Thermolabile Sex Determination Research Articles

Context-dependent thermolability of sex determination in a lacertid lizard with heteromorphic sex chromosomes.

Developmental conditions can profoundly impact key life history traits of the individual. In cases where offspring sex is driven by developmental reaction norms, permanent changes to the phenotype can fundamentally alter life history trajectories. Sex determination mechanisms in reptiles are remarkably diverse, including well-characterised genetic and temperature-dependent sex determination. In rarer, but increasingly more commonly documented cases, sex can also be determined by a combination of the two, with temperature overriding the genetically determined sex. Thus, sex-by-temperature interactions is a mechanism that can be contextually labile, where reaction norms of sex against developmental environment might only be observable under certain conditions. We examine the effects of incubation temperature on hatchling sex in an oviparous lizard with clearly defined heteromorphic sex chromosomes presumed to determine sex solely on a genetic basis. We also test the repeatability of our results by replicating incubation experiments across 3years. We show that warmer temperatures may override chromosomal sex and cause an overproduction of daughters. However, this effect was inconsistent among years, with high temperature only resulting in a daughter-significant bias in one year. Warm-incubated daughters were more efficient at converting yolk into tissue, which would allow for greater resource allocation to other fitness-related processes, such as growth. This suggests that thermolabile sex determination could be a trait under selection. More energy-efficient embryos also produced faster-growing offspring, suggesting that energy utilization patterns of the embryo were maintained into the juvenile stage, which could have important implications for the ontogenetic development and evolution of life histories.

Three dimensions of thermolabile sex determination.

The molecular mechanism of temperature-dependent sex determination (TSD) is a long-standing mystery. How is the thermal signal sensed, captured and transduced to regulate key sex genes? Although there is compelling evidence for pathways via which cells capture the temperature signal, there is no known mechanism by which cells transduce those thermal signals to affect gene expression. Here we propose a novel hypothesis we call 3D-TSD (the three dimensions of thermolabile sex determination). We postulate that the genome has capacity to remodel in response to temperature by changing 3D chromatin conformation, perhaps via temperature-sensitive transcriptional condensates. This could rewire enhancer-promoter interactions to alter the expression of key sex-determining genes. This hypothesis can accommodate monogenic or multigenic thermolabile sex-determining systems, and could be combined with upstream thermal sensing and transduction to the epigenome to commit gonadal fate.

Some Like it Hot: Temperature Selection during the Critical Period of Thermolabile Sex Determination in Pejerrey ( Odontesthes bonariensis )

Introduction: Many fish species have thermolabile sex determination (TSD) and the sex ratios of wild populations may be influenced by the thermal conditions during the reproductive season. The pejerrey (Odontesthes bonariensis) is an Atherinopsid fish that shows a remarkable level of TSD at environmentally relevant temperatures [1]. Thus, gonadal sex is determined between 1 and 5 weeks after hatching and the frequency of males varies from 0% at temperatures below 19°C to 100% at 29°C [2]. As a first step to model the effects of temperature on the sex ratios of wild populations and to clarify the adaptive significance of TSD, we examined the thermal preference of pejerrey larvae during the time of gonadal sex determination and how sex ratios vary under a situation where larvae can freely select the temperature. Methods: Newly hatched pejerrey larvae were stocked in a horizontal thermal gradient consisting of five interconnected aquaria kept at constant temperatures of 17, 20, 23, 26, and 29°C. Larvae were able to move freely through the entire gradient. Similar amounts of live food (Artemia nauplii) were delivered to each aquarium three times a day regardless of the presence of larvae. Larval behavior was monitored 24-hour/day for 5 weeks using overhead cameras and the number of larvae and time spent at each temperature was calculated. Sex ratios were analyzed at the end of the experiments by light histology. Results and Conclusion: The behavioral analysis revealed a preference for high, masculinizing temperatures (26-29°C) and the resulting sex ratios were highly male-biased (80-100%). We also observed a diurnal rhythm of temperature selection, with fish preferring higher temperatures at night compared to daytime. These results provide important clues to understand the ecology of TSD for this species and predict the sex ratios of wild populations as a function of temperature. They could be also useful for modeling the effects of global warming on pejerrey resources.

