Abstract
ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 30:145-155 (2016) - DOI: https://doi.org/10.3354/esr00737 Weather and sex ratios of head-started Agassiz’s desert tortoise Gopherus agassizii juveniles hatched in natural habitat enclosures Kenneth A. Nagy1,*, Gerald Kuchling2, L. Scott Hillard1, Brian T. Henen3 1Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095-1606, USA 2School of Animal Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia 3Natural Resources and Environmental Affairs, MAGTFTC MCAGCC, Twentynine Palms, California 92278, USA *Corresponding author: kennagy@biology.ucla.edu ABSTRACT: Head-starting of Agassiz’s desert tortoise, a means to aid recovery of this threatened species, may adversely affect offspring sex ratios via temperature-dependent sex determination combined with possible unnatural thermal conditions in head-start facilities. We determined sex ratios in juvenile tortoises hatched from first clutches of 4 annual cohorts at the head-start facility at the US Marine Corps Base, Twentynine Palms, California, USA, using non-fatal, endoscopic inspection of gonads. Cohort sexes ranged from 97% females (♀:♂ ratio of 6.25:1) in 2008 to 84% males (♀:♂ ratio of 0.19:1) in 2009, apparently primarily in response to local weather conditions during the temperature-sensitive phase of incubation. Warmer weather during development of a second clutch laid in 2009 led to fewer males (55%, ♀:♂ ratio of 0.82). Efforts to cool (artificially shade) some nesting burrows were unsuccessful in increasing the proportion of male hatchlings in 2009. Cohort sex ratios were associated with average daily air temperatures during incubation, such that more females were produced during warmer periods, in good agreement with published temperature-controlled laboratory experiments. These results suggest that weather played a major role in determining sex ratios, with apparently smaller or negligible influences resulting from initial location, structure and operation of the head-start facility; experimental shading of nests; and individual mothers’ variation in the timing of egg laying and placement of nests within the natal burrows. These results, obtained from a remote, mostly natural field site, indicate the potentially great sensitivity of sex determination in nests of wild, free-living desert tortoises to changes in climate. KEY WORDS: Agassiz’s desert tortoise · Climate change · Conservation · Head-start · TSD · Temperature-dependent sex determination · Weather Full text in pdf format PreviousNextCite this article as: Nagy KA, Kuchling G, Hillard LS, Henen BT (2016) Weather and sex ratios of head-started Agassiz’s desert tortoise Gopherus agassizii juveniles hatched in natural habitat enclosures. Endang Species Res 30:145-155. https://doi.org/10.3354/esr00737 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 30. Online publication date: May 31, 2016 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2016 Inter-Research.
Highlights
Agassiz’s desert tortoise Gopherus agassizii (Murphy et al 2011), which inhabits the Mojave and Colorado Deserts in California, Nevada, Utah and Arizona, was listed as a threatened species in 1990 (US Fish and Wildlife Service 1990) following major declines in densities of populations in the western part of the species’ range
The sex ratios increased from 67% female in 2006 to 97% in 2008 (Table 1), with ratios within years significantly different from 1:1 in 2007 and 2008, but marginally not so in 2006
We explored the possible influence of weather variation on sex ratio of neonate tortoises by examining 30-yr weather records (1986−2015) from the nearby Expeditionary Air Field
Summary
Agassiz’s desert tortoise Gopherus agassizii (Murphy et al 2011), which inhabits the Mojave and Colorado Deserts in California, Nevada, Utah and Arizona, was listed as a threatened species in 1990 (US Fish and Wildlife Service 1990) following major declines in densities of populations in the western part of the species’ range. The head-starting method usually begins with obtaining eggs and hatching them indoors in containers (e.g. Wibbels 2003, 2007), or in nests in soil in outdoor enclosures (Nagy et al 2015a,b). These procedures may alter the incubation temperatures of the eggs compared to temperatures in natural, unmanipulated nests (Baxter et al 2008). Head-starting may offer ways to counter a climate-change-induced tendency toward excess recruitment of female chelonians in wild populations This could be done by reducing nest temperatures in head-start facilities via added shading (Patino-Martinez et al 2012), locating nests in cooler (deeper, wetter, or greater natural shading) soils, or by placing eggs in air-conditioned spaces
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
