The effect of hormone manipulations on sex ratios varies with environmental conditions in a turtle with temperature-dependent sex determination

2017 ◽  
Vol 327 (4) ◽  
pp. 172-181 ◽  
Author(s):  
Daniel A. Warner ◽  
Timothy S. Mitchell ◽  
Brooke L. Bodensteiner ◽  
Fredric J. Janzen
Keyword(s):  
Sex Determination ◽  
Environmental Conditions ◽  
Sex Ratios ◽  
Temperature Dependent

scholarly journals Measurement and modelling of primary sex ratios for species with temperature-dependent sex determination

2018 ◽  
Vol 222 (1) ◽  
pp. jeb190215 ◽  
Author(s):  
Melanie D. Massey ◽  
Sarah M. Holt ◽  
Ronald J. Brooks ◽  
Njal Rollinson
Keyword(s):  
Sex Determination ◽  
Sex Ratios ◽  
Temperature Dependent

scholarly journals Population viability at extreme sex-ratio skews produced by temperature-dependent sex determination

2017 ◽  
Vol 284 (1848) ◽  
pp. 20162576 ◽  
Author(s):  
Graeme C. Hays ◽  
Antonios D. Mazaris ◽  
Gail Schofield ◽  
Jacques-Olivier Laloë
Keyword(s):  
Sex Determination ◽  
High Mortality ◽  
Egg Production ◽  
Incubation Temperature ◽  
Sea Turtles ◽  
Sex Ratios ◽  
Population Viability ◽  
Temperature Dependent ◽  
Population Extinction ◽  
The World

For species with temperature-dependent sex determination (TSD) there is the fear that rising temperatures may lead to single-sex populations and population extinction. We show that for sea turtles, a major group exhibiting TSD, these concerns are currently unfounded but may become important under extreme climate warming scenarios. We show how highly female-biased sex ratios in developing eggs translate into much more balanced operational sex ratios so that adult male numbers in populations around the world are unlikely to be limiting. Rather than reducing population viability, female-biased offspring sex ratios may, to some extent, help population growth by increasing the number of breeding females and hence egg production. For rookeries across the world ( n = 75 sites for seven species), we show that extreme female-biased hatchling sex ratios do not compromise population size and are the norm, with a tendency for populations to maximize the number of female hatchlings. Only at extremely high incubation temperature does high mortality within developing clutches threaten sea turtles. Our work shows how TSD itself is a robust strategy up to a point, but eventually high mortality and female-only hatchling production will cause extinction if incubation conditions warm considerably in the future.

scholarly journals Does sex-ratio selection influence nest-site choice in a reptile with temperature-dependent sex determination?

2013 ◽  
Vol 280 (1772) ◽  
pp. 20132460 ◽  
Author(s):  
Timothy S. Mitchell ◽  
Jessica A. Maciel ◽  
Fredric J. Janzen
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Nest Site ◽  
Sex Ratios ◽  
Temperature Dependent ◽  
Dioecious Species ◽  
Offspring Sex Ratio ◽  
Nest Sites ◽  
Offspring Sex ◽  
Nest Site Choice

Evolutionary theory predicts that dioecious species should produce a balanced primary sex ratio maintained by frequency-dependent selection. Organisms with environmental sex determination, however, are vulnerable to maladaptive sex ratios, because environmental conditions vary spatio-temporally. For reptiles with temperature-dependent sex determination, nest-site choice is a behavioural maternal effect that could respond to sex-ratio selection, as mothers could adjust offspring sex ratios by choosing nest sites that will have particular thermal properties. This theoretical prediction has generated decades of empirical research, yet convincing evidence that sex-ratio selection is influencing nesting behaviours remains absent. Here, we provide the first experimental evidence from nature that sex-ratio selection, rather than only viability selection, is probably an important component of nest-site choice in a reptile with temperature-dependent sex determination. We compare painted turtle ( Chrysemys picta ) neonates from maternally selected nest sites with those from randomly selected nest sites, observing no substantive difference in hatching success or survival, but finding a profound difference in offspring sex ratio in the direction expected based on historical records. Additionally, we leverage long-term data to reconstruct our sex ratio results had the experiment been repeated in multiple years. As predicted by theory, our results suggest that sex-ratio selection has shaped nesting behaviour in ways likely to enhance maternal fitness.

