scholarly journals Evolution of the gene network underlying gonadogenesis in turtles with temperature-dependent and genotypic sex determination

2008 ◽  
Vol 48 (4) ◽  
pp. 476-485 ◽  
Author(s):  
N. Valenzuela
Keyword(s):  
Sex Determination ◽  
Gene Network ◽  
Temperature Dependent ◽  
Genotypic Sex Determination

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 Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard

2007 ◽  
Vol 4 (2) ◽  
pp. 176-178 ◽  
Author(s):  
Rajkumar S Radder ◽  
Alexander E Quinn ◽  
Arthur Georges ◽  
Stephen D Sarre ◽  
Richard Shine
Keyword(s):  
Sex Determination ◽  
Female Offspring ◽  
Temperature Dependent ◽  
Sex Marker ◽  
Heteromorphic Sex Chromosomes ◽  
Offspring Sex ◽  
Current Classification ◽  
Genotypic Sex Determination ◽  
Incubation Temperatures ◽  
Bassiana Duperreyi

An individual's sex depends upon its genes (genotypic sex determination or GSD) in birds and mammals, but reptiles are more complex: some species have GSD whereas in others, nest temperatures determine offspring sex (temperature-dependent sex determination). Previous studies suggested that montane scincid lizards ( Bassiana duperreyi , Scincidae) possess both of these systems simultaneously: offspring sex is determined by heteromorphic sex chromosomes (XX–XY system) in most natural nests, but sex ratio shifts suggest that temperatures override chromosomal sex in cool nests to generate phenotypically male offspring even from XX eggs. We now provide direct evidence that incubation temperatures can sex-reverse genotypically female offspring, using a DNA sex marker. Application of exogenous hormone to eggs also can sex-reverse offspring (oestradiol application produces XY as well as XX females). In conjunction with recent work on a distantly related lizard taxon, our study challenges the notion of a fundamental dichotomy between genetic and thermally determined sex determination, and hence the validity of current classification schemes for sex-determining systems in reptiles.

scholarly journals Genotypic Males Play an Important Role in the Creation of Genetic Diversity in Gynogenetic Gibel Carp

2021 ◽  
Vol 12 ◽  
Author(s):  
Xin Zhao ◽  
Zhi Li ◽  
Miao Ding ◽  
Tao Wang ◽  
Ming-Tao Wang ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Sex Determination ◽  
Common Carp ◽  
Evolutionary Process ◽  
Gibel Carp ◽  
Temperature Dependent ◽  
Muller's Ratchet ◽  
Genotypic Sex Determination ◽  
Muller’S Ratchet ◽  
The Creation

Unisexual lineages are commonly considered to be short-lived in the evolutionary process as accumulation of deleterious mutations stated by Muller’s ratchet. However, the gynogenetic hexaploid gibel carp (Carassius gibelio) with existence over 0.5 million years has wider ecological distribution and higher genetic diversity than its sexual progenitors, which provides an ideal model to investigate the underlying mechanisms on countering Muller’s ratchet in unisexual taxa. Unlike other unisexual lineages, the wild populations of gibel carp contain rare and variable proportions of males (1–26%), which are determined via two strategies including genotypic sex determination and temperature-dependent sex determination. Here, we used a maternal gibel carp from strain F to be mated with a genotypic male from strain A+, a temperature-dependent male from strain A+, and a male from another species common carp (Cyprinus carpio), respectively. When the maternal individual was mated with the genotypic male, a variant of gynogenesis was initiated, along with male occurrence, accumulation of microchromosomes, and creation of genetic diversity in the offspring. When the maternal individual was mated with the temperature-dependent male and common carp, typical gynogenesis was initiated that all the offspring showed the same genetic information as the maternal individual. Subsequently, we found out that the genotypic male nucleus swelled and contacted with the female nucleus after fertilization although it was extruded from the female nucleus eventually, which might be associated with the genetic variation in the offspring. These results reveal that genotypic males play an important role in the creation of genetic diversity in gynogenetic gibel carp, which provides insights into the evolution of unisexual reproduction.

