Paul, which is stronger than strong

The bearded agama Pogona vitticeps , which has been erased in recent years, is known for the fact that the floor of the lizard depends on the temperature at which the egg developed. The bearded agama, like most scaly reptiles, has a pair of heteromorphic sex chromosomes: ZZ in males and ZW in females, they determine the sex of lizards at a wide temperature range. However, if the sand in which the eggs lie, warms up above 32 ºС, the floor reversal occurs in male embryos. Farroding females with a male set of chromosomes develop from them.

Thus, agama is virtually three sexes: genotypic and phenotypic males (ZZM), also called concordant, since their genotype and phenotype coincide, concordant females (ZW) and phenotypic females, but genetic males (ZZF) that appeared as a result of the reversal of the floor.

The effect of temperature on the determination of the floor is also described in other types of reptiles. This phenomenon would probably have remained among the biological enthusiasm if it were not for the research of Australian scientists under the leadership of Professor Kanberra University of Arthur George. For the first time, they examined the gender’s reversal in laboratory, but in natural conditions - P. Vitticeps live in the internal regions of Australia. Having collected data on 131 wild lizards, they found that the share of ZZF is growing from year to year. In 2003, it was 6.7%, in 2004-13.6%, and in 2011-22.2%[1]. DNA sequences were analyzed in females, and the absence of W-chromosomes was confirmed cytogenetically. Due to the small selection of differences, the differences cannot be considered reliable, but the trend is evident. Moreover, females with gender reversal are more fertile than concordant: in a year, such agama lays on average 47.3 eggs, and ZW - only 24.5.

Scientists continued the study in the laboratory. They crossed the ZZF and ZW females and analyzed the ratio of floors in the offspring. In normal females at temperatures from 22 to 32 ºС sons and daughters, he hatches approximately equally, their floor is determined genetically. With a further increase in temperature, the floor determination system switches from chromosomal to temperature, males with gender reverse appear in the offspring; And at 36 ºС, the eggs are removed almost exclusively by females.

In the offspring of ZZF, the genetic determination of the floor is impossible, since they have no W-chromosome (ZZF is crossed with ZZM). In such a situation, “wrong” females at 26–28 ºС are produced only by sons, and the analysis of one -okleotide replacements confirmed that small agamas are the result of sexual reproduction, and not partenogenesis inherent in some scaly reptiles. However, already at 33 ºС, the share of the daughters is 0.28, and at 34 ºС reaches 0.75. Researchers note that the offspring of “wrong” mothers are more sensitive to temperature, their reversal of the floor begins at 33.5 ºС, and in normal females - at 34.7 ºС.

Offspring can switch from one system for determining the floor to another very quickly, sometimes in just one generation. In extreme situations, for example, in an unprecedentedly hot year, in small natural populations, only their daughter can hatch. The increased fertility of ZZF and the sensitivity of their offspring to temperature will accelerate the loss of W-chromosomes in the population. Modeling showed that at a temperature above 33.4 ºС W-chromosome may disappear completely. Since the temperature conditions in the habitats of Agam are now on the verge of critical, this situation is real. Scientists fear that the feminization of the species will lead to its rapid extinction if the agams do not adapt the system of determining the floor to new conditions and do not provide a stable ratio of sexes. It seems that feminization is not always terrible (some types of rocky lizards of the genus Darevskia multiply only parthenogenetically), but this situation is evolutionarily unstable-partenogenetic species do not live for a long time due to the accumulation of harmful mutations.

Researchers do not consider the possibility of transition to agamas to parthenogenesis. They were more interested in whether the share of ZZF increases due to climate change and the loss of W-chromosomes in some populations, or “wrong” females have some features that increase their adaptability. This problem was solved by scientists of the University of Sydney under the leadership of Professor Richard Shine and Arthur George who joined them [2].

Researchers worked with immature lizards aged 29 to 519 days, who are bred at the University of Kanberra (bearded agamas reach maturity by two years). At the disposal of scientists, there were 20 ZZF females, 40 ZW female females and 55 ZZM males. In lizards, some phenotypic features (the length of the tail and head, body shape), physiological features (body temperature) and behavior features, which can affect the sexual, were determined.

ZW females weigh more males of the same length, and their tail is shorter. The ZZFs were heavier than normal females, and their tails are longer than the female. They are also “hot” concordant males, in which body temperature is slightly higher than that of ordinary females. The behavior of agamas with the reversal of the floor also retains the female features, and more pronounced.

Scientists have prepared several behavioral tests for lizards. They were placed on an open area and observed the research activity of reptiles. To evaluate neophobia, a moving bait for fish in a plastic vessel was put in front of Agama. The reaction of the lizard to an individual of the same species in a plastic perforated container made it possible to judge sociality, and the willingness to get out of shelter to an open place served as an indicator of courage. Each test lasted 15 minutes; Scientists evaluated how Agama came close to the object, at what speed it moves and how long, how many times it turns the head, after what time it looks out of the shelter. Research activity and courage are usually more characteristic of males than female ZW. But ZZF females in all behavioral tests surpassed males.

Thus, the bearded agams ZZF, being functional females, retained many real morphological, physiological and behavioral features that more developed in a significant number of individuals than in concordant males; And others have a mixture of signs that are not characteristic of individuals of any concordant floor. Before us is a new floor, stronger than strong.

In males with gender reverse, female gonads developed, which produce female sex hormones. In any case, it should be, the activity of hormones in the blood of ZZF was not measured. However, given their high fertility, it can be assumed that their endocrine profiles are similar to those in true females. Sex hormones can affect the development of many signs that males differ from females, but in this case this did not happen. The results indicate that some features inherent in gender, especially general activity and courage, depend more on genetic factors than on sex hormones.

Agam ZZF has the highest body temperature among the three floors, and the warmer the lizard, the more mobile it is. These lizards are bolder than others, the new one does not scare them. Courage and activity allow reptiles to hunt more successfully, which creates them reproductive advantages. Perhaps this explains the higher fertility of the ZZF females.

The combination of a female reproductive system with female activity and behavior affects the individual fitness of lizards and a sex determination system. In conditions when predators threaten the lizards, courage is not always appropriate and reduces individual adaptability. The agams will quickly eat too lively, and the floor in these populations will be determined by chromosomes. However, in an environment, where there are few predators, courage and activity create reproductive advantages, and the frequency of flooring can increase, since such individuals are more adapted than ordinary females. A small shift in the ratio of floors can lead to the creation of a local population in which the female sexual chromosome W is lost and the floor depends only on the temperature.

Researchers worked only with juvenile individuals, but they believe that behavioral features will not change with age and will remain in adults agamas. But finally clarify the evolution of the floor determination system could measure the frequency of survival and reproductions of different sexes in natural conditions.

1. Holleley CE, O'Meally D., Sarre SD, Marshall Graves Ja, Ezaz T., Matsubara K., AZAD B., Zhang X., Georges A. Sex Reversal Triggers The Rapid Tralanetic Genetic TO TemperatureDependent Sex // Nature. N 523. P. 79-82. Doi: 10.1038/Nature14574

2. Li H., Holleley Ce, Elphick M., Georges, Shine R. The Behaviural Consequences of Sex Reversal in Dragons // Proc. R. SOC. B. 2016. N 283: 20160217. DOI: 10.1098/RSPB 2016.0217