Facultative sex allocation in the viviparous lizard Eulamprus tympanum, a species with temperature-dependent sex determination

2003 ◽  
Vol 51 (4) ◽  
pp. 367 ◽  
Author(s):  
Kylie A. Robert ◽  
Michael B. Thompson ◽  
Frank Seebacher
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Breeding Season ◽  
Sex Allocation ◽  
Adult Population ◽  
Selective Advantage ◽  
Adult Males ◽  
Temperature Dependent ◽  
Maternal Manipulation

Females of the Australian scincid lizard Eulamprus tympanum can manipulate the sex of their offspring in response to gender imbalances in the population using temperature-dependent sex determination. Here we show that when adult males are scarce females produced male-biased litters and when adult males were common females produced female-biased litters. The cues used by a female to assess the adult population are not known but presumably depend upon her experience throughout the breeding season. Maternal manipulation of the sex ratio of the offspring in E. tympanum illustrates a selective advantage of temperature-dependent sex determination in a viviparous species.

scholarly journals Unexpected resilience of species with temperature-dependent sex determination at the Cretaceous–Palaeogene boundary

2010 ◽  
Vol 7 (2) ◽  
pp. 295-298 ◽  
Author(s):  
Sherman Silber ◽  
Jonathan H. Geisler ◽  
Minjin Bolortsetseg
Keyword(s):  
Climate Change ◽  
Sex Ratio ◽  
Sex Determination ◽  
Volcanic Eruptions ◽  
Egg Laying ◽  
Molecular Clocks ◽  
Temperature Dependent ◽  
Hell Creek Formation ◽  
Male Preponderance ◽  
Genotypic Sex Determination

It has been suggested that climate change at the Cretaceous–Palaeogene (K–Pg) boundary, initiated by a bolide impact or volcanic eruptions, caused species with temperature-dependent sex determination (TSD), including dinosaurs, to go extinct because of a skewed sex ratio towards all males. To test this hypothesis, the sex-determining mechanisms (SDMs) of Cretaceous tetrapods of the Hell Creek Formation (Montana, USA) were inferred using parsimony optimizations of SDMs on a tree, including Hell Creek species and their extant relatives. Although the SDMs of non-avian dinosaurs could not be inferred, we were able to determine the SDMs of 62 species; 46 had genotypic sex determination (GSD) and 16 had TSD. The TSD hypothesis for extinctions performed poorly, predicting between 32 and 34 per cent of survivals and extinctions. Most surprisingly, of the 16 species with TSD, 14 of them survived into the Early Palaeocene. In contrast, 61 per cent of species with GSD went extinct. Possible explanations include minimal climate change at the K–Pg, or if climate change did occur, TSD species that survived had egg-laying behaviour that prevented the skewing of sex ratios, or had a sex ratio skewed towards female rather than male preponderance. Application of molecular clocks may allow the SDMs of non-avian dinosaurs to be inferred, which would be an important test of the pattern discovered here.

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.

Long-term survival, length of breeding season, and operational sex ratio in a boreal population of common frogs, Rana temporaria L.

1990 ◽  
Vol 68 (1) ◽  
pp. 121-127 ◽  
Author(s):  
Johan Elmberg
Keyword(s):  
Sex Ratio ◽  
Breeding Season ◽  
Rana Temporaria ◽  
Return Rate ◽  
Operational Sex Ratio ◽  
Adult Males ◽  
Term Survival ◽  
Size Dependent ◽  
Survival Selection

A population of individually marked adult Rana temporaria was studied during the breeding season in 1979–1988 in east-central Sweden. Annual return rate averaged 31% (range 16–51%) in males and 16% (range 5–33%) in females. Return rate was not size dependent but increased with every successful previous hibernation, indicating an increased survival rate with age. Return rate was not correlated with winter harshness. Once adult, males had on average 1.5 (maximum 6) seasons with the possibility of reproducing. Corresponding values for females were 1.4 and 4. Mean length of the breeding season was 20 (SD = 2) days. Calling generally started at water temperatures below 3 °C. The lowest spawning temperature was 1 °C. Average temperatures at spawning onset and peak spawning were 5 and 6 °C, respectively. Large males tended to arrive earlier at the pond than small males. Males arrived earlier and stayed longer than did females. The overall population sex ratio was close to unity. The operational sex ratio (OSR) varied during the breeding season, averaging 0.54 (one female to two males). No male was observed to mate more than once per season. I argue that survival selection is more important to male lifetime mating success than is competition in the breeding pond (sexual selection as affected by OSR and length of the breeding season).

