Maternal energy investment in eggs and jelly coats surrounding eggs of the echinoid Arbacia punctulata

In free-spawning marine invertebrates, the amount of maternal energy that is invested in each egg has profound implications for all life-history stages of the offspring. The eggs of echinoids are freely spawned into the water and are surrounded by several structurally complex extracellular layers. These extracellular layers, or jelly coats, do not contribute energy to embryonic development but must impose an energy cost on the production of each egg. The investment of maternal energy reserves in the jelly coats of echinoid eggs may have important implications for the number of eggs that can be produced (i.e., fecundity) and the amount of energy that can be invested in each egg. We estimated the degree to which maternal energy is invested in the jelly coats surrounding eggs of the echinoid Arbacia punctulata. Estimates were derived from measurements of the amount of energy contained in the combined eggs and jelly coats, and in the eggs alone. The amount of energy contained in A. punctulata eggs ranged from 2.70 to 5.53 x 10(-4) J egg(-1). The amount of energy contained in the jelly coats ranged from 0.13 to 0.48 x 10(-4) J jelly coat(-1). The mean concentration of energy in the eggs was 2.15 mm(-3) and 0.29 J mm(-3) in the jelly coats. These results indicate that between 3% and 11% (mean = 7%) of the total energy invested in each A. punctulata egg is partitioned to the jelly coat alone. A significant positive relationship was found between the volumes of the jelly coats and the amount of energy they contained. Based on this relationship and an analysis of differences in the size of jelly coats between echinoid species, we suggest that the degree to which energy is invested in jelly coats may vary among echinoid species and is therefore likely to be an important life-history characteristic of these organisms.     

Life-history consequences of vegetative damage in scarlet gilia, a monocarpic plant

Although herbivory can occur throughout a plant's life, little is known about relative fitness impacts of damage at different life stages. In the long-lived monocarpic wildflower, Ipomopsis aggregata (scarlet gilia), for example, the response to browsing by ungulates in the year of flowering has been studied extensively, whereas damage and its fitness consequences during the preceding years of vegetative growth remain largely unexplored. As part of a long-term demographic study of I. aggregata , we mapped 5324 individual seedlings belonging to two annual cohorts in three natural populations, and followed these plants throughout their lives. Of the 30.4% of plants that survived past seedling stage, 15.3% suffered observable damage to the apical meristem of their single rosette of leaves, usually resulting in multiple rosettes in vegetative plants and multiple flowering stalks in plants that survived to flower. Vegetative damage reduced survival to flowering by ca 30%, and slowed growth, leading to an average delay in flowering of over one yr relative to undamaged plants. On average, damaged plants were 136% larger than undamaged members of their cohort in the summer before flowering, but produced only 86% as many flowers, and achieved 78% the overall fitness compared to undamaged plants when damage effects were integrated across their life history. Previously published studies from the same sites suggested that plants suffering browsing during only the year of flowering, achieved 47% of the fitness of unbrowsed plants. Our results indicate that plants are better able to recover from vegetative damage than from loss of their initial reproductive effort, perhaps because of the longer time over which recovery is possible in the former case. These results underscore the importance of studying the consequences of damage across the entire life history.     

Life-history constraints on the success of the many small eggs reproductive strategy

The reproductive strategy of most fishes is to produce a large number of tiny eggs, leading to a huge difference between egg size and asymptotic body size. The viability of this strategy is examined by calculating the life-time reproductive success R₀ as a function of the asymptotic body size. A simple criterion for the optimality of producing small eggs is found, depending on the rate of predation relative to the specific rate of consumption. Secondly it is shown that the success of the reproductive strategy is increasing with asymptotic body size. Finally the existence of both upper and lower limits on the allowed asymptotic sizes is demonstrated. A metabolic upper limit to asymptotic body size for all higher animals is derived.     

