[PDF] Evaluation Of Sex Ratios In Sea Turtle Populations eBook

Author : Jennifer Estes Layton
Publisher :
Page : 165 pages
File Size : 31,96 MB
Release : 2011
Category : Green turtle
ISBN :

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Aspects of TSD were examined in two different sea turtle populations, representing two sea turtle species. Sex ratio was examined in the juvenile portion of the loggerhead sea turtle population in the southeastern U.S. Blood samples were analyzed in a testosterone radioimmunoassay. The results suggest a significant female-biased sex ratio (2.5F:1.0M). The presence of a female-biased sex ratio has significant implications for the conservation of this population. Another study examined nesting beach temperatures throughout the range of loggerhead nesting in the southeastern U.S. from 2004-2009. Beach temperatures were simultaneously recorded at nest depth on nesting beaches used by this population. The results indicate that temperatures vary significantly between nesting beaches, with potential sex ratios ranging from highly female biased to male biased depending on the beach. The results provide an initial data set for evaluating long-term changes in beach temperatures associated with global climate change. A third study investigated temperature-dependent sex determination in the Hawaiian green turtle. Beach and nest temperatures from 2003-2009 were evaluated. Collectively, the data indicate that temperatures at FFS were low compared to those reported for other sea turtle nesting beaches. Such cool temperatures are not conducive to the production of female-biases which have been reported for other green turtle populations. An experiment was conducted to evaluate the effects of temperatures similar to those from the nesting beach on sex determination in the Hawaiian green. The hatchlings were subsequently reared in captivity and were sexed by laparoscopy prior to their release. The results indicate that the pivotal temperature for the Hawaiian green is not lower than those reported for other green populations. This finding plus the relatively cool temperatures recorded at FFS, indicate the overall hatchling sex ratio of Hawaiian greens is predicted to be unbiased or even male-biased. The purpose of the final chapter was to develop an educational module for high school and college students, which demonstrates how modern molecular genetics can be utilized for conservation of endangered species. This chapter includes implementation of the module into local high schools, UAB CORD Summer Science Institute, and the college curriculum at Dauphin Island Sea Lab.

Author : National Research Council
Publisher : National Academies Press
Page : 174 pages
File Size : 48,23 MB
Release : 2010-10-07
Category : Science
ISBN : 0309152550

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All six species of sea turtles found in U.S. waters are listed as endangered or threatened, but the exact population sizes of these species are unknown due to a lack of key information regarding birth and survival rates. The U.S. Endangered Species Act prohibits the hunting of sea turtles and reduces incidental losses from activities such as shrimp trawling and development on beaches used for nesting. However, current monitoring does not provide enough information on sea turtle populations to evaluate the effectiveness of these protective measures. Sea Turtle Status and Trends reviews current methods for assessing sea turtle populations and finds that although counts of sea turtles are essential, more detailed information on sea turtle biology, such as survival rates and breeding patterns, is needed to predict and understand changes in populations in order to develop successful management and conservation plans.

Author : Matthew Howland Godfrey
Publisher :
Page : 0 pages
File Size : 23,74 MB
Release : 1997
Category :
ISBN :

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To generate more data on sex ratios of sea turtle hatchlings, I developed a simple method of collecting daily mean sand temperatures on nesting beaches. Sand temperature can be used as an index of sex ratio. I then measured sand temperatures and sampled gonads of hatchlings of two sea turtle species on a nesting beach in Suriname during 1993. From histological analysis of the gonads, combined with information on the relative numbers of turtles nesting during the season, I generated overall estimates of sex ratio for green sea turtles (63.8% female) and for leatherback turtles (69.4% female). Relative numbers of male and female hatchlings varied throughout the season, and this corresponded to changes in sand temperatures and rainfall. From historical rainfall records and from past records of nesting frequency, I estimated overall sex ratios for another 13 seasons. Seasonal sex ratios fluctuated yearly. A revised estimate of the pivotal temperature (that constant incubation temperature which produces equal numbers of each sex) of green turtles in Suriname was 29.4$\sp\circ$C; this was slightly higher than past estimates. The transitional range of temperature (TRT), which is the range of incubation temperatures over which both sexes are produced, spanned several degrees. Metabolic warming was monitored in leatherback nests. It was found that eggs were about 0.8$\sp\circ$C warmer on average than the surrounding sand during the thermosensitive period of sexual differentiation. Because the leatherback has a narrow TRT, the influence of metabolic warming on sex ratio probably is restricted to a narrow range of incubation temperatures. Lastly, a new method of estimating sex ratios was devised, based on the rate of development of eggs and prevailing incubation temperatures. In general, nests with shorter incubation times produce mostly females and nests with longer incubation times produce mostly males. This relationship could be useful for generating predictions of sex ratio from natural nests for which only the incubation duration is known. In addition, by comparing this relationship from laboratory and field studies, it was possible to quantify the time it takes loggerhead hatchlings to dig up from the nest once they have hatched.

Author : Nicholas Mrosovsky
Publisher :
Page : 196 pages
File Size : 48,90 MB
Release : 1983
Category : Sea turtles
ISBN :

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Turtles are big; A brief life history; The tagging reflex; Head-starting: the heart has its reasons; Operation green turtle; The styrofoam box story; Kemp's ridley in a technological fix; The anathema of farming; Four thousand unwanted turtles; Dangerous categories; The alarmist strategy; Problem resolving; Splitting: strategy or science?; An egg-laying machine.

Author : Carrie Lynne Morjan
Publisher :
Page : 428 pages
File Size : 43,85 MB
Release : 2002
Category :
ISBN :

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Many reptiles exhibit temperature-dependent sex determination (TSD), a sex-determining mechanism in which the incubation environment permanently determines offspring sex. This research had two main objectives: (1) to evaluate the roles of two traits (nesting behavior by females and offspring sex ratios in response to thermal incubation conditions) thought to be important for maintaining sex ratios in this system, using the painted turtle (Chrysemys picta), and (2) evaluate the adaptive significance of TSD in a genotypic sex determining system (GSD). Observations on the nesting behavior of painted turtles suggest that either females in this population do not use soil surface temperature as a cue for selecting nest sites, or select sites with intermediate soil surface temperatures that may be less likely to bias sex ratios. Geographic comparisons from two populations of C. picta inhabiting differing climates (Illinois and New Mexico) demonstrated that the New Mexico population exhibited a significantly higher pivotal temperature (temperature producing a 1:1 sex ratio) than the Illinois population. However, this difference was small compared to differences in climatic conditions experienced by the populations. Chrysemys picta nests from Illinois and New Mexico experienced similar nest temperatures despite a relatively hot year in New Mexico. Nests in New Mexico were not laid in sites most likely to reduce nest temperatures, but instead at sites experiencing high soil moisture, which indirectly reduced nest temperatures. In simulation models, pivotal temperatures evolved more rapidly than did nest-site choice by females in response to perturbed sex ratios. Natal philopatry to nest sites also caused maladaptive nesting behavior in terms of Fisherian sex ratio selection. Simulation models demonstrated that TSD invades populations exhibiting GSD and reaches fixation through several avenues that do not include a widely accepted adaptive function for TSD (the Charnov-Bull model). Results from these studies suggest that the likelihood of TSD being relatively neutral compared to GSD in reptiles deserves more attention. Consequently, selection for female behavior and offspring thermal sensitivity to adaptively adjust sex ratios may be fairly weak. This conclusion is supported by the small observed differences in pivotal temperatures and lack of strong patterns of thermally-based nest-site selection.