The controlling factors limiting maximum body size of insects

The purpose of this study is to consider the controlling factors limiting maximum body size of insects. For this analysis, we set up and quantitatively verify the following working hypothesis: insect body sizes can be explained only by the historical changes in the oxygen supply. The present study focuses on the body size of the Protodonata and Odonata. The amount of oxygen needed and that of oxygen entering the insect body was calculated using allometric equations. The theoretical maximum sizes at each geologic time were estimated from palaeo‐atmospheric oxygen partial pressure and compared with the maximum size of known fossilized insects. The historical change in fossilized insect sizes was much larger than that in theoretical sizes. Additionally, from the Jurassic, despite an increase in the partial pressure of oxygen, which would theoretically increase maximum size, the maximum size of fossilized insects became smaller. These findings are inconsistent with the expectations of the working hypothesis. Oxygen supply is likely to partially limit the maximum size of insects with additional factors.     

Phenotypic correlations among plant parts in Iberian Papilionoideae (Fabaceae)

BACKGROUND AND AIMS: Different plant organs may show varying degrees of form diversification or conservatism across phylogenetically related taxa. The present study uses data from a recent systematic study of Iberian Papilionoideae to investigate diversification and covariation in reproductive and vegetative plant parts. The appropriateness of imprecise (but comprehensive) taxonomic quantitative information is tested. METHODS: Organ size covariation and phenotypic correlations were studied among tribes, genera and species. Scale relationships were investigated by Reduced Major Axis regression. Variables used were the maximum dimensions of calyx, corolla, keel petal, fruit, seed, stipule, leaflet and petiole. KEY RESULTS: As regards tribe averages, the length of the corolla and that of calyx correlated positively and significantly. In contrast, pod length was unrelated to corolla size and largely tribe-specific. Within genera, the sizes of calyx, corolla and fruit sometimes covaried linearly (e.g. Lathyrus species) and other times did not (Genista, Astragalus). CONCLUSIONS: Information from taxonomic studies can be useful to establish major phenotypic correlations in plants. Results underscore the implications of tribal ownership in the Papilionoideae and illustrate the extensive morphological diversification of pods relative to flowers in this group.     

Palynological evidence for the impact of colonial settlement within lowland fynbos: A high‐resolution study from the Verlorenvlei,southwestern Cape Province,South Africa

The present distribution of lowland fynbos of the southwestern Cape coastal forelands occupies a unique yet threatened existence. Long renowned for its extraordinary species richness, the lowland fynbos now reveals a decline in diversity following the impact of recent European settlement. Fine resolution pollen analysis, conducted on a dated sediment core from the Verlorenvlei, reveals a 250 year pattern of debilitating vegetation transformations. The arrival of European colonists in the area circa 1700 is noted in the sedimentary sequence, not only with respect to changes in the pollen spectra, but also through concomitant changes in the nature and timing of sedimentation. The rapid extermination of large mammalian fauna, overgrazing by domestic stock and decades of agricultural mismanagement in a marginal landscape are considered to be the principal factors responsible for deliterious alterations of the natural disturbance regime.     

Sinistral snail shells in the sea: developmental causes and consequences

The paucity of sinistral (left-coiling) relative to dextral (right-coiling) species of gastropods in the marine realm is an enigma. In Conus , one of the most diverse marine animal genera, sinistral shell coiling has evolved as a species-wide character only once. Fossils of this species, Conus adversarius , are found in Upper Pliocene and lowermost Pleistocene deposits in the southeastern USA. Conus adversarius had nonplanktonic larval development; this may have been a critical factor for the early establishment of the species, as well as sinistral marine species in other clades. Notably, most specimens of aberrantly sinistral modern Conus are derived from typically dextral species that have nonplanktonic development. If C. adversarius was reproductively isolated from dextral conspecifics, then this species may provide an example of nearly instantaneous sympatric speciation in the fossil record. Furthermore, the common and widespread – while geologically short-lived – fossil shells of C. adversarius show large amounts of variability in form and this variation may be related, at least in part, to a pleiotropic effect associated with the reversed coiling direction of this species.     

