Context
General Context
Climate change as multiple consequences on ecosystems, such as northward and upward shifts of species range and the acceleration of different stages of the life cycle of some organisms [1,2,3,4]. These consequences lead to changes in species interactions, including parasite-host interactions.
After an upward trend during several years, moose density and harvest through sport hunting recently stabilized in eastern North America. The harvest rate has even decreased in some regions and the winter tick (Dermacentor albipictus) could explain this situation, at least partly.
The winter tick is a hematophagus ectoparasite of large vertebrate in North America. Unlike the majority of tick species which spend the 3 phases of their life cycle on distinct hosts, the winter tick goes from larva to nymph and from nymph to adult on a single host during the winter, hence its name. As other ectoparasite (parasite staying on, rather than within, host), the winter tick is particularly sensitive to environmental conditions and thus to the effects of climate change. This is also the case for several parasites likely to infest moose and for which impact may be additive.
The life cycle of the winter tick: In fall, tick larvae are in the vegetation waiting for an animal to climb onto as it pass by. Once on the animal, larvae will feed on the blood of their host on multiple occasions and will transform into nymphs and then into adults. During winter, adult ticks will engorge with their host’s blood and will reproduce before dropping to the ground during spring. Once on the ground, females will lay their eggs which will hatch into larvae ready for the following fall. (figure adapted from MFFP by D. De Pierre)
The winter tick, in combination with other parasites such as the lungworm (Dictyocaulus viviparus), is responsible for mass mortalities in some moose populations[5,6,7]. In New Hampshire, Jones and collaborators[8] reported calf mortality rates around 70% during a particularly severe outbreak. In New-Brunswick, the proportion of mortality attributable to winter tick as also increase in recent years (see figure below). Moose are more likely to suffer from winter ticks than white-tailed deer (Odocoileus virginianus) or elk (Cervus canadensis) because of their lower propensity to groom themselves to get rid of ticks. Unlike these cervids which evolved in the presence of several species of ticks, such as the black-legged tick (Ixodes scapularis) or the American dog tick (Dermacentor variabilis), moose have not developed defense mechanisms against the winter tick which has been rare in their habitat historically.
Proportion of moose mortality attributable to winter tick in New-Brunswick (Source : D. Sabine, Fish And Wildlife Branch, Natural Resources, NB)
Relationship between winter tick and moose
The increase in moose abundance and the intensification of winter tick epidemics that ensued are recent phenomenon in eastern Canada. These phenomenon are however linked because the parasitic load is correlated to the host density through the increased infestation success of parasite when host are abundant and finding one is easier [9,10,11]. The parasite load is also dependent on climate as tick survival is closely link to environmental conditions (See section “Relationship between the winter tick and climate” below).
Example of a moose with a very severe infestation:
As such, the impact of winter ticks on moose (see figure below) varies according to the parasitic load and peaks during the period of engorgement of female adult ticks at the end of winter and early spring. At the same time, the availability of quality forage is limited and the energy reserves of moose are at their lowest level. High densities of moose amplify this phenomena through the degradation of the habitat[12] which results in a further decrease of body condition and reproduction of moose [13]. The additive effects of the parasitic load, winter conditions and high moose density may then decrease body condition, survival and ultimately survival of moose [5,6,14,15]. These additive effects however vary according to the sex and age of infested moose.
The ticks infest moose in fall which coincides with the rut. Male moose are then covering more grounds than female and are thus more likely to get infested by ticks. Moreover, males lose more than 10% of their body weight during the rut [16] so they start winter with an energy deficit which could make them more vulnerable to tick infestations than females [15].
For females, the high energy requirements associated with the end of gestation in April-May [11] worsen the negative effects of the tick[9]. This decreased body condition at the end of gestation and during lactation in May-June could indirectly reduce maternal investment and increase neonatal calf mortality [17].
Nonetheless, winter tick impacts should be more pronounced in calves[6,8], because, among other things, they need to replace a greater proportion of their blood volume compared to adults when they are infected. They are also more prone to heat stress [18], not to mention the fact that they have to spend more energy for locomotion in the snow than larger animals.
The influence of climatic and parasitic factors on the ecology of moose populations is not yet well understood[5,16].
Relationship between the winter tick and climate
Changes in precipitation and weather patterns induced by global warming could favorably affect tick population dynamics and their ability to infest moose.
Spring weather conditions are a key factor in the winter tick's life cycle as this is when females drop to the ground and lay their eggs.[9]. In the absence of snow, the probabilities of survival of female ticks are higher [20,21]. Earlier snowmelt is therefore favorable to the development of winter tick populations.
The period of larval infestation in the fall is also a critical period. Larvae must manage their limited energy reserves to make vertical migrations between their shelter habitat in the litter and lurking stations in tall vegetation [22]. During dry fall days, the larvae are forced to return to the ground shelter because they are prone to desiccation[[23,24]. If the fall season is dry, the larvae deplete their energy reserves through repeated vertical migrations and are thus less prone to find a host. Inversely, later frosts and snowfalls induced by climate change may increase the success of ticks in infesting moose by extending the suitable period for finding a host [24,25].
