Egg Water Content Research Articles

Effects of Soil Temperature and Moisture on the Development and Survival of Grasshopper Eggs in Inner Mongolian Grasslands

Grasshopper eggs overwinter in soil for almost half a year. Changes in soil temperature and moisture have a substantial effect on grasshopper eggs, especially temperature and moisture extremes. However, the combinatorial effect of temperature and moisture on the development and survival of grasshopper eggs has not been well studied. Here, we examined the effects of different soil moistures (2, 5, 8, 11, 14% water content) at 26°C and combinations of extreme soil moisture and soil temperature on the egg development and survival of three dominant species of grasshopper (Dasyhippus barbipes, Oedaleus asiaticus, and Chorthippus fallax) in Inner Mongolian grasslands. Our data indicated that the egg water content of the three grasshopper species was positively correlated with soil moisture but negatively correlated with hatching time. The relationship between hatching rate and soil moisture was unimodal. Averaged across 2 and 11% soil moisture, a soil temperature of 35oCsignificantly advanced the egg hatching time of D. barbipes, O. asiaticus, and C. fallax by 5.63, 4.75, and 2.63 days and reduced the egg hatching rate of D. barbipes by 18%. Averaged across 26 and 35°C, 2% soil moisture significantly delayed the egg hatching time of D. barbipes, O. asiaticus, and C. fallax by 0.69, 11.01, and 0.31 days, respectively, and decreased the egg hatching rate of D. barbipes by 10%. The hatching time was prolonged as drought exposure duration increased, and the egg hatching rate was negatively correlated with drought exposure duration, except for O. asiaticus. Overall, the combination of high soil temperature and low soil moisture had a significantly negative effect on egg development, survival, and egg hatching. Generally, the response of grasshopper eggs to soil temperature and moisture provides important information on the population dynamics of grasshoppers and their ability to respond to future climate change.

Dehydration during egg production alters egg composition and yolk immune function

Parent-offspring conflicts occur when resources are limited for allocation, and, historically, energy has been the primary currency of focus when examining these trade-offs. Water is a fundamental resource that has received far less consideration for parent-offspring conflicts. Previous research suggests that, when water is limited, reproductive females are compromised in favor of developing embryos. However, these studies limited their assessments to standard metrics such as clutch size and mass. We tested the hypothesis that the mother-offspring conflict over limited water resources leads to finer scale morphological and physiological impacts on the eggs in Children's pythons (Antaresia childreni). We predicted that water deprivation during gravidity alters female investment into her eggs, impacting egg water content and shell development. Additionally, we predicted that the yolk in these dehydrated eggs would have enhanced immune performance metrics, as has been documented in dehydrated adults. We found that eggs from water-deprived females were dehydrated as indicated by reduced percent water and greater yolk osmolality compared to eggs from females that received ad libitum water. We also found that eggs from dehydrated mothers had thinner shells and higher water loss rates. The impacts were not entirely negative as dehydrated eggs had higher antimicrobial capabilities. Also, thinner and more permeability eggshells might allow for elevated rates of rehydration from nest substrate. Overall, by examining an array of egg traits, we demonstrated that dehydration of gravid females impacts the eggs, not just the females as previously reported. As a result, the mother-offspring conflicts are indeed two-sided.

Fecundity, egg volume and reproductive output of Macrobrachium tenellum (Crustacea: Palaemonidae) from the northern coast of Jalisco, Mexico

Our knowledge of the reproductive biology of palaemonid shrimps is an important tool to assess potential candidates for aquaculture as well as being useful to develop adequate strategies for the conservation of the biodiversity. Here we analyzed the fecundity, volume and water content of the eggs, and the reproductive output (RO) of Macrobrachium tenellum in the Ameca River, Jalisco-Nayarit, Mexico. The total length of the females ranged from 26.6 to 67.0 mm (average 44.2 ± 8.8 mm) and fecundity (considering all stages) fluctuated between 253 and 10,384 eggs (average 2,418 ± 2,089 eggs). Females lost on average 26% of the initially produced eggs. The average egg length increased from 0.55 (recently produced eggs) to 0.66 mm (eggs close to hatching). The water content of eggs increased significantly during embryogenesis by 11.4%. The RO was not related to female length and fluctuated between 4.1 and 16.0%, which are values within the range reported for other decapods. The results of the current research contribute to laying the foundations for future studies that help to define strategies for the conservation and sustainable use of this crustacean.

