Life history of Xenodexia ctenolepis: implications for life history evolution in the family Poeciliidae

Xenodexia ctenolepis (Hubbs, 1950) is a uniquely asymmetrical species in the fish family Poeciliidae that is endemic to a remote region of Guatemala. In the present study, we describe its life history based on the dissection of 65 adult females from three different collections. We show that it is a livebearer, has superfetation, or the ability to carry multiple litters of young in different stages of development, and has matrotrophy, or placentation, which results in the dry mass of young at birth being three- to four-fold greater than the egg at fertilization. The size distribution of males is non-normal in a fashion that suggests a genetic polymorphism for age and size at maturity. Most phylogenies place Tomeurus gracilis as the sister taxon to the remaining members of the family Poeciliidae. Because Tomeurus is the sole egg-layer in the family, egg-laying is thought to represent the life history of the common ancestor. Because Xenodexia possesses three supposed derived traits (livebearing, superfetation and matrotrophy), this phylogenetic hypothesis suggests that Xenodexia has a highly derived life history with respect to other members of the family. By contrast, the most recent DNA-based phylogeny suggests Xenodexia is the sister taxon to the remainder of the family. If this proves to be true, it suggests that some or all of these life history traits may have been characteristic of the common ancestor to the family, then lost and re-evolved multiple times within the family.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 77–85.     

Decay of Branchiostoma: implications for soft-tissue preservation in conodonts and other primitive chordates

Decay experiments on the cephalochordate Branchiostoma lanceolatum ('amphioxus') demonstrate that the most decay resistant structures are the notochord sheath and the cartilaginous rods which support the gill bars. However, even more labile soft parts, such as the muscles and skin may survive for at least 124 days under totally anoxic conditions. As the chevron-shaped muscles of the myomeres shrink and collapse, those on opposite sides of the trunk maybe displaced, resulting in pronounced offsetting. Only 1.42% of the initial dry weight of Branchiostoma is resistant to alkali and acid hydrolysis, compared to 46% in the polychaete Nereis virens. Branchiostoma is only likely to be fossilized as a result of decay inhibition and replication by early diagenetic minerals. The results of these experiments cast light on the interpretation of a number of primitive fossil chordates. There is no reason to infer extracellular decay-resistant cuticle in the Burgess Shale Pikaia. The axial lies preserved in the conodont animal specimens from the Carboniferous of Edinburgh, Scotland, represent the notochord. The displacement of the elements to one side of the head reflects the true position of the apparatus - the surrounding tissue has been lost through decay. The chevron-shaped structures in the Carboniferous chordate Conopiscius are the muscles of the myomeres, not external scales. The lines delineating the segments in the Silurian Jamoytius most likely represent the myosepta. There is some doubt about the nature of the only specimen interpreted as a fossil cephalochordate, Palaeobranchiostoma hamatotergum from the Permian of South Africa. □ Taphonomy, decay, softparts, Cephalochordata , Branchiostoma, lancelet, Chordata , Pikaia, conodont , Conopiscius, Jamoytius, Palaeobranchiostoma.     

Water-Stress-Induced Changes in the Pattern of Protein Synthesis in Maize Seedling Mesocotyls: A Comparison with the Effects of Heat Shock

Cut segments from the growing and non-growing regions of 4-d-oldmaize seedling mesocotyls exhibit reduced protein synthesiswhen subjected to water-stress imposed directly by incubationin solutions of polyethylene glycol. Growing mesocotyl tissuecan recover full protein synthesis upon return to a fully-hydratedcondition following stress to –0.5 MPa, while non-growingtissue recovers well from greater stresses (–0.75 to –1.0MPa), and in lesser time. Using two-dimensional electrophoresisand fluorography of de novo synthesized proteins in vivo itwas possible to follow changes in protein synthesis in the non-growingtissue under water-stress and upon subsequent recovery. Thesynthesis of several proteins was reduced by stress, althoughthat of others intensified. Those proteins exhibiting reducedsynthesis under stress were synthesized at control levels (i.e. the same levels as in unstressed tissue) when the stresswas relieved. Some proteins whose synthesis was intensifiedunder stress retained this intensification upon return to fullhydration. No unique proteins were synthesized in response towater-stress, in contrast to the ‘heat-shock’ proteinsinduced when the mesocotyls were subjected to high temperature.Hence water-stress induces quantitative rather than qualitativechanges in the pattern of protein synthesis. Key words: Zea mays, Water-stress, Pattern of protein synthesis     

A method for identification of parallelism in discrete character sets

It is proposed that parallel and reverse changes constitute the main factor governing the accuracy of phylogenies reconstructed from sets of discrete data. The relationship between such changes and Le Quesne's concept of compatibility, extended to multi-state characters, is examined and used as the basis of a computerized method, to estimate the proportion of those character states resulting from parallel changes. The results of applying the procedure to simulated protein sequence data and a variety of real data sets are presented, and these suggest that it is possible to estimate accurately (2%) the number of parallel character state changes represented in a data set, without the need to assume a phylogeny for the operational taxonomic units concerned. When real data sets are compared using this method it becomes clear that mammalian cytochrome-c is an exceptionally good protein for the reconstruction of tionary history, and that all other protein sets so far examined are likely to produce phylogenies which are significantly further from the 'best' phylo     

A circadian rhythm of locomotor activity in newly emerged Ceratophyllus sciurorum

Abstract Circadian rhythm in newly emerged individuals of the Red Squirrel ( Scuirus vulgaris ) flea C.s. sciurorum was studied in a constant environment, using an insect activity monitor. Trials were run over 7 days using two start times (08.00 and 17.00 hours). The results show that, regardless of start time, the fleas display a 24 h activity rhythm. The presence of a rhythm under constant conditions gives a strong indication that C. s.sciurorum has a self-sustaining clock which is started by disturbance and is most likely to be linked to host activity patterns.     

