What makes a species vulnerable to extinction? Comparative life-history traits of two sympatric snakes

Although it is well known that species vary in their vulnerability to extinction, the reasons are poorly understood. Theory predicts that long-lived species with slow life histories (small litters, slow growth, late maturation) should be at greater risk than short-lived species with high potential rates of increase. This hypothesis was tested by comparing life-history traits of two species of sympatric, elapid snakes: the endangered broad-headed snake, Hoplocephalus bungaroides, and common small-eyed snake, Cryptophis nigrescens. From 1992 to 2000 a mark–recapture study of both species was undertaken in Morton National Park, south-eastern Australia, and this information was used to construct transition matrices for each species. The endangered H. bungaroides was found to mature late (6 years of age), had a high juvenile (54.7%) and adult (81.6%) survival rate, and a long generation length (10.4 years). In striking contrast, the common C. nigrescens matured early (within 3 years), had a lower juvenile (30.4%) and adult (74.4%) survival rate (but higher recruitment rate), and a substantially shorter generation length (5.9 years). Elasticity analyses revealed that H. bungaroides was considerably more sensitive to survival past the age of 2 years (68.6%) than C. nigrescens (37.4%). These results provide support for the hypothesis that species with slow life histories are more vulnerable to extinction.     

What to do with HLA-DO?

Antigenic peptide binding to MHC class II molecules in the endocytic pathway occurs via a multifactorial process that requires the support of a specialized lysosomal chaperone called HLA-DM. DM shows both in primary amino acid sequence and quaternary structure a high homology to both MHC class I and class II molecules. Like the peptide presenting class II molecules, DM is expressed in all professional antigen presenting cells. DM catalyzes the dissociation of peptides that do not bind stably to the class II peptide-binding groove, thereby leading to the preferential presentation of stably binding antigenic peptides. The recently discovered HLA-DO molecule is mainly expressed in B cells and associates with DM, thereby markedly affecting DM function. Like DM, the genes encoding the HLA-DO heterodimer lie within the MHC class II region and exhibit strong homology to classical class II molecules. This review evaluates the unique effects of DO on DM-mediated antigen presentation by MHC class II molecules and discusses the possible physiological relevance for the B cell-specific expression of DO and its function.     

Can life-history traits predict the response of forb populations to changes in climate variability?

1.  Climate change will cause changes in average temperature and precipitation as well as increased fluctuations around the mean, yet few studies have considered the impacts of altered climate variability on plant populations. We tested whether life-history traits (expected life span, generation time and seed size) can predict plant responses to increased environmental variability across similar plant species sharing the same habitat.
2.  We combined long-term demographic data on 10 prairie forb species with stochastic demography techniques to estimate the effects of potential changes in matrix element means and variances on the long-term stochastic population growth rate.
3.  For all 10 species, recruitment had higher contribution and elasticity values than survival, meaning that climate change is more likely to influence population growth through effects on recruitment than on survival for these relatively short-lived forbs. Species with longer generation times had lower elasticities to increases in matrix element variability.
4.   Synthesis. Our analysis of a unique, long-term data set suggests that longer-lived plant species will be less vulnerable to the effects of future increases in climate variability. While this relationship was previously reported for diverse taxa from many locations, our results show that it also applies within a guild of short-lived species from a single community. The generality of the pattern demonstrates the potential for using life-history traits to make predictions about which species may be the most vulnerable to climate change.     

Impacts of fever on locust life-history traits: costs or benefits?

Fever, like other mechanisms for defence against pathogens, may have positive and negative consequences for host fitness. In ectotherms, fever can be attained through modified behavioural thermoregulation. Here we examine potential costs of behavioural fever by holding adult, gregarious desert locusts at elevated temperatures simulating a range of fever intensities. We found no effect of fever temperatures on primary fitness correlates of survival and fecundity. However, flight capacity and mate competition were reduced, although there was no relation between time spent at fever temperatures and magnitude of the response. While these effects could indicate a direct cost of fever, they are also consistent with a shift towards the solitaria phase state that, in a field context, could be considered an adaptive life-history response to limit the impact of disease. These conflicting interpretations highlight the importance of considering complex defence mechanisms and trade-offs in an appropriate ecological context.     

Does habitat fragmentation affect temperature-related life-history traits? A laboratory test with a woodland butterfly

Habitat fragmentation may change local climatic conditions leading to altered selection regimes for life-history traits in small ectotherms, including several insects. We investigated temperature-related performance in terms of fitness among populations of the woodland butterfly Pararge aegeria (L.) originating from populations of a closed, continuous woodland landscape versus populations of an open, highly fragmented agricultural landscape in central Belgium. Female fecundity and longevity were evaluated in a temperature-gradient experiment. As predicted, females of woodland landscape origin reached higher maximum daily fecundity and lifetime number of eggs than did agricultural landscape females at low ambient temperatures, but this reversed at high ambient temperature. Egg weight decreased with temperature, and eggs of woodland butterflies were smaller. Contrary to what is generally assumed, remaining thorax mass was a better predictor of lifetime reproductive output than was abdomen mass. Since we used the F2 generation from wild-caught females reared under common garden conditions, the observed effects are likely to rely on intrinsic, heritable variation. Our results suggest that differential selection regimes associated with different landscapes intervene by intraspecific variation in the response of a butterfly to variation in ambient temperature, and may thus be helpful when making predictions of future impacts on how wild populations respond to environmental conditions under a global change scenario, with increasing temperatures and fragmented landscapes.     

