Differences in the timing of diapause and patterns of aestivation in tropical earthworms

Abstract

Summary Aestivation is a period of inactivity included within the life cycles of many soil organisms. Due to physiological, genetic and environmental heterogeneity, earthworm aestivation may take on different forms. In this paper we used the term aestivation to refer to the inactivity of populations at any time of the year. Several strategies found in some tropical earthworm species are given in this article. The results were obtained in detailed studies of earthworm communities conducted in savannas of Colombia and Mexico, several Mexican pastures and some Miombo-derived agroecosystems in Tanzania. Although all species built aestivation chambers in which they coiled up at certain periods of the year, different patterns of aestivation were found: two Neotropical species were found inside a plastered mucus sphere while two other species did not form any mucus sphere but layered the end of the gallery with several faecal blocks, and one African species created an aestivation chamber with large sand grains that adhered to the earthworm, preventing it from touching the surface of the chamber's walls. A detailed description and drawings of the aestivation chambers of five earthworm species are given plus a complete analysis of the mechanistic processes that determine this behavioural pattern for one anecic species from Colombia. The onset of aestivation differed in adults and juveniles for two glossoscolecid tropical species, i.e. Glossodrilus n. sp. and Martiodrilus carimaguensis , a native anecic earthworm from the tropical lowlands of Colombia which undergoes diapause by burrowing deep into the soil during late rainy season, while immature individuals enter into this phase four months earlier. Relationships between the aestivation period and the addition of new segments in earthworms have been established by several authors. In this study there was no relationship for the only species studied in more detail.