The first tomopterid, a polychaete from the Carboniferous of Scotland

Briggs, Derek E. G. & Clarkson, Euan N. K. 1987 07 15: The first tomopterid, a polychaete from the carboniferous of Scotland.
The first known example of a fossil tomopterid, Eotomopteris aldridgei , is described from the Lower Carboniferous of Granton, Edinburgh. The head bears tentacular cirri, and the trunk preserves evidence of at least 20 pairs of parapodia. The polychaete is associated with other soft-bodied and lightly skeletalized organisms including crustaceans, conodonts, an additional chordate, and branching structures which resemble hydroids. It is similar to living tomopterids and was probably pelagic. This discovery indicates that these polychaetes were well established by the early Carboniferous and probably before.     

The restoration of flattened fossils

Neither collapse, due to decay in a soft-bodied organism, nor compaction, due to overburden pressure, normally lead to significant lateral expansion in flattened fossils except in the case of some with rigidly mineralized skeletons. The fossils are thus analogous to a variety of two-dimensional views of a three-dimensional object. This realization provides a foundation for drawing and testing a reconstruction using either computer or manual graphic restoration methods. A complementary approach based on the photography of simple models, which is particularly useful where a complex three-dimensional morphology is under study, is described and illustrated by two examples, the Middle Cambrian arthropod Odaraia and the Upper Ordovician graptolite Direllograptus .     

The Effects of Rapid and Very Slow Speeds of Drying on the Ultrastructure and Metabolism of the Desiccation-Sensitive Moss Cratoneuron filicium (Hedw.) Spruce

The response of the semi-aquatic moss species Cratoneuron filicinumto desiccation varies with the speed at which it loses water.On rehydration following rapid drying the contents of all cellsare considerably disrupted and they become increasingly disorganizedover a 24 h time period. After very slow drying some cells havethe appearance of those after rapid drying, while others maintaintheir integrity, and the internal organization of mitochondriaand chloroplasts is evident The capacity to resume protein synthesison rehydration is reduced after very slow, slow, and rapid drying:the greater the speed of drying the more it is reduced. Rapidwater loss down to 50% of original fresh weight has no irreversibleeffect on protein synthesis. Respiration does not occur on rehydrationafter rapid drying, although failure to maintain sterile conditionsduring measurement of oxygen consumption can lead to artefactsdue to bacterial contamination. The results are contrasted withthose obtained previously from the desiccation-tolerant mossTortula ruralis, and possible reasons for the differences areoutlined.     

Response of body temperature to solar radiation in restrained nymphal migratory grasshoppers (Orthoptera: Acrididae): influences of orientation and body size

Abstract. .We restrained forty-nine nymphal migratory grasshoppers (Melanoplus sanguinipes) in a series of orientations to the sun and measured rate of temperature change due to radiation intercepted, compensating for temperature loss by convection and greybody reradiation. Direct solar radiation affected body temperature significantly, but diffuse radiation did not. The coefficient of direct solar heating ( H _dir), varied from 0.603 to 0.690 depending on how radiation interception was estimated, and on whether insect size was expressed as mass or as a function of length. H is the rate of temperature change as a proportion of the maximum rate assuming complete conversion of all incident radiation to heat. None of the H_dir estimates was significantly different from visible-spectrum absorbance to (0.722), suggesting that the latter is a reasonable approximation of H _dir
In simulations, equilibrium body temperature elevation decreased with body size where energy influx was expressed as the amount intercepted (W) , but increased with body size when expressed as insolation as (W m-²) because at a specified insolation, the amount of energy intercepted increases with body size. Expressing energy influx as the amount intercepted reveals the underlying biophysical mechanisms which determine body temperature.
This paper presents a model of body temperature elevation in which fundamental physical processes are assembled to provide good estimates. This basis in physics implies that the model can can be applied with confidence to conditions other than those in which it was derived.     

Desiccation and the Control of Expression of {beta}-Phaseolin in Transgenic Tobacco Seeds

Drying of seeds at certain stages prior to maturation, i.e.premature desiccation, will terminate synthetic events uniqueto development, for example, storage protein synthesis, andinitiate processes associated with germination. In this studywe have investigated the role of desiccation in the expressionof a storage protein gene, ß-phaseolin, to determineif such a developmentally-regulated gene remains sensitive todrying when controlled by a promoter that has no known sensitivityto this treatment. We compared, in transgenic tobacco seeds,the effects of maturation and premature drying on the expressionof a full ß-phaseolin gene, and ß-phaseolingenes driven by a cauliflower mosaic virus 35S promoter withor without an alfalfa mosaic virus (AMV) 5' untranslated leadersequence. The results indicate that the ß-phaseolinpromoter is directly down-regulated by desiccation during maturationand, although activated during the drying phase of a prematuredesiccation event, it is not active upon rehydration or imbibition.The 35S promoter is down-regulated also by both maturation dryingand premature desiccation but unlike the ß-phaseolinpromoter it is reactivated upon rehydration or imbibition. Key words: Desiccation, ß-phaseolin, gene regulation, Phoseolus vulgaris, seed development