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The Dietary Composition of Chrysemys picta picta (Eastern Painted Turtles) with Special Reference to the Seeds of Aquatic Macrophytes
Donald J. Padgett, Jeffrey J. Carboni, and Daniel J. Schepis

Northeastern Naturalist, Volume 17, Issue 2 (2010): 305–312

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2010 NORTHEASTERN NATURALIST 17(2):305–312 The Dietary Composition of Chrysemys picta picta (Eastern Painted Turtles) with Special Reference to the Seeds of Aquatic Macrophytes Donald J. Padgett1,*, Jeffrey J. Carboni1, and Daniel J. Schepis1 Abstract - Animals facilitate macrophyte seed dispersal in various ways despite specializations of macrophytes for water dispersal. Previous diet analyses of freshwater aquatic turtles revealed that several North American turtle species consume a variety and abundance of seeds among other plant material and animal prey. We quantified the dietary habits of Chrysemys picta picta (Eastern Painted Turtle) in a Massachusetts lake to examine if these animals included hydrophyte seeds in their diet and evaluate their capacity as passive seed-dispersal agents. Fifty-four turtles were trapped and housed to collect feces. Examination of feces revealed a diverse diet with comparatively high frequencies of animal, plant, and algal matter. Eight hundred fifty-seven seeds of at least nine plant species were egested (among 87% of turtles), with all but five (99%) seeds visibly intact. Seeds of Nuphar (473) and Decodon (305) were most abundant in the feces. Life-history characteristics of both C. p. picta and Nuphar suggest an effective endozoochorous seed dispersal association. Introduction Animal-facilitated seed transport (zoochory) is a key mechanism in plant population establishment, regeneration, and gene flow. Dispersal in aquatic vascular plants is common, but aquatic plant seed dispersal by animals is not fully understood (Cook 1987, Sculthorpe 1967). Many aquatic macrophytes are known to be specialized for water dispersal, and studies have shown that a variety of seed-ingesting animals, including waterfowl (Clausen et al. 2002, Figuerola et al. 2005, Santamaria et al. 2002) and fishes (Agami and Waisel 1988, Pollux et al. 2006), not only facilitate the dispersal of seeds within and between water bodies, but can enhance seed germination capability. Waterbirds and fishes have long been considered likely candidates to play a role in zoochory in aquatic plants (Charalambidou and Santamaria 2002, Cook 1987, Holt Mueller and van der Valk 2002, Schenck 1886). However, freshwater turtles could be an underappreciated, yet effective, vector for freshwater hydrophytes in gut-mediated seed dispersal (endozoochory). Several North American turtle species consume seeds amid a multitude of other plant and animal prey. For example, large quantities of intact Nymphaea odorata Aiton (American Waterlily) seeds have been found in Chelydra serpentina (L.) (Common Snapping Turtle), Chrysemys picta (Schneider) (Painted Turtle), and Trachemys scripta (Schoepff) (Yellow-bellied Slider) (Lagler 1943, Parmenter 1980). The diet of Sternotherus odoratus (Latreille in Sonnini and Latreille) (Musk Turtle) exhibits a moderate frequency and 1Department of Biological Sciences, Bridgewater State College, Bridgewater, MA 02325. *Corresponding author - dpadgett@bridgew.edu. 306 Northeastern Naturalist Vol. 17, No. 2 abundance of aquatic plant seeds, including seeds of American Waterlily, Nuphar advena (Aiton) Aiton f. (Yellow Pond-lily), Ludwigia (primrosewillow), Bidens (beggarticks), and others (Ford and Moll 2004, Lagler 1943). Acorns of a wetland Quercus (oak) species were the most abundant food by weight and volume of Macroclemys temmincki (Troost in Harlan) (Alligator Snapping Turtles) (Sloan et al. 1996). Despite seeds of various hydrophytes being listed as food items of turtles, the focus of these dietary studies centered on life-history aspects of the animal as opposed to the potential dispersal implications for plants. Painted Turtles (Family Emydidae) are common aquatic turtles, inhabiting slow-moving shallow waters of freshwater lakes, ponds, creeks, rivers, and wetlands over most of North America (Ernst et al. 1994). They are opportunistic omnivores that eat a wide variety of animals and plants as they forage among vegetation. Dietary studies of Painted Turtles indicate substantial geographic variation in degree of carnivory or herbivory, which may be related, at least in part, to certain