Evolution and development in cave animals: from fish to crustaceans

Cave animals are excellent models to study the general principles of evolution as well as the mechanisms of adaptation to a novel environment: the perpetual darkness of caves. In this article, two of the major model systems used to study the evolution and development (evo–devo) of cave animals are described: the teleost fish Astyanax mexicanus and the isopod crustacean Asellus aquaticus. The ways in which these animals match the major attributes expected of an evo–devo cave animal model system are described. For both species, we enumerate the regressive and constructive troglomorphic traits that have evolved during their adaptation to cave life, the developmental and genetic basis of these traits, the possible evolutionary forces responsible for them, and potential new areas in which these model systems could be used for further exploration of the evolution of cave animals. Furthermore, we compare the two model cave animals to investigate the mechanisms of troglomorphic evolution. Finally, we propose a few other cave animal systems that would be suitable for development as additional models to obtain a more comprehensive understanding of the developmental and genetic mechanisms involved in troglomorphic evolution

MOLECULAR BIOLOGY AND PHYSIOLOGY Genotypic Variation in Physiological Strategies For Attaining Cotton Lint Yield Production

ABSTRACT The quality and quantity of cotton (Gossypium hirsutum L.) lint produced are complex traits controlled by multiple processes. The physiology behind yield and quality variations is not completely understood. Objectives for this research were to document the physiological strategies diverse cotton genotypes take to achieve their yield and fiber quality. The genotypes 'DPL 444BR', 'DPL 555BR', 'FM 800BR', 'MD 9', 'MD 15-OP', 'MD 29', 'MD 51 normal', 'MD 51 okra', 'PM 1218BR', and 'ST 4892BR' were grown in the field from 2005-2008. Dry matter partitioning, leaf photosynthesis, chlorophyll concentration, root hydraulic conductance, lint yield, yield components, and fiber quality data were collected. Lint yields ranged from 1675 to 1119 kg ha -1 among the genotypes. The size of the available carbon assimilate pool generated by a genotype appeared to be related to lint yield production. Genotypes used different strategies to generate this carbon assimilate pool, i.e. through improved photosynthetic rates and/ or solar radiation interception, and then convert that carbon into lint production. Fiber quality variations, however, could not easily be explained by just variations in the plants ability to produce carbon assimilates. Beyond just the quantity of carbon assimilates, it is the manner in which the plant assembles these carbon skeletons into the cellular matrix that determines the quality of the fiber produced. These research findings can be utilized to meet the challenge of future yield and fiber quality improvements

MOLECULAR BIOLOGY AND PHYSIOLOGY Genotypic Variation in Physiological Strategies For Attaining Cotton Lint Yield Production

ABSTRACT The quality and quantity of cotton (Gossypium hirsutum L.) lint produced are complex traits controlled by multiple processes. The physiology behind yield and quality variations is not completely understood. Objectives for this research were to document the physiological strategies diverse cotton genotypes take to achieve their yield and fiber quality. The genotypes 'DPL 444BR', 'DPL 555BR', 'FM 800BR', 'MD 9', 'MD 15-OP', 'MD 29', 'MD 51 normal', 'MD 51 okra', 'PM 1218BR', and 'ST 4892BR' were grown in the field from 2005-2008. Dry matter partitioning, leaf photosynthesis, chlorophyll concentration, root hydraulic conductance, lint yield, yield components, and fiber quality data were collected. Lint yields ranged from 1675 to 1119 kg ha -1 among the genotypes. The size of the available carbon assimilate pool generated by a genotype appeared to be related to lint yield production. Genotypes used different strategies to generate this carbon assimilate pool, i.e. through improved photosynthetic rates and/ or solar radiation interception, and then convert that carbon into lint production. Fiber quality variations, however, could not easily be explained by just variations in the plants ability to produce carbon assimilates. Beyond just the quantity of carbon assimilates, it is the manner in which the plant assembles these carbon skeletons into the cellular matrix that determines the quality of the fiber produced. These research findings can be utilized to meet the challenge of future yield and fiber quality improvements

ALMA 1.3 Millimeter Map of the HD 95086 System

Planets and minor bodies such as asteroids, Kuiper-belt objects and comets are integral components of a planetary system. Interactions among them leave clues about the formation process of a planetary system. The signature of such interactions is most prominent through observations of its debris disk at millimeter wavelengths where emission is dominated by the population of large grains that stay close to their parent bodies. Here we present ALMA 1.3 mm observations of HD 95086, a young early-type star that hosts a directly imaged giant planet b and a massive debris disk with both asteroid- and Kuiper-belt analogs. The location of the Kuiper-belt analog is resolved for the first time. The system can be depicted as a broad ($\Delta R/R \sim$0.84), inclined (30\arcdeg$\pm$3\arcdeg) ring with millimeter emission peaked at 200$\pm$6 au from the star. The 1.3 mm disk emission is consistent with a broad disk with sharp boundaries from 106$\pm$6 to 320$\pm$20 au with a surface density distribution described by a power law with an index of --0.5$\pm$0.2. Our deep ALMA map also reveals a bright source located near the edge of the ring, whose brightness at 1.3 mm and potential spectral energy distribution are consistent with it being a luminous star-forming galaxy at high redshift. We set constraints on the orbital properties of planet b assuming co-planarity with the observed disk.Comment: accepted for publication in A

Observations of gas flows inside a protoplanetary gap

Gaseous giant planet formation is thought to occur in the first few million years following stellar birth. Models predict that giant planet formation carves a deep gap in the dust component (shallower in the gas). Infrared observations of the disk around the young star HD142527, at ~140pc, found an inner disk ~10AU in radius, surrounded by a particularly large gap, with a disrupted outer disk beyond 140AU, indicative of a perturbing planetary-mass body at ~90 AU. From radio observations, the bulk mass is molecular and lies in the outer disk, whose continuum emission has a horseshoe morphology. The vigorous stellar accretion rate would deplete the inner disk in less than a year, so in order to sustain the observed accretion, matter must flow from the outer-disk into the cavity and cross the gap. In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellar accretion through the inner disk. Here we report observations with the Atacama Large Millimetre Array (ALMA) that reveal diffuse CO gas inside the gap, with denser HCO+ gas along gap-crossing filaments, and that confirm the horseshoe morphology of the outer disk. The estimated flow rate of the gas is in the range 7E-9 to 2E-7 Msun/yr, which is sufficient to maintain accretion onto the star at the present rate

The surprisingly low carbon mass in the debris disk around HD 32297

Gas has been detected in a number of debris disks. It is likely secondary, i.e. produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15--30 Myr old A-type star HD 32297. We find that C$^0$ is located in a ring at $\sim$110 au with a FWHM of $\sim$80 au, and has a mass of $(3.5\pm0.2)\times10^{-3}$ M$_\oplus$. Naively, such a surprisingly small mass can be accumulated from CO photo-dissociation in a time as short as $\sim$10$^4$ yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C$^0$ and CO observations, is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of $\sim$15 M$_\oplus$ Myr$^{-1}$, much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and re-release. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.Comment: accepted for publication in the Ap