bluuebunny/crossref_metadata_2025 huggingface dataset:
FUNCTIONAL ASPECTS OF DROSOPHILA COURTSHIP
Authors: EWING ARTHUR W.
Published: January 2008

1. The elements that make up the courtship behaviour of males and of females are briefly described. It is pointed out that some of the terms used, such as female ‘repelling’ behaviour, are misleading as they do not reflect the known functions of the behaviours.

2. Evidence has been presented for a number of distinct pheromones with different functions during courtship. These claims are critically examined as the evidence is incomplete and at times conflicting. It seems unlikely that any pheromones other than those acting over a very short distance are involved in courtship. There is sound evidence for an aphrodisiac pheromone produced by all females which stimulates male courtship. A pheromone, which may be the same one, is produced by males less than 12 h old, which also stimulates male courtship. No function is ascribed to this pheromone. Fertilized females either produce less aphrodisiac pheromone or they may, in addition, produce one that inhibits male courtship. Mature males may also produce an inhibitory pheromone. Females produce a contact pheromone which is species‐specific and involved in sexual isolation. It is not at present clear whether this is different from the aphrodisiac pheromone.

3. There is considerable variability in the importance of vision in courtship. Many species will mate satisfactorily in the dark, suggesting that visual stimuli are not critical. Most species use vision to orient towards one another and for males to track and follow females. Even in light‐independent species such as D. melanogaster, specific visual signals may be used in courtship although they are not obligatory. Thus the red eye of the male is a sexual signal for females. Conversely, some light‐dependent species do not appear to make use of visual signals as a major factor in courtship. Some, however, do perform behaviours that are clearly visual and which may act to emphasize markings on wings, head or body.

4. The majority of Drosophila species perform courtship songs by vibrating one or both wings. The songs produced by males sexually stimulate the females. They are species specific and there is considerable indirect and some direct evidence that the songs are involved in sexual isolation. Males of many species produce two different songs during courtship and it is probable that one is concerned mainly with sexual stimulation and the other with species recognition. Females of certain species of Drosophila and Zaprionus also sing during courtship and these songs may aid species recognition by males. In addition males and unreceptive females perform ‘aggressive’ songs.

5. Almost all studies of Drosophila courtship have been made in very confined conditions in the laboratory. Interpretation of some of the results obtained in this way may require modification in the light of ecological research and observation of courtships under more natural conditions.
THE NATURAL CONTROL OF POPULATIONS OF BUTTERFLIES AND MOTHS
Authors: DEMPSTER J. P.
Published: January 2008

1. Life‐table data for 14 species of Lepidoptera are analysed by the k‐factor technique of Varley & Gradwell (1960). Two factors are shown to be of particular importance in determining fluctuations in abundance from one generation to the next. These key factors are predators and the failure of females to lay their full complement of eggs.

2. Data from 24 studies are reviewed to identify any density‐dependent factors that would be capable of regulating the populations about an equilibrium density. In eight studies no density‐dependent relationships could be identified, and in a further 13 the only density dependence demonstrated was due to intraspecific competition for resources. It is argued that competition is incapable of regulating populations at low density. In the other three studies, natural enemies are thought to be acting in a density‐dependent manner, but their ability to regulate the populations is questioned.

3. The frequency of over‐population and of extinction is reviewed and both appear to occur frequently in Lepidoptera. This, coupled with the failure of most studies to demonstrate the existence of density‐dependent processes capable of regulating populations, leads the author to reject the model of regulation about an equilibrium density in favour of a model of population limitation by a ceiling set by resources.

4. Fluctuations in resource availability may be important in determining variations in the abundance of many Lepidoptera, but at present too few ecologists have quantified the carrying capacity of habitats occupied by the species they study to generalize about this.
FACTORS AFFECTING THE SECRETION OF LUTEINIZING HORMONE IN THE EWE
Authors: MARTIN GRAEME B.
Published: January 2008

(1) Luteinizing hormone (LH) is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre‐pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle. Secretion is probably also pulsatile during the preovulatory surge of LH.

(2) The secretion of LH is affected by the ovarian steroids, oestradiol and progesterone, both of which act principally to reduce the frequency of the pulses. During the luteal phase the two steroids act synergistically to exert this effect, and during anoestrus oestradiol acts independently of progesterone. Androstenedione secreted by the ovary apparently has no role in the control of LH secretion.

(3) The amplitude of the pulses may also be affected by the steroids but there are conflicting reports on these effects, some showing that amplitude is lowered by the presence of oestrogen and others showing increases in amplitude in the presence of oestrogen and progesterone.

(4) The secretion of LH pulses is affected by photoperiod, social environment and nutrition. Under the influence of decreasing day‐length, oestradiol alone cannot reduce the frequency of pulses and the ewe experiences oestrous cycles. When day‐length is increasing, the hypothalamus becomes more responsive to oestradiol which reduces the frequency of the pulses.

