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Evolutionary Trends (evolutionary + trend)

Distribution by Scientific Domains

Life Sciences	73%
Earth and Environmental Science	11%
3 Other Domains	16%

Distribution within Life Sciences

Evolution	20%
Plant Science	15%

Selected Abstracts

The evolution of arthropod limbs

BIOLOGICAL REVIEWS, Issue 2 2004
Geoff A. Boxshall
ABSTRACT Limb morphology across the arthropods is reviewed using external morphological and internal anatomical data from both recent and fossil arthropods. Evolutionary trends in limb structure are identified primarily by reference to the more rigorous of the many existing phylogenetic schemes, but no major new phylogenetic inferences are presented. Tagmosis patterns are not considered, although the origins and patterns of heteronomy within the postantennulary limb series are analysed. The phenomenon of annulation is examined and two basic types of annuli are recognised: terminal and intercalary. The annulation of the apical segment of a limb results in the formation of terminal flagella, and is typical of primarily sensory appendages such as insect and malacostracan antennules and maxillary palps of some hexapods. Intercalary annulation, arising by subdivision of existing subterminal segments, is common, particularly in the tarsal region of arthropodan walking limbs. Differentiating between segments and annuli is discussed and is recognised as a limiting factor in the interpretation of fossils, which usually lack information on intrinsic musculature, and in the construction of groundplans. Rare examples of secondary segmentation, where the criteria for distinguishing between segments and annuli fail, are also highlighted. The basic crown-group arthropodan limb is identified as tripartite, comprising protopodite, telopodite and exopodite, and the basic segmentation patterns of each of these parts are hypothesised. Possible criteria are discussed that can be used for establishing the boundary between protopodite and telopodite in limbs that are uniramous through loss of the exopodite. The subdivision of the protopodite, which is typical of the postantennulary limbs of mandibulates, is examined. The difficulties resulting from the partial or complete failure of expression of articulations within the mandibulate protopodite and subsequent incorporation of partial proto-podal segments into the body wall, are also discussed. The development and homology between the various exites, including gills, on the postantennulary limbs of arthropods are considered in some detail, and the question of the possible homology between crustacean gills and insect wings is critically addressed. The hypothesis that there are only two basic limb types in arthropods, antennules and postantennulary limbs, is proposed and its apparent contradiction by the transformation of antennules into walking limbs by homeotic mutation is discussed with respect to the appropriate level of serial homology between these limbs. [source]

TRITURUS NEWTS DEFY THE RUNNING-SWIMMING DILEMMA

EVOLUTION, Issue 10 2006
Lumíl Gl
Abstract Conflicts between structural requirements for carrying out different ecologically relevant functions may result in a compromise phenotype that maximizes neither function. Identifying and evaluating functional trade-offs may therefore aid in understanding the evolution of organismal performance. We examined the possibility of an evolutionary trade-off between aquatic and terrestrial locomotion in females of European species of the newt genus Triturus. Biomechanical models suggest a conflict between the requirements for aquatic and terrestrial locomotion. For instance, having an elongate, slender body, a large tail, and reduced limbs should benefit undulatory swimming, but at the cost of reduced running capacity. To test the prediction of an evolutionary trade-off between swimming and running capacity, we investigated relationships between size-corrected morphology and maximum locomotor performance in females of ten species of newts. Phylogenetic comparative analyses revealed that an evolutionary trend of body elongation (increasing axilla-groin distance) is associated with a reduction in head width and forelimb length. Body elongation resulted in reduced maximum running speed, but, surprisingly, also led to a reduction in swimming speed. The evolution of longer tails was associated with an increase in maximal swimming speed. We found no evidence for an evolutionary trade-off between aquatic and terrestrial locomotor performance, probably because of the unexpected negative effect of body elongation on swimming speed. We conclude that the idea of a design conflict between aquatic and terrestrial locomotion, mediated through antagonistic effects of body elongation, does not apply to our model system. [source]

Double-nesting behaviour and sexual differences in breeding success in wild Red-legged Partridges Alectoris rufa

