Seasonal Incidence of Parasitism in the Painted Turtle, Chrysemys picta marginata Agassiz

Abstract

A total of 14 nematode and trematode species were recovered from 114 Chrysemys picta marginata collected in Wintergreen Lake, Kalamazoo County, Michigan. There was a distinctly higher incidence of nematode parasitism during warm months in both mature and immature hosts. The num- ber of nematodes per infected host increased from a low during the first growing season to a high in the fourth season. There was then a progressive decline in nematode load per infected host in succes- sive growing seasons until a low was reached in turtles over 10 years of age. It is suggested that these observations may reflect a reduced parasite tolerance to the lowered body temperature of the host and/ or to physiologic changes which accompany seasonal body temperature changes in the painted turtles. It is possible that diminished infection rates and reduced nematode loads in older turtles could be the result of immune responses, and/or changes in feeding habits of the host which occur at the onset of sexual maturity. Observed changes in nematode populations were not paralleled by trematode infec- tion rates.