Disjunctions in relict alpine plants: phylogeography of Androsace brevis and A. wulfeniana (Primulaceae)

Amplified Fragment Length Polymorphism (AFLP) was used to clarify the glacial history of the rare, disjunctly distributed, alpine cushion plant Androsace wulfeniana , which is endemic to the Eastern Alps (Austria and Italy). Disjunct populations in the Dolomites are genetically very distinct from those in the main distributional area. It is hypothesized that they are descendants of long-term isolated glacial survivors and are not a result of recent long-­distance dispersal. Within the main distributional area of the species in the central Eastern Alps, two groups of ­populations can be distinguished, which are congruent with hotspots of rare relictual vascular plant taxa. In the ­taxonomically closely related A. brevis growing in the Southern Alps (Italy, Switzerland), no genetic-geographical structure was found. Genetic variation is extremely low in disjunct populations of A. wulfeniana in the Dolomites and in A. brevis . In contrast, in the main distributional area of A. wulfeniana , genetic variation is similar to that of the colonizing widespread congener A. alpina .  © 2003 The Linnean Society of London, Botanical Journal of the ­Linnean Society , 2003, 141 , 437–446.     

Morphology and anatomy of roots in the filmy fern tribe Trichomaneae H. Schneider (Hymenophyllaceae, Filicatae) and the evolution of rootless taxa

The filmy ferns of the tribe Trichomaneae, synonymous with Tichomanes s.L., show various constructions of their root system that correspond to different growth forms as well as ecology. Most terrestrial species possess a short erect shoot with numerous thick roots, whereas epiphytic species have a long creeping rhizome that may develop a few thin roots. An evolutionary progression from ferns with well-developed roots to ferns without roots is postulated. Rootless species occur in two monophyletic groups, subgen. Crepidomanes and subgen. Didymoglossum. The results are summarized in a new classification for the tribe. Secondary simplification, e.g. loss of roots, is discussed as an adaptive trait in epiphytic plants. Transformed structures such as root-like shoots and adhesive hairs are observed in rootless taxa and their evolutionary significance is briefly discussed. Climbing filmy ferns are recognized as possible closely related species based on the similarities in their root systems.     

THE SCIENCE: LIMNOLOGY

SUMMARY

Lake Chilwa, which has a fishery of economic importance to Malawi, declined in water level from 1964–68 and dried up completely for a few months in 1968. It then regained its former depth of 2–3 m in one wet season of five months. In the pre-drying period, zoo-plankters produced different diapause forms; in the drying period, zooplankton appeared to die out; in the refilling period rotifers predominated in the first year and crustacean populations were low; in the post-filling period crustaceans predominated. The same species occurred both before and after dryness. The conditions that possibly determined these responses are considered. After a lag of one year numbers of zooplankters were high, but decreased annually when the three dominant, largely planktivorous species of fishes recolonised the lake in succession over three years.

A main detritus food web is postulated and evidence for it is discussed. A practical method for fish conservation in times of low lake level, using artificial ‘lagoons’ in the swamp, and boreholes, is suggested.     

Sensory Motor Interfacing in Acoustic Behavior of Anurans

SYNOPSIS. Anurans respond to different acoustic signals in adistinct manner. Moreover, acoustic behavior strongly dependson the inner state of the animal and the social context. Neuroanatomicalstudies as well as extra- and intracellular recordings werecarried out to examine the problem of audio-motor interfacing.Acoustic signals are processed in a partly hierarchical andpartly distributed manner in the anuran central nervous system.Features are represented in a topographical manner. Auditorymaps in the midbrain torus semicircularis are read by a subsetof neurons of the laminar and magnocellular subnuclei, whichinterconnect the auditory pathway and premotor centres. These,in turn, feed into neural networks controlling vocalization,locomotion, or autonomic functions. Our data on the cytoarchitectonicorganization and connectivity of the interfacing neurons giverise to a population coding hypothesis which may explain thedifferential evaluation of acoustic signals. Additionally, immunohistochemicalfindings reveal strong neuromodulatory and hormonal input, especiallyonto interfacing neurons, suggesting intense influence on thephysiological properties of these cells.     

