Home About us Contact
|
Home About us Contact | ||
|
|
||
Evolutionary Pathways (evolutionary + pathway)
Selected AbstractsEVOLUTIONARY PATHWAYS IN SHOREBIRD BREEDING SYSTEMS: SEXUAL CONFLICT, PARENTAL CARE, AND CHICK DEVELOPMENTEVOLUTION, Issue 10 2005Gavin H. Thomas Abstract Sexual selection, mating opportunities, and parental behavior are interrelated, although the specific nature of these relationships is controversial. Two major hypotheses have been suggested. The parental investment hypothesis states that the relative parental investment of the sexes drives the operation of sexual selection. Thus, the sex that invests less in offspring care competes more intensely and monopolizes access to mates. The sexual conflict hypothesis proposes that sexual selection (the competition among both males and females for mates), mating opportunities, and parental behavior are interrelated and predicts a feedback loop between mating systems and parental care. Here we test both hypotheses using a comprehensive dataset of shorebirds, a maximum-likelihood statistical technique, and a recent supertree of extant shorebirds and allies. Shorebirds are an excellent group for these analyses because they display unique variation in parental care and social mating system. First, we show that chick development constrains the evolution of both parental care and mate competition, because transitions toward more precocial offspring preceded transitions toward reduced parental care and social polygamy. Second, changes in care and mating systems respond to one another, most likely because both influenced and are influenced by mating opportunities. Taken together, our results are more consistent with the sexual conflict hypothesis than the parental investment hypothesis. [source] THE EVOLUTION OF GENETIC ARCHITECTURE UNDER FREQUENCY-DEPENDENT DISRUPTIVE SELECTIONEVOLUTION, Issue 8 2006Michael Kopp Abstract We propose a model to analyze a quantitative trait under frequency-dependent disruptive selection. Selection on the trait is a combination of stabilizing selection and intraspecific competition, where competition is maximal between individuals with equal phenotypes. In addition, there is a density-dependent component induced by population regulation. The trait is determined additively by a number of biallelic loci, which can have different effects on the trait value. In contrast to most previous models, we assume that the allelic effects at the loci can evolve due to epistatic interactions with the genetic background. Using a modifier approach, we derive analytical results under the assumption of weak selection and constant population size, and we investigate the full model by numerical simulations. We find that frequency-dependent disruptive selection favors the evolution of a highly asymmetric genetic architecture, where most of the genetic variation is concentrated on a small number of loci. We show that the evolution of genetic architecture can be understood in terms of the ecological niches created by competition. The phenotypic distribution of a population with an adapted genetic architecture closely matches this niche structure. Thus, evolution of the genetic architecture seems to be a plausible way for populations to adapt to regimes of frequency-dependent disruptive selection. As such, it should be seen as a potential evolutionary pathway to discrete polymorphisms and as a potential alternative to other evolutionary responses, such as the evolution of sexual dimorphism or assortative mating. [source] PARENTAL EFFECTS AND GENDER SPECIALIZATION IN A TROPICAL HETEROSTYLOUS SHRUBEVOLUTION, Issue 3 2000Germá;n Avila-Sakar Abstract., Male sterility in hermaphroditic species may represent the first step in the evolution toward dioecy. However, gender specialization will not proceed unless the male-sterile individuals compensate for fitness lost through the male function with an increase in fitness through the female function. In the distylous shrub Erythroxylum havanense, thrum plants are partially male-sterile. Using data collected throughout eight years, we investigated whether thrum individuals have an increased performance as female parents, thereby compensating for their loss of male fitness. We found that thrum plants outperformed pins in the probabilities of seed maturation and germination and long-term growth of the seedlings. In turn, pollen from pin plants achieved greater pollen tube growth rates. Our results suggest that the superior performance of the progeny of thrum maternal plants is a consequence of better seed provisioning via effects of the maternal environment, cytotype or nuclear genes. Overall, our results suggest that E. havanense is evolving toward a dioecious state through a gynodioecious intermediate stage. This evolutionary pathway is characterized by an unusual