Distribution of moose parasitized by winter ticks according to inventories conducted at recording stations by the MFFP in the fall of 2012 to 2017. Source: https://mffp.gouv.qc.ca/faune/sante-maladies/tique-orignal.jsp
A need for the acquisition of shared knowledge
This research project assessing the role of the winter tick in the ecology of moose population in eastern Canada was put in place by a large consortium of partners from government, industry, associations and universities in lights of the potential impacts of the winter tick on moose populations and the lack of knowledge on the mechanism involved in this host-parasite interaction. This project also represents a unique opportunity to assess the health of moose populations in eastern Canada. The telemetric monitoring of several hundred moose in five regions of Quebec and New Brunswick will provide survival rates and causes of mortality as well as the relative importance of mortality factors on moose population dynamic.
One of the main strengths of the project is the wide range of environmental conditions it covers. With study sites distributed across several regions of Quebec and New Brunswick, we will sample moose in areas where moose densities, climatic conditions and parasite loads, including ticks, are diverse. Moreover, experimental manipulation of tick load in each region through the application of acaricide products will allow us to precisely assess the impact of the winter tick on moose populations.
You can watch this video, made by our partner J. D. Irving, summarizing the project.
Research Objectives and Impacts
The objectives of the research work will be numerous and distributed according to 3 research axes that will lead to various impacts:
Axis 1: Moose Health, Ecology and Population Dynamics
. Assess the effects of winter ticks on moose health.
. Identify the interactions between winter tick and other moose parasites.
. Assess the role of winter ticks in moose population dynamics in interaction with environmental conditions and predation.
. Determine how winter tick load affects moose movement patterns.
. Assess activity budget and habitat selection of moose based on winter tick load.
Axis 2: Biology and epidemiology of the winter tick
. Determine the influence of climatic conditions on winter tick populations.
. Assess habitat selection by winter tick.
. Identify the conditions favoring the co-occurrence of moose and winter tick.
. Predict the effects of anticipated climate change on winter tick epidemiology.
Axis 3: Management and participatory science
. Develop a collaborative science approach to assess trends in moose populations and infestations.
Among other things, our work will lead to:
· A better understanding of the role forest management can play in the distribution and abundance of parasites such as ticks, and the risk of infestation for moose.
· The development of tools for short-term forecasting of tick outbreaks and their consequences on moose populations.
· The development of an epidemiological model to predict the evolution of interactions between winter ticks and moose according to anticipated climate change conditions.
· Evaluation of hunting exploitation rates and their adjustment, if necessary, in light of our knowledge of the causes and mortality rates. This step is crucial to prevent over-exploitation of populations in a sustainable development perspective.
· Improving our ability to adapt to climate change.
· Finally, the hundreds of thousands of GPS locations of moose that will be collected as part of this research project will improve our general knowledge of moose ecology. These precise data will provide information on the habitats used each season, the amplitude of daily and seasonal movements, the dispersion of juveniles, the impact of human activities on behavior, and many other aspects.
References
[1] Parmesan, C., and G. Yohe. 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature 421:37–42.
[2] Kutz, S. J., E. P. Hoberg, J. Nagy, L. Polley, and B. Elkin. 2004. “Emerging” Parasitic Infections in Arctic Ungulates. Integrative and comparative biology 44:109–118.
[3] Tingley, M. W., W. B. Monahan, S. R. Beissinger, and C. Moritz. 2009. Birds track their Grinnellian niche through a century of climate change. Proceedings of the National Academy of Sciences 106:19637–19643.
[4] Lavoie, M., P. BLanchette, S. Larivière, and J.-P. Tremblay. 2017. Winter and summer weather modulate the demography of wild turkeys at the northern edge of the species distribution. Population Ecology 59:239–249.
[5] Samuel, W. M. 2007. Factors affecting epizootics of winter ticks and mortality of moose. Alces 43:39–48.
[6] Musante, A. R., P. J. Pekins, and D. L. Scarpitti. 2010. Characteristics and dynamics of a regional moose Alces alces population in the northeastern United States. Wildlife Biology 16:185–204.
[7] Jones, H. 2016. Assessment of health, mortality, and population dynamics of moose in northern New Hampshire during successive years of winter tick epizootics. Mémoire de maîtrise, University of New Hampshire, Durham.
[8] Jones, H., P. J. Pekins, L. Kantar, I. Sidor, D. Ellingwood, A. Lichtenwalner, and M. O'Neal. 2018. Mortality assessment of calf moose (Alces alces) during successive years of winter tick (Dermacentor albipictus) epizootics in New Hampshire and Maine. Canadian Journal of Zoology 97:22–30.
[9] Samuel, B. 2004. White as a Ghost: Winter Ticks & Moose. Federation of Alberta Naturalists, Edmonton, Canada.
[10] Drew, M. L., and W. M. Samuel. 1986. Reproduction of the winter tick, Dermacentor albipictus, under field conditions in Alberta. Canadian Journal of Zoology 64:714-721.
[11] Addison, E. M., R. F. McLaughlin, P. A. Addison, and J. D. Smith. 2016. Recruitment of winter ticks (Dermacentor albipictus) in contrasting forest habitats, Ontario, Canada. Alces 52:29–40.
