Showing papers by "University of Liverpool published in 1974"

Courtship Persistence and Female-Guarding as Male Time Investment Strategies

Abstract: Time investment strategy is defined as the optimum allocation of times spent on given activities so as to achieve maximum reproductive success. Selective pressures on males to increase time invested in encountering females would be least in sessile and communally spawning species, and maximum in mobile species which spawn at low density and those which copulate. The present paper concerns male time investment in courtship persistence and female-guarding. Staying with a given female reduces the rate at which new females are encountered. Females are often unreceptive for some time after mating. Males often court unreceptive conspecific females; they can achieve a gain if the female rejection reactions can be overcome (rape) and the ejaculate can compete in the fertilization of the ova. Courtship of unreceptive females of closely related sympatric species is also considered adaptive. Though female unreceptivity will be favoured if hybrids are disadvantageous, males may gain by attempting rape if the fitness of hybrid offspring is high enough and the time investment favourable. A model is constructed to explain how optimum persistence durations are determined. This depends on 1) how the cumulative probability of insemination changes through time invested, 2) the encounter frequency, 3) the ejaculate cost (measured as feeding time investment/ejaculate), and 4) is modified by the pattern of gain from other types of female. Females can adapt to male persistence either by acceptance, by increasing rejection effectiveness, or by dispersing into another area where it is disadvantageous for males to search. This last solution may have been especially important in sympatric speciation. Male courtship duration with potentially receptive conspecific females may also be optimized. Variation in male persistence time may be due to assessment of particular situations. Female guarding has commonly evolved as a male time investment strategy. Precopulatory guarding appears to function to stake a claim to a female (or females) until she becomes receptive. This poses two problems : at what point in the female's reproductive life does it become advantageous for the male to guard, and how is guarding time optimized? Optimum guarding duration can be determined with the same model as for courtship persistence. If males adopt a given cue for closeness to receptivity for the onset of guarding, females showing the cue become scarce and selection may favour drive for earlier and earlier cues. This could be stabilized by the opposing selective pressures of 1) chances of finding a female closer to mating high enough, 2) female distribution suitably non-random with respect to mating, and 3) guarding investment more costly than searching investment in terms of male future reproductive success. Postcopulatory guarding appears to function to prevent loss in gain to a male due to sperm competition from other males. Such behaviour could evolve in conditions of high female receptivity and high encounter rate during an adequate overlap period (time per female during which ejaculates from different males can compete for fertilization of the ova), since males which guard after mating may waste less time and sperm than non-guarders. Its advantage is increased by a male-biassed sex ratio during the overlap period. The behaviour depends on the fact that second matings can compete in the fertilization of the ova, and postcopulatory guarding has its higlest advantage when the last male to mate fertilizes most eggs. Optimum guarding duration can be determined with basically the same model as before, and depends mainly on how sperm utilization is distributed within the overlap period.

The potential for evolution of heavy metals tolerance in plants.i. copper and zinc tolerance in agrostis tenuis

Abstract: A simple method of screening populations for the occurrence of metal tolerance was achieved by sowing seed samples on toxic formed by mixing metalliferous waste with a certain amount of ordinary potting soil: after 3-6 months tolerant individuals can easily be distinguished by their continuing growth whereas non-tolerant individuals will have died. Using this technique it was found that: i) Normal non-tolerant populations of the grass Agrostis tenuis contain a low frequency, 1-2 per cent, of individuals which survive on slightly ameliorated copper soil. Tests showed that some of these individuals have copper tolerances approaching those of fully tolerant populations. ii) The same occurred when populations were screened on zinc soil: but no survivors were found which had full zinc tolerance. iii) When already copper-tolerant seed was sown on zinc soil it behaved rather like non-tolerant seed. The survivors were shown to be both copper and zinc tolerant. This together with experiments on soil containing two metals indicates that tolerances to different metals are independent. iv) In all experiments individuals with a wide range of different tolerances could be found, and the number of survivors varied inversely with the amount of metal in the soil. This indicates that metal tolerance must be a continuously varying character with a threshold. v) It was concluded that high selection pressure acting on large populations can pick out rare gene combinations and change the characteristics of populations in a spectacular manner. Normal non-tolerant populations of the grass Agrostis tenuis contain a low frequency, 1-2 per cent, of individuals which survive on slightly ameliorated copper soil. Tests showed that some of these individuals have copper tolerances approaching those of fully tolerant populations. The same occurred when populations were screened on zinc soil: but no survivors were found which had full zinc tolerance. When already copper-tolerant seed was sown on zinc soil it behaved rather like non-tolerant seed. The survivors were shown to be both copper and zinc tolerant. This together with experiments on soil containing two metals indicates that tolerances to different metals are independent. In all experiments individuals with a wide range of different tolerances could be found, and the number of survivors varied inversely with the amount of metal in the soil. This indicates that metal tolerance must be a continuously varying character with a threshold. It was concluded that high selection pressure acting on large populations can pick out rare gene combinations and change the characteristics of populations in a spectacular manner.

