Fuels for development: evolution of maternal provisioning in asterinid sea stars

For marine invertebrates, larval developmental mode is inseparably linked to the nutritional content of the egg. Within the asterinid family of sea stars there have been multiple, independent, evolutionary transitions to lecithotrophic development from the ancestral, planktotrophic state. To investigate the evolution of maternal investment and development within the Asterinidae, we quantified individual lipid classes and total protein for eggs and larval stages of closely related species representing three developmental modes (planktotrophy, planktonic lecithotrophy and benthic lecithotrophy). Within species, maternal provisioning differed between females indicating that egg quality varied with parentage. Maternal investment was related to egg size but, after correcting for egg volume, we identified two major oogenic modifications associated with the evolution of lecithotrophic development: (1) a reduction in protein deposition that probably reflects the reduced structural requirements of nonfeeding larvae, (2) an increase in deposition of a single class of energetic lipid, triglyceride (TG). The exception was Parvulastra exigua, which has benthic, lecithotrophic development and lays eggs with a lipid to protein ratio close to that of planktotrophs. This oogenic strategy may provide P. exigua larvae with a protein “weight-belt” that assists in maintaining a benthic existence. Asterinids with planktotrophic development used a significant portion of egg TG to build a feeding bipinnaria larva. For Meridiastra mortenseni, female-specific differences in egg TG were still evident at the bipinnaria stage indicating that egg quality has flow-on effects for larval fitness. In lecithotrophic asterinids, TG reserves were not depleted in development to the larval stage whereas protein stores may help fuel early larval development. Available data indicate that there may be two evolutionarily stable egg lipid profiles for free-spawning, temperate echinoderms.     

Energy substrates for eggs and prefeeding larvae of the dolphinCoryphaena hippurus

Changes in the chemical composition of developing dolphin (Coryphaena hippurus) eggs and prefeeding yolksac larvae were determined in order to estimate probable dietary requirements of first-feeding larvae. Daily dry matter, protein nitrogen (PN), non-protein nitrogen (NPN), lipid, gross energy content, fatty acid and amino acid profiles from Day 1 to Day 2 eggs and Day 1 to Day 3 larvae were compared. Lipid was the primary endogenous energy source accounting for the daily caloric deficit through both the egg and larval stages, except over the day of hatching. The catabolism of lipid by embryos (0.078 cal d^–1) was greater than that by yolksac larvae (0.036 cal d^–1). The higher demand for energy by embryos was related to a greater rate of protein synthesis during the egg stage. The ratio of PN:NPN increased during egg development without change in total nitrogen content, but was constant throughout the yolksac larvae period. The lipid content per embryo did not decrease over the hatching period (Day 2 to 3, postspawning). However, there was a loss in amino acid content not totally accounted for by sloughing of the chorion at hatching. This loss, as protein, accounted for 0.053 cal of gross energy, which represented 70% of the total estimated energy needs of the fish over this period. Loss of non-essential amino acids (25%) was higher than that of essential amino acids (13%). Proline and tyrosine accounted for 32% of the total loss of amino acids at this time. The only preferential use of fatty acids over any period was a small but significant drop in the content of C22:6n-3 prior to the onset of feeding (Day 5, postspawning). It is speculated that the pattern of energy-substrate use of first-feeding dolphin larvae will reflect the pattern of endogenous energy use during the egg and prefeeding yolksac larval stages. Diets or feeding regimens with lipid as the primary energy source, and containing a fatty acid profile similar to that of eggs or yolksac larvae, should be useful in culturing this species, at least during the early feeding stages.     

