Sperm environment affects offspring quality in broadcast spawning marine invertebrates

The provisioning of offspring can have far-reaching consequences for later life in a wide range of organisms and generally this provisioning is thought to be under maternal influence or control. In experiments with a broadcast-spawning ascidian, we found that the size of offspring was determined by egg size and the abundance of sperm present during fertilization. Larger eggs were fertilized at low sperm concentrations, whilst smaller eggs were successfully fertilized at high sperm concentrations. These differences in fertilized egg size resulted in differences in the development rate, hatching success and mean size of the subsequent larvae. Our results suggest that, in contrast to females that reproduce by other mating systems, free-spawning mothers lack some control over the provisioning of offspring. Furthermore, because males can alter the sperm environment, they can exert paternal (non-genetic) control over key offspring characteristics.

Sources of variation in larval quality for free-spawning marine invertebrates: Egg size and the local sperm environment

There has been growing interest in the effects of variation in larval quality on the post-larval performance of adult marine invertebrates. Variation in egg/larval size is an obvious source of variation in larval quality but sources of variation have received little attention. For broadcast spawners, larval size may vary according to the local sperm environment but the generality of this result is unclear. Here, we show that, for a solitary ascidian, a polychaete and an echinoid, larval size is affected by the concentration of sperm present during fertilization. Larvae that are produced at high sperm concentrations are smaller than larvae that are produced from eggs exposed to low sperm concentrations. We also show that for three ascidians and an asteroid, egg size increases with maternal body size. These differences in larval size are likely to affect larval and subsequent adult performance in the field. Given that sperm concentrations in the field can fluctuate widely, it is likely that larval quality in free-spawning marine invertebrates will also vary widely.

The early sperm gets the good egg: mating order effects in free spawners

Mating order can have important consequences for the fertilization success of males whose ejaculates compete to fertilize a clutch of eggs. Despite an excellent body of literature on mating-order effects in many animals, they have rarely been considered in marine free-spawning invertebrates, where both sexes release gametes into the water column. In this study, we show that in such organisms, mating order can have profound repercussions for male reproductive success. Using in vitro fertilization for two species of sea urchin we found that the 'fertilization history' of a clutch of eggs strongly influenced the size distribution of unfertilized eggs, and consequently the likelihood that they will be fertilized. Males that had first access to a batch of eggs enjoyed elevated fertilization success because they had privileged access to the largest and therefore most readily fertilizable eggs within a clutch. By contrast, when a male's sperm were exposed to a batch of unfertilized eggs left over from a previous mating event, fertilization rates were reduced, owing to smaller eggs remaining in egg clutches previously exposed to sperm. Because of this size-dependent fertilization, the fertilization history of eggs also strongly influenced the size distribution of offspring, with first-spawning males producing larger, and therefore fitter, offspring. These findings suggest that when there is variation in egg size, mating order will influence not only the quantity but also the quality of offspring sired by competing males.

Anharmonic effects on a phonon-number measurement of a quantum-mesoscopic-mechanical oscillator

We generalize a proposal for detecting single-phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon-number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the read-out oscillator.

The benefits of polyandry in the free-spawning polychaete Galeolaria caespitosa

In many species, females are thought to benefit from polyandry due to the reduced risks of fertilization by genetically incompatible sperm. However, few studies that have reported such benefits have directly attributed variation in female reproductive success to the interacting effects of males and females at fertilization. In this paper, we determine whether male x female interactions influence fertilization in vitro in the free-spawning, sessile polychaete Galeolaria caespitosa. Furthermore, we determined whether polyandry results in direct fertilization benefits for females by experimentally manipulating the number of males contributing towards staged spawning events. To test for male x female interaction effects we performed an initial experiment that crossed seven males with six females (in all 42 combinations), enabling us to assess fertilization rates for each specific male-female pairing and attribute variation in fertilization success to males, females and their interaction. This initial experiment revealed a strong interaction between males and females at fertilization, confirming that certain male-female combinations were more compatible than others. A second experiment tested the hypothesis that polyandry enhances female reproductive success by exposing each female's eggs to either a single male's sperm (monandry) or the sperm from three males simultaneously (polyandry). We performed this second experiment at two ecologically relevant sperm concentrations. This latter experiment revealed a strong fertilization benefit of polyandry, independent of the effects of sperm concentration (which were also significant). We suggest that these direct fertilization gains arising from polyandry will constitute an important source of selection on females to mate multiply in nature.

Cell cycle model to describe animal cell size variation and lag between cell number and biomass dynamics

The use of cell numbers rather than mass to quantify the size of the biotic phase in animal cell cultures causes several problems. First, the cell size varies with growth conditions, thus yields expressed in terms of cell numbers cannot be used in the normal mass balance sense. Second, experience from microbial systems shows that cell number dynamics lag behind biomass dynamics. This work demonstrates that this lag phenomenon also occurs in animal cell culture. Both the lag phenomenon and the variation in cell size are explained using a simple model of the cell cycle. The basis for the model is that onset of DNA synthesis requires accumulation of G1 cyclins to a prescribed level. This requirement is translated into a requirement for a cell to reach a critical size before commencement of DNA synthesis. A slower gl-owing cell will spend more time in G1 before reaching the critical mass. In contrast, the period between onset of DNA synthesis and mitosis, tau(B), is fixed. The two parameters in the model, the critical size and tau(B), were determined from eight steady-state measurements of mean cell size in a continuous hybridoma culture. Using these parameters, it was possible to predict with reasonable accuracy the transient behavior in a separate shift-up culture, i.e., a culture where cells were transferred from a lean environment to a rich environment. The implications for analyzing experimental data for animal cell culture are discussed. (C) 1997 John Wiley & Sons, Inc.