(5) A hypothetical pheromone secreted by rams can increase the frequency of the LH pulses in anoestrous ewes and thereby induce ovulation, possibly by inhibiting the negative feedback exerted by oestradiol.

(6) The relationships between nutrition and reproduction are poorly understood, but it seems likely that the effects of nutrition are mediated partly through the hypothalamus and its control of the secretion of LH pulses.

(7) The pulses of LH secreted by the anterior pituitary gland are evoked by pulses of GnRH secreted by the hypothalamus. The location of the centre controlling the GnRH pulses and the neurotransmitter involved are not known.
DEVELOPMENTAL MECHANISMS UNDERLYING THE FORMATION OF ATAVISMS
Authors: HALL BRIAN K.
Published: January 2008

1. Atavisms emerge as evidence of localized modifications in development of an organ or of one of its parts. Different developmental processes can be triggered within the same organ rudiment, presumably in response to the same stimulus. We saw that that stimulus can have a genetic basis in a mutational event, which can be selected for. We also saw that atavism can be produced by experimental manipulation within developing systems ‐increased growth of the chick fibula, enamel production from avian ectoderm, and balancer formation in amphibians. Such atavisms are not based on heritable genetic changes. They indicate the developmental plasticity that exists within embryos and the relative ease with which development can be switched from one programme to another.

2. Examination of mutants (wingless chicks), limbless vertebrates and experimental manipulation of embryos, shows that cell death, inductive tissue interactions and altered patterns of growth are developmental mechanisms used in the formation of atavisms.

3. Differential development mechanisms can be triggered within the same organ at the same time to produce atavisms. In the guinea pig, formation of atavistic digit V involves prolongation of growth of metatarsal V whereas formation of atavistic digit I involves development of a new metatarsal I.

4. Secondary functional modifications ensure that the atavism is integrated with the other components of the functional unit, as illustrated by extra digits in horses or guinea pigs and fibulae in birds. Atavistic 2nd and 4th digits in horses arise by continued growth of their primordia. A consequent reduction in the growth rate of digit 3, the normal single functional digit, enables all three digits to attain approximately equal lengths and so potentially to function. The altered functional load transmitted to the limbs results in secondary but correlated alterations in muscles and skeletal elements in other portions of the limbs. The fact that embryonic digit 2 normally develops to a more advanced state than digit 4 explains why digit 2 more often develops atavistically, for if variation in growth rate is the basis for the atavistic digit, digit 2 has an advantage over digit 4.

5. Atavisms should not be an embarrassment to the evolutionary biologist. They are the outward and visible sign of a hidden potential for morphology change possessed by all organisms. Neither basic capacity to form the organ nor patterning information is lost. Modification of components of inductive tissue interactions helps to explain how organs are lost during evolution (also see Regal, 1977); retention of the basic mechanism explains how structures can be revived as atavisms (also see Rachootin & Thomson, 1981). Frequency of atavisms thus provides an indication of the degree of modification or loss of the underlying developmental programme.
PARASITISM AND THE UNIONACEA (BIVALVIA)
Authors: KAT PIETER W.
Published: January 2008

It is proposed that the incorporation of a unique parasitic stage in the life‐cycle of unionaceans which involves an obligate relationship between a vertebrate host, usually a fish, and a highly modified larval stage, the glochidium, has had far‐reaching consequences with respect to overall morphology, extent of species' geographic ranges, and rate of speciation in the group.

Glochidia are separable into three main types with respect to overall shape and attachment features, and are retained in variously modified brood pouches. When mature, glochidia are released in several different ways which reflect various adaptations involved in either attracting the fish host and/or increasing the probability of attachment. Glochidia do not seem capable of host selection, and the reaction of the host to the parasite seems to be the main factor in determining specificity. Release of glochidia is synchronized to correspond to periods of predictable host availability, such as during spawing migrations and nesting behaviour. Other adaptations include modifications of glochidial conglutinates to mimic host food items, and modifications of the unionacean mantle edges to attract hosts. In all cases, a good correlation exists between the type of lure used and host food preferences, but, despite these adaptations, host specificity among unionaceans seems low.

Parasitism among unionaceans is postulated to be mainly advantageous in terms of predictability of dispersal by habitat‐specific hosts, but parasitism is hypothesized to entail constraints in terms of the degree to which shell shape and life‐habit can be diversified among unionaceans. The type of host parasitized is considered to affect the rate of diversification among populations and speciation among unionaceans: those that parasitize strictly freshwater hosts are more likely to exhibit highly individualistic populations in different drainages with respect to molecular genetic and soft‐part characters, while those that parasitize anadromous or saltwater‐tolerant hosts show little differentiation among widely distributed populations.
BEHAVIOURAL ECOLOGY OF COCKROACHES*
Authors: SCHAL COBY , GAUTIER J.‐Y. , BELL WILLIAM J.
Published: January 2008

1. Cockroaches are ubiquitous in most habitats where insects occur. Although most reports on cockroaches are physiological in nature, sufficient information is available to indicate that forest, desert, and cave‐dwelling cockroaches select microhabitats on the basis of finely resolved environmental preferences. This is particularly true for oviparous females which select specific substrates for oviposition and embryogenesis. Selection and diel movements between microhabitats are related to diel changes in micrometeorological profiles and predation, feeding, and enhancement of sexual communication.

