Deep nesting in a lizard,déjà vudevil's corkscrews: first helical reptile burrow and deepest vertebrate nest

Abstract

Dating back to 255 Mya, a diversity of vertebrate species have excavated mysterious, deep helical burrows called Daimonelix (devil's corkscrews). The possible functions of such structures are manifold, but their paucity in extant animals has frustrated their adaptive explanation. We recently discovered the first helical reptile burrows, created by the monitor lizard Varanus panoptes. The plugged burrows terminated in nest chambers that were the deepest known of any vertebrate, and by far the deepest of any reptile (mean = 2.3 m, range = 1.0-3.6 m, N = 52). A significant positive relationship between soil moisture and nest depth persisted at depths > 1 m, suggesting that deep nesting in V. panoptes may be an evolutionary response to egg desiccation during the long (approximately 8 months) dry season incubation period. Alternatively, lizards may avoid shallower nesting because even slight daily temperature fluctuations are detrimental to developing embryos; our data show that this species may have the most stable incubation environment of any reptile and possibly any ectotherm. Soilfilled burrows do not support the hypothesis generated for Daimonelix that the helix would provide more consistent temperature and humidity as a result of limited air circulation in dry palaeoclimates. We suggest that Daimonelix were used mainly for nesting or rearing young, because helical burrows of extant vertebrates are generally associated with a nest. The extraordinary nesting in this lizard reflects a system in which adaptive hypotheses for the function of fossil helical burrows can be readily tested.

Claw morphometrics in monitor lizards: Variable substrate and habitat use correlate to shape diversity within a predator guild

“…Varanus gouldii can dig several burrows up to 5 meters long in sequence to excavate invertebrates (Thompson, 2004; Whitford, 1998). Varanus panoptes produces a complex spiraling burrow, the deepest reptile nest sites on record (Doody, James, Colyvas, McHenry, & Clulow, 2015; Doody et al., 2018). …”

Similar burrow architecture of three arid-zone scorpion species implies similar ecological function

“…Varanus panoptes (Storr, 1980), a burrowing varanid lizard, has a highly tortuous, helical segment leading to the nest in its nesting burrow (Doody et al 2015). The entrance of the burrow is plugged with soil, indicating that the tortuosity is not related to maintaining consistent temperature or humidity by limiting air circulation.…”

“…The entrance of the burrow is plugged with soil, indicating that the tortuosity is not related to maintaining consistent temperature or humidity by limiting air circulation. The helical segment requires greater energy expenditure than a straight burrow of the same incline (Meyer 1999); thus, there is an adaptive function that is yet to be described (Doody et al 2015).…”

Who are the important sea turtle nest predators at Wreck Rock beach?

“…Moreover, camera traps did not record foxes at nests, 241 and no fox tracks were observed over nests during this study indicating that the fox baiting 242 program deployed by park managers is currently effective at inhibiting fox predation of sea 243 turtle nests at Wreck Rock beach. 244 245 Doody et al (2014Doody et al ( , 2015 reported that yellow-spotted goannas can dig warren complexes that 246 required removal of sand from up to 3 m deep, and that both males and females contribute to 247 warren excavation. Hence, the job of digging into a sea turtle nest which is combatively shallow 248 (40 -80 cm), should be relatively easy as evidenced by it requiring only 16 minutes of digging to 249 gain access to eggs in one of our monitored nests.…”