NO SEASONAL SEX-RATIO SHIFT DESPITE SEX-SPECIFIC FITNESS RETURNS OF HATCHING DATE IN A LIZARD WITH 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.

Download Full-text

Female-biased sex ratio in adults of the turtle Emys orbicularis at the northern limit of its distribution in France: a probable consequence of interaction of temperature with genotypic sex determination

Canadian Journal of Zoology ◽

10.1139/z89-182 ◽

1989 ◽

Vol 67 (5) ◽

pp. 1279-1284 ◽

Cited By ~ 17

Author(s):

J. Servan ◽

P. Zaborski ◽

M. Dorizzi ◽

C. Pieau

Keyword(s):

Sex Ratio ◽

Sex Determination ◽

Emys Orbicularis ◽

Gonad Differentiation ◽

Adult Sex Ratio ◽

Probable Consequence ◽

Genotypic Sex Determination ◽

Female Genotype ◽

Biased Sex Ratio ◽

Female Bias

Adult sex ratio in the turtle Emys orbicularis was determined in populations from seven ponds in Brenne (Indre, France). In all populations, the sex ratio was biased toward females. Among 290 captured animals, the male:female ratio was close to 0.5. Among different demographic factors that could affect the adult sex ratio, the most influential was probably the sex ratio of hatchlings. In Emys orbicularis, a ZZ male/ZW female system of genotypic sex determination has been postulated. Moreover, gonad differentiation is dependent on temperature and sex-reversed individuals can occur. To evaluate the importance of sex reversal among adult females, the blood of 78 animals was typed for the serologically detectable H-Y antigen, used as a tool to identify sexual genotype. In 73 of them, the H-Y phenotype was positive, conforming with female genotype, but in the other 5 females, it was negative (as in genotypic males), revealing that the sexual phenotype of these animals had been inverted. As the percentage of these sex-reversed genotypic males is low, the influence of temperature would appear not to be the sole cause of the observed unbalanced sex ratio. The female bias can be partly explained by the interaction of temperature with the ZZ/ZW system of genotypic sex determination. Indeed, in this system, sexual inversion under the influence of an epigenetic factor increases the ratio of genotypic females (ZW and WW) in the progeny.

Download Full-text

Sex-ratio bias across populations of a freshwater turtle (Testudines : Chelidae) with genotypic sex determination

Wildlife Research ◽

10.1071/wr06047 ◽

2006 ◽

Vol 33 (6) ◽

pp. 475 ◽

Cited By ~ 6

Author(s):

Arthur Georges ◽

Fiorenzo Guarino ◽

Melissa White

Keyword(s):

Sex Ratio ◽

Sex Determination ◽

Sex Ratios ◽

Single Species ◽

Freshwater Turtle ◽

Freshwater Turtles ◽

Ratio Data ◽

Adult Sex Ratio ◽

Genotypic Sex Determination ◽

The Impact

Adult sex ratios vary considerably among populations of single species and across years, but the best evidence is drawn from species with temperature-dependent sex determination. It is difficult to disentangle the effects of bias in the production of the sexes and the effects of a range of other factors contributing to biased adult sex ratios. In this paper, we survey sex ratios across populations of a species constrained to produce 1 : 1 offspring sex ratios by genotypic sex determination and show considerable variation in adult sex ratios. Raw adult sex ratios of Emydura macquarii emmottii were significantly biased in nine of the 11 populations examined. In all but one case, the bias was strongly in favour of males. Part of the bias in sex ratio was attributed to the differing ages of maturity of males and females – males mature younger than females – which leads to more male cohorts being included in the calculations of sex ratio than female cohorts. However, correcting for this effect brought the sex ratios of the populations closer to parity, as expected, and accounted for an overall 62% of the male surplus evident in the adult sex ratio. Even so, it was insufficient to explain the strong male bias (1.2–2.9) in five of the nine populations initially showing such bias. This provides support to those who advise caution in interpreting adult sex ratio data for freshwater turtles in the context of demography, sex allocation or evaluating the impact of climate change.

Download Full-text

Cytogenetic Analysis of the Asian Box Turtles of the Genus Cuora (Testudines, Geoemydidae)

Genes ◽

10.3390/genes12020156 ◽

2021 ◽

Vol 12 (2) ◽

pp. 156

Author(s):

Lorenzo Clemente ◽

Sofia Mazzoleni ◽

Eleonora Pensabene ◽

Tomáš Protiva ◽

Philipp Wagner ◽

...

