Land crabs as key drivers in tropical coastal forest recruitment

Plant populations are regulated by a diverse assortment of abiotic and biotic factors that influence seed dispersal and viability, and seedling establishment and growth at the microsite. Rarely does one animal guild exert as significant an influence on different plant assemblages as land crabs. We review three tropical coastal ecosystems–mangroves, island maritime forests, and mainland coastal terrestrial forests–where land crabs directly influence forest composition by limiting tree establishment and recruitment. Land crabs differentially prey on seeds, propagules and seedlings along nutrient, chemical and physical environmental gradients. In all of these ecosystems, but especially mangroves, abiotic gradients are well studied, strong and influence plant species distributions. However, we suggest that crab predation has primacy over many of these environmental factors by acting as the first limiting factor of tropical tree recruitment to drive the potential structural and compositional organisation of coastal forests. We show that the influence of crabs varies relative to tidal gradient, shoreline distance, canopy position, time, season, tree species and fruiting periodicity. Crabs also facilitate forest growth and development through such activities as excavation of burrows, creation of soil mounds, aeration of soils, removal of leaf litter into burrows and creation of carbon-rich soil microhabitats. For all three systems, land crabs influence the distribution, density and size-class structure of tree populations. Indeed, crabs are among the major drivers of tree recruitment in tropical coastal forest ecosystems, and their conservation should be included in management plans of these forests.     

Analysis of amino acids in nectar from Silene colorata Poiret (Caryophyllaceae)

Nectar samples were collected from Silene colorata Poiret (Caryophyllaceae), in three different populations from south-western Spain: Zahara de la Sierra (Cádiz), Bornos (Cádiz) and Bormujos (Seville). Samples were analysed for amino acids by reverse-phase high-performance liquid chromatography with precolumn phenylisotiocyanate (PITC) derivatization. The method has the advantage of being highly sensitive, capable of detecting nanogram (ng) quantities of amino acids. Eighteen amino acids were identified and quantified. The mean number of amino acids in a nectar sample was 14 (SD = 2.8). Six amino acids (threonine, alanine, arginine, proline, tyrosine and methionine) were detected in all samples, accounting for 83% of the total amino acids content; proline and arginine were the most abundant amino acids, accounting for 40% and 20% of the total amino acids, respectively. The mean amounts of amino acids in nectar samples per population were 824, 782 and 356 µ m in Zahara de la Sierra, Bornos and Bormujos, respectively. Environmental variations such as temperature and sunlight are factors influencing the metabolic processes of nectar production. Our results may contradict the theory that the chemical constituents of floral nectar vary according to the kinds of pollinators.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 49–56.     

SYMPATRIC CONVERGENCE AND ENVIRONMENTAL CORRELATION BETWEEN TWO LAND-SNAIL SPECIES

In the southern Appalachian region of North America, the phylogenetically convergent shells of the polygyrid snails Triodopsinae Neohelix major (Binney) and Polygyrinae Mesodon normalis (Pilsbry) are even more convergent in size and shape in sympatry (7 sites) than in allopatry (23 and 10 sites). Environmental correlations account for 34% and 30% of size and shape variations in N. major (larger, taller, and more loosely coiled at northern, high-altitude, sheltered sites), but for only 14% and 9% in M. normalis (larger, flatter, and more loosely coiled at south-facing, exposed sites). The statistical significance of the sympatric convergence dropped out when these correlations were removed. This phenomenon helps account for the many cases in eastern North America of nearly identical land-snail shells in sympatry and questions the importance of competitive character displacement in the evolution of land-snail shell morphology. This apparently nonmimetic case of sympatric convergence provides an unusually precise and well-delimited, naturally replicated experiment in evolutionary morphology, which is analyzed for controlling factors in a follow-up paper.     

Field Hypothesis on the Self-regulation of Gene Expression

The mechanism of the self-regulation of gene expression in living cells is generally explained by considering complicated networks of key-lock relationships, and in fact there is a large body of evidence on a hugenumber of key-lock relationships. However, in the present article we stress that with the network hypothesis alone it is impossible to fully explain the mechanism of self-regulation in life. Recently, it has been established that individual giant DNA molecules, larger than several tens of kilo base pairs, undergo a large discrete transition in their higher-order structure. It has become clear that nonspecific weak interactions with various chemicals, suchas polyamines, small salts, ATP and RNA, cause on/off switching in the higher-order structure of DNA. Thus, the field parameters of the cellular environment should play important roles in the mechanism of self-regulation, in addition to networks of key and locks. This conformational transition induced by field parameters may be related to rigid on/off regulation, whereas key-lock relationships may be involved in a more flexible control of gene expression.     

