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Developmental Constraints (developmental + constraint)
Selected AbstractsPERSPECTIVE: EMBEDDED MOLECULAR SWITCHES, ANTICANCER SELECTION, AND EFFECTS ON ONTOGENETIC RATES: A HYPOTHESIS OF DEVELOPMENTAL CONSTRAINT ON MORPHOGENESIS AND EVOLUTIONEVOLUTION, Issue 5 2003Kathryn D. Kavanagh Abstract The switch between the cell cycle and the progress of differentiation in developmental pathways is prevalent throughout the eukaryotes in all major cell lineages. Disruptions to the molecular signals regulating the switch between proliferative and differentiating states are severe, often resulting in cancer formation (uncontrolled proliferation) or major developmental disorders. Uncontrolled proliferation and developmental disorders are potentially lethal defects in the developing animal. Therefore, natural selection would likely favor a tightly controlled regulatory mechanism to help prevent these fundamental defects. Although selection is usually thought of as a consequence of environmental or ecological influences, in this case the selective force to maintain this molecular switch is internal, manifested as a potentially lethal developmental defect. The morphogenetic consequences of this prevalent, deeply embedded, and tightly controlled mechanistic switch are currently unexplored, however experimental and correlative evidence from several sources suggest that there are important consequences on the control of growth rates and developmental rates in organs and in the whole animal. These observations lead one to consider the possibility of a developmental constraint on ontogenetic rates and morphological evolution maintained by natural selection against cancer and other embryonic lethal defects. [source] Iridescent hindwing patches in the Pipevine Swallowtail: differences in dorsal and ventral surfaces relate to signal function and contextFUNCTIONAL ECOLOGY, Issue 4 2010Ronald L. Rutowski Summary 1.,Iridescent colour signals are directional but, like diffusely reflected colours, vary within and among species in ways that may be adaptations to specific types of receivers in specific light environments. 2.,The hindwings of pipevine swallowtail butterflies exhibit brilliant blue and iridescent colour patches on the ventral surface in both sexes and on the dorsal wing surface in males. Evidence suggests that the ventral iridescent blue is a component of the warning coloration of this distasteful species, while the dorsal blue iridescent wing area is a sexual signal. Given differences in the function and ecological context of signal production, we analysed reflectance spectra from the iridescent blue areas of both field-caught and laboratory-reared animals to test several predictions about the iridescent colour patches on these wing surfaces. 3.,The ventral blue patches in the warning coloration of males and females should be most visible early and late in the day, due to wing orientation relative to sun angle. We therefore predicted that these iridescent colour patches would be brighter and of longer wavelengths than the male dorsal blue patch displayed during midday courtships. The prediction about reflectance intensity was supported but the prediction about hue was not. 4.,We predicted that the sexually selected dorsal hindwing iridescence of males would be more variable among individuals and condition dependent than the naturally selected ventral iridescent colour patches. To assess variation and condition dependence, laboratory-reared and field-captured individuals were compared. The prediction about variation was not supported, but only the dorsal wing surfaces showed evidence of being condition dependent. 5.,We investigated whether development of dorsal and ventral blue iridescence was coupled by determining correlations in colour properties between the wing surfaces. Our finding of positive correlations indicated a potential developmental constraint in the evolution of colour differences between the two wing surfaces. 6.,Results of this study suggest that some properties of iridescent coloration on the hindwing of the pipevine swallowtail (especially intensity) may have been fine-tuned by evolution in response to prevailing ambient light conditions and viewing perspectives that differ among types of signal receivers. [source] Variations in leaf stomatal density and distribution of 53 vine species in JapanPLANT SPECIES BIOLOGY, Issue 1 2008AI-CHEN TAY Abstract To determine variations in stomatal density and distribution in individual leaves of vine species with different growth/life forms and different habitat types, we quantified and compared leaf-area-based stomatal density, epidermal cell density and stomatal index (percentage of stoma on the epidermis to the total cell number, including epidermal and stomatal cells on the epidermis) of 53 species comprising 19 woody species (lianas) and 34 herbaceous vines growing in Japan. We counted the numbers of stomata on both the adaxial and abaxial leaf surfaces using a light microscope. Stomatal density and distribution on the leaf surfaces varied greatly among species. Most of the creeping herbaceous species had stomata on both the adaxial and abaxial leaf surfaces (amphistomatous); however, lianas had no stomata on the adaxial leaf surface. Species from coastal (probably drier) habitats had greater adaxial to abaxial ratios of stomatal density and stomatal indices compared with species from inland habitats. A positive correlation between stomatal density and epidermal cell density was found on the abaxial/adaxial leaf surfaces of the examined species. This suggests that there is a developmental similarity among vine species in which stomata are developed with differentiation of epidermal cells on the leaf surface. Thus, leaf stomatal density and distribution appear to vary among species with different growth/life forms from different habitats under a developmental constraint of leaf surface in vine plants in Japan. [source] Cell fate and timing in the evolution of neural crest and mesoderm development in the head region of amphibians and lungfishesACTA ZOOLOGICA, Issue 2009Rolf Ericsson Abstract Our research on the evolution of head development