Effects of aphids on foliar foraging by Argentine ants and the resulting effects on other arthropods

Abstract.  1. Although interactions between ants and honeydew-producing insects have received considerable study, relatively little is known about how these interactions alter the behaviour of ants in ways that affect other arthropods. In this study, field and greenhouse experiments were performed that examined how the presence of aphids ( Aphis fabae solanella ) on Solanum nigrum influenced the foraging behaviour of Argentine ants ( Linepithema humile ) and, in turn, modified the extent to which ants deter larval lacewings ( Chrysoperla rufilabris ), which are known aphid predators.
2. A field experiment demonstrated that the level of foliar foraging by ants increased linearly with aphid abundance, whereas no relationship existed between the level of ground foraging by ants and aphid abundance.
3. In the greenhouse, as in the field, foliar foraging by ants greatly increased when aphids were present. Higher levels of foliar foraging led to a twofold increase in the likelihood that ants contacted aphid predators. As a result of these increased encounters with ants, lacewing larvae were twice as likely to be removed from plants with aphids compared with plants without aphids. Once contact was made, however, the behaviour of ants towards lacewing larvae appeared similar between the two experimental groups.
4. Argentine ants drive away or prey upon a diversity of arthropod predators and parasitoids, but they also exhibit aggression towards certain herbivores. Future work should attempt to quantify how the ecological effects that result from interactions between honeydew-producing insects and invasive ants, such as L. humile , differ from those that result from interactions between honeydew-producing insects and native ants.     

Mitochondrial DNA and two perspectives on evolutionary genetics

This essay reviews comparative studies of animal mitochondrial DNA (mtDNA), with emphasis on findings made and ideas developed at Berkeley. It argues that such studies are bringing together two previous paths of progress in evolutionary biology. One path is that of those who worked far above the species level and were concerned with genealogical trees, time scales and the accumulation of new mutations on surviving molecular lineages. The other path is that of those who worked at and below the species level and were concerned mainly with population structure, migration and the frequencies of alleles that existed in an ancestral population. This fusion of paths is made possible by the high rate at which mutations accumulate on mtDNA lineages and by this molecule's uniparental and apparently haploid mode of inheritance. These properties make mtDNA a superb tool for building trees and time scales relating molecular lineages at and below the species level. In addition, owing to its mode of inheritance, mtDNA is more sensitive to bottlenecks in population size and to population subdivision than are nuclear genes. Joint comparative studies of both mtDNA and nuclear DNA variability give us valuable insights into how effective population size has varied through time. Such studies also give insight into the conditions under which mtDNA from one species can colonize another species.     

Molecular evidence for the phylogeny of Australian gekkonoid lizards

Partial sequences of the mitochondrial 12S rRNA and nuclear c-mos genes were determined for 12 species of gekkonoid lizards representing the four major taxa of the Australian region, the Diplodactyhni and Carphodactylini (forming the subfamily Diplodactylinae), the Pygopodidae and the Gekkoninae. One further species represented a non-Australian gekkonoid lineage, the Eublepharinae. The combined sequence data were used to reconstruct the underlying molecular phylogeny. We used the molecular phylogeny to test the monophyly of the diplodactyline tribes and conflicting hypotheses of relationships of die pygopods and of the genus Oedura. Monophyly of the Diplodactylinae is supported, while pygopods form a monophyletic sister lineage to all Diplodactylinae. The molecular data support the monophyly of the Diplodactyhni, with Oedura firmly placed as a diplodactylin. Monophyly of the Carphodactylini is not supported. The four carphodactylin genera form a paraphyletic cluster at the base of the Diplodactyhni. Pygopods are nested within the traditional Gekkonidae and pygopods plus diplodactylines form a well-supported monophyletic group with respect to the remaining gekkonoids, the gekkonines and eublepharines.     

Decolonizing Time Regimes: Lakota Conceptions of Work, Economy, and Society

One of the hegemonic forces associated with the spread of capitalism is a shift in the time sense of production from task orientation to labor timed by the clock. On the periphery of the global economy, Lakota households on the Pine Ridge reservation must make fragmentary allocations of time between clock-based wage jobs and task-oriented forms of production governed by social relationships. Despite a long and ongoing history of state policies designed to enforce the discipline of the clock, task orientation continues to dominate Lakota time-sense. Rather than active resistance to or internalization of clock time, Lakota practices flout time-values that interfere with the task-oriented demands of more materially certain, socially embedded economic activities. Lakota conceptions of time, born of their contemporary material conditions, are better understood when theoretical concepts of work and time are decolonized to remove the assumptions that emulating or opposing Euro-Americans is of central concern.     

Particle-Based Axenic Media for Tetrahymenids*

SYNOPSIS. Autoclavable, natural particulate media simplify axenic cultivation of tetrahymenid ciliates and presumably favor selection for phagotrophy. Viability is at least 2 months at room temperature (24–26 C) for the lipid-sensitive tetrahymenids Tetrahymena setosa, T. corlissi, T. paravorax, T. limacis, and T. patula, also for T. rostrata and (at 12 C), for strains of the T. pyriformis complex and Glaucoma chattoni. A typical medium consists of crude soy “lecithin”+ skim milk powder +Saccharomyces cerevisiae cells. Other useful particules readily available commercially are: whole liver powder, cells of Micrococcus lysodeikticus and Escherichia coli, and powdered residue of liver which had been extracted with 70% ethanol (liver #2). Preliminary experiments indicate that some of these media are suitable for the maintenance of Paramecium octaurelia stock 299S and Colpidium campylum. Such mixtures may serve as points of departure for devising media for more fastidious phagotrophs.