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 egg size in Drosophila melanogaster

We used a novel approach to study the effects of egg size on offspring fitness components in Drosophila melanogaster. Populations that differed genetically in egg size were crossed, and the female offspring from these reciprocal crosses were examined for life-history traits. These flies expressed effects of egg size, because they developed from eggs of different sizes as a result of maternal genetic effects, but displayed an equivalent range of nuclear genetic variation. The crosses used four independent pairs of outbred populations that differed in the pattern of covariation between egg size and life-history traits, so that the maternal genetic effects of egg size on offspring characters could be contrasted to the associations present among the parental populations. Egg size showed positive maternal genetic effects on embryonic viability and development rate, hatchling weight and feeding rate, and egg-larva and egg-adult development rate but no consistent effects on larval competitive ability, adult weight, or egg size in the offspring. Our method revealed a pattern of causality that could not be deduced from interpopulation comparisons and therefore provides a good way of disentangling the causes and consequences of variation in egg size while controlling for zygotic genetic effects.     

Life-history strategies in salmonids: the role of physiology and its consequences

Salmonids are some of the most widely studied species of fish worldwide. They span freshwater rivers and lakes to fjords and oceans; they include short- and long-distance anadromous migrants, as well as partially migratory and non-migratory populations; and exhibit both semelparous and iteroparous reproduction. Salmonid life-history strategies represent some of the most diverse on the planet. For this reason, salmonids provide an especially interesting model to study the drivers of these different life-history pathways. Over the past few decades, numerous studies and reviews have been published, although most have focused on ultimate considerations where expected reproductive success of different developmental or life-history strategies are compared. Those that considered proximate causes generally focused on genetics or the environment, with less consideration of physiology. Our objective was therefore to review the existing literature on the role of physiology as a proximate driver for life-history strategies in salmonids. This link is necessary to explore since physiology is at the core of biological processes influencing energy acquisition and allocation. Energy acquisition and allocation processes, in turn, can affect life histories. We find that life-history strategies are driven by a range of physiological processes, ranging from metabolism and nutritional status to endocrinology. Our review revealed that the role of these physiological processes can vary across species and individuals depending on the life-history decision(s) to be made. In addition, while findings sometimes vary by species, results appear to be consistent in species with similar life cycles. We conclude that despite much work having been conducted on the topic, the study of physiology and its role in determining life-history strategies in salmonids remains somewhat unexplored, particularly for char and trout (excluding brown trout) species. Understanding these mechanistic links is necessary if we are to understand adequately how changing environments will impact salmonid populations.     

Life-history consequences of resource allocation of two bdelloid rotifer species

Two bdelloid species,Macrotrachela quadricornifera (aquatic species) andPhilodina vorax (terrestrial moss species), with similar survival but different age-specific fecundity schedules, were analyzed daily to determine growth rates and the volume invested in reproduction. The two species had similar growth patterns and started reproduction while still growing. In both, the size at maturity was independent of age.M. quadricornifera resumed growth after reaching a size plateau when reproduction was over, whileP. vorax continued to reproduce until death. Although the net reproductive rate ofP. vorax was consistently lower than that ofM. quadricornifera, the same percent of adult volume was invested in reproduction over its life time because its eggs were relatively bigger. The difference in reproductive rates is probably related to different partitioning of equal amounts of relative biomass: more small eggs for the aquatic rotifer vs. fewer big eggs for the terrestrial rotifer. Egg size might be related to the selective pressures of the environments.     

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.     

Location of the 100 kd-50 kd accessory proteins in clathrin coats.

We present a three-dimensional map of the clathrin coat of coated vesicles, generated from tilt series of electron micrographs of unstained specimens embedded in vitreous ice. We have examined native placental coated vesicles and coats reassembled from their purified constituents, namely clathrin triskelions and accessory proteins of approximate mol. wts 100 kd and 50 kd. Our results show that the accessory proteins contribute a further shell of density within the double shell of the clathrin cage, extending from the terminal domains of the clathrin to the membrane of the vesicle. The thickness of the complete coat is approximately 22 nm.     

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.     

Fertilization in the sea: are the hazards of broadcast spawning avoided when free-spawned sperm fertilize retained eggs?

