house sparrows were introduced to north america in mid-19th century.
house sparrows were introduced to north america in mid-19th century.
when were house sparrows introduced to north america?
mid-19th century
Na
Na
in 1968, menaker provided evidence for the existence of extra-retinal photoreceptors that were sufficient for photoentrainment by measuring rhythmic locomotor behavior as the output signal of the house sparrows ("passer domesticus") circadian clock. he demonstrated that photoentrainment could occur in the absence of optic neurons, evidence for the presence of an extra-retinal photoreceptor(s) coupled to the house sparrow circadian clock. in this experiment, bilaterally enucleated house sparrows were exposed to an artificial light-dark cycle. they were kept in constant darkness to determine their free-running period and subsequently allowed to entrain to light cues. locomotor activity was recorded through observing perching behavior of the sparrows. he tested three possible confounding variables for entrainment: (1) temperature fluctuation, (2) post-enucleation retinal fragments remaining in the eye, and (3) ectoparasites that might transfer light information through their movements in the birds' skin. to study the effects of temperature on circadian rhythms, menaker exposed the enucleated sparrows to an electroluminescent panel. menaker treated sparrows with dry-die, an anti-parasitic agent, to eliminate any possible effects of light transferring by ectoparasites. since the sparrows did not entrain during tests of temperature fluctuation and the sparrows remained entrained 10 months after enucleation, a point at which any excess of the functional retina would have degraded, menaker ruled out these possible confounding variables. menaker's lab concluded the sparrows were able to entrain to environmental light cues. these results demonstrate that retinal light receptors are not necessary for photoentrainment, indicating there is an extra-retinal photoreceptor(s) contributing to circadian locomotor activity. menaker's findings in enucleated sparrows were consistent with aschoff’s rule, and he concluded that the retinae and the extra-retinal receptor(s) both contribute to the photoentrainment process.
michael menaker