life-history traits (e.g., growth rates, body size, and fecundity), seasonal food availability, and/or habitat type (Cooley et al. 2003, Knight and Gibbons 1968, Lindeman 1996, MacCulloch and Secoy 1983, Raney and Lachner 1942, Rowe and Bowen 2005, Rowe and Parsons 2000). Our objective was to examine the dietary composition of a population of adult Chrysemys picta picta (Schneider) (Eastern Painted Turtles), a common and ordinarily abundant turtle of the northeastern United States. Our principle focus was to determine the extent to which Painted Turtles include aquatic plant seeds as dietary items and evaluate their capacity as passive seed dispersal agents. The findings would represent the easternmost diet report for the species and provide baseline data for this eastern subspecies. Methods Our study site was Carver Pond in Bridgewater, Plymouth County, MA. This 14-ha (35-acre) lake has an extensive floating-leaf community dominated by American Waterlily and Nuphar variegata Durand (Bull-head Pond-lily). A diverse submersed community included various Potamogeton spp. (pondweeds), Utricularia spp. (bladderworts), and Ceratophyllum demersum L. (Hornwort). The shallow lake edge is dominated by a dense zone of Decodon verticillatus (L.) Elliott (Water-willow), and includes Cephalanthus occidentalis L. (Common Buttonbush) and Clethra alnifolia L. (Sweet Pepperbush). We collected Painted Turtles between 25 June and 10 July 2008. We captured 28 male and 24 female adults (i.e., straight-line carapace length >110 mm) using hoop nets or occasionally hand nets. No individuals were recaptured. Turtles were transported in buckets to the laboratory and housed individually in 10-gal. aquaria for a 5-day period. Fecal samples were collected daily and pooled by individual. Feces were preserved in 70% ethanol and later examined under a dissecting microscope for animal, plant, and algal remains. Prey items were identified to lowest possible taxon and grouped by 2010 D.J. Padgett, J.J. Carboni, and D.J. Schepis 307 animal, plant (seed), plant (non-seed), and alga categories. Mean numbers of prey items within animal and plant (seed) categories were compared among prey taxon and between sexes of turtles by two-factor ANOVA, followed by Tukey’s HSD post-hoc test. The effects of sex within diet categories were determined, as diet variations have been reported to vary by gender in aquatic turtles (e.g., Ford and Moll 2004). Analyses were run separately for animal prey and plant (seed) prey. Food item abundance comparisons between prey categories and within algal and plant (non-seed) categories were not tested due to the inability to effectively resolve single individuals in these groups. Results All but one turtle (98%) had identifiable animal remains in their feces, with a variety of animal matter overall (Table 1). The most frequent animal Table 1. Dietary composition of Chrysemys picta picta (Eastern Painted Turtles; n = 52) in Carver Pond, Bridgewater, MA based on fecal samples. See Table 2 for seed composition. A two-factor ANOVA (followed by Tukey’s HSD post-hoc test) of animal items revealed insects to be most abundant and indicated a sex-by-animal item effect with female feces exhibiting more insects than that of males. SD = standard deviation. Category/taxon Frequency (%) Mean (± SD) Animal material 98.0 41.3 (39.7) Insecta 92.3 16.7 (17.7) Diptera 82.7 9.6 (12.8) Odonata 59.6 1.5 (2.8) Hemiptera 53.8 2.6 (8.5) Trichoptera 50.0 2.0 (3.1) Coleoptera 42.3 0.6 (0.8) Ephemeroptera 17.3 0.2 (0.4) Hymenoptera 5.8 0.1 (0.3) Homoptera 3.8 0.1 (0.3) Megaloptera 1.9 0.0 (0.1) Plecoptera 1.9 0.0 (0.1) Crustacea 30.8 0.3 (0.5) Decopoda 25.0 0.3 (0.4) Isopoda 3.8 0.0 (0.2) Conchostraca 1.9 0.0 (0.1) Cladocera 1.9 0.0 (0.1) Mollusca 48.1 2.1 (3.7) Gastropoda 46.2 2.1 (3.5) Pelecypoda 7.7 0.1 (0.3) Arachnida 50.0 1.5 (2.0) Cnidaria 1.9 0.0 (0.1) Platyhelminthes 1.9 0.0 (0.1) Nematoda 40.4 1.5 (3.8) Anura 3.8 0.0 (0.2) Plant material (non-seed) 100.0 - Wolffia (water-meal) 100.0 - Lemna (duckweed) 100.0 - Ceratophyllum demersum (Hornwort) 96.2 - Unidentified 21.2 - Algae (filamentous) 100.0 - 308 Northeastern Naturalist Vol. 17, No. 2 prey were dipteran larvae (mostly Ceratopogonid midges) and odonate larvae (mostly Libellulid dragonflies), egested by 83% and 60% of the turtles, respectively. Other animal prey included adult water bugs (Hemiptera), caddisfly larvae (Trichoptera), and snails (mostly Planobidae). Among animal prey, insects (mean = 16.7, st. dev. = 17.7, per