IBIS, Issue 4 2009
FABIÁN CASAS
Double-nesting behaviour, a rare breeding system in which females lay in two nests, one incubated by herself and the other one by her mate, could be considered an intermediate stage in the evolutionary trend from biparental to uniparental care of single clutches. We examined the occurrence and success of double-nesting behaviour in Red-legged Partridges Alectoris rufa in Central Spain. Clutch size and hatching success were recorded, as well as the variation in these between years and between incubating sexes. Participation in incubation was higher for females (94.76%) than males (41.0%), and the proportion of incubating males varied markedly between years, with no incubating males in one dry year and approximately 50% of males incubating in other years. There was significant variation among years and between sexes in laying date, clutch size and hatching success. Clutch size decreased with later laying date in males and females. The probability of clutch loss to predation differed between sexes, being much higher for nests incubated by females. Our results suggest that both rainfall and predation influence the occurrence and success of double-nesting. [source]

Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis

JOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2008
P. HASALOVÁ
Abstract A detailed field study reveals a gradual transition from high-grade solid-state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular, foliation-parallel bodies of nebulitic migmatite within the eastern part of the Gföhl Unit (Moldanubian domain, Bohemian Massif). The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well-equilibrated banded microstructure by crystallization of new interstitial phases (Kfs, Pl and Qtz) along feldspar boundaries and by resorption of relict feldspar and biotite. The grain size of all felsic phases decreases continuously, whereas the population density of new phases increases. The new phases preferentially nucleate along high-energy like,like boundaries causing the development of a regular distribution of individual phases. This evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases. To explain these data, a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation. In this model, infiltrating melt passes pervasively along grain boundaries through the whole-rock volume and changes completely its macro- and microscopic appearance. It is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation. The melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding, indicating that the melt distribution was controlled by the deformation of the solid framework. The microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms. The migmatite microstructures developed by granular flow accompanied by melt-enhanced diffusion and/or melt flow. However, an AMS study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains. [source]

Opisthonotal glands in the Camisiidae (Acari, Oribatida): evidence for a regressive evolutionary trend

JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 1 2009
G. Raspotnig
Abstract Paired, sac-like and typically large opisthonotal glands (syn. oil glands), mainly considered for chemical protection and communication, characterize the so-called ,glandulate Oribatida' which include the Parhyposomata, Mixonomata, Desmonomata and Brachypylina but also the Astigmata. Among these groups distinct evolutionary trends affect the morphology of glands and their secretion profiles, thereby rendering them highly informative characters with phylogenetic significance. One striking tendency, convergently occurring in a few glandulate groups, leads to the degeneration or even complete regression of opisthonotal glands. In this study, a first example of coherent evolutionary steps towards opisthonotal gland degeneration is described by using desmonomatan Camisiidae as a model: Opisthonotal glands in representatives of genus Platynothrus still show morphologically and chemically ancient conditions with fairly-well developed glandular reservoirs. Secretion patterns mainly consist of a characteristic set of terpenes and aromatics (,astigmatid compounds') as found in outgroups such as desmonomatan Trhypochthoniidae. Progressive states of regression of opisthonotal glands, along with a reduction of component-richness and amounts of secretions, occur in representatives of Heminothrus and, more conspicuously, in species of Camisia, most likely indicating a consistent evolutionary trend. This trend towards opisthonotal gland atrophy may be due to novel alternative and cheap strategies of passive defense in more-derivative camisiids , such as mechanical protection by encrustation of the cuticle , that possibly compensate for the lack of chemical defenses. Zusammenfassung Paarige, sackförmige und typischerweise große opisthosomatische Drüsen (syn. Öldrüsen), deren Sekrete hauptsächlich zum chemischen Schutz und zur Kommunikation dienen sollen, kennzeichnen die sogenannten glandulaten Hornmilben. Innerhalb dieser Hornmilbengruppe, die die Parhyposomata, Mixonomata, Desmonomata, Brachypylina, aber auch die astigmaten Milben umfasst, waren die Öldrüsen offensichtlich in morphologischer und chemischer Hinsicht deutlich unterschiedlichen evolutiven Trends unterworfen; damit sind Öldrüsen ein phylogenetisch außerordentlich wichtiger Merkmalskomplex in der Oribatiden-Systematik geworden. Eine auffällige Tendenz allerdings, die offensichtlich mehrmals konvergent auftritt, führt zur Rückbildung der Drüsen in bestimmten glandulaten Gruppen. In der vorliegenden Arbeit wird zum ersten Mal eine zusammenhängende Linie solcher Rückbildungsstadien am Beispiel der Camisiidae (Desmonomata) beschrieben: die weitgehend noch gut ausgebildeten Öldrüsen von Vertretern der Gattung Platynothrus zeigen morphologisch und chemisch ursprüngliche Merkmale. Sekretprofile bestehen hauptsächlich aus einem charakteristischen Set von Terpenen und Aromaten ("astigmatid compounds'), das auch in Außengruppen wie z.B. bei Trhypochthoniiden auftritt. Fortschreitende Stadien der Rückbildung von Öldrüsen, verbunden mit einer Verarmung der Sekretprofile und einer Verringerung an Sekretmengen, treten in Vertretern von Heminothrus und, noch auffälliger, bei verschiedenen Arten von Camisia auf: dieses Phänomen, übereinstimmend mit einem auf morphologischen Daten basierenden Systemvorschlag, wird als evolutiver Trend innerhalb der Camisiidae gedeutet. Dieser Trend zur Öldrüsenrückbildung ist möglicherweise mit einer alternativen Strategie passiver Verteidigung bei weiter abgeleiteten Camisiiden zu erklären, die Krustenbildungen aus Cerotegument und Bodenpartikeln auf der Körperöberfläche als mechanischen Schutz gegen Prädatoren nützen. Diese möglicherweise energetisch billige Variante könnte den Verlust chemischer Verteidigung über Öldrüsensekretion kompensieren. [source]

