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Biogeographic and Conservation Significance of the Occurrence of the Canadian Endemic Sorex maritimensis (Maritime Shrew) in Northern New Brunswick
Donald F. McAlpine, Howard M. Huynh, and Karen J. Vanderwolf

Northeastern Naturalist, Volume 19, Issue 2 (2012): 253–358

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353 Biogeographic and Conservation Significance of the Occurrence of the Canadian Endemic Sorex maritimensis (Maritime Shrew) in Northern New Brunswick Donald F. McAlpine1,2, Howard M. Huynh1,3, and Karen J. Vanderwolf 1,2 Abstract - Sorex maritimensis (Maritime Shrew) is endemic to New Brunswick and Nova Scotia. We suggest that post-glacial dispersal northward by this species from a coastal plain refugium located in the mid-Atlantic, rather than dispersal from a refugium off Nova Scotia as previously proposed, is more parsimonious with current understanding of the glacial history of the region. A range extension into northeastern New Brunswick shows that the species is distributed north–south in New Brunswick and suggests that wetlands in heavily forested regions meet the ecological requirements of the Maritime Shrew. Such wetlands may provide avenues for dispersal and ensure connectivity among populations. Habitat descriptions for the Maritime Shrew indicate a wetland-associated species adaptable enough to utilize disturbance-dominated and anthropogenic wetlands. Further investigations of the biology of the Maritime Shrew are required to inform future habitat and wetland protection policies that should consider the requirements of this poorly known Canadian mammal. Smith (1939) was the first to recognize the unique nature of maritime populations of the shrew then known as Sorex arcticus Kerr (Arctic Shrew), ascribing the subspecific epithet maritimensis to populations from mainland Nova Scotia. On the basis of morphological and karyological evidence, van Zyll de Jong (1983) and Volobouev and van Zyll de Jong (1988) suggested maritimensis as an entity likely specific from S. arcticus. Stewart et al. (2002) used cytochrome-b genetic sequence data to demonstrate the specific status of S. maritimensis Smith (Maritime Shrew) and formally proposed that the species be recognized as distinct. At the time, the known range the Maritime Shrew was restricted to eastern mainland Nova Scotia and southern and eastern New Brunswick east of the Saint John River system. Perry et al. (2004) extended that range somewhat, suggesting that the species occupies the entirety of mainland Nova Scotia, and provided evidence of presence west of the Saint John River to near the Canada-United States border. Although Perry et al. (2004) state that suitable habitat for this species is present in Maine, the Maritime Shrew (Fig. 1) remains one of only four mammal species endemic to Canada and the only endemic Atlantic Canadian mammal (Forbes et al. 2010). Here we document a range extension of ≈140 km (≈80 km straight-line north) into northern New Brunswick for the Maritime Shrew and discuss the biogeographic and conservation significance of this report. On 11 August 2010, we captured a lactating female (placental scars = 5) Maritime Shrew at Doyles Meadow, Jacquet River Gorge Protected Natural Area (JRG PNA; 47.81755°N, 066.00163°W). The site is ≈13 km inland from the coastal community of Jacquet River and ≈45 km south-southeast of Dalhousie, NB. The area is encompassed by the Northern Uplands Ecoregion and is characterized by heavily forested, hilly plateaus and deep river gorges dominated by Abies balsamea (L.) Mill. (Balsam Fir), mixed with Picea rubens Sarg. (Red Spruce), P. mariana (Mill.) (Black Spruce), Pinus strobus L. (White Pine), Acer saccharum Marshall (Sugar Maple), and Betula papyrifera Marsh. (White Birch). Elevations in the JRG PNA range from 40 m, where the Belledune River delimits the boundary of the PNA in the north, to 340 m in the southwest. Major streams 1New Brunswick Museum, 277 Douglas Avenue, Saint John, NB, Canada E2K 1E5.2Department of Biology, University of New Brunswick, Fredericton, NB, Canada E3B 6E1. 3Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131. *Corresponding author - donald.mcalpine@nbm-mnb.ca. Notes of the Northeastern Nat u ral ist, Issue 19/2, 2012 354 Northeastern Naturalist Vol. 19, No. 2 and tributaries of the PNA have in many areas cut deeply incised, v-shaped valleys 75–180 m below plateau surfaces. The Maritime Shrew specimen (deposited in the New Brunswick Museum mammal collection as NBM 11821), was taken in a Museum Special snap trap during 282 trap-nights conducted 10–13 August 2010 in a marsh-meadow complex that extends ≈6 km straight-line distance along Antinouri Lake Brook (Fig. 2). The adjacent area is heavily forested with mixed stands of shade-tolerant and -intolerant hardwoods, Thuja occidentalis L. (Eastern White Cedar), Balsam Fir and spruce species. Associated small-mammal species trapped in order of abundance included Peromyscus maniculatus (Wagner) (Deer Mouse; n = 9), Microtus pennsylvanicus (Ord) (Meadow Vole; n = 4), S. fumeus Miller (Smokey Shrew; n = 1), Figure 1. The Maritime Shrew, Sorex maritimensis, is one of only four mammal species endemic to Canada (NBM/D. McAlpine photo). Figure 2. Habitat for the Maritime Shrew at Doyles Meadow, Jacquet River Gorge Protected Natural Area (NBM/K. Vanderwolf photo). 2012 Northeastern Naturalist Notes 355 Blarina brevicauda (Say) (Short-tailed Shrew; n = 1), and Myodes gapperi (Vigors) (Redbacked Vole; n = 1). Measurements for the S. maritimensis specimen are as follows: total length = 115 mm, tail vertebrae = 38.8 mm, hind foot = 13.2 mm, and weight = 12.3 g. The geographic distribution of the Maritime Shrew is still poorly delimited, and its morphology closely resembles that of the Arctic Shrew (van Zyll de Jong 1983); for this reason, we confirmed our tentative species identification based on morphology via molecular genetic sequencing of the cytochrome-b gene. Muscle and organ tissues were extracted, preserved in 95% ethanol, and stored at -40 °C. DNA was isolated from extracted muscle tissues using a QIAGEN blood and tissue kit, and the entire cytochrome-b gene was PCR amplified using primers L14841 (Kocher et al. 1989) and H15915 (Irwin et al. 1991). PCR products were viewed on a 1% agarose gel, with target bands excised and purified with a QIAGEN Gel Extraction kit. Purified samples were sent to the McGill University and Génome Québec Innovation Centre where double-stranded sequencing was performed on an Applied Biosystem 3730xl DNA Analyzer. Molecular sequence data for this specimen was compared to sequences deposited in Genbank and confirm that the specimen is a Maritime Shrew. Biogeography. Stewart et al. (2002) suggest that a molecular clock places the time of divergence between the Maritime Shrew and the Arctic Shrew at >2 MYA; i.e. early in the Pleistocene, presumably during the Nebraskan glacial. Stewart et al. (2002) also propose that the Maritime Shrew survived the Wisconsinan continental glaciation off Nova Scotia, as part of a northern coastal plain refugial fauna. They believed that the then known distribution suggested that the species was still expanding its range into New Brunswick from this relict population. According to Shaw et al. (2002, 2006), there is conclusive evidence that late Wisconsinan glaciers reached maximum positions near the shelf edges in Atlantic Canada. This placement of the glacial maxima would seem to preclude the establishment of refugia immediately offshore of the Maritimes. Georges Bank and the southern and eastern margins of the Grand Banks remained ice-free (south and north of the Maritimes, respectively; Shaw et al 2006), and may have provided refugial opportunities from which volant or wind-borne taxa might have colonized the mainland of maritime Canada; however, Soricidae would not have been among them. As has now been demonstrated for several maritime wetland taxa (e,g., amphibians and reptiles; see McAlpine 2010), the Maritime Shrew likely survived the Wisconsinan in a continental coastal plain refugium south of the ice margin and then dispersed northward with the retreating ice. Were the species a relatively late arrival in the Maritimes (i.e., less than 6 ka), it would have encountered marine