Biometrical and morphological analyses of Macrobrachium olfersii (Wiegmann, 1836) (Crustacea, Decapoda, Palaemonidae) embryos exposed to UVA and UVB radiation

ABSTRACT Macrobrachium olfersii (Wiegmann, 1836) is a prawn that lives in shallow and transparent freshwater in Southern Brazil. Aquatic organisms that inhabit these systems can be exposed to incident UV radiation. Many studies have demonstrated the effects of ultraviolet (UV) radiation on the development, survival rate, morphological abnormalities, and impairments in swimming behavior in crustaceans. However, fewer studies have elucidated how the embryos of crustaceans respond to the exposure of UV radiation. Thus, the aim of this study was to evaluate whether UVA and UVB affect biometrical and morphological parameters of eggs and embryos of M. olfersii. Embryos were divided into two groups: Group I, composed of embryonic day 7 (E7) to E10 and Group II, composed of E11 to E14. Both groups were irradiated with 60 min UVA and 30 min UVB. Non-irradiated embryos at the same stages were used as controls. UVA and UVB radiation induces variations in morphometric parameters, such as egg volume, egg water content, and eye index. UVB radiation also induced an increase of embryonic cell death. We conclude that the embryonic cells of M. olfersii respond differentially to UVA and UVB radiation in accordance with the evaluated parameters.

Early springtime water absorption by overwintering eggs of Mindarus abietinus (Hemiptera: Aphididae): possible implications for cold hardiness and diapause termination

AbstractEggs of the balsam twig aphid Mindarus abietinus Koch (Hemiptera: Aphididae) overwinter for several months in obligate diapause, which terminates in early springtime when embryogenesis of the stem mother supposedly resumes. Important shape and size changes were observed on eggs collected at regular intervals during late winter and early spring. These observations led to the visual classification of eggs into three shape categories: flat eggs (C1), semi-flat eggs (C2), and round and turgid eggs (C3). Egg mass significantly increased with time during late winter and early spring, which coincided with the noticeable changes in morphological composition (i.e., from C2 to C3). Our observations suggest that free water surrounding eggs on fir (Abies balsamea (Linnaeus) Miller; Pinaceae) shoots is essential for M. abietinus normal embryonic development during snowmelt. Also, reduced egg water content during winter could modify its supercooling point, and the renewed availability of water in springtime may signal diapause termination and/or initiate embryogenesis of the stem mother.

Effect of salinity on the embryonic development of Macrobrachium acanthurus (Decapoda: Palaemonidae)

The effect of salinity level on the embryonic development of Macrobrachium acanthurus was analyzed under laboratory conditions, considering characteristics of the egg (size, volume, and water content) and of the embryo (eye index). The experimental design was completely randomized, with five repetitions (ovigerous females) per treatment (0, 10, 17 and 20 ppt). During embryonic development, two eggs per female were taken daily for analyses of size, volume, water content, and eye index. Our results showed that salinity of 20 ppt leads to death and/or abortion of the embryo in all females. The size, volume and water content of eggs increased according to embryonic development, providing space in the egg for formation and organization of embryo. Salinity affected these egg characteristics, causing water loss to the hypertonic medium. Neither the duration of embryonic development nor embryo formation were affected by saltwater content. The results of the present study indicate that ovigerous females of M. acanthurus can survive in freshwater rivers as well as in low-salinity environments during incubation period and the successful larval development is not likely to rely on female migrating to estuaries. Larvae can easily be incubated in freshwater and complete development at higher salinities after hatch.

