Host-plant shifts and adult survival in the cactus breeding Drosophila mojavensis

Abstract. 1. In order to gain insight into how Drosophila mojavensis Patterson and Crow (which lives on the rotting tissue of cactus) successfully shifted host plants, from an Opuntia species to columnar cactus species, over evolutionary time, specific components of columnar cactus and Optunia tussue were examined for their effects on adult longevity.
2. The availability of free sugars affects the survival of adult D.mojavensis . The addition of a sugar to columnar cactus tissue significantly increased the longevity of adults that fed on those tissues. This increase in adult longevity was equal to the longevity observed on unsupplemented Opuntia tissue, which has free sugars present.
3. Live microorganisms added to Opuntia tissue had a slight detrimental effect on adult longevity (longevity was decreased by approximately 1 week).
4. Low concentrations of atmospheric ethanol (independent of diet) increased the longevity of adult D.mojavensis to levels comparable in magnitude to that provided by the addition of free sugars to the diet.
5. This information and the apparent lack of a year-round supply of free sugars for D.mojavensis in nature suggests that the ethanol (produced by fermentation) rather than free sugars per se is the most important component of rotting cactus tissue for the survival of this species and may explain its successful host-plant shift.     

Persistent effects of a discrete warming event on a polar desert ecosystem

A discrete warming event (December 21, 2001–January 12, 2002) in the McMurdo Dry Valleys, Antarctica, enhanced glacier melt, stream flow, and melting of permafrost. Effects of this warming included a rapid rise in lake levels and widespread increases in soil water availability resulting from melting of subsurface ice. These increases in liquid water offset hydrologic responses to a cooling trend experienced over the previous decade and altered ecosystem properties in both aquatic and terrestrial ecosystems. Here, we present hydrological and meteorological data from the McMurdo Dry Valleys Long Term Ecological Research project to examine the influence of a discrete climate event (warming of >2 °C) on terrestrial environments and soil biotic communities. Increases in soil moisture following this event stimulated populations of a subordinate soil invertebrate species (Eudorylaimus antarcticus, Nematoda). The pulse of melt-water had significant influences on Taylor Valley ecosystems that persisted for several years, and illustrates that the importance of discrete climate events, long recognized in hot deserts, are also significant drivers of soil and aquatic ecosystems in polar deserts. Thus, predictions of Antarctic ecosystem responses to climate change which focus on linear temperature trends may miss the potentially significant influence of infrequent climate events on hydrology and linked ecological processes.     

Herbivory in sun and shade

Observations of several plant species suggest that individuals incur greater herbivore damage in shaded than in nearby sunny areas. Two hypotheses are presented to explain this pattern of herbivory; a preliminary test of one suggests that plants growing in the sun are usually tastier, although eaten less, than those in the shade. The phenomenon has several implications for the nature of plant-herbivore interactions in terrestrial communities.     

Why do adult insects not moult?

Hypotheses are presented concerning why mayflies moult after functional wings develop and why most insects cease to moult at this time. The pattern of retention or loss of the subimaginal moult in extant mayflies suggests that this moult may be necessary to complete elongation of caudal filaments and forelegs of adults. It is then analogous to the pupal moult of holometabolous insects. I propose that selection for wing efficiency has normally confined the presence of functional wings to one instar only, which is also the last and reproductive stage. Selection for light wings has generally caused the epidermis of membranous insect wings to degenerate, thereby precluding otherwise advantageous adult moults.     

Monoclonal Antibodies Reveal Complex Structure in the Membrane Skeleton of Tetrahymena

ABSTRACT. Twelve monoclonal antibodies were raised that are specific for the membrane skeleton of Tetrahymena . Five were directed against T. pyrifomis and seven were directed against T. thermophila . Some cross-reactivity between species was found. Each monoclonal antibody recognized one of the three major components of epiplasm, i.e. the bands A, B, and C identified in electrophoretic separations of epiplasmic proteins. It was found, using these antibodies, that the epiplasmic proteins A, B, and C have overlapping but independent distributions within the cell.