How many lethal alleles?

Knowledge of the frequency of lethal mutant alleles in a population is important for our understanding of population genetics and evolution, and yet there have been few attempts to measure their number in wild populations. A new study has revealed unexpectedly low numbers of segregating lethal alleles in two species of fish. More experiments are needed, however, to know whether this result is general.     

How many birds are there?

Attempts to assess the magnitude of global biodiversity have focused on estimating species richness. However, this is but one component of biodiversity, and others, such as numbers of individuals or biomass, are at least as poorly known and just as important to quantify. Here, we use a variety of methods to estimate the global number of individuals for a single taxon, birds. The different methods yield surprisingly consistent estimates of a global bird population of between 200 billion and 400 billion individuals (1 billion=109). We discuss some of the implications of this figure.     

MSCs—cells with many sides

The field of mesenchymal stromal cell (MSC) biology and clinical cellular therapy has grown exponentially over the last few decades. With discovery of multiple tissue specific sources of stromal cells, invariably being termed MSCs, and their increasing clinical application, there is a need to further delineate the true definition of a mesenchymal stromal cell and to recognise the inherit differences between cell sources; both their potential and limitations.In this review, we discuss the importance of considering every stromal cell source as an independent entity and the need to critically evaluate and appreciate the true phenotype of these cells and their safety when considering their use in novel cell therapies.     

How many species are there?

How many species are there is a question receiving more attention from biologists and reasons for this are suggested. Different methods of answering this question are examined and include: counting all species; extrapolations from known faunas and regions; extrapolations from samples; methods using ecological models; censusing taxonomists' views. Most of these methods indicate that global totals of 5 to 15 million species are reasonable. The implications of much higher estimates of 30 million species or more are examined, particularly the question of where these millions of species might be found.     

How many markers or how many alleles per system are appropriate in zygosity testing?

Due to the development in DNA-PCR-technique more and more systems with a high number of alleles have been established in twin diagnosis. Because of their high effectiveness in resolving of genetic questions it is not amazing that some authors have postulated the thesis that typing of 5 to 10 DNA-PCR systems can prove monozygosity. For this paper the use of different systems (conventional and PCR systems) has been tested for twin diagnosis and the observed effects are discussed.     

The functional importance of parasites in animal communities: many roles at many levels?

Past research on parasites and community ecology has focussed on two distinct levels of the overall community. First, it has been shown that parasites can have a role in structuring host communities. They can have differential effects on the different hosts that they exploit, they can directly debilitate a host that itself is a key structuring force in the community, or they can indirectly alter the phenotype of their host and change the importance of the host for the community. Second, certain parasite species can be important in shaping parasite communities. Dominant parasite species can directly compete with other parasite species inside the host and reduce their abundance to some extent, and parasites that alter host phenotype can indirectly make the host more or less suitable for other parasite species. The possibility that a parasite species simultaneously affects the structure of all levels of the overall community, i.e. the parasite community and the community of free-living animals, is never considered. Given the many direct and indirect ways in which a parasite species can modulate the abundance of other species, it is conceivable that some parasite species have functionally important roles in a community, and that their removal would change the relative composition of the whole community. An example from a soft-sediment intertidal community is used to illustrate how the subtle, indirect effects of a parasite species on non-host species can be very important to the structure of the overall community. Future community studies addressing the many potential influences of parasites will no doubt identify other functionally important parasite species that serve to maintain biodiversity.     

Colour polymorphism in common primrose (Primula vulgaris Huds.): many colours–many species?

Primula vulgaris exhibits flower colour polymorphism in the eastern part of its range, especially pronounced on the NE coast of the Black Sea. This polymorphism in the Caucasian populations has been taxonomically described and some segregated species are listed as rare and endangered. We used sequence variation in two chloroplast noncoding regions (trnL–trnF and rpll32–trnL) and the complete nuclear internal transcribed spacer (ITS) of ribosomal DNA region to investigate correspondence between flower colour and geographical distribution of both nuclear and chloroplast haplotypes. It appears that variability in these DNA regions does not correlate with flower colour, being, however, clearly structured geographically. We used nested clade analysis to explore this geographical structure. It seems that the territory of the Colchis refugium on the E coast of the Black Sea contains both the highest flower colour and haplotype diversities. The results suggest that common primroses colonized the NE coast of the Black Sea from this refugium, spreading along the coast westward. At the same time, the analysis of ITS haplotypes indicates that P. vulgaris colonized the Crimea from NW Anatolia. This makes it clear that no segregated species can be recognized within flower colour polymorphic P. vulgaris in the Caucasus region. However, its phylogeography needs further detailed study on a broader scale.     

Why are so many trees hollow?

In many living trees, much of the interior of the trunk can be rotten or even hollowed out. Previously, this has been suggested to be adaptive, with microbial or animal consumption of interior wood producing a rain of nutrients to the soil beneath the tree that allows recycling of those nutrients into new growth via the trees roots. Here I propose an alternative (non-exclusive) explanation: such loss of wood comes at very little cost to the tree and so investment in costly chemical defence of this wood is not economic. I discuss how this theory can be tested empirically.