What to do in marine biotechnology?

During the symposium "Marine Biotechnology: Basics and Applications", held 25 February-1 March, 2003 in Matalasca?as, Spain, a special brainstorm session was organized. Two questions were addressed: 1, "What is the most desirable development in marine biotechnology"?; 2, "What is the most spectacular development in this field in your 'wildest' dreams"? The outcome of this session is reported in this paper. From the more than 250 ideas generated, concern for the environment and human health emerged as the most significant issues.     

Interfamily variation in amphibian early life-history traits: raw material for natural selection?

The embryonic development and time to hatching of eggs can be highly adaptive in some species, and thus under selective pressure. In this study, we examined the underlying interfamily variation in hatching timing and embryonic development in a population of an oviparous amphibian, the rough-skinned newt (Taricha granulosa). We found significant, high variability in degree of embryonic development and hatching timing among eggs from different females. Patterns of variation were present regardless of temperature. We also could not explain the differences among families by morphological traits of the females or their eggs. This study suggests that the variation necessary for natural selection to act upon is present in the early life history of this amphibian.     

What role do dauciform roots play? Responses of Carex filispica to trampling in alpine meadows based on functional traits

In China, dauciform roots were hardly studied and only reported in alpine meadows, where sedges showed a different tendency from other functional groups such as grasses and forbs with degradation. In addition, Carex species were proved to have shifting scaling relationships among LES (leaf economics spectrum) traits under disturbance. So, are these unique performances of sedges related to the presence of dauciform roots, and if so, how? An alpine meadow dominated by Carex filispica in Baima Snow Mountain was selected, and quantitative trampling was performed (0, 50, 200, and 500 passes). The cover and dauciform root properties of Carex filispica were measured, as well as the morphological, chemical traits and biomass of leaves and roots, their correlations and the differences between individuals with and without dauciform roots were analyzed. After the trampling, individuals with dauciform roots showed multiple resource‐acquisitive traits: Larger, thicker leaves, more aboveground biomass, higher efficiency of nutrient utilization, and slenderer roots. Additionally, they had a tighter correlation among belowground biomass, morphological and chemical traits, as well as dauciform root properties and morphology of leaves, suggesting that their traits were more related than those without dauciform roots. The presence of dauciform roots in Carex filispica was related to advantages in multiple traits after trampling, which is consistent with and might be responsible for the unique performances of sedges.     

What do mice select for in seeds?

Summary Knowledge of the basis upon which granivores select seeds is crucial to the understanding of granivory. In this study the preferences of three rodent granivores among seeds of 11 plants from the semi-arid Karoo of South Africa were estimated, and related to the physical and chemical attributes of the seeds. Seed weights and calorific, moisture, protein, polyphenol, ash, lipid and silica contents were estimated and cell contents, soluble ash and soluble carbohydrate contents were derived from these values. These attributes were determined for both the intact seeds and the portion of the seed that is ingested by the mice. The efficiency with which mice ingested the seeds (in terms of time and mass) was recorded. All three mouse species ranked the seeds similarly, and the two species for which handling efficiency was measured did not differ in this regard. Preference hierachies were highly correlated with the rate of energy intake, as predicted by optimal foraging theory. There was no correlation between rodent preferences and the gross energy content of the seeds, emphasising the importance of measuring relevant parameters. The energy yield of the seeds calculated here, in conjunction with rodent population energy requirements and dietary data, may be used to estimate potential granivore impact on the seed production of the plant community.     

What do family physicians see in practice?

Health care problems dealt with in their practices were recorded by seven family physicians over a period of 1 year (two others recorded for 3 months), each diagnosis being coded according to the Canuck Disease Classification Index. Problems were classified into four types: physical, psychosocial, diseases of choice (or lifestyle) and diseases of social impact. More than 85% of the 23 108 problems recorded were physical in origin and had physical manifestations. More time was spent on routine checkups and treatment of respiratory disease than on any other activity. Venereal disease and alcoholism were infrequent problems. The family physician is in a favourable position to act as health educator and counsellor and must be throughly trained in the physical aspects of disease.     

What can myosin VI do in cells?

The recently solved structure of the myosin VI motor demonstrates that the unique insert at the end of the motor is responsible for the reversal of the normal myosin directionality. A second class-specific insert near the nucleotide-binding pocket contributes to myosin VI's unique kinetic tuning, allowing it to function either as an actin-based transporter or as an anchoring protein. Recent biochemical and biophysical studies have shown that the native molecule can form dimers upon clustering, and cell biological studies have demonstrated that it clearly does play both transport and anchoring roles in cells. These mechanistic insights allow us to speculate on how unusual aspects of myosin VI structure and function allow it to fill unique niches in cells.