2. With some exceptions oviparous species live in wooded habitats; ovoviviparous species tend to occur in protected environments such as caves and logs. Oviparous species are exposed to greater predation, parasitism, and environmental pressures during embryogenesis than are ovoviviparous species, where internal incubation and some parental care reduce these risks. Most ovoviviparous species produce larger clutches, but the interval between broods is significantly longer than in oviparous species. Long gestation, clumping of food resources, and relatively little movement probably selected for male control of resources as a mate‐attraction tactic in ovoviviparous species; agonistic interactions, and in some cases morphological specializations for fighting, and highly ritualized behaviours are common. In most oviparous species, volatile pheromone communication and resource‐based aggregations are common. Rapid ovarian cycles and patchily distributed nutritional resources result in the need for greater mobility, and hence adults encounter greater risks.
Physiological Responses Of Birds To Flight And Running
Authors: BRACKENBURY JOHN
Published: January 2008

1. The energy required for sustained physical activity in flying and running birds is obtained from fatty acids mobilized from adipose stores under the influence of hormones. There is some evidence that glucagon, insulin and growth hormone may be involved in this process.

2. Energy expenditure can increase up to 14 times and 12 times resting values in flying and running birds, respectively. Energy expenditure varies only slightly over the normal range of flight speeds in individual species, but in running birds there is a linear correlation between oxygen consumption and speed. The slope of this relationship is an inverse function of body weight and indicates the energy cost of transport in ml O2.kg‐1.m‐1.

3. Increased oxygen demands by the working muscles are met by increased ventilation and circulation. Increased oxygen delivery by the blood is achieved by rises in cardiac output and oxygen extraction. Cardiac stroke volume changes relatively little and the increased cardiac output results mainly from an increase in heart rate. Regional blood distribution during exercise may be determined not only by the demands of the locomotory muscles but also by the need to increase heat loss from the skin and respiratory tract.

4. Ventilatory movements during flight are frequently synchronized in a I:I fashion with wing movements. Increased ventilation during flight and running may be stimulated, not only by the need for increased gas exchange, but also in order to raise heat loss by respiratory evaporation. Thermal hyperventilation carries a risk of CO, washout from the lungs and consequent blood alkalosis. The risk is minimized in some species by appropriate alterations in the rate and depth of breathing, which help to confine excess ventilation to the respiratory dead space.

5. Metabolic heat produced during exercise is either lost from the respiratory linings and the skin, or stored by the body with a resultant rise in body temperature. Changes in peripheral blood perfusion and active regulation of the feathers may assist cutaneous heat loss. Respiratory evaporation usually accounts for less than 30% of the total heat loss, even at high air temperatures, and becomes progressively less efficient at higher exercise intensities. At high air temperatures and high exercise intensities, most of the metabolic heat is stored, and exercise duration is limited as the body temperature approaches the upper lethal limit.
EVOLUTION OF CARDIOVASCULAR BARORECEPTOR CONTROL
Authors: BAGSHAW ROGER J.
Published: January 2008

During animal evolution the circulatory system has shown a progressive modification in structure, function and short‐term control.

Short‐term circulatory control has evolved from the limitation of a rising blood pressure via a reflex bradycardia to bidirectional control of blood pressure by appropriate reflex changes in heart rate, vascular resistance and impedance.

Relevant experimental data ranges from extensive in mammals to nugatory in invertebrates. Baroreceptor research in intervening animal groups is varied, being particularly sparse in birds. This research is reviewed. There are few interspecies comparisons of baroreceptor physiology. Available data is complicated by variation in the techniques employed for assessing baroreceptor function. In non‐mammalian research the correlation of heart rate changes to pharmacologically induced changes in blood pressure predominate. In mammalian baroreceptor research methods based upon the ability of discrete baroreceptor sites to effect changes in the peripheral vasculature are more prevalent. All methods are susceptible to modification by other experimental variables, particularly the anaesthetic state of the animal.

Available evidence shows a consistent response of a decreasing heart rate to baroreceptor loading throughout the vertebrates, with a progressive increase in the ability of the baroreceptors to change peripheral vascular resistance. These findings are consistent with the known, progressive trend from cholinergic to adrenergic control of the vascular system during evolution.

Known baroreceptor sites appear to be located so as to protect the end‐organ or‐organs primarily at risk from inappropriate blood pressure changes; namely the gill vasculature in the fish, pulmonary circulation in the Amphibia and Reptilia, and the brain and heart in higher animal groups.

