The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

Mucilage secretion in seeds of Mediterranean species: hypotheses about its origin and function

An outstanding modification of the diaspore surface structure in many species of the Angiosperms is the presence of a mucilaginous layer. In these species, when the dry seed coat or the pericarp comes in contact with water, imbibes the outer cell wall completely and release a mucilaginous substance; a phenomenon known as myxospermy. Mucilage is composed of polysaccharides, mostly of pectins, and forms a gel like envelop around the diaspore that holds a considerable amount of water due to its hydrophilic nature. The seed weight as well as the volume increases significantly once the mucilage is released. Once it dries up, mucilage becomes stiff then gluing the diaspore to the surface on which it settles. There are differences in mucilage composition depending on the species. However, the main component of the mucilage of the pericarp and seed coat in all species are pectins. The polysaccharide and acidic qualities of mucilage make them very hydrophilic so in the presence of water they hydrate rapidly, thus forming super absorbent hydrogels. After water absorption, the mucilage breaks through the cell wall forming the mucilaginous envelope surrounding the seed. In addition to pectin, mucilage in some species also contains strands of elementary fibrils of cellulose of different widths embedded in the pectin envelope. Mucilage can therefore be distinguished in “true” mucilage consisting almost exclusively of pectin, and “cellulosic” mucilage, which, additionally to pectin, also contains cellulose fibrils. Cellulosic mucilage seems to add an additional strength to the pectin mucilage layer and has been hypothesized that it prevents mucilage of being washed away from the seed coat or fruit pericarp making the mucilage more rigid and thus, resulting in an enhanced adhesion of the mucilage to the diaspore.During the time of the elaboration of this dissertation I have enjoyed a scholarship from the program >Junta para la Ampliación de Estudios-JAE Predoctoral para la Formación y Especialización de Personal Investigador del Consejo Superior de Investigaciones Científicas>. The work has been financed by projects from the Spanish Government ARIDERO (CGL2005-03912) and ROSMARINUS (CGL2009-07262).Peer Reviewe

Mucilage secretion by seeds doubles the chance to escape removal by ants

9 páginas, 3 figuras.-- Título en el preprint: Post-dispersal seed anchorage to soil in semiarid plant communities, a test of the hypothesis of Ellner and ShmidaPost-dispersal seed predation is a risk for plants in semiarid environments, leading to strategies to protect their propagules from seed collection by animals. In this study, we evaluated the importance of mucilage secretion in seeds as a mechanism to reduce seed collection by ants. We selected three Mediterranean species with strong mucilage secretion on their seeds which become sticky upon wetting. Seeds of Rosmarinus officinalis, Fumana ericoides, and Fumana thymifolia were exposed to ants and survival was compared between dry loose seeds and seeds glued to the soil with previously secreted mucilage. The study site was in the Sierra Calderona, 25 km north of Valencia (Spain). The ant-plant interaction was analyzed by scrutinizing seed collection by ants and by analyzing the waste piles of ant nests. To test survival, groups of 10 seeds were placed on the ground. Each group consisted of five control (dry) and five mucilaginous seeds (previously mucilage secreted) and was covered by the cover of a Petri dish modified to permit only the entry of ants. Seeds were inspected weekly for seed disappearance and the survival function (Kaplan-Meier estimator) was calculated. Seeds of the target species were important food items for ants and were actively collected, and more than 50 % of the experimental seeds that were glued to the ground with their own mucilage survived at the end of the study period but only 0-20 % of the control seeds survived after the same time of exposure. The implications for plant establishment of these findings are discussed.This research was supported by the Spanish "Plan Nacional de I + D + I" projects CGL2005-03912 (ARIDERO) and CGL2009-07262 (ROSMARINUS)]. We would especially like to thank Xavier Espadaler for his identification of the ant species and Cristian Escrihuela for his continuous help in the laboratory and in the field. Also we would like to thank Santiago Donat, Svenja Stadtschreiber, and Mechtild Engelbrecht for their assistance in the field and to two anonymous reviewers for their comments that greatly improved the manuscript. Meike Engelbrecht enjoyed a grant from the Spanish National Research Council (CSIC) [JAE-Pre 08 00758]. The National Meteorological Agency of Spain kindly provided the precipitation data of the 1990–2011 periods.Peer reviewe