Ecophysiological studies on the developing eggs and embryos of the European lobster Homarus gammarus

During the course of its embryonic development, the European lobster Homarus gammarus Linnaeus exhibits progressive increases in content of water (54.0 to 83.1%), ash (2.7 to 16.7%), protein (47.4 to 50.9%) and non-protein nitrogen (1.0 to 2.4%), and steady decreases in content of fat (43.8 to 25.4%) and energy (6343 to 5431 cal/g dry organic substance). Cumulative yolk utilization efficiency during the total development is 81.8% for dry weight; the corresponding value for energy is 60.1, for protein 75.6 and for fat 47.4%. Energy content of a single egg is 10.49 cal. Of 4.20 cal expended for metabolic processes of the embryo, only 13.3% energy is drawn from protein oxidation; fat oxidation supplies as much as 87.7% energy, that of carbohydrate only 2.3%. Embryonic development results in a remarkable decrease in net yolk utilization efficiency, which falls from 85.5% in the early developmental stages, to less than 70% in later developmental stages. The mean dry weight of a single egg membrane increases from 38 g (2.2% of egg weight) in a freshly laid and attached egg, to 81 g in an egg with an almost completely developed embryo. This result supports the earlier observation of Cheung (1966) that the formation of the inner chitinous egg membrane occurs after the egg is laid and attached to the setum. Protein seems to be the major constituent of the egg membrane (4049 cal/g dry weight), which has the following composition: protein 70.4%, non-protein nitrogen 0.13%, ash 2.83%. Initial permeability of the egg membrane to water (about 6% of the total water requirement is let in) is followed by a period during which the egg membrane is almost impermeable to water (stages I to III); the egg membrane becomes permeable to water again and lets in 85% of the total water requirement (the rest, i.e. 9%, is metabolic water) at a relatively advanced stage of development. These assumed changes in egg membrane permeability appear to be indicative of variations in the egg's osmoconcentration leading to shiftings in net transport of water. Rates of water and salt uptake during embryonic development are essentially parallel (Fig. 1). The egg membrane remains permeable to salts throughout development; salt intake almost doubles after the egg passes through stage III. A single egg, weighing 3.7 mg requires 4.9 mg water for successful completion of embryonic development. The imbibition of water by the developing marine demersal egg seems to (1) serve in osmotic hatching; (2) float the hatched larva by means of specific gravity reduction; (3) aid the larva to quickly adjust its body temperature. The simple osmotic hatching mechanism, proposed by previous workers, seems to be inadequate to account for the events and timing of the hatching process in the lobster. It is suggested that hatching time is determined not solely by increased internal pressure caused by inflow of water and salts, but also by some unknown internal factor. In the lobster egg, as well as in many other marine demersal eggs, protein metabolism is suppressed to a considerable extent, and fat metabolism is geared up Thus, the non-cleidoic lobster eggs exhibit metablic properties which are typical of cleidoic eggs. This finding is discussed in the light of Needham's (1950) concept of cleidoicterrestrial and non cleidoic-aquatic eggs.Dedicated to Professor P. Kochukutta Menon, Montreal, on his 62nd birthday, June 3, 1970.     

Ontogenetic variation in metabolism, biochemical composition and energy content during the early life stages of Farfantepenaeus paulensis (Crustacea: Decapoda: Penaeidae)

Dry weight (DW), oxygen consumption, ammonia-N excretion, proximate biochemical composition (total protein, carbohydrate, lipid, water and ash), and energy content (estimated from biochemical composition and by wet combustion) were determined in early developmental stages of cultured Farfantepenaeus paulensis. Pooled samples from embryonic, larval and postlarval stages (at 26 ± 1 °C and 34 ± 1‰) were used for measurements. The study focused on physiological and biochemical processes during transitional periods of ontogeny, such as hatching, lecithotrophic and planktotrophic stages, metamorphosis, and the attainment of a benthic existence in postlarva. DW showed higher increment between protozoea I (PZ I) and mysis I (M I) than in the next mysid and postlarval stages. Individual rates of oxygen consumption and ammonia-N excretion increased, while weight-specific rates presented significant reduction throughout development. Higher weight-specific oxygen consumption was registered in nauplius III (N III) and PZ I, following a decrease in subsequent stages. Postlarval stages PL V–VI and PL X–XII exhibited the lowest values among the stages studied. Weight-specific excretion was high in N III and protozoeal stages, with maximum values in PZ II, while the following stages were marked by lower rates. O:N ratios indicated higher protein catabolism in the stages between egg and M I and a shift to more lipid utilization close to metamorphosis. Water content was higher in the protozoeal stages and decreased afterwards. Higher percentages of protein, lipid and carbohydrate (%DW) were observed in egg and nauplius stages. Protein and lipid decreased from the egg through the naupliar and protozoeal stages, rising again in mysis stages. Lipid content (%DW) decreased in PL V–VI and PL X–XII. Lipid:protein ratios showed an increase of the importance of lipid between PZ III and M II. Carbohydrates represented a minor fraction of body composition, and ash percentages increased from egg to a maximum in PZ II, decreasing in subsequent stages. Energy content determined by wet combustion or calculated by energy equivalents presented the same trend throughout development, varying similarly to protein. Protein was the main energy contributor to body energy in all stages, while the importance of lipid was higher in egg and early naupliar stages. Trends observed in metabolic rates and body composition may be associated to morphological and behavioral changes during the early stages of penaeid development, such as the transition from herbivory to omnivory, and the adoption of a benthic existence. Different ontogenetic energy strategies contribute to succeed through such diverse type of development. Received: 4 July 2000 / Accepted: 6 December 2000     