It is postulated that the carotid sinus baroreceptors have developed in the Mammalia as a second functional baroreceptor site to provide extra protection against hypoperfusion of vital organs, particularly the heart and brain. In humans the dynamic aspects of cardiovascular carotid sinus control, particularly of skeletal muscle flow and integration with cardiopulmonary baroreceptors, may represent a specific response to the adoption of an upright stance. Extremes of environmental stress encountered in contemporary life may exceed the limitation of baroreceptor function in humans, as, for example, during gravitational loading particularly following periods of weightlessness and modification by endurance training.
KIN RECOGNITION: FUNCTIONS AND MECHANISMS A REVIEW
Authors: HEPPER PETER G.
Published: January 2008

General Summary

1. The aim of this paper has been to review the theory behind kin recognition to examine the benefits individuals obtain by recognizing their kin and to review the mechanisms used by individuals in their recognition of kin.

2. The ability to discriminate between kin and non‐kin, and between different classes of kin gives individuals advantages in fitness greater than individuals unable to recognize their kin. Four specific areas of benefit were considered: altruistic behaviour, co‐operative behaviour, parental care and mate choice. Finally the possibility that kin recognition has arisen as a byproduct from some other ability was discussed.

3. Mechanisms of kin recognition were considered with respect to three essential components of kin recognition. The cue used to discriminate kin, how individuals classify conspecifics as kin, etc. and how the ability to recognize kin develops.

4. Individuals can use a number of cues to discriminate kin from non‐kin. These were divided into cues presented by conspecifics (conspecific cues), of which three types were considered: individual, genetic and group/colony cues, and non‐conspecific cues, environmental, state and no cues. Kin recognition could be achieved by use of all these cues.

5. How individuals classify their conspecifics as kin, etc. can be achieved in a number of ways; dishabituation or self‐matching, which require no learning of kinship cues, or by phenotype matching or familiarity, both of which require the learning of kinship information.

6. It may be necessary for individuals to acquire information concerning kinship. This may be learned, and can be achieved in a number of ways; physiological imprinting, exposure learning or associative learning. Acquisition by these means is non‐selective, in that the cues which are most salient in the individual's environment will be learned. Selectivity can be introduced into this process to increase the probability of acquiring kinship information by a number of means; learning from parents, sensitive periods for learning and prenatal learning. Finally, kinship information could be supplied by recognition genes.

7. A distinction is drawn between cues which are used by an individual in the discrimination of kin, discriminators, and cues which are used by individuals in the acquisition of information about kinship, acquisitors.

8. Experiments used to support previous categories of mechanisms of kin recognition were examined in the light of this discussion and it was found that the results were open to a number of different interpretations and yielded little specific information about the mechanisms of kin recognition.

9. It was concluded that there was much evidence, both theoretical and experimental to support the proposed benefits individuals gain from recognizing kin, but much more research is required before the mechanisms of kin recognition are fully understood.
NITROGEN EXCRETION IN MARINE AND FRESH‐WATER CRUSTACEA
Authors: REGNAULT MICHÈLE
Published: January 2008

1. The major characteristic of aquatic Crustacea is ammonotelism as shown by the relative importance of various nitrogenous end‐products of their nitrogen metabolism.

2. In contrast to urico‐ and ureo‐genesis pathways, ammoniogenesis pathways have received recent attention; some specific enzymes such as glutamate dehydrogenase, AMP‐deaminase and glutaminase are now admitted to play a possible key role in ammoniogenesis of various crustacean species.

3. Processes involved in ammonia output through the gill epithelium (diffusion and/or ionic exchanges) are discussed though few data related to Crustacea are as yet available compared to those obtained in ammonotelic fishes.

4. The effects of some environmental factors as well as the physiological state of animals on nitrogen excretion of Crustacea are envisaged. The effects of temperature, salinity and NH4 concentration in the external medium are discussed first, followed by the changes in nitrogen excretion associated with the moult cycle, the nutritional state of animals and possible neuroendocrine control. It is demonstrated that the response of the excretion rate to these factors presents various patterns according to the species, its osmoregulatory abilities and its body reserves. Changes can also occur in the requisite metabolic pathways, thus increasing the difficulty of generalization.

5. In spite of the great diversity encountered within Crustacea an attempt to bring out general trends of their nitrogen excretion is proposed.

6. The present review is focused on metabolic and physiological aspects of crustacean nitrogen excretion but the significance of nitrogen release in nutrient regeneration in marine and fresh‐water ecosystems is foreseen.
THE EFFECT OF ADDED NITROGEN ON THE RATE OF DECOMPOSITION OF ORGANIC MATTER
Authors: FOG KÅRE
Published: January 2008

(1) N added to decomposing organic matter often has no effect or a negative effect on microbial activity, at least in the long term. More than 60 papers are cited in support of this statement.

(2) The negative effect of N is mainly found with recalcitrant organic matter with a high C/N ratio (straw, wood, etc.), whereas a positive effect of N is common for easily degradable organic material with low C/N ratio.

