Female reproductive variation among populations of Sonoran mud turtles (Kinosternon sonoriense)

Rosen, Phillip

Sonoran mud turtles were observed and studied at various locations in Arizona, including Montezuma Well. Reproductive traits were examined, including the start of ovulation, egg size, and egg width and pelvis opening; includes figures, tables, maps, and a list of literature cited. Life history and ecology of Sonoran Mud Turtles (Kinosternon sonoriense) were studied in 10 populations in Arizona. Ovulation occurred for the first time at close to 6 years of age in females from all populations, but slow-growing individuals in one population failed to mature until a minimum size was reached. Populations varied in egg size and relationship between egg width and pelvic opening. Within populations egg size appeared to be optimized, but variation among populations indicated coevolution of egg size and pelvic opening, and apparent concommitant evolution of shell shape. Hatchlings were large in populations with large eggs. These populations also had high adult survivorship but low pre-adult survivorship. Other reproductive traits covaried among populations. Populations characterized by large eggs had small clutches (by weight and number of eggs), low growth rates and high reproductive outputs in early adulthood, and weak size-fecundity relationships. Small egg populations consistently had the reverse of these characteristics. Additionally, data on clutch frequency indicate females in large egg populations produce more clutches/yr than those in small egg populations, holding annual reproductive output (weight of eggs as a proportion of body size) relatively constant. Size-fecundity relationships, but not adult survivorship, appear to have a strong effect on reproductive pattern. Reproductive pattern in large egg populations could not be explained by demographic models requiring maximized lifetime output of eggs. It appeared that females were maximizing the number of lifetime clutches in response to low and/or variable nest, hatchling, and early juvenile survivorship. (Copied verbatim from the thesis.)