Sex-specific provisioning behaviour in a monomorphic seabird with a bimodal foraging strategy

Sexual differences in foraging and provisioning behaviour have been observed in several size-dimorphic seabird species. These differences are usually thought to be driven by size-related mechanisms such as the ability to compete for food or defend the nest. However, recent studies on monomorphic species suggest that sexual differences in foraging may arise independently of size. Selective forces driving sex-specific patterns are poorly known but essential to understand parental strategies. In this study, we examine sex differences in the provisioning behaviour of a monomorphic species, the Little Auk Alle alle . Using automated recording systems during two consecutive seasons at two colonies, we found that both sexes used a bimodal foraging strategy in which they regularly alternated single foraging trips of long duration with a cycle of several short-trips. The duration of long-trips was substantially longer in females than in males, and the sexes differed in the number of short-trips they performed in between long-trips, resulting in male-biased provisioning rates in both years. In species with a bimodal foraging strategy, long-trips have been interpreted as self-feeding trips to replenish body reserves. Our results therefore suggest that female Little Auks allocate more time to self-maintenance at the cost of chick provisioning, possibly due to different energetic constraints of the sexes prior and/or subsequent to chick-rearing. Our findings contribute to accumulating evidence that sex-specific foraging patterns may be widespread in sexually size-monomorphic seabird species.     

Structure and Variation in the Sarcotubular System of the Extraocular Muscle Fibres in the Shark Scyliorhinus canicula L.

The microscopic anatomy of the extraocular eye muscles of the shark Scyliorhinus canicula is described. In contrast to swimming muscles, the fibres are not differentiated into distinct fibre type groups. The sarcoplasmic reticulum has narrow terminal cisternae in the Z band region, longitudinal tubules and a fenestrated cisterna in the H band region. Triads or dyads are mostly located at the Z discs. A number of variations from this general pattern is described, with main emphasis on triad location, orientation and structure. Since triads in vertebrates usually are located either at the Z disc or at the A-I junction, and with a fixed structure, these variations in shark muscles are of phylogenetic interest, as they may provide basis for an explanation of development to the two different triad locations.     

Forest and Landscape Structure as Predictors of Capercaillie Occurrence

ABSTRACT Capercaillie (Tetrao urogallus) is a large, endangered forest grouse species with narrow habitat preferences and large spatial requirements that make it susceptible to habitat changes at different spatial scales. Our aim was to evaluate the relative power of variables relating to forest versus landscape structure in predicting capercaillie occurrence at different spatial scales. We investigated capercaillie-habitat relationships at the scales of forest stand and forest-stand mosaic in 2 Swiss regions. We assessed forest structure from aerial photographs in 52 study plots each 5 km². We classified plots into one of 3 categories denoting the observed local population trend (stable, declining, extinct), and we compared forest structure between categories. At the stand scale, we used presence-absence data for grid cells within the plots to build predictive habitat models based on logistic regression. At this scale, habitat models that included only variables relating to forest structure explained the occurrence of capercaillie only in part, whereas variables selected by the models differed between regions. Including variables relating to landscape features improved the models significantly. At the scale of stand mosaic, variables describing forest structure (e.g., mean canopy cover, proportion of open forest, and proportion of multistoried forest) differed between plot categories. We conclude that small-scale forest structure has limited power to predict capercaillie occurrence at the stand scale, but that it explains well at the scale of the stand mosaic. Including variables for landscape structure improves predictions at the forest-stand scale. Habitat models built with data from one region cannot be expected to predict the species occurrence in other regions well. Thus, multiscale approaches are necessary to better understand species-habitat relationships. Our results can help regional authorities and forest-management planners to identify areas where suitable habitat for capercaillie is not available in the required proportion and, thus, where management actions are needed to improve habitat suitability.