Nocturnality and species survival.

Surveys of butterfly and moth diversity in tropical forest fragments suggest that nocturnality confers a dispersal, and possibly a survival, advantage. The butterfly faunas of smaller fragments were depauperate; in contrast, the species richness of nocturnal moths was similar in all fragments and even in pasture. The lack of correlation between butterfly and moth species richness among fragments (r2 = 0.005) is best explained by movements of moths at night when ambient conditions in forest and pasture are most similar; butterflies face substantial daytime temperature, humidity, and solar radiation barriers. This interpretation is supported by information on birds, beetles, and bats.

Twilight-zone and canopy shade induction of the Athb-2 homeobox gene in green plants.

We present evidence that a novel phytochrome (other than phytochromes A and B, PHYA and PHYB) operative in green plants regulates the "twilight-inducible" expression of a plant homeobox gene (Athb-2). Light regulation of the Athb-2 gene is unique in that it is not induced by red (R)-rich daylight or by the light-dark transition but is instead induced by changes in the ratio of R to far-red (FR) light. These changes, which normally occur at dawn and dusk (end-of-day FR), also occur during the daytime under the canopy (shade avoidance). By using pure light sources and phyA/phyB null mutants, we demonstrated that the induction of Athb-2 by changes in the R/FR ratio is mediated for the most part by a novel phytochrome operative in green plants. Furthermore, PHYB plays a negative role in repressing the accumulation of Athb-2 mRNA in the dark and a minor role in the FR response. The strict correlation of Athb-2 expression with FR-induced growth phenomena suggests a role for the Athb-2 gene in mediating cell elongation. This interpretation is supported by the finding that the Athb-2 gene is expressed at high levels in rapidly elongating etiolated seedlings. Furthermore, as either R or FR light inhibits cell elongation in etiolated tissues, they also down-regulate the expression of Athb-2 mRNA. Thus, these data support the notion that changes in light quality perceived by a novel phytochrome regulate plant development through the action of the Athb-2 homeobox gene.

How caterpillar-damaged plants protect themselves by attracting parasitic wasps.

Parasitic and predatory arthropods often prevent plants from being severely damaged by killing herbivores as they feed on the plants. Recent studies show that a variety of plants, when injured by herbivores, emit chemical signals that guide natural enemies to the herbivores. It is unlikely that herbivore-damaged plants initiate the production of chemicals solely to attract parasitoids and predators. The signaling role probably evolved secondarily from plant responses that produce toxins and deterrents against herbivores and antibiotics against pathogens. To effectively function as signals for natural enemies, the emitted volatiles should be clearly distinguishable from background odors, specific for prey or host species that feed on the plant, and emitted at times when the natural enemies forage. Our studies on the phenomena of herbivore-induced emissions of volatiles in corn and cotton plants and studies conducted by others indicate that (i) the clarity of the volatile signals is high, as they are unique for herbivore damage, produced in relatively large amounts, and easily distinguishable from background odors; (ii) specificity is limited when different herbivores feed on the same plant species but high as far as odors emitted by different plant species and genotypes are concerned; (iii) the signals are timed so that they are mainly released during the daytime, when natural enemies tend to forage, and they wane slowly after herbivory stops.