Time scales, causes and consequences of social instability, Octodon degus (Molina, 1782) as a study model
Authors:   , Riquelme De La Fuente Juan Daniel 
Published: June 2024

Sociability may arise from social interactions between individuals in relatively permanent and cohesive groups, with associations established in different contexts, such as foraging and burrowing, which may result in biological fitness benefits. To cope with ecological and social conditions during foraging, individuals experience temporary changes in group cohesion, called fission-fusion dynamics. In the same way, although some species experience permanent and short-term social instability, individuals can maintain associations in different contexts, where short-term dynamics generate multiple interactions that contribute to stabilizing associations in the long term. Therefore, the central objective of this thesis was to evaluate the role of socioecological factors in the social dynamics of foraging groups and to evaluate the contribution of short-term dynamics on long-term ones, in a natural population of Octodon degus, a highly social rodent. To evaluate whether social instability during foraging represents a behavioral mechanism to cope with heterogeneous ecological conditions, where social factors can influence these changes (chapter 1), I used 290 records from 2019, with 11 females and 11 focal males from winter; as well as 14 females and 11 focal males from spring. The results showed that degu forages in small groups of mixed sexual composition, where social stability increases by increasing quality food coverage (in winter), by decreasing interindividual distance and the risk of predation, and with the presence of predators. Furthermore, the stability of foraging groups was differentially sensitive to the opposite sex ratio in females and males. Finally, the social stability experienced by male and female foragers was greater during spring than winter. To evaluate whether short-term associations (i.e., social foraging during the mating season) represent a “meeting arena” for individuals to stabilize current long-term associations (i.e., burrow use during offspring rearing) (hypothesis 1), or establish different long-term associations (hypothesis 2) (chapter 2), I contrasted the information separated by sex, for 20 females and 16 males during mating in 2018; 17 females and 6 males during mating in 2019; 17 females and 15 males during offspring rearing in 2018; 17 females and 14 males during offspring rearing in 2019. To evaluate the role of social stability of foraging groups during mating season (based on burrow use) on the social stability of burrow use groups during offspring rearing, I used the information from 7 females and 7 males during 2019. To evaluate the role of social bonds in the number of offspring produced, I used 11 females without social bond and 6 females with social bond from 2018. The results showed that foraging associations at the time of mating were positively linked to associations in burrow use (2018-2019), and that this connection was stronger in females during 2018 compared to 2019. Consequently, females that showed social bonds with other females weaned more offspring in 2018. Similarly, foraging associations during mating were positively associated with associations based on the use of burrows during offspring rearing in both sexes (2018-2019), but more strongly in males during 2019. Genetic relatedness within foraging associations during mating had a sex-dependent influence on associations based on burrow use during mating (2018-2019) and offspring rearing (2019). Crucially, there was a positive association between the social stability of foraging groups during mating and the social stability of burrow-based groups during offspring rearing (2019). Taken together, this study highlights how individuals within a foraging social dynamic respond flexibly based on the socioecological conditions experienced. These findings provide limited but relevant evidence supporting that associations during foraging represent a social context that allows individuals to maintain associations in a different context, such as burrow sharing and communal care of offspring.