pattern of gender dimorphism with thrums becoming females and pins becoming males. We propose that this pattern may be better explained by the interaction between male-sterility cytoplasmic genes and the heterostyly supergene. [source] Origin of the novel chemoreceptor Aesthetasc "Y" in Ostracoda: morphogenetical thresholds and evolutionary innovationEVOLUTION AND DEVELOPMENT, Issue 2 2008Tomonari Kaji SUMMARY The morphology and developmental processes of the two types of ostracod chemoreceptors, the Aesthetasc "Y" and the "Grouped setae," were compared. Cypridoidea and Pontocypridoidea, belonging to Cypridocopina, have a large baseball bat-like seta as an autapomorphic character on the second antenna, whereas most ostracod taxa with plesiomorphic characters bear "Grouped setae" consisting of multiple setae on the second antenna. Their budding positions, morphology, and ontogenetic changes were compared, and our deduction is that the Aesthetasc "Y" originated from "Grouped setae-like" organ in the Paleozoic. The morphogenetic processes in the molting period of these chemoreceptors were compared at the cellular level. The observations suggest that the "Grouped setae" are formed by hypodermal cells and share sheath cells corresponding to those of the Aesthetasc "Y" as a common constraint in the molting process of setae. We conclude that modification of the morphogenetic processes in the molting period of the "Grouped setae" gave rise to the Aesthetasc "Y" as a novel organ in the evolutionary pathway of the Ostracoda. [source] A possible evolutionary pathway to insect flight starting from lepismatid organizationJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 2 2002I. HASENFUSS Starting from the hypothesis that flight in Pterygota evolved from lepismatid organization of their ancestors, the functional anatomy of the thorax was studied in Lepisma saccharina Linnaeus, 1758, and a Ctenolepisma sp. in regard to both the adaptations to the adaptive zone of Lepismatidae and to pre-adaptations for the evolution of Pterygota. Well-preserved parts of three subcoxal leg segments were found in the pleural zone participating in leg movement. The lepismatid strategy of escaping predators by running fast and hiding in narrow flat retreats led to a dorso-ventrally flattened body which enabled gliding effects when dropped, followed by flight on the ground. The presumed exploitation of soft tissue at the tips of low growing Devonian vascular plants opened a canalized pathway to the evolution of the flying ability. Locomotion to another plant was facilitated by dropping. It is possible that threat by spider-like predators favoured falling and gliding as escape reactions by selection. Falling experiments with `lepismatid' models revealed a narrow `window' for gliding, with optimum dimensions of 8 mm body length and 8 mg weight. An equation was derived which describes the glide distance as function of weight, area of the horizontal outline, the specific glide efficiency of the body, and a non-linear function of the falling height. Improved gliding was made possible by enlarging thoracic paratergites into broad wing-like extensions of light-weight organization. The disadvantage of the lateral lobes for locomotion on the ground could be minimized by tilting them vertically when running and horizontally when gliding. This movability could be attained by the intercalation of a membranous strip between tergite and paratergite and the utilization of the pre-existing muscular system and the articulation between the two most basal subcoxal sclerites as a pivot. The dorsal part of the most basal subcoxa was thus integrated into the wing. Initiation of active flight was possible by flapping movements during gliding. Morphological, ontogenetic and ecological aspects of the origin of Pterygota are discussed. Ein möglicher, von der lepismatiden Organisation ausgehender Evolütionsweg zum Flugvermögen der Insekten Ausgehend von der Hypothese daß die Evolution des Flugvermögens der Pterygota mit der lepismatiden Organisation ihrer Ahnen begann, wurde die funktionelle Anatomie des Thorax von Lepisma saccharina und einer Ctenolepisma sp. im Hinblick auf Adaptationen an die adaptive Zone der Lepismatidae und im Hinblick auf Praeadaptationen für die Evolution der Pterygota untersucht. Es wurden in der Pleuralzone gut erhaltene Teile von drei subcoxalen Beingliedern gefunden, die an der Beinbewegung teilnehmen. Die Strategie der Lepismatidae, vor Feinden durch rasches Laufen zu fliehen und sich in flachen Spalten zu verstecken, führte zu einer dorsoventralen Abflachung des Körpers, die beim Herabfallen Gleiteffekte und weitere Flucht am Boden ermöglichte. Im Zusammenhang mit der vermuteten Ernährung von Triebspitzen der im Devon noch niedrigen Gefäßpflanzen eröffnete dies einen kanalisierten Evolutionsweg