Lipid biochemistry and reproductive biology in two species of Gammaridae (Crustacea: Amphipoda)

Gammarus oceanicus Segerstråle, 1947 and Echinogammarus marinus (Leach, 1815) were sampled during the breeding season from Oslofjord in 1984, and their lipid composition examined in relation to reproductive condition. In G. oceanicus, female lipid content increased as the ovary matured. Both the amount of lipid stored and the rate of accumulation were greater in spring than in winter. Spring eggs contained 12.4 g lipid, of which 63% was triacylglycerol and 27% phospholipid. Both fractions decreased steadily during embryonic development. Winter eggs contained 19.2g lipid, of which 52% was triacylglycerol and 43% phospholipid. During the early stages of embryonic development the amount of phospholipid decreased sharply, whereas that of triacylglycerol increased, suggesting that some of the fatty acid released from phospholipid was sequestered temporarily as triacylglycerol. When newly spawned, both winter and spring eggs were richer in monoenoic fatty acids than adult amphipods and these acids were the major fuel consumed during development. 6 fatty acids were utilised more slowly than 3 acids, and egg carotenoid pigment content remained constant. Female E. marinus increased in lipid content as the ovary matured. Spring eggs contained 14.7 g lipid when newly spawned and this increased to 16.6 g during the early stages of development. This increase was entirely triacylglycerol, which declined in later stages; the source of the extra lipid was unclear. Eggs contained very little phospholipid or sterol, and both of these components remained at a steady low level during development. E. marinus eggs were not significantly rich in thonoenoic acids compared with adults, and saturated, monoenoic and polyenoic acids were utilised about equally during development. Both adults and eggs were rich in 20.46, which was utilised at a slower rate than the 3 polyunsaturated acids during embryonic development; again, egg carotenoid pigment content remained constant. In both species there was a decrease in the size of the egg (and as a result, of the newly hatched juvenile), but an increase in total reproductive output (i.e., the total weight of the egg clutch) per female as the breeding season proceeded. The reproductive output of an individual female is probably related to food availability during the period of ovarian maturation, whereas the size of an individual egg is dictated largely by feeding conditions for the juveniles once they are independent of the female. The different patterns of lipid utilisation during development found in this study emphasize the flexibility of response in the reproductive biology of gammarid amphipods. It is not yet possible, however, to relate the differing patterns in a simple way either to egg size or total female reproductive output. Two outstanding problems are the source of extra triacylglycerol during the early stages of development of E. marinus and the metabolic cost of brooding eggs.     

Variations de la teneur en acide ascorbique dans les oeufs de Cancer pagurus et Palaemon serratus (Crustacea: Decapoda) au cours de l'embryogenèse

Variations of ascorbic acid content were studied during different stages of embryogenesis in the two crustaceans Cancer pagurus and Palaemon serratus. Variations in the egg volume of P. serratus were also measured at each stage of embryogenesis. The eggs appeared able to synthesize ascorbic acid during the earlier embryonic stages. Ascorbic acid changes in the crustaceans' eggs are discussed in relation to the variations of proline, chitin, glycogen and glucose already studied. Ascorbic acid appears to play an important role in the survival of eggs incubating under unfavourable environmental conditions. Before hatching, the ascorbic acid content is as high as after spawning.     