Comparative study between N -body and Fokker,Planck simulations for rotating star clusters , I. Equal-mass system

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Eunhyeuk Kim
ABSTRACT We have carried out N -body simulations for rotating star clusters with equal mass and compared the results with Fokker,Planck models. These two different approaches are found to produce fairly similar results, although there are some differences with regard to the detailed aspects. We confirmed the acceleration of the core collapse of a cluster due to an initial non-zero angular momentum and found a similar evolutionary trend in the central density and velocity dispersion in both simulations. The degree of acceleration depends on the initial angular momentum. Angular momentum is being lost from the cluster due to the evaporation of stars with a large angular momentum on a relaxation time-scale. [source]

Genetic parsimony: a factor in the evolution of complexity, order and emergence

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2006
A. R. D. STEBBING
Two conjectures, drawn from Gregory Chaitin's Algorithmic Information Theory, are examined with respect to the relationship between an algorithm and its product; in particular his finding that, where an algorithm is minimal, its length provides a measure of the complexity of the product. Algorithmic complexity is considered from the perspective of the relationship between genotype and phenotype, which Chaitin suggests is analogous to other algorithm-product systems. The first conjecture is that the genome is a minimal set of algorithms for the phenotype. Evidence is presented for a factor, here termed ,genetic parsimony', which is thought to have helped minimize the growth of genome size during evolution. Species that depend on rapid replication, such as prokaryotes which are generally r -selected are more likely to have small genomes, while the K -strategists accumulate introns and have large genomes. The second conjecture is that genome size could provide a measure of organism complexity. A surrogate index for coding DNA is in agreement with an established phenotypic index (number of cell types), in exhibiting an evolutionary trend of increasing organism complexity over time. Evidence for genetic parsimony indicates that simplicity in coding has been selected, and is responsible for phenotypic order. It is proposed that order evolved because order in the phenotype can be encoded more economically than disorder. Thus order arises due to selection for genetic parsimony, as does the evolution of other ,emergent' properties. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88, 295,308. [source]

Polyploidy and new chromosome counts in Helichrysum (Asteraceae, Gnaphalieae)

BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2008
MERCÈ GALBANY-CASALS
Mitotic chromosome numbers are reported for 31 populations representing 28 taxa of Helichrysum. Twelve are new and eight others provide confirmation of a unique previous reference. A new chromosome number, 2n = 42, is reported for H. odoratissimum. Polyploidy is confirmed as the most significant evolutionary trend in chromosome number within the genus. Chromosome data agree with trends observed in phylogenetic studies: a South African and diploid origin of the genus, followed by a radiation and diversification in southern Africa and several migrations towards the north of the African continent, the Mediterranean basin and Asia. Expansion and diversification of the genus have been accompanied by several genome duplications which have led to the acquisition of the tetraploid, hexaploid and octoploid levels, all in several independent events. Both autopolyploidy and allopolyploidy are suggested as probable speciation agents within the genus. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 511,521. [source]