Densitometry from digitized images of X-radiographs: Methodology for measurement of coral skeletal density

Skeletons of massive coral colonies contain annual density bands that are revealed by X-radiography of slices cut along growth axes. These bands allow measurement of skeletal growth parameters such as annual extension rate and annual calcification rate. Such measurements have been important in understanding coral growth, in assessing environmental impacts and in recovering proxy environmental information. Measurements of coral calcification rate from annual density banding require measurements of skeletal density along tracks across skeletal slices and, until now, such density measurements have depended upon specialized and expensive equipment. Here, we describe a straightforward, inexpensive and accurate technique for measuring skeletal density from digitized images of X-radiographs of coral skeletal slices. An aragonitic step-wedge was included in each X-radiograph of a coral slice together with two aluminium bars positioned along the anode-cathode axis. Optical density was measured along tracks across the X-ray images of these different objects. The aragonite step-wedge provided a standard for converting optical density to skeletal density. The aluminium bars were used to correct for the heel effect—a variation in the intensity of the X-ray beam along the anode-cathode axis that would, otherwise, introduce large errors into measurements of skeletal density. Exposure was found to vary from X-radiographs to X-radiograph, necessitating the inclusion of the calibration standards in each X-radiograph of a coral slice. Results obtained using this technique compared well with results obtained by direct gamma densitometry of skeletal slices.     

Effect of the acclimation to high environmental temperature on the activity of hepatic glycogen phosphorylase (a+b and a), liver glycogen content and blood glucose level in rats

(1) Changes in the activity of hepatic glycogen phosphorylase a+b and a (GPh-ase a+b and a), liver glycogen content and blood glucose level during acclimation to moderate high environmental temperature (35±1 °C) were studied. (2) Experiments were carried out on adult fed Wistar rats of both sexes, previously given either short-term (1, 4 and 7 days) or long-term (14, 21, 30 and 60 days) exposure to high environmental temperature. The controls were continuously kept at room temperature (20±2 °C). (3) The results obtained showed that in the period of short-term exposure the liver glycogen content was decreased significantly (after the first and fourth days in male rats and after first day in female rats) and the GPh-ase a activity increased (after first day in male rats and after first, fourth and seventh day in female rats). Long-term exposure caused significant increased liver glycogen content (beginning from the 14th day in male rats and the 21st day in female rats) until the end of the acclimation period (60 days). The elevated activity of GPh-ase a persists after 14th day of exposure only in female rats while there are no significant changes over the rest of the acclimation period in both sexes. There were no significant changes in total GPh-ase activity during the whole period of exposure. Blood glucose level was significantly decreased throughout the whole period of acclimation to high environmental temperature, in both sexes (except in the 1 day exposed groups). (4) The increased activity of hepatic GPh-ase a and decreased glycogen content suggested that the short-term exposure to heat stimulates the glycogenolytical processes. Decreased blood glucose level, and elevated liver glycogen content (r=-0.7467 in male and r=-0.6548 in female rats) suggested that prolonged exposure to high environmental temperature stimulated glycogenogenesis, without changes in the GPh-ase activity.     

Degradation of Machine Oil by Nocardioform Bacteria

Gas liquid chromatography (GLC) was used for the first time to screen for machine oil–degrading microorganisms. Oil degradation was evaluated from the microorganism respiratory activity during the utilization of oil as the sole carbon and energy source. The results are consistent with those obtained by the conventional weighing method. Substrate specificity of the active strains with respect to different machine oils was studied. Bacterial communities exhibited the highest activity, whereas a Rhodococcus erythropolisstrain was the most active among pure cultures. Various stages of bacterial interaction with oil drops were followed by means of fluorescent microscopy.     