Maternal provisioning for larvae and larval provisioning for juveniles in the toxopneustid sea urchin <Emphasis Type="Italic">Tripneustes gratilla</Emphasis>

Lipid and protein biochemistry of eggs (84 μm in diameter), embryos and early larvae of the tropical echinoid Tripneustes gratilla (Linnaeus 1758) were quantified to determine how maternal provisions are used to fuel development of the echinopluteus. The eggs contained a mean of 30.82 ng lipid and 87.32 ng protein. Energetic lipids were the major lipid component (55.52% of total lipid) with the major class being triglyceride (TG: mean 15.9 ng, 51.58% of total). Structural lipid was dominated by phospholipid (PL: mean 11.18 ng, 36.26% of total). Early embryogenesis was not a major drain on egg energetic lipid and protein. Development of the functional feeding larva used ca. 50% of initial egg energetic lipid and most of this was TG. Maternal TG was still present in the 8-day echinoplutei and it was estimated that this energetic lipid would be depleted in unfed larvae by day 10. There was no change in PL. In a separate experiment lipid biochemistry of rudiment stage larvae and early developing juveniles were quantified to determine how lipids are used during metamorphosis. Fed larvae accumulated lipid (mean 275.49 ng) with TG and PL being the major energetic and structural lipids, respectively. Larval lipid stores were not appreciably depleted by metamorphosis and so were available for the early benthic stage juvenile. Juveniles started their benthic existence with 314 ng total lipid (TG: mean 46.84 ng, 14.9% of total, PL: mean 137.51 ng, 43.67% of total). Nile Red histochemistry and histology showed that the stomach serves as a nutrient storage organ and, that lipid stores accrued by larvae sustain developing juveniles for up to 4 days post settlement. Triglyceride supported both non-feeding stages of development and the prefeeding larval and perimetamorphic benthic stage. In this first study of lipid stores in settlement stage echinoderm larvae, we show that T. gratilla larvae sequester the same major energetic lipid (TG) to support the early juvenile that the female parent provided them to fuel early development.     

Free amino acids as energy substrate in developing eggs and larvae of the cod Gadus morhua

The content of free amino acids (FAA) in the cod (Gadus morhua L.) egg is about 200 nmol at spawning, decreasing by about 100 nmol/egg during the egg stage and about 75 nmol/larva during the yolksac larval stage. Together, alanine, leucine, serine, isoleucine, lysine, and valine account for about 75% of the decrease. Ammonium accumulates gradually during the egg stage and is quickly excreted after hatching. The body protein content is maintained during the egg and yolksac larval stages. The measured oxygen uptake of the cod embryo during the egg and yolksac larval stages accounts for about 85% of the oxygen necessary to catabolize the FAA disappearing during this period. Ammonia excretion of the cod embryo, as taken from literature data, is similar to the expected ammonia production from catabolism of the FAA. Our data suggest that FAA are a major substrate for aerobic energy production in cod eggs and yolksac larvae. The implication of this finding for the production of a favourable first-feed for cod and other cultivated marine fish larvae, and for the selection of high quality eggs of marine fishes, is stressed.     

The ecological significance of lipid/fatty acid synthesis in developing eggs and newly hatched larvae of Pacific cod (Gadus macrocephalus)

