2010 NORTHEASTERN NATURALIST 17(2):223–228 Effect of Bot Fly Parasitism on Vertical Habitat Use by Peromyscus leucopus Gregory P. Klein1, Cory C. Christopher1,3, Guy N. Cameron1,*, and Gary W. Barrett2 Abstract - Peromyscus leucopus (White-footed Mouse) use the 3-dimensional space of their habitat. We studied whether Cuterebra fontinella (Bot Fly) larvae affected rate of capture in traps set above ground compared to traps set on the ground in deciduous forests in Ohio and Georgia. Rates of infestation were nearly three-fold greater in Ohio than in Georgia. Infested animals were captured equally in traps on the ground and in traps 1.5 m above ground in Ohio, but were captured less frequently in traps on the ground than in traps 1.5 m above ground in Georgia. Sex of animals did not affect these results. Infested animals were not captured in traps 4.5 m above the ground in Georgia, suggesting a possible limit to use of vertical habitat space by infested mice. Introduction Peromyscus leucopus Rafinesque (White-footed Mouse) is a common inhabitant of eastern deciduous forest (Lackey et al. 1985). Cuterebra fontinella Clark (Bot Fly) is an obligate parasite that uses White-footed Mice as hosts to complete its life cycle (Catts 1982, Slansky 2007). Since mass of Bot Fly larvae can represent up to 5% of host body mass (Munger and Karasov 1994, Slansky 2007), investigators have asked how infestations of Bot Fly larvae affect White-footed Mice. Infestations do not affect reproduction (Smith 1977), metabolism (Hunter and Webster 1974, Munger and Karasov 1994), survival (Munger and Karasov 1991), body condition or population demography (Cramer and Cameron 2006), movement distance (Cramer and Cameron 2010), or social behavior (Cramer and Cameron 2007). In fact, contrary to expectations that animals suffer an energetic cost of infestation, infested animals survived longer than uninfested animals (Clark and Kaufman 1990, Cramer and Cameron 2006, Jaffe et al. 2005), and animals with multiple Bot Fly larvae survived longer than animals with a single Bot Fly larva (Cramer and Cameron 2006). Longevity, however, may be at the expense of decreased reproductive output by females (Burns et al. 2005). Bot fly larvae often are located in inguinal regions of mice and may impact movement, activity, or avoidance of predators (Dalmat 1943, Scott and Snead 1942, Smith 1978, Wecker 1962). Some laboratory studies reported awkward movement by infested rodents (Dunaway et al. 1967, Scott and 1Department of Biological Sciences, University of Cincinnati, Cincinnati, OH 45221. 2Eugene P. Odum School of Ecology, University of Georgia, GA 30602. 3Current address - Department of Biology, Washington University, St. Louis, MO 63130. *Corresponding author - g.cameron@uc.edu. 224 Northeastern Naturalist Vol. 17, No. 2 Snead 1942, Smith 1978), but others found no discernable effect of infestation on mobility (Hunter et al. 1972, Smith 1978). In addition, movement distances or home ranges were not affected by infestations of Bot Fly larvae (Burns et al. 2005, Cramer and Cameron 2010, Hunter et al. 1972). Additionally, Cramer and Cameron (2010) found no difference in movement between animals with single or multiple infestations, and females moved more than males when infested. An experimental study by Steen et al. (2002) showed that probability of predation was similar between infested and uninfested Microtus townsendii Bachman (Townsend’s Vole). The White-footed Mouse is semi-arboreal (Fitzgerald and Wolff 1988), preferring trees for travel routes, nest sites, and day refuges (Barry et al. 1984). G.P. Klein and G.N. Cameron (unpubl. data) found that 66% of captures of White-footed Mice were in elevated traps in eastern deciduous forests in Ohio. In deciduous forests in the Piedmont Region of Georgia, Jennison et al. (2006) surmised that higher infestations by Bot Fly larvae in White-footed Mice (41.7%) than in Ochrotomys nuttalli Harlan (Golden Mouse; 6.3–12.5%) were related to greater activity and use of the 3-dimensional habitat by White-footed Mice, possibly resulting in higher exposure to Bot Fly eggs. However, only general locations of oviposition sites by female Cuterebra are known (e.g., foliage, twigs, exposed