The influence of daily temperature fluctuations during incubation upon the phenotype of a freshwater turtle M. A. Micheli-Campbell 1 , M. A. Gordos 2 , H. A. Campbell 1 , D. T. Booth 1 & C. E. Franklin 1 1 School of Biological Sciences, The University of Queensland, St. Lucia, QLD, Australia 2 NSW DPI (Fisheries), Wollongbar Agricultural Institute, Wollongbar, NSW, Australia Keywords Elusor macrurus; hatchling; performance; nest temperature; ambient conditions; embryo mortality. Correspondence Mariana A. Micheli-Campbell, The University of Queensland, School of Biological Sciences, Room 367, Goddard Building, St. Lucia, Brisbane, QLD 4072, Australia. Tel: +61 7 33651390; Fax: +61 7 33651655 Email: m.campbell4@uq.edu.au Editor: Nigel Bennett Received 22 December 2011; revised 13 March 2012; accepted 30 April 2012 doi:10.1111/j.1469-7998.2012.00934.x Abstract Incubation temperature influences the phenotype of the hatchling turtles. The aims of the present study were to investigate the daily fluctuations in temperature to which eggs of the freshwater turtle Elusor macrurus are exposed to in the wild and examine how these fluctuations may affect the phenotype and performance of the hatchlings. Eggs in the wild experienced an overall mean daily fluctuation of 5.7°C throughout the incubation period, but on particular days, the variation was as low as 2°C and as high as 22°C. Fifty-four eggs were collected from the wild and incubated in the laboratory at one constant (28°C) and two fluctuating (28  3 and 28  6°C) thermal regimes. Egg mass, incubation length and hatching success (89%) were similar for the 28 and 28  3°C groups, whereas the 28  6°C group only had a 5% hatching success, and the incubation length was 10 days longer. Upon hatching, there was no significant difference in body mass or straight carapace length between the 28 and 28  3°C groups, and within the first 8 weeks of hatching, there was no significant difference in growth rate, self-righting time, crawling speed and swimming performance. A single survivor from the 28  6°C group had a body mass that was 27% less compared with the other two groups and it did considerably poorer in all the performance tests. The study findings illus- trated that daily fluctuations in incubation temperature up to 6°C had no effect upon hatchling E. macrurus phenotype, but there was a limit (12°C) by which the extent and recurrence of these fluctuations became detrimental. These thermal regimes are not yet apparent in the wild but will occur within the geographical range of this species according to climate change predictions. Introduction Most oviparous reptiles bury their eggs in underground cham- bers for incubation (Deeming & Ferguson, 1991; Deeming, 2004; Booth, 2006). This is an evolved behavioural strategy, which not only protects the eggs from predation but also buffers the temperatures and hydric regime that the clutch experiences during incubation (Miller & Dinkelacker, 2008). In freshwater turtles, research has demonstrated that shifts in mean constant incubation temperature of only a few degrees can significantly affect the phenotype of the hatchlings by altering morphology, physiology and locomotor performance (Janzen, 1993; Bobyn & Brooks, 1994a,b; Roosenburg & Kelley, 1996; Booth, 2000; Steyermark & Spotila, 2001; Du & Ji, 2003; Booth et al., 2004; Delmas et al., 2007; Micheli- Campbell et al., 2011). In the wild, however, the eggs are rarely exposed to constant temperatures, as the females of most freshwater species lay shallow nests where the variation in daily temperature is increased by the proximity of the clutch to the substrate surface (Booth, 2006). To date, little is known about the effects of such thermal regimes upon the phenotype of hatchling turtles. The majority of empirical thermal incubation studies in freshwater turtles have focused upon species with temperature-dependent sex determination (Schwarzkopf & Brooks, 1985; Demuth, 2001; Les, Paitz & Bowden, 2007; Du, Shen & Wang, 2009). These studies have shown that daily fluctuations in incubation temperature produced a larger pro- portion of females when compared with the constant treat- ments. Alterations in other morphological and physiological traits were also observed and the extent of these responses varied widely between species. For example, fluctuating incu- bation temperatures resulted in a smaller body mass of hatch- ling Chinemys reevesii compared with those incubated at a constant temperature (Du et al., 2009). Swimming ability and immune response were improved in Chrysemys picta and Tra- chemys scripta when eggs were incubated under the fluctuating thermal regimes (Ashmore & Janzen, 2003; Les et al., 2007; Journal of Zoology Journal of Zoology. Print ISSN 0952-8369 Journal of Zoology •• (2012) ••–•• © 2012 The Authors. Journal of Zoology © 2012 The Zoological Society of London 1