Reproductive strategy of the ghost shrimp Callichirus major (Crustacea: Axiidea: Callianassidae) from the southwestern Atlantic: sexual maturity of females, fecundity, egg features, and reproductive output

Reproduction and reproductive investment of females is an intriguing feature in axiidean shrimps. They have a cryptic behavior and great ecological importance in sediment turnover, and recycling of organic material and nutrient. Herein, we describe different aspects of the reproductive biology (size at sexual maturity of females, fecundity, egg characteristics, and reproductive output [RO]) of the ghost shrimp Callichirus major from the southeastern coast of Brazil. Females reached sexual maturity at sizes ≥11.85 mm dorsal oval length. Fecundity increased significantly with female size and varied between 1455 and 9931 eggs (average 4564 eggs). Individual egg volume almost doubled during embryogenesis, and average egg water content increased during the incubation period from 75.0 to 93.3%. The egg mass comprised on average 13.2% of the dry body weight of females. This relatively high RO value is probably compensatory to the relatively low number of ovigerous females in axiidean populations. The few published data on RO values suggest that female investment in reproduction of axiidean shrimps is somewhat higher than in other decapods. The high investment in egg production reflects most likely an effort to maximize the viability of the progeny. Studies with additional congeneric species will clarify whether there is a tendency of axiidean shrimps to have RO values at the upper end of the range reported for decapods.

Effects of dehydration on cardiovascular development in the embryonic American alligator (Alligator mississipiensis)

Effects of dehydration on reptilian embryonic cardiovascular function are unknown. Here, we present the first morphological and physiological data quantifying the cumulative effects of four acute dehydration events on the embryonic American alligator, Alligator mississipiensis. We hypothesized that dehydration would alter embryonic morphology, reduce blood volume and augment the response to angiotensin II (Ang II), a key osmotic and blood volume regulatory response element in adult vertebrates. Drying events at 30%, 40%, 50%, and 60% of embryonic incubation reduced total egg water content by 14.43±0.37g, a 3.4 fold increase relative to controls. However, embyronic blood volume was greater in the dehydration group at 70% of embryonic incubation compared to controls (0.39±0.044mLg−1 and 0.22±0.03mLg−1, respectively), however, both groups were similar at 90% of incubation (0.18±0.02mLg−1 in the controls and 0.23±0.03mLg−1 in the dehydrated group). Dehydration altered the morphological phenotype and resulted in an overall reduction in embryonic mass at both incubation time points measured. Dehydration also altered the physiological phenotype, resulting in embryonic alligators that were relatively bradycardic at 90% of incubation. Arterial Ang II injections resulted in a dose dependent hypertension, which increased in intensity over the span of incubation studied. While progressive incubation altered the Ang II response, dehydration had no impact on the cardiovascular responses to the peptide. Quantification of Ang II type-1 receptor protein using western blot analysis illustrated that dehydration condition and incubation time point did not alter protein quantity. Collectively, our results show that dehydration during embryonic development of the American alligator alters embryonic morphology and baseline heart rate without altering arterial pressure and response to Ang II.

Reproductive plasticity in Petrolisthes armatus (Anomura, Porcellanidae): a comparison between a Pacific and an Atlantic population

The porcellanid crab Petrolisthes armatus, with a known geographic distribution covering a wide range of latitudes, was selected to conduct a comparative study on egg production and reproductive output between two populations from Pacific and Atlantic coasts. Ovigerous females were collected between September and November 2005 in Punta Morales, Pacific coast of Costa Rica (n = 137) and from March 2005 to July 2006 in Araca region, Sao Paulo, Brazil (n = 46). The mean size of females was statistically different between both populations with larger females from Brazil than Costa Rica (7.9 ± 1.31 and 6.6 ± 0.95 mm CW, respectively). Likewise, egg production was significantly different in both populations and started in Pacific Costa Rica at a smaller female size than in Brazil. Specimens from Pacific Costa Rica produced roughly three times more eggs than equally sized females from Brazil, while newly extruded embryos were larger in Brazil than in Costa Rica (0.045 and 0.039 mm3, respectively). Egg volume increased during embryogenesis by 112.8 and 164.5% in Costa Rican and Brazilian populations, respectively. The egg water content increased steadily in both populations; however, eggs produced in Brazil contained always more water than those from the same developmental stage in Costa Rica. Average reproductive output (based on dry weight) was substantially lower in Brazil (0.031) than in Costa Rica (0.065). Our results confirm an impressive intraspecific plasticity of reproductive features in an intertidal decapod. The observed phenotypical variability might be related to local environmental conditions as well as to the location of the studied population concerning its geographic range of distribution.

