The Underwater Life of Secondarily Aquatic Plants: Some Problems and Solutions

The freshwater secondarily aquatic plants, most of which are higher plants, are those returned to the water environment after spending a period of time living on land. The readaptation to living underwater has made it necessary for these plants to put in place morphological and functional strategies to cope with some major problems due to features of the aquatic environment, but also deriving from the specialized organization of their “terrestrial” bodies. The poor O₂ availability underwater accounted for the evolution of wide aerenchyma tissues throughout the plant organs to improve the photosynthetic O₂ flux from the shoot to the roots buried in anoxic sediments and to the neighboring rhizosphere. This favors sediment oxygenation, sustains the aerobic metabolism of roots, and improves the availability and uptake of mineral nutrients, whose delivery to the entire plants, without a transpirational flux, is ensured by an acropetal mass transport depending on root pressure, guttation from hydathodes and channeling by apoplast closure around the vascular tissues. A great expansion of leaf surfaces and an enhanced surface:volume ratio of chloroplast-rich photosynthetic cells help to contact the water medium and to increase the cell/environment exchanges to gain inorganic carbon. Furthermore, different physiological mechanisms operate to cope with the scarce availability of CO₂ and the prevalence of HCO₃ ^? as inorganic carbon form in water. Some of them, like cell wall acidification through H⁺ extrusion by a light-dependent APTase or activation of an apoplastic carbonic anhydrase, operate outside the cells, leading to a conversion of HCO₃ ^? to CO₂, which then diffuses into the cells. Others, on the contrary, act inside the cells to load the active site of Rubisco with CO₂, thus favoring photosynthesis and lowering photorespiration. Aquatic macrophytes with isoetid life form, moreover, can obtain most ot the fixed CO₂ from sediments. In submerged species, in additin to the C₃ cycle, the C₄ and CAM-like photosynthetic metabolisms can also operate, and are modulated by the environmental inorganic carbon availability and the plant photosynthetic demand. Interestingly, in the aquatic plants the C₄ pathway, which can be concomitant with the C₃ one, does not depend on the Kranz anatomy of leaves, but relies on the intracellular compartmentation of carboxylative and decarboxylative enzymes. The CAM-like pathway, defined AAM, which also coexists with the C₃, allows the submerged plants to fix CO₂ in the dark, thus exploiting the higher CO₂ availability in the water medium during the night, and extending to 24?h the period of inorganic carbon assimilation. In almost all the aquatic macrophytes the AAM is only expressed in the submersion state, whereas it is quickly inactivated in emerging leaves in a cell by cell way.     

Salmonella Typhoid Toxin PltB Subunit and Its Non-typhoidal Salmonella Ortholog Confer Differential Host Adaptation and Virulence

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The evolution of placentas and superfetation in the fish genus Poecilia (Cyprinodontiformes: Poeciliidae: subgenera Micropoecilia and Acanthophacelus)

Complex adaptations are often found in nature, although our ability to discern how and why such traits evolved is limited because their origin occurred in the distant past and the details of their evolution have been lost through extinction (e.g. all placental mammals inherited their placentas from a single common ancestor that lived over 100 Mya). In poeciliid fishes, placentas have evolved independently multiple times and portions of the path to the evolution of complexity can be found in living species. In the present study, we describe the life histories of six species within the genus Poecilia that includes the subgenera Micropoecilia and Acanthophacelus (the guppy; Poecilia reticulata). We demonstrate that extensive placentotrophy and superfetation, the ability to simultaneously carry more than one developing brood, have evolved within this clade. These fish represent the third clade in which we have discovered the independent origin of a placenta that also includes close relatives that lack a placenta. We discuss possible adaptive advantages of the joint evolution of extensive placentation and superfetation in these fishes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 784–796.     

