Development, growth and allometry in a cohort of the tarantula Grammostola vachoni (Araneae: Theraphosidae)

Abstract

Spiders are perfect model for developmental stage and growth studies because the juvenile period is broken into instars. Theraphosidae family, are largest and longest-lived spiders and females continue to grow and molt over the sexually mature stage is reached. However, their development and growth are still unknown. Thus, our objective was describe in detail the development of the juveniles of Grammostola vachoni until reaching the adulthood, estimate the growth of somatic and spermathecae dimensions, and analyze any possible allometric relation between the spermathecae and body size during the development. The mortality of individuals was 10.7% per year; and both sexes molted between once and twice by a year with a peak in the molt frequency in the third year of life. The intermolt interval was similar between sexes and tended to increase during development. The spermathecae appeared in the immature females more frequently in the 8th molt (4.03 years) and males reached adulthood frequently at the 11th molt (7.03 years). Both sexes had similar growth percentage (38%) and its was constant throughout their whole development. In contrast, the spermathecae growth percentage was 98% and always was higher than the percentage of body growth. The somatic characters did not show any differences between females and males. The spermathecae measurements showed positive allometric growth related to the body size. The results of our study completes the baseline biology information about the development, growth and its relationship, aspects mostly unknown in tarantulas.