Fish with thermolabile sex determination (TSD) as models to study brain sex differentiation

As fish are ectothermic animals, water temperature can affect their basic biological processes such as larval development, growth and reproduction. Similar to reptiles, the incubation temperature during early phases of development is capable to modify sex ratios in a large number of fish species. This phenomenon, known as thermolabile sex determination (TSD) was first reported in Menidia menidia, a species belonging to the family Atherinopsidae. Since then, an increasing number of fish have also been found to exhibit TSD. Traditionally, likewise in reptiles, several TSD patterns have been described in fish, however it has been recently postulated that only one, females at low temperatures and males at high temperatures, may represent the “real” or “true” TSD. Many studies regarding the influence of temperature on the final sex ratios have been focused on the expression and activity of gonadal aromatase, the enzyme involved in the conversion of androgens into estrogens and encoded by the cyp19a1a gene. In this regard, teleost fish, may be due to a whole genome duplication event, produce another aromatase enzyme, commonly named brain aromatase, encoded by the cyp19a1b gene. Contrary to what has been described in other vertebrates, fish exhibit very high levels of aromatase activity in the brain and therefore they synthesize high amounts of neuroestrogens. However, its biological significance is still not understood. In addition, the mechanism whereby temperature can induce the development of a testis or an ovary still remains elusive. In this context the present review is aimed to discuss several theories about the possible role of brain aromatase using fish as models. The relevance of brain aromatase and therefore of neuroestrogens as the possible cue for gonadal differentiation is raised. In addition, the possible role of brain aromatase as the way to keep the high levels of neurogenesis in fish is also considered. Several key examples of how teleosts and aromatase regulation can offer more insight into basic mechanisms of TSD are also reviewed.

Characterization and expression profile of the ovarian cytochrome P‐450 aromatase (cyp19A1) gene during thermolabile sex determination in pejerrey, Odontesthes bonariensis

Cytochrome P450 aromatase (cyp19) is an enzyme that catalyzes the conversion of androgens to estrogens and may play a role in temperature-dependent sex determination (TSD) of reptiles, amphibians, and fishes. In this study, the ovarian P450 aromatase form (cyp19A1) of pejerrey Odontesthes bonariensis, a teleost with marked TSD, was cloned and its expression profile evaluated during gonadal differentiation at feminizing (17 degrees C, 100% females), mixed-sex producing (24 and 25 degrees C, 73.3 and 26.7% females, respectively), and masculinizing (29 degrees C, 0% females) temperatures. The deduced cyp19A1 amino acid sequence shared high identity (>77.8%) with that from other teleosts but had low identity (<61.8%) with brain forms (cyp19A2), including that of pejerrey itself. The tissue distribution analysis of cyp19A1 mRNA in adult fish revealed high expression in the ovary. Semi-quantitative reverse transcription polymerase chain reaction analysis of the bodies of larvae revealed that cyp19A1 expression increased before the appearance of the first histological signs of ovarian differentiation at the feminizing temperature but remained low at the masculinizing temperature. The expression levels at mixed-sex producing temperatures were bimodal rather than intermediate, showing low and high modal values similar to those at the feminizing and masculinizing temperatures, respectively. The population percentages of high and low expression levels at intermediate temperatures were proportional to the percentage of females and males, respectively, and high levels were first observed at about the time of sex differentiation of females. These results suggest that cyp19A1 is involved in the process of ovarian formation and possibly also in the TSD of pejerrey.

Patterns of sex ratio response to water temperature during sex determination in honmoroko Gnathopogon caerulescens

The sex ratios of the offspring of males from broods of honmoroko Gnathopogon caerulescens that displayed thermolabile sex determination (TSD), and those from eggs collected from the wild, strongly suggest that the combination of parents plays an important supplementary role in TSD in this species. The proportion of females in all broods from eight pairings of fish captured in the field decreased significantly at 30°C compared to 20°C, and one brood was entirely female at the lower temperature. These results suggest that phenotypic males (XX-males) exist in nature, probably as a result of sex change from genetic females caused by TSD. Sex ratios in relation to water temperature fall into five patterns, two of which seem to result from normal pairings of XX-females and XY-males, and from pairings of XX-males and XX-females with non-thermosensitivity. Two other patterns are thought to result from the same types of pairing, but with thermosensitivity. The last pattern, which shows male bias at both low and high temperature, is not explained only by the combination of genotypic sex determination (XX/XY) and TSD. Fluctuating temperatures close to natural conditions showed little potential to masculinize broods laid in the field between April and early June. However, the sex ratios of fish spawned in early June showed male bias at low and high temperatures. The sex determination mechanism in G. caerulescens may involve the interaction between temperature and sex-determining genetic factors, and the relative importance of each component differs with breeding season.