focuses on understanding the developmental origins of morphological innovations and involves asking questions like: How flexible (or conserved) are cell fates, patterns of cell migration or the timing of developmental events (heterochrony)? How do timing changes, or changes in life history affect head development and growth? Our ,model system' is a comparison between lungfishes and representatives from all three extant groups of amphibians. Within anuran amphibians, major changes in life history such as the repeated evolution of larval specializations (e.g. carnivory), or indeed the loss of a free-swimming larva, allows us to test for developmental constraints. Cell migration and cell fate are conserved in cranial neural crest cells in all vertebrates studied so far. Patterning and developmental anatomy of cranial neural crest and head mesoderm cells are conserved within amphibians and even between birds, mammals and amphibians. However, the specific formation of hypobranchial muscles from ventral somitic processes shows variation within tetrapods. The evolution of carnivorous larvae in terminal taxa is correlated with changes in both pattern and timing of head skeletal and muscle development. Sequence-heterochronic changes are correlated with feeding mode in terminal taxa and with phylogenetic relatedness in basal branches of the phylogeny. Eye muscles seem to form a developmental module that can evolve relatively independently from other head muscles, at least in terms of timing of muscle differentiation. [source] ON THE ADAPTIVE ACCURACY OF DIRECTIONAL ASYMMETRY IN INSECT WING SIZEEVOLUTION, Issue 11 2008Christophe Pélabon Subtle left,right biases are often observed in organisms with an overall bilateral symmetry. The evolutionary significance of these directional asymmetries remains uncertain, however, and scenarios of both developmental constraints and adaptation have been suggested. Reviewing the literature on asymmetry in insect wings, we analyze patterns of directional asymmetry in wing size to evaluate the possible adaptive significance of this character. We found that directional asymmetry in wing size is widespread among insects, with left- and right-biased asymmetries commonly observed. The direction of the asymmetry does not appear to be evolutionarily conserved above the species level. Overall, we argue that the very small magnitude of directional asymmetry, 0.7% of the wing size on average, associated with an extremely imprecise expression, precludes directional asymmetry from playing any major adaptive role. [source] Selection on defensive traits in a sterile caste , caste evolution: a mechanism to overcome life-history trade-offs?EVOLUTION AND DEVELOPMENT, Issue 1 2009Estelle A. Roux SUMMARY During development and evolution individuals generally face a trade-off between the development of weapons and gonads. In termites, characterized by reproductive division of labor, a caste evolved,the soldiers,which is completely sterile and which might be released from developmental trade-offs between weapons and testes. These soldiers are exclusively dedicated to defense. First, we investigated whether defensive traits are under selection in sterile termite soldiers using allometric analyses. In soldiers of the genus Cryptotermes phragmotic traits such as a sculptured and foreshortened head evolve rapidly but were also lost twice. Second, we compared the scaling relationships of these weapons with those in solitary insects facing a trade-off between weapons and gonads. Defensive traits consistently had lower slopes than nondefensive traits which supports the existence of stabilizing selection on soldier phragmotic traits in order to plug galleries. Moreover, soldier head widths were colony specific and correlated with the minimum gallery diameter of a colony. This can proximately be explained by soldiers developing from different instars. The scaling relationships of these termite soldiers contrast strikingly with those of weapons of solitary insects, which are generally exaggerated (i.e., overscaling) male traits. These differences may provide important insights into trait evolution. Trade-offs constraining the development of individuals may have been uncoupled in termites by evolving different castes, each specialized for one function. When individuals in social insect are "released" from developmental constraints through the evolution of castes, this certainly contributed to the ecological and evolutionary success of social insects. [source] Carbon limitation in treesJOURNAL OF ECOLOGY, Issue 1 2003Christian Körner Summary 1The ongoing enrichment of the atmosphere with CO2 raises the question of whether growth of forest trees, which represent close to 90% of the global biomass carbon, is still carbon limited at current concentrations of close to 370 p.p.m. As photosynthesis of C3 plants is not CO2 -saturated at such concentrations, enhanced ,source activity' of leaves could stimulate ,sink activity' (i.e. growth) of plants, provided other resources and developmental controls permit. I explore current levels of non-structural carbon in trees in natural forests in order to estimate the potential for a carbon-driven stimulation of growth. 2The concentration of non-structural carbohydrates (NSC) in tree tissues is considered a measure of carbon shortage or surplus for growth. A periodic reduction of NSC pools indicates either that carbon demand exceeds con-current supply, or that both source and sink activity are low. A steady, very high NSC concentration is likely to indicate that photosynthesis fully meets, or even exeeds, that needed for growth (surplus assimilates accumulate). 3The analysis presented here considers data for mature trees in four climatic zones: the high elevation treeline (in Mexico, the Alps and Northern Sweden), a temperate lowland forest of central Europe, Mediterranean sclerophyllous woodland and a semideciduous tropical forest in Panama. 4In all four climatic regions, periods of reduced or zero growth show maximum C-loading of trees (source activity exceeding demand), except for dry midsummer in the Mediterranean. NSC pools are generally high throughout the year, and are not significantly affected by mass fruiting episodes. 