(3) The negative effect of N could be explained by: (i) N disturbs the outcome of competition between potent and less potent decomposers; (ii) through ‘ammonia metabolite repression’, N blocks production of certain enzymes, at least in basidiomycetes, and enhances breakdown of the most available cellulose, whereby recalcitrant lignocellulose accumulates; (iii) amino compounds condense with polyphenols and other decomposition products, forming ‘browning precursors’ which are toxic or inhibitory.

(4) The effect of adding N may depend on the microflora present.

(5) There are indications that some microorganisms have a ‘luxury uptake’ of N when it is present in sufficient amounts, thereby delaying N mineralization.

(6) The addition of N seems to increase the formation of water‐soluble, brown, recalcitrant compounds, but to decrease the amount of humus formed.
DEVELOPMENTAL PROCESSES, DEVELOPMENTAL SEQUENCES AND EARLY VERTEBRATE PHYLOGENY
Authors: LANGILLE ROBERT M. , HALL BRIAN K.
Published: January 2008

(1) We have put forth the position that evolutionary sequences can be deduced by an analysis of fundamental developmental sequences. Such sequences are highly conserved within a group and ‘contain steps which are necessary to achieve a developmental fate’. The premise of our work then, is that such fundamental sequences do not arise de novo time and time again but can be traced back through their evolutionary history in organisms which contain portions of the sequence.

(2) These highly conserved developmental sequences are in fact developmental constraints to evolution in as much as natural selection has not been able to discard them, but rather has utilized them in achieving evolutionary change.

(3) We have demonstrated the ability to use developmental data by producing an evolutionary sequence for the origin of the vertebrates using the processes of neuralization and cephalization, the latter due primarily to the influences of the neural crest and epidermal placodes. The evolutionary sequence created, while not novel in structure, is distinct in that it was created solely by following a developmental sequence that is highly conserved among the vertebrates. The sequence is:

(a) Chordamesoderm differentiates from the surrounding mesoderm and induces an overlying neural tube.

(b) Through the influence of neuralizing morphogens, the neural tube differentiates into anterior (fore‐, mid‐ and hindbrain) and posterior (spinal cord) parts. Cephalization has begun.

(c) Cephalization proceeds via the development of two new populations of embryonic cells, the neural crest, a derivative of the neural epithelium and the epidermal placodes, derivatives of the ectoderm immediately adjacent to the neural tube. These two populations contribute significantly to the subsequent development of the vertebrate head including the skeleton, connective tissues, cranial nerve and sensory organs.

Sequence (a) occurs in the most primitive protochordates and is one of the differences between the chordates and deuterostome invertebrates. Sequence (b) occurred next leading to a protochordate with a differentiated central nervous system, but lacking most vertebrate head structures. Sequence (c) signalled the beginning of the true vertebrates or branchiates (after the branchial arches which all vertebrates' share) since the production of a neurocranium, viscerocranium, cephalic armour, teeth and cranial peripheral ganglia was only possible with the acquisition of this developmental step.

(4) Current investigations into the cellular, molecular and biochemical basis of developmental sequences will allow biologists to test for the integrity of these developmental sequences and to test for their presence in the ontogenies of any species in question. These investigations will ascertain the validity of determining an evolutionary sequence based on a particular developmental process(es) as outlined in the present paper.
WILD MICE IN THE COLD: SOME FINDINGS ON ADAPTATION
Authors: BARNETT S. A. , DICKSON R. G.
Published: January 2008

The house mouse, Mus domesticus, can thrive in natural environments much below its optimum temperature. Thermogenesis is then above that at more usual temperatures. In addition, body weight, and the weights of brown adipose tissue and the kidneys, may be higher than usual. In free populations of house mice cold lowers fertility and may prevent breeding. Other possible limiting factors on breeding are food supply, shelter for nesting and social interactions.

In captivity, wild‐type house mice exposed to severe cold (around o °C) at first adapt ontogenetically by shivering and reduced activity. But raised thermogenesis is soon achieved without shivering; nest‐building improves; and readiness to explore may be enhanced. Endocrine changes probably include, at least initially, a rise in adrenal cortical activity and in catecholamine secretion. Some females become barren, but many remain fertile. The maturity of fertile females is, however, delayed and intervals between births are lengthened; nestling mortality rises. A limiting factor during lactation may be the capacity of the gut. Similar adaptive changes are observed during winter in some species of small mammals that do not hibernate. But neither the house mouse nor other species present a single, universal pattern of cold‐adaptation.

Wild‐type mice bred for about 10 generations in a warm laboratory environment (20–23 °C) change little over generations. In cold they become progressively heavier and fatter at all ages; they mature earlier, and nestling mortality declines. The milk of such ‘Eskimo’ females is more concentrated than that of controls. If ‘Eskimo’ mice are returned to a warm environment, they are more fertile, and rear heavier young, than controls that remained in the warm. Despite the heavier young, litter size is not reduced: it may be increased, probably as a result of a higher ovulation rate.