Mucilage secretion works as mechanism to reduce seed removal by soil erosion

Poster presentado en el 12th European Ecological Federation Congress celebrado en Ávila del 25 al 29 de septiembre de 2011Mucilage segregation in diaspores after wetting has been related to different functions but there has not been an approach to the benefit of mucilage as an adherence mechanism under erosive conditions. We want to understand the advantages of mucilage segregation for plants experiencing soil erosion and to establish a quantitative relation between the phenotypic expression and the success of seed adherence. We also aimed to know if changes in erosive conditions influence mucilage segregation in species and the specific composition of plant communities. We related the amount of mucilage segregation with the number of drop impacts needed to remove the seeds under simulated rain in Helianthemum violaceum and Fumana ericifolia (Cistaceae) and measured seed removal distance because water runoff in seeds with and without mucilage of H. violaceum. Also, we compared the amount of seed mucilage segregation of plants living under erosive and non-erosive conditions and the proportion of species with mucilaginous diaspores of Mediterranean semiarid plant communities under those contrasted conditions. The amount of segregated mucilage positively related to longer resisting rain drop impacts in F. ericifolia but not in H. violaceum seeds. However, H. violaceum seeds with intact mucilage layer moved half of the distance because of runoff than those without. Moving from non-erosive to high-erosive sites, near 10% increase in mucilage segregation was found in seeds of F. ericifolia but a decrease of 1% in H. violaceum. Likewise, the presence of species with mucilaginous diaspores increases 9-28% in plant communities living in those contrasted conditions. Mucilage segregation by diaspores is an effective way to reduce seed removal by erosion in plants, even if it operates in different ways depending on the species. Intensification of the exposition of plants to erosive conditions produces a quantitative response in the expression of this mechanism in one of two species tested and at community level.Peer Reviewe

Is myxospermy a trait selected because soil erosion?

Ponencia presentada en el 4th International Society for Seed Science Meeting on Seeds and the Envoronment celebrado en Shenyang (China) del 22 al 26 junio de 2013Introduction: Soil particle detachment and transport along hillslopes caused by raindrops and runoff are the main mechanisms of soil erosion by rainfall in semiarid regions. Seeds resting on the soil surface after seed dispersal are at a risk of being removed downslope by erosion and deposited in the lower parts of hillslopes where seed burial or competition with pre-established vegetation may reduce plant fitness of plant species with low competitive abilities. Diaspores of many plant species inhabiting open vegetation in semiarid environments secrete mucilage after wetting (myxospermy), gluing them to the ground and preventing further movement when the mucilage dries. Although several different ecological roles have been proposed for myxospermy, in the present paper we tested whether mucilage secretion may be considered a response to soil erosion in plant species inhabiting semiarid environments. Methods: We related the amount of mucilage secretion by seeds of Helianthemum violaceum and Fumana ericifolia (Cistaceae) with the number of raindrop impacts needed to remove these seeds after gluing them with their own mucilage to the ground and the time that these seeds resist water runoff without detaching,. We also compared the amount of seed mucilage production by plants growing in habitats with contrasted erosion. Results and Conclusions: Our results show an important phenotypic variation in the amount of mucilage secretion in both species but suggest that the effect of mucilage secretion in the rate of seed removal by erosion is species and mechanism dependent. In F. ericifolia, the amount of mucilage secreted by the seeds is directly proportional to their resistance to raindrop impacts and is positively related, although weakly, to the intensity of erosion processes that plants experience. Nevertheless, all the seeds resist the force of runoff during 60 minutes irrespective of the amount of mucilage they produce. However, in H. violaceum mucilage secretion per se, but not the amount of mucilage produced by the seeds has an effect on the rate of seed removal by erosion processes and relates weak but inversely to the intensity of these processes that plants experience.Peer Reviewe

Mucilage secretion: an adaptative mechanism to reduce seed removal by soil erosion?

Diaspores of many plant species inhabiting open vegetation in semi-arid environments secrete mucilage after wetting (myxospermy) that glues the diaspores to the ground and prevents movement when the mucilage dries. In the present study, we test whether mucilage secretion can be considered as a selective response to soil erosion in plant species inhabiting semi-arid environments. We relate the amount and type of mucilage secretion by seeds of Helianthemum violaceum and Fumana ericifolia (Cistaceae) to the number of raindrop impacts needed to remove these seeds after gluing them with their own mucilage to the ground and also the time that these seeds resist water run-off without detaching. We also compare the amount of seed mucilage production by plants growing in habitats without erosion and plants affected by severe erosion by fitting mixed effect models. Our results show an important phenotypic variation in the amount of mucilage secretion in both species, although it is suggested that the effect of mucilage secretion in the rate of seed removal by erosion is species- and mechanism-dependent. For F. ericifolia, the amount of mucilage secreted by the seeds is directly proportional to their resistance to raindrop impacts and is positively related to the intensity of the erosive processes that the plants experience. Nevertheless, all the seeds resist the force of run-off during 60 min, irrespective of the amount of mucilage they produce. In H. violaceum, mucilage secretion per se, and not the amount of mucilage produced by the seeds, has an effect on the rate of seed removal by erosive processes. Furthermore, cellulosic fibrils were found only in the mucilage of F. ericifolia but not in H. violaceum. Overall, our results only partially support the hypothesis that a selective response to soil erosion exists. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 241–251.This research was supported by the Spanish ‘Plan Nacional de I+D+I’ [project CGL2005-03912]. Meike Engelbrecht received grants from the Spanish National Research Council (CSIC) [JAEPre 08 00758] and the CSIC-Fundación BANCAJA [BOE 185 de 03/08/2007] of Spain.Peer Reviewe

