The Relationships between Phase and Period Responses to Light Pulses

Current theories of stable circadian entrainment postulate phase delays should be associated with period lengthening, while phase advances should be associated with period shortening. While characterising features of the rat PRC to light, we noted substantial numbers of responses that displayed the opposite pattern. Forty-eight rats provided data for 192 phase responses. Limiting our analysis to phase shifts greater than 1 hour, we found 44 displayed the expected predicted relationship, and 33 displayed the contrary paradoxical relationship. Paradoxical responders possessed significantly shorter initial activity periods, compared to predicted responders. Activity was significantly lengthened by paradoxical responders and shortened by predicted responders following light pulse exposure. These results suggest a second mode of stable entrainment. Additionally, these results indicate entrainment mode, predicted or paradoxical, is based upon activity period duration. Short activity period durations will be associated with paradoxical responses, long durations will be associated with predicted responses. We argue that, given the dynamic changes in photoperiod, both modes of entrainment are necessary to provide stable entrainment across the year.     

NdhO,a Subunit of NADPH Dehydrogenase,Destabilizes Medium Size Complex of the Enzyme in Synechocystis sp. Strain PCC 6803

Two mutants that grew faster than the wild-type (WT) strain under high light conditions were isolated from Synechocystis sp. strain PCC 6803 transformed with a transposon-bearing library. Both mutants had a tag in ssl1690 encoding NdhO. Deletion of ndhO increased the activity of NADPH dehydrogenase (NDH-1)-dependent cyclic electron transport around photosystem I (NDH-CET), while overexpression decreased the activity. Although deletion and overexpression of ndhO did not have significant effects on the amount of other subunits such as NdhH, NdhI, NdhK, and NdhM in the cells, the amount of these subunits in the medium size NDH-1 (NDH-1M) complex was higher in the ndhO-deletion mutant and much lower in the overexpression strain than in the WT. NdhO strongly interacts with NdhI and NdhK but not with other subunits. NdhI interacts with NdhK and the interaction was blocked by NdhO. The blocking may destabilize the NDH-1M complex and repress the NDH-CET activity. When cells were transferred from growth light to high light, the amounts of NdhI and NdhK increased without significant change in the amount of NdhO, thus decreasing the relative amount of NdhO. This might have decreased the blocking, thereby stabilizing the NDH-1M complex and increasing the NDH-CET activity under high light conditions.     

Striking difference in response to expanding brood parasites by birds in western and eastern Beringia

Two species of obligate brood‐parasitic Cuculus cuckoos are expanding their ranges in Beringia. Both now breed on the Asian side, close to the Bering Strait, and are found in Alaska during the breeding season. From May to July 2017, we used painted 3D‐printed model eggs of two cuckoo host‐races breeding in northeastern Siberia to test behavioral responses of native songbirds on both sides of the Bering Strait, with particular attention to species that are known cuckoo hosts in their Siberian range. Each host nest was tested after the second egg was laid and, if possible, again 4 days later with a model of a different type. Although our Siberian study site was also outside the known breeding ranges of the cuckoos, we found that Siberian birds had strong anti‐parasite responses, with 14 of 22 models rejected. In contrast, birds in Alaska had virtually no detectable anti‐parasite behaviors, with only one of 96 models rejected; the rejecters were Red‐throated Pipits (Anthus cervinus). Such differences suggest that the cuckoos might successfully parasitize naïve hosts and become established in North America whether or not their historic host species are widely available.     

Pest problems: The view of New Zealand federated farmers

Abstract

Agriculture is fundamental to the well being of the New Zealand economy. We are very much a trading nation and will continue, for the foreseeable future, to depend upon primary production for the generation of New Zealand's wealth.