Parental effects have been analyzed by cross‐fostering and hybridizing. Survival, growth and fertility are all favourably influenced by the intra‐uterine and nest environments provided by ‘Eskimo’ females. ‘Eskimo’ males are also better fathers. Hence after ten generations the phenotype of cold‐adapted house mice shows the combined effects of (a) an ontogenetic response to cold, (b) a superior parental environment and (c) a changed genotype.

The secular changes in the cold that lead to this phenotype give the appearance of evolution in miniature; but it is equally possible that they represent a genetical versatility that allows rapid, reversible shifts in response to environmental demands. The adaptation of house mice to extreme environments, whether progressive or reversible, is aided by a complex interaction between generations.
HOW FREQUENT ARE SUPERIOR GENOTYPES IN PLANT BREEDING POPULATIONS?
Authors: SIMMONDS N. W.
Published: January 2008

A search of plant breeding literature has produced 69 examples in which reasonable judgements could be made as to potential for genetic advance. The crops covered are all inbreeders (predominantly cereals) or outbred clones. The average potential for genetic advance (roughly 60 % of examples were favourable) seemed to be far higher than would usually be expected and to indicate therefore that excellent new crop varieties should be more frequent than experience suggests. The discrepancy may be partly explained by various biases but the main conclusion is that superior genotypes are indeed fairly frequent but that selection efficiency is too low to take better advantage of them.
PATTERNS IN THE GEOGRAPHICAL RANGES OF SPECIES
Authors: GASTON KEVIN J.
Published: January 2008

1. A growing number of studies have documented patterns in species geographic ranges relevant to the study of community structure. These include patterns in the frequency of geographic ranges of different sizes, and in the interaction of range sizes with population abundances and variabilities, body sizes, trophic characteristics and extinction probabilities.

2. Agreement between hypothesized and observed relationships is reasonably good, but we do not know how general the patterns are. Analysis of patterns has focused upon a few taxonomic groups, a bias largely resulting from a lack of information on the geographic distributions of most taxa.

3. Many of the patterns are interrelated, and although theoretical bases to all the patterns can be suggested, it is possible that some are artifacts.

4. Taylor power plots give us a means of making predictions about population behaviour as it pertains to geographic ranges. Some of these predictions suggest that previous conceptions of such interactions have been too narrow, but empirical analyses of these patterns will be hampered by the difficulty of measuring population variability.

5. In general, our knowledge of the structure, and spatial and temporal behaviour, of species geographic ranges remains poor.
SEX RATIOS AND CONDITIONS REQUIRED FOR ENVIRONMENTAL SEX DETERMINATION IN ANIMALS
Authors: KORPELAINEN HELENA
Published: January 2008

Conclusions and Summary

Environmental sex determination (ESD) is a system of sexual determination that is influenced by a variable environment. Once sex is determined it is then fixed for life. The model of Charnov & Bull (1977) proposes that ESD is favoured by natural selection when an individual's fitness as a male or female is strongly influenced by environmental conditions and when the individual has little control over which environment it will experience. Adaptive sex ratio variation is considerably easier for organisms with ESD, and this feature is the ultimate cause for the evolution and maintenance of ESD. ESD is taxonomically widely expressed, and more cases are likely to be discovered. Both environmental and genotypic sex determination mechanisms are found in closely related species. Evidence of geographical variation in the degree and in the critical environmental values of ESD within the same species has also been discovered, e.g. in the fish Menidia menidia and in the crustacean Gammarus duebeni.

The factors causing sex determination in invertebrates include temperature, daylength, nutrition, density, humidity, ionic composition of the environment, pH, carbon dioxide, UV light, metabolic products, parasites, exposure to the opposite sex of the same species, and in parasitoids also host size, age and type. In vertebrates temperature is the dominant factor causing sex determination, though in fish also pH, salinity, light, water quality and nutrition, and in turtles water potential of the substrate have some effect on the sex expression. Most of these factors influence growth through resource availability or developmental speed. In most cases of ESD in invertebrates and fish, the environmental factor has a gradual effect on the sex expression, in contrast to the typical steep threshold mode found in reptiles. These differences might be due to the fact that invertebrates exhibiting ESD are commonly parasitic or confined to aquatic environments, where less spatial microhabitat differentiation exists. Sex ratio data available from nature for animals with ESD are quite limited, except for reptiles. In the laboratory sex ratios can be varied more widely than what is observed in nature.

There are a number of characteristic features some of which are found in each species exhibiting ESD: (1) Patchy environments, (2) variable sex ratios, (3) parthenogenesis in addition to bisexuality, (4) parasitism, (5) aquatic habitats, (6) sexual dimorphism, (7) females larger than males, and (8) local mate competition.
AUTOXIDATION OF OXYMYOGLOBIN: A MEETING POINT OF THE STABILIZATION AND THE ACTIVATION OF MOLECULAR OXYGEN
Authors: SHIKAMA KEIJI
Published: January 2008

The primary events of haemoprotein reactions with molecular oxygen have been re‐examined by placing special emphasis upon the reduction properties of dioxygen.

