The effects of season and devil facial tumour disease on the reproductive physiology of the male Tasmanian devil (Sarcophilus harrisii)

Transmissible cancer influences immune gene expression in an endangered marsupial, the Tasmanian devil (Sarcophilus harrisii)

Understanding the effects of wildlife diseases on populations requires insight into local environmental conditions, host defence mechanisms, host life‐history trade‐offs, pathogen population dynamics, and their interactions. The survival of Tasmanian devils (Sarcophilus harrisii) is challenged by a novel, fitness limiting pathogen, Tasmanian devil facial tumour disease (DFTD), a clonally transmissible, contagious cancer. In order to understand the devils’ capacity to respond to DFTD, it is crucial to gain information on factors influencing the devils’ immune system. By using RT‐qPCR, we investigated how DFTD infection in association with intrinsic (sex and age) and environmental (season) factors influences the expression of 10 immune genes in Tasmanian devil blood. Our study showed that the expression of immune genes (both innate and adaptive) differed across seasons, a pattern that was altered when infected with DFTD. The expression of immunogbulins IgE and IgM:IgG showed downregulation in colder months in DFTD infected animals. We also observed strong positive association between the expression of an innate immune gene, CD16, and DFTD infection. Our results demonstrate that sampling across seasons, age groups and environmental conditions are beneficial when deciphering the complex ecoevolutionary interactions of not only conventional host‐parasite systems, but also of host and diseases with high mortality rates, such as transmissible cancers.

Multiple paternity and precocial breeding in wild Tasmanian devils, Sarcophilus harrisii (Marsupialia: Dasyuridae)

Polyandry, a common reproductive strategy in various animal species, has potential female benefits, which include enhanced offspring fitness. Benefits can be direct, such as reduced risk of male infanticide of offspring, or indirect, such as increased genetic diversity of offspring and the acquisition of ‘good genes’. Multiple paternity of litters has been recorded in numerous marsupial species but has not been reported in Tasmanian devils, Sarcophilus harrisii (Boitard). We investigated whether multiple paternity occurred in litters within a wild population of Tasmanian devils. Using major histocompatibility complex-linked and neutral microsatellite markers, the paternity of nine litters was analysed. We found multiple paternity in four out of nine litters and that yearling (> 1, < 2 years old) male devils were siring offspring. This is the first record of multiple paternity and of male precocial breeding in wild Tasmanian devils. To date, there are no data relating to the subsequent survival of devils from single- vs. multiple-sired litters; therefore, we do not know whether multiple paternity increases offspring survival in the wild. These results have implications for the Tasmanian devil captive insurance programme, because group housing can lead to multiple-sired litters, making the maintenance of genetic diversity over time difficult to manage.

Sex bias in ability to cope with cancer: Tasmanian devils and facial tumour disease

Knowledge of the ecological dynamics between hosts and pathogens during the initial stages of disease emergence is crucial to understanding the potential for evolution of new interspecific interactions. Tasmanian devil (Sarcophilus harrisii) populations have declined precipitously owing to infection by a transmissible cancer (devil facial tumour disease, DFTD) that emerged approximately 20 years ago. Since the emergence of DFTD, and as the disease spreads across Tasmania, the number of devils has dropped up to 90% across 80% of the species's distributional range. As a result, the disease is expected to act as a strong selective force on hosts to develop mechanisms of tolerance and/or resistance to the infection. We assessed the ability of infected devils to cope with infection, which translates into host tolerance to the cancer, by using the reaction norm of the individual body condition by tumour burden. We found that body condition of infected hosts is negatively affected by cancer progression. Males and females presented significant differences in their tolerance levels to infection, with males suffering declines of up to 25% of their body condition, in contrast to less than 5% in females. Sex-related differences in tolerance to cancer progression may select for changes in life-history strategies of the host and could also alter the selective environment for the tumours.

Density trends and demographic signals uncover the long-term impact of transmissible cancer in Tasmanian devils

1. Monitoring the response of wild mammal populations to threatening processes is fundamental to effective conservation management. This is especially true for infectious diseases, which may have dynamic and therefore unpredictable interactions with their host. 2. We investigate the long-term impact of a transmissible cancer, devil facial tumour disease (DFTD), on the endemic Tasmanian devil. We analyse trends in devil spot-light counts and density across the area impacted by the disease. We investigate the demographic parameters which might be driving these trends, and use spatial capture-recapture models to examine whether DFTD has affected home range size. 3. We found that devils have declined by an average of 77% in areas affected by DFTD, and that there is a congruent trend of ongoing small decline in spotlight counts and density estimates. Despite this, devils have persisted to date within each of nine monitoring sites. One site is showing as yet unexplained small increases in density 8-10 years after the emergence of DFTD. 4. We also found the prevalence of DFTD has not abated despite large declines in density and that diseased sites continue to be dominated by young devils. The long-term impact of the disease has been partially offset by increased fecundity in the form of precocial breeding in 1-year-old females, and more pouch young per female in diseased sites. The lower densities resulting from DFTD did not affect home range size. 5. Synthesis and applications. Transmission of devil facial tumour disease continues despite large declines in devil density over multiple generations. Plasticity in life history traits has ameliorated the impact of devil facial tumour disease, however broad-scale trends in density show ongoing decline. In light of this, devil facial tumour disease and the impact of stochastic events on the reduced densities wrought by the disease, continue to threaten devils. In the absence of methods to manage disease in wild populations, we advocate managing the low population densities resulting from disease rather than disease per se.

