Social thermoregulation and communal nesting
Extensive fieldwork has shown that D. gliroides nests and hibernates communally, in tree holes or bamboo stems but, in some cases, nesting occurs with animals individually curled up instead of grouped in the nest (Figure 7a). Nests built by D. gliroides are spherical, with a single entrance, built with plant materials from Chusqueaspp. leaves, Hymenophyllum spp. ferns, and lined with many moss species (Figure 7b). Occasionally, nests are used more than once, although they prefer to build new ones. Based on these observations, Franco et al. (2012; 2011) and Celis-Diez et al. (2012) showed that communal nesting is common in D. gliroides using nest-boxes in two localities of southern Chile (near Valdivia and in Chiloe), with a mean of 2.3 animals per nesting box. Monitoring of nest boxes suggested that D. gliroides is resident throughout the year and uses torpor during cold seasons. Ageing negatively correlates with D. gliroides communal nesting, as juveniles usually nest in groups (17% are found nesting solitary), whereas adults usually nest solitary (83% found nesting solitary; Celis-Diez et al., 2012). Neither sex nor body mass seems to influence communal nesting in D. gliroides . Several Australian marsupials (Baker & Dickman, 2018), American rodents (Arnold, 1988; Boyles, Storm, & Brack, 2008; Bustamante, Nespolo, Rezende, & Bozinovic, 2002; Edelman & Koprowski, 2007; Schradin, Schubert, & Pillay, 2006; Viñals, Bertolino, & Gil-Delgado, 2017; Wilson, O’Riain, Hetem, Fuller, & Fick, 2010), and Neotropical bats (Roverud & Chappell, 1991) obtain significant energetic savings by hibernating in groups (Gilbert et al., 2010). This phenomenon remains little explored in D. gliroides . Preliminary laboratory measurements indicate, however, that grouped individuals do not benefit from thermoregulatory savings during torpor (Franco et al., 2012), which suggests that for D. gliroides, the energetic benefits of communal nesting are secondary to the benefits of sociality itself (Boix-Hinzen & Lovegrove, 1998; Ebensperger, 2001; Schradin et al., 2006). These observations were confirmed by recent mesocosms experiments performed in hibernating individuals in the field using thermographic images, which suggest that clustered D. gliroides do not conserve heat better than animals hibernating in isolation (Nespolo, Fontúrbel, et al., 2021; Figure 7c). These individuals were not related, discards the idea that communal nesting is driven by kin relatedness or parental care (Franco et al., 2011; see Figure 7d).
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