Life-history consequences of bidirectional selection for male morph in a male-dimorphic bulb mite

Intralocus sexual conflict (IASC) arises when males and females have different trait optima. Some males pursue different alternative reproductive tactics (ARTs) with different trait optima, resulting in different strengths of IASC. Consequently, for instance daughter fitness is differentially affected by her sire’s morph. We tested if—and which—other life-history traits correlatively change in bidirectional, artificial selection experiments for ARTs. We used the male-dimorphic bulb mite Rhizoglyphus robini, the males of which are high-fitness ‘fighters’ or low-fitness ‘scramblers’. Twice in each of the five generations of selection, we assessed clutch composition (number of mites of the various life stages present) and size (total number of offspring). Furthermore, we tracked offspring from egg to adulthood in the first and final generation to detect differences between selection lines in the size and duration of stages, and in maturation time. We found that selection for male morph increased the frequency of that morph. Furthermore, compared to fighter lines, scrambler lines produced more females, which laid larger eggs (in the final generations), and maintained a higher egg-laying rate for longer. Otherwise, our results showed no consistent differences between the selection lines in clutch size and composition, life stage size or duration, or maturation time. Though we found few correlated life-history trait changes in response to selection on male morph, the differences in egg laying rate and egg size suggest that IASC between fighters is costlier to females than IASC with scramblers. We hypothesize that these differences in reproductive traits allow fighter-offspring to perform better in small, declining populations but scrambler-offspring to perform better in large, growing populations.     

Life-history variation related to the first adult instar in daphnids derived from diapausing and subitaneous eggs

Vibrio cholerae is the causative agent of the severe dehydrating diarrheal disease cholera. This bacterium has been detected in many estuaries around the world and the United States. In this study we examine the abundance and distribution of V. cholerae in recreational beach waters and tributaries of Southern California. Water samples were taken from 11 beach locations adjacent to freshwater runoff sources between February 8th and March 1st, 1999. Water samples were also taken from rivers, creeks and coastal wetlands along the Southern California coast between May 19th and June 28th, 1999. In addition to the detection of V. cholerae, environmental parameters including temperature, salinity, coliphage counts, viable heterotrophic plate counts and total bacterial direct counts were also determined to understand the relationships between the presence of V. cholerae and environmental conditions. A direct colony hybridization method using an oligonucleotide probe specific for the 16S–23S intergenic spacer region of V. cholerae, detected V. cholerae in 3 of the 11 beach samples with the highest concentration (60.9 per liter) at the mouth of Malibu Lagoon. V. cholerae and coliphage were not correlated for beach samples, indicating that the presence of V. cholerae is independent of sewage pollution. V. cholerae were detected in all samples taken from rivers, creeks and wetlands of coastal Southern California where salinities were between 1 to 34 parts per thousand (ppt), but was not found at a freshwater sampling site in upper San Juan Creek. The highest density of V. cholerae was found in San Diego Creek with a concentration of 4.25×10⁵ CFU/L. The geographical distribution of V. cholerae was inversely correlated with salinity. High concentrations of V. cholerae were more frequently detected in waters with lower (but above 0) salinity. The results of this study provide insight into the ecology of this aquatic species and are potentially important to the understanding of the epidemiology of cholera on a global scale.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Golgi complex beads in vertebrates and their relationship with clathrin coats

Addition of tannic acid to the primary glutaraldehyde fixative and the viewing of thin sections by stereo electron microscopy greatly simplifies the detection of vertebrate cell Golgi complex beads which are otherwise difficult to see since they do not stain with bismuth. These results confirm the generality of conclusions from experiments on arthropod beads which are easily observed because of their bismuth affinity. In vertebrate and arthropod cells, bead rings encircle the base of forming transition vesicles below the growing portion of the vesicle that is covered with a clathrin coat. Their unique position at such a sharp functional and structural boundary in intercompartmental transport suggests that the bead rings may specify a select region of rough endoplasmic reticulum devoid of ribosomes where clathrin coats can induce transition vesicle formation and prevent intermixing of the elements of a returning transition vesicle.     

Binding of IGF-I to preimplantation rabbit embryos and their coats

It is known that insulin-like growth-factor I (IGF-I) promotes early embryonic development from the morula to the blastocyst stage in rabbits (28). Therefore we used autoradiography to investigate whether IGF-I binds to preimplantation embryos and its coats. From Day 3 after mating onwards, a clear binding of IGF-I to the embryos was observed. There was no difference in binding to the embryoblast or trophoblast cells. Using ligand blot, several IGF-binding proteins (IGFBP; 31 kDa, 33 kDa, 36 kDa, three overlapping bands at 40 to 55 kDa) were obvious in the embryoblast and trophoblast. A 120 to 130 kDa protein was observed exclusively in the embryoblast. Significant binding of (125)I IGF-I to the coats of embryos older than 3 d was detected, and IGF-I was bound via a 38 kDa protein, as detected by ligand blot. To investigate the origin of this protein, the patterns of IGFBP were determined in the oviductal and uterine fluids of pregnant animals (Days 0 to 6). The following binding proteins were observed regularly in the oviductal and uterine flushings: 28 kDa, 32 kDa and 3 overlapping bands in the area of 40 to 55 kDa. In the oviduct the main IGF binding protein was the 32 kDa band (38.7% to 45.9%), while in the uterus it was the 3 overlapping bands at 40 to 55 kDa (42.5% to 24.1%). Because IGF-I is produced in the oviduct and uterus (27), IGFBPs are found in oviductal and uterine fluids, IGF-I is stored in the coats, IGF-I binds to preimplantation embryos and IGF-I promotes early embryonic development (28), the IGF system seams to have a function in the maternal-embryonic interaction.     