Major stages in the evolution of primate neurocrania

An important constraint on the evolution of primate skeletons is the isometric relationship which exists between skeletal weight and body weight. The evolution of primate skulls during the Tertiary and Quaternary periods indicates that redeployment of bone mass took place largely within the skull (i.e. between proximate ossifying centres) and that the major vector was from the splanchnocranium towards the neurocranium. This vector of bone mass redeployment accords well with the general treand within primates of increased encephalisation over time. There are however, several interesting examples of vectors which were oriented in the opposite sense, in particular in the robust australopithecine lineage, in which the emphasis on bone mass deployment was towards the splanchnocranium and away from the neurocranium. A fuller understanding of skeletal isometry, and a wider application in comparative anatomy may throw much light on the evolution of skeletal systems, and it may resolve somelong-standing debates. Among these may be identification of the selection pressures which have led to dental and alveolar reduction inHomo sapiens sapiens (bone mass redeployment into the neurocranium) and perhaps an explanatation for some types of osteoporosis in old people whose body weight decreases may result in isometric skeletal mass decreases (for every 100 gms muscle tissue loss, there will be about 7 gms of bone tissue loss).     

Body-size scaling in an SEI model of wildlife diseases

A number of wildlife pathogens are generalist and can affect different host species characterized by a wide range of body sizes. In this work we analyze the role of allometric scaling of host vital and epidemiological rates in a Susceptible-Exposed-Infected (SEI) model. Our analysis shows that the transmission coefficient threshold for the disease to establish in the population scales allometrically (exponent = 0.45) with host size as well as the threshold at which limit cycles occur. In contrast, the threshold of the basic reproduction number for sustained oscillations to occur is independent of the host size and is always greater than 5. In the case of rabies, we show that the oscillation periods predicted by the model match those observed in the field for a wide range of host sizes.The population dynamics of the SEI model is also analyzed in the case of pathogens affecting multiple coexisting hosts with different body sizes. Our analyses show that the basic reproduction number for limit cycles to occur depends on the ratio between host sizes, that the oscillation period in a multihost community is set by the smaller species dynamics, and that intermediate interspecific disease transmission can stabilize the epidemic occurrence in wildlife communities.     

一个新的养分效应数学模型

在养分效应研究中,多采用二次抛物线模型,从容（1991）在米氏方程的基础上提出一个改进抛物线模型,这两种模型都是对称性模型,也即是把养分正负效应的速率视为相同,而大多数实际情形并非如此．本文建立了一个反映养分效应普遍现象的非对称性模型,两个应用实例表明新模型较之原来的模型无论在拟合度（残差平方和）还是在生物学意义方面都具有明显的优越性．     

Plant physiology in theory and practice: An analysis of the WBE model for vascular plants

The theoretical model of West, Brown and Enquist (hereafter WBE) proposed the fractal geometry of the transport system as the origin of the allometric scaling laws observed in nature. The WBE model has either been criticized for some restrictive and biologically unrealistic constraints or its reliability debated on the evidence of empirical tests. In this work, we revised the structure of the WBE model for vascular plants, highlighting some critical assumptions and simplifications and discuss them with regard to empirical evidence from plant anatomy and physiology. We conclude that the WBE model had the distinct merit of shedding light on some important features such as conduit tapering. Nonetheless, it is over-simplistic and a revised model would be desirable with an ontogenetic perspective that takes some important phenomena into account, such as the transformation of the inner sapwood into heartwood and the effect of hydraulic constraints in limiting the growth in height.     

Generation of oscillatory behavior in the Laisk model of photosynthetic carbon assimilation

The metabolic pathways in photosynthesis are modelled as an interconnected series of chemical reactions representing the electron transfer system, the carbon reduction cycle and starch and sucrose synthesis according to the model of Laisk and Walker [Proc R Soc Lond 227, 281–302 (1986)]. The model is formulated as a set of non-linear differential equations using mass-action kinetics, and stimulated for transient behaviour using an interactive simulation language. The model responses to switched light demonstrate the existence of oscillatory behaviour, similar to that found experimentally in O₂ evolution and chlorophyll fluorescence, and explain known transient behaviour. The model is also used to investigate the source of oscillatory behaviour in the phosphate translocator, and other transient phenomena associated with the cyclic electron transfer system.Abbreviations PQ plastoquinone - PQH₂ plastoquinol - PC_red reduced plastocyanin - PC_ox oxidised plastocyanin - P_i ortho (inorganic) phosphate in chloroplasts - P_io inorganic orthophosphate in cytosol - TP triose phosphate - Ru5P ribulose-5-phosphate - RuBP ribulose bisphosphate - PGA phosphoglyceric acid - HP hexose phosphate - HP_o hexose phosphate-total sugar phosphate in cytoplasm - S starch - SU sucrose     

Epizoochorous and post-dispersal processes in a rare plant species: Jurinea cyanoides (L.) Rchb. (Asteraceae)

