A new view on Nematothallus: coralline red algae from the Silurian of Gotland

Abstract:  The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land‐plant, despite the absence of a convincing modern analogue. Exceptionally well‐preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close‐packed layer of palisade‐like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore‐like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filament‐fringed apertures to their reproductive conceptacles, we reconstruct the Nematothallopsis organism as an extinct rhodophyte and re‐evaluate the putative terrestrial habit of cuticular nematophytes in general.     

Feeding ecology and phylogenetic structure of a complex neotropical termite assemblage,revealed by nitrogen stable isotope ratios

1. In the current ecological classification of termites, four feeding groups (I–IV) are recognised, corresponding to a gradient of decomposition from sound wood to highly mineralised organic matter in the soil. 2. Nitrogen stable isotopes (hereafter δ¹⁵N) were used to place termites from French Guiana rainforests along a wood‐soil decomposition gradient, to test (i) whether feeding group assignation based on morphological characters was accurate and actually represented diet specialisation thresholds, and (ii) to what extent the dietary specialization of species is explained by phylogeny (phylogenetic autocorrelation). 3. δ¹⁵N values vary over a range of 13‰, suggesting that diet diversification contributes to the high species diversity in French Guiana. δ¹⁵N values span a similar interval in all Termitidae subfamilies. Ranges of different subfamilies broadly overlap, although each of them diversified preferentially on one side of the wood‐soil decomposition gradient. Congeneric species share similar feeding habits, whereas distant species tend to feed on distinct substrates. 4. Feeding groups did not completely match stable isotope data: there was no discontinuity between Groups III and IV, and no correlation between anatomical criteria used to distinguish these groups and δ¹⁵N values. Nor was there any consistent difference in δ¹⁵N values between wood feeders of the families Rhinotermitidae (Group I) and Termitidae (Group II). We also suggest that species feeding outside the wood‐soil gradient should be distinguished for their peculiar feeding requirements.     

Vision and the foraging technique of Great Cormorants Phalacrocorax carbo: pursuit or close‐quarter foraging?

Predatory diving birds, such as cormorants (Phalacrocoracidae), have been generally regarded as visually guided pursuit foragers. However, due to their poor visual resolution underwater, it has recently been hypothesized that Great Cormorants do not in fact employ a pursuit-dive foraging technique. They appear capable of detecting typical prey only at short distances, and primarily use a foraging technique in which prey may be detected only at close quarters or flushed from a substratum or hiding place. In birds, visual field parameters, such as the position and extent of the region of binocular vision, and how these are altered by eye movements, appear to be determined primarily by feeding ecology. Therefore, to understand further the feeding technique of Great Cormorants we have determined retinal visual fields and eye movement amplitudes using an ophthalmoscopic reflex technique. We show that visual fields and eye movements in cormorants exhibit close similarity with those of other birds, such as herons (Ardeidae) and hornbills (Bucerotidae), which forage terrestrially typically using a close-quarter prey detection or flushing technique and/or which need to examine items held in the bill before ingestion. We argue that this visual field topography and associated eye movements is a general characteristic of birds whose foraging requires the detection of nearby mobile prey items from within a wide arc around the head, accurate capture of that prey using the bill, and visual examination of the caught prey held in the bill. This supports the idea that cormorants, although visually guided predators, are not primarily pursuit predators, and that their visual fields exhibit convergence towards a set of characteristics that meet the perceptual challenges of close-quarter prey detection or flush foraging in both aquatic and terrestrial environments.     

An Experimental Investigation into the Response of Some New Zealand Sand Dune Species to Salt Spray

The tolerance to salt spray of 29 species, mainly from New Zealandsand dunes, was investigated. Plants were grown in water culturein a glasshouse and subjected to overhead salt spraying at intervals.Growth rates in many species were reduced by salt spray buta significant decrease occurred only in six native herbs. However,many species showed sensitivity in leaf necrosis. Tolerant speciesincluded Scirpoides nodosa, Elymus farctus and Desmoschoenusspiralis. Ammophila arenaria, tolerant of spray as an adult,was less so when younger. There was little correlation between tolerance to salt sprayand tolerance to root salinity. Some species were tolerant toboth, e.g. S. nodosa and E. farctus, and some intolerant toboth, e.g. Wahlenbergia congesta. One species, Lupinus arboreus,was glycophytic in respect to root salt but tolerant of aerialsalt. Other species, such as Senecio elegans L. and Austrofestucalittoralis, were intolerant of salt spray but tolerant of mediumroot salinities. For some species salt spray tolerance correlated well with fielddistribution, e.g. D. spiralis and Bromus diandrus. However,some species present in semi-fixed dunes close to the sea havemuch lower tolerance than would be expected from their fieldsituation, e.g. W. congesta. This apparent inconsistency couldbe explained by the ameliorating high rainfall on the West Coast,or protection by ridges. One environmental variable alone, suchas salt spray, could not explain the field distribution formany species. Salt spray, growth rate, live leaf area, New Zealand, dune species, root salinity     

Central control of tarsal thresholds for proboscis extension in the blowfly

ABSTRACT. The literature contains contrary reports with respect to the control of the proboscis extension of blowflies in response to stimulatory solutions. Control could be effected centrally, peripherally or by a combination of both. In this report a comparison of (i) behavioural responsiveness to sucrose (measured by tarsal thresholds for proboscis extension) and (ii) sensitivity of tarsal sugar receptors (measured from 0.1 to 1.1 s after stimulus onset) both before and 1 h after feeding of male Protophormia terraenovae suggests that the observed decrease in behavioural responsiveness after feeding is due to central inhibition rather than to a decline in peripheral sensitivity.