Relative Egg Size Research Articles

Reproductive biology of female humpback whitefish Coregonus pidschian in the Chatanika River, Alaska

Summary Humpback whitefish Coregonus pidschian are found throughout Alaska and support both subsistence and personal-use fisheries. Long-term sustainability of these fisheries requires an understanding of life-history characteristics and reproductive biology to provide fisheries managers with the tools required for science-based management. The objective of this study was to examine the reproductive characteristics of humpback whitefish in the Chatanika River, Alaska, from late August through September 2008. Absolute fecundity, relative fecundity, gonadosomatic index (GSI), relative egg size, and age were examined for 60 female humpback whitefish. Mean absolute fecundity was 45 000 eggs female−1 (range, 11 747–108 426 eggs female−1) and was positively related to both fork length (r2 = 0.74) and wet weight (r2 = 0.83). Gonadosomatic index values averaged 15.5% (range, 6.4–23.7%). Relative fecundity was positively related to GSI (r2 = 0.76) and showed a positive relationship with age until ages 15–20 before declining thereafter. Relative egg size was inversely related to GSI (r2 = 0.38) and age (r2 = 0.22) for female humpback whitefish. The results of our study provide information that will allow for better management of the personal use fishery for humpback whitefish in the Chatanika River and increase our understanding of the reproductive biology of this species throughout its geographic distribution.

Seasonal Variation of Egg Size and Shape in Ypthima multistriata (Lepidoptera: Satyridae) in Relation to Maternal Body Size as a Morphological Constraint

Abstract To evaluate the role of the constraint on egg size imposed by maternal size, we examined the relationships between female body size and egg size and shape in the grass-feeding satyrine butterfly Ypthima multistriata Butler (Lepidoptera: Satyridae). In this species, larger and smaller mothers occur in the first and second generations, respectively. Egg size relative to maternal body size (relative egg size) was larger in the second generation than in the first generation. However, no body size constraint on egg volume was apparent in either generation. The degree of egg elongation (the ratio of egg length to egg width) increased significantly with relative egg size only in the second generation, but the correlation was quite weak. These results indicate that body size does not strongly constrain the determination of egg size; therefore, mothers have little need to elongate their eggs to respond to morphological constraints.

Egg size and asymmetric sibling rivalry in red-winged blackbirds

How big to make an egg is a life history decision that in birds is made coincident with a series of other similar decisions (how many eggs to have, whether to fortify them with maternally derived hormones or immune system boosters, whether to hatch the eggs synchronously or asynchronously). Though within-population variation in egg size in birds has been well studied, its adaptive significance, if any, is unclear. Here we examine within-population variation in egg size in relation to asymmetric sibling rivalry in a 17-year study of red-winged blackbirds (Agelaius phoeniceus), an altricial songbird. Egg mass showed a twofold range of variation, with roughly 80% of the variation occurring across clutches. By commencing incubation before the clutch is complete, mothers create advantaged core and disadvantaged marginal elements within their brood. Previous work on this system has shown that sibling competition is asymmetric, and that core offspring enjoy priority access to food, and as a consequence show higher growth and lower mortality than marginal offspring. Here we examine the effect of initial egg size on nestling growth and survival in relation to these competitive asymmetries. Egg mass was strongly linked to hatchling mass, and remained significantly related to the mass of both core and marginal nestlings; the effect of egg size was stronger for core offspring early in the nestling period, but the disparity between core and marginal nestlings narrowed as they approached fledging age, and slower growing marginals fell victim to brood reduction. The effect of egg mass on survival differed dramatically between core and marginal nestlings. Egg mass was significantly related to the survival of marginal but not core nestlings: below average egg mass was associated primarily with very early mortality. Asymmetric sibling competition is clearly a strong determinant of the consequences of egg size variation.