scholarly journals Temperature-Dependent Sex Determination and Artificial Incubation of Tuatara, Sphenodon Punctatus

2021 ◽  
Author(s):  
◽  
Nicola J Nelson
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Hatching Success ◽  
Conservation Management ◽  
Incubation Temperature ◽  
Management Tool ◽  
Relative Fitness ◽  
Temperature Dependent ◽  
Sphenodon Punctatus ◽  
Artificial Incubation

<p>Juveniles resulting from artificially induced and incubated eggs are often used to found or augment populations of rare reptiles, but both procedures may compromise the health of hatchlings or their fitness in natural environments. I aimed to test whether these procedures affected size or performance of juvenile tuatara, Sphenodon punctatus, New Zealand reptiles with temperature-dependent sex determination (TSD). Size and performance are phenotypic traits likely to influence fitness and eventual lifetime reproductive success, and are thus important measures of the suitability of artificial induction and incubation techniques for conservation management. I incubated 320 tuatara eggs artificially at 18, 21 and 22ºC; 52% of these were obtained by induction, the remainder were collected from natural nests. An additional 25 natural nests were left intact for investigation of TSD and effects of incubation temperature in nature. Juveniles from all incubation regimes were kept for ten months post-hatching in similar rearing conditions and sexed by laparoscopy. Induced eggs were significantly smaller than naturally laid eggs, and resulted in significantly smaller hatchlings, even when variation among clutches was accounted for. Incubation temperature did not greatly influence size at hatching, but was an important determinant of size by ten months of age; initial egg mass was the most important factor affecting size of hatchlings. Data indicate that TSD occurs in nature. The sex of hatchlings from 21 nests was investigated: 10 nests produced 100% male hatchlings, 4 nests produced 100% female hatchlings, and only 7 nests produced mixed sex ratios which ranged from 11% to 88% males. Sex of juveniles was related to temperature with a larger proportion of males produced in warmer nests. The overall percentage of male hatchlings in natural nests was 64%. Hatching success was 65% from natural nests during the 1998/99 season. Incubation temperatures throughout the year ranged from 2.9 to 34.4ºC. Global warming is likely to skew the hatchling sex ratio towards males if female tuatara are unable to select nest sites according to environmental cues. Evidence from size patterns of tuatara incubated in natural nests supports differential fitness models for the adaptive significance of TSD. The evaluation of artificial incubation as a conservation management tool demonstrated that it is a procedure that benefits conservation as it can be used reliably to produce founders; hatching success was 94% during this study. The sex ratio of artificially incubated juveniles can be easily manipulated; the pivotal temperature lies between 21 and 22ºC. Constant artificial incubation conditions resulted in larger juveniles by ten months of age than those from natural incubation. Naturally incubated juvenile tuatara, however, were faster for their size, their reaction norm to predator stimuli was to run, and they were possibly more aggressive, suggesting naturally incubated juveniles could survive better in nature. No firm conclusions can be reached on the quality of artificially incubated juvenile tuatara because further research will be required to establish the relevance of performance test results in nature and consequences of incubation regimes in the longer term with respect to relative fitness of individuals.</p>

scholarly journals Conservation of sex-linked markers among conspecific populations of a viviparous skink, Niveoscincus ocellatus, exhibiting genetic and temperature dependent sex determination

2018 ◽  
Author(s):  
Peta Hill ◽  
Christopher P. Burridge ◽  
Tariq Ezaz ◽  
Erik Wapstra
Keyword(s):  
Linkage Disequilibrium ◽  
Sex Ratio ◽  
Sex Determination ◽  
Temperature Dependent ◽  
Offspring Sex Ratio ◽  
Evolutionary Transitions ◽  
Offspring Sex ◽  
Determination System ◽  
Sex Determination System ◽  
Male Heterogamety