roots; Slansky 2007), so it is unclear how infestations are manifest. No study has specifically examined whether infestation by Bot Fly larvae hinders use of shrubs or trees by White-footed Mice, and thus, narrows their use of the 3-dimensional habitat. We predicted that if movement by infested mice is hampered by presence of Bot Fly larvae, infested mice should be less likely to be caught in elevated traps than uninfested mice. Methods Study sites Study sites were located in Ohio and Georgia. Study sites in Ohio were in East Fork Wildlife Area, approximately 39 km SE of Cincinnati (39°1'N, 84°4'W) and consisted of 6–25-ha forest fragments bordered by Glycine max (L.) Merr. (Soybean) crops. Ohio sites contained second-growth forest dominated by Fagus grandifolia Ehrh. (American Beech), Acer saccharum Marsh. (Sugar Maple), Quercus rubra L. (Red Oak), Q. alba L. (White Oak), and Carya ovata (Mill.) K. Koch (Shagbark Hickory). Undergrowth was dominated by Toxicodendron radicans (L.) Kuntze (Poison Ivy), Parthenocissus quinquefoila (L.) Planch (Virginia Creeper), Alliaria petiolata [Biebe] Cavara & Grande (Garlic Mustard), Rosa multiflora Thunb. (Multiflora Rose), and Lonicera maackii (Rupr.) Herder (Amur Honeysuckle). Study sites in Georgia were at the HorseShoe Bend Experimental Research Site located in Clarke County, near Athens, GA (33°57'N, 83°23'W). Habitat in the Georgia sites was upland forest dominated by White Oak and American Beech, and bottomland deciduous forest dominated by Betula nigra L. (River Birch). Quercus nigra L. (Water Oak), Ligustrum sinense Lour. (Chinese Privet), 2010 G.P. Klein, C.C. Christopher, G.N. Cameron, and G.W. Barrett 225 Smilax L. (Greenbrier), Amur Honeysuckle, and L. japonica Thunb. (Japanese Honeysuckle) were abundant in both habitats. Trapping In Ohio, animals were trapped on three 0.54-ha grids, with 140 traps/ grid. In Georgia, animals were trapped in 4 (in 2000) and 8 (in 2001) 0.21-ha grids, with 12 traps/grid. In all grids, two Sherman live traps were placed at 10-m intervals—one on the ground, and another on a platform 1.5 m off the ground, affixed to the trunk of a nearby tree. At the Georgia site in 2001, on alternating weeks, 4 additional Sherman live traps were placed 4.5 m above the ground in each trapping grid, alternating with traps placed on the ground and at 1.5 m. In Ohio, trapping was conducted for 5 days each month from June through September 2004 (2800 trap nights/grid). In Georgia, trapping was conducted for 2 days each week from late March through early November 2000 and 2001. Trapping effort in Georgia was 1248 trap nights/plot using ground and 1.5-m traps in 2000, and 816 trap nights/plot using ground and 1.5-m traps and 136 trap nights/plot using 4.5-m traps in 2001. Bot Fly larvae were present in White-footed Mice from early July through early November in Ohio, with peaks in proportion of animals parasitized in mid-July and early October (Cramer and Cameron 2006). In Georgia, Bot Fly larvae were present from early June through mid-August, with a peak in mid-July 2001 (Jennison et al. 2006). Data collected for each captured animal included: location of capture (ground or elevated trap), body mass, sex, hind-foot length, reproductive condition (open or closed vaginal orifice, abdominal or scrotal testes, pregnant, or lactating), and number of Bot Fly larvae present. All animals were marked with metal ear tags and released at their site of capture. Trapping and handling of animals followed guidelines of the American Society of Mammalogists (Gannon et al. 2007). Statistical methods We compared total number of captures in ground and elevated traps with a 2 x 2 Chi–square contingency table (infestation status, trap location) separately for Ohio and Georgia to determine whether the proportion of infested animals captured in elevated traps differed from the proportion of infested animals captured in ground traps; captures from 4.5-m elevated traps were excluded from this analysis because none of the animals captured in 4.5-m high traps were infested, creating a cell with a zero as data. We also analyzed males and females in separate contingency tables for Ohio and Georgia to determine if there was a sex