Larval diet affects number of femoral 'brush' scales in male Helicoverpa punctigera moths (Lepidoptera : Noctuidae)

Males of Helicoverpa punctigera (Wallengren) show considerable variation in the number of femoral scales on the prothoracic legs. Such intraspecific variation in adult morphology could indicate the presence of undetected sibling species, or it may be related to larval diet. Helicoverpa putactigera is polyphagous, and different host plant species are likely to represent diets of different quality. Femoral lengths and the numbers of femoral scales on the prothoracic legs were therefore determined from: (i) individuals that had been collected as larvae from various host species in the field; and (ii) individuals that had been laboratory-reared, in split-family tests, on different diets, namely cotton, lucerne, sowthistle and artificial diet. Host plant species (and therefore presumably diet quality) influenced femoral length of H. punctigera males and, perhaps in conjunction with this, the number of femoral scales on the fore leg. The rearing experiment indicated, in addition, that the effect of host plant quality varies with larval stage, and that the pattern of this variation across the immature stages is dependent on host plant species. The recorded variation in the morphology of field-collected H. punctigera males is therefore most readily explained as a consequence of different individuals developing (at least for most of their larval life) on different host plant species, with diet quality varying significantly with species. The relevance of these results for insect developmental studies and evolutionary interpretations of host relationships is outlined.

Wolbachia-mediated sperm modification is dependent on the host genotype in Drosophila

Estimates of Wolbachia density in the eggs, testes and whole flies of drosophilid hosts have been unable to predict the lack of cytoplasmic incompatibility (CI) expression in so-called mod(-) variants. Consequently, the working hypothesis has been that CI expression, although related to Wolbachia density, is also governed by unknown factors that are influenced by both host and bacterial genomes. Here, we compare the behaviour of the mod(-) over-replicating Wolbachia popcorn strain in its native Drosophila melanogaster host to the same strain transinfected into a novel host, namely Drosophila simulans. We report that (i) the popcorn strain is a close relative of other D. melanogaster infections, (ii) the mod(-) status of popcorn in D. melanogaster appears to result from its inability to colonize sperm bundles, (iii) popcorn is present in the bundles in D. simulans and induces strong CI expression, which demonstrates that the bacterial strain does not lack the genetic machinery for inducing CI and that there is host-species-specific control over Wolbachia tissue tropism, and (iv) infection of sperm bundles by the mod(-) D. simulans wCof strain indicates that there are several independent routes by which a strain can be a CI non-expressor.

Ecology, shell morphology, anatomy and sperm ultrastructure of the caenogastropod Pyrgula annulata, with a discussion of the relationship between the 'Pyrgulidae' and Caspian and Baikalian rissooideans

The composition of the Pyrgulidae and its relationships to other member families of the caenogastropod superfamily Rissooidea are examined after a consideration of new anatomical (including gross anatomy, sperm ultrastructure), conchological (including protoconch features), ecological, biogeographical and palaeontological data and a re-evaluation of existing literature. Pyrgulidae can be distinguished from hydrobiids unequivocally only with the aid of the radula. Sperm ultrastructural features suggest a very close relationship between the Pyrgulidae, the Hydrobiidae and the Bithyniidae (in fact no family-diagnostic sperm characters can be found to separate these three taxa). Based upon neontological and fossil evidence it is likely that pyrgulids represent a Miocene offshoot from a paratethyal hydrobiid lineage. Pyrgulids may also represent the stock from which the baicaliids arose, in which case the Pyrgulidae must be considered a paraphyletic group. The huge biogeographic gap between the Caspian Sea and Lake Baikal is to some extent bridged by the finding of a Neogene pyrgulid from the Altai Mountains. An alternative scenario for the origin of baicaliids is presented.

The number of long-lasting functional memory CD8(+) T cells generated depends on the nature of the initial nonspecific stimulation

The mechanism of generation of memory cytotoxic T cells (CTL) following immunization remains controversial. Using tumor protection and IFN-gamma ELISPOT assays in mice to detect functional CTL, we show that the initial effector CTL burst size after immunization is not directly related to the amount of functional memory CTL formed, suggesting that memory CTL are unlikely to arise stochastically from effector CTL. Induction of MHC class II-restricted T helper cells at the time of immunization by inclusion of a T helper peptide or protein in the immunogen, is necessary to generate memory CTL, although no T helper cell induction is required to generate effector CTL to a strong MHC class I-binding peptide. Host protective T cell memory correlates with the number of CTL epitope responsive IFN-gamma-secreting memory T cells as measured in an ELISPOT assay at the time of tumor challenge. We conclude that a different antigen presenting environment is required to induce long-lasting functional memory CTL, and non-cognate stimulation of the immune system is essential to allow generation of a long-lasting host protective memory CTL response.