zum aktiven Flug wobei möglicherweise spinnenartige Prädatoren den Selektionsdruck verstärkten. Gleitversuche mit `lepismatiden' Modellen zeigten ein enges Gleitfenster mit dem Optimum von 8 mg Gewicht und 8 mm Körperlänge. Es wurde eine Gleichung gefunden, die die Gleitdistanz als Funktion der Gleitfläche, der Masse, der Gleiteffizienz des Fallkörpers und einer nicht-linearen Funktion der Fallhöhe beschreibt. Vergrößerung der Gleitdistanz war möglich, wenn die Körpermasse veringert, die lateral vorragenden thorakalen Paratergite vergrößert wurden und als `Flügel' nicht länger als breit waren. Die Behinderung der Flucht am Boden durch laterale `Flügel' konnte durch deren Vertikalstellung beim Laufen und durch Horizontalstellung beim Gleiten vermindert werden. Die Beweglichkeit war durch Einfügen eines Membranstreifens zwischen Tergit und Paratergit sowie die Nutzung des vorhandenen Gelenks zwischen zwei basalen Subcoxalgliedern mit dem vorhandenen Muskelsystem möglich. Demnach ist der dorsale Teil eines ursprünglichen Beingliedes im Flügel der Pterygota integriert. Auf- und Abbewegung der Flügel während des Gleitens ermöglichten den Beginn des aktiven Fluges. Die dafür erforderlichen Transformationen sowie deren ontogenetische und ökologische Aspekte werden diskutiert. [source] Patagial morphology of Draco volans (Reptilia: Agamidae) and the origin of glissant locomotion in flying dragonsJOURNAL OF ZOOLOGY, Issue 4 2001Anthony P. Russell Abstract The integrative patagial morphology of Draco volans was examined to elucidate the possible evolutionary pathway of origin of active patagia in the flying dragons and in extinct taxa that are thought to have possessed similarly constructed flight membranes. The area of the patagia and accessory aerodynamic surfaces is compared between Draco volans and Ptychozoon kuhli, a gekkonid with passive patagia. Comparisons of patagial area are also made between selected species of Draco. Scale architecture of the patagium of Draco is described and is related to pertinent aspects of the structure and properties of the integument. The relationships of these characteristics to the morphology of the ribs and their related musculature are emphasized. The overall assessment of these features in relation to patagial form is employed to develop an evolutionary scenario for the origin of active patagia. [source] The disulfide bond pattern of catrocollastatin C, a disintegrin-like/cysteine-rich protein isolated from Crotalus atrox venomPROTEIN SCIENCE, Issue 7 2000Juan J. Calvete Abstract The disulfide bond pattern of catrocollastatin-C was determined by N-terminal sequencing and mass spectrometry. The N-terminal disintegrin-like domain is a compact structure including eight disulfide bonds, seven of them in the same pattern as the disintegrin bitistatin. The protein has two extra cysteine residues (XIII and XVI) that form an additional disulfide bond that is characteristically found in the disintegrin-like domains of cellular metalloproteinases (ADAMs) and PIII snake venom Zn-metalloproteinases (SVMPs). The C-terminal cysteine-rich domain of catrocollastatin-C contains five disulfide bonds between nearest-neighbor cysteines and a long range disulfide bridge between CysV and CysX. These results provide structural evidence for a redefinition of the disintegrin-like and cysteine-rich domain boundaries. An evolutionary pathway for ADAMs, PIII, and PII SVMPs based on disulfide bond engineering is also proposed. [source] New chromosome reports in the subtribes Diocleinae and Glycininae (Phaseoleae: Papilionoideae: Fabaceae)BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2008SHIRLEY M. ESPERT The base chromosome number of x = 11 is the most probable in all the subtribes included in tribe Phaseoleae, although some aneuploid reduction is evident in Collaea and Galactia (Diocleinae) and chromosome duplications are seen in Amphicarpaea, Cologania and Glycine (Glycininae). The aims of this study were to improve the cytological knowledge of some species of Collaea and Galactia and to examine the anomalous counts reported for Calopogonium (Glycininae) and verify its taxonomic position. In addition, a molecular phylogeny was constructed using nuclear ribosomal DNA sequences (internal transcribed spacer region), and the chromosome number was optimized on the topology. In this work, the chromosome counts for Galactia lindenii, Galactia decumbens and Collaea cipoensis (all 2n = 20), and Calopogonium sericeum (2n = 22) are reported for the first time. The new reports for Galactia and Collaea species are in agreement with the chromosome number proposed for subtribe Diocleinae. The study rejects the concept of a cytologically anomalous Calopogonium and, based on the phylogenetic analysis, corroborates the position of this genus within subtribe Glycininae. The ancestral basic chromosome number of x = 11 proposed for Phaseoleae is in agreement with the evolutionary pathway of chromosome numbers analysed in this work. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 336,341. [source] New Record of Palaeoscolecids from the Early Cambrian of Yunnan, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2008HU Shixue Abstract: A new palaeoscolecid, Guanduscolex minor Hu, Luo et Fu gen. et sp. nov., with preserved soft parts of introvert and intestines comes from the Lower Cambrian Guanshan fauna of Yunnan, South China. Microstructural details of the cuticle revealed by scanning electron microscopy (SEM) show that each annulation bears three rows of plates and each plate bears 9,10 marginal and 4,5 central nodes. This discovery sheds new light on the relationships and evolutionary pathway of the palaeoscolecids and other early priapulids. [source] Can pharmacokinetic,pharmacodynamic parameters provide dosing regimens that are less vulnerable to resistance?CLINICAL MICROBIOLOGY AND INFECTION, Issue 11 2008P. Courvalin Abstract Dissemination of antibiotic resistance in bacteria is associated with prescription of the corresponding drugs. Various pharmacokinetic,pharmacodynamic parameters have been developed with the intention of reducing the spread of resistance. In this review, it is considered whether dosing regimens based on these parameters can delay this spread. The evolution of bacterial resistance to antibiotics involves two successive but distinct and independent mechanisms. The first occurs by mutation in the genome, including the host chromosome and mobile accessory genetic elements such as plasmids or transposons, or, following acquisition of a resistance determinant from another bacterium, by horizontal gene transfer. These two genetic events happen by chance, which means that they do not rely on the presence of an antibiotic in the environment; that is, they are not induced, but simply revealed and propagated by the drugs. The second step is dissemination of resistance which can be due to the spread of bacteria (clonal epidemics), of replicons (plasmid epidemics) or of resistance determinants (gene epidemics). Resistance dissemination by each one of these three levels which superimpose in nature, is not only infectious but also exponential, since all three are associated with DNA replication (duplication) of the host chromosome, of a plasmid, or of a transposon. As opposed to emergence, dissemination is clearly associated with the selective pressure exerted by antibiotic prescription [1,2]. The consequence of this dual evolutionary pathway is that proper use of antibiotics will, at best, delay the spread of resistance. In this review, the pharmacokinetic,pharmacodynamic (PK,PD) parameters that are intended to lower resistance dissemination are considered exclusively. [source] Comparative morphology and evolutionary pathways of the mouthparts in spore-feeding Staphylinoidea (Coleoptera)ACTA ZOOLOGICA, Issue 3 2003Oliver Betz Abstract This study surveys the external morphology of the mouthparts in the guild of spore-feeders among the coleopterous superfamily Staphylinoidea, evaluating the influence of different phylogenetic and ecological starting points on the formation of their mouthparts. Our emphasis is on a scanning electron microscope analysis (SEM) of the involved trophic structures in spore-feeding larvae and adults of the Ptiliidae, Leiodidae and Staphylinidae, describing the fine structure of their main functional elements. Functionally, mouthpart structures resemble brushes, brooms, combs, rakes, rasps, excavators, knives, thorns, cram-brushes, bristle troughs, blocks and differently structured grinding surfaces. Their different involvement in the various aspects of the feeding process (i.e. food gathering, transporting, channelling and grinding) is deduced from our SEM analyses plus direct video observations. We infer five different patterns of food transport and processing, discriminating adults of ptiliids, leiodids plus staphylinids (excluding some aleocharines), several aleocharine staphylinids, and the larvae of leiodids and staphylinids. The structural diversity of the mouthparts increases in the order from (1) Ptiliidae, (2) Leiodidae towards (3) Staphylinidae, reflecting the increasing systematic and ecological diversity of these groups. Comparisons with non-spore-feeders show that among major lineages of staphylinoids, shifts from general microphagy to sporophagy are not necessarily constrained by, nor strongly reflected in, mouthpart morphology. Nevertheless, in several of these lineages the organs of food intake and grinding have experienced particular fine-structural modifications, which have undergone convergent evolution, probably in response to specialized mycophagy such as spore-feeding. These