Pappas M.J.,Michaels Restaurant |
Congdon J.D.,Savannah River Ecology Laboratory |
Brecke B.J.,22675 Co. Boulevard 18 No. 58 A |
Freedberg S.,St. Olaf College
Herpetological Conservation and Biology | Year: 2013
Tilled crop fields and natural nesting areas of many freshwater turtles have common characteristics that attract nesting females, but as some crops mature, their canopies block access to natural environmental cues used by hatchlings during orientation and dispersal from nests. We examined orientation of 417 naïve and 232 experienced hatchling Blanding's turtles (Emydoidea blandingii) and snapping turtles (Chelydra serpentina) during dispersal from experimental nests in three 60-m square arenas located in soybean and corn fields or by tracking re-located experienced hatchlings in a corn field at weaver dunes, minnesota, USA. for both species, orientation patterns of naïve hatchlings in crop fields were primarily random (indicating no environmental cues were available) and secondarily bimodal in both directions of crop row alignment (a dispersal pattern consistent with following paths of least resistance). In contrast to naïve individuals, dispersal patterns of natural-experienced hatchling Blanding's turtles were non-random, not in the direction of crop row alignment, and in the directions they had been moving prior to being released in crop fields. Hatchling Blanding's and snapping turtles with 45-150 minutes dispersal experience at different times of day in a prairie arena were able to disperse directionally when re-released in a corn plot, a result that supports rapid development of a compass for maintaining headings when targets are not visible. Morning and afternoon-experienced hatchling Blanding's turtles dispersed in different directions in a corn plot and in a different direction or pattern (random versus directional) from their previous dispersal in the prairie arena. The results of our study indicate that mature crop canopies that block access to natural environmental cues used for dispersal from nests pose more substantial orientation problems for naïve hatchlings than for experienced hatchlings that are able to use a compass to maintain dispersal headings when environmental cues are not available. © 2013 Michael Pappas. All Rights Reserved.
Freedberg S.,St. Olaf College |
Lee C.,University of Michigan |
Pappas M.,Michaels Restaurant
Biological Conservation | Year: 2011
Anthropogenic changes to the environment have the opportunity to impact natural systems, particularly in organisms that exhibit phenotypic plasticity. Species with environmental sex determination (ESD) are uniquely susceptible to changes in the stimuli that affect sexual development, potentially leading to maladaptive sex ratios. We studied the factors affecting sex determination and sex ratios in the common snapping turtle, Chelydra serpentina, in an area heavily impacted by agricultural practices. We investigated the effects of soybean, corn, and sunflower planting on incubation temperatures, sex ratios, and depredation in naturally laid nests. We also identified and analyzed a novel mitochondrial microsatellite in order to examine the presence of natal homing and determine the likelihood that nest sites impacted by agricultural practices could be transmitted across generations. Females frequently chose to nest in agricultural fields over sand prairie sites, and offspring sex ratios and depredation rates were significantly influenced by crop planting. Despite detecting considerable genetic variation in our population, we found no relationship between relatedness and nesting location, suggesting that females are not transmitting nesting sites across generations. Our results suggest that agricultural practices can directly impact populations of animals with ESD, and will need to be considered in management decisions. © 2011.
Congdon J.D.,Savannah River Ecology Laboratory |
Pappas M.,Michaels Restaurant |
Brecke B.,22675 Co. Blvd. 18 |
Capps J.,Alterra Environmental Inc.
Chelonian Conservation and Biology | Year: 2011
We examined the orientation of 76 naïve painted turtles (Chrysemys picta belli) and 746 snapping turtles (Chelydra serpentina) during initial dispersal from experimental nests in the Weaver Dunes area of southeastern Minnesota. We conducted 15 releases into large circular arenas in 4 natural nesting areas and 2 atypical areas. Hatchling orientation and dispersal for both species were 1) all nonrandom, 2) appeared to be based on vision (i.e., nonpolarized light), and 3) toward nearby, open, and highly illuminated horizons, regardless of whether or not they were associated with the wetlands. A first-order estimate of hatchling snapping turtle perception distance was 55-90 m. We found no evidence that suggests that specular light from the wetlands, olfaction, or humidity gradients were important in orientation. At 2 of 3 locations, substantial changes in orientation direction occurred when hatchling snapping turtles were released in morning vs. late afternoon. Changes in dispersal directions in the morning and afternoon indicated that hatchlings were not orienting toward the sun per se but toward different highly illuminated nearby prairie areas. At one site, hatchling orientation in the afternoon (but not in the morning) was toward a nearby wetland and was consistent with either dispersal toward highly illuminated near horizon or with the perception and use of reflected polarized light from the wetland. Collectively, the results from our study also indicate that 1) hatchlings disperse toward open horizons rather than toward wetlands themselves (i.e., open areas that are not necessarily associated with wetlands), 2) dispersal direction is influenced by time of day, apparently because of changes in the degree of illumination of different horizons, and 3) far horizons apparently were not used because they were beyond the perception distance of hatchlings. The most parsimonious evolutionary explanation of solutions to orientation problems is that, for each species, both adults and hatchlings have similar perception distances and use the same sensory modes and types of environmental cues during terrestrial movements. Comprehensive conservation and management plans for aquatic turtles should include consideration of how habitat changes in nesting areas might alter the environmental cues that determine the initial orientation and successful dispersal of hatchlings. We compared the results from this study with the dispersal patterns of naïve hatchling Blanding's turtles (Emydoidea blandingii) that emerge from nests located much farther from wetlands. © 2011 Chelonian Research Foundation.