Look who's talking too: graduates developing skills through communication

Greater opportunities for young scientists to present their doctoral research to large general audiences will encourage development of transferable skills and involvement in the scientific community. We look at ways students communicate their research and explore the benefits of student-led meetings. The organization of the first Sanger-Cambridge Ph.D. Symposium provides an example of how students can act to establish forums for their work and we call on other young scientists to do the same.     

Look who's talking: nuclear receptors in the liver and gastrointestinal tract

The Nuclear Receptors in Liver and Digestive Diseases research workshop was held in Rockville, Maryland, on November 7 and 8, 2007, under the auspices of the National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health. Over 130 researchers from around the world gathered to assess the pathophysiology of nuclear receptors in the liver and gastrointestinal tract and to explore their potential use as therapeutic targets. This review covers some of the highlights of the meeting, including important areas of future investigation.     

Look who's talking: communication and quorum sensing in the bacterial world

For many years bacteria were considered primarily as autonomous unicellular organisms with little capacity for collective behaviour. However, we now appreciate that bacterial cells are in fact, highly communicative. The generic term 'quorum sensing' has been adopted to describe the bacterial cell-to-cell communication mechanisms which co-ordinate gene expression usually, but not always, when the population has reached a high cell density. Quorum sensing depends on the synthesis of small molecules (often referred to as pheromones or autoinducers) that diffuse in and out of bacterial cells. As the bacterial population density increases, so does the synthesis of quorum sensing signal molecules, and consequently, their concentration in the external environment rises. Once a critical threshold concentration has been reached, a target sensor kinase or response regulator is activated (or repressed) so facilitating the expression of quorum sensing-dependent genes. Quorum sensing enables a bacterial population to mount a co-operative response that improves access to nutrients or specific environmental niches, promotes collective defence against other competitor prokaryotes or eukaryotic defence mechanisms and facilitates survival through differentiation into morphological forms better able to combat environmental threats. Quorum sensing also crosses the prokaryotic-eukaryotic boundary since quorum sensing-dependent signalling can be exploited or inactivated by both plants and mammals.     

Fumonisins: current research trends in developmental toxicology

Fumonisin B₁ (FB₁) is a mycotoxin produced byFusarium verticillioides that is found in maize and maize-based foods. Reproductive studies in CD1 mice, rats and rabbits initially found no evidence that fumonisins are teratogenic. However, more recent findings suggest that they might increase the risk of neural tube defects (NTDs) in populations consuming large amounts of fumonisin-contaminated corn. When ≥15 mg/kg body weight fumonisin B₁ (FB₁) was given to pregnant LM/Bc mice by intraperitoneal (ip) injection, all litters were positive for NTDs. To determine if NTD induction is unique to the inbred LM/Bc mouse strain, NTD induction in LM/Bc and CD1 mice was compared: (a) in a study in whichF. verticillioides culture material providing ≤150 ppm FB₁ was fed to female mice before and during gestation, and (b) in a study in which FB₁ was given by ip injection to CD1 dams on gestation days 7 and 8, the critical time for NTD development. In the feeding study, one of five LM/Bc litters from dams fed the 150 ppm FB₁ diet was positive for NTDs whereas no NTDs were found in the CD1 litters. In the ip injection study, 40% of the litters at the highest dose tested, 45 mg/kg body weight, were positive for NTDs and one of nine low-dose (15 mg/kg body weight) litters was also positive. Thus, FB₁ induced NTDs in both LM/Bc and CD1 mice although the latter strain appears less sensitive. Comparative investigations using these strains will be useful for elucidating the mechanisms underlying fumonisin-induced NTDs in mice and determining the suitability of mouse models for studying the relationships between fumonisins and NTDs in humans.     

Body size and cell size in Drosophila: the developmental response to temperature

In Drosophila, like most ectotherms, development at low temperature reduces growth rate but increases final adult size. Cultures were shifted from 25 degrees C to low (16.5 degrees C) or to high (29 degrees C) temperature at regular intervals through larval and pupal stages, and the flies of both sexes showed an increase or decrease, respectively, in the size of thorax, wing and abdominal tergite. Size changes in the wing blade resulted from changes in the size of the epidermal cells (with only a small increase in cell number in males reared at low temperature). The temperature-shifts became less effective as they were made at successively later developmental stages, demonstrating a cumulative effect of temperature on adult size. The thorax and wing develop from the same imaginal disc, with most cell division occurring in larval stages, but they differ in timing of temperature sensitivity, which extends only to pupariation or into the late pupal stage, respectively. Growth of the adult abdomen occurs largely after pupariation but its size is temperature-sensitive through both larval and pupal stages. We discuss growth control in Drosophila and the likely effects of temperature on food assimilation, growth efficiency and allocation of nutrients to the production of different tissues.     