Two Zosterophyll Plants from the Lower Devonian (Lochkovian) Xitun Formation of Northeastern Yunnan, China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009
Jinzhuang XUE
Abstract: Two zosterophyll plants are described from the Lower Devonian (Lochkovian) Xitun Formation of Qujing, Yunnan, China. Xitunia spinitheca gen. et sp. nov. has stalked sporangia laterally attached on the axis in a helical arrangement. Sporangia are dorsoventrally flattened and composed of two unequal valves; the adaxial valve is round in face view, while the abaxial valve is larger than the former, triangular or wedge-shaped, and radially bears long spiny appendages along the distal margin. Xitunia shows new variation of sporangial morphology within the zosterophylls. Zosterophyllum minorstachyum sp. nov. has K-shaped branchings at the basal parts and small-sized terminal spikes, which consist of round to elliptical sporangia arranged helically. This paper provides new data on the diversity of plant types during Lochkovian when rare vascular plants were reported. As for various species of Zosterophyllum in South China, their apparent evolutionary trend of features from the Late Silurian to Early Devonian (Emsian) is discussed. [source]

Technology Forecasting: From Emotional to Empirical

CREATIVITY AND INNOVATION MANAGEMENT, Issue 2 2001
Michael S. Slocum
Technology Forecasting has evolved from being a methodology based on emotional responses to one predicated on data collection. The Theory of Inventive Problem Solving (TRIZ) is a theory based on empirical data that relates technological evolution to the same stages of biological macro-evolution. This paper will explore the major emotional forecasting methods as well as discuss part of TRIZ Technology Forecasting called Maturity Mapping. The reader will briefly be introduced to eight evolutionary trends based on TRIZ. [source]

A contribution to the phylogeny of annual species of Astragalus (Fabaceae) in the Old World using hair micromorphology and other morphological characters

FEDDES REPERTORIUM, Issue 5-6 2007
F. Taeb
A cladistic analysis including 32 annual and nine perennial species of Astragalus along with four outgroups from related genera is performed using characters from hair micromorphology, floral morphology and some other morphological sources. The hair characters show the similar evolutionary trends as known earlier for the genus Astragalus, but they exhibit lower variability in comparison with other major subgroups of Astragalus. The obtained data was compared with the data from molecular systematics. The most important results of this study are: 1) medifixed hairs are developed at least two times among annual Astragalus, 2) fruit morphology, does not provide strong evidence in delimitation of the sections within annual Astragalus, 3) presence of long and thick hairs with largely tuberculate base should be considered as an advanced character, and can be regarded as an important synapomorphy among annual Astragalus, 4) the position of some species of the large and heterogeneous sect. Sesamei, e.g. A. persepolitanus and A. coronilla, and their possible close relationship with the species of the sect. Oxyglottis should be re-assessed, 5) the species of the sect. Ankylotus show close relationship to sect. Platyglottis, based on floral morphology and hair characters, 6) there are not enough supports from hair, floral morphology and biogeography for considering A. annularis, A. epiglottis (as Glottis epiglottis), A. pelecinus (as Biserrula pelecinus) and A. vogelii (as Podlechiella vogelii) as separated from Astragalus (as suggested by molecular data). Moreover, the inclusion of Barnebyella calycina again in Astragalus is well supported by morphological data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Zur Phylogenie annueller Arten von Astragalus (Fabaceae) in der Alten Welt auf der Basis der Haar-Mikromorphologie und anderer morphologischer Merkmale Eine kladistische Analyse, umfassend 32 annuelle und neun perennierende Arten von Astragalus mit vier Nebengruppen verwandter Gattungen, wurde auf der Basis von Mikromorphologie, Blütenmorphologie und einiger anderer morphologischer Quellen vorgenommen. Die Merkmale der Haare zeigen ähnliche evolutionäre Tendenzen wie sie bereits früher von der Gattung Astragalus bekannt waren, doch zeigen sie im Vergleich zu anderen, umfassenderen Untergruppen von Astragalus, eine geringere Variabilität. Die so gewonnenen Daten werden mit Daten der molekularen Systematik verglichen. Die wichtigsten Ergebnisse dieser Studie sind: 1. Die im mittleren Bereich fixierten Haare entwickelten sich innerhalb der annuellen Astragalus zweimal; 2. Die Morphologie der Früchte liefert keinen eindeutigen Beweis zur Abgrenzung der Sektionen innerhalb der annuellen Astragalus -Arten; 3. Die Anwesenheit langer, dicker Haare mit einer großen tuberkularen Basis ist als abgeleitetes Merkmal zu betrachten und kann als wichtige Synapomorphie innerhalb annueller Astragalus -Arten betrachtet werden; 4. Die Stellung einiger Arten der großen, heterogenen Sekt. Sesamei, z. B. A. persepolitanus und A. coronilla und ihre möglicherweise enge Verwandtschaft mit den Arten der Sekt. Oxyglottis sollte neu beurteilt werden. 5. Die Arten der Sekt. Ankylotus zeigen aufgrund ihrer Blütenmorphologie und der Merk- male ihrer Haare enge Verwandtschaft zur Sekt. Platyglottis; 6. Es gibt nicht genügend Hinweise bezüglich Haare, Blütenmorphologie und Biogeographie um A. annularis, A. epiglottis (als Glottis epiglottis), A. pelecinus (als Biserrula pelecinus) und A. vogelii (als Podlechiella vogelii) von Astragalus abzutrennen (wie es die molekularen Daten aussagen). Dagegen ist die Wiedereingliederung von Barnebyella calycina in die Gattung Astragalus gut durch die morphologischen Daten gestützt. [source]