Sexual dimorphism of egg size in the European Blackbird Turdus merula

Recently, a number of studies have shown that female birds are able to control the sex of their progeny at the stage of the gamete. There is also some evidence that females adjust their investment in offspring depending on the sex of the embryo during egg formation. Differential maternal investment to the eggs depending on their sex is usually interpreted as an adaptive strategy, by which females can increase competitive abilities of the smaller sex, or preferentially invest towards the sex with the potentially higher fitness returns. Here, we studied variation in egg size in relation to embryo sex and laying order in the European Blackbird Turdus merula. We found male and female eggs to differ in size, with larger eggs containing male embryos, as well as a significant interaction between embryo sex and laying order. This interaction resulted from the fact that egg size increased with the laying sequence among eggs bearing females but did not change with laying order among eggs bearing males. There was no relationship between offspring sex and the laying sequence within a clutch. We suggest that sexual dimorphism in egg size recorded in the European Blackbird may reflect favouritism of the sex which may give higher fitness returns.

Egg-spot pattern rather than egg colour affects conspecific egg rejection in the house sparrow (Passer domesticus)

Brood parasitism could be a selective pressure on each female to have a type of egg that permits recognition. House sparrows (Passer domesticus) undergo conspecific brood parasitism and can recognise parasitic eggs. In this study, we analyse the effect of relative size in experimental parasitic eggs compared to the host eggs. We modified egg colour and the spot pattern to determine the influence of these characteristics on egg rejection. Furthermore, we examine whether egg rejection increases with “stimulus summation”. Our results show that egg rejection is not affected by relative egg size. However, changes in the spot pattern proved to exert the highest influence on egg rejection (32.4% of trials), significantly higher than when only egg colour is changed (3.8%). Therefore, our results suggest that parasitism may be a pressure favouring the maintenance of spotted eggs in house sparrow.

Effects of Soil Type and Adult Size on Mating Propensity and Reproductive Output in Two Populations of the Land SnailArianta arbustorum(Linnaeus)

Life-history traits in terrestrial gastropods may be influenced by both abiotic and biotic factors. This study examines the effects of soil type and adult size (shell volume) on mating propensity and female and male reproductive output (number and mass of eggs, number of sperm delivered and spermatophore mass) in individuals of the simultaneous hermaphrodite land snail Arianta arbustorum from two populations kept both on calcium-(Ca-)rich and Ca-poor soil. Snails from the two populations differed in adult size, relative shell growth, mating propensity and egg size. Furthermore, in both populations the number of egg batches deposited, egg size and spermatophore size scaled allometrically with shell volume, but not the total number of eggs produced and number of sperm delivered. Independent of population and shell size, the type of soil on which the snails were maintained influenced mating propensity, the total number of eggs produced and the mass of the albumen gland (another measure of female reproductive output). The mating propensity was higher and the total number of eggs produced was larger in snails kept on Ca-poor soil than in individuals reared on Ca-rich soil. This surprising finding could be explained by the fact that the Ca-poor soil used in the experiment still contained enough Ca to allow reproduction, and that the snails ingested Ca through the food consumed (lettuce grown on Ca-rich soil was available ad libitum). Moreover, the Ca-rich soil could contain minerals or (unknown) substances which discourage reproduction in A. arbustorum. Our study highlights the complexities faced when interpreting differences in the life history of gastropods. Explaining interpopulational differences in life-history patterns requires not only the understanding of the influence of snail origin, but also an understanding of the effects of shell size, substratum type (soil type), food and local climate.

Maternal effects on offspring Igs and egg size in relation to natural and experimentally improved food supply

