The Western Pond Turtle: Natural and Evolutionary History

Transcription

1 The Western Pond Turtle: Natural and Evolutionary History Adam Talamantes February, 10, 2011 This paper reviews literature on the western pond turtle. This paper presents the natural and evolutionary history of Clemmys marmorata: description, taxonomy, evolution of subspecies, habitat, diet, predators, reasons for decline, and the current status of the western pond turtle. The information presented here is invaluable when considering the conservation, the endangered western pond turtle. Key Words: Western Pond Turtle, Clemmys marmorata, Testudines, Evolution, Natural History Introduction Turtles are old, like really old. The first known turtles of the order Testudines date back to the late Triassic period, about 215 million years ago. They have existed in the western United States from at least the late Pliocene (Ashton et al., 1997). Testudines is the order of reptiles that have boney of cartilaginous shells that develop from there ribs. The shell is a defining characteristic. It can be either hard or soft. It is used as a shield for protection. Turtles are more ancient than lizards, snakes and crocodiles. Currently many members of this order are highly endangered, such as the once common western pond turtle (Clemmys marmorata).

2 Description The western pond turtle is a native fresh water turtle to the North American West coast. They can reach a maximum length of 210mm and may exceed a weight of 1200g (Ashton et al., 1997; Hays, et al., 1999). Their color, marking, and size vary geographically, by age and sexually. Usually they are dark brown to olive dorsally and yellowish, occasionally with dark blotches ventrally (Ashton et al., 1997; Hays, et al., 1999). Hatchlings are 25-31mm and weigh 3 7 g (Ashton et al., 1997; Hays et al., 1999). When identifying a western pond turtle in the field it is best to know all of the characteristics, and see if most of them match the turtle you are identifying. For more complete descriptions, and for more identification sources, see Ashton et al., Taxonomy The western Pond Turtle (Clemmys marmorata) has been referred to by various names, such as the Pacific pond turtle, western mud turtle, Pacific mud turtle, Pacific terrapin, and Pacific freshwater turtle (Hays et al., 1999). The first specimens of WPT were collected in 1841 by Stelacoom and named Emys Mmarmorato (Ashton et al, 1997; Hays et al., 1999). Later, in 1862, it was renamed Clemmys marmorata by Strauch. Then in 1945, two sub species were identified the northwestern pond turtle (Clemmys mormorata mormorata) and the southwestern pond turtle (Clemmys marmorata pllida) by Sleeliger (Ashton et al., 1997; Hays et al., 1999).

3 Differences Among Subspecies and Evolutionary Histories The northwestern pond turtle varies physically and genetically from the southwestern pond turtle. Northwestern pond turtles are larger, vary in head and neck coloring, and are a darker olive than their southwest affiliates parts. Also in northern populations, the male is larger than females (Hays et al., 1999). These physical differences were known, but were not genetically explored as of June 1997 (Ashton et al., 1997). When the subspecies were looked at genetically, they saw two distinct genetic groups emerge. The turtle populations in Washington and Oregon are very similar genetically but differ greatly from those in California (Hays et al., 1999). For the Washington populations, the Puget Sound turtles were very similar to the Willamette Valley ones, but differed significantly from the Colombia Gorge population. Also, the Colombia Gorge population was most similar to the Oregon population (Hays et al., 1999). The California turtles show the most genetic diversity across an entire population and within their subpopulations (Spinks and Shaffer, 2005). It is important to note that there is more genetic diversity within a population, than when two or more populations are compared. Overall, the northern species have a less fit homogenous gene pool than the southern species, making the northern more susceptible to extinction. Keeping mind the numerous glacier recessions and advances of the western United States, and looking at the data at hand, it is likely the northwestern and southwestern subspecies evolved through allopatric speciation and isolation (Gray, 1995; Spinks and Shaffer, 2005). However we can not tell, with one hundred percent certainty, what and when historical geological events (such as glaciers) affected the speciation of the western pond turtle (Spinks and Shaffer, 2005). We can not determine it because the

4 western pond turtle only lives in aquatic environments. When a species only occurs in small pockets and its dispersal is limited, as is the case here, genetic mutations happen more rapidly, thus making it difficult to determine when speciation started to occur (Spinks and Shaffer, 2005). In a study by David W. Weisrock and Fredric J. Janzen, Comparative Molecular Phylogeography of North American Softshell Turtles (Apalone): Implications for Regional and Wide-ScaleHistorical Evolutionary Forces (1999) they concluded that Apalone, related to western pond turtles in order, went through allopathic speciation due to Pleistocene glacial advances and retreats. I would expect the same for the western pond turtle. Habitat Western pond turtles are found in streams, ponds, lakes, permanent and ephemeral wetlands. The substrates of these areas can differ greatly from solid rock, boulders, cobbles, gravel, sand, mud, decaying vegetation, and combinations of these. In many areas turtles are found in rocky streams with little or no emergent vegetation. In other areas they occur in slow-moving streams or backwaters with abundant emergent vegetation such as cattails or bulrush. They prefer warm, shallow and slow moving water. Turtles have been observed to be active in water temperatures as low as 1-2C (37F) and as high as 38C (100F). In general, turtles avoid prolonged exposure to water above 35C (95F). Visibility through water in areas inhabited by turtles may range from less than 15cm (6 in) to more than 10 m (33 ft) (Hays et al., 1999). Due to the historical range of the species, being able to live in diverse conditions came naturally.

