Adaptive Complexity: The Thermoregulatory Postures of the Golden-web Spider, Nephila clavipes, at Low Latitudes

Abstract

The golden-web spider, Nephila clavipes (L.), responds to insolation from a wide range of compass bearings and altitudes by making postural adjustments that minimize the surface area of the body exposed to the heat source. The thermoregulatory postures involve pointing the apex of the abdomen at the sun and aligning the long axis of the body parallel to the sun's direction. Experimental and observational studies show that the spider can adjust its position in response to dorsal, ventral (through the web) and lateral solar illumination, and to complex combinations of these types of illumination. It is thus able to effect reduction of insolation irrespective of the compass orientation of the web. Full descriptions of the range of postures are given along with an analysis of actual web bearings. Web orientation is primarily determined by the requirements of efficient prey capture and the availability of web supports. Thermoregulation by postural adjustment may be particularly complex at low latitudes because of the potentially high heating effect of the sun over the greater part of its daily transit. Many arthropods that are exposed to insolation at fixed sites (e.g., some web-building spiders, other sedentary raptors and cryptic animals that rest by day on a matching background) can be expected to possess complex behavioral adaptations related to thermoregulation.