Gonadotropin-releasing hormone neuronal development during the sensitive period of temperature sex determination in the pejerrey fish, Odontesthes bonariensis

The development of gonadotroping-releasing hormone (GnRH) neurons was studied in relation to the sensitive period of thermolabile sex determination in the pejerrey Odontesthes bonariensis, an atherinid fish from South America. Fish were raised from hatching at three different temperatures: 17 °C (100% females), 24 °C (70% females), and 29 °C (100% males). Three groups of immunoreactive GnRH (ir-GnRH) neurons were identified at the terminal nerve ganglion (TNG), the midbrain tegmentum (MT), and the preoptic area (POA). Immnoreactive GnRH (ir-GnRH) neurons were identified in the TNG at hatching (day 0) and in the MT at day 3 at all the experimental temperatures. In the POA ir-GnRH neurons were identified in the nucleus preopticus periventricularis simultaneously with the first appearance of ir-GnRH fibers in the pituitary on days 11, 14, and 17 for larvae kept at 29, 24, and 17 °C, respectively. The number of ir-GnRH neurons in the TNG did not show any statistical difference between temperatures. The number of ir-GnRH neurons in the MT increased in number during the experiment for larvae kept at 17 and 24 °C but decreased between days 17 and 31 in larvae kept at 29 °C. The number of ir-GnRH neurons in the POA increased during development with a peak at day 28 for all temperatures studied and the magnitude of this peak showed a correlation with incubation temperature. These results reinforce the notion that the hypothalamus–pituitary–gonadal axis is active during sex determination in pejerrey suggesting a possible role of the central nervous system and GnRH in this process. It is also suggested that GnRH neurons located in the preoptic area might be the physiological transducers of temperature during the temperature sensitive period in this species.

Potential use of otolith microchemistry for field studies of temperature-dependent sex determination and gonadal degeneration in fish

This paper describes a novel approach to study the expression of temperature-related reproductive phenomena such as thermolabile sex determination (TSD) and heat-induced germ cell loss in wild fish populations. The proposed approach is based on the reconstruction of the past thermal history of individual fish through the microchemical analysis of the otoliths (mineralized structures responsible for the sense of balance). As an example, we outline the preliminary results of an investigation on the natural occurrence of TSD in pejerrey Odontesthes bonariensis, an atherinid fish in which all-female to all-male populations can be produced by experimental manipulation of the rearing temperature during the critical time of sex differentiation, from Lake Kasumigaura, Japan.

Ontogenetic variations of thermal optimum for growth, and its implication on thermolabile sex determination in blue tilapia

Ontogenetic variations of thermal optimum for growth, and its implication on thermolabile sex determination in blue tilapia

Ontogenetic variations of thermal optimum for growth, and its implication on thermolabile sex determination in blue tilapia

Knowledge of how the optimum temperature for growth (T° opt ) varies during ontogeny, and how close it is to the temperatures that induce phenotypic masculinization is fundamental to the understanding of the evolution of thermolabile sex determinism (TSD) in fishes. In blue tilapia Oreochromis aureus, T° opt is 32.6° C at the start of exogenous feeding (10 mg fish) and it decreases by c. 1° C each time that the fish body mass increases by an order of magnitude. Temperatures <35° C are not sufficient to induce complete phenotypic masculinization. Based on a multiple-regression model (r 2 =0.938) plotting growth against body mass and water temperature, genotypically female tilapia living at high temperatures during the thermosensitive period (21-28 days) and being reversed into phenotypic males would incur an initial growth disadvantage over fish living at T° opt , but not over those living at slightly colder temperatures (27-29° C). This initial disadvantage would be later compensated for by faster growth because of between-sex growth dimorphism to the detriment of phenotypic females. These arguments suggest that there is no definite pressure against the selection of TSD in blue tilapia and probably other Oreochromis spp.

Ontogenetic variations of thermal optimum for growth, and its implication on thermolabile sex determination in blue tilapia

Knowledge of how the optimum temperature for growth (T°opt) varies during ontogeny, and how close it is to the temperatures that induce phenotypic masculinization is fundamental to the understanding of the evolution of thermolabile sex determinism (TSD) in fishes. In blue tilapia Oreochromis aureus, T°opt is 32·6° C at the start of exogenous feeding (10mg fish) and it decreases by c. 1° C each time that the fish body mass increases by an order of magnitude. Temperatures &lt;35° C are not sufficient to induce complete phenotypic masculinization. Based on a multiple‐regression model (r2=0·938) plotting growth against body mass and water temperature, genotypically female tilapia living at high temperatures during the thermosensitive period (21–28 days) and being reversed into phenotypic males would incur an initial growth disadvantage over fish living at T°opt, but not over those living at slightly colder temperatures (27–29° C). This initial disadvantage would be later compensated for by faster growth because of between‐sex growth dimorphism to the detriment of phenotypic females. These arguments suggest that there is no definite pressure against the selection of TSD in blue tilapia and probably other Oreochromis spp.

Thermal thresholds and critical period of thermolabile sex determination in two atherinid fishes,Odontesthes bonariensis andPatagonina hatcheri

Atherinidae is a family of fishes known to include at least three species with documented thermolabile sex determination. In Odontesthes bonariensis, fish exposed to about 17°C from hatching to juvenile stage become all-female, whereas groups exposed to about 25°C become male-biased. In contrast, sex in another atherinid, Patagonina hatcheri, appears to be under stronger genotypic control because the sex ratios are always balanced (1:1) within the same range of temperatures. The main purpose of this study was to determine the effect of temperature on the sex ratios of both species over their full range of viable temperatures. In addition, we determined the critical time of thermolabile sex determination in O. Bonariensis at female- and male-forming temperatures. O. Bonariensis larvae survived at temperatures between 13 and 29°C, but growth was negligible at 13 and 15°C. The proportions of females were 100% at 13–19°C, 95% at 21°C, 81.2% at 23°C, 29.4% at 25°C, 10% at 27°C, and 0% at 29°C. These results indicate a gradual transition from female- to male-forming temperatures evenly spread over the range of viable temperatures and hence the absence of any marked thermal threshold for thermolabile/genotypic control of sex; they also suggest weak or no genotypic control of sex in this species. In addition, prolonged exposure to 29°C caused disappearance of germ cells. The critical time of thermolabile sex determination in O. Bonariensis was estimated to be 3–5 wk, 2–4 wk, and 1–4 wk after hatching at 17, 19, and 27°C, respectively. Survival of P. Hatcheriwas limited to temperatures between 13 and 27°C (only 8.7% at the latter temperature) with slow but steady growth at 13 and 15°C. The proportions of females were 88.9 and 89.5% at 13 and 15°C, respectively, about 50% at temperatures between 17 and 23°C, and 30.8% at 25°C, hence, showing one clear threshold for thermolabile/genotypic control of sex at 15–17°C and possibly another at or around 25°C. These results confirmed that gonadal sex in this species is under genotypic control at intermediate temperatures but also showed that this control can be overridden at low (and possibly also at high) temperatures. J. Exp. Zool. 278:167–177, 1997.© 1997 Wiley-Liss, Inc.

Thermal thresholds and critical period of thermolabile sex determination in two atherinid fishes, Odontesthes bonariensis and Patagonina hatcheri

Thermal thresholds and critical period of thermolabile sex determination in two atherinid fishes, Odontesthes bonariensis and Patagonina hatcheri

Temperature effects on sex differentiation of two South American atherinids, Odontesthes argentinensis and Patagonina hatcheri

The present study investigated the effects of water temperature (18, 21, and 25 °C) on the histological process of gonadal sex differentiation of two commercially important atherinid fishes from South America, Odontesthes argentinensis (sea pejerrey) and Patagonina hatcheri (Patagonian freshwater pejerrey). In both species, female gonadal sex differentiation began with the formation of lateral stromal cell outgrowths and the appearance of meiotic oocytes. The male gonads remained quiescent for about twice as long as the female gonads, with differentiation becoming evident by the formation of the main sperm duct and of cysts of germ cells at the periphery of the gonads. Meiosis in males occurred relatively long after somatic differentiation of the testis. The ovaries of O. argentinensis differentiated at 28 days (20.3 mm) at 25 °C, 42 days (24.0 mm) at 21 °C, and 56 days (23.8 mm) at 18 °C. In the males, differentiation was observed at 98 days at 25 and 21 °C (39.4 mm and 40.4 mm, respectively), but at 112 days under 18 °C (40.7 mm). In P. hatcheri, differentiation of females occurred at 21 days (17.8 mm) at 25 °C, 28 days (20.8 mm) at 21 °C, and 35 days (23.2 mm) at 18 °C. Male differentiation became evident at 56 days under 25 and 21 °C (30.8 and 32.7 mm, respectively), and at 70 days (37.7 mm) at 18 °C. The sex-ratios of O. argentinensis reared at 18 or 21 °C were female-biased whereas those at 25 °C were not; groups reared at 18 °C had significantly more females than groups from the same progeny reared at 25 °C. In contrast, the sex-ratios in all groups of P. hatcheri did not differ significantly from 1:1 and no significant differences were found between groups of the same progeny reared at different temperatures. These results suggest the occurrence of thermolabile sex determination (TSD) in O. argentinensis whereas in P. hatcheri gonadal sex appears to be strongly genetically determined.

Evidence of thermolabile sex determination in pejerrey*

Temperature regimes of 17 ± 1°C and 21 ±1°C early in development of pejerrey Odontesthes bonariensis produced nearly all females, whereas at 25 ± 1°C variable, sometimes male‐biased sex‐ratios were obtained. The critical period of thermolabile sex determination seemed to occur between 25 and 50 days post‐hatch (about 11 and 21 mm s.i.) at low temperatures (17–20°C) and between 0 and 25 days (about 7 and 15 mm) at high temperatures (22–25°C). The likelihood of expression of temperature‐dependent sex determination in natural populations and the possible adaptive significance of environmental sex determination in pejerrey are discussed.