CHEMOTAXIS IN THE NUDIBRANCH HERMISSENDA CRASSICORNIS: DOES INGESTIVE CONDITIONING INFLUENCE ITS BEHAVIOUR IN A Y-MAZE?

The nudibranch mollusc Hermissenda crassicornis can be culturedeasily in the laboratory and has been used as a biomedical modelfor learning and memory studies. Cultured animals whose onlyprey was Tubu-laria crocea were tested for responses to otherprey. Naive slugs were conditioned with six different dietsand tested for behaviour in a Y-maze. H. crassicornis was ableto detect chemotactically food items which it had never beenin contact with (such as Pennaria), but it did not detect someof the conditioning diets (e.g. Metridium). At least three hydroidspecies induce a chemotactic behaviour in the slug. It is shownthat ingestive conditioning does affect their response in single-choiceand double-choice experiments. As food items other than cnidariansare also detected, it is likely that different kairomones areresponsible for the nudibranch's behaviours. ^*Present address: Centre d'Estudis Avançats de Blanes,C.S.I.C., Cami de Sta. Bárbara s/n. 17300 Blances (Girona)Spain. (Received 10 March 1997; accepted 25 June 1997)     

Promising eco-physiological traits for genetic improvement of cereal yields in Mediterranean environments

Breeding for improved productivity has been tremendously successful in the last half‐century, but needs to be even more efficient in the future. Hope based on contributions from molecular biology for improved yield potential seems to depend upon an improved knowledge of yield physiology. This knowledge may assist breeding either directly, recommending selection criteria, or indirectly identifying simpler traits that could be reliably mapped and selected for through marker‐assisted selection. Physiological traits associated with improved performance under water‐limited conditions, include phenology (that allows the crop to escape stresses) and those associated with improved water use, water use efficiency and partitioning. Undoubtedly, earliness has been the predominant trait improved for under Mediterranean conditions, and may not be a prospective trait for future breeding. Different traits that may confer the ability to the crop for capturing more water, such as deeper root systems or osmotic adjustment, may be unworkable in terms of their direct use in selection and surrogates would be needed. For instance, canopy temperature depression and discrimination against 13C may be used to assess improved ability to capture water (in these cases yield is positively related to discrimination against ¹³C in grains). Early vigour, which allows faster ground coverage, also increases the amount of water actually transpired by the canopy by reducing direct evaporation and presents substantial intraspecific variation, and selection for this trait may be successfully carried out either directly or through the use of vegetation indexes. Improved water use efficiency based on transpiration efficiency is largely restricted to conditions where additional water is not available. A constitutively low stomatal conductance or a high stomatal sensitivity may optimise the transpiration efficiency. In this context, discrimination against ¹³C is also a simple and reliable measure of water use efficiency, and in cases in which no major differences in capturing water is possible discrimination against ¹³C correlates negatively with yield. Substantial further improvements in partitioning may be limited in most cereals.     

REVIEW OF THE GENUS DENDRODORIS EHRENBERG, 1831 (GASTROPODA: NUDIBRANCHIA) IN THE ATLANTIC OCEAN

Six valid species of the nudibranch genus Dendrodons Ehrenberg,1831 inhabit the Atlantic Ocean, including the Mediterraneanand Caribbean Seas. Dendrodons lumbata (Cuvier, 1804), Dendrodonsgrandiflora (Rapp, 1827), Dendrodons nigra (Stimpson, 1855)(immigrant from the Red Sea), Dendrodons krebsu (Mörch,1863), Dendrodoru senegalensis Bouchet, 1975 and Dendrodonswarta Marcus & Gallagher, 1976. Additional data about thebiology and geographical distribution of these species are presented.New evidence suggests that other species assigned to the genusDendrodons, Dendrodons racemosa Pruvot-Fol, 1951 and Dendrodonsminima Pruvot-Fol, 1951, must be included in the genus DoriopsillaBergh, 1880. Three new species of Dendrodoris are describedfrom the Northeastern Atlantic and West Africa;Dendrodons angolensis,Dendrodoris guineana and Dendrodons herytra. The variable external morphology makes species recognition difficult.Instead, the diagnostic characters utilised to separate speciesare the shape of the male cirrus hooks, the structure of thereproductive system and features of the egg-mass. (Received 25 April 1995; accepted 1 August 1995)     

THE GROWTH OF PELTODORIS ATROMACULATA BERGH, 1880 (GASTROPODA: NUDIBRANCHIA) IN THE LABORATORY

The growth of Peltodons atromaculata Bergh, 1880, measured astotal dorsal body area, was followed in the laboratory for 15months. The growth of dorsal brown patches was compared to thetotal area of the mantle, and was shown to be approximatelyconstant over time in the different animals. This numericalapproach can be useful to quantify the body pigmentation clinepreviously described for Mediterranean specimens. P atromaculatahas an annual life-cycle in the laboratory, reaching its maximumsize before opposition. Post-spawning mortality followed a decreasein size for all specimens. Mantle margin autotoray in P atromaculataseems not to be related to defence against predation, but itis a process that takes place before death in laboratory. (Received 1 December 1994; accepted 28 April 1995)