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 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.

scholarly journals Thyroid hormone modulates offspring sex ratio in a turtle with temperature-dependent sex determination

2016 ◽  
Vol 283 (1841) ◽  
pp. 20161206 ◽  
Author(s):  
Bao-Jun Sun ◽  
Teng Li ◽  
Yi Mu ◽  
Jessica K. McGlashan ◽  
Arthur Georges ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Sex Ratio ◽  
Sex Determination ◽  
Sex Differentiation ◽  
Developmental Rate ◽  
Temperature Dependent ◽  
Gene Encoding ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Underlying Mechanisms

The adaptive significance of temperature-dependent sex determination (TSD) has attracted a great deal of research, but the underlying mechanisms by which temperature determines the sex of a developing embryo remain poorly understood. Here, we manipulated the level of a thyroid hormone (TH), triiodothyronine (T 3 ), during embryonic development (by adding excess T 3 to the eggs of the red-eared slider turtle Trachemys scripta , a reptile with TSD), to test two competing hypotheses on the proximate basis for TSD: the developmental rate hypothesis versus the hormone hypothesis . Exogenous TH accelerated embryonic heart rate (and hence metabolic rate), developmental rate, and rates of early post-hatching growth. More importantly, hyperthyroid conditions depressed expression of Cyp19a1 (the gene encoding for aromatase) and levels of oestradiol, and induced more male offspring. This result is contrary to the direction of sex-ratio shift predicted by the developmental rate hypothesis , but consistent with that predicted by the hormone hypothesis . Our results suggest an important role for THs in regulating sex steroid hormones, and therefore, in affecting gonadal sex differentiation in TSD reptiles. Our study has implications for the conservation of TSD reptiles in the context of global change because environmental contaminants may disrupt the activity of THs, and thereby affect offspring sex in TSD reptiles.

Skewed Sex-Ratio, Monogeny, and Maternal Sex Determination in Two Geographical Populations of Asellus Aquaticus (L., 1758) (Isopoda)

Crustaceana ◽  
1996 ◽  
Vol 69 (4) ◽  
pp. 455-475 ◽  
Author(s):  
Giovanna Vitagliano ◽  
Enzo Marchetti ◽  
Eleonora Vitagliano
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
The Other ◽  
Italian Population ◽  
Asellus Aquaticus ◽  
Offspring Sex Ratio ◽  
New Born ◽  
Offspring Sex ◽  
Geographical Populations ◽  
Biased Sex Ratio

AbstractFor the great majority of the amphipods and isopods a biased sex ratio is attributed to photoperiod or to micro-organisms present in the cytoplasm of the oocytes. Since monogenous pairs are found in orders and species phylogenetically very far from each other, in order to try and clarify this phenomenon, two geographical populations of Asellus aquaticus (Isopoda) were collected in the Netherlands and in Italy, where the duration of the cold season and the photoperiods are very different. From these parental (P) populations, 200 females and 200 males per population were randomly subsampled and bred under standard conditions of temperature and nutrition. One half of each P generation was subjected to 18 hours light per day, the other to 14 hours light per day. New-born of each pair (laboratory F1) were grown up to differentiation of external sexual characters under the same photoperiod experienced by the parents. Also, hybrid F1 generation, born from mating between the two populations, was conceived in both photoperiods, but, after birth, one half of the new-born was maintained in the same photoperiod in which they were conceived, the other half was grown under the other photoperiod. No significant difference between the sex ratios was found in the two photoperiods, neither between Italian nor between Dutch Asellus. The sex ratio of Dutch F1 is female biased, while it is male biased in Italian Asellus. The female- or male-biased sex ratio can be ascribed to the high proportion of monogenous pairs in which offspring sex ratio is significantly biased towards females (in the Dutch population) and/or in which offspring sex ratio is significantly biased towards males (in the Italian population). On the basis of these results we can rule out the influence of photoperiod in sex determination for this species. The results shown by the hybrids suggest some form of maternal inheritance. In fact, the hybrids' sex ratio as indeed the frequency of pairs breeding one sex alone, was skewed towards the same sex for which the maternal population showed a bias. We therefore consider the possibility of sex determination associated with a cytoplasmic factor (a mitochondrial DNA?), which would inactivate only one of the two sets of genes governing sex determination.

scholarly journals Transgenerational epigenetic sex determination: Environment experienced by female fish affects offspring sex ratio

2021 ◽  
Vol 277 ◽  
pp. 116864
Author(s):  
Fabien Pierron ◽  
Sophie Lorioux ◽  
Débora Héroin ◽  
Guillemine Daffe ◽  
Bruno Etcheverria ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Female Fish ◽  
Offspring Sex Ratio ◽  
Offspring Sex

scholarly journals The XX-XY Sex-determination System in Oryzias luzonensis and O. mekongensis Revealed by the Sex Ratio of the Progeny of Sex-reversed Fish

