Received: 25 April, 2008. Accepted: 6 July, 2009. Original Research Paper Dynamic Soil, Dynamic Plant ©2009 Global Science Books Nest and Feeding Chamber Construction for Cocoon Incubation in the Tropical Earthworm: Pontoscolex corethrurus Angel I. Ortiz-Ceballos * • María Eréndira C. Hernández-García • Jorge Galindo-González Instituto de Biotecnología y Ecología Aplicada, Dirección General de Investigaciones, Universidad Veracruzana, Campus para la Cultura, las Artes y el Deporte, AP 250, Xalapa, Ver. 91090, Mexico Corresponding author: * angortiz@uv.mx ABSTRACT Details on how earthworm cocoons are deposited in soil have not been documented, nor whether they are abandoned or protected. This study provides the first detailed description of nest- and feeding-chamber construction for tropical earthworm species. The reproductive behaviour of the earthworm Pontoscolex corethrurus was observed using 11 “Evans Box” terraria, including one earthworm each. During the progression of the reproductive behaviour of P. corethrurus, observations were made at regular intervals for a period of 120 days. P. corethrurus built nest chambers with the mouths, coating them internally with a compact layer of fine soil and mucus. One cocoon was deposited in each nest chamber, then suspended from the nest walls by mucus filaments. During incubation, P. corethrurus frequently entered nest chambers for repairing or cleaning the inner walls. Besides, earthworms left no casts on the soil surface, but deposited them into underground nests built close to the site where the cocoon was deposited, and entered these underground nests to feed. Juveniles that emerged left the nest to feed on casts deposited in the feeding chamber. Our observations suggest that P. corethrurus displays parental care by building and caring for nest and feeding chambers, an aspect which deserves further investigation. _____________________________________________________________________________________________________________ Keywords: behaviour, cast, mucus, Oligochaeta, reproduction, terraria INTRODUCTION Earthworms belong to the class Oligochaeta (Annelida: Cli- tellata); in most soil types they dominate the soil fauna and have inhabited terrestrial environments for over 600 million years (Stephenson 1930; Lavelle and Spain 2001; Coleman et al. 2004). They have been referred to as “ecosystem’s engineers” for their abundance and biological activity in soil (Jones et al. 1994; Lavelle and Spain 2001; Hastings et al. 2007). Most earthworm species display sexual reproduction, although some are parthenogenetic; mating takes place mostly in soil throughout the year, except under unfavoura- ble environmental conditions; some species, such as Lum- bricus terrestris, mate on the soil surface; the cocoon con- tains a nutritive albuminous fluid produced by clitellar gland cells located in the anterior part of the body (only in mature worms), and both ova and spermatozoa are dis- charged into it as the tube passes the spermathecal openings. Fertilization is external, taking place inside the cocoon. The earthworm sheds the cocoon by sliding it over the peristome (Stephenson 1930; Lee 1985; Edwards and Bohlen 1996; Lavelle and Spain 2001; Coleman et al. 2004). However, details on how cocoons are deposited in soil have not been documented, nor whether they are abandoned or protected; the only aspect reported is that cocoons possess an extraor- dinary capacity to withstand drought (Holmstrup and Zacha- riassen 1996) and infections, and that cocoon production and incubation duration vary with species, soil temperature and moisture (Stephenson 1930; Lee 1985; Edwards and Bohlen 1996). To date, no reports are available on whether earthworms have any behaviour patterns to help increase offspring survival (Ortiz-Ceballos and Fragoso 2006; Gri- goropoulou et al. 2008). Pontoscolex corethrurus Muller, 1856 (Glossoscoleci- dae) is a primarily parthenogenetic earthworm species com- monly found in disturbed and natural tropical ecosystems, and is widely tolerant to edaphic and climatic changes (Lavelle et al. 1987). P. corethrurus is an endogeic species that ingests large amounts of soil with a preference for rich organic soils, continuously building mostly horizontal bran- ching burrows (Lavelle et al. 1987). Ortiz-Ceballos et al. (2005) and Ortiz-Ceballos and Fragoso (2006) found coc- oons of P. corethrurus and B. pearsei inside well-defined nest chambers, and these cocoons rapidly dehydrated when kept in the open air. The aim of the present study was to provide a detailed description of nest chamber construction by P. corethrurus, to address the question of how earthworms build the nests where cocoons are deposited. Our hypothesis is that nest chambers are built with earthworm cast. MATERIALS AND METHODS P. corethrurus earthworms were collected by manual hand sorting from a mango plantation located 79 km southwest (17° 48 N, 93° 28 W) of Villahermosa, Tabasco, Mexico. Earthworms were rep- roduced inside a box containing soil from the collection site, at 25 to 27°C. Earthworms used for this study were obtained from this box. The reproductive behaviour of P. corethrurus was investi- gated in earthworms transferred to eleven terraria (52 × 36 cm) made of two flat glass sheets separated by 5 mm-thick polystyrene pieces placed around the edges (Evans 1947; Capowiez 2000). One kilogram, equivalent oven-dry weight, of well-mixed soil (26.9% clay, 31.6% silt, 41.5% sand and 2.7% organic matter) was placed in each terrarium and moistened. One sub-adult (without a developed clitellum) of P. corethrurus was placed in each ter- rarium. To each side of the terrarium a clear acetate sheet was placed to draw the location of cocoons and label each one with a number by order of appearance. The dates in which each cocoon appeared and juveniles hatched were registered. Nest-chamber and cocoon diameters were measured with a digital calliper. Hatched juvenile behaviour was observed throughout the first 15 days of life. ®