A comparison of non-surgical methods for sexing young gopher tortoises (Gopherus polyphemus) (original) (raw)
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Herpetologica, 2007
The sex of young sea turtles is difficult to determine because they lack externally dimorphic characteristics and heteromorphic sex chromosomes, yet internal dimorphic morphology is defined at hatching. We tested the reliability of nine internal gonad and accessory duct characteristics to identify the sex of 558 posthatchling loggerhead sea turtles accurately. We modified existing laparoscopic procedures, previously used to classify the sex of larger sea turtles and other turtle species, for use in posthatchlings. Here we describe our approach and quantify the reliability of our morphological criteria. Sex was verified by histological examination of gonadal biopsies from a subset of the turtles. We noted seasonal shifts in early gonadal structure so that some characters which were reliable in the summer and fall were not reliable other times of the year. Thus, we confined the analysis to the six characters that were reliable year round: gonad shape, paramesonephric duct size, gonad size, paramesonephric duct lumen presence, paramesonephric duct mobility, and gonad attachment. Using discriminant analyses of the biopsy and morphological data, we found high correlations between sex from tissue biopsies and these six morphological characters; this analysis misclassified just 2% of the animals with histological verification. Applying the classification functions to animals without histology and comparing those results to our visual classification resulted in 2% reclassification. The analysis reclassified animals that we or the histology correctly identified that had both female-like and male-like characters. Our method provided accurate identification of sex in very young sea turtles. This methodology enables sex ratio assessments in early life stages, which are critical to species recovery efforts. Additionally, sex assignment data are basic to our understanding of patterns and processes directing dimorphic changes of the gonads and their ducts.
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 (f:m ratio of 6.25:1) in 2008 to 84% males (f:m 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%, f:m 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.
Scientific Reports, 2020
Temperature-dependent sex determination, present in most turtle species, is a mechanism that uses temperature to direct the sex of the embryo. The rapid increase of global temperatures highlights the need for a clear assessment of how sex ratios of organisms with TSD are affected. In turtles with TSD, quantifying primary sex ratios is challenging because they lack external dimorphism and heteromorphic sex chromosomes. Here we describe a new technique used to identify sex in neonate turtles of two TSD species, a freshwater turtle (Trachemys scripta) and a marine turtle (Caretta caretta) via analysis of small blood samples. We used an immunoassay approach to test samples for the presence of several proteins known to play an important role in sex differentiation. Our results show that Anti-Mullerian Hormone (AMH) can be reliably detected in blood samples from neonate male turtles but not females and can be used as a sex-specific marker. Verification of sex via histology or laparoscopy ...
Journal of Herpetological Medicine and Surgery, 2010
In 2004, a subset of a translocated population of gopher tortoises (n = 14; Gopherus polyphemu s) were captured to determine the overall health of individuals and to investigate the prevalence of selected pathogens. Additionally, ultrasonography and endoscopic visualization of the reproductive tract were compared as methodologies to accurately determine sex and reproductive status. Tortoises were premedicated with butorphanol and induced with propofol. The hematology and biochemical profile values obtained were within the reference ranges previously reported for gopher tortoises. Tortoises were parasitized with Alaeuris spp. of pinworms and trichostrongyles. Ten of the tortoises (71%) were also parasitized by hemogregarines. None of the animals had clinical signs indicative of acute upper respiratory disease (URTD); however, six animals had signs consistent with previous upper respiratory infections. One tortoise had an antibody titer against Mycoplasma agassizii, considered to be positive, while an additional five animals had antibody titers considered to be "suspect." We failed to detect Mycoplasma sp., Salmonella sp., or Chlamydophila sp. DNA from any of the animals. In general, morphometric characteristics reliably predicted the correct sex in the majority of animals that were >15 yr of age. When compared to endoscopy, ultrasound examination of the gonads was accurate for sex determination in 57% of the tortoises examined and was 86% accurate in animals >15 yr of age. Ultimately, endoscopy provided the most accurate method for determining sex in chelonians, particularly in juveniles or during nonreproductive seasons.
A Simplified Method for Determining Sex In Hatchling Sea Turtles
Copeia, 1985
LITERATURE CITED COOPER, WE, JR., L. J. VITT, LD VANGILDER AND JW GIBBONS. 1983. Natural nests and brooding behavior of Eumecesfasciatus. Herp. Rev. 14:65-66. COWLES, RB 1944. Parturition in the yucca night lizard. Copeia 1944:98-100. DUVALL, ...
