1. Three common species of freshwater phytoplankton, the diatom Nitzschia sp., green alga Sphaerocystis schroeteri and cyanobacterium Phormidium luridum, were grown under contrasting daylengths [18 : 6 h light : dark cycles (LD) versus 6 : 18 h LD] and phosphorus (P) regimes (P-sufficient versus 1 lM P). The rates of growth and photosynthesis, as well as growth efficiencies and pigment concentr...

Fluctuations in the length of the day affect developmental processes and behaviors of many organisms. Mammals and birds reproduce in spring in response to lengthening days and insects pupate in autumn when daylength shortens. These phenomena, called photoperiodism, allow detection of seasonal changes and anticipation of environmental conditions such as low temperatures and desiccation. Photoper...

Many plants use the seasonal change in daylength as a signal for flowering. Daylength sensing in Arabidopsis has now been shown to occur by an external coincidence mechanism, which operates by the circadian and light regulation of CONSTANS.

Two genetic loci control the vernalization response in winter cereals; VRN1, which encodes an AP1-like MADS-box transcription factor, and VRN2, which has been mapped to a chromosome region containing ZCCT zinc finger transcription factor genes. We examined whether daylength regulates expression of HvVRN1 and HvVRN2. In a vernalization-responsive winter barley (Hordeum vulgare), expression of Hv...

In order to elucidate the developmental basis for smolting, Atlantic salmon, Salmo salar, parr (b11.5 cm) and smolts (N12.5 cm) were exposed to natural daylength (LDN) and increased daylength (LD16:8) starting in late February and gill Na,K– ATPase activity and circulating hormone levels monitored from January to May. Gill Na,K–ATPase activity remained low and constant in both groups of parr. I...

The Asian tiger mosquito, Aedes albopictus (Skuse), is perhaps the most successful invasive mosquito species in contemporary history. In the United States, Ae. albopictus has spread from its introduction point in southern Texas to as far north as New Jersey (i.e., a span of approximately 14 degrees latitude). This species experiences seasonal constraints in activity because of cold temperatures...

Photoperiod, and not high ambient temperature, appears to be the major cause of seasonal infertility in pigs. Attempts to counter depressed fertility during summer by cooling sows are often unsuccessful. In contrast, artificially reducing daylength during summer shortened the wean-to-oestrus interval of a commercial sow herd by 18d to 5.7d. A similar programme also improved boar fertility. Howe...

Many plants are adapted to flower at particular times of year, to ensure optimal pollination and seed maturation. In these plants flowering is controlled by environmental signals that reflect the changing seasons, particularly daylength and temperature. The response to daylength varies, so that plants isolated at higher latitudes tend to flower in response to long daylengths of spring and summe...

Larval behavioral diapause was shown to be the major factor controlling the 1-yr generation pattern of Amblyomma cajennense (F.) (Acari: Ixodidae) in Brazil. During fieldwork, this behavior was shown to coincide with long daylength (>12 h) and high mean ground temperature (approximately =25 degrees C), which prevail during spring-summer in Brazil. The current study evaluated biological paramete...