Changes in maternal investment in eggs can affect population dynamics

The way that mothers provision their offspring can have important consequences for their offspring's performance throughout life. Models suggest that maternally induced variation in life histories may have large population dynamical effects, even perhaps driving cycles such as those seen in forest Lepidoptera. The evidence for large maternal influences on population dynamics is unconvincing, principally because of the difficulty of conducting experiments at both the individual and population level. In the soil mite, Sancassania berlesei, we show that there is a trade-off between a female's fecundity and the per-egg provisioning of protein. The mother's position on this trade-off depends on her current food availability and her age. Populations initiated with 250 eggs of different mean sizes showed significant differences in the population dynamics, converging only after three generations. Differences in the growth, maturation and fecundity of the initial cohort caused differences in the competitive environment for the next generation, which, in turn, created differences in their growth and reproduction. Maternal effects in one generation can therefore lead to population dynamical consequences over many generations. Where animals live in environments that are temporally variable, we conjecture that maternal effects could result in long-term dynamical effects.     

Saprolegniosis in salmonids and their eggs in Japan

An epizootic of the fungal infection saprolegniosis that occurred in freshwater-cultured salmons and their eggs at some hatcheries in Hokkaido (Japan) was investigated. In almost all cases, the initial clinical sign was characterized by the growth of cotton-like mycelia on the fishs' body surface, especially the head, adipose fin, and caudal fin, but the mycelia were not visible to the naked eye in the internal organs. Thirty-three strains isolated from lesions were classified in the genus Saprolegnia according to their morphological and biological characteristics on hemp seed cultures at various temperatures. Fifteen of the strains were identified as Saprolegnia parasitica, 16 were identified as S. salmonis, and two were identified as S. australis.     

Life-history consequences of predation for a subantarctic beetle: evaluating the contribution of direct and indirect effects

1. Recently, a small predatory beetle, Trechisibus antarcticus (Carabidae), was accidentally introduced onto the island of South Georgia, sub-Antarctic.
2. From the presumed site of introduction the beetle is invading the coastal lowland area, building up high densities locally in the tussock-forming grass Parodiochloa flabellata .
3. In the coastal area the endemic detritivorous/herbivorous beetle Hydromedion sparsutum (Perimylopidae) is common, especially in and beneath the tussocks.
4. The first three, out of six, larval instars of H. sparsutum are easily taken prey by the carabid.
5. In sites colonized by the carabid, total abundance and the ratio between larval and adult numbers of H. sparsutum are far lower, and its adult body size clearly larger, than in comparable sites where the carabid is absent.
6. Two hypotheses are proposed for explaining the increase in adult body size of H. sparsutum : (i) the increase is a direct effect of predation: selection by the predator favours large hatchlings and/or larvae with a high growth rate; and (ii) the increase is an indirect effect of predation: by lowering the density of H. sparsutum , predation has increased its per capita food supply, enabling a higher growth rate and a larger adult body size.
7. A food addition experiment in a carabid-free site showed availability of high quality food to be insufficient for sustaining the initial larval population.
8. In the laboratory, females from the predator-infested sites produced larger eggs and hatchlings than females from the carabid-free sites, but mass specific growth rates of the larvae were not higher.
9. Field and laboratory data give stronger support to the food hypothesis than to the size selectivity hypothesis.     