barriers to dispersal that appear to have prevented aquatic salamanders and some freshwater fishes from populating Prince Edward Island and Nova Scotia (Curry and Gautreau 2010, McAlpine 2010). However, based on Maritime Shrew habitat requirements (i.e., wetland habitats) there is no reason to believe northward dispersal was delayed. The apparent absence of the Maritime Shrew on Prince Edward and Cape Breton Islands may reflect insufficient collecting in appropriate habitat or lack of suitable habitat. The latter seems the least likely; in our own experience, the few recent small-mammal surveys in these regions have not focused on habitat suitable for the Maritime Shrew. Dawe et al. (2009) identified separate clades of Maritime Shrew in New Brunswick and Nova Scotia and proposed that these had come back into secondary contact following the Younger Dryas (i.e., <11.5 ka), during which time conditions inhospitable to gene flow across the Isthmus of Chignecto may have been present. While the record presented here cannot in itself refute the suggestion of Stewart et al. (2002) that the Maritime Shrew is still undergoing range expansion, it does show that the species is widely distributed north–south in New Brunswick (Fig. 3). Our belief is that the only recent range expansion this species has undergone is in the immediate area of the secondary contact zone in the Isthmus of Chignecto region, as 356 Northeastern Naturalist Vol. 19, No. 2 demonstrated by Dawe et al. (2009), and that Maritime Shrew post-glacial dispersal was northward from an Atlantic coastal plain refugium located in the mid-Atlantic. Conservation. As one of Canada’s very few endemic mammals, the conservation status of the Maritime Shrew should be of particular interest and concern. Upon recognizing the Maritime Shrew as distinct, Stewart et al. (2002) called for its conservation status to be assessed. Forbes et al. (2010) state that the Maritime Shrew should be a priority among Atlantic maritime mammals for research and monitoring. Dawe et al. (2009) conclude that the Maritime Shrew in New Brunswick and Nova Scotia should be considered a single evolutionarily significant unit, but that separate, semi-isolated management units on each side of the Isthmus of Chignecto should be recognized for conservation purposes. Herman and Scott (1992, 1994) assessed the relative vulnerability of various Nova Scotia vertebrates to climate warming and found the Maritime Shrew (as S. arcticus maritimensis) had the highest climatic sensitivity score and the greatest total general vulnerability score of any mammal in the province. A significant portion of their general vulnerability score for this species follows from a perceived sensitivity to winter/ spring flooding in the species’ “rare and fragmented habitat”. Other factors that contributed to the high score for this species were the lack of management activities directed at the Maritime Shrew, that its population trends were not monitored, and a belief that the species' range size in Nova Scotia was limited. Using their system, the assigned score would have been higher had the Maritime subspecies been then recognized as distinct from the Arctic Shrew. While a re-scoring of this species in light of new information on distribution (i.e., Perry et al. [2004] suggest the species occupies the entirety of Nova Scotia) and an apparently broader habitat tolerance might reduce its general vulnerability score, data on the biology of the species remains scant. Smith (1940) reported the most favored habitat for the Maritime Shrew as “the edges of freshwater swamps and marshes which had become overgrown with tangled grass and rushes”, but also collected the species “under brush piles in dry orchard land, in runways Figure 3. Distribution of Sorex maritimensis (solid circles) compiled from van Zyll de Jong (1983), Bowman (2000), Perry et al. (2004) and Dawe et al. (2009), with current range extension shown (solid triangle). Stars mark communities mentioned in the text. 2012 Northeastern Naturalist Notes 357 of Microtus”, and in “moss-grown swamps and damp ditch-rows in a hayfield”. Nordstom and Dilworth (1972) found this