A comparison of non-surgical methods for sexing young gopher tortoises (Gopherus polyphemus)

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dc.contributor.authorLoope, Kevin J.en
dc.contributor.authorRostal, David C.en
dc.contributor.authorWalden, M. A.en
dc.contributor.authorShoemaker, Kevin T.en
dc.contributor.authorHunter, Elizabeth A.en
dc.date.accessioned2022-11-30T14:45:39Zen
dc.date.available2022-11-30T14:45:39Zen
dc.date.issued2022-06-14en
dc.description.abstractMany turtle species have temperature-dependent sex determination (TSD), raising the prospect that climate change could impact population dynamics by altering sex ratios. Understanding how climate change will affect populations of animals with TSD requires a reliable and minimally invasive method of identifying the sexes of young individuals. This determination is challenging in many turtles, which often lack conspicuous external sexual dimorphism until years after hatching. Here, we explore four alternatives for sexing three age classes of captive-reared young gopher tortoises (Gopherus polyphemus), a terrestrial turtle of conservation concern native to the southeastern United States: (1) naive testosterone levels, (2) testosterone levels following a follicle stimulating hormone (FSH) challenge, (3) linear morphological measurements, and (4) geometric morphometrics. Unlike some other turtle species, male and female neonatal gopher tortoises have overlapping naive testosterone concentration distributions, justifying more complicated methods. We found that sex of neonates (<7 days old) is best predicted by a "random forest" machine learning model with naive testosterone levels and morphological measurements (8% out-of-bag error). Sex of hatchlings (4-8 months old) was predicted with 11% error using a simple threshold on naive testosterone levels, or with 4% error using a simple threshold on post-FSH testosterone levels. Sex of juveniles (approximately 3.5 years old) was perfectly predicted using a simple threshold on naive testosterone levels. Sexing hatchlings at >4 months of age is the easiest and most reliable non-surgical method for sex identification. Given access to a rearing facility and equipment to perform hormone assays, these methods have the potential to supplant laparoscopic surgery as the method of choice for sexing young gopher tortoises.en
dc.description.notesThis work was supported by funding from the Georgia Southern University Research Development Fund, and the Department of Defense Strategic Environmental Research and Development Program (RC18-C1-1103) . The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.en
dc.description.sponsorshipGeorgia Southern University Research Development Fund; Department of Defense Strategic Environmental Research and Development Program [RC18-C1-1103]en
dc.description.versionPublished versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.7717/peerj.13599en
dc.identifier.issn2167-8359en
dc.identifier.othere13599en
dc.identifier.pmid35722258en
dc.identifier.urihttp://hdl.handle.net/10919/112737en
dc.identifier.volume10en
dc.language.isoenen
dc.publisherPeerJen
dc.rightsCC0 1.0 Universalen
dc.rights.urihttp://creativecommons.org/publicdomain/zero/1.0/en
dc.subjectSex determinationen
dc.subjectTestosteroneen
dc.subjectCheloniansen
dc.subjectTortoisesen
dc.subjectFollicle-stimulating hormoneen
dc.subjectGeometric morphometricsen
dc.subjectSex hormonesen
dc.titleA comparison of non-surgical methods for sexing young gopher tortoises (Gopherus polyphemus)en
dc.title.serialPeerJen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten

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