The lipid/fatty acid composition of marine fish eggs and larvae is linked with buoyancy regulation, but our understanding of such processes is largely restricted to species with pelagic eggs. In this study, we examined developmental changes in the lipid/fatty acids of eggs and embryos of Pacific cod (Gadus macrocephalus), a species that spawns demersal eggs along coastal shelf edges, but as larvae must make a rapid transition to the upper reaches of the water column. Adult Pacific cod were collected in the Gulf of Alaska during the spawning season and eggs of two females were artificially fertilized with sperm from three males for each female. The eggs were subsequently reared in the laboratory to determine (1) how lipids/fatty acids were catabolized during egg and larval development, and (2) whether lipid/fatty acid catabolism had measurable effects on egg/embryo density. Eggs incubated at 4°C began hatching after 3-weeks and continued to hatch over a 10-day period, during which there was a distinct shift in lipid classes (phospholipids (PL), triacyglycerols (TAG), and sterols (ST)) and essential fatty acids (EFAs: 22:6n-3 (DHA), 20:5n-3 (EPA), and 20:4n-6 (AA)). In the egg stage, total lipid content steadily decreased during the first 60% of development, but just prior to hatch we observed an unexpected 2–3-fold lipid increase (~6–9 μg individual⁻¹) and a significant drop in egg density. The increase in lipids was largely driven by PL, with evidence of long-chained fatty acid synthesis. Late-hatching larvae had progressively decreasing lipid and fatty acid reserves, suggesting a shift from lipogenesis to lipid catabolism with continued larval development. Egg density measures suggest that lipid/fatty acid composition is linked to buoyancy regulation as larvae shift from a demersal to a pelagic existence following hatch. The biochemical pathway by which Pacific cod are apparently able to synthesize EFAs is unknown, therefore representing a remarkable finding meriting further investigation.     

Lipids and fatty acids as indicators of egg condition,larval feeding and maternal effects in Cape hakes (<Emphasis Type="Italic">Merluccius paradoxus</Emphasis> and <Emphasis Type="Italic">M. capensis</Emphasis>)

Cape hakes, Merluccius paradoxus and M. capensis, are important gadoid fish that are commercially harvested in the Benguela Current system off Namibia and South Africa. The aim of this study was to elucidate the nutritional condition and feeding preferences of their larvae. Hake eggs and larvae were sampled in austral spring of two consecutive years, 2007 and 2008, off the west coast of South Africa. They were identified to species using genetics, and total lipid content and fatty acid (FA) composition were analysed for each individual egg and larva to compare the condition of different early life stages of both hake species. Higher abundances of M. paradoxus eggs and larvae were consistently found compared to M. capensis. In both species, eggs contained wax esters (WE) and had significantly higher lipid content per dry mass than larvae. Lipid content as well as FA composition changed with the developmental stage of larvae. Quantities of essential fatty acid (EFA) increased with feeding of larvae due to dietary lipid incorporation. In 2007, yolk-sac larvae contained significantly lower total lipids than in 2008. It is argued that this was due to reduced lipid transfer by the spawning females to the eggs. These findings indicate that maternal effects are important in determining condition of hake larvae and that this may have an effect on their survival and subsequent recruitment.     

Yolk utilization in the gastropod Crepidula fornicata

The increases in constituents per unit weight of eggs during embryonic development of the gastropod Crepidula fornicata amounted to 14.6% for ash, 1.0% for protein, and 0.3% for non-protein nitrogen. During the same stages, fat content decreased from 33.7 to 20.3%, carbohydrate from 10.2 to 7.7% and energy content from 6209 to 5298 cal/g dry organic substance. The cumulative efficiencies for yolk utilization were 83.8% for dry weight, 61.0% for energy, 85.1% for protein, 50.7% for fat, and 63.6% for carbohydrate. A single egg contained 0.0269 cal, a single veliger 0.0164 cal. Of the 0.0105 cal expended on metabolic processes of the embryo, oxidation of fat contributed as much as 65.3%, while that of protein and carbohydrate amounted only to 18.8 and 6.3%, respectively. On the basis of ecophysiological considerations, a new classification of eggs is proposed.This paper is based on a lecture presented during the first Convention of the Indian Association of Biological Sciences in Madras, December, 1968.     

Lipid composition of eggs and adductor muscle in giant scallops (Placopecten magellanicus) from different habitats

Scallops (Placopecten magellanicus Gmelin) were collected during August 1989 from shallow water (10 m) and deep water (31 m) habitats at Sunnyside, Trinity Bay, Newfoundland, to compare the lipid composition of eggs and adductor muscle tissue. Less favorable food levels and lower temperature conditions associated with deeper water have previously been shown to produce slower growth and reduced fecundity in individuals from this habitat. Triacylglycerol reserves consistently accounted for 60% of the total lipids present in both groups. The total lipid content of the eggs and the composition of their triacylglycerol fatty acid pools were similar in shallow water and deep water scallops, indicating very little if any nutritional difference between the two groups. Relative to their counterparts from shallow water, individuals from deeper water contained higher proportions of docosahexaenoic acid [22:6(n-3)] in the egg phospholipids and higher levels of 24-methylenecholesterol (a phytosterol commonly found in diatoms) in the adductor muscle. Differences in fatty acid composition are interpreted as biochemical adjustments of cell membranes to increase membrane fluidity, thereby compensating for the lower temperatures prevailing at the greater depth.     

