The ecology of the sandy estuaries of North Devon and Carmarthen Bay

The estuaries of the Taf, Tywi, Gwendraeth and Loughor (Carmarthen Bay, South Wales), and the Taw and Torridge (North Devon) were surveyed during the spring and summer of 1988, as part of a four year study of harbours, rias and estuaries in southern Britain commissioned by the Nature Conservancy Council. The aims of these surveys were to describe the major marine habitats and communities present in each estuary, and to assess their nature conservation importance. This paper outlines the results of these surveys, concentrating on the many environmental similarities between the six estuaries.     

Dispersal of adult Trichoptera at a Danish forest brook

• 1 The dispersal of adult Trichoptera at the small Danish forest brook, Stamperenden, was studied from 10 May to 6 October 1990 using Malaise traps placed across the brook, parallel to the brook at distances of 2, 20 and 40m, and perpendicular to it at a distance of 1–3m.
• 2 Of the total of 4175 specimens caught, lotic species breeding in Stamperenden accounted for 95.6%. The dominant species were Agapetus fuscipes, Lype reducta, Plectrocnemia conspersa, Potamophylax nigricornis and Silo pallipes.
• 3 The sex ratios in the catches of most species were uneven. Agapetus fuscipes males were in excess, probably because males fly more frequently than females.
• 4 The dominant species flew predominantly above the surface of the brook. Whereas both sexes of A. fuscipes, L. reducta and S. pallipes were rarely found even as little as 20–40m from the brook, the dispersal range of P. conspersa was much wider.
• 5 The implications of low dispersal for the biological recovery of damaged but subsequently restored streams and stream catchments are discussed. It is concluded that complete biological recovery may be a process requiring decades unless the original aquatic fauna is re-established artificially.

     

BIOCHEMICAL COMPOSITION OF HELIX SNAILS: INFLUENCE OF GENETIC AND PHYSIOLOGICAL FACTORS

This paper describes the biochemical composition of differentspecies (Helix lucorum, Helix pomatia) and sub-species of snails(Helix aspersa aspersa, Helix aspersa maxima) reared in thesame conditions with a feed (‘Helixal’) speciallydesigned for edible snails. In addition, the composition ofwild H. pomatia and H. lucorum is presented to allow comparisonbetween snails of different origins. Analyses determined thepercentages of proteins, lipids and minerals. They reveal bothsimilarities and differences in composition according to thespecies and the part analysed (whole body, pedal mass, and visceralmass). H. pomatia contains the highest percentage of mineralmatter and the lowest percentage of lipids. Surprisingly, proteincontents are slightly different between artificially rearedH. aspersa maxima of 3 months old and wild H. pomatia. The resultsmake it possible to evaluate nutritional quality of snails withthe composition of the body of four edible snail species. (Received 16 September 1996; accepted 24 May 1997)     

Host plant finding in the specialised leaf beetle Cassida canaliculata: an analysis of small-scale movement behaviour

Abstract.  1. Host plant finding in walking herbivorous beetles is still poorly understood. Analysis of small-scale movement patterns under semi-natural conditions can be a useful tool to detect behavioural responses towards host plant cues.
2. In this study, the small-scale movement behaviour of the monophagous leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) was studied in a semi-natural arena ( r = 1 m). In three different settings, a host ( Salvia pratensis L., Lamiales: Lamiaceae), a non-host ( Rumex conglomeratus Murr., Caryophyllales: Polygonaceae), or no plant was presented in the centre of the arena.
3. The beetles showed no differences in the absolute movement variables, straightness and mean walking speed, between the three settings. However, the relative movement variables, mean distance to the centre and mean angular deviation from walking straight to the centre, were significantly smaller when a host plant was offered. Likewise, the angular deviation from walking straight to the centre tended to decline with decreasing distance from the centre. Finally, significantly more beetles were found on the host than on the non-host at the end of all the trials.
4. It is concluded that C. canaliculata is able to recognise its host plant from a distance. Whether olfactory or visual cues (or a combination of both) are used to find the host plant remains to be elucidated by further studies.     

Life-cycle regulation and life history plasticity in the speckled wood butterfly: are reaction norms predictable?

We investigated whether interpopulational variation in life-cycle regulation and life-history plasticity, in response to photoperiod, is predictable from considerations of what would be the adaptive life cycle and life history in a given environment. The investigation was performed on five populations of the speckled wood butterfly, Pararge aegeria (L.) (Lepidoptera: Nymphalidae), from central and south Sweden, England, Spain and Madeira. Insects from all five populations were reared at all daylengths from 10 h to 20 h at 17^oC. Larval and pupal development times were noted. Predictions were met regarding the type of life-cycle regulation and the shape of reaction norms. Evidence for diapause (larval summer and winter diapause, pupal winter diapause) was found in the three northern populations (P. a. tircis) but not in the two southern populations (P. a. aegeria). Photoperiodic thresholds for diapause induction followed the predicted latitudinal patterns, and this was also the case regarding quantitative regulation of development time (by photoperiod) among directly developing individuals. Under direct development, development time was progressively shorter in shorter daylengms in the two Swedish populations, where this signals progressively later dates. This was not found in the English, Spanish and Madeiran populations where such a response is likely to be maladaptive, because one or more generations of larvae are present before summer solstice. There were also unexpected results, for which we propose preliminary adaptive explanations.     

Insights into the history of the legume‐betaproteobacterial symbiosis

The interaction between legumes and rhizobia has been well studied in the context of a mutualistic, nitrogen‐fixing symbiosis. The fitness of legumes, including important agricultural crops, is enhanced by the plants’ ability to develop symbiotic associations with certain soil bacteria that fix atmospheric nitrogen into a utilizable form, namely, ammonia, via a chemical reaction that only bacteria and archaea can perform. Of the bacteria, members of the alpha subclass of the protebacteria are the best‐known nitrogen‐fixing symbionts of legumes. Recently, members of the beta subclass of the proteobacteria that induce nitrogen‐fixing nodules on legume roots in a species‐specific manner have been identified. In this issue, Bontemps et al. reveal that not only are these newly identified rhizobia novel in shifting the paradigm of our understanding of legume symbiosis, but also, based on symbiotic gene phylogenies, have a history that is both ancient and stable. Expanding our understanding of novel plant growth promoting rhizobia will be a valuable resource for incorporating alternative strategies of nitrogen fixation for enhancing plant growth.