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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