Functional rarefaction: estimating functional diversity from field data

Studies in biodiversity-ecosystem function and conservation biology have led to the development of diversity indices that take species' functional differences into account. We identify two broad classes of indices: those that monotonically increase with species richness (MSR indices) and those that weight the contribution of each species by abundance or occurrence (weighted indices). We argue that weighted indices are easier to estimate without bias but tend to ignore information provided by rare species. Conversely, MSR indices fully incorporate information provided by rare species but are nearly always underestimated when communities are not exhaustively surveyed. This is because of the well-studied fact that additional sampling of a community may reveal previously undiscovered species. We use the rarefaction technique from species richness studies to address sample-size-induced bias when estimating functional diversity indices. Rarefaction transforms any given MSR index into a family of unbiased weighted indices, each with a different level of sensitivity to rare species. Thus rarefaction simultaneously solves the problem of bias and the problem of sensitivity to rare species. We present formulae and algorithms for conducting a functional rarefaction analysis of the two most widely cited MSR indices: functional attribute diversity (FAD) and Petchey and Gaston's functional diversity (FD). These formulae also demonstrate a relationship between three seemingly unrelated functional diversity indices: FAD, FD and Rao's quadratic entropy. Statistical theory is also provided in order to prove that all desirable statistical properties of species richness rarefaction are preserved for functional rarefaction.     

C-Type Virus Released from Cultured Human Rhabdomyosarcoma Cells

RD-114 virus, released from human rhabdomyosarcoma cells, has all the characteristics of a mammalian C-type virus. Immunological tests indicate that it differs from all known C-type viruses and is the most likely candidate for a human C-type virus yet described.     

Fusion of lipid bilayers: a model involving mechanistic connection to HII phase forming lipids.

A model for the molecular mechanism of the fusion of lipid bilayers is described. A crucial feature of this model and related to the lamellar-->hexagonal phase HII transition is a novel, hypothetical lipid conformation, tentatively referred to here as extended. During fusion this conformation could manifest itself in the contact site between two vesicles in close proximity and involves the extension of the acyl chains of a phospholipid molecule in opposite directions, i.e. embedded into the two opposing bilayers while maintaining the headgroup in the interface. Although evidence for the occurrence of the extended conformation for phospholipids is sparse this conformation appears to be compatible with currently available experimental data. Of importance also is that the extended conformation allows for the fusion of two bilayer membranes to proceed with minimal exposure of the lipid hydrocarbon chains to water. It can also account for other features of membrane fusion such as lipid mixing in the intermediate state without mixing of the vesicle contents as well as for the molecular basis of the action of fusogenic lipids.     

The impact of tick parasites on the behaviour of the lizard Tiliqua rugosa

Populations of the Australian sleepy lizard, Tiliqua rugosa, near Mt. Mary, South Australia carry natural infestations of two tick species Aponomma hydrosauri and Amblyomma limbatum. In field experiments at two sites, 18 km apart, lizards with experimentally increased tick loads had smaller home ranges, moved shorter distances in a day, and were found basking more but moving less often than lizards from which ticks were experimentally removed. The results were consistent for adult lizards in two years, and for sub-adults in a third year. Laboratory trials showed that juvenile lizards that had tick infestations had lower sprint speeds than uninfested siblings, and that adults with tick infestations had less endurance than those that were uninfested. The results contrast with those of a previous survey that showed that lizards with high tick loads had greater body size and remained longer at a site, but indicate that there may be a balance, for lizards, between the fitness advantages in occupying habitats with high-quality resources, and the costs from parasites that also prefer those habitats. Received: 02 March 1999 / Accepted: 07 October 1999     

Mechanism of the development of functional hyperemia in the palatal salivary glands of the rat

At various regimens of the secretory activity in the palatile salivary glands, changes occurring in the transversal profiles of the postcapillary venules, but not of the blood capillaries, are most noticeable. Under food stimulation of secretion, the former dilate essentially, that can demonstrate certain functional hyperemia developing in the palatine salivary glands. Some previous experiments concerning interpretation of principles on the microcirculatory bed spatial organization give a good reason to suggest that dilatation of the postcapillary venules is connected with an increased blood perfusion in the canals of the preferrable blood stream. The postcapillary dilatation is possible because blood from the precapillaries gets into the capacitance blood microvessels and its volume at that moment is greater than the capacity of the venous microvessels. A suggestion is made that filtrative function of the palatile salivary glands depends on development of the functional hyperemia. It is possible, that this mechanism is universal, since owing to it, reflectory reactions of the salivary glands directed to the immediate secure of the oral cavity with a necessary amount of liquor become possible.     

Interaction of phytotropins with the NPA receptor

The chemical and stereochemical properties of phytotropins are described in terms of a receptor model, based on their ability to bind to a receptor isolated from maize coleoptiles. Their root gravitropic properties are correlated with their ability to bind to the receptor. It is suggested that their ability to inhibit auxin transport, without more, may not be enough to explain their physiological effects.