Analysis of the nest environment of tuatara Sphenodon punctatus

Abstract

Water potential and temperature were monitored in 20 natural nests of tuatara, Sphenodon punctatus, through 12 months of incubation on Stephens Island, New Zealand. Tuatara nest in rookeries in open pasture, in sites that often are more than 100m from residential burrows located beneath the closed canopy of native bush. Nest tunnels are approximately 197 mm long, 73mm wide, and 45mm high, and have a slightly expanded chamber at the end. Eggs are generally deposited in 1‐3 layers in the terminal chamber. The top eggs are 30‐155mm below the soil surface, and an air space of as much as 20 mm may exist between the uppermost egg and the top of the chamber. Each nest receives an average of 8.6 eggs that imbibe water and swell during incubation. Only 48% of eggs have hatched or are still alive 12 months after oviposition. Survival by embryos is higher in moist nests than in dry ones. Variation in temperature in nests has only a small influence on survival, and this influence may be mediated indirectly by effects of temperature on the water exchanges experienced by incubating eggs. Water potentials in the soil of closed canopy forest on Stephens Island are high enough to support embryogenesis, but temperatures are too low. Thus, females leave the forest to nest in areas where soil temperatures are suitable for incubation.

Temperature-Dependent Sex Determination in Vertebrates

“…Eggs have been collected and artificially incubated to produce founders for new captive and wild populations and to augment rare existing populations (Daugherty 1998;Nelson 1998). These long-lived animals have low fecundity, do not exhibit secondary sexual characteristics until several years of age, and do not reach sexual maturity until they are at least 11 or more years old (Dawbin 1982;Castanet et al 1988;Cree 1994;Thompson et al 1996).…”

“…Female tuatara nest once every two to five years, and incubation takes on average one year to complete (Cree et al 1991;Thompson et al 1996), exposing eggs of a single cohort to both seasonal and annual fluctuations in temperature. The nesting season on Stephens Island occurs throughout November and December (early summer), when nesting females congregate in exposed rookeries (Thompson et al 1996). Tuatara nests are unsuccessful under full forest cover because temperatures are too low for embryonic development (Thompson et al 1996).…”

“…The nesting season on Stephens Island occurs throughout November and December (early summer), when nesting females congregate in exposed rookeries (Thompson et al 1996). Tuatara nests are unsuccessful under full forest cover because temperatures are too low for embryonic development (Thompson et al 1996).…”

“…Hatching success is generally very high at constant temperatures between 18 and 22˚C (e.g., 93% for S. punctatus; Nelson 2001). Eggs of S. guntheri have also been incubated at variable regimes in which temperature was increased, by 0.5-1˚C intervals every two weeks, from 18 to 23˚C, then decreased in the same stepwise manner to 18˚C, mimicking mean daily ambient temperatures in midsummer on Stephens Island, the most populous of all tuatara islands (Newman 1982;Cree et al 1995;Thompson et al 1996). Temperatures during the middle third of the variable incubation regime (the thermosensitive period, TSP, in other reptiles) were between 22 and 23˚C (Cree et al 1995).…”

Effect of cold temperature on the length of incubation of Chamaeleo chamaeleon

“…During winter, eggs exhibit slow or no development until spring or summer conditions favour development (Ewert, 1985). The developmental arrest is known to occur in several turtle species laying eggs in autumn or winter (Ewert and Wilson, 1996;Booth, 2000), in chameleons (Bons and Bons, 1960;Andrews and Donoghue, 2004), and have been hypothesized for other species having very long incubation (see review in Ewert, 1991 andin Andrews, 2004) as Tuataras (Thompson et al, 1996).…”