The contributions of programmed developmental change and phenotypic plasticity to within-individual variation in leaf traits in Dicerandra linearifolia

Variation among modules of a single genet could provide a means of adaptation to environmental heterogeneity. Two mechanisms that can give rise to such variation are programmed developmental change and phenotypic plasticity. I quantified the relative roles of these two mechanisms in causing within-individual variation in six leaf traits of an annual plant. Under controlled temperatures, morphological, anatomical, and physiological traits of leaves produced by the same individual differed as a function of both the node at which they were produced and the temperature they experienced during development. Temperature, node, and interactions between them all contributed significantly to the pattern of within-individual variation in leaf traits, although the relative contributions of programmed developmental change and phenotypic plasticity differed for different traits. I hypothesize that these two mechanisms for generating within-individual variation in module phenotype are favored by different patterns of environmental heterogeneity; when the sequence of environments encountered by modules of a single individual is predictable, programmed developmental change may be favored, and phenotypic plasticity may be favored when the sequence of environments is irregular with respect to individual ontogeny and therefore not predictable.     

Characteristics of the ichthyofaunas of southwestern Australian estuaries,including comparisons with holarctic estuaries and estuaries elsewhere in temperate Australia: A review

Data on the species compositions and the ages, sizes, reproductive biology, habitats and diets of the main species in the ichthyofaunas of seven estuaries in temperate southwestern Australia have been collated. Twenty-two species spawn in these estuaries, of which 21 complete their lifecycles in the estuary. The latter group, which includes several species of atherinids and gobies with short lifecycles, make far greater contributions to the total numbers of fish in the shallows of these estuaries than in those of holarctic estuaries, such as the Severn Estuary in the United Kingdom. This is presumably related in part to far less extreme tidal water movements and the maintenance of relatively high salinities during the dry summers, and thus to more favourable conditions for spawning and larval development. However, since estuaries in southwestern Australia have tended to become closed for periods, there would presumably also have been selection pressures in favour of any members of marine species that were able to spawn in an estuary when that estuary became landlocked. Furthermore, the deep saline waters, under the marked haloclines that form in certain regions during heavy freshwater discharge in winter, act as refugia for certain estuarine species. The contributions of estuarine-spawning species to total fish numbers in the shallows varied markedly from 33 or 34% in two permanently open estuaries to ≥ 95% in an intermittently open estuary, a seasonally closed estuary and a permanently open estuary on the south coast, in which recruitment of the 0 + age class of marine species was poor. The larger estuarine species can live for several years and reach total lengths of ~ 700 mm and some estuarine species move out into deeper waters as they increase in size. Several marine species use southwestern Australian estuaries as nursery areas for protracted periods. However, sudden, marked increases in freshwater discharge in winter and resultant precipitous declines in salinity in the shallows, and in other regions where haloclines are not formed, are frequently accompanied by rapid and pronounced changes in ichthyofaunal composition, partly due to the emigration of certain marine species. In contrast, the ichthyofaunal compositions of macrotidal holarctic estuaries undergo annual, cyclical changes, due largely to the sequential entry of the juveniles of different marine species for short periods. The ichthyofaunal compositions of the narrow entrance channels, wide basins and saline riverine reaches of large, permanently open southwestern Australian estuaries vary, reflecting the marked tendency for some species to be restricted mainly to one or two of these regions. Comparative data indicate that the characteristics determined for ichthyofaunas in southwestern Australian estuaries apply in general to estuaries elsewhere in temperate Australia.     

Analysis of the demersal community of fish and cephalopods on the Agulhas Bank, South Africa

The demersal fish and cephalopod communities of the continental shelf and upper slope from 17 to 395m deep were studied during five annual cruises between Cape Agulhas and Port Alfred, South Africa. The cruises showed a consistent pattern of an inshore community (<100m), a shelf community ( c . 90–190m) and a shelf-edge/upper slope fauna (>200m). These groups were identified by dendrograms and multidimensional scaling cluster analysis, which supported on-board observations of catch variation with depth. Although the boundaries are not clearly defined, examination of physical features at the clustered stations suggests that depth, temperature and, to a lesser extent, oxygen concentration are important in the grouping. Occasional, apparently anomalous associations of inshore stations suggested that water temperature and oxygen may over-ride the normal depth distributions of the species groups. This intimates that patterns offish and cephalopod distribution may be dynamic and in part related to the physical parameters of the water body.