The severe form of alpha thalassaemia is caused by a haemoglobin gene deletion.

Abstract: Two independent groups show that the absence of all or part of the globin α-chain gene is the origin of the homozygous α thalassaemia.

Quaternary Refugia in Tropical America: Evidence from Race Formation in Heliconius Butterflies

Abstract: The hypothesis of Haffer, Turner, and others, that patterns of race and species formation in the tropical forests of South America are the result of the isolation of populations in forest refugia during widespread climatic changes in the geologically recent past, is supported by the distribution of races in the butterfly genus Heliconius: the location of the refuges for these butterflies shows an excellent accord with the refuges deduced by Haffer in his studies of forest birds. The strict parallel variation through most of South America of the various races of H. melpomene, H. erato and of ten similarly-patterned species shows the result of selection for Mullerian mimicry; as the patterns must be subject to strong stabilizing selection, and as the low vagility of the butterflies normally produces isolation by distance even in a continuous population, it is suggested that the extreme divergence of pattern that some (but not all) Heliconius underwent in the forest refugia results from selection pressure in favour of mimicking the most abundant or distasteful local species, which would vary from refuge to refuge, rather than from geographical isolation per se.

The potential for evolution of heavy metal tolerance in plants

Abstract: The effects of increase in copper contamination in potting compost/copper mine waste mixtures on the germination and growth of the following species has been examined: Agrostis tenuis, Poa trivialis, Lolium perenne, Dactylis glomerata, Cynosurus cristatus, Anthoxanthum odoratum, Arrhenatherum elatius, Plantago lanceolata and Trifolium repens. Copper tolerant A. tenuis from Parys Mountain was used as control. Plant dry weight and plant height decreased with increase in proportion of copper contaminated soil in the mixtures, a conspicuous characteristic was the continued survival and growth of some individuals and the death of others at 1-4, 1-8 and mine soil levels. Agrostis tenuis and Dactylis glomerata produced fully copper tolerant survivors at a frequency of 0·08 per cent. By contrast Poa trivialis, Lolium perenne, Arrhenatherum elatius and Cynosurus cristatus produced survivors having indices of tolerance ranging from 7 to 20 per cent, tolerance, values too low to be considered as fully copper tolerant. Plantago lanceolata, Anthoxanthum odoratum, and Trifolium repens, failed to produce any survivors at all. The heritability of copper tolerance in the selected material: Agrostis tenuis, Lolium perenne, Dactylis glomerata, Arrhenatherum elatius, and copper tolerant A. tenuis was determined. Heritability is discussed in terms of breeding value. The results suggested that while the evolution of tolerance would be easy in A. tenuis it would be difficult in species such as Lolium perenne. The data presented are interpreted as evidence that the exclusion of some species from mine areas is because of their inability to evolve metal tolerance.

The reproductive behaviour and the nature of sexual selection in scatophaga stercoraria l. (diptera: scatophagidae). ix. spatial distribution of fertilization rates and evolution of male search strategy within the reproductive area.

