Abstract
Nest construction is a common form of parental care in soil organisms. However, it is unknown whether the tropical earthworm Pontoscolex corethrurus produces nests in soils with low nutritional quality habitats. Here we studied the reproductive behaviour and nest site selection of P. corethrurus, and tested the hypothesis whether P. corethrurus produces more cocoons in habitats with low nutritional quality. In bidimensional terrariums we evaluated the combined effect of the nutritional quality of habitat: (Poor Quality Habitat = PQH, Medium Quality Habitat = MQH, High Quality Habitat = HQH) and soil depth (Shallow, Intermediate, Deep) in a factorial 32 design. The number and biomass of cocoons, progeny and the production of internal and external excreta were evaluated. The quality habitat and depth of soil and their interaction had a significant effect on nest site construction and the deposition of internal excreta. Pontoscolex corethrurus built a higher amount of nests in the PQH-Intermediate and MQH-Intermediate treatments while more internal excreta were found in the HQH-Intermediate treatment. Offspring biomass was positively associated with internal excreta in the PQH (soil only) and MQH (soil + grass) treatments, suggesting that this could be a form of parental care. Since P. corethrurus produces more cocoons in low and medium quality habitats, while produces more internal excreta at high quality habitats, there does not seem to be an association between number of offspring and parental care. We suggest P. corethrurus could have two reproductive strategies that act as diversified bet-hedging (do not put all cocoons in one basket) behavior in unpredictable environment, and thus build a higher amount of nests in low and medium quality habitats; and another where they produce more internal excreta as a form of parental care in high quality habitats. Parental care in the form of internal excreta may be particularly important in poor and medium quality habitats where offspring biomass increased with internal excreta. Further research is needed on the ecological conditions that favour the evolution of parental care in earthworms according to their ecological category (epigeic, endogeic and anecic).
Highlights
Most animals, including the majority of invertebrates, do not provide any form of care for their offspring (Smiseth, Kölliker & Royle, 2012)
Some soil organisms develop parental care in order to increase the survival of their progeny; for example, in at least 11 families of beetles, ants and termites, parental care seems to be a response to severe environments (Currie, 2001; Muller et al, 2005; Mori & Chiba, 2009; Smiseth, Kölliker & Royle, 2012)
More internal excreta where deposited at the high quality habitat (HQH)-Intermediate treatment, which corresponds to the high quality environment
Summary
Most animals, including the majority of invertebrates, do not provide any form of care for their offspring (Smiseth, Kölliker & Royle, 2012). Some soil organisms develop parental care in order to increase the survival of their progeny; for example, in at least 11 families of beetles, ants and termites, parental care seems to be a response to severe environments (Currie, 2001; Muller et al, 2005; Mori & Chiba, 2009; Smiseth, Kölliker & Royle, 2012). Despite the fact that earthworms are among the most ecologically important soil organisms (Lee, 1985; Edwards & Bohlen, 1996), it is unknown whether they exhibit parental care towards their progeny
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