In the stepwise reduction of O2 to water via hydrogen peroxide, the addition of the first electron is an unfavourable, uphill process with the midpoint potential of –0.33 V, all the subsequent steps being downhill. This thermodynamic barrier to the first step is, therefore, a most crucial ridge located between the stabilization and the activation of dioxygen performed by haemoproteins.

If the proteins have a redox potential much higher than –0.33 V, molecular oxygen must bind to the proteins stably and reversibly. In Mb or Hb, however, the FeO2 centre is always subject to a nucleophilic attack of the water molecule or hydroxyl ion, which can enter the haem pocket from the surrounding solvent. These can cause irreversible oxidation of the FeO2 bonding to the ferric met‐form with generation of the superoxide anion.

In cases of the oxygen activation, if haemoproteins have a redox potential lower than or close to –0.33 V, the first reduction of O2 to O−2 would be a spontaneous process. Cytochrome P‐450 provides such an example and can facilitate the subsequent addition of electrons that leads to the breaking of the O–O bond to yield the hydroxylating species.

As to the proteins whose redox potential is not facilitative and appreciably higher than –0.33 V, a bimetallic, concerted, two‐equivalent reduction of the bound dioxygen to the peroxide level would be much more favoured without the intermediate formation of O−2. This is probably the case of cytochrome c oxidase for the reduction of O2 to water.

The redox potential diagrams thus visualize various aspects of the ways haemoproteins overcome their thermodynamic constraints and carry out their specific functions in the stabilization and the activation of molecular oxygen.
GENETICS OF HORIZONTAL RESISTANCE TO DISEASES OF CROPS
Authors: SIMMONDS N. W.
Published: January 2008

(1) Horizontal resistance (HR) to diseases of crops has the following leading features: it is polygenically controlled and must be studied by biometrical‐genetic methods; it is pathotype‐non‐specific and essentially ‘durable’; it has several components (e.g. infection rate, latency period, sporulation potential) which tend to be correlated; its use is relevant to the control of all classes of pathogen (fungi, bacteria, viruses, insects, nematodes); though often unrecognized, it is very common and generally the means by which ‘minor’ diseases remain minor. HR may be contrasted with ‘vertical resistance’ (VR) which is procured by major genes and is pathotype‐specific. VR has uses in particular circumstances but has often failed against airborne epidemic pathogens such as many rusts; hence the importance of understanding HR.

(2) In this review the genetic evidence of HR is reviewed and examples are summarized in appendices. Very diverse crops, places and pathogens are represented. So far as may be judged, HR is indeed universal, and found or constructable wherever sought. The most important genetic evidence is based on generation mean and variance analysis, general and specific combining ability, offspring‐parent regression and response to selection. Useful supplementary evidence comes from historical observations, continuity and repeatability of resistance and yield‐related effects.

(3) The main conclusions are that HR is universally available, usually highly heritable and responsive to selection, already keeps a host of crop diseases down to acceptably low levels and has socio‐economically attractive features that are likely to increase its use in the future. In particular, it offers long‐term stability of performance that must be valuable to small farmers in the Third World and is environmentally attractive because successful breeding programmes minimize the need for environmentally damaging chemical protectants. ‘Green’ pressures are likely to favour HR and some relevance to public policy is thereby implied.
OF MICE AND KIN: THE FUNCTIONAL SIGNIFICANCE OF KIN BIAS IN SOCIAL BEHAVIOUR
Authors: BARNARD C. J. , HURST J. L. , ALDHOUS PETER
Published: January 2008

1. Sharing recent ancestry (kinship) increases the degree of genetic similarity between individuals, where genetic similarity could mean anything from sharing a particular allele to sharing an entire genome.

2. Genetic similarity can influence behavioural and other responses between individuals in a number of ways, discriminatory and non‐discriminatory. All are likely to result in kin bias, because of the correlation between genetic similarity and kinship, but only some should be regarded as involving kin discrimination.

3. Non‐discriminatory kin bias could arise through close relatives sharing, for instance, physical characteristics (such as those influencing competitive ability), thresholds of behavioural response or requirements for particular resources.

4. Discriminatory kin bias could arise through the direct perception of genetic similarity between individuals (direct similarity discrimination) or the use of cues likely to correlate with genetic similarity (indirect similarity discrimination – of which kin discrimination is one form). Alternatively, it could arise incidentally through mistaken identity or discrimination at some other level, such as species identification.

5. Experiments with laboratory and wild house mice have revealed kin bias in a number of contexts, including (a) parental and infanticidal behaviour, (b) sexual development and behaviour and (c) investigatory behaviour and passive body contact among juveniles and adults.