Lopingian (Late Permian) high-resolution conodont biostratigraphy in Iran with comparison to South China zonation

GEOLOGICAL JOURNAL, Issue 2-3 2010
Shu-Zhong Shen
Abstract Lopingian (Late Permian) conodonts and stratigraphy in northwest and central Iran have become hotly debated issues recently. We here use a sample-population approach, to develop a high-resolution conodont biostratigraphic framework for the Lopingian of Iran based on a re-examination of collections studied by Sweet from the Kuh-e-Ali Bashi area, northwest Iran; samples from the Abadeh C section and a nearby Permian-Triassic boundary section in the Abadeh area; and on published data. Six Wuchiapingian conodont zones, the Clarkina dukouensis, C. asymmetrica, C. leveni, C. guangyuanensis, C. transcaucasica and C. orientalis zones, and eight Changhsingian conodont zones, the Clarkina wangi, C. subcarinata, C. changxingensis, C. bachmanni, C. nodosa, C. yini, C. abadehensis and C. hauschkei zones, are described and figured. Diagnoses of ontogenetic characteristics to population variations of all the zone-naming species are re-described based on a sample-population taxonomic concept. The high-resolution Lopingian conodont zonation in Iran is closely correlative with its counterpart in South China. However, slightly different evolutionary trends in Clarkina populations existed at the very end of the Changhsingian in Iran and South China. This reflects a geographical cline and/or facies dependence and endemism in Clarkina populations rather than stratigraphic incompleteness of sections in either Iran or South China. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Thermal evolution of pre-adult life history traits, geometric size and shape, and developmental stability in Drosophila subobscura

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2006
M. SANTOS
Abstract Replicated lines of Drosophila subobscura originating from a large outbred stock collected at the estimated Chilean epicentre (Puerto Montt) of the original New World invasion were allowed to evolve under controlled conditions of larval crowding for 3.5 years at three temperature levels (13, 18 and 22 °C). Several pre-adult life history traits (development time, survival and competitive ability), adult life history related traits (wing size, wing shape and wing-aspect ratio), and wing size and shape asymmetries were measured at the three temperatures. Cold-adapted (13 °C) populations evolved longer development times and showed lower survival at the highest developmental temperature. No divergence for wing size was detected following adaptation to temperature extremes (13 and 22 °C), in agreement with earlier observations, but wing shape changes were obvious as a result of both thermal adaptation and development at different temperatures. However, the evolutionary trends observed for the wing-aspect ratio were inconsistent with an adaptive hypothesis. There was some indication that wing shape asymmetry has evolutionarily increased in warm-adapted populations, which suggests that there is additive genetic variation for fluctuating asymmetry and that it can evolve under rapid environmental changes caused by thermal stress. Overall, our results cast strong doubts on the hypothesis that body size itself is the target of selection, and suggest that pre-adult life history traits are more closely related to thermal adaptation. [source]

Sexually antagonistic coevolution in insects is associated with only limited morphological diversity