turtle) were statistically more abundant than all other animal items and did show a sex-by-animal item effect (F = 3.83, df = 7, P < 0.001), with female feces exhibiting more insects than that of males. Filamentous algae (unidentified) and vegetative plant material were found in all turtles (Table 1). Non-food items evident in the feces included pebbles, styrofoam, fishing line, and glass. Seeds of nine aquatic plant taxa were identified in feces, with an overall seed egestion frequency of over 86% (Table 2). The most frequently egested seeds were those of Water-willow (75%) followed by Yellow Pond-lily (29%). The abundance of both Yellow Pond-lily seeds (mean = 9.1 per turtle) and Water-willow seeds (mean = 5.6 per turtle) was statistically higher (P < 0.05) than other seed items. There was no significant sex-by-seed item interaction (F = 0.8, df = 8, P = 0.6), indicating neither the abundance of any particular seed nor the total number of seeds egested is dependent on the sex of the turtle. Yellow Pond-lily represented the highest quantity of seeds from a single turtle, with 156 in a female, followed by Water-willow with 48 seeds in a female. Seeds were passed intact and only few (2 of Yellow Pond-lily, 3 of Water-willow) of the 857 seeds appeared damaged. Discussion Our findings on Eastern Painted Turtles corroborate the assertion that this species is omnivorous (Ernst et al. 1994). In Eastern Painted Turtles, both animal and plant material are ingested at similarly high frequencies, with a variety in either prey group. The dietary composition of the eastern subspecies differs from the animal matter bias in other Painted Turtle subspecies Table 2. Seeds recovered from feces of Chrysemys picta picta (Eastern Painted Turtles; n = 52) from Carver Pond, Bridgewater, MA, their frequency of occurrence, and abundance per turtle. Means were compared among seed species and between turtle sex by two-factor ANOVA followed by Tukey’s HSD post-hoc test (* signifies a significant difference at P < 0.05). SD = standard deviation. No effect of sex was determined. Plant taxon Number Freq. (%) Mean (±SD) Nuphar variegata Durand (Yellow Pond-lily) 473 28.8 9.1 (25.8)* Decodon verticillatus (L.) Elliott (Water-willow) 305 75.0 5.9 (8.6)* Bidens (beggartick) 19 26.9 0.4 (0.7) Potamogeton (pondweed) 16 11.5 0.3 (1.1) Grass (Poaceae) 12 17.3 0.2 (0.6) Najas flexilis (Willd.) Rostk. & Schmidt (Common Naiad) 10 9.6 0.2 (0.6) Nymphaea odorata Aiton (American Waterlily) 4 5.8 0.1 (0.3) Carex (Sedge) 5 5.8 0.1 (0.4) Other 13 19.2 0.3 (0.6) Total 857 85.2 16.5 (27.8) 2010 D.J. Padgett, J.J. Carboni, and D.J. Schepis 309 (Knight and Gibbons 1968, Lindeman 1996, MacCulloch and Secoy 1983, Rowe and Bowen 2005). However, it should be noted that these investigations relied on stomach contents and not feces. Most remarkable was the large number, and high frequency of occurrence, of intact hydrophyte seeds found in this study. Studies have demonstrated that terrestrial and aquatic turtle species can be effective agents of seed dispersal (Braun and Brooks 1987, Calvino- Cancela et al. 2007, Liu et al. 2004, Moll and Jansen 1995, Varela and Bucher 2002, Woodbury and Hardy 1948). Aquatic turtles that have largely indiscriminate diets and inadvertently ingest seeds could be probable seed dispersal agents. In consideration of our seed egestion data (Table 2), several life-history traits of Painted Turtles indicate an effective endozoochorous involvement with hydrophytes. For example, Painted Turtles are usually locally abundant (e.g., up to 941 individuals per hectare; MacCulloch and Secoy 1983), and are often the most abundant turtle in a suitable water body (Ernst et al.1994). Their feeding activities, which involve gulping small prey, are confined to the aquatic environment. They have home ranges of up to 2.7 ha within which they forage, and aquatic travel distances can average 68 m per day. Notably, these turtles do make overland movements to establish nearby aquatic activity centers (Rowe 2003), and some populations have exhibited interpond movement distances of up to 3.3 km (Bowne 2008, Bowne and White 2004). While there are no seed retention data published for Painted Turtles, experimental gut transit times for 2- x 2-mm particulate markers averaged >2 days in this species (Guard 1980). The natural history of the Painted Turtle seems to complement the pondlily seeds in their diet. The abundance of Yellow Pond-lily seeds (55% of all seeds expelled) in Painted Turtle feces indicates that