Studies on the effect of low temperature on the duration of embryonic life, hatching percentage, wet weight, water and glucose levels and acid phosphatase activity during embryogenesis in eggs of Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae)

Laboratory experiments were performed to study the effects of low temperature on the duration of embryonic life, hatching percentage, wet weight, water content, glucose levels and acid phosphatase activity during embryonic development in the rice moth, Corcyra cephalonica. A significant increase occurred in the duration of embryonic life with decreasing temperature. Lowering the temperature from 28 o C to 24 o C did not affect the hatching percentage of eggs. However, when incubated at 28 o C, wet weight and water content of eggs significantly decreased with advancing egg age up to 40-48 h and 32-40 h respectively. Moreover, the rate of decrease in wet weight and water content lowered with decreasing incubation temperature. A significant decrease in glucose levels (g/egg and g/mg wet weight of egg sample) occurred during the initial stages followed by an increase, during the later stages of embryogenesis in eggs incubated at all three temperatures, although the levels of variation decreased with decreasing temperature. Acid phosphatase activity showed a more or less, sigmoid pattern of change, with a lowering rate of increase, corresponding to decreasing incubation temperature.

Fecundity, brood loss and egg development through embryogenesis of Armases cinereum (Decapoda: Grapsidae)

The present work is a comprehensive study of reproduction and embryonic development of Armases cinereum. Ovigerous A. cinereum (Bosc, 1802) females from Sebastian Inlet, Florida (9.88–19.4 mm CW) lay 2,000–12,000 eggs per brood, depending on their CW (mm): fecundity = 24.662 CW1.9432. A. cinereum displayed significant brood loss through development (ca. 500 eggs per brood) independently from their CW (no senescence). However, since smaller females lay fewer eggs than larger ones, the percentage of eggs lost during embryonic development is greater in smaller females. The number of eggs carried on a later stage of development (potential fertility = 5.5593 CW2.4417) is a more accurate estimate of the reproductive output and subsequent recruitment. Egg volume increased during development (64%, 0.025–0.041 mm3 or 0.36–0.43 mm of diameter, N = 270) and was strongly correlated with egg water content increase (19.21%, r = 0.89). Lipids, particularly fatty acids, seem to be the major energy source for embryonic development, decreasing 56.31 and 37.08% (respectively) during embryonic development; both are negatively correlated with egg volume (r = −0.90). The utilization of fatty acids through the different developmental stages of A. cinereum is presented. The most consumed fatty acids are the monounsatured (43.33 μg mg−1 dw), followed by the saturated (29.91 μg mg−1 dw) and polyunsaturated (24.03 μg mg−1). Palmitic (16:0) and linoleic (18:2n-6) acids are preferentially consumed (19.5 and 17.9 μg mg−1 dw, respectively). The high proportion of essential polyunsaturated fatty acids of C18 and C20 reflects the consumption of primary producers such as mangrove leaves. EPA/DHA ratio (2.85–3.84) and low DHA content indicated that this species appears in a medium-low level of the trophic chain. The low ratio of 18:1n-7/18:1n-9 and high percentage of 18:1n-9 (marker of carnivory) may be a sign of the consumption of juvenile invertebrates. The high percentage of odd-numbered FA indicated the occurrence of detritivores/scavenger behaviours. The fatty acid composition of the eggs reflects adult feeding ecology (omnivorous) and habitat.