effect. Finally, we analyzed data from Georgia in 2000 and 2001 in separate contingency tables to determine if there was a year effect at that location. Results Abundance of White-footed Mice varied seasonally from 2–25/ha in Georgia and from 5–47/ha in Ohio (Christopher and Barrett 2006, Cramer and Cameron 2006). Overall rates of infestation were 2–3 times higher in 226 Northeastern Naturalist Vol. 17, No. 2 Ohio than Georgia (Table 1). Capture ratios of infested males and females did not differ between elevated (1.5-m high) versus ground traps in Ohio (males: χ2 = 0.06, df = 1, P > 0.05; females: χ2 = 0.16, df = 1, P > 0.05) or Georgia (males: χ2 = 0.07, df = 1, P > 0.05; females: χ2 = 1.66, df = 1, P > 0.05); therefore, sexes were pooled for subsequent analyses. Significantly more infested animals were captured in elevated traps (1.5 m) compared to ground traps in Georgia when data were pooled for 2000 and 2001 (χ2 = 4.97, df = 1, P < 0.05; Table 1). However, when years were analyzed separately, captures of infested animals were significantly higher in elevated traps only during 2000 (χ2 = 4.06, df = 1, P < 0.05). In Ohio, there was no difference in rates of capture of infested or uninfested animals between elevated (1.5-m high) versus ground-level traps (χ2 = 0.13, df = 1, P > 0.05; Table 1). Discussion Contrary to our prediction, climbing movement was not hampered by presence of Bot Fly larvae in White-footed Mice, and infested mice were not less likely to be captured in elevated traps. Infestation by Bot Fly larvae did not affect the ability of White-footed Mice to climb in Ohio, since there was no difference in number of infested animals captured in ground traps versus 1.5-m elevated traps. In Georgia, animals infested with Bot Fly larvae occurred more often in elevated traps (1.5-m high) versus ground traps, although this result only held for 2000. This between-year difference in Georgia may have resulted because fewer acorns were available on the ground during the non-mast year of 2000 compared to the mast year of 2001, and animals may have been forced to forage more extensively in elevated sites in 2000 (Christopher and Barrett 2006). Mast years were not a variable in the Ohio study site because oaks were a minor part of the flora. The finding that infestations by Bot Fly larvae did not hamper Whitefooted Mice from climbing into above-ground vegetation contradicted our hypothesis that mass added by Bot Fly larvae would have negative effects upon climbing by White-footed Mice. On the other hand, none of the animals captured in 4.5-m elevated traps in Georgia in 2000 were infested with Bot Fly larvae, which suggests that presence of Bot Fly larvae hindered their use of habitat beginning somewhere between 1.5 and 4.5 m off the ground. This Table 1. The number of Peromyscus leucopus (White-footed Mice) infested with Cuterebra fontinella (Bot Fly) larvae was significantly higher in traps elevated 1.5-m above ground than in traps on the ground in Georgia (χ2 = 4.97, P < 0.05), but not in Ohio (χ2 = 0.13, P > 0.05). No infested individuals were captured in elevated traps at 4.5 m in Georgia. Georgia Ohio Traps elevated at Ground Traps elevated Ground 1.5 m 4.5 m traps at 1.5 m traps Infested 39 0 27 75 43 Uninfested 665 36 809 443 236 Percent infested 5.54 0 3.22 14.48 15.41 2010 G.P. Klein, C.C. Christopher, G.N. Cameron, and G.W. Barrett 227 conclusion is reinforced by the finding that animals captured in 4.5-m elevated traps in Georgia were also captured in ground and 1.5-m elevated traps. This finding ruled out the possibility that animals captured in 4.5-m elevated traps were uninfested with Bot Fly larvae because they were exposed to a different subset of the habitat as animals trapped in ground or 1.5-m elevated traps. Our results do not address whether agility was hampered in infested animals while they negotiated above-ground vegetation. Nevertheless, our findings substantiate the growing body of literature that shows a surprising lack of significant effects of infestation by Bot Fly larvae on the biology of White-footed Mice. Acknowledgments We thank the staff at HorseShoe Bend Experimental Site in Georgia for field assistance and the staff at East Fork Wildlife Area in Ohio for allowing us to conduct studies on their property and for field assistance. Financial support for field work and analyses was received from the Department of Biological Sciences, University of Cincinnati, and the Odum School of Ecology, University of Georgia. Literature Cited Barry, R.E., Jr., M.A. Botje, and L.B. Grantham. 