Floral symmetry and nectar guides: ontogenetic constraints from floral development, colour pattern rules and functional significance

The accord between symmetries of flower shape (external contours) and nectar guides (internal contours) was examined using the bulbous flora of South Africa, and in the general floras of Britain, Alpine Colorado, Canadian Arctic and Israel. It was found that radially symmetrical flowers have radially symmetrical nectar guides whereas bilaterally symmetrical flowers have bilaterally symmetrical nectar guides. It is suggested that the complementarity between the external and the internal contours of the flower increases the probability that, and efficiency with which, a bee moves into the flower's centre and towards the sporophylls and access to floral rewards, regardless of the flower's form and the bee's previous experience. Patterns of coloration of tepals against background and nectar guides against tepals also accord with behavioural and sensory characteristics of pollinators. It is suggested that the complementarity of contours is probably constrained by floral development, but patterns of coloration of tepals against background and nectar guides against tepals is constrained by pollinators' sensory physiology.     

Light-limited growth and photosynthetic characteristics of two planktonic desmid species

1. Staurastrum chaetoceras, originating from a eutrophic environment, and Cosmarium abbreviatum var. planctonicum, from an oligo-mesotrophic one, were grown at 20°C in continuous-flow culture under varied light conditions. 2. Maximum growth rate in S. chaetoceras was approximately 50% higher than in C. abbreviatum, corresponding to a higher photosynthetic capacity. 3. Higher dry weight values and dark respiration rates in C. abbreviatum (compared with S. chaetoceras) support the suggestion from growth-irradiance curves that C. abbreviatum has to invest a greater part of its photosynthetic energy in the construction and maintenance of specific cell components. 4. The differences in growth and photosynthetic parameters might be related to the presence of a copious mucilaginous cell envelope in C. abbreviatum; such an envelope is lacking in S. chaetoceras. 5. The possible ecological significance of these species-specific differences is discussed.     

Fossil epithelial cell imprints as indicators of conodont biology

von Bitter, P.H. & Norby, R.D. 1994 10 15: Fossil epithelial cell imprints as indicators of conodont biology.
Size and growth characteristics of microsculpture polygons on the cup nodes of the bladelike Pa elements of the conodont Lochriea commutata support the hypothesis that they are epithelial cell imprints. They are ˜2–6 pn wide and ˜4–10 pn long and are the same size throughout growth of the element. The epithelial imprints increased in number with growth, either linearly or periodically; the latter possibility may be important for defining specific growth stages of conodont elements. The imprint location on the top of nodes suggests that the latter were tissue-covered and that the scissor-model of function applies to these bladelike Pa elements. The location of the imprints also reflects evolutionary history: a probable ancestor, L. cracoviensis (Belka), also lacks a platform and possesses well-developed microsculpture polygons on broad cup nodes. Finally, correlation between internal white matter and external microsculpture suggests that internal osteocytes may have supplied the external secreting cells with calcium phosphate from the inner storage bank. Conodont biology, fossil epithelial imprints, polygonal microsculpture, Carbonferous, Lochriea commutata .     

The effect of a foliar disease (rust) on the development of Gastrophysa viridula (Coleoptera: Chrysomelidae)

Abstract.

• 1 Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae) and the pathogenic rust fungus Uromyces rumicis (Schum.) Wint. both occur on leaves of Rumex crispus L. and R.obtusifolius L. Individual stages of beetle development, and egg laying, were compared on healthy and infected leaves of each plant species in the laboratory. Oviposition choice was investigated in the field and laboratory.
• 2 Beetles reared on infected leaves of each species had greater larval mortality and slower development than those reared on healthy leaves. Although larvae feeding on infected leaves consumed up to 2.5 times more dry weight than those reared on healthy leaves, they had a lower relative growth rate and pupated at a lower weight. These changes were consistent with the reduced nutritive quality of rust-infected Rumex leaves.
• 3 Fecundity of beetles reared on infected leaves of both species was considerably reduced. Eggs laid by beetles feeding on infected R.crispus leaves also had a reduced viability.
• 4 The beetle developed consistently poorer on healthy R.crispus than on healthy R.obtusifolius throughout its life-cycle. Differences in larval performance were greater between host species than between infected and healthy leaves.
• 5 Oviposition was similar on infected and healthy R.crispus in both the laboratory and field. However, adults consumed less, and laid fewer eggs on infected than on healthy R.obtusifolius. The pattern of egg laying on different aged leaves was affected by rust infection: a greater proportion of eggs was laid on the older, infected leaves, than on the equivalent aged leaves on the healthy plants. Few larvae survived from eggs laid on rusted leaves in the field.

     

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.

     

Genetics and Molecular Biology of Mouse Pigmentation

The formation of mouse coat color is a relatively complex developmental process that is affected by a large number of mutations, both naturally occurring and induced. The cloning of the genes in which these mutations occur and the elucidation of the mechanisms by which these mutations disrupt the normal pigmentation pattern is leading to an understanding of the way interactions between gene products lead to a final phenotype.