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2006
W. Eberhard
Abstract Morphological traits involved in male,female sexual interactions, such as male genitalia, often show rapid divergent evolution. This widespread evolutionary pattern could result from sustained sexually antagonistic coevolution, or from other types of selection such as female choice or selection for species isolation. I reviewed the extensive but under-utilized taxonomic literature on a selected subset of insects, in which male,female conflict has apparently resulted in antagonistic coevolution in males and females. I checked the sexual morphology of groups comprising 500,1000 species in six orders for three evolutionary trends predicted by the sexually antagonistic coevolution hypothesis: males with species-specific differences and elaborate morphology in structures that grasp or perforate females in sexual contexts; corresponding female structures with apparently coevolved species-specific morphology; and potentially defensive designs of female morphology. The expectation was that the predictions were especially likely to be fulfilled in these groups. A largely qualitative overview revealed several surprising patterns: sexually antagonistic coevolution is associated with frequent, relatively weak species-specific differences in males, but male designs are usually relatively simple and conservative (in contrast to the diverse and elaborate designs common in male structures specialized to contact and hold females in other species, and also in weapons such as horns and pincers used in intra-specific battles); coevolutionary divergence of females is not common; and defensive female divergence is very uncommon. No cases were found of female defensive devices that can be facultatively deployed. Coevolutionary morphological races may have occurred between males and females of some bugs with traumatic insemination, but apparently as a result of female attempts to control fertilization, rather than to reduce the physical damage and infections resulting from insertion of the male's hypodermic genitalia. In sum, the sexually antagonistic coevolution that probably occurs in these groups has generally not resulted in rapid, sustained evolutionary divergence in male and female external sexual morphology. Several limitations of this study, and directions for further analyses are discussed. [source]

The continuity of microevolution and macroevolution

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2002
Andrew M. Simons
Abstract A persistent debate in evolutionary biology is one over the continuity of microevolution and macroevolution , whether macroevolutionary trends are governed by the principles of microevolution. The opposition of evolutionary trends over different time scales is taken as evidence that selection is uncoupled over these scales. I argue that the paradox inferred by trend opposition is eliminated by a hierarchical application of the ,geometric-mean fitness' principle, a principle that has been invoked only within the limited context of microevolution in response to environmental variance. This principle implies the elimination of well adapted genotypes , even those with the highest arithmetic mean fitness over a shorter time scale. Contingent on premises concerning the temporal structure of environmental variance, selectivity of extinction, and clade-level heritability, the evolutionary outcome of major environmental change may be viewed as identical in principle to the outcome of minor environmental fluctuations over the short-term. Trend reversals are thus recognized as a fundamental property of selection operating at any phylogenetic level that occur in response to event severities of any magnitude over all time scales. This ,bet-hedging' perspective differs from others in that a specified, single hierarchical selective process is proposed to explain observed hierarchical patterns of extinction. [source]

Opisthonotal glands in the Camisiidae (Acari, Oribatida): evidence for a regressive evolutionary trend

The DEEP2 galaxy redshift survey: evolution of the colour,density relation at 0.4 < z < 1.35

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
Michael C. Cooper
ABSTRACT Using a sample of 19 464 galaxies drawn from the DEEP2 Galaxy Redshift Survey, we study the relationship between galaxy colour and environment at 0.4 < z < 1.35. We find that the fraction of galaxies on the red sequence depends strongly on local environment out to z > 1, being larger in regions of greater galaxy density. At all epochs probed, we also find a small population of red, morphologically early-type galaxies residing in regions of low measured overdensity. The observed correlations between the red fraction and local overdensity are highly significant, with the trend at z > 1 detected at a greater than 5, level. Over the entire redshift regime studied, we find that the colour,density relation evolves continuously, with red galaxies more strongly favouring overdense regions at low z relative to their red-sequence counterparts at high redshift. At z, 1.3, the red fraction only weakly correlates with overdensity, implying that any colour dependence to the clustering of ,L* galaxies at that epoch must be small. Our findings add weight to existing evidence that the build-up of galaxies on the red sequence has occurred preferentially in overdense environments (i.e. galaxy groups) at z, 1.5. Furthermore, we identify the epoch (z, 2) at which typical ,L* galaxies began quenching and moved on to the red sequence in significant number. The strength of the observed evolutionary trends at 0 < z < 1.35 suggests that the correlations observed locally, such as the morphology,density and colour,density relations, are the result of environment-driven mechanisms (i.e. ,nurture') and do not appear to have been imprinted (by ,nature') upon the galaxy population during their epoch of formation. [source]