1. Maternal effects have been suggested to function as a mechanism for transgenerational plasticity, in which the environment experienced by the mother is translated into the phenotype of the offspring. In birds and other oviparous vertebrates where early development is within the egg, mothers may be able to improve the viability prospects of their offspring at hatching by priming eggs with immunological and nutritional components. 2. We studied how resource availability affects maternal investment in offspring by feeding Ural owl (Strix uralensis, Pall.) females prior to egg-laying in 3 years of dramatically different natural food conditions. 3. Supplementary feeding prior to laying increased body mass and the level of Igs of females measured at clutch completion. Supplementary fed Ural owl females laid larger eggs than control females, and had offspring with higher levels of Igs at hatching compared to offspring of control females. 4. We found variation in maternal allocation of resources to the eggs in response to environmental conditions: during a year of rapidly declining food abundance, maternal Igs in hatchlings were higher, whereas egg size was smaller compared to years with a more stable food supply. 5. Egg size had a positive effect on offspring body mass at fledging, whereas Igs at hatching did not affect Igs at fledging. 6. We conclude that maternal body condition and maternal Igs, as well as hatchling Igs and egg size are limited by food resources during egg production. Hatchlings rely on maternally derived Igs and, hence, our results suggest that mothers with high levels of Igs passively transfer higher Igs levels to their eggs instead of active manipulation of Igs levels in eggs. Ural owl egg size appears to be highly sensitive to short-term changes in food abundance, with important consequences for nestling growth.

Ovarian dynamics, egg size, and egg number in relation to temperature and mating status in a butterfly

AbstractAlthough the temperature‐size rule, that is, an increase in egg (and body) size at lower temperatures, applies almost universally to ectotherms, the developmental mechanisms underlying this consistent pattern of phenotypic plasticity are hitherto unknown. By investigating ovarian dynamics and reproductive output in the tropical butterfly Bicyclus anynana (Butler) (Lepidoptera: Nymphalidae: Satyrinae) in relation to oviposition temperature and mating status, we tested the relevance of several competing hypotheses for temperature‐mediated variation in egg size and number. As expected, females ovipositing at a lower temperature laid fewer but larger eggs than those ovipositing at a higher temperature. Despite pronounced differences in egg‐laying rates, oocyte numbers were equal across temperatures at any given time, while oocyte size increased at the lower temperature. In contrast, there were greatly reduced oocyte numbers in mated compared to virgin females. Our results indicated that temperature‐mediated plasticity in egg size cannot be explained by reduced costs of somatic maintenance at lower temperatures, enabling the allocation of more resources to reproduction (reproductive investment was higher at the higher temperature). Furthermore, there was no indication for delayed oviposition (no accumulation of oocytes at the lower temperature, in contrast to virgin females). Rather, low temperatures greatly reduced the oocyte production (i.e., differentiation) rate and prolonged egg‐maturation time, causing low egg‐laying rates. Our data thus suggested that oocyte growth is less sensitive to temperature than oocyte production, resulting in a lower number of larger eggs at lower temperatures.

Determinants of interspecific variation in population declines of birds after exposure to radiation at Chernobyl

SummaryRadiation can reduce antioxidant levels dramatically because of the use of antioxidants to eliminate free radicals produced in the presence of radiation. Antioxidants are crucial biochemicals for elimination of free radicals, which can cause permanent damage to DNA and other molecules. If antioxidants are a limiting resource, we would expect individuals of species with a high expenditure of antioxidants to suffer the most from radiation. We tested this hypothesis by investigating interspecific variation in the relationship between abundance and level of radiation in breeding birds inhabiting forests around Chernobyl, Ukraine. We used bird point counts to estimate abundance of 57 species of birds at 254 locations where background radiation levels were quantified.Migratory birds use large amounts of antioxidants during their annual migrations to neutralize free radicals, and migrants have depleted antioxidant levels upon arrival at their breeding grounds. Consistently, abundance decreased with increasing levels of radiation in species that migrated the longest distances.Bird species with long dispersal distances may experience deficiencies in antioxidant levels because of physical activity but also because of exposure to novel antigens, implying that species with long dispersal distances should suffer the most from exposure to radiation. Indeed, the slope of the relationship between abundance and radiation decreased with increasing dispersal distance.Female birds deposit large amounts of antioxidants in their eggs, with the total amount deposited often exceeding the total amount in a female's. Accordingly, the decrease in abundance with radiation level increased with relative egg size in different species.Many bird species have plumage that is coloured by carotenoids, which cannot be recovered once deposited in feathers. Therefore, bird species with carotenoid‐based plumage should show stronger declines with increasing levels of radiation than species with melanin‐based or structural coloration. In accordance with this prediction, the decline in abundance with radiation was the strongest in species of birds with carotenoid‐based plumage.Synthesis and applications. These findings highlight the importance of antioxidants for understanding the ecological consequences of radiation on the abundance of free‐living animals, showing that species using large amounts of antioxidants will be particularly susceptible to the effects of low‐level radiation.