Ultrastructure of opossum oocyte investing coats and their sensitivity to trypsin and hyaluronidase

Ovulated opossum oocytes are surrounded by a zona pellucida, but not by cumulus cells. Opossum sperm carry at least four acrosomal hydrolases (hyaluronidase, acrosin, N-acetylhexosaminidase, and arylsulfatase); the functions of these enzymes in opossum fertilization are uncertain. To identify possible substrates for these hydrolases, the ultrastructure of opossum oocytes was examined after fixation in the presence of ruthenium red which stabilizes extracellular matrices. This oocyte is unusual in having a wide perivitelline space containing a highly structured extracellular matrix (ECM). The ECM is comprised of granules and filaments, and it resembles matrices known to contain hyaluronic acid in other systems. Hydrolases, known to be present in opossum acrosomes, were tested for their effect on the ultrastructure of the zona pellucida and matrix of the perivitelline space. Trypsin dissolved the zona pellucida and decreased the size of the granules in the perivitelline space. Streptomyces hyaluronidase, which specifically attacks hyaluronic acid, removed only matrix filaments. Arylsulfatase, N-acetylhexosaminidase, and beta-glucuronidase did not affect the zona pellucida or ECM in our assay. These observations are consistent with the ideas that (1) opossum sperm must penetrate two oocyte investments, the zona pellucida and ECM of the perivitelline space; (2) the ECM contains hyaluronic acid (filaments) and protein (granules); (3) opossum sperm acrosin may function in penetration of the zona pellucida and ECM; and (4) opossum sperm hyaluronidase may function in penetration of the ECM by degrading hyaluronic acid (filaments). Dissolution of the granules and filaments from oocyte microvilli is probably necessary to permit close apposition and fusion of the sperm and oocyte membranes. The evolutionary significance of these results is discussed.     

Extracellular coats on the surface of Strongylocentrotus purpuratus eggs: stereo electron microscopy of quick-frozen and deep-etched specimens

Summary Sea urchin (Strongylocentrotus purpuratus) eggs were fixed, quick-frozen, deep-etched, and rotary-replicated, and the three-dimensional structure of the external surface of the egg visualized using stereo electron microscopy. The cell surface is coated with three layers of filaments: the sheetlike vitelline layer adhering closely to the plasma membrane, a second layer of oblique fibrils extending from microvillar tips to the vitelline layer below, and a third, outermost layer of horizontal filaments coursing in bundles over the microvillar tips. After fertilization, the newly elevated vitelline envelope is transformed into a three-layered structure, the central layer being a tightly knit network of fine filaments decorated on each side with a loose network of thicker fibrils. Subsequently, the envelope becomes coated with paracrystalline protein released from the cortical granules, and microvillar casts are reshaped into angular, jagged peaks having two to five sides. The final structure of the fertilization envelope consists of a thick central layer of compact fibrillar material that is coated on each side with thin plates of paracrystalline protein.     

Lethal toxin actions and their consequences

After entry of infectious anthrax spores into the body, host-specific signals induce spore germination, outgrowth of vegetative bacilli and the expression of lethal toxin and other virulence factors. Anthrax lethal toxin (LeTx) is a virulence factor responsible for the major pathologies seen during systemic anthrax infections. Injection of sterile LeTx into test animals mimics the shock and sudden death seen during active bacterial infections. Once large levels of LeTx are produced within the body, destruction of bacteria by administration of antibiotics is usually unsuccessful. The LeTx is believed to be secreted into the bloodstream where it circulates freely throughout the body and binds and enters host cells. Once in the cytoplasm, the lethal factor acts as a zinc-metalloprotease disrupting normal homoeostatic functions. Macrophages are a uniquely sensitive cell type that seem to be vital global mediators of toxin-induced pathologies. Removal of macrophages from mice renders them insensitive to LeTx challenge. Low levels of lethal toxin induce macrophage production, in vitro, of the shock-inducing cytokines TNF and Il-1beta. Higher levels of LeTx cause over-production of reactive oxygen intermediates, bursting of macrophages and release of mediators of shock. We believe that agents capable of blocking key steps of the lethal toxin cascade may prove useful in combating anthrax pathologies.     

Resting eggs of conchostracans and their adaptive possibilities

The dimensional specifications and morphology of the resting eggs of ten conchostracan species (Cyzicus tetracerus, Eocyzicus orientalis, Caenestheria davidi, C. perrieri, Leptestheria dahalacensis, Eoleptestheria ticinensis, Limnadia lenticularis, Imnadia yeyetta, Lynceus brachyurus, and L. dauricus) have been studied. The data are presented on the number of eggs produced by females. Unlike other crustaceans, no correlation between the eggs size and their quantity was found. Although the number of eggs can vary one to two times, their size is relatively stable (variation coefficient <5%). The wet (1.5–5.4 μg) and dry (0.41–0.93 μg) weights of eggs and the share of clutch (11.4–21.6%) in the female’s wet weight were determined for eight species. The polyfunctionality of the external envelope of the egg was considered under anhydrobiosis conditions.