AbstractSex determination systems are exceptionally diverse and have undergone multiple and independent evolutionary transitions among species, particularly reptiles. However, the mechanisms underlying these transitions have not been established. Here we tested for differences in sex-linked markers in the only known reptile that is polymorphic for sex determination system, the spotted snow skink, Niveoscincus ocellatus, to quantify the genomic differences that have accompanied this transition. In a highland population, sex is determined genetically, whilst in a lowland population, offspring sex ratio is influenced by temperature. We found a similar number of sex-linked loci in each population, including shared loci, with genotypes consistent with male heterogamety (XY). However, population-specific linkage disequilibrium suggests greater divergence of sex chromosomes in the highland population. Our results suggest that transitions between sex determination systems (GSD and TSD-like systems) can be facilitated by subtle genetic differences.

scholarly journals Breeding ecology and bias in offspring sex ratio in little grassbirds (Megalurus gramineus)

2003 ◽  
Vol 51 (5) ◽  
pp. 505 ◽  
Author(s):  
Rebecca R. McIntosh ◽  
Romke Kats ◽  
Mathew Berg ◽  
Jan Komdeur ◽  
Mark A. Elgar
Keyword(s):  
Sex Ratio ◽  
Breeding Season ◽  
Salt Marshes ◽  
Sex Allocation ◽  
Breeding Ecology ◽  
Offspring Sex Ratio ◽  
Reed Beds ◽  
Primary Sex Ratio ◽  
Sex Ratio Bias ◽  
Offspring Sex

Little grassbirds (Megalurus gramineus) are small, sexually monomorphic passerines that live in reed beds, lignum swamps and salt marshes in southern Australia. The breeding biology and patterns of sex allocation of the little grassbird were investigated over a single breeding season. Our observations of this species in the Edithvale Wetland Reserve revealed a highly male-biased population sex ratio, with some breeding territories containing several additional males. Nevertheless, there was little compelling evidence that little grassbirds breed cooperatively. The growth rates of male and female nestlings were similar and, as predicted by theory, there was no overall primary sex ratio bias. However, the primary sex ratio was female-biased early in the breeding season and became increasingly male-biased later in the breeding season.

Sex determination in Cagle's map turtle: implications for evolution, development, and conservation

1991 ◽  
Vol 69 (10) ◽  
pp. 2693-2696 ◽  
Author(s):  
Thane Wibbels ◽  
Flavius C. Killebrew ◽  
David Crews
Keyword(s):  
North America ◽  
Reproductive Success ◽  
Sex Ratio ◽  
Sex Determination ◽  
Low Temperatures ◽  
River System ◽  
Temperature Dependent ◽  
Interspecific Variations ◽  
Incubation Temperatures ◽  
Pivotal Temperature

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 0.5–1.0 °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).

Intraspecific genome size variation in a turtle (Trachemys scripta) exhibiting temperature-dependent sex determination

1991 ◽  
Vol 69 (9) ◽  
pp. 2306-2310 ◽  
Author(s):  
Samuel F. Lockwood ◽  
Brenden S. Holland ◽  
John W. Bickham ◽  
Brian G. Hanks ◽  
James J. Bull
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Genome Size ◽  
Incubation Temperature ◽  
Size Variation ◽  
Developmental Rate ◽  
Trachemys Scripta ◽  
Temperature Dependent ◽  
Genome Size Variation ◽  
Different Temperatures

Variation in genome size within and among populations of the pond slider, Trachemys scripta, a species with temperature-dependent sex determination, was investigated. Because genome size has been shown to affect developmental rate in various organisms, as does incubation temperature, it was hypothesized that genome size could influence sex determination in species with environmental sex determination. Significant variation in DNA content was found between geographic populations and among clutches. No significant differences in mean genome size were observed among samples incubated at different temperatures or between sexes of turtles hatched at a temperature that yields a mixed sex ratio. Thus, it appears that sex determination in T. scripta is accomplished in the absence of sex-specific and incubation-temperature-specific differences in genome size. Preliminary data from two populations, however, suggest that genome size may be significantly correlated with the threshold incubation temperature at which a mixed sex ratio is produced.

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