Distal Retinal Pigment of the Fiddler Crab,Uca pugilator: Release of the Dark-Adapting Hormone by Methionine Enkephalin and FMRFamide

The neuropeptides methionine enkephalin and FMRFamide, when injected into intact fiddler crabs, Uca pugilator, produce dark adaptation of the distal retinal pigment. Furthermore, both neuropeptides stimulate release of distal retinal pigment dark-adapting hormone activity from the isolated eyestalk neuroendocrine complex. It is hypothesized that both neuropeptides, when injected into intact fiddler crabs, act only indirectly on the distal retinal pigment, by stimulating release of this dark-adapting hormone.     

Endocrine Correlates of Seasonal Body Mass Dynamics in the Collared Lemming (Dicrostonyx groenlandicus)

Many winter-active temperate rodent species show seasonal, photoperiod-mediatedchanges in body mass that correlate with changes in food availability,gaining mass when food is abundant. The collared lemming (Dicrostonyxgroenlandicus), an arctic species, also undergoes a seasonaltransition in body mass, but one that is temporally out of phasewith that observed in species from lower latitudes; whereastemperate species increase in mass when exposed to relativelylong day lengths, collared lemmings do so under long but decreasingday lengths. This adaptation may be in response tothe timingof peak above-ground biomass in the arctic. Validation of thishypothesis requires a more thorough examination of both collaredlemmings and other arctic species. In the collared lemming, photoperiod-mediated changes in bodymass are correlated with changes in serum concentrations ofprolactin, thyroid hormones, corticosterone, and growth hormone,and pineal concentrations of melatonin. These observations arecompared to those obtained with temperate small mammals, andpossible cause-and-effect relationships between body mass andhormonal parameters are discussed.     

Cellular Aspects of the Control of Physiological Color Changes in Crustaceans

SYNOPSIS. Red chromatophores(erythrophores) of the prawn, Palaemonetesvulgaris, are controlled by pigment—dispersing and -concentratinghormones. Recent experiments on the modes of action of thesehormones are described, followed by a theory which satisfactorilyexplains the data. Red pigment-concentrating hormone is dependentupon sodium ions for a strong response to occur. There is asimilar dependency of red pigment—dispersing hormone uponcalcium ions. Ouabain inhibits the response to red pigment—concentratinghormone; tetrodotoxin enhances it. Erythrophores with maximallydispersed pigment had a transmembrane potential of 55±15mv inside negative in one series of experiments and 56±4mv in another. No appreciable changes in permeability occurwhen depolarizing and hyperpolarizing currents are passed througha microelectrode within the chromatophore. Red pigmentconcentratinghormone causes hyperpolarization of the transmembrane potential.The magnitude of hyperpolarization is directly related to thedegree of pigment concentration. Adenosine 3`;, 5`-monophosphate(cyclic AMP) causes dispersion of the red pigment but has nopigment-concentrating effect. The primary action of red pigmentconcentratinghormone is most likely stimulation of a pump which exchangessodium ions from inside the chromatophore with potassium ionsfrom the outside, whereas red pigment-dispersing hormone quitelikely stimulates entry of calcium ions into the chromatophore.     

Untangling associations between chironomid taxa in Neotropical streams using local and landscape filters