We used Jurinea cyanoides as a model plant species to ask the question whether sheep play a dual role in enabling the establishment of a rare species (1) by epizoochorous transport of diaspores and (2) by influencing post-dispersal processes. We carried out two field experiments in sand grassland (Jurineo–Koelerietum glaucae) in the northern upper Rhine valley, Germany. In the first one, we attached diaspores to the fleeces of sheep and assessed retention time, seed shadow, seedling emergence and establishment. In the second one, diaspore displacement by sheep trampling was investigated.It could be shown that establishment of J. cyanoides is possible after sheep-epizoochorous dispersal, but is severely limited by several factors. First, retention time is mostly short (only 18% of the diaspores remained in the fleeces >2 h). Thus, the seed shadow is concentrated around the place of attachment (mostly <5 m distance, maximum 17 m). Second, seedling emergence of dispersed achenes is severely limited by above-ground granivory (99%). Third, establishment is limited by seedling mortality (68%) due to summer drought. The seedlings germinated from achenes that had been incorporated into the soil (or into deeper parts of the bryophyte layer). The second experiment showed that sheep trampling significantly enhanced the incorporation of achenes into the soil compared with controls. Our study gives evidence that sheep can play a dual role: diaspore transport and facilitation of establishment by trampling.     

Mode of life of the Silurian uncoiled gastropod Semitubina sakoi n. sp. from Japan

Semitubina sakoi n. sp. from the late Silurian of Japan represents the second species of this genus and also the first record of a Silurian gastropod in Japan. The gastropod shells occur in a thin mudstone bed and were found to be encrusted exclusively by corallites of ? Favosites sp. These corallites reveal that encrustation proceeded as the gastropod shells grew. The ecological relationship between the two organisms is considered to be symbiotic. This mode of life allowed the coral to live on a muddy substrate because clear sea water passed over the colony as the gastropod moved along. The gastropod benefited from this relationship by being protected from shell-boring or shell-crushing predators by the encrusting corallite. In Semitubina sakoi the body whorl is separated from the penultimate one by a considerable gap in a later growth stage and S. sakoi has been cited as one of the uncoiled gastropods. The uncoiling of this gastropod results primarily from rapidly increasing whorl translation rate in the latest growth stage. Taking the symbiotic relationship with ? Favosites sp. into consideration, a deposit feeding or benthic scavenging mode of life is suggested for this gastropod.     

Common allometric response of open-grown leader shoots to tree height in co-occurring deciduous broadleaved trees

Background and Aims

Morphology of crown shoots changes with tree height. The height of forest trees is usually correlated with the light environment and this makes it difficult to separate the effects of tree size and of light conditions on the morphological plasticity of crown shoots. This paper addresses the tree-height dependence of shoot traits under full-light conditions where a tree crown is not shaded by other crowns.

Methods

Focus is given to relationships between tree height and top-shoot traits, which include the shoot''s leaf-blades and non-leafy mass, its total leaf-blade area and the length and basal diameter of the shoot''s stem. We examine the allometric characteristics of open-grown current-year leader shoots at the tops of forest tree crowns up to 24 m high and quantify their responses to tree height in 13 co-occurring deciduous hardwood species in a cool-temperate forest in northern Japan.

Key Results

Dry mass allocated to leaf blades in a leader shoot increased with tree height in all 13 species. Specific leaf area decreased with tree height. Stem basal area was almost proportional to total leaf area in a leader shoot, where the proportionality constant did not depend on tree height, irrespective of species. Stem length for a given stem diameter decreased with tree height.

Conclusions

In the 13 species observed, height-dependent changes in allometry of leader shoots were convergent. This finding suggests that there is a common functional constraint in tree-height development. Under full-light conditions, leader shoots of tall trees naturally experience more severe water stress than those of short trees. We hypothesize that the height dependence of shoot allometry detected reflects an integrated response to height-associated water stress, which contributes to successful crown expansion and height gain.     

Postpleistocene evolution of the brain?

The number of extraneurons (N_c) has been calculated with the formulae of Jerison ('63) for prehistoric population samples to check the hypothesis that N_c may not only increase by increasing of cranial capacity but also by decreasing of body-weight (gracilisation). Body weight of skeletal populations has been estimated by the formula of Debetz ('67). Samples from the Western part of Europe and Egypt support the hypothesis, but Eastern europoid samples display opposite relations: N_c increases with robusticity. It seems (as Jerison already suggested) that N_c is no measurement of the level of behavior in the populations of H. sapiens; but it may point towards allometric differences between West and East, which are also known for other characters.