Ontogeny as a whole: Some developmental trends

In many animal groups, rudimentary organs of adult organisms appear at early stages of egg cleavage, when there is no trace of morphological differentiation. More than half a century ago, I. I. Schmalhausen developed a profound concept of integrity of the organism in the course of development. He emphasized that mutual adaptation of organs is based on correlations, involving the so-called nonhereditary modifications, which are transformed into hereditary traits by means of natural selection. There are many exceptions to the biogenetic law, as it was understood by de Beer. In particular, embryo of the pouched tree frog Gastrotheca shows a retarded development and is spread over the yolk surface. As a result, it becomes similar somewhat to embryos of amniotes. After the metamorphosis, Xenopus returns to ammonotelism. The integrity of ontogeny at the molecular level has much in common with the neutrality theory.     

Position and developmental trends in fibrinolytic therapy

Increasing insight into the mechanism of fibrinolysis and particularly into the formation and release of plasminogen activator has led to more effective thrombolytic therapy. The understanding of the mechanism of thrombolysis has provided the possibility to improve the therapeutic effects of the fibrinolytic agents streptokinase and urokinase. Further advances in thrombolytic therapy are expected by the use of the plasminogen activator from tissue endothelium and pro-urokinase. Acylation of fibrinolytic enzymes will lead to beneficial effects (depot effect, protection from intrinsic inhibitors). Due to the extensive research into substances with fibrinolytic and thrombolytic effects a new generation of activators of fibrinolysis is expected that interfere with the biosynthesis and release of plasminogen activator of the vessel wall and that are suited for treatment of hypofibrinolytic states.     

Genome size evolution in vertebrates: trends and constraints

1. Studies on the genomic evolution in vertebrates have highlighted the differences existing between anamniotes and amniotes, both in quantitative and compositional terms. 2. These differences do not seem to depend on a different tendency to genic amplification, but rather on the existence of more strict and efficient constraints in amniotes. 3. Some constraints, that may be defined as "intrinsic", would act directly on the genome; among these particularly important is the chiasma frequency during meiosis. 4. Other, "extrinsic", constraints, would act indirectly through genic products or through cell morphometric parameters. 5. The genome size increase seems to depend on various mechanisms. The most wide-spread one seems to be the amplification of interspersed repetitive and non-repetitive sequences.     

Genome size and developmental parameters in the homeothermic vertebrates.

Although unrelated to any intuitive notions of organismal complexity, haploid genome sizes (C values) are correlated with a variety of cellular and organismal parameters in different taxa. In some cases, these relationships are universal--notably, genome size correlates positively with cell size in each of the vertebrate classes. Other relationships are apparently relevant only in particular groups. For example, although genome size is inversely correlated with metabolic rate in both mammals and birds, no such relationship is found in amphibians. More recently, it has been suggested that developmental rate and (or) longevity are related to genome size in birds. In the present study, a large dataset was used to examine possible relationships between genome size and various developmental parameters in both birds and mammals. In neither group does development appear to be of relevance to genome size evolution (except perhaps indirectly in birds through the intermediation of body size and (or) within the rodents), a situation very different from that found in amphibians. These findings make it clear that genome size evolution cannot be understood without reference to the particular biology of the organisms under study.     

Environmental and scale-dependent evolutionary trends in the body size of crustaceans

The ecological and physiological significance of body size is well recognized. However, key macroevolutionary questions regarding the dependency of body size trends on the taxonomic scale of analysis and the role of environment in controlling long-term evolution of body size are largely unknown. Here, we evaluate these issues for decapod crustaceans, a group that diversified in the Mesozoic. A compilation of body size data for 792 brachyuran crab and lobster species reveals that their maximum, mean and median body size increased, but no increase in minimum size was observed. This increase is not expressed within lineages, but is rather a product of the appearance and/or diversification of new clades of larger, primarily burrowing to shelter-seeking decapods. This argues against directional selective pressures within lineages. Rather, the trend is a macroevolutionary consequence of species sorting: preferential origination of new decapod clades with intrinsically larger body sizes. Furthermore, body size evolution appears to have been habitat-controlled. In the Cretaceous, reef-associated crabs became markedly smaller than those in other habitats, a pattern that persists today. The long-term increase in body size of crabs and lobsters, coupled with their increased diversity and abundance, suggests that their ecological impact may have increased over evolutionary time.     

Kin recognition: knowing who's boss in wasp colonies

Paper wasps recognise the dominant individual in their colony and surrender reproduction to this alpha individual. Contrary to expectations her dominance status is not signalled by a chemical indicator of fertility.     

Gyrodactylid developmental biology: historical review, current status and future trends

