Rate of intersexual interactions affects injury likelihood in Tasmanian devil contact networks

Abstract

Identifying the types of contacts that result in disease transmission is important for accurately modeling and predicting transmission dynamics and disease spread in wild populations. We investigated contacts within a population of adult Tasmanian devils (Sarcophilus harrisii) over a 6-month period and tested whether individual-level contact patterns were correlated with accumulation of bite wounds. Bite wounds are important in the spread of devil facial tumor disease, a clonal cancer cell line transmitted through direct inoculation of tumor cells when susceptible and infected individuals bite each other. We used multimodel inference and network autocorrelation models to investigate the effects of individual-level contact patterns, identities of interacting partners, and position within the social network on the propensity to be involved in bite-inducing contacts. We found that males were more likely to receive potentially disease-transmitting bite wounds than females, particularly during the mating season when males spend extended periods mate-guarding females. The number of bite wounds individuals received during the mating season was unrelated to any of the network metrics examined. Our approach illustrates the necessity for understanding which contact types spread disease in different systems to assist the management of this and other infectious wildlife diseases.

Activity and social interactions in a wide-ranging specialist scavenger, the Tasmanian devil (Sarcophilus harrisii), revealed by animal-borne video collars

“…The low rate of injurious contacts we recorded during active travel and at dens and carcasses is similar to direct observations of interactions recorded around carcasses [11] and potentially lower than rates of biting injury during mating interactions indicated by indirect methods-proximity-sensing radiocollars and new injuries recorded when these collared individuals are trapped [17]. It is the injurious mating interactions that are thought to contribute most to transmission [17]. Our study thus contributes new information towards building a holistic understanding of the frequency and context of social contacts between devils that are relevant to transmission of DFTD.…”

“…Little is known about the ecology of wild devil dens but one study found that individuals use between one and ten dens and change dens every few days [19]. The low rate of injurious contacts we recorded during active travel and at dens and carcasses is similar to direct observations of interactions recorded around carcasses [11] and potentially lower than rates of biting injury during mating interactions indicated by indirect methods-proximity-sensing radiocollars and new injuries recorded when these collared individuals are trapped [17]. It is the injurious mating interactions that are thought to contribute most to transmission [17].…”

“…Direct behavioural observations are limited to those around carcasses of prey [9][10][11] and incidental observations near roads at night [12]. Inferences about foraging and social behaviour are made from tracking studies, including spool-and-line tracking [13], and VHF, GPS or proximity-sensing radio collars [14][15][16][17].…”

“…Knowledge of social contact and biting behaviours relevant to disease transmission is crucial for understanding disease spread and epidemic outcome, and for informing disease management options. Proximitysensing radio collars have been used to investigate interactions amongst devils [14,17] but they do not provide any information on location or whether the interactions were agonistic, although the latter can be inferred when coupled with examination of bite wounds from collared animals that are regularly trapped [17]. Video collars can provide a more detailed understanding of the location and nature of social interactions among devils.…”

Tracing the rise of malignant cell lines: Distribution, epidemiology and evolutionary interactions of two transmissible cancers in Tasmanian devils

“…disease ecology, emerging infectious disease, epidemiology, Tasmanian devil facial tumour disease, transmissible cancer season (Hamede, McCallum, & Jones, 2008;Hamede et al, 2013;Hamilton et al, 2019), DFTD transmission has been described as frequency-dependent and affects mostly sexually mature adult devils . The low DFTD prevalence in subadults might be attributed to the low number of bite wounds in this demographic group, (Hamede et al, 2013), an apparent extended latent period of DFTD ) and/or differences in immune function between subadults and adults (Cheng et al, 2017;Ujvari, Hamede, et al, 2016).…”