Interannual Variability of Fecundity and Egg Size of an Invasive Cyprinid, Carassius gibelio: Effects of Density-Dependent and Density-Independent Factors

ABSTRACT A population of the invasive Prussian carp (Carassius gibelio) was examined over a three-year period in a mesotrophic reservoir to find out interannual variations of fecundity and egg size and the influence of maternal condition (total length, TL, and age class) and environmental factors (water temperature and fish density) on these variables. Prussian carp reproduction was synchronous, with only a single batch, and fecundity ranged from 1,250 to 62,400 eggs per female. Relative fecundities and egg size showed no significant between-year differences. Fecundity increased with age, whereas egg diameter remained unchanged with age and TL. Fecundity was affected positively by TL and negatively by fish density, whereas temperature had no significant effect. Egg size was not affected by fish density or temperature.

Mound and Mate Choice in a Polyandrous Megapode: Females Lay More and Larger Eggs in Nesting Mounds With the Best Incubation Temperatures

AbstractMales of the polyandrous Australian Brush-turkey (Alectura lathami) build mounds of leaf litter, in which incubation heat is produced by microbial decomposition. Females lay eggs singly, at intervals of several days, over many months. For each egg, they select an incubation mound in which to lay, and they then typically copulate with the male mound-owner; mound choice is, thus, usually equal to mate choice. Freed from incubation and maternal care, these females can invest considerable time and energy in assessing and choosing their potential mates. Low or high incubation temperatures inside the mounds have negative effects on embryos and chicks, and temperatures vary considerably both between and within mounds. Here, I show that mounds with mean incubation temperatures ranging from approximately 32°C to 35°C received more eggs than cooler or warmer mounds. Similarly, when the size of each egg was compared with its temperature when found in the mound, larger eggs were deposited mainly in mound material at temperatures between approximately 32°C and 35°C, whereas smaller eggs were laid at temperatures above and below this range. Egg size was included as a factor describing female mate choice, because egg size in relation to body size is exceptionally large, which indicates considerable female investment. Overall, these results suggest that the temperature in the males’ incubation mounds considerably affects female mate choice.Selección del Montículo y de la Pareja en un Megápodo Poliándrico: Las Hembras Ponen Más y Mayores Huevos en los Montículos de Nidificación con las Mejores Temperaturas de Incubación

Maternal condition influences phenotypic selection on offspring

1. Environmentally induced maternal effects are known to affect offspring phenotype, and as a result, the dynamics and evolution of populations across a wide range of taxa. 2. In a field experiment, we manipulated maternal condition by altering food availability, a key factor influencing maternal energy allocation to offspring. We then examined how maternal condition at the time of gametogenesis affects the relationships among early life-history traits and survivorship during early development of the coral reef fish Pomacentrus amboinensis. 3. Maternal condition did not affect the number of embryos that hatched or the number of hatchlings surviving to a set time. 4. We found no significant difference in egg size in relation to the maternal physiological state. However, eggs spawned by supplemented mothers were provisioned with greater energy reserves (yolk-sac and oil globule size) than nonsupplemented counterparts, suggesting that provision of energy reserves rather than egg size more closely reflected the maternal environment. 5. Among offspring originating from supplemented mothers, those with larger yolk-sacs were more likely to successfully hatch and survive for longer periods after hatching. However, among offspring from nonsupplemented mothers, yolk-sac size was either inconsequential to survival or offspring with smaller yolk-sac sizes were favoured. Mothers appear to influence the physiological capacity of their progeny and in turn the efficiency of individual offspring to utilize endogenous reserves. 6. In summary, our results show that the maternal environment influences the relationship between offspring characteristics and survival and suggest that energy-driven selective mechanisms may operate to determine progeny viability.