Abstract: The present series of papers is aimed towards constructing a comprehensive model of sexual selection and its influence on reproductive strategy in the dung fly, Scatophaga stercoraria. The technique used links ecological and behavioral data obtained in the field with laboratory data on sperm competition, for which a model has already been developed (Parker, 1970a) . The reproductive behavior can be summarized as follows (see also Hammer, 1941, and previous papers in this series). Males wait around fresh cattle droppings for gravid females as they arrive to mate and lay their eggs in the dung. Females can mature several batches of eggs, but visit the dung only for mating and oviposition. Here males outnumber females by over 4: 1 (males spend much more time around the dung) and intra-male competition for females is intense. Mating may occur on the dropping or in the surrounding grass, and afterwards the male stays paired to the female (in a passive phase; Parker, 1970e) while she oviposits. Paired males guard females with elaborate reactions, but take-overs can occur in attacks from unpaired males. Here the new male mates immediately, before the female starts or resumes oviposition. The average number of eggs which will be fertilized by a given male as a result of a mating with a newlyarrived (\"incoming\") female can be calculated; so can egg gains due to take-overs either during mating or oviposition (Parker, 1970a). Evidence has been given (Parker, 1970b)

1,2,3-Triazoles

Abstract: Publisher Summary This chapter focuses on the chemistry of monocyclic1,2,3-triazoles as much of the chemistry of benzotriazoles and other fused systems has little in common with monocyclic triazole chemistry and provides a broad survey of methods of synthesis and reactions of triazoles. There has been considerable interest in 1,2,3-triazoles as light stabilizers and as optical brightening agents. They are also used as precursors for azapurines and similar heterocyclic systems that are potential carcinostatic agents. Three recognized classes of 1,2,3-triazoles are 1 H -, 2 H -, and 4 H -1,2,3-triazoles. Triazoles unsubstituted on nitrogen can be regarded either as 1 H - or as 2 H -derivatives, depending upon what tautomer is preferred. The first two classes can be regarded as aromatic systems whereas the third, the 4 H -system, cannot. This is reflected in the abundance of examples of 1 H - and 2 H -triazoles and the rarity of 4 H -triazoles. The thermal cycloaddition of azides to acetylenes is the most versatile route to 1 H -1,2,3-triazoles because of the wide range of substituents that can be incorporated into the acetylene and azide components. The base-catalyzed condensation of azides with activated methylene compounds is a well-established route to 1 H -triazoles and is the best route to triazoles bearing a 5-amino or hydroxy substituent and an aryl or carbonyl-containing function in the 4-position. The structure and spectroscopic and physical properties of triazole are discussed in the chapter.

Cathode spot structure and dynamics in low-current vacuum arcs

Abstract: A study has been made of cathode spot structure and dynamics in copper vacuum arcs for currents between 25 and 100 A using a high-magnification optical technique. The cathode spot consists of one or more electron emission zones or fragments with areas fluctuating between 10?10 m2 and 5?10?8 m2. The spot generally exists in one of two types. In the second type the average current density is about 5?1010 A m?2 and in the first type it is about (0?5-1)?1010 A m?2. The cathode spot undergoes continuous rebuilding in the form of fluctuations in the number and size of the fragments such that transitions in spot type, from type 1 to type 2 and vice versa, occur on average every 100 ?s. A possible explanation of the observations in terms of a cathode spot model based on temperature-field electron emission is discussed.

Phytosterol side chain biosynthesis.

Abstract: The typical plant sterols contain a substituent at C-24 of the side chain. This can be a methylene, ethylidene, methyl, or ethyl group; with the last three groups, all possible isomers have been reported in nature. The C-24 alkyl groups are derived by a transmethylation reaction from methionine. The details of several distinct alkylation mechanisms, which are now recognized in a range of lower and higher plants, have been reviewed. The operation of these different routes may have some phylogenetic significance.

Lipids in Glycan Biosynthesis

Abstract: Publisher Summary This chapter discusses the role of lipids in biosynthesis of glycan. The proper functioning of any living cell involves the control of phenomena at its surface and often beyond. This control is frequently mediated through polymers present in the vicinity of the cell surface and these are entirely carbohydrate (glycans) or contain a carbohydrate moiety attached to a peptide (peptidoglycans), a protein (proteoglycans), or a lipid portion (lipoglycans). The molecule of glycose, generalized sugar, is transferred from the nucleotide donor to a molecule of polyprenol monophosphate to form a molecule of polyprenol monophosphate glycose. The polyprenol phosphate glycoses are soluble in polar organic solvents and have frequently been termed lipid-linked intermediates. The glycosyl transferases of bacteria are generally assumed to be members of a membrane-bound synthetase complex. These involve sugars linked to undecaprenol monophosphate or to the diphosphate. It appears that di-or oligosaccharides are built up on the diphosphate intermediates and then transferred to polymer whereas only monosaccharides are transferred via monophosphate intermediates.