Adaptive associations between total body color dimorphism and climatic stress‐related traits in a stenothermal circumtropical Drosophila species

Abstract Low desiccation resistance of Drosophila ananassae reflects its rarity outside the humid tropics. However, the ability of this sensitive species to evolve under seasonally varying subtropical areas is largely unknown. D. ananassae flies are mostly lighter during the rainy season but darker and lighter flies occur in the autumn season in northern India. We tested the hypothesis whether seasonally varying alternative body color phenotypes of D. ananassae vary in their levels of environmental stress tolerances and mating behavior. Thus, we investigated D. ananassae flies collected during rainy and autumn seasons for changes in body melanization and their genetic basis, desiccation‐related traits, cold tolerance and mating propensity. On the basis of genetic crosses, we found total body color dimorphism consistent with a single gene model in both sexes of D. ananassae. A significant increase in the frequency of the dark morph was observed during the drier autumn season, and body color phenotypes showed significant deviations from Hardy‐Weinberg equilibrium, which suggests climatic selection plays a role. Resistance to desiccation as well as cold stress were two‐ to three‐fold higher in the dark body color strain as compared with the light strain. On the basis of no‐choice mating experiments, we observed significantly higher assortative matings between dark morphs under desiccation or cold stress, and between light morphs under hot or higher humidity conditions. To the best of our knowledge, this is the first report on the ecological significance of seasonally varying total body color dimorphism in a tropical species, D. ananassae.     

Behavioural adaptations of the fiddler crabs Uca vocans borealis (crane) and Uca lactea lactea (De Haan) for coexistence on an intertidal shore

The distribution and coexistence of the fiddler crabs U. vocans borealis and U. lactea lactea was investigated in the upper shore of a sandy beach with respect to particle size, water content and total organic carbon content of the sediments. A clear segregation of habitats between the two species was apparent. U. lactea lactea were only found in sediments with significantly lower total organic carbon content. U. lactea lactea had a higher ratio for the size of third maxilliped to body size than U. vocans borealis. There was no statistical difference in the median sediment particle size of the habitats where both species were found on the study shore. U. lactea lactea was larger on shores where U. vocans borealis were absent. Smaller U. vocans borealis individuals occupied sediments with higher water content and finer particles. Smaller individuals of U. vocans borealis also possessed fewer spoon-tipped setae on second maxilliped than their larger conspecifics, which were found mostly on coarser sediments. U. lactea lactea spent significantly more time on the surface than in the burrow during low tide when compared with U. vocans borealis. Both Uca species exhibited similar desiccation resistance. U. lactea lactea tends to keep its frontal region in close contact with sediments to maintain moisture when being exposed to air.     

Scanning electron microscopy of olfactory rosette in sea trout

Summary Scanning electron microscopy has been employed to study the central axis and laminae of the olfactory rosette in adult sea trout (Salmo trutta trutta L.) caught in the River Umeälven when they were homing from sea.—Both flat sides of the primary laminae are secondarily folded all over their surface. In one organ there are about 200 secondary laminae usually arranged in longitudinal, parallel ridges crossing the surface of the primary laminae. Initially they are covered with sensory epithelium, but as the folds grow they become covered with an increasing area of indifferent ciliar epithelium with bushes of cilia separated by microvilli cells and goblet cells. Parts of the central axis and primary laminae have a nonciliar indifferent epithelium. The sensory epithelium has irregularly arranged cilia. Like those of the indifferent epithelium they have uniform thickness and granulated surface. The function of laminae, secretion and cilia is discussed.The author wish to acknowledge the technical facilities and assistance in the use of the scanning electron microscope to Jeolco Stockholm office. This research was supported by grants 2389-10, 2389-11 and 2389-13 from the Swedish Natural Science Research Council.     

Searching the genome for our adaptations

The current genomic revolution represents a turning point in our understanding of human evolution. For the first time, we are able to begin to investigate human evolutionary adaptations by comparing our entire genome with the genomes of other animal species with which we are related by descent. We are also able to begin fully investigating the genetic differences within and among human populations to understand exactly how human populations have evolved and adapted over time.     

Rewiring of hormones and light response pathways underlies the inhibition of stomatal development in an amphibious plant Rorippa aquatica underwater

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