1. Analyses of species association have major implications for selecting indicators for freshwater biomonitoring and conservation, because they allow for the elimination of redundant information and focus on taxa that can be easily handled and identified. These analyses are particularly relevant in the debate about using speciose groups (such as the Chironomidae) as indicators in the tropics, because they require difficult and time‐consuming analysis, and their responses to environmental gradients, including anthropogenic stressors, are poorly known. 2. Our objective was to show whether chironomid assemblages in Neotropical streams include clear associations of taxa and, if so, how well these associations could be explained by a set of models containing information from different spatial scales. For this, we formulated a priori models that allowed for the influence of local, landscape and spatial factors on chironomid taxon associations (CTA). These models represented biological hypotheses capable of explaining associations between chironomid taxa. For instance, CTA could be best explained by local variables (e.g. pH, conductivity and water temperature) or by processes acting at wider landscape scales (e.g. percentage of forest cover). 3. Biological data were taken from 61 streams in Southeastern Brazil, 47 of which were in well‐preserved regions, and 14 of which drained areas severely affected by anthropogenic activities. We adopted a model selection procedure using Akaike’s information criterion to determine the most parsimonious models for explaining CTA. 4. Applying Kendall’s coefficient of concordance, seven genera (Tanytarsus/Caladomyia, Ablabesmyia, Parametriocnemus, Pentaneura, Nanocladius, Polypedilum and Rheotanytarsus) were identified as associated taxa. The best‐supported model explained 42.6% of the total variance in the abundance of associated taxa. This model combined local and landscape environmental filters and spatial variables (which were derived from eigenfunction analysis). However, the model with local filters and spatial variables also had a good chance of being selected as the best model. 5. Standardised partial regression coefficients of local and landscape filters, including spatial variables, derived from model averaging allowed an estimation of which variables were best correlated with the abundance of associated taxa. In general, the abundance of the associated genera tended to be lower in streams characterised by a high percentage of forest cover (landscape scale), lower proportion of muddy substrata and high values of pH and conductivity (local scale). 6. Overall, our main result adds to the increasing number of studies that have indicated the importance of local and landscape variables, as well as the spatial relationships among sampling sites, for explaining aquatic insect community patterns in streams. Furthermore, our findings open new possibilities for the elimination of redundant data in the assessment of anthropogenic impacts on tropical streams.     

A new species of Ilex (Aquifoliaceae) from Espinhaço Range, Bahia, Brazil

A new species, Ilex mucugensis Groppo sp. nov. (Aquifoliaceae), is described and illustrated. The species is known only from 'campos rupestres' (vegetation of rock outcrops at high altitude) in the vicinity of Mucugê, Bahia State, Brazil, in the mountains of the Espinhaço Range. Comments on affinities, geographical distribution and phenology of the new species are also provided.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 153–156.     

Disturbances in semi-arid shrubland and arid grassland in the Karoo, South Africa: mammal diggings as germination sites

Mammals (mainly aardvark Orycteropus ufer , porcupine Hystrix austro-africanae , bat-eared fox Otocyon megalotis and Cape fox Vulpes chama ) which excavate holes in hard-capped soils in Karoo shrubland and inter-dune pans create microsites where seeds, detritus and water accumulate, and seeds germinate. Holes with seedlings were significantly deeper (6.7 ± 0.4 cm) than holes without seedlings (4.5 ± 0.3 cm). In open, inter-shrub sites, significantly more seedlings germinated in diggings than on the flat soil surface, but there was no difference in the proportion of seedlings germinating under shrubs and in diggings. In inter-dune pans, 96% of all seedlings found were growing in diggings.

Résumé

Les mammifères (surtout l'oryctérope Orycreropus afer , le porcépic Hystrix austro-ajricanae , l'otocyon Otocyion megalotis , et le renard du Cap Vulpes chama ) qui creusent des trous dans les régions buissonneuses du Karoo et dans les creux entre les dunes créent des microsites où les semences, les déchets et l'eau se rassemblent, et les semences germent. Les trous où elles germent sont significativement plus profonds (6,7 ± 0,4 cm) que ceux où elles ne germent pas (4,5± 0,3 cm). Aux endroits buissonneux ouverts, il pousse plus de jeunes plantes dans des creux qu'à la surface du sol, mais il n'y a pas de différence entre les proportions de celles qui poussent sous les buissons et dans les creux. Dans les creux entre les dunes, 96% des jeunes pousses croissent dans les excavations.     

Endocrine Mechanisms in Crayfish, with Emphasis on Reproduction and Neurotransmitter Regulation of Hormone Release

SYNOPSIS. The neuroendocrine system of crustaceans, crayfishin particular, has been extensively studied. As among vertebrates,a wide variety of processes are hormonally regulated, includingreproduction, growth, carbohydrate metabolism and color changes.The sinus gland, a neurohemal organ in the crayfish eyestalk,is the major neuroendocrine center. Herein, crayfish reproductivecycles and their hormonal control, particularly by the gonad-stimulatingand gonad/inhibiting hormones, are a major focus. In addition,the aminergic and peptidergic neuroregulators identified incrayfish central nervous organs that either have been or likelymay be shown to have neurotransmitter/neuromodulator roles incontrolling hormone release are discussed with respect to localizationand identified roles.