The extended reproductive season of tent tortoises ( Psammobates tentorius tentorius): A response to an arid and unpredictable environment

In arid environments, limited resources may compromise allocations to reproduction, while unpredictable rainfall may confound the timing of reproductive events. Here we evaluate how female tent tortoises ( Psammobates tentorius tentorius) allocate resources to reproduction while coping with low and unpredictable rainfall. Vitellogenesis in tent tortoises started in autumn, when rainfall was highest and most predictable. Tent tortoises required a high body condition and large follicles to ovulate their first clutches, but a temperature threshold for ovulation may have prevented breeding during the winter months. Females produced small clutches (1.78±0.63; 1–3 eggs) but produced several clutches (3.7±1.6; 1–6 clutches) from spring to late autumn. Clutch frequency (CF) was correlated to body condition, and CF rather than clutch size (CS) determined annual fecundity. Although body size influenced egg size, body size had no effect on CS, CF or fecundity. There was no trade-off between relative egg size and CS. The small clutches of tent tortoises limit the risks of producing too many offspring at one time, a scenario that may leave females without resources for their own needs. When clutches are small, an extended breeding season enhances reproductive output by providing females more time and opportunities to leave offspring.

Reproductive biology of female shovelnose sturgeon in the upper Wabash River, Indiana

Shovelnose sturgeon Scaphirhynchus platorynchus are commercially important, supporting a viable roe fishery throughout much of the Mississippi River drainage. We examined the reproductive attributes of stage-5 female shovelnose sturgeon captured from the upper Wabash River, Indiana, from March to June 2004. Shovelnose sturgeon were collected using boat electrofishing and experimental gill nets, measured for fork length (FL) and wet weight, and sexed externally if possible. Size- and age-at-maturity, absolute and relative fecundity, relative egg size, and gonadosomatic index (GSI) were determined for 49 female shovelnose sturgeon (range, 601- to 858-mm FL). Female shovelnose sturgeon reached sexual maturity at approximately 600 mm and age-at-maturity ranged from ages 6 to 12 (median age = 9). Relative fecundity ranged from 11 220 to 23 956 eggs kg−1 (mean = 18 156 eggs kg−1). Absolute fecundity ranged from 14 294 to 65 490 eggs female−1 (mean = 30 397 eggs female−1) and was positively related to FL (r2 = 0.76) and wet weight (r2 = 0.82). The number of eggs g−1 of ovary weight ranged from 72 to 170 (mean = 98 eggs g−1) and was negatively correlated with GSI. GSI values ranged from 9.4 to 27.2 (mean = 19.3) and were positively correlated to FL (r2 = 0.18). Our results increase our understanding of shovelnose sturgeon reproductive biology and recruitment dynamics and provide input for models to evaluate the effects of harvest on this species.

Differences in Population Growth and Morphometric Characteristics of Three Strains of Brachionus angularis

ABSTRACT Three strains of the rotifer Brachionus angularis Gosse collected respectively from localities near Qingdao, Guangzhou, and Wuhu cities were cultured at 25±1°C to compare their population growth and morphometric characteristics when their were fed different algal foods (Chlorella pyrenoidosa, Scenedesmus obliquus, or a 1:1 mixture of both algae). The population growth rate, body size, egg size, and relative egg size were all significantly affected by food type. Among the three types of food, the rotifers fed C. pyrenoidosa had the lowest population growth rate. Rotifers fed S. obliquus had larger body size and egg size than those fed C. pyrenoidosa. Among the three rotifer strains, the population growth rate and the body size of Wuhu strain was the lowest and largest, respectively, and the ratio of body width to body length of Wuhu strain was the smallest. There were significant relationships between body size and egg size in all three strains. With all three strains, larger bodied rotifers tended to produce larger clutches of eggs, and, except for the Qingdao strain, there was a positive correlation between clutch size and egg size. Eggs of the Qingdao strain were the largest at clutch size 3.

