Flora Europaea: the background to the revision of Volume One

AKEROYD, J. R. & WALTERS, S. M. 1987. Flora Europaea: the background to the revision of Volume One. Flora Europaea, published 1964-80, is a synthetic catalogue of Europe's vascular plants. Its publication has provided a relatively stable taxonomic and nomenclatural framework for the study of the flora of the continent, and has stimulated much further research and publication. The revision of the first volume of Flora Europaea, at Reading University, has been necessary in order to accommodate new information, to satisfy the continued demand for a complete Flora of Europe, and to update the original text. The revision is being carried out in cooperation with other European and Mediterranean floristic projects.     

Dispersal ecology of Nuphar luteum (L.) Sibthorp & Smith: abiotic seed dispersal mechanisms

Nuphar luteum (Nymphaceae) is a water lily indigenous to the glacial lakes of the Rocky Mountains of the western United States. The seeds are negatively buoyant, but are dispersed across the water surface in two different manners: (1) within the floating fruits, and (2) within a buoyant, but water-soluble matrix that surrounds the seeds. Seed dispersal via fruits results in a clumped distribution, while seed dispersal mediated by the buoyant matrix results in scattered seed distributions. Experimental release of tagged fruits and seeds in nature show that fruit and seeds can travel up to 80 m/h on the water surface. Although seeds only float for about 72 h, this is adequate time for dispersal, especially in small glacial lakes that are connected via streams. By comparing historical lake-specific population distributions of N. luteurn using aerial photographs taken over a 36 year period we found little change in the overall intralake distribution of each population. We believe these historical patterns to be related to the mechanisms of fruit and seed dispersal.     

From primary to secondary growth: origin and development of the vascular system

Vascular tissue differentiation is essential to enable plant growth and follows well-structured and complex developmental patterns. Based on recent data obtained from Arabidopsis and Populus, advances in the understanding of the molecular basis of vascular system development are reviewed. As identified by forward and/or reverse genetics, several gene families have been shown to be involved in the proliferation and identity of vascular tissues and in vascular bundle patterning. Although the functioning of primary meristems, for example the shoot apical meristem (SAM), is well documented in the literature, the genetic network that regulates (pro)cambium is still largely not deciphered. However, recent genome-wide expression analyses have identified candidate genes for secondary vascular tissue development. Of particular interest, several genes known to regulate the SAM have also been found to be expressed in the vascular cambium, highlighting possible overlapping regulatory mechanisms between these two meristems.     

The origin and success of polyploids in the boreal circumpolar Flora: A new analysis

Summary

Data are summarised that support the secondary contact-balanced hybridity of polyploid evolution in plants. This states that polyploids are most likely to arise and achieve initial success in regions where alternate isolation plus differentiation followed by reunion and hybridisation, in the broadest sense of the word, are most likely to occur. The initial polyploids vary greatly in their evolutionary success. With the passage of time, a small proportion of the original neopolyploids evolve into mesopolyploids, that are widespread, aggressive colonisers, and become abundant over a broad geographical and ecological range. Even later, some of these become diploidised. The resulting paleopolyploids are more like diploids than their original polyploid ancestors with respect to gene pools, geographical distribution and different ecological situations occupied in any region. These conclusions are well supported by a preliminary analysis of polyploidy in the flora of Alaskan Beringia, but more extensive and thorough analyses are needed. Additional data support the hypothesis that chromosome doubling by itself does not adapt plants to withstand severe ecological conditions, such as cold and drought. Finally, high chromosome numbers in some species of angiosperms, plus even higher numbers in a few groups of spore bearing vascular plants, indicate that there is no generally valid ceiling to chromosome numbers. Polyploidisation occurs in cycles. If favourable adjustments of gene dosage occur between cycles, later cycles can include multiplication of base numbers that are already polyploid with reference to the original number of the genus or family.     

Ctenoplectridae and the origin of long-tongued bees*

The Ctenoplectridae (for the genera Ctenoplectra and Ctenoplectrina) are separated from the Melittidae, in which they have commonly been included. Ctenoplectrids differ from melittids in many characters, and are more closely related to the long-tongued families Fideliidae, Megachilidae, Anthophoridae, and Apidae than to the Melittidae and other short-tongued families. Ctenoplectrids are the sister-group of the long-tongued bees (and could be considered as long as long-tongued bees with labial palpi of short-tongued bees); melittids are the sister-group to the ctenoplectrids plus long-tongued bees. Characters are listed that support these relationships. Ctenoplectra species appear to be oil collectors from flowers of curcurbits. Some behavioural observations are included. Ctenoplectrina is a probable parasite in nests of Ctenoplectra, as it lacks the pollen and oil manipulating apparatus.     

From The Origin of Species to the origin of bacterial flagella

In the recent Dover trial, and elsewhere, the 'Intelligent Design' movement has championed the bacterial flagellum as an irreducibly complex system that, it is claimed, could not have evolved through natural selection. Here we explore the arguments in favour of viewing bacterial flagella as evolved, rather than designed, entities. We dismiss the need for any great conceptual leaps in creating a model of flagellar evolution and speculate as to how an experimental programme focused on this topic might look.     

From the origin of sex-determining factors to the evolution of sex-determining systems

Sex determination is typically classified as either genotypic or environmental. However, this dichotomy obscures the developmental origin and evolutionary modification of determinants of sex, and therefore hinders an understanding of the processes that generates diversity in sex-determining systems. Recent research on reptiles and fish emphasizes that sex determination is a multifactorial regulatory process that is best understood as a threshold dichotomy rather than as the result of genetically inherited triggers of development. Here we critically assess the relationship between the developmental origin of sex-determining factors and evolutionary transitions in sex-determining systems. Our perspective emphasizes the importance of both genetic and nongenetic causes in evolution of sex determination and may help to generate predictions with respect to the evolutionary patterns of sex-determining systems and the underlying diversity of developmental and genetic regulatory networks.     

The problem of reinforcement. From behavioural control to neurochemical background and the development of psychopathologies

At the first part of the paper a number of conceptions about psychophysiological mechanisms of reinforcement and its role in brain system activity is presented. At the second part, a significance of the mesolimbic and mesocortical dopaminergic systems in reinforcement process and the relationships between different components of behavioural control (signal, memory, actions, etc.) and intensity of dopamine transmission at the level of n. accumbens and frontal cortex are considered. At the final part of the paper the results of development of some psychopathologies and marginal conditions, related to a low or high content of dopamine in the above-mentioned structures, and possible neurophysiological mechanisms of their formation are presented.