Potential Fertility and Egg Development (Volume, Water, Lipid, and Fatty Acid Content) through Embryogenesis of Uca Rapax (Decapoda: Brachyura: Ocypodidae)

We examined potential fertility, egg volume, and water, lipid, and fatty acid content through embryogenesis in a population of female U. rapax from Sebastian Inlet, Florida. Carapace width (CW) ranged from 10.80 to 20.09 mm (N = 184), and each female carried 5000 to 30,000 eggs in the last stage of development. Female CW was found to be a good predictor of the number of eggs in the later stage of development (potential fertility = 7.908 CW2.7655, R2 = 0.749). Egg volume increases (from 0.0079 to 0.0134 mm3) was mildly correlated (r = 0.79) with an increase in egg water content (from 60 to 69%). Egg lipid and fatty acid content decreased through embryogenesis, due to its importance as energy source. The most consumed fatty acids were the monounsaturated (97.81 μg . mg dw−1) followed by the saturated (64.34 μg · mg dw−1) and polyunsaturated (38.69 μg · mg dw−1). Fatty acids 16:0, 18:2n-6, 16:1n-7, and 18:2n-6 are consumed preferentially (39.91, 38.45, 29.4 and 23.93 μg · mg dw−1, respectively), while essential polyunsaturated fatty acids, particularly docosahexaenoic acid (22:6n-3) and eicosapentaenoic acid (20:5n-3), are conserved. Egg fatty acid profile also reflects diet and habitat of adults. A medium-low EPA/DHA ratio suggests U. rapax occupies a medium trophic level. The low ratio (18:1n-7/18:1n-9) and high percentages of 18:1n-9 fatty acid (18%) and essential C18 and C20 polyunsaturated fatty acids (19-23%) suggests adults are omnivores consuming primary producers (like algae and mangrove leaves) and small invertebrates. The high percentage of odd-numbered fatty acids (above 3-3.5%) also suggests scavenger/detritivore behaviour.

Do mothers producing large offspring have to sacrifice fecundity?

We artificially selected on egg size in a butterfly to study the consequences for fecundity, reproductive effort and offspring fitness. Correlated responses in either pupal mass, larval or pupal development time were virtually absent. Offspring size was positively related to fitness, but only partly traded off against fecundity. Rather, total reproductive effort (measured as fresh mass), egg water content and the decline of egg size with female age increased in the large-egg selected lines compared to either small-egg or control lines. Accounting for these effects showed that reproductive investment (in dry mass) was in fact similar across lines. Such mechanisms may enable increased investment in (early) offspring without a reduction in their number, revealing a much more complex picture than a simple trade-off between offspring size and number. Substantial variation among replicates suggests that there are different underlying mechanisms for change, rather than any single, unitary pathway.

Geographic variation in snapping turtle (Chelydra serpentina serpentina) egg components across a longitudinal transect

Common snapping turtles (Chelydra serpentina serpentina) have an extensive range across North America, inhabiting aquatic habitats in diverse thermal and hydric climates. Although geographic variation in reproductive characters such as female size, clutch size, and egg mass have been investigated, little is known about geographic variation in egg components. In this study, we examined variation in the water content, solid content, and shell mass of snapping turtle eggs from four populations dispersed along a longitudinal geographic transect (Pennsylvania, Michigan, Minnesota, and Nebraska). Initial egg mass and dry shell mass were similar among these four populations. However, water contents of eggs correlated positively with longitude, whereas dry content mass correlated negatively with longitude. Moreover, water content of eggs correlated negatively with the average number of days per year where average air temperatures exceeded 15 °C in a particular region (an indicator of regional thermal climate), and dry content of eggs correlated positively with both the number of days per year where average air temperatures exceeded 15 °C and the average total precipitation for the months of May through September (an indicator of regional hydric climate). These findings suggest that egg content (and perhaps egg quality) in this wide-ranging species of turtle varies in a manner reflecting differences in climate.

Respiration and energetics of embryonic development in a large altricial bird, the Australian pelican (Pelecanus conspicillatus).