pond-lilies, in general, may be well suited for turtle-mediated dispersal. Seeds of this genus have been mentioned in other dietary studies of North American aquatic turtles. For example, Actinemys marmorata (Baird and Girard) (Western Pond Turtles) were observed to feed “extensively” on fruits of Nuphar polysepala Engelmann (Western Pond-lily; Evenden 1948), Musk turtles had Common Pond-lily seeds as a major component of their gut contents (Lagler 1943), and pond-lily seeds were found at moderate frequencies within Chrysemys picta marginata Agassiz (Midland Painted Turtles; Raney and Lachner 1942, Rowe and Parsons 2000). Pond-lily species are floating-leaved, highly clonal hydrophytes thought to be dispersed primarily by water (Padgett 2007). Their abundant, leathery, berry-like fruits (0.5–5 cm in diameter) ripen at the water surface and dehisce irregularly to release numerous, floating, mucilaginous, seed-bearing units known to travel on the water surface for days before the seeds sink (Hart and Cox 1995, Smits et al. 1989). Numerous floating seed masses could be enticing to foraging Painted Turtles (an animal that often cooccurs with pond-lily, evidently does not discriminate seed prey by gender, and colonizes areas of dense, floating-leaved vegetation), and pond-lily’s hard seeds are more likely to pass through an animal intact (Pollux et al. 2006, 310 Northeastern Naturalist Vol. 17, No. 2 Santamaria et al. 2002). Moreover, as a truly aquatic species, seeds of Yellow Pond-lily (which must remain wet to retain viability; Padgett 2007) are likely to be deposited into a suitable environment by aquatic turtles. In our study, 99% of Yellow Pond-lily seeds egested by Eastern Painted Turtles were visibly unharmed, an observation consistent with that of other researchers (e.g., Raney and Lachner 1942). In two other emydid turtles, the effects of digestion on the capacity of seeds to germinate—paramount to seed dispersal success— have been shown not to influence (Moll and Jansen 1995) or only marginally influence (by 9% on average; Calvino-Cancela et al. 2007) germination levels. Any germination effect of Painted Turtle digestion on pond-lily seeds has yet to be ascertained. Germination analyses of seeds were not possible in our study due to the alcohol preservation of feces prior to seed detection. Little is known about seed dispersal in Water-willow. Like pond-lily species, Water-willow is a highly clonal plant and primarily specialized for water dispersal (Graham 2007). Its small (0.6 cm in diameter) fruits are dry and held above the water surface. When the capsules dehisce, the small (ca. 1 mm) seeds drop onto the water surface where they float (Graham 2007). The seeds are known to be eaten by waterfowl (Tiffney 1981). In a review of seed dispersal by animals, Schupp (1993) concluded that there are both quantity and quality components to consider when evaluating disperser effectiveness. As defined by Schupp (1993), Eastern Painted Turtles would have high potential to be “effective” dispersers for hydrophytes like pond-lilies. In terms of the quantity of dispersal, Painted Turtles are usually abundant, capable of handling a high number of seeds, and have a high probability of dispersing a handled seed. In regard to quality of seed dispersal, these turtles provide a high quality of treatment, as seeds are egested intact (with the assumption that such seeds are viable), and a high quality of deposition, as seeds are likely deposited in water. Acknowledgments We are grateful to the Office of Undergraduate Research at Bridgewater State College (BSC); K. Curry for technical support; C. Bloch for statistical analyses; H. Moore, C. Edge, and two anonymous reviewers for critical review of the manuscript; and the Massachusetts Division of Fisheries and Wildlife for a scientific collection permit. This research was funded largely by The Adrian Tinsley Program at BSC. Literature Cited Agami, M., and Y. Waisel. 1988. The role of fish in distribution and germination of seeds of the submerged macrophytes Najas marina L. and Ruppia maritima L. Oecologia 76:83–88. Bowne, D.R. 2008. Terrestrial activity of Chrysemys picta in Northern Virginia. Copeia 2008:306–310. Bowne, D.R., and H.R. White. 2004. Searching strategy of the Painted Turtle Chrysemys picta across spatial scales. Animal Behaviour 68:1401–1409. Braun, J., and G.R. Brooks. 1987. Box Turtles (Terrapene carolina) as potential agents for seed dispersal. 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