Egg protein insolubility inLymantria dispar versus other forest Lepidoptera

Summary A standard buffer (5 mM phosphate at pH 7) which is used to extract protein from insect eggs provided complete protein solubility for eggs from three of four tree-feeding lepidopteran species: obliquebanded leaf roller (Choristoneura rosaceana), forest tent caterpillar (Malacosoma disstria), and the eastern tent caterpillar (Malacosoma americanum). Under the same extraction protocol, egg proteins from the gypsy moth (Lymantria dispar), remained nearly insoluble. An array of methods typically used to solubilize insect egg proteins were tried and all but the most denaturing (2% SDS) were ineffective. Extraction buffers with typically high pH values were then evaluated. The results indicated that 1) solubility of gypsy moth egg proteins was pH dependent, and full solubility of most egg proteins required the extraction buffer to have a pH of 12 or more prior to the addition of eggs. We also determined that 2) the gypsy moth egg has a buffering capacity which must be surpassed for complete protein extraction, 3) low salt/high pH buffers gave slightly higher total protein values than did high salt/high pH buffers, 4) parental nutritional history (host species utilized) and egg developmental state (pre-embryonatedvs postembryonated/pre-hatch) were unrelated to the requirements for complete egg protein solubilization, and 5) the presence of soluble phenolics, compounds that have the potential to bind to protein and cause insolubility, was confirmed for the gypsy moth egg with 2-D paper chromatography and several other tests. Based on these results, we present a hypothesis about the cause of egg protein insolubility in the gypsy moth.     

Reproductive biology of the common shrimp Crangon crangon (Decapoda: Crangonidae) in the central Irish Sea

Aspects of the reproductive biology of the common shrimp Crangon crangon (L.) were studied in Port Erin Bay, Isle of Man, Irish Sea. Size at sexual maturity was determined from the proportions of ovigerous females and of females with maturing ovaries. The size at which 50% of females are mature is estimated (±95% confidence intervals) as 12.5±0.48 mm carapace length. Based on the proportions of ovigerous females and of mature females, the main breeding season was from January to June. Mean ovarian dry weights indicated two broods (winter and summer), with females bearing winter broods (WB) having higher gonad indices than those with summer broods (SB). WB females with non-eyed eggs and with eyed eggs differed in the regression of ovarian dry weight on carapace length, indicating preparation for laying a second brood. In both broods the moult stages of berried females were related to egg stage. Moulting will occur following the release of the brood. During embryonic development, mean egg length and egg volume were larger in all stages, and the mean dry weight of individual eggs of all stages heavier, in WB than in SB; there was no difference in egg number, however. Consequently, reproductive investment, the proportion of female weight devoted to egg production, was 67% higher in WB (0.20±0.04) than in SB (0.12±0.03). There is a significant effect of egg volume on brood weight, but not on egg number. In both broods, egg number was a negatively allometric function of female body size in non-eyed eggs and an isometric function of female body size in eyed eggs. Brood mortality during incubation was higher in SB (17%) than WB (10%). Differences in the reproductive variables and investment between the two broods of C. crangon are discussed in the light of reproductive strategies and life history.Communicated by J.P. Thorpe, Port Erin     

The influence of temperature on the development of Baltic Sea sprat (Sprattus sprattus) eggs and yolk sac larvae