modifications involve advanced galeal rakes, galeal or lacinial ,spore brushes' with arrays of stout bristles, reinforced obliquely ventrad orientated prosthecal lobes and the differentiations of the molar grinding surfaces into stout teeth or tubercles. In addition, several staphylinids of the tachyporine and oxyteline groups with reduced mandibular molae have evolved secondary trituration surfaces, which in some aleocharines are paralleled by considerable re-constructions of the labium,hypopharynx. [source] Differential correlates of diet and phylogeny on the shape of the premaxilla and anterior tooth in sparid fishes (Perciformes: Sparidae)JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2004M. Linde Abstract We explore the correlational patterns of diet and phylogeny on the shape of the premaxilla and anterior tooth in sparid fishes (Perciformes: Sparidae) from the western Mediterranean Sea. The premaxilla is less variable, and in spite of the presence of species-specific features, a common structural pattern is easily recognizable in all species (i.e. the ascending and the articular processes are fused in a single branch, as in many percoid fishes). In contrast, tooth shape is more variable, and different structural types can be recognized (e.g. canine-like or incisive). Coupling geometric morphometric and comparative methods we found that the relationship between shape, diet and phylogeny also differs between premaxilla and tooth. Thus, the shape of the premaxilla is significantly correlated with food type, whereas the shape of the teeth is not correlated with diet, and probably reflects the species phylogenetic relationships. Two biological roles, resistance against compressive forces generated in the buccal cavity and the size of the oral gape, would explain the ecomorphological patterns of the premaxilla. The premaxilla and anterior tooth appear to evolve at different rates (mosaic evolution) and represent an example of morphological traits belonging to the same functional unit but following uncoupled evolutionary pathways. [source] Design and Analysis of Bioenergy NetworksJOURNAL OF INDUSTRIAL ECOLOGY, Issue 2 2009A Complex Adaptive Systems Approach Summary This article presents a new methodology for designing industrial networks and analyzing them dynamically from the standpoint of sustainable development. The approach uses a combination of optimization and simulation tools. Assuming "top-down" overarching control of the network, we use global dynamic optimization to determine which evolutionary pathways are preferred in terms of economic, social, and environmental performance. Considering the autonomy of network entities and their actions, we apply agent-based simulation to analyze how the network actually evolves. These two perspectives are integrated into a powerful multiscale modeling framework for evaluating the consequences of new policy instruments or different business strategies aimed at stimulating sustainable development as well as identifying optimal leverage points for improved performance of the network in question. The approach is demonstrated for a regional network of interdependent organizations deploying a set of bioenergy technologies within a developing-economy context. [source] Ultrastructure of Gnathostomaria lutheri Ax (Gnathostomulida: Scleroperalia).I.MARINE ECOLOGY, Issue 1-2 2001An Hypothesis About the Origin of Micropodia in Scleroperalian Sperm Abstract. Initially described as an aberrant taxon of turbellarian flatworms, the Gnathostomulida were recognized as a distinct phylum by Rupert Riedl already in 1969. Yet these microscopic, non-segmented marine worms remain organisms of enigmatic phylogenetic affiliation, and although they are often the dominant invertebrate taxon in detritus-rich, oxygen-poor sands, our knowledge of their biology is still very scanty. About 90 gnathostomulid species are known to date; they are grouped in two orders, one with two suborders. Sperm structure, often a useful instrument for clarifying evolutionary pathways in metazoan taxa, differs so widely between the orders and suborders that sperm phylogeny within the Gnathostomulida also remains uncertain. We here report on the ultrastructural features of a peculiar type of sperm, the aflagellar "megasperm" of Gnathostomaria lutheri, and discuss new and older interpretations of sperm cytology of the taxon. [source] Simple evolutionary pathways to complex proteinsPROTEIN SCIENCE, Issue 9 2005Michael Lynch Abstract A recent paper in this journal has challenged the idea that complex adaptive features of proteins can be explained by known molecular, genetic, and evolutionary mechanisms. It is shown here that the conclusions of this prior work are an artifact of unwarranted biological assumptions, inappropriate mathematical modeling, and faulty