In the viviparous gyrodactylids, embryos develop one inside another within the parental uterus, a phenomenon with major implications for the biology of this species-rich group. Development occurs via two routes: first-born daughters develop at the centre of an embryo cluster in utero, whereas all other daughters develop from oocytes. The resulting offspring are, however, morphologically indistinguishable. We review here the history of gyrodactylid embryology in the context of current knowledge and, present additional cytogenetic and ultrastructural observations of embryonic development. These progenetic parasites are highly modified for viviparity; oocyte maturation and sperm storage occur in a single chamber, the Egg Cell Forming Region, and a mature oocyte passes into the uterus after the birth of the preceding, fully developed offspring. The uterus has a syncytial lining derived from anterior and posterior cap cells. These cells are the first to differentiate in the female reproductive system and may be involved in controlling development. Embryos receive nutrients via the uterus rather than from vitelline cells. Traditionally, development of the first-born daughter has been considered a form of polyembryony, although paedogenesis has also been suggested. In contrast to previous studies, we could not trace lineage of the first-born daughter to a single quiescent macromere. However, only mitotic divisions have been conclusively observed in the intraembryonic generation, indicating an asexual origin. All other daughters are formed from meiotically derived oocytes by sexual reproduction or automictic parthenogenesis. The latter may involve pre-meiotic doubling of chromosomes, but the precise mechanism and the relative proportion of sexual and parthenogenetic offspring are unknown. Exceptionally, cleavage in Gyrodactylus spp. occurs by duets rather than quartets (a pattern previously only recorded in acoels) and is characterised by extensive cell rearrangements. Blastomeres may be connected by fine cytoplasmic processes or completely disassociated and are readily redistributed by the muscular actions of the parental uterus. This process resembles 'Blastomeren-Anarchie' of rhabdocoels but without the structural support of vitelline cells. It prevents generation of early cell fate maps and indicates regulative, rather than mosaic, development. Structures such as the gut and excretory system differentiate late, and are highlighted, together with the attachment apparatus, as examples of post-embryonic differentiation. Molecular and cellular techniques are now essential to further elucidate mechanisms of gyrodactylid reproduction, which will in turn contribute to current debates with animal embryology.     

Age-related changes and secular trends in hand bone size

The aim of the present study was to evaluate age- and sex-related changes in the size and shape of long hand bones in a large Chuvashian cohort using cross-sectional and longitudinal study designs. The data were gathered in 1994 (557 individuals) and 2002 (513 individuals). The latter sample included 260 individuals that were studied only during the second expedition, and 253 individuals who were previously investigated in 1994. Statistical analyses included a maximum likelihood-based model-fitting technique and a t-test comparison. We found evidence for secular trend of hand bone size in both males and females within the Chuvashian population. In males, the length and total area of the long hand bones were greater in younger individuals, but mid-shaft bone width remained almost the same in individuals born at different periods of the last century. In females, the length of the hand bones and total bone area remained unchanged in women born after 1937. However, bone mid-shaft width gradually decreased in women born after 1940. Therefore, we argue that, at least within the Chuvashian population, there is a secular trend towards a more gracile appendicular skeleton in both males and females.     

Mechanisms behind active trends in body size evolution of the Canidae (Carnivora: Mammalia)

Clade-level interactions can impart trends on observed characters. In this study, origination and extinction events were compiled for the three subfamilies of the Canidae (dogs): Hesperocyoninae, Borophaginae, and Caninae. These events were binned into 2-million-year time slices, and median body masses were calculated for each time slice. Originations and extinctions were classified as "large" or "small" relative to these median values. Likelihood ratios demonstrate that originations were significantly biased from random in four time slices, while extinctions were never significantly different from random. Two models were chosen by the Akaike Information Criterion to describe the evolutionary dynamics of canid body size. Both proposed a consistent, significant bias toward larger originations, punctuated by episodic "pulses" of increased bias toward larger originations and a Quaternary "pulse" favoring smaller originations, tracking the Quaternary diversification of foxlike canids. These pulses correspond in each subfamily to periods of rapid taxonomic diversification and the appearances of morphologies associated with hypercarnivorous diets. Together, the diversity data, the appearance of hypercarnivory, and the biases in originations document competitive interactions between Hesperocyoninae and Borophaginae and suggest that body size trends were driven, in part, by clade-level dynamics in the Canidae.     

Body size trends in a Holocene island bird assemblage

Despite the robust observation in macroecology that there are many small-bodied species, recent comparative studies have found little evidence for elevated net rates of diversification among small-bodied species within taxa. Here we examine the relationship between body size and species richness using the New Zealand land bird fauna, a well resolved palaeoecological Holocene assemblage. We test whether there is any evidence that net cladogenesis depended on body size in an assemblage prior to the impact of human-induced extinction. We also test whether net cladogenesis depends on the level at which taxa are endemic to New Zealand, to see whether there is evidence for bursts of cladogenesis following taxon establishment, and examine how the body sizes of New Zealand land birds relate to those in Australia, the most likely source pool for colonising taxa. Most New Zealand land bird species are small-bodied. We find no evidence, however, that this is due to higher net cladogenesis in small-bodied taxa. The body mass distributions of endemic and recent colonist species do not differ statistically, but recent colonists tend to be smaller-bodied than their closest endemic relative. This tendency is more marked for small-bodied than large-bodied taxa. More endemic taxa do not tend to be more species rich in New Zealand, although there is a positive relationship between level of endemism and species richness for forest taxa. The body mass distribution of New Zealand birds is very similar to that for Australia. Body mass does not dictate the likelihood that a family has colonised New Zealand from Australia, but the number of species in the family does: it is the species rich Australian families that have successfully colonised. We discuss the implications of these results for the evolution of body size distributions, and for the island rule of body size evolution on islands.