Thursday, 22 December 2022

Creationism in Crisis - Rappid Evolution of Spermatogenesis

Rapid Evolution of Spermatogenesis - Universität Heidelberg
The evolution of mammalian spermatogenesis. The image illustrates a sperm cell and the evolutionary relationship of mammalian species covered in the study.
Illustration: Florent Murat (icons partly adapted from Murat et al., Nature 2022, 10.1038/s41586-022-05547-7 | CC BY 4.0)
News that scientists have now shown how spermatogenesis in mammals is the result of a rapid evolutionary process and that mammals share many of the same genes, indicating common descent, as predicted from the Theory of Evolution (ToE), should come as a shock to Creationists fooled into thinking that the ToE is being increasingly rejected as the best available explanation for biodiversity and much else in nature, if only they could take their hands away from their eyes and read about it.

In fact, as this research shows, the ToE is fundamental to understanding biology and interpreting what can be observed.

The research was carried out by an international team of researchers led by Prof. Dr Henrik Kaessmann from the Center for Molecular Biology of Heidelberg University. The results are reported in Nature.
The research and its significance is explained in the Heidelberg University press release:
Evolutionary pressure across male mammals to guarantee the procreation of their own offspring led to a rapid evolution of the testicle. Bioinformatic studies – conducted by an international team of researchers led by Prof. Dr Henrik Kaessmann from the Center for Molecular Biology of Heidelberg University – show that this pressure particularly accelerated the evolution of later stages of sperm formation. The aim of these contrastive studies was, for the first time, to decode the genetic regulation of sperm formation in various species of mammals and in human beings, thereby tracing the evolution of this spermatogenesis. At the same time, the researchers were also able to detect genes whose activity had remained unchanged in the course of evolution.

[The understanding of the genetic programming had been largely confined to the mouse] Consequently little was known about the genetic foundations that constitute the big differences in spermatogenesis across different mammals, both with regard to the number of sperm cells formed and also to their properties.

Dr. Noe Mbengue, co-lead author
Center for Molecular Biology (ZMBH)
DKFZ-ZMBH Alliance
Heidelberg University, Heidelberg, Germany
Spermatogenesis in the testicle is controlled by a finely coordinated, complex interplay of the activity of different genes – also known as gene expression. Hitherto the understanding of these genetic programmes had been largely confined to the mouse... The Heidelberg scientists have now succeeded in defining the expression of all genes at the level of individual cells during the whole of spermatogenesis for ten different mammals. The organisms they studied represent all major groups of mammals and include humans as well as their closest relatives, great apes. To do so, the researchers used state-of-the-art single-cell genomics technologies.

While the genetic programmes in the early stages of spermatogenesis are very similar among mammals, in later stages they differ greatly; that means that the rapid evolution of the testicle is a result of major differences in cells during late spermatogenesis.

Dr Florent Murat, co-lead author
Center for Molecular Biology (ZMBH)
DKFZ-ZMBH Alliance
Heidelberg University, Heidelberg, Germany.
And National Research Institute for Agriculture, Food and Environment (INRAE)
Rennes, France.
Based on this data they were subsequently able to trace the evolution of spermatogenesis with the aid of bioinformatic comparisons between the different mammals. According to Prof. Kaessmann, these comparative studies uncovered a time-related pattern... Further analyses by the scientists revealed genes whose activity had remained unchanged in the course of evolution. They regulate fundamental processes of sperm cell formation that are the same for all mammals. “Hence our data also supplies valuable elements for researching fertility disorders in men,” Prof. Kaessmann explains.

Finally, the scientists’ data enabled them for the first time to distinguish sperm cells that carry either an X or a Y chromosome and thus determine the sex of the offspring. With the aid of this division, the researchers succeeded in systematically studying the gene expression on these sex chromosomes. As these investigations showed, gene expression on the sex chromosomes of all male mammals is downregulated during the maturation division known as meiosis. This mechanism is presumably fundamental for preventing a disadvantageous genetic exchange between the X and Y chromosome during meiosis.
Technical detail can be found in the team's paper in Nature:

The testis produces gametes through spermatogenesis and evolves rapidly at both the morphological and molecular level in mammals1,2,3,4,5,6, probably owing to the evolutionary pressure on males to be reproductively successful7. However, the molecular evolution of individual spermatogenic cell types across mammals remains largely uncharacterized. Here we report evolutionary analyses of single-nucleus transcriptome data for testes from 11 species that cover the three main mammalian lineages (eutherians, marsupials and monotremes) and birds (the evolutionary outgroup), and include seven primates. We find that the rapid evolution of the testis was driven by accelerated fixation rates of gene expression changes, amino acid substitutions and new genes in late spermatogenic stages, probably facilitated by reduced pleiotropic constraints, haploid selection and transcriptionally permissive chromatin. We identify temporal expression changes of individual genes across species and conserved expression programs controlling ancestral spermatogenic processes. Genes predominantly expressed in spermatogonia (germ cells fuelling spermatogenesis) and Sertoli (somatic support) cells accumulated on X chromosomes during evolution, presumably owing to male-beneficial selective forces. Further work identified transcriptomal differences between X- and Y-bearing spermatids and uncovered that meiotic sex-chromosome inactivation (MSCI) also occurs in monotremes and hence is common to mammalian sex-chromosome systems. Thus, the mechanism of meiotic silencing of unsynapsed chromatin, which underlies MSCI, is an ancestral mammalian feature. Our study illuminates the molecular evolution of spermatogenesis and associated selective forces, and provides a resource for investigating the biology of the testis across mammals.
So, a basic creationist lie is refuted by scientific data, and, as usual, without any intention on the part of the scientists who revealed the truth that did so.

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