms per kilogram Cr as chromium propionate supplementation improved shell thickness (P?<?0.05). 200 μg/kg Cr as chromium propionate supplementation decreased the uric acid concentration by 31 % (P?<?0.05). However, supplemental Cr did not affect the egg chromium deposition of hens (P?>?0.05). These data indicated that feeding of late-phase laying hens with chromium propionate could improve egg production, increase eggshell thickness, but do not result in abnormal levels of chromium deposition in eggs.     

INTERACTIVE EFFECTS OF OFFSPRING SIZE AND TIMING OF REPRODUCTION ON OFFSPRING REPRODUCTION: EXPERIMENTAL,MATERNAL, AND QUANTITATIVE GENETIC ASPECTS

We demonstrate that egg size in side-blotched lizards is heritable (parent-offspring regressions) and thus will respond to natural selection. Because our estimate of heritability is derived from free-ranging lizards, it is useful for predicting evolutionary response to selection in wild populations. Moreover, our estimate for the heritability of egg size is not likely to be confounded by nongenetic maternal effects that might arise from egg size per se because we estimate a significant parent-offspring correlation for egg size in the face of dramatic experimental manipulation of yolk volume of the egg. Furthermore, we also demonstrate a significant correlation between egg size of the female parent and clutch size of her offspring. Because this correlation is not related to experimentally induced maternal effects, we suggest that it is indicative of a genetic correlation between egg size and clutch size. We synthesize our results from genetic analyses of the trade-off between egg size and clutch size with previously published experiments that document the mechanistic basis of this trade-off. Experimental manipulation of yolk volume has no effect on offspring reproductive traits such as egg size, clutch size, size at maturity, or oviposition date. However, egg size was related to offspring survival during adult phases of the life history. We partitioned survival of offspring during the adult phase of the life history into (1) survival of offspring from winter emergence to the production of the first clutch (i.e., the vitellogenic phase of the first clutch), and (2) survival of the offspring from the production of the first clutch to the end of the reproductive season. Offspring from the first clutch of the reproductive season in the previous year had higher survival during vitellogenesis of their first clutch if these offspring came from small eggs. We did not observe selection during these prelaying phases of adulthood for offspring from later clutches. However, we did find that later clutch offspring from large eggs had the highest survival over the first season of reproduction. The differences in selection on adult survival arising from maternal effects would reinforce previously documented selection that favors the production of small offspring early in the season and large offspring later in the season—a seasonal shift in maternal provisioning. We also report on a significant parent-offspring correlation in lay date and thus significant heritable variation in lay date. We can rule out the possibility of yolk volume as a confounding maternal effect—experimental manipulation of yolk volume has no effect on lay date of offspring. However, we cannot distinguish between genetic effects (i.e., heritable) and nongenetic maternal effects acting on lay date that arise from the maternal trait lay date per se (or other unidentified maternal traits). Nevertheless, we demonstrate how the timing of female reproduction (e.g., date of oviposition and date of hatching) affect reproductive attributes of offspring. Notably, we find that date of hatching has effects on body size at maturity and fecundity of offspring from later clutches. We did not detect comparable effects of lay date on offspring from the first clutch.     

Nutritional needs for egg formation in the Shag Phalacrocorax aristotelis

Egg production does not impose a major food need in the Shag Phalacrocorax aristotelis because the eggs are small, are formed slowly and are laid at 3-day intervals. I used dye-dosing of females, laying time and, after fixing and staining the yolk, daily ring counts to estimate the amounts of protein and energy needed each day to produce a clutch of three eggs. Maximum daily nutrient needs during egg formation were only 1.15 g per day additional protein and 34 kJ per day energy. Yolk formation times of 40 eggs were 13.5 (±1.2 s.d.) days. Based on yolk-ring counts and laying dates of 15 eggs that contained dye, the lag period between yolk completion and laying was 3.1 ± 0.06 days. The distinct light and dark rings of the stained yolk resulted from differences in the transparency of the yolk spheres. In the dark rings, the spheres were relatively clear, so more depth of stained yolk could be seen than in the light rings, which reflected the incident light.     

