摘要:

Studies on insect reproduction in The Netherlands concern long-term projects on (a) the relationship between diapause and reproduction, (b) endocrinology and reproduction, (c) the relationship between food and reproduction, and more recently on (d) the background and evolution of parthenogenetic reproduction, (e) the link between reproduction and blood and sugar feeding in mosquitoes, and (f) the role of male sex-peptides in reproduction and mate protection. Examples of this work are presented and the importance of these fundamental studies to applied work will be discussed. At universities, curiosity-driven pure research on reproduction should have the first priority and this type of research will almost always result in applications, as we have experienced in insect pest management. Modern agriculture leads to serious environmental problems, human health problems and a dramatic reduction in biodiversity, as a result of intensive fertilizer use and frequent application of chemical pesticides. Pure scientific research in insect reproduction is enabling us to find unexpected solutions for crop protection problems in current agriculture; for example, we have helped to develop (a) programs with greatly reduced applications of conventional chemicals based on our diapause work, (b) selective chemical control with insect growth regulators based on endocrinological studies, and (c) more economic biological control programs based on diapause and parthenogenesis studies.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652672

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Metals accumulated within the tissues of earthworms are not homogeneously distributed. Rather, they are sequestered predominantly within the posterior alimentary fraction. The clear organotropism of non-essential metals is reinforced by the subcellular compartmentation of metals according to their known ligand-binding affinities: in earthworm chloragocytes and intestinal epithelial cells,in situX-ray mapping in high-pressure frozen thin cryosections revealed that Pb, Zn, Ca and P were co-distributed in a discrete subcellular compartment, whilst Cd and S were co-distributed in another. Tissue homogenization and fractionation confirmed these differences. Cd is sequestered by cysteine-rich metallothionein isoforms; one isoform may be a true Cd-detoxification protein because it bears two putative glycosylation sites, and may thus deliver Cd to the lysosomal system for cytological isolation. Metal accumulation imposes metabolic costs that can reduce somatic growth and/or reproduction in earthworms: the sequestered bioinactive metal fraction “diverts” energy into enhanced metallothionein synthesis and associated processes; the bioavailable metal fraction(s) may cause direct toxicological damage by competitive inhibition of metalloenzymes and metal-dependent transcription factors, and indirect damage if repair and compensatory stress responses are invoked. Molecular responses to metal-exposure stress are, in principle, linked to whole organism life-cycle parameters which, in turn, are ecologically relevant.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652673

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Key factors governing polar ocean ecosystems are low temperatures and a pronounced seasonal variability of ice cover, light regime and primary production. Depending on their ecological niche and trophic position, zooplankton species at high latitudes have developed a variety of reproductive strategies and energetic adaptations to cope with these extreme environmental conditions. Life-cycle strategies of the herbivorous copepods and euphausiids, which make up the major portion of polar zooplankton biomass, include seasonal vertical migration, dormancy (diapause, quiescence) and the accumulation of energy reserves. These lipid stores help to buffer the pulsed seasonal food supply, and they play an important role in fueling reproduction independent of phytoplankton. Only a smaller fraction of the lipid reserves accumulated during spring and summer are usually catabolized for metabolic maintenance during the food-limited dark season. These deposits are retained until the end of winter and allow early egg production and spawning prior to—or coinciding with—the onset of vernal primary production. It enables the new generation to make full use of the short productive season for growth and development to reach viable overwintering stages. The Antarctic krillEuphausia superbais an exception since it uses its depot lipids for metabolic maintenance during the dark season. It therefore relies on external resources (Primary production) for reproductive processes, resulting in a later spawning period as compared to the other euphausiids. Another important component of the herbivorous Antarctic zooplankton, the salps, have developed a very different reproductive strategy. They are able to switch from sexual reproduction to asexual budding (metagenesis), which allows extreme multiplication rates under favourable feeding conditions. Due to these successful adaptations, herbivores are able to build up huge stocks, in spite of the short productive period. Omnivorous and carnivorous zooplankton species, e.g., amphipods or chaetognaths, are not much constrained by the seasonality problem, but experience a more constant food supply. They show a tendency towards K strategies with a prolonged reproductive period, reduced egg numbers and increasing parental care. However, they do not exhibit such typical “polar adaptations” as developed by the herbivorous species.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652674