Keyword(s):

Sex Determination ◽

Sex Chromosomes ◽

Wide Distribution ◽

Iucn Red List ◽

Telomeric Repeats ◽

Rdna Loci ◽

Box Turtles ◽

Genotypic Sex Determination ◽

Poorly Differentiated ◽

Almost All

The Asian box turtle genus Cuora currently comprises 13 species with a wide distribution in Southeast Asia, including China and the islands of Indonesia and Philippines. The populations of these species are rapidly declining due to human pressure, including pollution, habitat loss, and harvesting for food consumption. Notably, the IUCN Red List identifies almost all species of the genus Cuora as Endangered (EN) or Critically Endangered (CR). In this study, we explore the karyotypes of 10 Cuora species with conventional (Giemsa staining, C-banding, karyogram reconstruction) and molecular cytogenetic methods (in situ hybridization with probes for rDNA loci and telomeric repeats). Our study reveals a diploid chromosome number of 2n = 52 chromosomes in all studied species, with karyotypes of similar chromosomal morphology. In all examined species, rDNA loci are detected at a single medium-sized chromosome pair and the telomeric repeats are restricted to the expected terminal position across all chromosomes. In contrast to a previous report, sex chromosomes are neither detected in Cuoragalbinifrons nor in any other species. Therefore, we assume that these turtles have either environmental sex determination or genotypic sex determination with poorly differentiated sex chromosomes. The conservation of genome organization could explain the numerous observed cases of interspecific hybridization both within the genus Cuora and across geoemydid turtles.

Download Full-text

Sex Ratios in a Warming World: Thermal Effects on Sex-Biased Survival, Sex Determination, and Sex Reversal

Journal of Heredity ◽

10.1093/jhered/esab006 ◽

2021 ◽

Vol 112 (2) ◽

pp. 155-164

Author(s):

Suzanne Edmands

Keyword(s):

High Temperature ◽

Sex Ratio ◽

Sex Determination ◽

Heat Tolerance ◽

Sex Ratios ◽

Sex Reversal ◽

Survival Sex ◽

Ratio Distortion ◽

Warming World ◽

Sex Ratio Distortion

Abstract Rising global temperatures threaten to disrupt population sex ratios, which can in turn cause mate shortages, reduce population growth and adaptive potential, and increase extinction risk, particularly when ratios are male biased. Sex ratio distortion can then have cascading effects across other species and even ecosystems. Our understanding of the problem is limited by how often studies measure temperature effects in both sexes. To address this, the current review surveyed 194 published studies of heat tolerance, finding that the majority did not even mention the sex of the individuals used, with <10% reporting results for males and females separately. Although the data are incomplete, this review assessed phylogenetic patterns of thermally induced sex ratio bias for 3 different mechanisms: sex-biased heat tolerance, temperature-dependent sex determination (TSD), and temperature-induced sex reversal. For sex-biased heat tolerance, documented examples span a large taxonomic range including arthropods, chordates, protists, and plants. Here, superior heat tolerance is more common in females than males, but the direction of tolerance appears to be phylogenetically fluid, perhaps due to the large number of contributing factors. For TSD, well-documented examples are limited to reptiles, where high temperature usually favors females, and fishes, where high temperature consistently favors males. For temperature-induced sex reversal, unambiguous cases are again limited to vertebrates, and high temperature usually favors males in fishes and amphibians, with mixed effects in reptiles. There is urgent need for further work on the full taxonomic extent of temperature-induced sex ratio distortion, including joint effects of the multiple contributing mechanisms.

Download Full-text

Sex Determination and Sex Ratio Patterns in Parasitic Hymenoptera

Evolution and Diversity of Sex Ratio ◽

10.1007/978-1-4684-1402-8_14 ◽

1993 ◽

pp. 442-476 ◽

Cited By ~ 26

Author(s):

Robert F. Luck ◽

Richard Stouthamer ◽

Leonard P. Nunney

Keyword(s):

Sex Ratio ◽

Sex Determination ◽

Parasitic Hymenoptera

Download Full-text

Analysis of the sex ratio in Bradysia matogrossensis (Diptera, Sciaridae)

Genetics and Molecular Biology ◽

10.1590/s1415-47572000000100018 ◽

2000 ◽

Vol 23 (1) ◽

pp. 97-103 ◽

Cited By ~ 4

Author(s):

Lincoln S. Rocha ◽

André Luiz P. Perondini

Keyword(s):

Sex Ratio ◽

Sex Determination ◽

X Chromosome ◽

Control Mechanism ◽

Sex Ratios ◽

Laboratory Strain ◽

Chromosome Elimination ◽

Common Control ◽

Males And Females ◽

Successive Generations

In sciarid flies, the control of sex determination and of the progeny sex ratio is exercised by the parental females, and is based on differential X-chromosome elimination in the initial stages of embryogenesis. In some species, the females produce unisexual progenies (monogenic females) while in others, the progenies consist of males and females (digenic females). The sex ratio of bisexual progenies is variable, and departs considerably from 1:1. Bradysia matogrossensis shows both monogenic and digenic reproduction. In a recently established laboratory strain of this species, 15% of the females were digenic, 10% produced only females, 13% produced only males, and 62% produced progenies with one predominant sex (33% predominantly of female and 29% predominantly male progenies). These progeny sex ratios were maintained in successive generations. Females from female-skewed progenies yielded female- and male-producing daughters in a 1:1 ratio. In contrast, daughters of females from male-skewed progenies produce bisexual or male-skewed progenies. The X-chromosome of B. matogrossensis shows no inversion or other gross aberration. These results suggest that the control of the progeny sex ratio (or differential X-chromosome elimination) involves more than one locus or, at least, more than one pair of alleles. The data also suggest that, in sciarid flies, monogeny and digeny may share a common control mechanism.

Download Full-text