logic. Numerous simple pathways exist by which adaptive multi-residue functions can evolve on time scales of a million years (or much less) in populations of only moderate size. Thus, the classical evolutionary trajectory of descent with modification is adequate to explain the diversification of protein functions. [source] Varying patterns of coexistence of two mouse lemur species (Microcebus ravelobensis and M. murinus) in a heterogeneous landscapeAMERICAN JOURNAL OF PRIMATOLOGY, Issue 11 2009Romule Rakotondravony Abstract The coexistence of closely related species is not easily understood on the basis of ecological theories. This study investigates the extent of coexistence of two congeneric species of Microcebus murinus (MUR) and M. ravelobensis (RAV) in northwestern Madagascar. Their presence and local relative population densities were determined by capturing and nocturnal transect counts and compared at 22 study sites in the Ankarafantsika National Park. All sites were characterized with regard to their altitude, access to surface water, and 19 structural vegetation characteristics. RAV and MUR were not equally distributed over this regional scale. RAV occurred in more sites and at higher maximum densities than MUR. The relative population densities of both species were significantly and negatively correlated with each other. Whereas the relative population densities of MUR increased with altitude and were highest in dry habitats far from surface water, the relative population densities of RAV generally decreased with altitude and were highest in low altitude habitats close to surface water. The results of the vegetation characteristics also reflect these general trends. The divergent pattern of local and regional coexistence of these two species is discussed and can be best explained either by the existence of a spatially heterogeneous competitive environment or by independent evolutionary pathways in different historic environments. Am. J. Primatol. 71:928,938, 2009. © 2009 Wiley-Liss, Inc. [source] Extended phenotypes as signalsBIOLOGICAL REVIEWS, Issue 2 2009Franziska C. Schaedelin ABSTRACT Animal signals may result from construction behaviour and can provide receivers with essential information in various contexts. Here we explore the potential benefits of extended phenotypes with a signalling function as compared to bodily ornaments and behavioural displays. Their independence of the body, their physical persistence and the morphological and cognitive conditions required for their construction allow unique communication possibilities. We classify various levels of information transfer by extended phenotype signals and explore the differences between secreted signals and signals resulting from collection and construction, which usually involve higher behavioural complexity. We examine evolutionary pathways of extended phenotypes with a signalling function with help of a comparative evaluation and conclude that often constructions first provide a direct fitness benefit, with a signalling function becoming more and more prominent during evolutionary progression. The abundance and variability of extended phenotypes as signals is impressive and provides unique possibilities for animal communication research. [source] The evolution of male mate choice in insects: a synthesis of ideas and evidenceBIOLOGICAL REVIEWS, Issue 3 2001RUSSELL BONDURIANSKY ABSTRACT Mate choice by males has been recognized at least since Darwin's time, but its phylogenetic distribution and effect on the evolution of female phenotypes remain poorly known. Moreover, the relative importance of factors thought to underlie the evolution of male mate choice (especially parental investment and mate quality variance) is still unresolved. Here I synthesize the empirical evidence and theory pertaining to the evolution of male mate choice and sex role reversal in insects, and examine the potential for male mating p to generate sexual selection on female phenotypes. Although male mate choice has received relatively little empirical study, the available evidence suggests that it is widespread among insects (and other animals). In addition to ,precopulatory' male mate choice, some insects exhibit ,cryptic' male mate choice, varying the amount of resources allocated to mating on the basis of female mate quality. As predicted by theory, the most commonly observed male mating p are those that tend to maximize a male's expected fertilization success from each mating. Such p tend to favour female phenotypes associated with high fecundity or reduced sperm competition intensity. Among insect species there is wide variation in mechanisms used by males to assess female mate quality, some of which (e.g. probing, antennating or repeatedly mounting the female) may be difficult to distinguish from copulatory