Circadian rhythms and the evolution of photoperiodic timing in insects

PHYSIOLOGICAL ENTOMOLOGY, Issue 4 2009
DAVID S. SAUNDERS
Abstract. This review discusses possible evolutionary trends in insect photoperiodism, mainly from a chronobiological perspective. A crucial step was the forging of a link between the hormones regulating diapause and the systems of biological rhythms, circadian or circannual, which have independently evolved in eukaryotes to synchronize physiology and behaviour to the daily cycles of light and darkness. In many of these responses a central feature is that the circadian system resets to a constant phase at the beginning of the subjective night, and then ,measures' the duration of the next scotophase. In ,external coincidence', one version of such a clock, light now has a dual role. First, it serves to entrain the circadian system to the stream of pulses making up the light/dark cycle and, second, it regulates the nondiapause/diapause switch in development by illuminating/not illuminating a specific light sensitive phase falling at the end of the critical night length. Important work by A. D. Lees on the aphid Megoura viciae using so-called ,night interruption experiments' demonstrates that pulses falling early in the night lead to long-day effects that are reversible by a subsequent dark period longer than the critical night length and also show maximal sensitivity in the blue,green range of the spectrum. Pulses falling in the latter half of the night, however, produce long-day effects that are irreversible by a subsequent long-night and show a spectral sensitivity extending into the red. With movement to higher latitudes, insects develop genetic clines in various parameters, including critical night length, the number of long-night cycles needed for diapause induction, the strength of the response, and the ,depth' or intensity of the diapause thus induced. Evidence for these and other types of photoperiodic response suggests that they provided strong selective advantages for insect survival. [source]

Ecological and evolutionary trends in wetlands: Evidence from seeds and seed banks in New South Wales, Australia and New Jersey, USA

PLANT SPECIES BIOLOGY, Issue 2 2000
Mary A. Leck
Abstract Aquatic plants include a variety of life forms and functional groups that are adapted to diverse wetland habitats. Both similarities and differences in seed and seed-bank characteristics were discovered in comparisons of Australian (New South Wales) temporary upland wetlands with a North American (New Jersey) tidal freshwater marsh having both natural and constructed wetlands. In the former, flooding and drying are unpredictable and in the latter water levels vary diurnally and substrate is constantly moist. The hydrologic regimen provides the overriding selective force, with climate an important second factor. Other factors related to water level, such as oxygen availability, temperature and light, vary spatially and temporally, influencing germination processes, germination rates and seedling establishment. Seed and seed-bank characteristics (size, desiccation and inundation tolerance, germination cues and seed-bank longevity and depletion) differ, with the Australian temporary wetland being more similar to the small-seeded persistent seed bank of the constructed wetland site than to the natural tidal freshwater site with its larger seeds, transient seed bank and seasonal spring germination. Some non-spring germination can occur in the tidal constructed wetland if the soil is disturbed. In contrast, seeds in the temporary Australian wetlands germinated in response to wet/dry cycles rather than to season. Functional groups (e.g. submerged, amphibious) are more diverse in the Australian temporary wetlands, where all species tolerate drying. We suggest that the amphibious zone, with its hydrologic gradient, is the site of selection pressure determining establishment of wetland plants from seed. In this zone, multiple selective factors vary spatially and temporally. [source]

Bony ponticles of the atlas (C1) over the groove for the vertebral artery in humans and primates: Polymorphism and evolutionary trends

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2004
Jean-Marie Le Minor
Abstract The aim of this study was to ascertain the distribution in primates of the three possible bony ponticles over the groove for the vertebral artery (ventral, lateral, and dorsal ponticles), in order to attempt to understand the variants observed in humans and to ascertain possible evolutionary trends in primates. The material consisted of 393 atlases of extant nonhuman primates representative of 41 genera, and of 500 human atlases (dried bones of adults). For each atlas, we studied the existence and morphology of the ponticles, and the type of association of these three ponticles on a given side, which are theoretically of eight in number (types A,H). The occurrence of these ponticles varied from complete absence to constant presence, according to the genera and taxa of primates. The presence of each of these ponticles in primates can be interpreted as a primitive or plesiomorphic character, and their absence as a derived or apomorphic character. The strepsirhines-platyrrhines-cercopithecines group, presenting a predominant primitive pattern (type A), appeared to be separated from the colobines-hominoids group, presenting predominant derived patterns (type C in colobines, Pongo pygmaeus, and Pan troglodytes, and the more derived type D in Hylobates, Gorilla gorilla, and Homo sapiens). The last derived stage, corresponding to the disappearance of the three atlantal ponticles (type H), was only observed in some individuals in hominoids. A marked intraspecific polymorphism characterized the hominoids. The presence of lateral and dorsal ponticles in humans appeared to correspond to their persistence within the progressive disappearance of the atlantal ponticles, constituting an evolutionary tendency characteristic of primates and particularly of hominoid evolution. Am J Phys Anthropol, 2004. © 2004 Wiley-Liss, Inc. [source]

Forty years on and still going strong: the use of hominin-cercopithecid comparisons in palaeoanthropology