Detection of Transgenic and Endogenous Plant DNA Fragments and Proteins in the Digesta,Blood, Tissues,and Eggs of Laying Hens Fed with Phytase Transgenic Corn

The trials were conducted to assess the effects of long-term feeding with phytase transgenic corn (PTC) to hens on laying performance and egg quality, and investigate the fate of transgenic DNA and protein in digesta, blood, tissues, and eggs. Fifty-week old laying hens (n = 144) were fed with a diet containing 62.4% PTC or non-transgenic isogenic control corn (CC) for 16 weeks. We observed that feeding PTC to laying hens had no adverse effect on laying performance or egg quality (P>0.05) except on yolk color (P<0.05). Transgenic phyA2 gene and protein were rapidly degraded in the digestive tract and were not detected in blood, heart, liver, spleen, kidney, breast muscle, and eggs of laying hens fed with diet containing PTC. It was concluded that performance of hens fed diets containing PTC, as measured by egg production and egg quality, was similar to that of hens fed diets formulated with CC. There was no evidence of phyA2 gene or protein translocation to the blood, tissues, and eggs of laying hens.     

Oviposition behavior and progeny allocation of the polyembryonic waspCopidosoma floridanum (Hymenoptera: Encyrtidae)

Oviposition behavior was used to determine the primary clutch size and sex ratio of the polyembryonic wasp Copidosoma floridanumAshmead (Hymenoptera: Encyrtidae) parasitizing Pseudoplusia includens(Walker) (Lepidoptera: Noctuidae). The laying of a female egg was associated with a pause in abdominal contractions during oviposition, while the laying of a male egg was associated with uninterrupted abdominal contractions. Although unmated females produced only male broods, they also displayed male and female egg oviposition movements. Wasps always laid a primary clutch of one or two eggs. For mated females if only one egg was laid, the emerging secondary clutch was all male or female, but if two eggs were laid a mixed brood of males and females was almost always produced. The secondary clutch of single sex broods was usually between 1000 and 1200 individuals, but the secondary clutch of mixed broods averaged 1143 females and 49 males. Thus, the primary sex ratio for mixed broods was 0.5 (frequency males), but the secondary sex ratio was 0.042. Manipulation of the sequence of male and female egg oviposition or of the primary clutch did not produce major alterations in the secondary clutch size or sex ratio.     

Embryonic growth and mobilization of energy and material during incubation in the checkered keelback snake, Xenochrophis piscator

We collected 20 checkered keelback snakes (Xenochrophis piscator) to study embryonic growth and mobilization of energy and material during incubation. Females laid eggs between late May and late June. The eggs were incubated at 27 degrees C (+/-0.3). One egg from each clutch was dissected at five-day intervals starting at oviposition. The mean incubation length at 27 degrees C was 48.9 days. We identified three phases of embryonic growth or yolk depletion in X. piscator. Phase 1, between oviposition and Day 20, was one of minimal transfer of energy and material from yolk to embryo. Phase 2, between Day 20 and Day 39-40, was characterized by increasingly rapid embryonic growth or yolk depletion. Phase 3, between Day 39-40 and hatching, was characterized by reduced embryonic growth or yolk depletion. Approximately 71% of dry mass, 53% of non-polar lipids and 66% of energy were transferred from the egg contents to the hatchling during incubation. Our data confirm that oviposition is not timed to coincide with the onset of rapid embryonic growth in oviparous squamate reptiles. The greater conversion efficiencies of energy and material from egg to hatchling in snakes can be attributed to their lower energetic costs of embryonic development and greater residual yolk sizes.     

