Evolution of morphological integration: developmental accommodation of stress-induced variation

Extreme environmental change during growth often results in an increase in developmental abnormalities in the morphology of an organism. The evolutionary significance of such stress-induced variation depends on the recurrence of a stressor and on the degree to which developmental errors can be accommodated by an organism's ontogeny without significant loss of function. We subjected populations of four species of soricid shrews to an extreme environment during growth and measured changes in the patterns of integration and accommodation of stress-induced developmental errors in a complex of mandibular traits. Adults that grew under an extreme environment had lower integration of morphological variation among mandibular traits and highly elevated fluctuating asymmetry in these traits, compared to individuals that grew under the control conditions. However, traits differed strongly in the magnitude of response to a stressor--traits within attachments of the same muscle (functionally integrated traits) had lower response and changed their integration less than other traits. Cohesiveness in functionally integrated complexes of traits under stress was maintained by close covariation of their developmental variation. Such developmental accommodation of stress-induced variation might enable the individual's functioning and persistence under extreme environmental conditions and thus provides a link between individual adaptation to stress and the evolution of stress resistance.     

Extreme environmental change and evolution: stress-induced morphological variation is strongly concordant with patterns of evolutionary divergence in shrew mandibles

Morphological structures often consist of simpler traits which can be viewed as either integrated (e.g. correlated due to functional interdependency) or non-integrated (e.g. functionally independent) traits. The combination of a long-term stabilizing selection on the entire structure with a short-term directional selection on an adaptively important subset of traits should result in long historical persistence of integrated functional complexes, with environmentally induced variation and macroevolutionary change confined mostly to non-integrated traits. We experimentally subjected populations of three closely related species of Sorex shrews to environmental stress. As predicted, we found that most of the variation in shrew mandibular shape was localized between rather than within the functional complexes; the patterns of integration did not change between the species. The stress-induced variation was confined to nonintegrated traits and was highly concordant with the patterns of evolutionary change--species differed in the same set of non-integrated traits which were most sensitive to stress within each species. We suggest that low environmental and genetic canalization of non-integrated traits may have caused these traits to be most sensitive not only to the environmental but also to genetic perturbations associated with stress. The congruence of stress-induced and between-species patterns of variation in non-integrated traits suggests that stress-induced variation in these traits may play an important role in species divergence.     

A geometric morphometric analysis of hominin upper premolars. Shape variation and morphological integration

This paper continues the series of articles initiated in 2006 that analyse hominin dental crown morphology by means of geometric morphometric techniques. The detailed study of both upper premolar occlusal morphologies in a comprehensive sample of hominin fossils, including those coming from the Gran Dolina-TD6 and Sima de los Huesos sites from Atapuerca, Spain, complement previous works on lower first and second premolars and upper first molars. A morphological gradient consisting of the change from asymmetric to symmetric upper premolars and a marked reduction of the lingual cusp in recent Homo species has been observed in both premolars. Although percentages of correct classification based on upper premolar morphologies are not very high, significant morphological differences between Neanderthals (and European middle Pleistocene fossils) and modern humans have been identified, especially in upper second premolars. The study of morphological integration between premolar morphologies reveals significant correlations that are weaker between upper premolars than between lower ones and significant correlations between antagonists. These results have important implications for understanding the genetic and functional factors underlying dental phenotypic variation and covariation.     

Genetic and morphological variation in a partially isolated population of Caucasian shrew sorex Satunini (Mammalia)

Morphological and genetic variation at microsatellite loci of Caucasian shrew Sorex satunini Ogn. is examined and compared with that of the common shrew S. araneus L. Genetic distance at microsatellite loci between the common shrew and Caucasian shrew proved to be threefold higher than between chromosome races of the common shrew. The Caucasian shrew manifested low polymorphism in studies of both microsatellites and morphometric mandibular traits. The heterozygote deficit was also typical. These properties may be a consequence of partial isolation of the population and gene drift.     

Pleiotropic effects on mandibular morphology I. Developmental morphological integration and differential dominance

Pleiotropy refers to a single genetic locus that affects more than one phenotypic trait. Pleiotropic effects of genetic loci are thought to play an important role in evolution, reflecting functional and developmental relationships among phenotypes. In a previous study, we examined pleiotropic effects displayed by quantitative trait loci (QTLs) on murine mandibular morphology in relation to mandibular structure and function. In replicating most of our previous QTLs and increasing our sample size, this study strengthens and extends our earlier results. As in our previous study, we find that QTL effects tend to be restricted to developmentally or functionally related traits. In addition, we examine patterns of differential dominance for pleiotropic QTL effects. Differential dominance occurs when dominance patterns for a single locus vary among traits. We find that multivariate overdominance is a common and substantial phenomenon, and may potentially provide an explanation for the persistence of heterozygosity in natural populations.     

