Wavelength dependent cis-trans isomerization in vision.

The primary event in vision is the light-driven cis-trans isomerization of the 11-cis-retinal chromophore in the G-protein coupled receptor rhodopsin. Early measurements showed that this photoisomerization has a reaction quantum yield phi of approximately 0.67 [Dartnall (1936) Proc. R. Soc. A 156, 158-170; Dartnall (1968) Vision Res. 8, 339-358] and suggested that the quantum yield was wavelength independent [Schneider (1939) Proc. Natl. Acad. Sci. U.S.A. 170, 102-112]. Here we more accurately determine phi(500) = 0.65 +/- 0.01 and reveal that phi surprisingly depends on the wavelength of the incident light. Although there is no difference in the quantum yield between 450 and 480 nm, the quantum yield falls significantly as the photon energy is reduced below 20 000 cm(-1) (500 nm). At the reddest wavelength measured (570 nm), the quantum yield is reduced by 5 +/- 1% relative to the 500 nm value. These experiments correct the long-held presumption that the quantum yield in vision is wavelength independent, and support the hypothesis that the 200 fs photoisomerization reaction that initiates vision is dictated by nonstationary excited-state vibrational wave packet dynamics.

A new role for temperature in insect dormancy: cold maintains diapause in temperate zone Diptera.

In early autumn, high temperatures terminate diapause in the alfalfa blotch leafminer Agromyza frontella; low temperatures maintain diapause. These responses subserve a thermally malleable dormancy and allow flexibility in the annual number of generations. The view that favorable conditions cannot reverse the course of diapause are contradicted by the data on A. frontella. A better understanding to life history studies and phenological models in insect pest management.

Sympatric speciation based on allelic changes at three Loci: evidence from natural populations in two habitats.

Allelic changes at three loci largely explain Chrysopa downesi's sympatric speciation from a Chrysopa carnea-like ancestor. Disruptive selection first produced a stable polymorphism based on a single pair of alleles that adapted individuals to two habitats, and second, it established seasonal asynchrony in reproduction through allelic substitutions at two loci.

A genetic model for sympatric speciation through habitat diversification and seasonal isolation.

Based on studies with natural populations, we offer a genetic model for sympatric speciation that could have broad application to polyphagous animals with habitat differences. The model comprises three steps, each of which includes simple genetic changes and plausible selective forces.

Two genes control seasonal isolation in sibling species.

Interspecific hybridization tests between Chrysopa carnea and Chrysopa downesi show that single allele differences at two unlinked autosomal loci cause large differences in photoperiodic responses. These differences produce asynchronous seasonal reproductive cycles, thus forming an effective temporal reproductive barrier between the two sympatric species. The results subserve the development of a genetic model for allochronic speciation.

Photoperiodic induction and termination of diapause in an insect: response to changing day lengths.

Chrysopa carnea diapaused after experiencing a decrease in day length above the critical photoperiod. Animals experiencing increasing day lengths less than the critical photoperiod did not diapause, and those in diapause began to reproduce. These experiments are the first to demonstrate that insects respond to the direction of change in photoperiods (both increasing and decreasing) which do not encroach on the critical photoperiod.