Life History of Teenage Mutant Painted Turtles

THE BACKGROUND

When Splinter discovered four baby turtles in a New York City sewer, he had no idea what the glowing green goo was that covered their bodies. He simply cleaned them off and gave them a home. Shortly thereafter, these turtles grew very rapidly and mutated into anthropomorphic beings with proclivities for num-chucks, pizza, and fighting crime. Obviously, this is the origin story for the fictional Teenage Mutant Ninja Turtles (TMNT), but the change that occurred to the turtles at the center of this story is, in many ways, becoming common in our own world. Turtles are increasingly living in urban wetlands, forcing them to cope with a variety of altered settings, such as increased nutrients from runoff. Previous work in urban aquatic systems has shown that life history traits are affected by environmental exposure, yet what this means for long-lived turtles remains unclear. Recently, we published a study (Meshaka et al., 2023) examining the demographic responses of a painted turtle (Chrysemys picta) population to living in an urban wetland within a Pennsylvania city.

THE STUDY

We trapped, measured, and marked turtles over a 9-year period, during which we captured 375 individuals 718 times. This capture effort resulted in 240 males, 82 females, and 53 juveniles used for analysis. We found that demographic traits were accelerated relative to those from non-urban sites, including a population from a natural wetland nearby. Growth was particularly affected, such that many turtles reached sexual maturity much more rapidly and at larger sizes than those from natural sites. Variation in juvenile growth rates, especially for females, has a profound effect on age at sexual maturity, such that faster-growing juveniles can have more lifetime egg output than slow-growing individuals. Based on the average clutch sizes of females in Congdon et al. (2018), the earliest-maturing females at our site could produce 12 eggs over two years before the oldest-maturing females from other sites first laid eggs. It would take these females decades until they caught up in lifetime egg output.

THE IMPLICATIONS

The altered chemistry of wetlands in urban areas is somewhat analogous to the green ooze from TMNT, such that turtles are growing faster and maturing more rapidly in these environments relative to those living elsewhere. The Teenage aspect of TMNT, where younger-than-ready individuals do adult things (e.g., ordering pizza), is particularly relevant as our turtles matured more rapidly than counterparts from natural sites, yet they still mated and nested all the same. Our results indicate that altered aquatic habitats are highly influential in shaping variation in important life-history traits. We argue that such demographic responses are likely common among urban populations of aquatic turtles worldwide. Future work exploring the implications for survival and reproduction of this “grow fast” lifestyle in urban populations would be fruitful. Ultimately, the urban slew is not a neutral environment. Rather, it can alter the pace and trajectory of a turtle’s life history, especially for teenagers.

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Read the study

Meshaka, W.E., Jr., E. Wingert, J.D. Riedle, S. Boback, and D.F. Hughes. 2023. Demography of a Painted Turtle intergrade (Chrysemys picta picta X C. p. marginata) population from an altered wetland. The Herpetological Journal 33: 14­–24. https://doi.org/10.33256/33.1.1424

Featured image: iNaturalist observation of painted turtles by iWalk. Some rights reserved (CC BY-NC)