6. While kin bias in mice has been interpreted as evidence for kin discrimination, there are several problems with such an interpretation. These include (a) pronounced and complex effects of familiarity on discrimination, (b) a high risk of error‐proneness in the indirect cues used in apparent kin discrimination and (c) weak and easily disrupted kin bias effects in certain contexts.

7. Consideration of social structure and discriminatory responses within populations of wild house mice leads to an alternative explanation for some kin bias in terms of incidental discrimination based on social group membership.

8. Several results from laboratory experiments suggest incidental discrimination is a more parsimonious explanation than kin discrimination for some intrasexual kin bias in behaviour. However, kin or direct similarity discrimination appears to be the most likely explanation for other aspects of intrasexual kin bias and for intersexual kin bias.
THE CONTROL OF SEXUAL MORPHOGENESIS IN THE ASCOMYCOTINA
Authors: DYER PAUL S. , INGRAM DAVID S. , JOHNSTONE KEITH
Published: January 2008

(1) A series of factors controls sexual morphogenesis in the Ascomycotina, a process involving the formation of novel structures such as ascocarps (fruit bodies) and asci (sacs containing spores) during sexual reproduction.

(2) Environmental and genetic factors must be correct before Ascomycetes may sexually reproduce. Compatibility in many heterothallic species is under polygenic control, with the mating type loci and also other genetic factors determining the productivity of sexual crosses.

(3) Classical genetic studies have shown that sexual morphogenesis involves the expression of a series of developmentally regulated genes, and this has been confirmed by recent molecular studies which have demonstrated changes in patterns of mRNA and protein synthesis during ascocarp formation.

(4) Hyphal differentiation leading to the formation of mature fruit bodies occurs in response to a series of signals, which include various physical and chemical factors.

(5) Chemical sex factors have been identified which are believed to have important regulatory or nutritional roles in sexual morphogenesis. These include the following.

(a) Diffusible sex hormones which may regulate developmental switching between asexual and sexual modes of reproduction, including (i) pheromones involved with the induction of gametangia and gamete attraction, and (ii) sex morphogens involved with triggering particular stages of fruit body formation. (b) Sexual growth substances which are required as nutrients, and may be precursors for the production of sex hormones, or metabolites used in the synthesis of novel sexual structures. Most of these sex factors are lipids.

(6) Certain sex morphogens and sexual growth substances have been shown to exhibit activity in a variety of fungal species, suggesting that fungi of related phylogenetic descent may utilize similar metabolites or signalling factors during sexual reproduction.

(7) Phenoloxidase enzymes may catalyse hyphal aggregation in developing fruit bodies.

(8) Initial stages of ascocarp development may occur independently of the events of the sexual cycle. However, a link(s) with the functional ascogenous hyphae is needed for the formation of morphologically mature ascocarps.

(9) Suitable environmental conditions are sufficient to trigger sexual morphogenesis in homothallic Ascomycetes. However, an extra level of control is present in heterothallic species, with a compatible partner required to complete sexual reproduction. This may be partly because novel regulatory products, formed by the combined action of the mating type loci of different partners, are required for further ascocarp development.

(10) Further research is required to identify more fungal chemical sex factors and to determine the role of environmental stress in controlling sexual morphogenesis, and how this may be related to temporal patterns in the expression of mating type genes.
STRESS, EXTINCTIONS AND EVOLUTIONARY CHANGE: FROM LIVING ORGANISMS TO FOSSILS
Authors: PARSONS P. A.
Published: January 2008

1. Natural populations are exposed to environmental stress of varying intensities. This provides a reference point for extrapolations from the living biota to fossils and vice versa.

2. Evolutionary change is likely when there are resources in excess of maintenance and survival needs. It is largely precluded at species borders by the metabolic costs of stress; from this follows climatic tracking by species.

3. A relatively small increase in abiotic stress could underlie extinctions of stress‐sensitive endemic species and the spread of stress‐resistant generalist and widespread species. Widespread fossil species appear resistant to extinction under the stress level of normal background extinctions.

4. Synergistic interactions among generalized stresses should increase the likelihood of extinctions, especially for stresses with energetic consequences.

5. Some marine organisms survived the K‐T mass extinction event because of stress‐evasion mechanisms such as stress‐resistant life‐cycle stages with low metabolic rates.

6. In moderately stressed and narrowly fluctuating environments, sufficient genetic variability and metabolic energy should be available to permit adaptation. In these environments phyletic gradualism is expected.

7. In highly stressed and widely fluctuating environments, a punctuated evolutionary pattern is expected whereby stasis occurs most of the time.

8. Evolutionary patterns therefore can vary depending on the details of the interaction between stress, environmental fluctuations, energy availability and genetic variability.

9. Little evolutionary change is expected when the availability of energy is severely restricted. Examples include cave animals in stable but stressed environments and ‘living fossils’ in widely fluctuating but stressed environments.

10. Since the primary effect of abiotic stress may be at the level of energy carriers, a reductionist approach permits generalisations in considering extinctions and conditions under which diversification is likely.