Abstract
Leaving the water to bask (usually in the sun) is a common behavior for many freshwater turtles, with some species also engaging in “nocturnal basking.” Ectoparasite removal is an obvious hypothesis to explain nocturnal basking and has also been proposed as a key driver of diurnal basking. However, the efficacy of basking, day or night, to remove leeches has not been experimentally tested. Therefore, we examined the number of leeches that were removed from Krefft's river turtles (Emydura macquarii krefftii) after experimentally making turtles bask at a range of times of day, durations, and temperatures. Turtles had high initial leech loads, with a mean of 32.1 leeches per turtle. Diurnal basking under a heat lamp for 3 hr at ~28°C significantly reduced numbers of leeches relative to controls. In diurnal trials, 90.9% of turtles lost leeches (mean loss of 7.1 leeches per turtle), whereas basking for 30 min under the same conditions was not effective (no turtles lost leeches, and all turtles were still visibly wet). Similarly, “nocturnal basking” at ~23°C for 3 hr was not effective at removing leeches. Only 18% of turtles lost leeches (one turtle lost one leech and another lost four leeches). Diurnal basking outdoors under direct sunlight for 20 min (mean temp = 34.5°C) resulted in a small reduction in leeches, with 50% of turtles losing leeches and an average loss of 0.7 leeches per turtle. These results indicate basking can remove leeches if temperatures are high or basking durations are long. However, it was only effective at unusually long basking durations in this system. Our data showed even the 20‐min period was longer than 70.1% of natural diurnal basking events, many of which took place at cooler temperatures. Therefore, leech removal does not appear to be the purpose of the majority of basking events.
Highlights
Ectoparasites can adversely impact host health by absorbing nutrients and spreading diseases (Bower et al, 2019)
Our result that leeches are more common on the skin than on the shell is consistent with most other studies (Dodd, 1988; Brooks et al 1990; Readel et al, 2008; but see Reshk, 2009); those studies generally found higher leech loads on the posterior portion of the turtles, whereas we found a higher abundance on the anterior region around the neck and front legs
Our study provides the first experimental evidence that basking could serve as a method to remove ectoparasites living on freshwater turtles; the amount of time required to effectively remove leeches via desiccation was substantially longer than most basking intervals used by turtles in our population during either the day or night
Summary
Ectoparasites can adversely impact host health by absorbing nutrients and spreading diseases (Bower et al, 2019). Most studies that have attempted to test the parasite removal hypothesis have done so by comparing parasite loads among species that do and do not bask regularly (Mcauliffe, 1977; Strohlein & Christensen, 1984; Siddall & Desser, 1992; Ryan & Lambert, 2005; Gaertner et al, 2008; Readel et al, 2008; Davis & Sterrett, 2011; Rossow et al, 2013). We provided much-needed data on leech prevalence and intensity in an Australian turtle
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