Post-dispersal seed anchorage to soil in semiarid plant communities, a test of the hypothesis of Ellner and Shmida

In this paper we test the Ellner and Shmida's hypothesis that in semiarid environments aridity may select for the lack of seed dispersal mechanisms (atelechory) of many plants, whereas post-dispersal selective forces such as soil erosion, seed predation or limitations to water uptake by seeds may select for structures facilitating seed anchorage to the ground (antitelechory). We analyzed the proportions of species with seed anchorage mechanisms and that of atelechoric species in shrublands colonizing flat areas and hillslopes in two sites differing in climate dryness. Their relation with several soil properties involved in runoff generation, seed-soil contact and water uptake by seeds and with nest density of granivorous ants was also explored. Our results support the hypothesis that in semiarid shrublands the proportion of species with seed anchorage mechanisms increases because of soil erosion but not because of climate dryness. This is the first time that a direct relation between the proportion of species with seed anchorage mechanisms and soil erosion is shown in plant communities; supporting the view that soil erosion shapes species composition in communities. © 2013 Springer Science+Business Media Dordrecht.This research was supported by the Spanish “Plan Nacional de I+D+i” [projects CGL2005-03912 and CGL2009-07262]. Meike Engelbrecht was funded by grants from the Spanish National Research Council [JAEPre-0800758] and the CSIC-Fundación BANCAJA [2007] of Spain.Peer Reviewe

¿Es la erosion del suelo un agente de ensamblaje de comunidades y de selección natural de plantas?

Ponencia presentada en el XI Congreso Nacional de la Asociación Española de Ecología Terrestre celebrado en Pamplona del 6 al 10 de mayo de 2013La erosión del suelo se considera habitualmente sólo como un problema ambiental. En la presente comunicación pretendemos mostrar que debería considerarse también un factor de selección natural y ensamblaje de comunidades. Para ello analizamos la relación entre la erosión y la mixospermia - la capacidad de semillas y frutos de algunas especies de secretar sustancias mucilaginosas en contacto con el agua y que las fija al suelo. A partir de experimentos con propágulos de 140 especies de plantas de ambientes secos y semiáridos, hemos determinado que la tasa de remoción por erosión depende principalmente del tamaño del propágulo. Pero también encontramos que ma mixospermia disminuye notablemente la probabilidad de arrastre de los propágulos por de las clases de tamaño menores. En comunidades vegetales del matorral en ambientes semiáridos encontramos que el aumento de la erosión pero no el de la aridez incrementan la proporción de especies con diásporas mixospérmicas. En especies leñosas de esas mismas comunidades vegetales encontramos una importante variabilidad fenotípica en la expresión de la mixospermia. Dicha variabilidad se relaciona positivamente con su capacidad de evitar la remoción por distintos mecanismos a través de los cuales actúa la erosión. En las especies en las que dicha relación existe, encontramos además que la variabilidad fenotípica en la expresión de la mixospermia se correlaciona positivamente con la intensidad de la erosión que experimentan las poblaciones. Las evidencias obtenidas apoyan que la erosión del suelo debería considerarse un factor de ensamblaje de comunidades vegetales y de selección natural en ambientes semiáridos.Peer Reviewe

Phylogeny, biogeography and morphological ancestral character reconstruction in the Mediterranean genus Fumana (Cistaceae)

Fumana is a diverse genus of the Cistaceae family, consisting of 21 currently accepted species. In this study, nuclear (ITS) and plastid (matK, trnT‐L) molecular markers were used to reconstruct the phylogeny and to estimate divergence times, including 19 species of Fumana. Phylogenetic analyses (Bayesian Inference, Maximum Parsimony and Maximum Likelihood) confirmed the monophyly of Fumana and did not support the infrageneric divisions previously established. The results support four main clades that group species that differ in vegetative and reproductive characters. Given the impossibility to define morphological characters common to all species within the clades, our proposal is to reject infrageneric divisions. Molecular dating and ancestral area analyses provide evidence for a Miocene diversification of the genus in the north‐western Mediterranean. Ancestral state reconstructions revealed ancestral character states for some traits related to xeric and arid habitats, suggesting a preadaptation to the Mediterranean climate.This research has been supportedby the Spanish “Plan Nacional de I+D+I” project “Romero” [CGL2005–03912] and the Botanical Garden of the University of Valencia for permitting to use laboratory facilities. Meike Engelbrecht received a grant from the Spanish National Research Council (CSIC) [JAEPre 08 00758].Peer reviewe