Ontogenetic approach to variation in Middle Pleistocene hominids. Evidence from the Atapuerca-SH mandibles

The ontogenetic processes underlying the variation detected in the European Middle Pleistocene hominids are explored. Regulation of growth parameters of the ontogenetic trajectory of these hominid is discussed in the context of heterochrony schemes. The sample of mandibles coming from the Atauuerca-SH site is used as a study case. The variability shown by these mandibles can be arranged along a morphological gradient, and study of growth directions has shown that the remodelling patterns are in line with the existence of a single morphogenetic pattern controlling the process. In addition, the spectrum of morphology detected in the Atapuerca sample virtually encompasses the entire range of variability detected in European Middle Pleistocene samples. From a morphological viewpoint, a hypermorphic pattern seems to be the responsible for the individual variation detected in the sample. Yet, when this information is related to mandibular growth and craniofacial interactions, evidence of an interindividual gradient of somatic development for the Atapuerca hominids is provided. Several hypotheses concerning growth parameters, however, may account for this gradient. Time and rate hypermorphosis hypothesis are discussed. Coincidence of the gradient of variation detected in this sample and the general mandibular growth trajectory of living species, support the hypothesis that is “time of maturation” of the organism the key factor.     

Pleiotropic effects on mandibular morphology II: differential epistasis and genetic variation in morphological integration

The evolution of morphological modularity through the sequestration of pleiotropy to sets of functionally and developmentally related traits requires genetic variation in the relationships between traits. Genetic variation in relationships between traits can result from differential epistasis, where epistatic relationships for pairs of loci are different for different traits. This study maps relationship quantitative trait loci (QTLs), specifically QTLs that affect the relationship between individual mandibular traits and mandible length, across the genome in an F2 intercross of the LG/J and SM/J inbred mouse strains (N = 1045). We discovered 23 relationship QTLs scattered throughout the genome. All mandibular traits were involved in one or more relationship QTL. When multiple traits were affected at a relationship QTL, the traits tended to come from a developmentally restricted region of the mandible, either the muscular processes or the alveolus. About one-third of the relationship QTLs correspond to previously located trait QTLs affecting the same traits. These results comprise examples of genetic variation necessary for an evolutionary response to selection on the range of pleiotropic effects.     

Inferring developmental modularity from morphological integration: analysis of individual variation and asymmetry in bumblebee wings

Organisms are built from distinct modules, which are internally coherent but flexible in their relationships among one another. We examined morphological variation within and between two candidate modules: the fore- and hindwings of bumblebees (Hymenoptera: Apidae: Bombus empatiens). We used the techniques of geometric morphometrics (Procrustes superimposition) to analyze the variation of landmark configurations in fore- and hindwings. Regression was used to correct for size-related shape variation (allometry). Principal component analysis revealed patterns of variation that were remarkably similar for individual variation and fluctuating asymmetry (FA). Because covariation of FA among parts must be due to direct transmission of the developmental perturbations causing FA, this agreement of patterns suggests that much of individual variation is also due to direct developmental interactions within each developing wing. Moreover, partial least squares analysis indicated that the patterns of shape covariation between fore- and hindwings were nearly the same as the patterns of within-wing variation. Shape covariation of FA was only found in bees that had been reared under elevated CO(2) concentration but not in bees from the control treatment, suggesting that the mechanisms of developmental interactions between fore- and hindwings are related to gas exchange. We conclude that the fore- and hindwings are developmental modules that maintain internal coherence through direct developmental interactions and are connected to each other only by relatively few links that use the system of interactions within modules.     