Some patterns of age and geographical variation in fish fecundity

Some patterns of age and geographical variation in fecundity indices were analyzed in three freshwater fishes (river perch, bream, and Sevan khramulya). A trend to increase in the ovarian relative weight and mature egg size with age has been revealed. Two species with a wide range (perch and bream) demonstrated a tendency to decrease in the ovarian relative weight and increase in the definitive oocyte weight in females of populations living in the geographical center of the range. The coefficient of correlation between the absolute individual fecundity and body weight of females was proposed as a population marker of the fish reproductive system.

Female freshwater crayfish adjust egg and clutch size in relation to multiple male traits

Females may invest more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred partners may be fitter than offspring sired by non-preferred ones. In this study, we tested the differential maternal allocation hypothesis in the freshwater crayfish, Austropotamobius italicus, by means of a pairing experiment aimed at evaluating the effects of specific male traits (body size, chelae size and chelae asymmetry) on female primary reproductive effort. Our results showed that females laid larger but fewer eggs for relatively small-sized, large-clawed males, and smaller but more numerous eggs for relatively large-sized, small-clawed males. Chelae asymmetry had no effects on female reproductive investment. While the ultimate consequences of this pattern of female allocation remain unclear, females were nevertheless able to adjust their primary reproductive effort in relation to mate characteristics in a species where inter-male competition and sexual coercion may mask or obscure their sexual preferences. In addition, our results suggest that female allocation may differentially affect male characters, thus promoting a trade-off between the expression of different male traits.

Limited male incubation ability and the evolution of egg size in shorebirds

In bird species where males incubate but are smaller than females, egg size may be constrained by male body size, and hence ability to incubate the eggs. Using data from 71 such shorebird species, we show that egg size decreases as the degree of female-biased sexual size dimorphism increases, after controlling for female body mass. Relative egg size was not related to mean clutch size. However, when controlling for mating system, the relationship between female-biased sexual size dimorphism and relative egg size was only significant in polyandrous species. The relatively small eggs of socially polyandrous shorebirds have previously been explained as an energy-saving strategy associated with the production of multiple clutches. Our findings suggest that egg size evolution is better explained by male incubation limitation in these birds.

Why does a grasshopper have fewer, larger offspring at its range limits?

Analysis of size of offspring reared through three laboratory generations from populations of the field grasshopper Chorthippus brunneus from 27 sites around the British Isles showed that offspring were larger towards the cooler-wetter conditions in the western and northern limits of the range. This variation had a significant genetic component. There was a trade-off between clutch size and offspring size between and within populations. Under favourable thermal and feeding conditions maternal fitness was optimal when individuals produced the largest clutches of the smallest eggs, but under poor conditions maternal fitness was optimal when individuals produced small clutches of very large offspring. Calculation of geometric mean fitness over time indicated that having larger offspring near to the edge of the range could be advantageous as a conservative risk-spreading strategy. As well as geographic variation in egg size, significant environment-genotype interactions in egg size in relation to temperature were observed.

Egg size in relation to sex of embryo, brood sex ratios and laying sequence in northern lapwings (Vanellus vanellus)

AbstractThis study focuses on possible sources of egg size variation in the northern lapwing Vanellus vanellus, a polygynous shorebird with more variable male than female reproductive success. From the hypothesis that female birds allocate more resources into male than female eggs to improve their sons' abilities to compete for mates, male eggs were predicted to be larger than female eggs, and the proportion of sons was predicted to increase with mean egg volume of clutches. However, no size differences between male and female eggs were found. Corresponding with earlier reports in the species, egg size was positively correlated with female body condition, but no relationship between offspring sex ratios and intra‐clutch mean egg volumes was detected. These results suggest that a higher variation in reproductive success among males than among females is not sufficient for sexually dimorphic eggs to evolve in birds. Moreover, previous studies have suggested that shorebird eggs are subject to stabilizing selection for equal size within clutches. In contrast, this study demonstrates a consistent variation in egg size, with a significant increase in egg breadth between first and second eggs, and decreases in both breadth and volume between the third and the final fourth egg. The volume of last‐laid eggs was on average 2.3% smaller than the mean size of the preceding three eggs. Among the shorebirds studied so far, this consistent pattern of intra‐clutch egg size variation is unique to lapwings.