In spring 2004 and 2005 we performed two sets of experiments with Baltic sprat (Sprattus sprattus balticus Schneider) eggs and larvae from the Bornholm Basin simulating ten different temperature scenarios. The goal of the present study was to analyse and parameterise temperature effects on the duration of developmental stages, on the timing of important ontogenetic transitions, growth during the yolk sac phase as well as on the survival success of eggs and early larval stages. Egg development and hatching showed exponential temperature dependence. No hatching was observed above 14.7°C and hatching success was significantly reduced below 3.4°C. Time to eye pigmentation, as a proxy for mouth gape opening, decreased with increasing temperatures from 17 days post hatch at 3.4°C to 7 days at 13°C whereas the larval yolk sac phase was shortened from 20 to 10 days at 3.8 and 10°C respectively. Maximum survival duration of non-fed larvae was 25 days at 6.8°C. Comparing the experimental results of Baltic sprat with existing information on sprat from the English Channel and North Sea differences were detected in egg development rate, thermal adaptation and in yolk sac depletion rate (YSDR). Sprat eggs from the English Channel showed significantly faster development and the potential to develop at temperatures higher than 14.7°C. North Sea sprat larvae were found to have a lower YSDR compared to larvae from the Baltic Sea. In light of the predictions for global warming, Baltic sprat stocks could experience improved conditions for egg development and survival.     

Costs of brood parasitism and the lack of defenses on the yellow-winged blackbird - shiny cowbird system

The shiny cowbird (Molothrus bonariensis) is a generalist brood parasite that lays either white-immaculate or spotted egg morphs in eastern Argentina and Uruguay. Some hosts accept both morphs, others accept spotted eggs and reject the white morph, but no host has been found to accept white eggs and reject spotted ones. It has been suggested that the yellow-winged blackbird (Agelaius thilius) may be that type of host. The finding of a white acceptor-spotted rejector species would help to explain the occurrence and maintenance of the parasite egg polymorphism. We studied the incidence of shiny cowbird parasitism on this host, its costs for their reproductive success and the presence of antiparasitic defenses in the yellow-winged blackbird - shiny cowbird system. The parasite affected the reproductive success of the host in two ways. Cowbirds punctured host eggs causing a reduction in clutch size, and yellow-winged blackbirds deserted their nests whenever they suffered high egg loss. In addition, parasitized nests suffered higher predation during the nestling stage, but not during egg stages, indicating that the difference found was related to the presence of the cowbird chick, and not to higher exposure of parasitized nests to both parasites␣and predators. Despite the costs imposed by the parasite, yellow-winged blackbirds have not evolved antiparasitic defenses. This host did not reject any egg morph of the shiny cowbird nor desert parasitized nests unless it had suffered high egg loss. Current explanations for the host lack of defenses, the “time lag” and the “equilibrium” hypothesis, are discussed. Received: 29 August 1997 / Accepted after revision: 10 January 1998     

Allocation of organic material and energy to the holdfast,stipe, and fronds inPostelsia palmaeformis (Phaeophyta: Laminariales) on the California coast

Postelsia palmaeformis were collected from the lower intertidal at Pigeon Point, California, USA, in May 1987, and the proximate composition and allocation of energy to the various body components were determined. The holdfast and stipe have a proximate composition (% dry weight) of ca. 40% ash, 5.3% protein, 1% lipid, 2% soluble carbohydrate, and 55% insoluble carbohydrate. The fronds have a proximate composition of ca. 25% ash, 6.5% protein, 2% lipid, 3% soluble carbohydrate, and 65% insoluble carbohydrate. The energetic level was ca. 12 kJ g^-1 dry wt and ca. 19 kJ g^-1 ash-free dry wt. The relative proportion of three plant components varied, comprising 26, 39, and 35% wet wt and 20, 42, and 38% kJ for the holdfast, stipe, and fronds, respectively. A plant with a basal stipe diameter of 33 mm contains 114 g wet wt and 266 kJ. The maximal density found in May 1987 was 826 plants, 49 301 g wet wt, and 106 157 kJ m^-2.P. palmaeformis differs in these characteristics from another intertidal pheophyte,Durvillaea antarctica, that is found in a high-energy intertidal zone.     