scholarly journals Molecular evolution of Dmrt1 accompanies change of sex-determining mechanisms in reptilia

2014 ◽  
Vol 10 (12) ◽  
pp. 20140809 ◽  
Author(s):  
Daniel E. Janes ◽  
Christopher L. Organ ◽  
Rami Stiglec ◽  
Denis O'Meally ◽  
Stephen D. Sarre ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Molecular Evolution ◽  
Sex Determination ◽  
Sex Differentiation ◽  
Evolution Of Sex ◽  
Temperature Dependent ◽  
Exon 2 ◽  
Ancestral Condition ◽  
Genotypic Sex Determination

In reptiles, sex-determining mechanisms have evolved repeatedly and reversibly between genotypic and temperature-dependent sex determination. The gene Dmrt1 directs male determination in chicken (and presumably other birds), and regulates sex differentiation in animals as distantly related as fruit flies, nematodes and humans. Here, we show a consistent molecular difference in Dmrt1 between reptiles with genotypic and temperature-dependent sex determination. Among 34 non-avian reptiles, a convergently evolved pair of amino acids encoded by sequence within exon 2 near the DM-binding domain of Dmrt1 distinguishes species with either type of sex determination. We suggest that this amino acid shift accompanied the evolution of genotypic sex determination from an ancestral condition of temperature-dependent sex determination at least three times among reptiles, as evident in turtles, birds and squamates. This novel hypothesis describes the evolution of sex-determining mechanisms as turnover events accompanied by one or two small mutations.

scholarly journals Oestrogens and temperature-dependent sex determination in reptiles: all is in the gonads

2004 ◽  
Vol 181 (3) ◽  
pp. 367-377 ◽  
Author(s):  
C Pieau ◽  
M Dorizzi
Keyword(s):  
Sex Determination ◽  
Incubation Temperature ◽  
Sex Differentiation ◽  
Future Research ◽  
Aromatase Activity ◽  
Temperature Dependent ◽  
Aromatase Gene ◽  
Ovarian Differentiation ◽  
Genotypic Sex Determination ◽  
Thermosensitive Period

In many species of oviparous reptiles, the first steps of gonadal sex differentiation depend on the incubation temperature of the eggs. Feminization of gonads by exogenous oestrogens at a male-producing temperature and masculinization of gonads by antioestrogens and aromatase inhibitors at a female-producing temperature have irrefutably demonstrated the involvement of oestrogens in ovarian differentiation. Nevertheless, several studies performed on the entire gonad/adrenal/mesonephros complex failed to find differences between male- and female-producing temperatures in oestrogen content, aromatase activity and aromatase gene expression during the thermosensitive period for sex determination. Thus, the key role of aromatase and oestrogens in the first steps of ovarian differentiation has been questioned, and extragonadal organs or tissues, such as adrenal, mesonephros, brain or yolk, were considered as possible targets of temperature and sources of the oestrogens acting on gonadal sex differentiation.In disagreement with this view, experiments and assays carried out on the gonads alone, i.e. separated from the adrenal/mesonephros, provide evidence that the gonads themselves respond to temperature shifts by modifying their sexual differentiation and are the site of aromatase activity and oestrogen synthesis during the thermosensitive period. Oestrogens act locally on both the cortical and the medullary part of the gonad to direct ovarian differentiation. We have concluded that there is no objective reason to search for the implication of other organs in the phenomenon of temperature-dependent sex determination in reptiles. From the comparison with data obtained in other vertebrates, we propose two main directions for future research: to examine how transcription of the aromatase gene is regulated and to identify molecular and cellular targets of oestrogens in gonads during sex differentiation, in species with strict genotypic sex determination and species with temperature-dependent sex determination.

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