THE JOURNAL OF THE ROYAL ANTHROPOLOGICAL INSTITUTE, Issue 1 2006
Sarah Elton
Hominin-cercopithecid comparisons have been used in palaeoanthropology for over forty years. Fossil cercopithecids can be used as a ,control group' to contextualize the adaptations and evolutionary trends of hominins. Observations made on modern cercopithecids can also be applied to questions about human evolution. This article reviews the history of hominin-cercopithecid comparisons, assesses the strengths and weaknesses of cercopithecids as comparators in studies of human evolution, and uses cercopithecid models to explore hominin inter-specific dynamics. Cercopithecids appear to be excellent ecological referents, but may be less good when considering the cognitive abilities and cultural adaptations of hominins. Comparison of cercopithecid and hominin adaptations at Koobi Fora in East Africa indicates that, whereas the cercopithecids were largely grass- or leaf-eating, the hominins occupied a generalist niche, apparently excluding other primate generalist-frugivores. If any of the hominin species at Koobi Fora were sympatric, analogies with modern cercopithecids suggest that inter-specific contact cannot be discounted and may even have been beneficial. [source]

The multiple directions of evolutionary change

BIOESSAYS, Issue 6 2008
Diego Rasskin-Gutman
The theory of Punctuated Equilibria challenges the neo-Darwinian tenet that evolution is a uniform process. Recently, an article by Hunt1 has found that directional change during the evolution of a lineage is relatively small (occurring only in 5% of 250 analyzed traits). Of those traits that were shown to follow a trend, size was more likely to show gradual changes, whereas shape changes were more random. Here, we provide a short view of the nature of evolutionary trends, showing that directional change within lineages and among clades provides valuable evolutionary information about the processes involved in their generation. BioEssays 30:521,525, 2008. © 2008 Wiley Periodicals, Inc. [source]

Body size variation in insects: a macroecological perspective

BIOLOGICAL REVIEWS, Issue 1 2010
Steven L. Chown
Body size is a key feature of organisms and varies continuously because of the effects of natural selection on the size-dependency of resource acquisition and mortality rates. This review provides a critical and synthetic overview of body size variation in insects from a predominantly macroecological (large-scale temporal and spatial) perspective. Because of the importance of understanding the proximate determinants of adult size, it commences with a brief summary of the physiological mechanisms underlying adult body size and its variation, based mostly on findings for the model species Drosophila melanogaster and Manduca sexta. Variation in nutrition and temperature have variable effects on critical weight, the interval to cessation of growth (or terminal growth period) and growth rates, so influencing final adult size. Ontogenetic and phylogenetic variation in size, compensatory growth, scaling at the intra- and interspecific levels, sexual size dimorphism, and body size optimisation are then reviewed in light of their influences on individual and species body size frequency distributions. Explicit attention is given to evolutionary trends, including gigantism, Cope's rule and the rates at which size change has taken place, and to temporal ecological trends such as variation in size with succession and size-selectivity during the invasion process. Large-scale spatial variation in size at the intraspecific, interspecific and assemblage levels is considered, with special attention being given to the mechanisms proposed to underlie clinal variation in adult body size. Finally, areas particularly in need of additional research are identified. [source]

Inevitable evolution: back to The Origin and beyond the 20th Century paradigm of contingent evolution by historical natural selection

BIOLOGICAL REVIEWS, Issue 3 2008
Lars Witting
Abstract Since neo-Darwinism arose from the work of Darwin and Mendel evolution by natural selection has been seen as contingent and historical being defined by an a posteriori selection process with no a priori laws that explain why evolution on Earth has taken the direction of the major evolutionary trends and transitions instead of any other direction. Recently, however, major life-history trends and transitions have been explained as inevitable because of a deterministic selection that unfolds from the energetic state of the organism and the density-dependent competitive interactions that arise from self-replication in limited environments. I describe differences and similarities between the historical and deterministic selection processes, illustrate concepts using life-history models on large body masses and limited reproductive rates, review life-history evolution with a wider focus on major evolutionary transitions, and propose that biotic evolution is driven by a universal natural selection where the long-term evolution of fitness-related traits is determined mainly by deterministic selection, while contingency is important predominately for neutral traits. Given suitable environmental conditions, it is shown that selection by energetic state and density-dependent competitive interactions unfolds to higher level selection for life-history transitions from simple asexually reproducing self-replicators to large bodied organisms with senescence and sexual reproduction between males and females, and in some cases, to the fully evolved eusocial colony with thousands of offspring workers. This defines an evolutionary arrow of time for open thermodynamic systems with a constant inflow of energy, predicting similar routes for long-term evolution on similar planets. [source]