5 These turtles require out of water habitats to bask, aestivate, nest and to over winter in. Basking sites are rocks, logs, grassy areas, and animal carcasses, basically anything that is in the sun on a sunny day. Good basking sites can be floating on or out of water. They are usually fought over when population densities are high (Hays et al., 1999; Reese and Welsh, 1997). Aestivating, nesting, and over wintering is done in upland grassy areas (Hays et al., 1999; Reese and Welsh, 1997). In search of these sites they usually travel between 50m to 500m away from a body of water (Hays et al., 1999; Reese and Welsh, 1997). In California, turtles frequently cross roads in agricultural areas in search of these sites (Reese and Welsh, 1997). They can use the same sites over and over, or find a new one each time. Overwintering is more common and longer in northern populations, and aestivating is more common and longer in southern populations (Hays et al., 1999; Reese and Welsh, 1997). Diet Western pond turtles are omnivorous and generalists, who can only swallow in water. They generally eat small invertebrates, such as beetle larva, snails, leaches, caddis flies, stoneflies, dragon flies and crustaceans. They also eat small fish, frog eggs, tad poles and larger carrion prey (Ashton et al., 1997; Hays et al., 1999). Herbivorous feeding is less frequent, but more common by females than males (Ashton et al, 1997; Hays 1999). Plant foods include cattail roots, lily pods, tule, and green filamentous algae (Ashton et al., 1997; Hays 1999). It is important to note that western pond turtles do not feed on live bull frogs, when bull frogs are present. They do not eat their eggs, tad poles, or them in any other metamorphic state. They have only been observed eating the bull

6 frog carcass (Hays; 1999). Bull frogs are the main invasive species that preys on the turtle. Predators The western pond turtle has many predators. Through out much of its range the Bull Frog has been introduced (Hays et al., 1999) and it is a main predator to hatchlings. Hatchlings, due to there small size, can be swallowed whole (Ashton et al., 1997). Other predators include: raccoon, coyote, grey fox, river otter, domesticated dog, mink, osprey, bald eagles, large mouth bass, giant water bugs, northern red legged frog, California red legged frog, garter snake, red fox, nutria, beaver, bobcat, black bear, red shouldered hawk, golden eagle, great blue heron, lack-crowned night-heron, and humans. Decline There are four main reasons for the decline of the western pond turtle. Two of these reasons fall under human interactions. The first is destruction of wetlands and altering lake, pond and stream habitats. This is a common story heard in conservation biology. The second is due to humans removing, and then trading, keeping as a pet, or eating the turtle, another common theme in conservation biology. The third is the introduction of the bull frog, again, a common theme. The fourth is very odd, due to its low reproductive rate turtles can not easily rebound in population size. Turtles can reproduce offspring once they reach 10 years of age (Germano and Rathbun, 2009; Hays et al., 1999). Also, the young turtles have a very high mortality rate. While they are small, and have soft shells, they are easily predated upon.

7 Current Status Western pond turtles used to span from the north shore of Lake Washington in the Puget Sound to Sierra San Pedro Martir in Baja California Norte (Ashton et al., 1997; Hays et al., 1999) and isolated inland populations in Washington (i.e. Colombia Gorge and the Puget Sound lowlands), Oregon, California, Nevada and Idaho (Ashton et al., 1997). Currently the western pond turtle is classified in Washington, under WAC , as an endangered species as of November Unless allowed by special permit, western pond turtles may not be collected, harassed, possessed (live or dead), or sold (Hays et al., 1999). Washington is currently implementing the Head Start conservation and recovery plan, for more information on this, and other conservation strategies, please see Danny Maloney, The species is listed as sensitive in California, and a species of special concern in Oregon (Ashton et al., 1997; Hays et al., 1999; Reese and Welsh, 1997).

8 Literature Cited Ashton, D., Lind, A. and Schlick, K. (1997) Western Pond Turtle (Clemys marmorata). Natural History. Redwood Science Laboratory, Arcata CA Germano, D. and Rathbun, G. (2008) Growth, Population Structure, and Reproduction of Western Pond Turtles (Acitinemys marmorata) on the Central Coast of California. Chelonian Conservation and Biology 7(2): Gray, E (1995) DNA Fingerprinting Reveals a Lack of Genetic Variation in Northern Populations of the Western Pond Turtle (Clemmys marmorata). Conservatin Biology 9(5) Reese, D. and Welsh, H. (1997) Use of Terrestrial Habitat by the Western Pond Turtles, Clemmys marmorata: Implications for Management. New York Turtle and Tortoise Society Spinks, P. and Shaffer, H. (2005) Range-wide molecular analysis of the western pond turtle (Emys marmorata): cryptic variation, isolation by distance, and their conservation implications. Molecular Ecology (2005) 14, Weisrock, D. and Janzen, F. (1999) Comparative Molecular Phylogeography of North American Softshell Turtles (Apalone): Implications for Regional and Wide-Scale Historical Evolutionary Forces. Molecular Phylogenetics and Evolution Vol. 14, No. 1, January, pp , 2000 Hays, D., McAlliser, K., Richardson, S., and Sinson, D. ( 1999) Washington State Recovery Plan for the Western Pond Turtle. Washington Department of Fish and Wildlife 600 Capitol Way North Olympia, Washington