Significant decline in anticancer immune capacity during puberty in the Tasmanian devil

Tasmanian devils (Sarcophilus harrisii) are at risk of extinction in the wild due to Devil Facial Tumour Disease (DFTD), a rare contagious cancer. The prevalence of DFTD differs by age class: higher disease prevalence is seen in adults (2–3 years) versus younger devils (<2 years). Here we propose that immunological changes during puberty may play a role in susceptibility to DFTD. We show that the second year of life is a key developmental period for Tasmanian devils, during which they undergo puberty and pronounced changes in the immune system. Puberty coincides with a significant decrease in lymphocyte abundance resulting in a much higher neutrophil:lymphocyte ratio in adults than subadults. Quantitative PCR analysis of gene expression of transcription factors T-bet and GATA-3 and cytokines interferon gamma (IFN-γ) and interleukin 4 (IL-4) revealed a drastic increase in GATA-3 and IL-4 expression during puberty. These changes led to a significantly lower IFN-γ:IL-4 ratio in 2-year-olds than <1 year olds (on average 1.3-fold difference in males and 4.0-fold in females), which reflects a major shift of the immune system towards Th2 responses. These results all indicate that adult devils are expected to have a lower anticancer immune capacity than subadults, which may explain the observed pattern of disease prevalence of DFTD in the wild.

Nuclear organization of cholinergic, catecholaminergic, serotonergic and orexinergic systems in the brain of the Tasmanian devil (Sarcophilus harrisii)

This study investigated the nuclear organization of four immunohistochemically identifiable neural systems (cholinergic, catecholaminergic, serotonergic and orexinergic) within the brains of three male Tasmanian devils (Sarcophilus harrisii), which had a mean brain mass of 11.6g. We found that the nuclei generally observed for these systems in other mammalian brains were present in the brain of the Tasmanian devil. Despite this, specific differences in the nuclear organization of the cholinergic, catecholaminergic and serotonergic systems appear to carry a phylogenetic signal. In the cholinergic system, only the dorsal hypothalamic cholinergic nucleus could be observed, while an extra dorsal subdivision of the laterodorsal tegmental nucleus and cholinergic neurons within the gelatinous layer of the caudal spinal trigeminal nucleus were observed. Within the catecholaminergic system the A4 nucleus of the locus coeruleus complex was absent, as was the caudal ventrolateral serotonergic group of the serotonergic system. The organization of the orexinergic system was similar to that seen in many mammals previously studied. Overall, while showing strong similarities to the organization of these systems in other mammals, the specific differences observed in the Tasmanian devil reveal either order specific, or class specific, features of these systems. Further studies will reveal the extent of change in the nuclear organization of these systems in marsupials and how these potential changes may affect functionality.

Development and evaluation of electroejaculation techniques in the Tasmanian devil (Sarcophilus harrisii)

Electroejaculation (EEJ) has been used successfully to collect samples suitable for genome resource banking from a variety of endangered wildlife species. Ejaculates can also be used to evaluate the reproductive potential of individuals and provide information on seminal characteristics to aid in the development of sperm cryopreservation techniques. Electroejaculation techniques used for marsupial and eutherian species were tested on Tasmanian devils (n = 35). Spermic ejaculates were collected in 54% (19/35) of EEJ attempts. Spermic ejaculates were low in volume (3.9 ± 6.5 × 102 µL, range 10–3000 µL) and contained low numbers of spermatozoa (3.3 ± 7.8 × 103 spermatozoa per ejaculate, range 6–33 000). The osmolality and pH of presumptive urine-free ejaculates were 389 ± 130 mOsm kg–1 (range 102–566) and 7.0 ± 0.9 (range 6.0–8.0), respectively. Prostatic bodies were observed in 79% (26/33) of ejaculates. Episodic fluctuations in serum testosterone concentrations were not detected during the EEJ procedure (P > 0.05). Increases observed in serum cortisol concentrations during EEJ were less (P < 0.05) than those observed after an adrenalcorticotropic hormone challenge and diurnal variation suggested that cortisol concentrations are greater during the day than at night (P < 0.05). This information can be used to provide range values for the future examination of basic endocrine responses and the adrenal–pituitary axis of this species. This study also demonstrated that spermatozoa-rich devil electroejaculates are more difficult to obtain and poorer in quality than those of other marsupials.