shrew in areas in Kouchibouguac National Park near marshes where “tangled shrubs, grasses, and ferns overlying a groundcover of sphagnum or decaying plant material” were predominant. Other previously reported habitat for this species has been characterized as “abandoned agricultural fields and meadow-marsh complexes” (Morton 1980), and a “re-vegetated abandoned Beaver dam” (Morton and Savoie 1984). Van Zyll de Jong (1983) included damp grassy banks of ditches, dikes, and railway embankments among the favored habitats for the species. Herman and Scott (1994) report that Maritime Shrew habitat consists mainly of “low-lying floodplain wet meadows and marsh margins”, and Scott and Hebda (2004) state the species uses “floodplain wet meadows and marsh margins, especially dyked coastal marshland”. Dawe (2005) found the grass Calamagrostis canadensis (Michx.) P. Beauv. (Blue-Node) was a positive predictor of Maritime Shrew presence, but states that the species “is associated with characteristics typical of marsh and wet meadow habitats” and that the species tends “toward less saturated microhabitats in wet habitat types”. Dawe (2005) also found the Maritime Shrew frequently associated with the ecotone along trails and paths. Both Herman and Scott (1994) and Dawe et al. (2009) characterize the Maritime Shrew as stenotopic (i.e., narrowly adapted to the environment) and with limited dispersal capabilities. Comparative studies have shown that stenotopic species have a far greater tendency to become extinct than those considered eurytopic (i.e., broadly adapted; Purvis et al. 2000). While the habitat descriptions for the Maritime Shrew indicate a wetland-associated species, they also suggest a species adaptable enough to utilize disturbance-dominated and anthropogenic wetlands, both coastally and inland in heavily forested regions. The record reported here suggests that wetlands in heavily forested habitat not only meet the ecological requirements of the Maritime Shrew, but may also provide avenues for dispersal and ensure connectivity among populations. Herman and Scott (1994) and Dawe et al. (2009) also stress that maintenance of contiguous wetland habitat is needed to ensure connectivity and gene flow among populations of the Maritime Shrew across its restricted range. As maritime Canada’s only endemic mammal and one of the very few mammals restricted to Canada, jurisdictions in Canada face the responsibility and unique challenges of ensuring the conservation of the Maritime Shrew. Further investigations of Maritime Shrew biology could help inform habitat and wetland protection policies that in future should consider the requirements of this poorly known and secretive small mammal. Acknowledgments. The specimens report here were collected during a small-mammal inventory conducted during the Jacquet River Gorge Protected Natural Area Bioblitz, organized 27 July–19 August 2010 by the New Brunswick Museum Centre for Biodiversity Research. For assistance with small-mammal trap lines, we thank Sarah Best, Michael Rybak, and Katelyn Vandenbroeck. Permits to undertake scientific collecting in the PNA were kindly provided by Maryse Bourgoise and Dr. Maureen Toner, New Brunswick Fish and Wildlife Branch. Principal funding for the program was supplied by the New Brunswick Environmental Trust Fund, Salamander Foundation, New Brunswick Department of Natural Resources, and the New Brunswick Wildlife Trust Fund. We are grateful to the Belledune Regional Environmental Association for its support during our time in the region, especially that provided by Andy Flanagan. We also thank Dr. Donald Stewart, Acadia University, for generously allowing our use of his laboratory for DNA extraction and PCR. Literature Cited Bowman, J. 2000. The spatial structure of small-mammal populations in a managed forest. Unpublished Ph.D. Thesis. University of New Brunswick, Fredericton, NB, Canada. Curry, R.A., and M.D. Gautreau. 2010. Fishes of the Atlantic Maritime Ecozone. Pp. 599–612, In D.F. McAlpine and I.M. Smith (Eds.). Assessment of Species Diversity in the Atlantic Maritime Ecozone. 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