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Hermaphrodites are generally seen as species adapted to conditions of low mate availability. This is primarily because hermaphrodites can adjust allocation of resources to each sex function in response to current conditions, making reproduction more efficient. Adaptation to low density is further enhanced because many have the ability to self-fertilize and because the encounter rate of potential mates is twice as high for a hermaphroditic than for a gonochoric species. Yet, many hermaphrodites often occur at consistently high densities. Herein I review the consequences of high density on hermaphrodite sexual behaviour and show that this approach can explain the presence of a number of obvious adaptations known from hermaphrodites. These adaptations cannot be explained by assuming that low density has been the rule in their evolutionary past.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652675

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The mosaic behavior of blastomeres isolated from ascidian embryos has been taken as evidence that localized ooplasmic factors (cytoplasmic determinants) specify tissue precursor cells during embryogenesis. Experiments involving the transfer of egg cytoplasm have revealed the presence and localization of various kinds of cytoplasmic determinants in eggs ofHalocynthia roretzi.Three cell fates, epidermis, muscle and endoderm, are fixed by cytoplasmic determinants. The three kinds of tissue determinants move in different directions during ooplasmic segregation. Prior to the onset of the first cleavage the three kinds of determinants reside in egg regions that correspond to the future fate map of the embryo and then they are differentially partitioned into specific blastomeres. In addition to tissue-specific determinants, there is evidence suggesting that ascidian eggs contain localized cytoplasmic factors that are responsible for controlling the cleavage pattern and morphogenetic movements. Transplantation of posterior-vegetal egg cytoplasm to an anterior-vegetal position causes a reversal of the anterior-posterior polarity of the cleavage pattern. Localized cytoplasmic factors in the posterior-vegetal region are involved in the generation of a unique cleavage pattern. When vegetal pole cytoplasm is transplanted to the animal pole or equatorial position of the egg, ectopic gastrulation occurs at the site of transplantation. This finding supports the idea that vegetal pole cytoplasm specifies the site of gastrulation. Recently, we started a cDNA project to analyze maternal mRNAs. An arrayed cDNA library of fertilized eggs ofH. roretziwas constructed, and more than 2000 clones have been partially sequenced so far. To estimate the proportion of the maternal mRNAs that are localized in the egg and embryo, 150 randomly selected clones were examined byin situhybridization. We found eight mRNAs that are localized in the eight-cell embryo, of which three were localized to the myoplasm (a specific region of the egg cytoplasm that is partitioned into muscle-lineage blastomeres) of the egg, and then to the postplasm of cleavage-stage embryos. These results indicate that the proportion of localized messages is much higher than we expected. These localized maternal messages may be involved in the regulation of various developmental processes.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652676

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In insects, the regulation of embryonic development has been intensively studied in model species likeDrosophila melanogaster.Previous comparative studies have suggested that the developmental processes documented inDrosophilawell describe embryogenesis of holometabolous insects generally. However, there have been few attempts to take into account how life history has influenced insect embryogenesis or to characterize early development of species with life histories fundamentally different from flies. Our studies of advanced insects in the order Hymenoptera suggest that punctuated shifts in life history can profoundly influence these events. In particular, alterations associated with the evolution of endoparasitism argue that departures from the fly paradigm may occur commonly among insects that develop under conditions different from typical terrestrial species.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652677

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Over the last few years vulva development in nematodes has been used as a model system to study the evolution of developmental processes by carrying out cell lineage and cell ablation studies in various nematodes. Furthermore, a genetic and molecular analysis of vulva development has been initiated inPristionchus pacificus.Evolutionary interpretation of these comparative developmental studies requires a phylogenetic understanding of nematodes. Recently, a molecular phylogeny for the phylum Nematoda has been published. Here, we place the comparative data of vulva development onto this phylogeny of nematodes to infer the direction of evolutionary change.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652678

