Relevant Life Stages Research Articles

Life cycle maintenance and drug-sensitivity assays for early drug discovery in Schistosoma mansoni

Drug discovery for schistosomiasis is still limited to a handful of academic laboratories worldwide, with only a few novel antischistosomal lead compounds being actively researched. Despite recent international mobilization against the disease to stimulate and promote antischistosomal drug discovery, setting up a drug-screening flow with schistosome parasites remains challenging. Whereas numerous different protocols to obtain and cultivate schistosomes have been published, those describing the drug-screening process are scarce, and none gather together parasite cultivation and early drug discovery procedures. To help overcome this hurdle, we provide here a set of integrated methods either adapted from already-published protocols or based on our long-term experience in schistosomiasis research. Specifically, we detail the establishment and maintenance of the complex and several-week-long Schistosoma mansoni life cycle in a laboratory setting, as well as the means of retrieving and culturing the parasites at their relevant life stages. The in vitro and in vivo assays that are performed along the drug-screening cascade are also described. In these assays, which can be performed within 5 d, the effect of a drug is determined by phenotypic assessment of the parasites' viability and morphology, for which stage-specific scoring scales are proposed. Finally, the modalities for testing and evaluating a compound in vivo, constituting a procedure lasting up to 10 weeks, are presented in order to go from in vitro hit identification to the selection of early lead candidates.

Spatial ecology of the Mariana Crow Corvus kubaryi: Implications for management strategies

SummaryKnowledge of species-specific spatial ecology is critical for applying appropriate management strategies to maximise conservation outcomes. We used radio-telemetry to describe spatial behaviour of the critically endangered, island-endemic Mariana Crow Corvus kubaryi. To determine whether management strategies should reflect life stage, we measured the home ranges and daily movements of 22 Mariana Crows. Fledgling mobility was low during the first 31 days post-fledging and effects of age (fledgling or sub-adult) and time (months post-fledging or post-dispersal) were often driven entirely by this period. After controlling for reduced fledgling mobility, cumulative home range size increased over time for both age classes and was, on average, more than twice the area for sub-adults than fledglings. Sub-adults also tended to make longer daily movements than fledglings. Non-cumulative, monthly home range areas did not increase over time but the average overlap in home range area between consecutive months was only 63%, suggesting large shifts in space use each month. These results highlight the dynamic nature of Mariana Crow home ranges and suggest that large-scale management efforts are critical for protecting both breeding and non-breeding individuals. The application of the traditional home range concept to Mariana Crows and other wide-ranging passerine birds may result in sub-optimal management strategies. Instead, we recommend that the spatial and temporal scale of conservation efforts be informed by species-specific spatial behaviour across all relevant life stages.

Life-course data reconstruction using complementary information taken from linked lives

Recently, research on travel behaviour has focused on life-course and socialisation effects. As residential decisions are considered to be long-term decisions which affect daily travel behaviour significantly, knowledge of residential experiences made over the life-course may lead to a deeper understanding of later residential decisions and thus travel behaviour. Quantitative retrospective surveys are carried out to gather this information. These studies deal with missing information on particular life stages, e.g. childhood. This paper shows a new methodological approach for quantitative studies, illustrating how such missing life-course data can be reconstructed using complementary information taken from linked lives. The data used have been retrospectively collected from a sample of spatial planning students at TU Dortmund University, their parents and grandparents. The parents’ residential biography from birth until the setting up of a household of their own is reconstructed using information from the grandparents. The reconstructed data are compared with the statements the parents made for the relevant life stages, thus testing how well the reconstruction worked. The results show that the reconstruction works better for the mothers (than fathers) using the grandmothers’ information (rather than the grandfathers'). The findings also indicate that the reconstruction is more or less successful for various types of reconstructed data. The paper concludes with guidelines for future data reconstruction.

Evolutionary constraints of warning signals: A genetic trade-off between the efficacy of larval and adult warning coloration can maintain variation in signal expression.

To predict evolutionary responses of warning signals under selection, we need to determine the inheritance pattern of the signals, and how they are genetically correlated with other traits contributing to fitness. Furthermore, protective coloration often undergoes remarkable changes within an individual's lifecycle, requiring us to quantify the genetic constraints of adaptive coloration across all the relevant life stages. Based on a 12 generation pedigree with > 11,000 individuals of the wood tiger moth (Arctia plantaginis), we show that high primary defense as a larva (large warning signal) results in weaker defenses as adult (less efficient warning color), due to the negative genetic correlation between the efficacy of larval and adult warning coloration. However, production of effective warning coloration as a larva did not incur any life-history costs and was positively genetically correlated with reproductive output. These results provide novel insights into the evolutionary constraints on protective coloration in animals, and explain the maintenance of variation in the signal expression despite the strong directional selection by predators. By analyzing the genetic and environmental effects on warning signal and life-history traits in all relevant life stages, we can accurately determine the mechanisms shaping the evolutionary responses of phenotypic traits under different selection environments.