[12] McPherson, M., A. W. Shostak, and W. M. Samuel. 2000. Climbing simulated vegetation to heights of ungulate hosts by larvae of Dermacentor albipictus (Acari: Ixodidae). Journal of Medical Entomology 37:114–120.
[13] Yoder, J. A., P. J. Pekins, H. F. Jones, B. W. Nelson, A. L. Lorenz, and A. J. Jajack. 2016. Water balance attributes for off-host survival in larvae of the winter tick (Dermacentor albipictus; Acari: Ixodidae) from wild moose. International Journal of Acarology 42:26–33.
[14] Holmes, C. J., C. J. Dobrotka, D. W. Farrow, A. J. Rosendale, J. B. Benoit, P. J. Pekins, and J. A. Yoder. 2018. Low and high thermal tolerance characteristics for unfed larvae of the winter tick Dermacentor albipictus (Acari: Ixodidae) with special reference to moose. Ticks and Tick-borne Diseases 9:25–30.
[15] Ball, K. 2017. Moose density, habitat, and wintertick epizootics in a changing climate. Mémoire de maîtrise, University of New Hampshire, Durham.
[16] Wilmers, C. C., E. Post, R. O. Peterson, and J. A. Vucetich. 2006. Predator disease out-break modulates top-down, bottom-up and climatic effects on herbivore population dynamics. Ecology Letters 9:383–389.
[17] Mooring, M. S., and B. L. Hart. 1995. Differential grooming rate and tick load of territorial male and female impala, Aepyceros melampus. Behavioral Ecology 6:94–101.
[18] Lankester, M. W., and W. M. Samuel. 1998. Ecology and Management of the North American Moose. Pages 479–517 in A. W. Franzmann and C. C. Schwartz, editors. Ecology and Management of the North American Moose. Smithsonian Institution Press, Washington, D.C., USA.
[19] De Vrient, L., S. Lavoie, M. Barrette, and J.-P. Tremblay. From delayed succession to alternative successional trajectory: how different moose browsing pressures contribute to forest dynamics. Journal of Vegetation Science, submitted.
[20] Gingras, J., S. Couturier, S. D. Côté, and J.-P. Tremblay. 2014. Opposite responses of body condition and fertility in adjacent moose populations. Journal of Wildlife Management 78:830–839.
[21] McLaughlin, R. F., and E. M. Addison. 1986. Tick (Dermacentor albipictus)-induced winter hair-loss in captive moose (Alces alces). Journal of Wildlife Diseases 22:502–510.
[22] Bergeron, D. H., and P. J. Pekins. 2014. Evaluating the usefulness of three indices for assessing winter tick abundance in northern New Hampshire. Alces 50:1–15.[23] Mysterud, A., E. J. Solberg, and N. G. Yoccoz. 2005. Ageing and reproductive effort in male moose under variable levels of intrasexual competition. Ecology 74:742–754.
[24] Garner, D. L., M. L. Wilton, F. New Hampshire, and D. Game. 1993. The potential role of winter tick (Dermacentor albipictus) in the dynamics of a south-central Ontario moose population. Alces 29:169–173.
[25] Musante, A. R., P. J. Pekins, and D. L. Scarpitti. 2007. Metabolic impacts of winter tick infestations on calf. Alces 43:101–110.
References for the figure "Impacts of winter tick on moose health" :
Campbell, G. D., E. M. Addison, I. K. Barker, and S. Rosendal. 1994. Erysipelothrix rhusiopathiae, serotype-17, septicemia in moose (Alces alces) from Algonquin Park, Ontario. Journal of Wildlife Diseases 30:436–438.
Glines, M. V., and W. M. Samuel. 1989. Effect of Dermacentor albipictus (Acari, Ixodidae) on blood composition, weight-gain and hair coat of moose, Alces alces. Experimental & Applied Acarology 6:197-213. 10.1007/bf01193980
Mooring, M. S., and W. M. Samuel. 1999. Premature loss of winter hair in free-ranging moose (Alces alces) infested with winter ticks (Dermacentor albipictus) is correlated with grooming rate. Canadian Journal of Zoology 77:148-156. 10.1139/cjz-77-1-148
Musante, A. R., P. J. Pekins, and D. L. Scarpitti. 2007. Metabolic impacts of winter tick infestations on calf. Alces 43:101–110.
Samuel, W. M. 1991. Grooming by moose (Alces alces) infested with the winter tick, Dermacentor albipictus (Acari) - a mechanism for premature loss of winter hair. Canadian Journal of Zoology 69:1255-1260. 10.1139/z91-176
Vaumourin, E., G. Vourc'h, P. Gasqui, and M. Vayssier-Taussat. 2015. The importance of multiparasitism: examining the consequences of co-infections for human and animal health. Parasites & Vectors 8:545-545.
Welch, D. A., W. M. Samuel, and R. J. Hudson. 1990. Bioenergetic consequences of alopecia induced by Dermacentor albipictus (Acari, Ixodidae) on moose. Journal of Medical Entomology 27:656-660.