Changes in metabolic substrates during early development in anchoveta Engraulis ringens (Jenyns 1842) in the Humboldt Current

We assessed the ontogenetic changes in protein content and free amino acids (FAA) in eggs and early larvae of Engraulis ringens (anchoveta) off central Chile on different dates during the spawning season. On all sampling dates, a reduction in embryonic yolk-sac volume, proteins and FAA concentrations occurred during development. Protein electrophoresis (SDS–PAGE) of eggs and larvae showed at least 22 protein bands: 11 were consumed early and not detected after hatching. The proportion of essential FAA (EFAA) was higher than the proportion of non-essential FAA (NEFAA) in early eggs and in 7 day-old larvae (82.5-73% EFAA respectively). During egg development, the FAA pool was dominated by leucine, alanine and lysine, three amino acids contributing 35–44% of the total FAA in eggs. During larval development, histidine was the most abundant FAA. In July, total FAA constituted 13–18% of the egg dry weight. A similar proportion (45–51%) occurred in July between protein plus FAA and total lipids. The differences in egg size during the spawning season along with variability in batch composition suggests that the female spawning condition is a major factor determining egg quality and early offspring success.     

Factors influencing egg size in the gammarid amphipod Gammarus insensibilis

Developmental and seasonal changes in egg volume were examined in a population of the amphipod Gammarus insensibilis Stock occurring on the south coast of England, towards its northern limit of distribution. Results showed a marked increase in egg volume during development (2.9 times by Egg Stage V), resulting from water uptake and from the conversion of yolk reserves into structural elements. The maximum rate of increase coincides with the period of organ and limb development. At hatching, after initial rupture of the egg membrane by urosome spines, egg volume increases rapidly over a short period (15 to 20 min) by a further 30% (uptake rate 3.6×10^–5 mm³s^–1), followed by a post-hatching decrease in juvenile volume. Increase in size at hatching is the result of drinking by embryos, although changes in body-wall permeability may contribute. Females carrying eggs in an advanced stage of development exhibit egg-collecting behaviour. This is seen as an adaptation to an increased likelihood of egg loss with increase in volume of the brood as hatching approaches. Seasonal changes in Stage I (early) egg size are marked in this species, with winter eggs as much as 60% greater in volume than summer eggs. Egg size is inversely related to the temperature during oocyte development. A simple model has been derived to account for the observed seasonal pattern in egg size. The consequences of seasonal variation in egg and juvenile size are considered.     

Physiological and biochemical aspects of embryonic and larval development of the winter flounder Pseudopleuronectes americanus

Eggs and larvae of the winter flounder Pseudopleuronectes americanus Walbaum were hatched and raised in the laboratory under controlled conditions. Biochemical composition was measured during development and found to be similar to that of other species: 65 to 80 percent protein, 15 to 30 percent fat, and 0 to 5 percent carbohydrate. Ash content was 7 to 10 percent of dry weight. The chorion comprised more than half of the weight of an egg and the data suggested that it was possibly a source of nutrition to the developing embryo. The sequence of utilization appeared to be carbohydrate and then protein to hatching, lipid, mixed lipid and protein, the predominantly protein until feeding began. Carbohydrate was accumulated at first feeding and depleted when growth began. Protein and lipid were deposited in approximately constant proportions. Respiration rates of eggs were low, 0.002–0.015 l O₂ egg^-1 h^-1, but rose gradually from fertilization to hatching. Respiration rates of early larvae were from two to eight times that of eggs (0.033–0.131 l O₂ larva^-1 h^-1). Variation in larval respiration rates indicated a three-fold difference in rate according to level of activity. Eggs excreted ammonia at an increasing rate from fertilization to hatching. Larvae excreted ammonia, primary amines, and other unidentified organic nitrogenous substances. Rates of excretion and proportions of excretory products varied with stage of development. Primary amine excretion was variable and a major component in early stages. Ammonia-N excreted was two to 20 times primary amine N excreted. Unidentified substances were the predominant form of N excretion during early feeding. Ammonia accounted for most of the N excreted in older larvae. Early specific growth rates were 2.1 and 5.5%. Net caloric conversion and net and gross nitrogen efficiencies were low in first feeding larvae compared to adult fishes (32.2, 27.7, and 10.7% respectively).Contribution no. 5071 from the Woods Hole Oceanographic Institution