How did sex pop up? a study of hermaphrodites (Introduction)

by David Turell , Wednesday, June 15, 2022, 16:53 (684 days ago) @ David Turell

Organisms with hermaphroditic sex analyzed:

https://phys.org/news/2022-06-parasitic-worms-reveal-insights-evolution.html

:Animals or plants with separate sexes are widespread in nature, and result from independent transitions from their hermaphroditic ancestor. The actual mechanism involved in the transitions between asexual and sexual reproductive modes, in other words, how is sex originated, remains an important and unanswered question. Excluding insects, about one third of the animal species, such as earthworms, snails, and some teleosts, are hermaphroditic.

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:The research group collected already published genome and transcriptome data of 41 nematode species and 13 flatworm species, the latter of which comprise mostly hermaphroditic species except for schistosomes (blood flukes). Among these, they identified sex chromosome composition of 17 nematode species in terms of "Nigon elements." These are ancestral chromosome units which are shared by all nematodes, and named after the nematode biologist Victor Nigon (in parallel to "Muller elements" of fruitfly, another genetic model species). With this comparison, the authors showed that the great diversity of nematode sex chromosomes is a result of different combinations of Nigon elements. By recurrent addition of different Nigon elements—which previously had been non-sex chromosomes—onto the ancestral sex chromosomes, different nematode species extended their sex-linked regions which later suppressed recombination during evolution.

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:Another important finding comes from the comparison of the sexually reproducing blood flukes to related hermaphroditic species. The transition into the state of separate sexes in the parasite occurred relatively recently, around 70 million years ago. The authors showed that during this transition, the gonad genes of schistosomes became less "feminized." In other words, they overall showed a lower ovary expression level compared to their counterpart in the hermaphroditic related species. They also identified a candidate gene, mag-1, whose disruption in schistosomes causes enlarged testis. Mutations in this gene might have played a critical role for the transition into the separate sexes of schistosomes."

Comment: this study of hermaphrodites really adds little. They hve both sexes to begin with. Tht dows not explain how teh two sexes appearfed fron ognaisms that simply used binary fission. This is one of the biggest developmental gaps in which sex's origin is not known.