Support for a rare pattern of temperature-dependent sex determination in archaic reptiles : evidence from two species of tuatara (Sphenodon)

Nicki Mitchell, N.J. Nelson, A. Cree, S. Pledger, S.N. Keall, C.H. Daugherty

    Research output: Contribution to journalArticle

    46 Citations (Scopus)

    Abstract

    BackgroundThe sex of many reptiles is determined by the temperature an embryo experiences during its development. Three patterns of temperature-dependent sex determination (TSD) have been defined, but one pattern where only males are produced above an upper temperature threshold (Type IB) is controversial. Here we report new data on the relationship between constant temperature incubation and sexual phenotype in two species of tuatara (Sphenodon), archaic reptiles of enormous zoological significance as the sole representatives of a once widespread reptilian order.ResultsIn both species, the pattern observed with constant incubation temperatures from 18 to 23°C (or 24°C) supported a female→male (FM or Type IB) pattern of TSD: in Sphenodon guntheri males were produced above a pivotal temperature of 21.6°C, and in S. punctatus (unnamed subspecies on Stephens Island, Cook Strait), males were produced above a pivotal temperature of 22.0°C. The pivotal temperatures and scaling parameters differed between species (p <0.001). The thermosensitive period (TSP), where temperature influences gonad morphogenesis, occurs between 0.25 and 0.55 of embryonic development. While it is possible that the more common female→male→female (FMF or Type II) pattern exists, with a second pivotal temperature above 23–24°C, we review several lines of evidence to the contrary. Most notably, we show that in S. punctatus, the warmest natural nests during the TSP produce predominantly males.ConclusionAn FM pattern of TSD could be currently adaptive in promoting sexual size dimorphism in tuatara. However, an FM pattern has particularly serious consequences for S. guntheri because current patterns of global warming could exacerbate the male bias already present in the relic population.
    Original languageEnglish
    Pages (from-to)online - approx 5-20pp
    JournalFrontiers in Zoology
    Volume3
    Issue number29
    DOIs
    Publication statusPublished - 2006

    Fingerprint Dive into the research topics of 'Support for a rare pattern of temperature-dependent sex determination in archaic reptiles : evidence from two species of tuatara (Sphenodon)'. Together they form a unique fingerprint.

    Cite this