Colonisation of the early ocean floor

Abstract: THE earliest well documented evidence of macroscopic life is provided by stromatolitic algae from sediments deposited in intertidal or shallow marine environments at least 2,700 m.y. ago1. It is generally agreed that the earliest metazoan animals were soft-bodied forms which are rarely preserved but have left tracks, trails and burrows, collectively known as trace fossils. The earliest reliably identified trace fossil is a burrow system considered to have been produced by a worm-like organism, probably an annelid, found in shallow marine clastic sediments of the Grand Canyon Series (USA) suggested to be over 1,000 m.y. old2. Vertical burrows have been found in the Buckingham Sandstone in North Australia, also a shallow water deposit dated radiometrically as more than 790 m.y. old2, and in the Areyonga Formation, of similar age3. A more extensive collection of trace fossils has recently been recorded by Webby4 from the clastic shallow marine late Precambrian (about 600 m.y. old) Torrawangee Group of New South Wales (Australia) with three trace fossil genera positively identified: Planolites, Cochlichnus and Torrawanga. The late Precambrian Ediacara Beds of South Australia, also interpreted as shallow water clastic deposits, have yielded one positively identified trace fossil genus (Cochlichnus) and five other forms, all thought to have been produced by metazoa2. The common factor in these occurrences is the shallow water environment. Most of the trace fossils are burrows of infaunal deposit feeders which inhabited offshore environments of relatively quiet water; but the record of vertical burrows, now most commonly found in the high energy intertidal zone, may indicate occupation of even the shallowest water niches. There is as yet no indication of colonisation of the deep oceans during Precambrian times.

Malaria and the permeability of the host erythrocyte.

Abstract: WHEN an animal is infected with malaria some of the properties of the membrane of its erythrocytes are changed1. The fragility is increased2–5 and the transport of sodium, potassium and amino acids across the membrane is altered6–10. In most cases these alterations have been shown to be present in all erythrocytes from an infected animal and not just those containing parasites, which suggests a general pathological effect rather than a direct action of the parasite on its host cell.

Haemoglobin Icaria, a new chain-termination mutant which causes α thalassaemia

Abstract: THE human haemoglobin (Hb) variant Constant Spring (Hb CS) occurs in a number of racial groups and is involved in the aetiology of as many as 50% of all cases of Hb H disease, a disorder which presents a major public health problem in south-east Asia1,2. It has an elongated α chain of 172 residues which has probably arisen by mutation of the normal α-chain-terminating codon (UAA) at position 142 to a glutamine codon (CAA), allowing read-through into extrastructural codons at the 3′-end of the α mRNA3. We report here the characterisation of Hb Icaria, a second Hb with an elongated α chain of 172 residues. Its structure is identical with that of Hb CS except that residue α 142 is lysine instead of glutamine.

Motorway investment, industrial transport costs, and sub-regional growth: A case study of the M62

Abstract: Dodgson J. S. (1974) Motorway investment, industrial transport costs, and subregional growth: A case study of the M62, Reg. Studies 8, 75–91. This paper is concerned with the effects of motorway investment on regional economic growth. The role of regional development benefits in cost-benefit appraisals of highway investments is briefly reviewed. A model relating areal employment growth rates to transport costs and to other variables is developed, and then tested for a 30-zone area of the North of England using multiple regression techniques. Transport cost indices of accessibility developed in this model are then used to calculate the effect of a particular motorway, the M62, on industrial transport costs in the areas through which it passes. These results are used to give a very tentative indication of the employment changes in these areas which might follow the highway's construction.

The effect of kinetin and abscisic acid on water and ion transport in isolated maize roots

Abstract: Summary Exudation from the xylem of excised maize roots was studied in roots bathed in solutions containing kinetin or abscisic acid (ABA). Kinetin reduced the water permeability of the roots whilst ABA increased it. The action of both hormones was reversible and both were effective at concentrations of 10-6M and below. The possible in vivo role of these two hormones is discussed.