1984. Vertical stratification of Peromyscus leucopus and P. maniculatus in southwestern Virginia. Journal of Mammalogy 65:145–148. Burns, C.E., B.J. Goodwin, and R.S. Ostfeld. 2005. A prescription for longer life? Bot Fly parasitism of the White-footed Mouse. Ecology 86:753–761. Catts, E.P. 1982. Biology of New World botflies: Cuterebridae. Annual Review of Entomology 27:313–338. Christopher, C.C., and G.W. Barrett. 2006. Coexistence of White-footed Mice (Peromyscus leucopus) and Golden Mice (Ochrotomys nuttalli) in a southestern forest. Journal of Mammalogy 87:102–107. Clark, B.K., and D.W. Kaufman. 1990. Prevalence of botfly (Cuterebra sp.) parasitism in populations of small mammals in eastern Kansas. American Midland Naturalist 124:22-30. Cramer, M.J., and G.N. Cameron. 2006. Effects of Bot Fly (Cuterebra fontinella) parasitism on a population of White-footed Mice (Peromyscus leucopus). Journal of Mammalogy 87:1103–1111. Cramer, M.J., and G.N. Cameron. 2007. Effects of Bot Fly, Cuterebra fontinella, parasitism on male aggression and female choice in Peromyscus leucopus. Animal Behaviour 71:1419–1427. Cramer, M.J., and G.N. Cameron. 2010. Effects of Bot Fly parasitism on movements of Peromyscus leucopus. American Midland Naturalist 163:455–462. Dalmat, H.T. 1943. A contribution to the knowledge of the rodent warble flies (Cuterebridae). Journal of Parasitology 29:311–318. Dunaway, P.B., J.A. Payne, L.L. Lewis, and J.D. Story. 1967. Incidence and effects of Cuterebra in Peromyscus. Journal of Mammalogy 48:38–51. Fitzgerald, V.J., and J.O. Wolff. 1988. Behavioral responses of escaping Peromyscus leucopus to wet and dry substrata. Journal of Mammalogy 69:825–828. 228 Northeastern Naturalist Vol. 17, No. 2 Gannon W.L., R.S. Sikes, and the Animal Care and Use Committee of the American Society of Mammalogists. 2007. Guidelines of the American Society of Mammalogists for the use of wild mammals in research. Journal of Mammalogy 88:809–823. Hunter, D.M., and J.M. Webster. 1974. Effects of cuterebrid larval parasitism on Deer-mouse metabolism. Canadian Journal of Zoology 52:209–217. Hunter, D.M., R.M.F.S. Sadleir, and J.M. Webster. 1972. Studies on the ecology of cuterbrid parasitism in Deermice. Canadian Journal of Zoology 50:25–29. Jaffe, G., D.A. Zegers, M.A. Steele, and J.F. Merritt. 2005. Long-term patterns of Botfly parasitism in Peromyscus maniculatus, P. leucopus, and Tamias striatus. Journal of Mammalogy 86:39–45. Jennison, C.A., L.R. Rodas, and G.W. Barrett. 2006. Cuterebra fontinella parasitism on Peromyscus leucopus and Ochrotomys nuttalli. Southeastern Naturalist 5:157–164. Lackey, J.A., D.G. Huckaby, and B.G. Ormiston. 1985. Peromyscus leucopus. Mammalian Species 247:1–10. Munger, J.C., and W.H. Karasov. 1991. Sublethal parasites in White-footed Mice: Impact on survival and reproduction. Canadian Journal of Zoology 69:398–404. Munger, J.C., and W.H. Karasov. 1994. Costs of Bot Fly infection in White-footed Mice: Energy and mass flow. Canadian Journal of Zoology 72:166–173. Scott, T.G., and E. Snead. 1942. Warbles in Peromyscus leucopus noveboracensis. Journal of Mammalogy 23:94–95. Slansky, F. 2007. Insect/mammal associations: Effects of cuterebrid Bot Fly parasites on their hosts. Annual Review of Entomology 52:17–36. Smith, D.H. 1977. Effects of experimental Bot Fly parasitism on gonad weights of Peromyscus maniculatus. Journal of Mammalogy 58:679–681. Smith, D.H. 1978. Effect of Bot Fly (Cuterebra) parasitism on activity patterns of Peromyscus maniculatus in the laboratory. Journal of Wildlife Diseases 14:28–39. Steen, H., M. Taitt, and C.J. Krebs. 2002. Risk of parasite-induced predation: An experimental field study on Townsend's Voles (Microtus townsendii). Canadian Journal of Zoology 80:1286–1292. Wecker, S.C. 1962. The effects of Bot Fly parasitism on a local population of the White-footed Mouse. Ecology 43:561–565.