Functional integration for enrolment constrains evolutionary variation of phacopid trilobites despite developmental modularity

Modularity and integration are variational properties expressed at various levels of the biological hierarchy. Mismatches among these levels, for example developmental modules that are integrated in a functional unit, could be informative of how evolutionary processes and trade‐offs have shaped organismal morphologies as well as clade diversification. In the present study, we explored the full, integrated and modular spaces of two developmental modules in phacopid trilobites, the cephalon and the pygidium, and highlight some differences among them. Such contrasts reveal firstly that evolutionary processes operating in the modular spaces are stronger in the cephalon, probably due to a complex regime of selection related to the numerous functions ensured by this module. Secondly, we demonstrate that the same pattern of covariation is shared among species, which also differentiate along this common functional integration. This common pattern might be the result of stabilizing selection acting on the enrolment and implying a coordinate variation between the cephalon and the pygidium in a certain direction of the morphospace. Finally, we noticed that Austerops legrandi differs slightly from other species in that its integration is partly restructured in the way the two modules interact. Such a divergence can result from the involvement of the cephalon in several vital functions that may have constrained the response of the features involved in enrolment and reorganized the covariation of the pygidium with the cephalon. Therefore, it is possible that important evolutionary trade‐offs between enrolment and other functions on the cephalon might have partly shaped the diversification of trilobites.     

Functional Golgi units in microtubule-disrupted cultured atrial myocytes.

We examined the effects of disassembly of microtubules (MT) on the structure and the functions of the Golgi apparatus (GA) in cultured atrial myocytes. MT disassembly with nocodazole led to fragmentation of the GA into small units. The fragmented Golgi units retained their cis-trans polarity and post-cisternal elements, including the trans-Golgi network (TGN). Neither endocytosis of lectin-labeled membrane nor its delivery to the fragmented Golgi units was interrupted by fragmentation of the GA after MT disassembly with nocodazole treatment. A fraction of the secretory granules associated with the fragmented Golgi units was also labeled with the internalized tracer. These results suggest that in nocodazole-treated cultured atrial myocytes, the fragmented Golgi units appear to be structurally and functionally intact despite the altered geometric arrangement of the GA in the cells.     

青岛耐冬山茶的多样性：Ⅰ分布与形态变异

青岛崂山沿海岛屿有天然古山茶（ＣａｍｅｌｌｉａｊａｐｏｎｉｃａＬ．）分布,为山茶类植物中的耐寒类型,而被称作“耐冬”。耐冬古山茶个体间有形态上的明显变异。在野生状态下,产生了长蕊、少瓣、大花类等性状分化稳定的多种类型。青岛海岛耐冬山茶不仅有较高观赏价值,且可视为北方山茶的基因库。本文介绍了青岛耐冬山茶的分布与现状、生态生物学特征及其不同的变异类型,并对耐冬山茶多样性研究的意义作了简要说明。     

Evolution of mating systems inLycopersicon hirsutum as deduced from genetic variation in electrophoretic and morphological characters

Populations in the central part of the distribution are mostly self-incompatible and tend to be highly variable for allozymic and morphological characters; those in the north and south limits are entirely self-compatible and tend to be genetically highly uniform. Gradations in variability are observed in the intermediate regions. Flower size tends to diminish in the peripheral areas. The extensive differences in genotype observed between the north and south marginal populations are not compatible with the concept of a single origin of self-compatibility, but suggest, along with other evidence, that the substitution of different alleles resulted from differentiation in the marginal areas from older, self-incompatible stocks of the central region. The conclusions regarding patterns of genetic variation and nature of evolution of mating systems inL. hirsutum conform to a remarkable extent with those reached previously forL. pimpinellifolium, a species that is distinct in morphology and ecological preferences yet has a similar latitudinal distribution.     

Functional study of hyperpolarization activated channel (I h ) in Drosophila behavior

Hyperpolarization-activated, cyclic nucleotide-gated and cation-nonselective ion channels (I _h channels, or HCN channels) are known to play important roles in mammals. Their physiological functions in invertebrate remain largely unclear. Here, we report our studies with I _h channel in Drosophila melanogaster. Drosophila Ih channel mutants are found with several defects by behavioral analyses. Their lifespan is reduced, and their chemical sensitivity is shifted. In addition, their length of sleep at light-dark condition is mildly reduced. We generated transgenic flies of I _h promoter-driven Gal4 and examined its expression pattern in both larvae and adult flies. Our results suggest that I _h channel may play diverse roles in Drosophila and provide a basis to further expand our understanding of Drosophila Ih channel function in vivo.     

Functional significance of variation in the shape of mandibles,wings, ovipositor,and abdomen in chalcidoid wasps (Hymenoptera,Chalcidoidea)

In parasitic chalcidoid wasps, the shape of mandibles, the degree of wing development, and the configuration and length of the ovipositor depend on adaptations to the solidity of the host mummy integument, peculiarities of the host search, oviposition into unprotected or protected hosts, and of the host size.     

