Fission–fusion dynamics in the social networks of a North American pitviper

Abstract

Many animal species exist in fission–fusion societies, where the size and composition of conspecific groups change spatially and temporally. To help investigate such phenomena, social network analysis (SNA) has emerged as a powerful conceptual and analytical framework for assessing patterns of interconnectedness and quantifying group‐level interactions. We leveraged behavioral observations via radiotelemetry and genotypic data from a long‐term (>10 years) study on the pitviper Crotalus atrox (western diamondback rattlesnake) and used SNA to quantify the first robust demonstration of social network structures for any free‐living snake. Group‐level interactions among adults in this population resulted in structurally modular networks (i.e., distinct clusters of interacting individuals) for fidelis use of communal winter dens (denning network), mating behaviors (pairing network), and offspring production (parentage network). Although the structure of each network was similar, the size and composition of groups varied among them. Specifically, adults associated with moderately sized social groups at winter dens but often engaged in reproductive behaviors—both at and away from dens—with different and fewer partners. Additionally, modules formed by individuals in the pairing network were frequently different from those in the parentage network, likely due to multiple mating, long‐term sperm storage by females, and resultant multiple paternity. Further evidence for fission–fusion dynamics exhibited by this population—interactions were rare when snakes were dispersing to and traversing their spring–summer home ranges (to which individuals show high fidelity), despite ample opportunities to associate with numerous conspecifics that had highly overlapping ranges. Taken together, we show that long‐term datasets incorporating SNA with spatial and genetic information provide robust and unique insights to understanding the social structure of cryptic taxa that are understudied.

Heat stress conditions affect the social network structure of free‐ranging sheep

“…Second, we calculated modularity as it gives insight into the internal structure of the social network and measures the extent to which a network is divided into different groups or clusters (Sosa et al., 2021 ). Networks with high modularity are characterised by many and strong connections within the group or cluster, while connections between groups are sparser (Tetzlaff et al., 2023 ). Fission–fusion societies, such as sheep (Della Libera et al., 2023 ), are structured into sub‐groups and modularity measures are higher compared to cohesive groups (Sosa et al., 2021 ).…”

“…Second, we calculated modularity as it gives insight into the internal structure of the social network and measures the extent to which a network is divided into different groups or clusters (Sosa et al, 2021). Networks with high modularity are characterised by many and strong connections within the group or cluster, while connections between groups are sparser (Tetzlaff et al, 2023).…”

Societies with fission–fusion dynamics as complex adaptive systems: the importance of scale

“…This distinction is especially prominent if we consider clades that are greatly neglected in FF literature because they may be cryptic in behaviour and/or do not easily conform to mammalian, avian or arthropod-based notions of ‘social’ groups, such as reptiles [ 89 ]. North American pit vipers ( Crotalus atrox ), for instance, can live up to 60 years and hunt solitarily but vary their associations during communal winter denning, mating and offspring production [ 90 ]. Individuals show extremely high fidelity to denning sites over multiple years but denning networks show low genetic relatedness and females are less likely to den communally than males.…”