A LINEAR-MODEL FOR DESCRIPTION OF THE RELATIONSHIP BETWEEN THE LOWER THRESHOLD TEMPERATURE AND THERMAL CONSTANT IN SPIDERS (ARANEAE, ARACHNIDA)

The thermal constant (K) and the threshold temperature (T-0) for devel opment of eggs were estimated by using linear regression for 16 specie s (17 populations) of spiders. T-0 ranged between 4.2 and 16.8 degrees C, K between 64.1 and 217.4 day-degrees (dd). When T-0 was plotted ag ainst K, the data were scattered along a single regression line (T-0 = 18.05-0.063 K) which predicted a 0.63 degrees C decrease in T-0 per 1 0 nd increase in K. The present paper is the first report, in spiders, of a linear relationship between T-0 and K at interspecific level. Th e typical development time (VDT) and the extent of its deceleration by low temperature (DD) varied between species. DD increased with increa sing VDT, but the relative effect of low temperature on development ti me (DD/VDT ratio) varied independently of VDT, reflecting thermal adap tations consistent with the life history of the species. There is evid ence that the DD/VDT ratio for eggs of spiders is smaller than that of insects. (C) 1998 Elsevier Science Ltd. All rights reserved.