宁波滑蜥两性异形和雌性繁殖

蜥蜴的雌性繁殖特征对理解两性异形的进化原因起着重要作用。于2011年4月在安徽滁州采集宁波滑蜥(Scincella modesta),定量研究该种形态特征的两性异形和雌性繁殖特征,检验成体形态特征两性异形与雌性繁殖的相关性。研究共采集43条(17♀♀,26♂♂)宁波滑蜥,雄性和雌性个体的最大体长分别为47.4 mm和46.6 mm。雌雄两性在体长和头宽上没有差异,而在腹长和头长上差异显著,雄性有较大的头长,雌性有较大的腹长。宁波滑蜥年产单窝卵。窝卵数和窝卵重与雌体体长及腹长呈正相关,卵重与雌体体长无相关性。窝卵数及卵重的变异系数分别为0.20和0.12。卵长径与窝卵数呈负相关,而卵短径与窝卵数无关。雌体主要通过增加窝卵数来增加繁殖输出。这些结果表明,宁波滑蜥是雌雄个体大小同形的两性异形模式,性选择使得雄性有着较大的头长,以具有较高的交配成功率,生育力选择使得雌性有着较大的腹长,以具有较大的生育力和繁殖输出。     

Egg clutch patterning in Lestes virens (Odonata,Lestidae) with evolutionary emphasis on endophytic oviposition in lestid dragonflies

Egg deposition within plants is one of the most widely distributed and ancient behaviors in Odonata. The resulting clutch consists of eggs placed in peculiar pattern that can be a characteristic for certain groups of Odonata. Despite their importance for paleontological and evolutionary research, data on egg‐clutch positioning are missing or insufficient for most species. Here, patterning of egg clutches in Lestes virens was measured and described in detail for the first time. The female usually produces a linear row of single eggs directed at an angle rightward or leftward to the longitudinal axis of plant substrate. Less often eggs are arranged in egg‐sets consisting of up to 4 eggs. Apparently, the female insect follows the rigid behavior stereotypes during oviposition and is unable to easily switch to the alternate stereotypical behavior of single egg deposition or production of multiegg sets. Based on a literature review and original data, egg clutch patterning of European Lestidae is overlaid on preexisting phylogenies. The resulting evolutionary scenario of egg‐clutch patterning can be considered in the framework of egg‐laying behavior in Lestidae.     

Egg quality of Japanese quail depends on layer age and storage time

The aim of the study was to analyse egg quality changes of Japanese quail during the reproductive season and after several days of storage. A significantly higher egg weight was recorded in week 9 than in week 25 and week 31 of age ofbirds. The egg specific gravity value of eggs also decreased with the age of quails. The smallest yolk weight and its percentage proportion in egg mass were observed in week 25. Eggs laid in weeks 9 and 25 were characterised by similar and lower (P < or = 0.05) white weight in comparison to those examined on the last date. The highest white proportion in egg weight was recorded during the 25th week. The value of this trait was similar or smaller on the remaining dates. Similar and lower values of the white index and Haugh units, in comparison with the first date, were determined in eggs laid on weeks 25 and 31, whereas similar and greater eggshell thickness than in the 9th week of age was recorded on the last two dates of examination. Lower (P < or = 0.05) egg weight was observed after 5 and 8 than after 0 (measured on the day of laying) days of storage. Likewise, smaller egg specific gravity was recorded after three consecutive periods of storage in comparison with the eggs examined on the day of laying. Eggs examined after 3, 5 and 8 days of storage, in comparison with those stored for 0 days, were characterised by lower yolk index. Significantly smaller weight and white index than after 0 days were determined in eggs stored, respectively, for 5 and 8 as well as for 3, 5 and 8 days. Similarly, smaller numbers of Haugh units were determined after 3 consecutive storage periods in comparison with the eggs examined on the day of laying. Eggs stored for 0 and 3 days were characterised by a greater eggshell weight than those examined after 5 and 8 days. The weight of Japanese quail eggs decreased significantly from day 5 onwards, whereas the egg specific gravity-- from the 3rd day of storage. Yolk and white quality began to deteriorate already after 3 days of egg storage. It appears, therefore, that egg storage of Japanese quails before hatching lasting more than 3 days in the analysed conditions deteriorated the eggshell quality and internal egg traits.     

Maternal androgens in the pied flycatcher: timing of breeding and within-female consistency

Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk androgen levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of androgens. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk androgen levels.