FACTORS AFFECTING PREY CHOICE AND FEEDING TECHNIQUE IN THE CARNIVOROUS SNAIL EUGLANDINA ROSEA FERUSSAC

Euglandina feeds on other gastropods either by quickly suckingthe contents from the shell, or by swallowing the prey whole,which can be more time consuming. When Euglandina were offeredprey species of various sizes, they preferentially consumedthe smaller individuals, and often swallowed these whole. Handlingtime increased with decreasing density since swallowing preywhole became more frequent at the lower densities. The relationship between prey size, predator size, handlingtime and feeding technique was examined. For the two feedingtechniques observed, handling time increased exponentially withthe size of the prey and decreased exponentially with the sizeof the predator. Predators of intermediate size tended to swallowprey whole more frequently than did the smallest and largest. These data are interpreted in terms of the animal behaving insuch a way as to balance its rate of intake of both organicmatter, which resides mainly in the soft parts, and of calcium,which resides mainly in the shell. (Received 11 July 1988; accepted 31 October 1988)     

Double trouble for grasshopper molecular systematics: intra-individual heterogeneity of both mitochondrial 12S-valine-16S and nuclear internal transcribed spacer ribosomal DNA sequences in Hesperotettix viridis (Orthoptera: Acrididae)

Abstract.  Hesperotettix viridis grasshoppers (Orthoptera: Acrididae: Melanoplinae) exhibit intra-individual variation in both mitochondrial 12S-valine-16S and nuclear internal transcribed spacer (ITS) ribosomal DNA sequences. These findings violate core assumptions underlying DNA sequence data obtained via polymerase chain reaction (PCR) amplification for use in molecular systematics investigations. Undetected intra-individual variation of this sort can confound phylogenetic analyses at a range of taxonomic levels. The use of a DNA extraction protocol designed to enrich mitochondrial DNA as well as an initial long PCR of approximately 40% of the grasshopper mitochondrial genome failed to control for the presence of paralogous mitochondrial DNA-like sequences within individuals. These findings constitute the first demonstration of intra-individual heterogeneity in mitochondrial DNA-like sequences in the grasshopper subfamily, Melanoplinae, and only the second report of intra-individual variation in nuclear ITS ribosomal DNA sequences in grasshoppers. The fact that intra-individual variation was detected in two independent DNA marker sets in the same organism strengthens the notion that the orthology of PCR-derived DNA sequences should be examined thoroughly prior to their use in molecular phylogenetic analyses or as DNA barcodes.     

The performance of morphological characters in broad-scale phylogenetic analyses

In view of their propositional content (i.e. they can be right or wrong), character statements (i.e. statements that predicate characters of organisms) are treated as low-level hypotheses. The thesis of the present study is that such character statements, as do more complex scientific theories, come with variable scope. The scope of a hypothesis, or theory, is the domain of discourse over which the hypothesis, or theory, ranges. A character statement is initially introduced within the context of a certain domain of discourse that is defined by the scale of the initial phylogenetic analysis. The doctrine of 'total evidence' requires the inclusion of previously introduced characters in subsequent studies. As a consequence, the initial scope of character statements is widened to the extent that the scale of subsequent analyses is broadened. Scope expansion for character statements may result in incomplete characters, in the subdivision of characters, or in ambiguity of reference (indeterminacy of the extension of anatomical terms). Character statements with a wide scope are desirable because they refer to characters with the potential to resolve deep nodes in phylogenetic analyses. Care must be taken to preserve referential unambiguity of anatomical terms if the originally restricted scope of a character statement is expanded to match a broad-scale phylogenetic analysis.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 297–308.     

Regulation of K+ Influx in Barley: Evidence for a Direct Control of Influx by K+ Concentration of Root Cells

Siddiqi, M. Y. and Glass, A. D. M. 1987. Regulation of K⁺ influxin barley: Evidence for a direct control of influx by K⁺ concentrationof root cells.—J. exp. Bot. 38: 935–947. The kinetics of K⁺ (⁸⁶Rb⁺) influx into intact roots of barley(Hordeum vulgare L. cv. Fergus) seedlings having different combinationsof root and shoot [K⁺], different growth rates and differentroot:shoot weight ratios were studied. K⁺ influx was stronglycorrelated with root [K⁺]; shoot [K⁺], growth rates, and root:shoot ratios appeared to have little effect on K⁺ influx. Adetailed study showed that both V_max and K_m for K⁺ influx wereaffected by root [K⁺] but not by shoot [K⁺]. We have suggestedthat factors such as growth rates and root: shoot ratio mayaffect K⁺ influx indirectly primarily via their influence onroot factors such as root [K⁺]. We have reiterated that othertypes of kinetic control, e.g. increased or decreased synthesisof ‘carrier systems’, may operate in addition todirect (allosteric?) control of K⁺ influx by root [K⁺]. Thenegative feedback signal from root [K⁺] appeared to be the primeeffector in the regulation of K⁺ influx. Key words: Barley, K⁺ influx     

ONTOGENY AND THE HIERARCHY OF TYPES

Abstract— The long history of belief in a parallelism between ontogeny and a hierarchical order of natural things is reviewed. The meaning of von Baerian recapitulation is analyzed and its implications for cladistic methodology are discussed at two levels: ontogeny and homology. The basic problem inherent in the purported parallelism is that the order of natural things (i.e., the taxic approach to homology) is part of the "world of being" of Platonic ideas, whereas ontogeny and phylogeny (i.e., the transformational approach to homology) belong to Plato's "world of becoming." These two "genera of existence," as Plato put it, being and becoming, are incompatible but complementary views of nature.     

Temporal constancy in grasshopper assemblies (Orthoptera: Acrididae)

ABSTRACT.

• 1 Temporal constancy in the structure of grasshopper assemblies (about forty-five species each) from two types of North American grasslands was assessed; one site was followed 25 years and the other 7 years.
• 2 Densities and relative abundances varied but composition of assemblies based on ranks suggested significant structure when three or more species were included in the analysis.
• 3 Results compared favourably with other insect herbivore assemblies which have been examined; variability in population change was intermediate along the spectrum of organisms which have been studied.