In broadcast-spawning marine animals, rapid dilution and short lifespan of sperm following release may impose severely localized patterns of mating. Partial or total failure of external fertilization due to sperm limitation appears commonplace. However, it is not clear to what extent the restrictive kinetics of fertilization in water also constrain mating in animals that release sperm but retain their eggs for fertilization.<BR>The compound ascidian Diplosoma listerianum liberates sperm that are dispersed to other colonies and taken in prior to internal cross-fertilization. The fertile lifespan of sperm was found to be long (half-life ca. 8 hours), and a substantial number of fertilizations occurred with 24-hour-old sperm. Fertilizations were obtained from sperm concentrations that would typically produce little or no external fertilization. In a separate experiment, a very small piece of D. listerianum (dry weight less than 2 mg) sired abundant progeny throughout a 3840 l tank. Paternity of progeny in these experiments was confirmed by molecular markers. The same markers were used to extend, to over seven weeks, the known maximum period of storage of exogenous sperm prior to fertilization in this species.<BR>The production of only a few thousand sperm at a time by each zooid, poor synchronization of release between zooids, and the existence of many well-spaced exhalant openings in large colonies suggest that D. listerianum is incapable of generating a dense plume of sperm, even close to the source. It is suggested that, unlike external fertilization, successful internal cross-fertilization in D. listerianum is not dependent upon the interception of a dense cloud of gametes just released by a near neighbour. It seems instead that dilute, long-lived sperm can be extracted efficiently from seawater by this suspension feeder, potentially over a period of time. This capability, and other features of the life history, make it unlikely that sperm limitation is an acute problem in this species and comparable taxa, a conclusion with potential significance for expected patterns of mating, sex allocation and gamete attributes in sessile aquatic invertebrates. Variance in reproductive success between individuals due to differences in fertilization rate may be much lower than in broadcast spawners exhibiting external fertilization.     

Age-related location of manifest accessory pathway and clinical consequences

Background

Accessory pathway (AP) ablation is not always easy. Our purpose was to assess the age-related prevalence of AP location, electrophysiological and prognostic data according to this location.

Methods

Electrophysiologic study (EPS) was performed in 994 patients for a pre-excitation syndrome. AP location was determined on a 12 lead ECG during atrial pacing at maximal preexcitation and confirmed at intracardiac EPS in 494 patients.

Results

AP location was classified as anteroseptal (AS)(96), right lateral (RL)(54), posteroseptal (PS)(459), left lateral (LL)(363), nodoventricular (NV)(22).Patients with ASAP or RLAP were younger than patients with another AP location. Poorly-tolerated arrhythmias were more frequent in patients with LLAP than in other patients (0.009 for ASAP, 0.0037 for RLAP, <0.0001 for PSAP).Maximal rate conducted over AP was significantly slower in patients with ASAP and RLAP than in other patients. Malignant forms at EPS were more frequent in patients with LLAP than in patients with ASAP (0.002) or PSAP (0.001).Similar data were noted when AP location was confirmed at intracardiac EPS. Among untreated patients, poorly-tolerated arrhythmia occurred in patients with LLAP (3) or PSAP (6). Failures of ablation were more frequent for AS or RL AP than for LL or PS AP.

Conclusions

AS and RLAP location in pre-excitation syndrome was more frequent in young patients. Maximal rate conducted over AP was lower than in other locations. Absence of poorly-tolerated arrhythmias during follow-up and higher risk of ablation failure should be taken into account for indications of AP ablation in children with few symptoms.     

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.     

Spike sequences and their consequences

Spatio-temporal patterns of spikes have an advantage of representing information by their spike composition similar to words of languages. First we review the models of neuronal coding, then we discuss technical aspects of detecting spatio-temporal spike patterns. We argue by presenting data from rat hippocampus that spike trains recorded simultaneously from multiple pyramidal cells are not independent. Their hidden dependency structure can be revealed by spike 'sequences', defined as a set of neurons which fire in a specific temporal order with certain delay between successive spikes. The only way to prove their existence in vivo is to show that they recur with higher than by-chance frequency. We observed that 'sequences' possess 'compositional' features and that a given spike composition is time scale invariant. We illustrate that the same neuron can be a part of different 'sequences' and 'sequences' recur in a temporally compressed fashion during slow wave sleep. The statistical significance of 'sequences' is testable. Their biological significance has been implicated by experiments where recurrence rate of the sequences during different behavioral sessions were compared. As consistent with the 'replay hypothesis' of memory consolidation, new sequences generated during the wake state are persistent during the subsequent sleep. Thus, information acquired during the wake state and represented by spatio-temporal patterns of spikes may transfer to the neocortex during sleep. Our results suggest that 'sequences' reflect the activation of specific but configurable circuitries during exploratory behavior, followed by spontaneous re-activation of the same circuitry during sleep. Whether the delay structure of spikes as a combination is an effective input to single neurons downstream or 'sequence' components are being processed in parallel pathways and evaluated independently is an open question.     

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.