Sex determination in northern painted turtles: effect of incubation at constant and fluctuating temperatures

1985 ◽  
Vol 63 (11) ◽  
pp. 2543-2547 ◽  
Author(s):  
Lin Schwarzkopf ◽  
Ronald J. Brooks
Keyword(s):  
Sex Determination ◽  
Sex Ratios ◽  
Chrysemys Picta ◽  
Temperature Dependent ◽  
Northern Population ◽  
Painted Turtles ◽  
Threshold Temperatures ◽  
Warm Summer ◽  
Summer Temperatures ◽  
Fluctuating Temperatures

Temperature-dependent sex determination was studied in a northern population of painted turtles (Chrysemys picta) in both laboratory and field. Eggs incubated at constant temperatures of 30 and 32 °C produced females only, whereas those kept at 22, 24, and 26 °C produced males only. Both sexes occurred at 20 and 28 °C. The threshold temperatures (temperatures producing 50% males) were estimated to be 27.5 and 20.0 °C, and were similar to those reported for more southerly populations of C. picta. In both 1983 (a relatively warm summer) and 1984 (an average summer), temperatures in natural nests regularly fluctuated above and below both threshold temperatures. Mean nest temperatures were warmer in 1983 than in 1984, but were not useful to predict nest sex ratios. Mean nest temperatures were not similar to constant temperatures in their effect on sex ratio. Sex ratios in nests could be described best by the total number of hours for which the temperature at each nest was intermediate to the two threshold temperatures. Sex ratios (proportion male) of hatchlings in 1983 and 1984 were similar and female biased (0.12 and 0.13, respectively).

Hatchling Sex Ratios are Independent of Temperature in Field Nests of the Long-necked Turtle, Chelodina longicollis (Testudinata : Chelidae)

1991 ◽  
Vol 18 (2) ◽  
pp. 225 ◽  
Author(s):  
M Palmer-Allen ◽  
F Beynon ◽  
a Georges
Keyword(s):  
Sex Determination ◽  
Constant Temperature ◽  
Sex Chromosomes ◽  
Sex Ratios ◽  
Seasonal Trend ◽  
Temperature Dependent ◽  
Sharp Drop ◽  
Heteromorphic Sex Chromosomes ◽  
Chelodina Longicollis ◽  
Incubation Temperatures

Eastern long-necked turtles, Chelodina longicollis, are known to lack heteromorphic sex chromosomes and to lack temperature-dependent sex determination when incubated under constant conditions. This study determined whether sex ratios of hatchlings emerging from natural nests of C. longicollis were different from that expected from constant temperature experiments. Temperatures in the eight nests monitored varied considerably each day (by 1.7-12.6�C), with eggs at the top of the nest experiencing the greatest variation (mean range 9.0�C) and eggs at the bottom experiencing least variation (mean range 5.3�C). Temperatures experienced by the top and bottom eggs differed by as much as 5.7�C at any one time. No monotonic seasonal trend was evident, but rainfall caused a sharp drop in nest temperatures. Sex ratios in hatchlings from 14 field nests of C. longicollis did not differ significantly from 1:1, a result in agreement with previous studies conducted at constant incubation temperatures in the laboratory.

scholarly journals Do Covariances Between Maternal Behavior and Embryonic Physiology Drive Sex-Ratio Evolution Under Environmental Sex Determination?

2019 ◽  
Vol 110 (4) ◽  
pp. 411-421 ◽  
Author(s):  
Fredric J Janzen ◽  
David M Delaney ◽  
Timothy S Mitchell ◽  
Daniel A Warner
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Environmental Conditions ◽  
Oviposition Behavior ◽  
Thermal Sensitivity ◽  
Sex Ratios ◽  
Theoretical Work ◽  
Environmental Sex Determination ◽  
Turtle Species ◽  
Primary Sex Ratio

Abstract Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination (ESD) are particularly vulnerable to experiencing skewed sex ratios when environmental conditions vary. Theoretical work has modeled sex-ratio dynamics for animals with ESD with regard to 2 traits predicted to be responsive to sex-ratio selection: 1) maternal oviposition behavior and 2) sensitivity of embryonic sex determination to environmental conditions, and much research has since focused on how these traits influence offspring sex ratios. However, relatively few studies have provided estimates of univariate quantitative genetic parameters for these 2 traits, and the existence of phenotypic or genetic covariances among these traits has not been assessed. Here, we leverage studies on 3 species of reptiles (2 turtle species and a lizard) with temperature-dependent sex determination (TSD) to assess phenotypic covariances between measures of maternal oviposition behavior and thermal sensitivity of the sex-determining pathway. These studies quantified maternal behaviors that relate to nest temperature and sex ratio of offspring incubated under controlled conditions. A positive covariance between these traits would enhance the efficiency of sex-ratio selection when primary sex ratio is unbalanced. However, we detected no such covariance between measures of these categories of traits in the 3 study species. These results suggest that maternal oviposition behavior and thermal sensitivity of sex determination in embryos might evolve independently. Such information is critical to understand how animals with TSD will respond to rapidly changing environments that induce sex-ratio selection.

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