courtship. According to theory, selection for male choosiness is an increasing function of mate quality variance and those reproductive costs that reduce, with each mating, the number of subsequent matings that a male can perform (,mating investment'). Conversely, choosiness is constrained by the costs of mate search and assessment, in combination with the accuracy of assessment of potential mates and of the distribution of mate qualities. Stronger selection for male choosiness may also be expected in systems where female fitness increases with each copulation than in systems where female fitness peaks at a small number of matings. This theoretical framework is consistent with most of the empirical evidence. Furthermore, a variety of observed male mating p have the potential to exert sexual selection on female phenotypes. However, because male insects typically choose females based on phenotypic indicators of fecundity such as body size, and these are usually amenable to direct visual or tactile assessment, male mate choice often tends to reinforce stronger vectors of fecundity or viability selection, and seldom results in the evolution of female display traits. Research on orthopterans has shown that complete sex role reversal (i.e. males choosy, females competitive) can occur when male parental investment limits female fecundity and reduces the potential rate of reproduction of males sufficiently to produce a female-biased operational sex ratio. By contrast, many systems exhibiting partial sex role reversal (i.e. males choosy and competitive) are not associated with elevated levels of male parental investment, reduced male reproductive rates, or reduced male bias in the operational sex ratio. Instead, large female mate quality variance resulting from factors such as strong last-male sperm precedence or large variance in female fecundity may select for both male choosiness and competitiveness in such systems. Thus, partial and complete sex role reversal do not merely represent different points along a continuum of increasing male parental investment, but may evolve via different evolutionary pathways. [source] Morphology and development of the subterranean organs of the achlorophyllous Sciaphila polygyna (Triuridaceae)BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2004STEPHAN IMHOF The subterranean organs of the achlorophyllous Sciaphila polygyna (Triuridaceae) are described, depicted, and structurally explained for the first time. Unlike other Triuridaceae, the subterranean system of S. polygyna appears as a complex star-like structure of short, but thickened, roots as well as scale leaves and shoots. A complete series of sections revealed the following construction. In the axil of a scale leaf at a shoot of first order, a side shoot of second order as well as a pair of endogenous shoot-borne roots arise. This side shoot of second order also develops a scale leaf very early in ontogeny, which again gives rise to a side shoot of third order and a pair of shoot-borne roots. Other scale leaves at shoots of any order may also bear shoots and root pairs. This growth pattern occurs in a very close manner without internode elongation, resulting in the clumped, star-like appearance. The structures described superficially resemble the root systems of many mycoheterotrophic plants from other families. Comparisons with respect to how they develop, however, show that these similar root systems can result from distinct developmental patterns, suggesting independent evolutionary pathways and a considerable evolutionary pressure towards abbreviated and thickened roots in mycoheterotrophic plants. Possible advantages as well as evolutionary implications of the structures described are discussed. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 146, 295,301. [source] Growth rules based on the modularity of the Canarian Aeoniwm (Crassulaceae) and their phylogenetic valueBOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2000TOVE H. JORGENSEN Growth forms of 22 species of Aeonium (Crassulaceae) were quantified. Since all species are simple in their modular construction, models were developed to predict module length, branching mode and flowering probability using linear and logistic regression. When combined, the parameters of these models are species specific. A discriminant analysis generates a statistically significant separation of species at the level of phylogenetic sections. The results therefore demonstrate the phylogenetic value of growth rules in plants. This dynamic approach strongly contrasts with the traditional static view on forms in systematics and morphology. It also leaves scope for predicting the evolutionary pathways of morphological change which have caused the great diversity of growth forms in the genus Aeonium. [source] | |||||||||||||||||||||||||