Parasite impacts on arthropod hosts may even increase in the future, because parasitoids are disproportionately benefitting from rapidly warming temperatures relative to other arthropod groups ( Koltz et al., 2018c). Host-parasite interactions may play a particularly important role in food web dynamics in the Arctic, where arthropod communities exhibit a high diversity of parasitoids relative to overall arthropod diversity ( Stahlhut et al., 2013). The surprising lack of parasitism in the north suggests that populations of this widespread spider species have different eco-evolutionary histories and may respond differentially to climate change. While up to 13% of egg sacs were parasitized annually in the low-arctic site, we found no evidence of it at the high-arctic site despite the presence of congeneric parasitoid species at both locations. We investigated potential changes in egg sac parasitism rates at two rapidly warming sites in Greenland: a high-arctic site (18 years of data, 1,088 egg sacs) and a low-arctic site (5 years of data, 538 egg sacs). Wolf spiders are dominant and ecologically important arctic predators that experience high rates of egg sac parasitism by wasps. In the Arctic, a high diversity of parasitoids relative to potential hosts suggests that parasitoids may exert strong selection pressure on arthropods, but the extent to which these interspecific linkages drive arthropod population dynamics remains unclear. Parasitoids can affect host population dynamics with community-level consequences. 7Department of Bioscience Kalø, Aarhus University, Aarhus, Denmark.6Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, Davis, CA, United States.5Arctic Research Centre, Aarhus University, Aarhus, Denmark.4Canadian Forest Service-Atlantic Forestry Centre, Corner Brook, NL, Canada.3Institute of Arctic Studies, Dartmouth College, Hanover, NH, United States.2Environmental Studies Program, Dartmouth College, Hanover, NH, United States.1Department of Biology, Washington University in St. Moreover, given that wolf spiders are a widely distributed, important tundra predator, we may expect to see population and food web consequences of their increased reproductive rates.Amanda M. This could be a common but overlooked phenomenon due to the challenges associated with long-term collection of life history data in the Arctic. Our results provide the first evidence for Arctic invertebrates producing additional clutches in response to warming. Clutch size for first clutches was correlated to female size, while this was not the case for second clutches. This is likely a result of female spiders producing their first clutches earlier in those years and allowing them time to produce another clutch. In years with earlier snowmelt, first clutches occurred earlier and the proportion of second clutches produced was larger. We found that assigned second clutches appeared significantly later in the season than first clutches. We tested whether the median capture date differed among first and second clutches, whether clutch size was correlated to female size, and whether the proportion of second clutches produced within a season was related to climate. Upon discovery of a bimodal frequency distribution of clutch sizes, as is typical for wolf spiders at lower latitudes producing a second clutch, we assigned egg sacs to being a first or second clutch depending on clutch size. We dissected individual egg sacs and counted the number of eggs and partially developed juveniles, and measured carapace width of the mothers. To determine if this is already happening, we used specimens of the wolf spider Pardosa glacialis caught by pitfall traps from the long-term (1996-2014) monitoring program at Zackenberg, Northeast Greenland. Yet the timing of snowmelt is advancing in the Arctic, which may allow some species to produce an additional clutch. Spiders at southern latitudes commonly produce multiple clutches, but this has not been observed at high latitudes where activity seasons are much shorter.
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