We examined whether the previously reported low cost of embryonic development in pelicans could be attributed to a more efficient conversion of egg energy to hatchling tissues as a result of high initial egg water content, low embryonic metabolic rate and growth later in incubation than in more precocious species. We therefore determined egg and hatchling composition and the development of embryonic respiration in the Australian pelican Pelecanus conspicillatus, which lays one of the largest eggs (140-210 g) with an altricial developmental mode. The small yolk fraction (21%) is typical of all pelecaniforms; however, we found that intraspecific variability in fresh egg mass was related to water content (principally in the albumen), but independent of yolk mass (mean 13 g dry mass). P. conspicillatus eggs have, on average, 635 kJ of energy, irrespective of egg mass across the whole range of egg mass. The embryonic developmental pattern of O(2) consumption and CO(2) production showed clear plateaus lasting 2-3 days immediately prior to internal pipping, resembling the typical precocial pattern. However, the rate of pre-internal pipping O(2) consumption was low in comparison with that of precocial species of similar egg mass. There is no evidence to support the hypothesis that the observed plateau in rates of O(2) uptake is due to a diffusion limitation of the eggshell gas conductance in this species. Embryonic metabolic rate nearly doubled during the pipping period, but the mass-independent metabolic rate of the hatchling was low in comparison with that of the resting adult. The total O(2) consumed (11 063 ml) is equivalent to 217.3 kJ (or 34% of egg energy) based on indirect calorimetry and the observed respiratory exchange ratio of 0.71. Thus, the cost of development (direct calorimetry) was 0.29 kJ J(-1) in the egg (mean egg mass 168 g), which is one of lowest reported values. As a result, the production efficiency of pelican embryonic development was 61.6%, higher than the average for birds in general (56.9%) and, in particular, of seabirds that have prolonged incubation periods on the basis of egg mass. High efficiency in embryonic development in this species was attained as a result of rapid embryonic growth later in incubation, low hatchling energy density (23.6 kJ g(-1) dry matter) and dry matter content, low embryonic metabolic rate throughout incubation and a shorter than expected incubation period of 33 days (predicted 36 days).

Brood Loss During Incubation in Philocheras Trispinosus (Decapoda) in Port Erin Bay, Isle of Man

Brood loss during incubation was studied in the crangonid shrimp Philocheras trispinosus. Concurrent changes in length, volume, and water content of eggs were followed. During embryonic development, egg length increased by some 40%, egg volume by about 130%, and water content increased from 69-85%. Egg number was an isometric function of body size in all 5 incubation stages. Brood loss did not vary with female size, and averaged 30% in egg number and 33% in brood dry weight. Brood loss occurred mainly during early and late incubation stages, predominantly the latter. Potential causes of early incubation loss are incomplete fertilization and inadequate attachment of eggs to the pleopods. Possible reasons for the large late-incubation loss include abrasion with substrate during burrowing, exacerbated by the increased egg volume.

Physiological mechanisms of buoyancy in eggs from brackish water cod

Newly fertilized eggs of brackish water (Gotland, Baltic Sea) and marine (Lofoten, Norway) cod were investigated with regard to specific gravity, wet and dry weight, water content, chorion weight, and content of protein, free amino acids (FAA), and ions. The eggs had neutral buoyancies equivalent to a salinity of 14.3% (range 11.5–16.2%) in brackish water, and 33.0% (range 31.8–34.5%) in the marine environment. A buoyancy model was developed and showed that this difference was mainly caused by differences in egg water content which was 96.6 ± 0.47% and 92.7 ± 0.45% in the brackish and marine eggs, respectively. The higher water content of the brackish eggs resulted from increased water uptake during final oocyte maturation due to higher intracellular contents of FAA, Cl – and NH4+. SDS polyacrylamide gel electrophoresis of eggs and oocytes, and measurements of egg protein content suggested that the FAA pool of both egg types originated from hydrolysis of specific yolk proteins. The main contributor seemed to be a protein with a molecular weight of 100 kDa.