Temporal trends and metric variation in the mandibles and dentition of Australopithecus afarensis

The Pliocene hominin samples from Hadar and Laetoli are thought to represent one species, Australopithecus afarensis, that exhibits stasis throughout its temporal range and has high levels of skeletal sexual dimorphism. In this paper, we test the hypothesis of stasis in dental and mandibular dimensions using nonparametric rank correlation methods to detect temporal trends and randomization tests to evaluate their statistical significance. We then use two methods (CV resampling; Fligner-Killeen test) to compare overall levels of variation in the fossil sample to those of extant hominoid species. Together, these analyses allow us to gauge the effects of changes through time on variation in mandibles and teeth of A. afarensis.P(3)mesiodistal length, M(3)size, and canine shape change through time but do not appear unusually variable in the sample as a whole. These temporal trends possibly reflect differences between the Laetoli and Hadar site-samples. For mandibles, a pronounced trend towards greater corpus size occurs late in the temporal sequence and contributes to high levels of variation compared to African apes. These results show that significant directional changes do occur in the A. afarensis mandibles and teeth, and in these elements, at least, the species is not static. Temporal variation is clearly an important component of overall variation in the A. afarensis lineage, even though other factors, such as sexual dimorphism, may also play a part.     

Experimental studies of variation in hepaticae. I. Induced variation in lophocolea heterophylla

Quantitative analyses of eleven vegetative characters were obtained from five genetically distinct clones of the leafy hepatic,Lophocolea heterophylla, grown in pure culture in a variety of controlled environments.     

Functional assessment of morphological homoplasy in stem-gnathostomes

Osteostraci and Galeaspida are stem-gnathostomes, occupying a key phylogenetic position for resolving the nature of the jawless ancestor from which jawed vertebrates evolved more than 400 million years ago. Both groups are characterized by the presence of rigid headshields that share a number of common morphological traits, in some cases hindering the resolution of their interrelationships and the exact nature of their affinities with jawed vertebrates. Here, we explore the morphological and functional diversity of osteostracan and galeaspid headshields using geometric morphometrics and computational fluid dynamics to constrain the factors that promoted the evolution of their similar morphologies and informing on the ecological scenario under which jawed vertebrates emerged. Phylomorphospace, Mantel analysis and Stayton metrics demonstrate a high degree of homoplasy. Computational fluid dynamics reveals similar hydrodynamic performance among morphologically convergent species, indicating the independent acquisition of the same morphofunctional traits and, potentially, equivalent lifestyles. These results confirm that a number of the characters typically used to infer the evolutionary relationships among galeaspids, osteostracans and jawed vertebrates are convergent in nature, potentially obscuring understanding of the assembly of the gnathostome bodyplan. Ultimately, our results reveal that while the jawless relatives of the earliest jawed vertebrates were ecologically diverse, widespread convergence on the same hydrodynamic adaptations suggests they had reached the limits of their potential ecological diversity—overcome by jawed vertebrates and their later innovations.     

植物DNA甲基化及胁迫诱导的变异

DNA中碱基的化学修饰近年来一直是生命科学领域研究的热点之一。DNA甲基化是一种常见的表观遗传现象,它能在不改变DNA序列的前提下改变遗传表型。各种胁迫因素能诱导植物DNA甲基化产生变异,但其应答胁迫机制仍然未知。本文对植物DNA甲基化研究进展进行了综述,结合本课题组的研究结果,对7Li离子束注入、~(60)CO-γ射线诱变诱导产生的DNA甲基化变异进行了报道,以期为DNA甲基化可能参与涉及植物的表型可塑性提供一定的依据。     

Developmental plasticity, morphological variation and evolvability: a multilevel analysis of morphometric integration in the shape of compound leaves

The structure of compound leaves provides flexibility for morphological change by variation in the shapes, sizes and arrangement of leaflets. Here, we conduct a multilevel analysis of shape variation in compound leaves to explore the developmental plasticity and evolutionary potential that are the basis of diversification in leaf shape. We use the methods of geometric morphometrics to study the shapes of individual leaflets and whole leaves in 20 taxa of Potentilla (sensu lato). A newly developed test based on the bootstrap approach suggests that uncertainty in the molecular phylogeny precludes firm conclusions whether there is a phylogenetic signal in the data on leaf shape. For variation among taxa, variation within taxa, as well as fluctuating asymmetry, there is evidence of strong morphological integration. The patterns of variation are similar across all three levels, suggesting that integration within taxa may act as a constraint on evolutionary change.