A Model of Mosquito–Mangrove Basin Ecosystems with Implications for Management

A model of the mosquito–mangrove basin ecosystem is presented detailing the habitat of the saltwater mosquito Aedes vigilax utilizing mangrove basin forests in Australia. The modeling included a synthesis of empirical observations and published descriptions including the insect’s relevant life-stages, mangrove basin topography and hydrodynamics. Shallow mangrove basins periodically connected by only the highest 10% of high tides with a hummocky substrate micro-topography characterize the main mangrove form conducive to Ae. vigilax breeding. Other essential features include the synchronization of the mosquito’s lifecycle to basin hydrodynamics and thus an intricate relationship between hydrodynamics and basin structure. Very small decreases in basin water level (~1 cm/day) lead to significant decreases in extent of standing water (for example, 60% over 6 days) across the basin. This results in corresponding increases in the extent of exposed substrate. Also, the modeling demonstrated sensitivity of the mosquito–mangrove basin ecosystem to sea level changes. A hydrologic model of the basin was used to predict mosquito breeding episodes which were tested against a mosquito management larviciding program. The model predicted 75% of all 29 larviciding treatments undertaken. Comparing the model against the two triggers used by mosquito control, tides and rainfall, the model predicted 92% of tidally instigated treatments and 60% of rainfall instigated treatments. Application of the model enables consideration of environment-based minimal habitat modification for mosquito control in mangroves, not previously possible. The model will be applicable to similar species, such as Ae. taeniorhynchus, found in Florida’s (USA) mangroves.

Underexplored niches in research on plant pathogenic bacteria.

Despite rapid advances on certain aspects of plant pathogenic bacteria, many economically important pathosystems are largely unexplored and biologically relevant life stages of even familiar systems remain poorly understood. We know remarkably little about end-stage disease, latent infections, survival away from the host, interactions among multiple microbes in a plant, and the effects of quantitative virulence factors. While no thoughtful researcher would dispute the effectiveness of reductionist experiments, we propose that this approach be combined with a broader perspective that includes the ecology, histopathology, and community population biology of phytopathogenic bacteria. We offer examples of exciting recent discoveries resulting from this natural history-based approach. In particular, in situ studies using biologically realistic inoculation followed by analyses with microscopy, gene expression profiling, community analyses, or application of key computational tools can offer new insights into old questions. Research that combines cutting-edge tools with a biological perspective is especially lacking on high-impact diseases of subsistence crops. Understanding the biology underlying important practical issues such as copper resistance, eradication from seed and cuttings, and rapid, sensitive detection could be of significant utility. Overall, we endorse a broader biological approach to research on plant pathogenic bacteria.

The vocal development of the Red-crowned Crane Grus japonensis

ABSTRACT Most studies on avian vocal ontogenesis have focused on taxa exhibiting some kind of vocal learning. This study provides a detailed analysis of vocal processes through early and late ontogenesis in 17 chicks of the Red crowned Crane Grus japonensis, a species lacking vocal learning. Three basic structural classes: trills, PE-chirps and PS-chirps and their transitional forms are described. Trends in call parameter values are presented for 10 age classes in the course of a period from birth to 9.5 months. We discuss our vocal classification with those reported for other crane species, relate the revealed stages of vocal ontogenesis in the Red-crowned Crane to biologically relevant life stages in this species and advance a hypothesis for the proposed function of retaining high juvenile frequencies in adolescent cranes for a prolonged period, up to voice breaking (a rapid significant decrease in fundamental frequency). We conclude, that voice breaking is universal for both sexes and that the retained...

Feminisation of young males of the common carp, Cyprinus carpio, exposed to 4- tert-pentylphenol during sexual differentiation

In recent years, a hierarchy of techniques has become available for detecting chemicals which may cause endocrine disruption in the aquatic environment. The molecular structure of a chemical provides a first indication about estrogenic activity, i.e. their likelihood of interfering with the female hormone receptor. In vitro competitive binding assays for this receptor and specific cell cultures are also used to demonstrate an estrogenic response, but this does not adequately indicate whether the substance will cause adverse reproductive effects in an entire organism. An elevated level of vitellogenin, a typical female lipoprotein in the plasma of male fish is an in vivo estrogen-mediated response. However, its direct relationship to reproductive developmental effects is as yet unclear. The present study aims at investigating this relationship for assessing endocrine disruption in fish exposed to an estrogenic substance during relevant life stages. A monosex population of male carp, Cyprinus carpio, was exposed to 4-tert-pentylphenol (TPP) and to 17 β-estradiol as a positive control during the period of sexual differentiation, starting at 50 days post hatch. The fish were sampled every 10 days for the histological examination of the development of the testes, i.e. the formation of the reproductive tract, the multiplication and subsequent meiosis of the primordial germ cells, and gametogenesis in the early gonad. At the end of the experiment, blood was extracted for the quantification of vitellogenin by radioimmunoassays in the plasma. The average number of primordial germ cells (PGCs) per gonadal section was significantly reduced ( P<0.001) at all sampling periods in the testes of carp exposed to 17 β-estradiol (positive control). The PGCs had commenced oogenesis after 50 days exposure and developed into oocytes as in a `normal' ovary. The number of PGCs in the testes of the carp exposed to TPP was reduced in a dose dependent manner. Spermatogenesis was severely inhibited in the testes of the TPP-exposed carp, where, few oocytes were ever observed. 20 days exposure to 17 β-estradiol were sufficient to induce the formation of an oviduct instead of a male vas deferens, whereas this occurred after 30 days in TPP-exposed carp. A dose effect relationship with TPP was established and the EC 50 calculated (63 μg TPP l −1). Vitellogenin levels were significantly elevated in the plasma of the carp exposed to both 17 β-estradiol concentrations, but only at the highest 4-tert-pentylphenol concentration (256 μg TPP l −1, P<0.05). At the end of the exposure, the no observed effect concentration for the oviduct formation was <36 μg TPP l −1 and that for increased levels of vitellogenin was between 90 and 256 μg TPP l −1.