INTRASPECIFIC VARIATION IN EGG SIZE AND EGG COMPOSITION IN BIRDS: EFFECTS ON OFFSPRING FITNESS

1. There is little unequivocal evidence to date in support of a positive relationship between egg size and offspring fitness in birds. Although 40 studies (of 34 species) have considered the effect of variation in egg size on chick growth and/or survival up to fledgling only 12 studies have controlled for other characters potentially correlated both with egg size and offspring fitness. Of these only two have reported a significant residual effect of egg size on chick growth (in the roseate tern and European blackbird) and three a residual effect on chick survival (all in seabirds: common tern, lesser black-backed gull and kittiwake). 2. More consistent evidence exists, though from fewer studies, for a positive relationship between egg size and offspring fitness early in the chick-rearing period; chick growth and chick survival being dependent on egg size in 8 of 10 studies and 4 of 5 studies respectively. It is suggested that the most important effect of variation in egg size might be in determining the probability of offspring survival in the first few days after hatching. 3. Egg size explains on average 66% of the variation in chick mass at hatching (n = 35 studies) but only 30% of the variation in chick body size (n = 18). When effects of hatching body size are controlled for chick mass remains significantly correlated with egg size, though the reverse is not true. This supports the hypothesis that large eggs give rise to heavier chicks at hatching, i.e., chicks with more nutrient (yolk) reserves, rather than structurally larger chicks. 4. Egg composition increased isometrically with increasing egg size in about half the studies so far reported (n equals approximately 20). However, in seabirds, and some passerines, larger eggs contain disproportionately more albumen, whilst in some waterfowl percentage yolk content increases with increasing egg size. Changes in albumen content largely reflect variation in the water content of eggs, but changes in yolk content involve variation in lipid content, and therefore in egg 'quality.' The adaptive significance of variation in egg composition is considered; females may adjust egg composition facultatively to maximise the benefits to their offspring of increased reproductive investment. 5. Considerations for future research are discussed with particular emphasis on experimental studies and the application of new techniques.

Regulation of ooplasmic sodium and potassium activities in developing locust eggs

AbstractOoplasmic activities of potassium and sodium were measured with ion sensitive microelectrodes before and during the period of maximal water uptake which occurs 3–5 days after oviposition for eggs incubated at 37°C. Potassium activity increased from 84 mM in eggs before fertilization at 118 mM in eggs 1 day after fertilization (d1). Sodium activity increased from 8 mM to 29 mM over the same period. These changes exceeded those predicted from the decrease in water content (8%) during the first day after oviposition. Between d1 and d3, potassium and sodium activities decreased to values predicted on the basis of the 88% increase in egg water content. Although water content increased an additional 46% between d3 and d5, ooplasmic sodium activity remained constant at 11 mM and potassium activity increased from 64 mM to 74 mM during this time. Declines in concentrations of sodium and potassium measured in whole eggs by atomic absorption spectrometry mirrored the increase in egg water content. The results suggest that regulation of ooplasmic sodium and potassium activities is accomplished by release of these ions from internal stores, possibly the york spheres. © 1992 Wiley‐Liss, Inc.

Differences in breeding Lake Superior pink salmon (Oncorhynchus gorbuscha (Walbaum)) associated with variation in thyroid hyperplasia

Pink salmon (Oncorhynchus gorbuscha (Walbaum)) from eastern Lake Superior exhibit various degrees of thyroid hyperplasia. A link between goitrogenesis and growth is suggested by the increased prevalence of large lesions among large fish of both sexes. Despite males being larger than females, however, lesion prevalence did not differ between the sexes. More large lesions occurred among late migrants, especially males, indicating a seasonal increase in hyperplasticity. Delayed stream entry occurred in overtly lesioned fish of both sexes, evidence of a possible inhibition of maturation. Males and females differed in condition (weight-at-length) with lesion severity. Females with overt lesions showed reduced secondary sexual character development, more so than males. The pre- and post-spawning testis characteristics of males generally did not differ with lesion size, although the testes of spawned-out males with large lesions did have higher water contents. In females, the reduced water content of eggs in severely lesioned individuals was evidence of delayed maturation. Enlarged livers occurred in badly lesioned females, but not in males. In neither sex did severely lesioned fish exhibit shorter breeding life-spans. In overview, this study demonstrates that a wide range of effects is associated with differences in the severity of thyroid hyperplasia exhibited by Lake Superior pink salmon, these also being mediated by apparent differences in physiology between the sexes.