Ecology: Biology of Interaction. V-17. Adaptive Biorhythms and Photoperiodism

V-17. Adaptive biorhythms and photoperiodism a broken window in the room and in the cage feathers blood bird's handwriting a note instincts autumn goodbye Midori ("little pie") The influence of sunlight on a number of biological phenomena occurs through changes in light intensity during the day, changes in the duration of daylight, and the associated alternation of seasons. An important factor that sets periodic changes is the dynamics of the Moon's gravity, as well as lunar phases. These and other factors lead to the emergence of adaptive biological rhythms in living organisms: diurnal, tidal, seasonal, multi-year, and others. The ability of organisms to measure time intervals and regulate their life activities accordingly has been called the biological clock. For example, even under constant conditions in deep caves, circadian (diurnal) or circadiant (close in duration to a day) rhythms are characteristic of humans and representatives of other species. The biological clock allows physiological rhythms to be synchronized with the rhythm of the environment and makes it possible to predict diurnal, seasonal, and other periodic fluctuations in illumination, temperature, tides, etc. The rhythms of daily animal activity are a response to lighting conditions during the day. In addition to physiological features, they are also influenced by ecological factors that shape the living and feeding conditions of organisms. The exception is species that are active throughout the day, regardless of lighting conditions. Three main types of daily activity are distinguished in animals: diurnal, nocturnal, and continuous. Daily biorhythms of plants can manifest in leaf movements and changes in metabolism. For example, the lotus raises its leaves above the water surface during the day and lowers them into the water at night. Plants with CAM photosynthesis fix carbon dioxide only at night, etc. Features of the seasonal life cycle are associated with seasonal changes, which are a consequence of the Earth's rotation around the Sun, accompanied by seasonal changes. In seasonal climates, environmental conditions favor population growth only during specific limited periods. With certain seasons, periods of reproduction, development, dormancy (e.g., hibernation), migration, etc., are associated with organisms. In most areas of the temperate and Arctic zones, temperature is the main manifestation of seasonal change. In the tropics, the seasonal cycle of activity is determined by the rainy season. Tidal biorhythms are a consequence of the Moon's influence as it orbits the Earth. Organisms living in the intertidal zone have adapted to the lunar day (24 hours 50 minutes), during which there are two high and two low tides. During low tide, inhabitants of this zone close their shells and houses or bury themselves in the sand. The reproduction of some fish and polychaete worms, as well as horseshoe crabs, is associated with the rhythm of tides. Many organisms exhibit less pronounced multi-year cycles associated with non-periodic changes in solar activity over many years. For example, mass breeding of migratory locusts is linked to this (Fig. 4.16.3). Photoperiodism is the regulation of the seasonal cycle depending on the length of daylight. It is a regulatory mechanism widespread in the temperate zone (i.e., where seasons differ in daylight length and other environmental factors important for the seasonal cycle of organisms). Unlike circadian rhythms, which are regulated by the alternation of light and dark, annual (circannual) rhythms are controlled by daylight length. Daylight length is a parameter determined by the astronomical features of the Earth-Sun system and therefore changes quite regularly. Changes in factors important for most organisms (temperature, humidity, food availability, etc.) depend on both astronomical causes and the action of many random causes. Daylight length is a typical signaling factor. Although humans have long since transitioned to non-seasonal reproduction, they retain rudimentary photoperiodic regulatory mechanisms. One manifestation of their action is the increase in the concentration of sex hormones in the blood in spring (more precisely, even at the end of winter), with increasing daylight hours. The regulation of circannual rhythms in vertebrates is carried out by the hypothalamus-pituitary system. The pineal gland (a rudimentary light-sensitive organ) plays a significant role in this regulation.