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The fitness of a female mosquito is determined by the success of sugar- and blood-feeding and reproduction. The behaviours associated with feeding and reproduction are mediated by chemical cues of different origin, and therefore the producers of these cues can determine the ultimate survival of a mosquito population. Mosquitoes respond to the odours of a wide range of flowers and extra-floral nectar sources for sugar-feeding. For blood-feeding, the mosquito responds to a range of emanations produced by the vertebrate host. Carbon dioxide is the compound used by most mosquitoes, but specialized species respond better to host-specific cues. Fatty acids and lactic acid are present in large quantities on the skin of humans, unlike in other vertebrates, and these compounds have been implicated in host-seeking behaviour of anthropophilic mosquitoes. One-octen-3-ol, a compound present in bovine emanations, is attractive for host-seeking zoophilic mosquitoes, especially if combined with carbon dioxide. Oviposition stimuli are present as pheromones in the apical droplets of freshly deposited eggs in several culicine mosquito species, and as attractants in emanations of organically enriched water (grass and hay infusions, water containing animal and human faeces). It is concluded that many behaviours of mosquitoes are mediated by a wide range of semiochemicals, and that the degree of sensitivity to these stimuli will therefore affect the reproductive success, and thus fitness, of these important insects.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652679

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The possible relationship between certain oocyte and embryo characteristics and larvae viability was investigated with reference to the following aspects: (1) morphological—oocyte diameter and shape; (2) cytological—overall ultrastructure and membrane integrity; (3) biochemical—content of lipids, proteins and carbohydrates; and (4) physiological—respiration. The rate of survival and incidence of abnormality were estimated 24 h after fertilization. The first results showed that 80–90% of oocytes were cytologically viable before fertilization. Eighty to 90% of oocytes are apparently viable before fertilization on the basis of staining with Trypan blue, but this parameter shows little correlation with larval viability. However, Trypan blue staining is of value in allowing the recognition of oocytes with damaged membranes. Respiration was measured for unfertilized oocytes 5 min after stripping, after 6 h, and for 3-h embryos. Positive correlations were found between the O2-consumption of embryos and both the rate of fertilization and the hatching rate of 24-h larvae. In contrast, no correlation was found between hatching parameters and the O2-consumption of unfertilized oocytes. These results suggest that embryos possess quality indicators, relating to metabolic characteristics, which can be quantified more easily than those of oocytes.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652680

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

To overcome the problem of getting crustaceans to reproduce in captivity, eyestalk ablation or X-organ sinus gland removal is commonly utilized in commercially important species such as shrimp. We have investigated the effect of unilateral and bilateral eyestalk ablation on methyl farnesoate (MF) production by mandibular organs (MOs) and on ovarian maturation in female spider crabsLibinia emarginata, a useful model since these animals are in a terminal molt and are devoid of a functional Y-organ. Non-reproductive, over-wintering femaleL. emarginatawere induced to be reproductive by feeding and increasing the holding temperature to stimulate the endocrine system. In addition, we removed X-organ sinus glands by eyestalk ablation either unilaterally (UEA) or bilaterally (BEA) to further stimulate MF synthesis by MOs. Endogenous MF in the hemolymph was extracted and quantified by means of HPLC and in some cases by GC/MS. Oocyte growth and egg quality were studied simultaneously to determine how they were related to MF levels found during vitellogenesis. The initial MF concentration in unablated controls was low, 0.31 ng/ml of hemolymph, and this increased (p<0.05) to about 1 ng/ml by 2 weeks, remaining at about that level for the remainder of the experiment. Eyestalk ablation significantly stimulated MF concentrations by week 1 to nearly 2 and 3.5ng/ml in the UEA (p<0.01) and BEA (p<0.001) animals, respectively. Oocytes appeared to respond to increased MF levels, as ovarian maturation was initiated from the point at which MF increased (p<0.05). Thereafter, the rate of oocyte growth was directly correlated with the extent of elevation of MF. The gonado-somatic index [(GSI) = gonad weight/body weight × 100] of controls at the start was about 1.5 and increased to 6.5 by week 4. Mature oocytes were reached at a GSI around 7. Oocyte maturation was accomplished at week 2 in BEA, week 3 in UEA, and later than week 4 in controls. After maturation, oocytes started to degrade in some ablated animals, particularly in the bilaterally ablated ones where the highest MF concentrations were observed. These data indicate that MF elevations are required for stimulating ovarian maturation in Crustacea. MF appears to accelerate gonad development during the vitellogenic process, but may be deleterious at high concentrations. These results have a significant and important application and implications for aquaculture.

ISSN:0792-4259    

DOI:10.1080/07924259.1999.9652681

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor