Body length shrinkage in an endangered amphibian is associated with drought N. F. Bendik 1 & A. G. Gluesenkamp 2 1 Watershed Protection Department, City of Austin, Austin, TX, USA 2 Texas Parks and Wildlife Department, Austin, TX, USA Keywords body length; shrinkage; growth; drought; Eurycea tonkawae. Correspondence Nathan F. Bendik, City of Austin, Watershed Protection Department, Suite 1100, 505 Barton Springs Rd, Austin, TX 78704, USA. Tel: +1 512 974 2040; Fax: +1 512 974 2846. Email: nathan.bendik@austintexas.gov Editor: Nigel Bennett Received 8 August 2012; revised 15 November 2012; accepted 20 November 2012 doi:10.1111/jzo.12009 Abstract Shrinkage in body length, followed by growth, has rarely been documented in vertebrates and has been associated with stressful energetic and environmental conditions. Here, we document reversible shrinkage in an amphibian for the first time. Jollyville Plateau salamanders Eurycea tonkawae are neotenic (attain matu- rity while retaining an aquatic larval form) and inhabit springs and caves of a dissected aquifer in Travis County, TX, USA. We conducted mark-recapture surveys on a spring-dwelling population before and after an exceptional drought in 2008. Use of unique marks and digital photographs of individuals provided precise information on salamander growth rates during and after a period in which salamanders retreated to underground refugia to avoid desiccation during the drought. Tail width decreased significantly during the drought indicating a reduction in energy stores, a consequence of stressful environmental conditions. Unexpectedly, body length shrinkage also occurred during the drought and was followed by positive growth when spring flow resumed. Body length shrinkage could be an adaptation to coping with long periods of low food availability although its long-term effects are unknown. Given the influence of body size on many ecological and physiological characteristics of organisms, plasticity in body size may have important consequences that go undetected by researchers if shrink- age is ignored. Introduction Despite the frequency with which body size is measured in vertebrate studies and its importance as a physical trait, exam- ples of negative growth in body length (shrinkage) are rare. Currently, reversible shrinkage has been demonstrated only in cichlids (Hofmann, Benson & Fernald, 1999), salmon (Huusko et al., 2011), iguanas (Wikelski & Thom, 2000), tor- toises (Field et al., 2007; Loehr, Hofmeyr & Henen, 2007) and shrews (Saure & Hyvärinen, 1965), although some inverte- brates (krill) also experience this phenomenon (Nicol et al., 1992). For example, Antarctic krill may shrink to conserve energy during the winter (Ikeda & Dixon, 1982). Wikelski & Thom (2000) proposed that shrinkage is also adaptive in marine iguanas, as smaller individuals have an energetic advantage when foraging and exhibit higher survivorship during energetically stressful periods. Whether shrinkage is adaptive or merely a consequence of energetic stress, it may have significant consequences for individuals and populations given the importance of body size on an individual’s metabo- lism, growth rate, survival and fecundity (Blueweiss et al., 1978; Peters, 1986; Bonner, 2006). Climate change has been implicated as a driving force for declines in amphibian populations around the world (Pounds et al., 2006; Blaustein et al., 2010), and increasing tempera- tures and more frequent droughts, as predicted by climate change models (Meehl et al., 2007), can have dire conse- quences for amphibians. Drought can be especially disruptive to pond-breeding species because insufficient rainfall and shortened hydroperiods result in reduced reproductive output (Semlitsch, 1987; Dodd, 1993, 1994; Richter et al., 2003; Palis, Aresco & Kilpatrick, 2006; Taylor, Scott & Gibbons, 2006), population declines (Daszak et al., 2005) and even extirpation (McMenamin, Hadly & Wright, 2008). More directly, drought increases the threat of desiccation (Dodd, 1993), resulting in periods of decreased activity where an individual’s ability to survive long periods of food deprivation may ultimately deter- mine its fate (e.g. Snodgrass et al., 1999). The increased ability of amphibians to store fat and their low resting metabolic rates compared with other vertebrates (Wells, 2007) are adap- tations well suited for enduring starvation and, in some species, individuals can survive over a year without food (e.g. Amphiuma means, Rose, 1966; Siren lacertina, Martof, 1969). The predominant physical change observed in food- deprived amphibians is a loss of body mass from reduction of energy reserves (Rose, 1966; Gunter, 1968; Martof, 1969; Grably & Piery, 1981; Mould & Sever, 1982; Merkle & Hanke, 1988). However, more recent observations of body length Journal of Zoology Journal of Zoology. Print ISSN 0952-8369 Journal of Zoology •• (2012) ••–•• © 2012 The Zoological Society of London 1