Population genetic structure, ontogenetic color change and color-associated foraging variation in Nephila maculata.
In giant wood spider (Nephila maculata Fabricius 1793) populations in western Taiwan, some individuals are almost morphologically indistinguishable from the typical females except their brown body color. In this study, I investigated the color polymorphism by the following questions: (1) is there significant genetic differentiation between these two color morphs; (2) how brown morphs obtain their melanic coloration during development; (3) will the difference in body color be associated with a change in body surface reflection property and (4) will individuals of different colors differ in foraging success and thus reproductive output. Intra-population genetic structure was estimated by allozyme electrophoresis using 12 enzymes. An examination on allele frequencies and distribution patterns showed that genetic differentiation between typical and brown morphs was low (p = 0.0233). This result suggests that the genetic structuring between two morphs is congruent with that estimated from a highly-interbreeding population. Monthly field census conducted in Foyan Shan, Miauli County from July 1999 to July 2000 showed that no brown morphs were found in spiders smaller than 7 mm, indicating that color transformation occurred when spiders reached certain developmental stage. Among juveniles kept in laboratory under identical conditions, some became darker and darker after successive molts. This result suggests that color variation in N. maculata may not be induced by environments. An examination of body-surface reflection properties showed that typical morphs reflected significantly more visible and ultra-violet light than brown morphs. To understand whether this reflectance variation affects spiders' foraging success, prey interception rates were examined in a population in Foyan Shan in July 2000. No significant difference in prey-interception rates was found between two morphs. A comparison of body weight and egg sac mass of pregnant females collected in fall of 2000 also showed no significant difference. These results showed that although N. maculata of different colors differ in reflection properties, this phenotypic variation does not seem to affect foraging success and reproductive output of the population in Foyan Shan.
Updated: Mar-10-2014 01:22:51 (Taiwan, GMT+08:00).