Sex determination in Cagle's map turtle: implications for evolution, development, and conservation
Canadian Journal of Zoology, 1991
WIBBELS, T., KILLEBREW, F. C., and CREWS, D. 1991. Sex determination in Cagle's map turtle: implications for evolution, development, and conservation. Can. J. Zool. 69: 2693-2696. Sex determination was investigated in Cagle's map turtle, Graptemys caglei, which has a restricted distribution which is the southernmost of all Graptemys species. This species exhibits temperature-dependent sex determination, with high incubation temperatures producing only females and low temperatures producing only males. The estimated pivotal temperature (approximately 30.0°C) is higher than those reported for other species of Graptemys in North America; however, the interspecific variations in pivotal temperature are small (approximately 0.5-1 .O°C). Temperature appears to affect the ovarian or testicular nature of the gonads in an "all or none" fashion, but exerts a graded effect on the length of ovaries. In addition, temperature appears to exert a graded effect on the regression of the oviducts in males. The occurrence of temperature-dependent sex determination in this species is also of conservational importance, since alterations to a single river system could potentially impact the reproductive success of this species by changing nest temperatures and, thus, population sex ratio(s).
An Immunohistochemical Approach to Identify the Sex of Young Marine Turtles
Anatomical record (Hoboken, N.J. : 2007), 2017
Marine turtles exhibit temperature-dependent sex determination (TSD). During critical periods of embryonic development, the nest's thermal environment directs whether an embryo will develop as a male or female. At warmer sand temperatures, nests tend to produce female-biased sex ratios. The rapid increase of global temperature highlights the need for a clear assessment of its effects on sea turtle sex ratios. However, estimating hatchling sex ratios at rookeries remains imprecise due to the lack of sexual dimorphism in young marine turtles. We rely mainly upon laparoscopic procedures to verify hatchling sex; however, in some species, morphological sex can be ambiguous even at the histological level. Recent studies using immunohistochemical (IHC) techniques identified that embryonic snapping turtle (Chelydra serpentina) ovaries overexpressed a particular cold-induced RNA-binding protein in comparison to testes. This feature allows the identification of females vs. males. We modif...
Canadian Journal of Zoology, 2001
Temperature-dependent sex determination is one of the best documented yet evolutionarily enigmatic sexdetermining systems. The classical theoretical framework suggests that temperature-dependent sex determination will be adaptive when males and females benefit differentially from development at certain temperatures. Empirical evidence has not provided convincing support for this "differential-fitness" hypothesis. Furthermore, since most experiments utilize constant temperature incubation treatments to explore phenotypic response to temperature, few studies have addressed the consequences of incubation under natural conditions. In this study I utilized constant-temperature laboratory incubations and natural-nest incubations to determine the effects of temperature on sex, size, growth, and locomotor performance in the tortoise Gopherus polyphemus. Constant-temperature incubations do induce substantial growth and performance variation in these tortoises. However, the data do not clearly support the differential-fitness hypothesis because (i) growth variation does not result in adult size dimorphism, (ii) performance differences are confined to a very short period after hatching, and (iii) natural incubation temperatures do not vary sufficiently to produce significant phenotypic variation in traits other than sex.
Predetermination of sexual fate in a turtle with temperature-dependent sex determination
Developmental Biology, 2014
Egg incubation temperature determines offspring sex in many reptilian species, including red-eared slider turtles, where embryos incubated at low temperatures during the initial stages of gonad formation develop as males, while those kept at higher temperatures develop as females. Incubation at the threshold, or pivotal, temperature (PvT) yields an even ratio of males and females. This strong susceptibility to temperature indicates that each embryo of this species is competent to develop as a male or a female. However, the mechanism that determines sexual fate at the PvT has not been identified. One possibility is that sexual fate is stochastic at the PvT, but coordinated by systemic signals within a single embryo. If this is the case, gonads explanted separately to culture should not coordinate their fate. Here we show that gonad pairs from embryos incubated at the PvT share a strong predisposition for one sex or the other when cultured in isolation, indicating that they were affected by shared genetic signals, maternally-deposited yolk hormones or other transient influences received prior to the stage of dissection. In ovo studies involving shifts from the male-or female-producing temperature to the PvT further indicate that embryos adopt a sexual differentiation trajectory many days prior to the onset of morphological differentiation into testes or ovaries and usually maintain this fate in the absence of an extreme temperature signal favoring the development of the other sex. Our findings therefore suggest that the outcome of sex determination in these reptiles is heavily influenced (i) by an inherent predisposition at the PvT and (ii) by the sexual differentiation trajectory established early in gonad development under male-or female-producing temperatures.