5It is concluded that, irrespective of the reason for its periodic cessation, growth does not seem to be limited by carbon supply. Instead, in all the cases examined, sink activity and its direct control by the environment or developmental constraints, restricts biomass production of trees under current ambient CO2 concentrations. 6The current carbohydrate charging of mature wild trees from the tropics to the cold limit of tree growth suggests that little (if any) leeway exists for further CO2 -fertilization effects on growth. [source] The Roles of L1 Influence and Lexical Aspect in the Acquisition of Temporal MorphologyLANGUAGE LEARNING, Issue 1 2002Laura Collins Two cross-sectional studies (N= 70; N= 91) used a replication design to investigate the degree to which adult Francophone ESL learners' use of tense/aspect markers in past contexts supported the predictions of the aspect hypothesis (Andersen & Shirai, 1994; Bardovi-Harlig, 1994) and the degree to which it showed L1 influence. Consistent with the aspect hypothesis, the learners were significantly more successful in using simple past with telics, struggled most with statives, and, in their nontarget responses, preferred progressive for activities and present for statives. The Role of the L1 was restricted to the learners' association of nontarget perfect (a French-influenced form) with telics. The interpretation of the findings takes into account methodological issues and developmental constraints. [source] Social bonds in birds are associated with brain size and contingent on the correlated evolution of life-history and increased parental investmentBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010SUSANNE SHULTZ In birds, large brains are associated with a series of population-level phenomena, including invasion success, species richness, and resilience to population decline. Thus, they appear to open up adaptive opportunities through flexibility in foraging and anti-predator behaviour. The evolutionary pathway leading to large brain size has received less attention than behavioural and ecological correlates. Using a comparative approach, we show that, independent of previously recognized associations with developmental constraints, relative brain size in birds is strongly related to biparental care, pair-bonding, and stable social relationships. We also demonstrate correlated evolution between large relative brain size and altricial development, and that the evolution of both traits is contingent on biparental care. Thus, biparental care facilitates altricial development, which permits the evolution of large relative brain size. Finally, we show that large relative brain size is associated with pair-bond strength, itself a likely consequence of cooperation and negotiation between partners under high levels of parental investment. These analyses provide an evolutionary model for the evolution of and prevalence of biparental care, altricial development, and pair-bonding in birds. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 111,123. [source] Roles of synorganisation, zygomorphy and heterotopy in floral evolution: the gynostemium and labellum of orchids and other lilioid monocotsBIOLOGICAL REVIEWS, Issue 3 2002PAULA J. RUDALL ABSTRACT A gynostemium, comprising stamen filaments adnate to a syncarpous style, occurs in only three groups of monocots: the large family Orchidaceae (Asparagales) and two small genera Pauridia (Hypoxidaceae: Asparagales) and Corsia (Corsiaceae, probably in Liliales), all epigynous taxa. Pauridia has actinomorphic (polysymmetric) flowers, whereas those of Corsia and most orchids are strongly zygomorphic (monosymmetric) with a well-differentiated labellum. In Corsia the labellum is formed from the outer median tepal (sepal), whereas in orchids it is formed from the inner median tepal (petal) and is developmentally adaxial (but positionally abaxial in orchids with resupinate flowers). Furthermore, in orchids zygomorphy is also expressed in the stamen whorls, in contrast to Corsia. In Pauridia a complete stamen whorl is suppressed, but the ,lost' outer whorl is fused to the style. The evolution of adnation and zygomorphy are discussed in the context of the existing phylogenetic framework in monocotyledons. An arguably typological classification of floral terata is presented, focusing on three contrasting modes each of peloria and pseudopeloria. Dynamic evolutionary transitions in floral morphology are assigned to recently revised concepts of heterotopy (including homeosis) and heterochrony, seeking patterns that delimit developmental constraints and allow inferences regarding underlying genetic controls. Current evidence suggests that lateral heterotopy is more frequent than acropetal heterotopy, and that full basipetal heterotopy does not occur. Pseudopeloria is more likely to generate a radically altered yet functional perianth, but is also more likely to cause acropetal modification of the gynostemium. These comparisons indicate that there are at least two key genes or sets of genes controlling adnation, adaxial stamen suppression and labellum development in lilioid monocots; at least one is responsible for stamen adnation to the style (i.e. gynostemium formation), and another controls adaxial stamen suppression and adaxial labellum formation in orchids. Stamen adnation to the style may be a product of over-expression of the genes related to epigyny (i.e. a form of hyper-epigyny). If, as seems likely, stamen-style adnation preceded zygomorphy in orchid evolution, then the flowers of Pauridia may closely resemble those of the immediate ancestors of Orchidaceae, although existing molecular phylogenetic data indicate that a sister-group relationship is unlikely. The initial radiation in Orchidaceae can be attributed to the combination of hyper-epigyny, zygomorphy and resupination, but later radiations at lower taxonomic levels that generated the remarkable species richness of subfamilies Orchidoideae and Epidendroideae are more likely to reflect more subtle innovations that directly influence pollinator specificity, such as the development of stalked pollinaria and heavily marked and or spur-bearing labella. [source] | ||||||||||