2004 ◽  
Vol 21 (10) ◽  
pp. 1015-1018 ◽  
Author(s):  
Satoshi Hamaguchi ◽  
Yota Toyazaki ◽  
Ai Shinomiya ◽  
Mitsuru Sakaizumi
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Determination System ◽  
Sex Determination System

scholarly journals Environmental stress maintains trioecy in nematode worms

2019 ◽  
Author(s):  
Ashlyn G. Anderson ◽  
Louis T. Bubrig ◽  
Janna L. Fierst
Keyword(s):  
Life History ◽  
Sex Determination ◽  
Environmental Conditions ◽  
Natural Habitat ◽  
Population Level ◽  
Evolutionary Transitions ◽  
Sexual Systems ◽  
Determination System ◽  
Stable Maintenance ◽  
Sex Determination System

AbstractSex is determined by chromosomes in mammals but it can be influenced by the environment in many worms, crustaceans and vertebrates. Despite this, there is little understanding of the relationship between ecology and the evolution of sexual systems. The nematode Auanema freiburgensis has a unique sex determination system in which individuals carrying one X chromosome develop into males while XX individuals develop into females in stress-free environments and self-fertile hermaphrodites in stressful environments. Theory predicts that trioecious populations with coexisting males, females and hermaphrodites should be unstable intermediates in evolutionary transitions between mating systems. In this article we study a mathematical model of reproductive evolution based on the unique life history and sex determination of A. freiburgensis. We develop the model in two scenarios, one where the relative production of hermaphrodites and females is entirely dependent on the environment and one based on empirical measurements of a population that displays incomplete, ‘leaky’ environmental dependence. In the first scenario environmental conditions can push the population along an evolutionary continuum and result in the stable maintenance of multiple reproductive systems. The second ‘leaky’ scenario results in the maintenance of three sexes for all environmental conditions. Theoretical investigations of reproductive system transitions have focused on the evolutionary costs and benefits of sex. Here, we show that the flexible sex determination system of A. freiburgensis may contribute to population-level resilience in the microscopic nematode’s patchy, ephemeral natural habitat. Our results demonstrate that life history, ecology and environment may play defining roles in the evolution of sexual systems.

scholarly journals Meiotic drive and sex determination: molecular and cytological mechanisms of sex ratio adjustment in birds

2007 ◽  
Vol 363 (1497) ◽  
pp. 1675-1686 ◽  
Author(s):  
Joanna Rutkowska ◽  
Alexander V Badyaev
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Sex Chromosomes ◽  
Sex Ratios ◽  
Relative Fitness ◽  
Compensatory Mechanisms ◽  
Offspring Sex Ratio ◽  
Epigenetic Effects ◽  
Offspring Sex ◽  
Sex Ratio Adjustment

Differences in relative fitness of male and female offspring across ecological and social environments should favour the evolution of sex-determining mechanisms that enable adjustment of brood sex ratio to the context of breeding. Despite the expectation that genetic sex determination should not produce consistent bias in primary sex ratios, extensive and adaptive modifications of offspring sex ratio in relation to social and physiological conditions during reproduction are often documented. Such discordance emphasizes the need for empirical investigation of the proximate mechanisms for modifying primary sex ratios, and suggests epigenetic effects on sex-determining mechanisms as the most likely candidates. Birds, in particular, are thought to have an unusually direct opportunity to modify offspring sex ratio because avian females are heterogametic and because the sex-determining division in avian meiosis occurs prior to ovulation and fertilization. However, despite evidence of strong epigenetic effects on sex determination in pre-ovulatory avian oocytes, the mechanisms behind such effects remain elusive. Our review of molecular and cytological mechanisms of avian meiosis uncovers a multitude of potential targets for selection on biased segregation of sex chromosomes, which may reflect the diversity of mechanisms and levels on which such selection operates in birds. Our findings indicate that pronounced differences between sex chromosomes in size, shape, size of protein bodies, alignment at the meiotic plate, microtubule attachment and epigenetic markings should commonly produce biased segregation of sex chromosomes as the default state, with secondary evolution of compensatory mechanisms necessary to maintain unbiased meiosis. We suggest that it is the epigenetic effects that modify such compensatory mechanisms that enable context-dependent and precise adjustment of primary sex ratio in birds. Furthermore, we highlight the features of avian meiosis that can be influenced by maternal hormones in response to environmental stimuli and may account for the precise and adaptive patterns of offspring sex ratio adjustment observed in some species.

Offspring sex ratio in moose Alces alces in relation to paternal age: an experiment

2004 ◽  
Vol 10 (1) ◽  
pp. 51-57 ◽  
Author(s):  
Bernt-Erik Sæther ◽  
Erling J. Solberg ◽  
Morten Heim ◽  
John E. Stacy ◽  
Kjetill S. Jakobsen ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Alces Alces ◽  
Paternal Age ◽  
Offspring Sex Ratio ◽  
Offspring Sex
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