Emergence and stabilization of a neo-Y chromosome in nematode species with rare males
Abstract
How do sex chromosomes evolve in the transition to asexuality? So far, species that depart from canonical sexual reproduction-for example, parthenogens with rare sex or species where the paternal genome is set aside-have been found to carry either no sex chromosomes or sex chromosomes but no male-specific sex chromosome (i.e. no Y). Here we reveal that, in Mesorhabditis nematodes, a new Y chromosome evolved once, from sexual ancestors, in species that have transitioned into an unconventional mode of reproduction called autopseudogamy. In this reproductive system, females produce clonal females plus rare (∼10%) males that are needed for fertilization but that do not contribute to the female genome. Analyzing the Y chromosomes of two autopseudogamous species, we found high levels of degeneration, most likely due to loss of recombination, and two additional conserved features: (i) they accumulated male-beneficial genes, and (ii) they display a strong fertilization drive, in that mainly Y-bearing sperm fertilize female oocytes. Both features are likely evolutionarily favorable in the context of autopseudogamy. Our results suggest that male-specific chromosomes can still be maintained in systems with rare, and possibly "genetically useless," males.
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BibTeX
@article{letcher2026emergence,
title = {{Emergence and stabilization of a neo-Y chromosome in nematode species with rare males}},
author = {Brice Letcher and Lewis Stevens and Nathanaëlle Saclier and Andrew Hsiao and Manuela Kieninger and Eva Wenger and Caroline Launay and Mark Blaxter and Marie Delattre},
journal = {Molecular Biology and Evolution},
year = {2026},
month = aug,
doi = {10.1093/molbev/msag177},
url = {https://hal.science/hal-05848535v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Emergence and stabilization of a neo-Y chromosome in nematode species with rare males
AU - Brice Letcher
AU - Lewis Stevens
AU - Nathanaëlle Saclier
AU - Andrew Hsiao
AU - Manuela Kieninger
AU - Eva Wenger
AU - Caroline Launay
AU - Mark Blaxter
AU - Marie Delattre
PY - 2026
DA - 2026/08/01
JO - Molecular Biology and Evolution
DO - 10.1093/molbev/msag177
UR - https://hal.science/hal-05848535v1
AB - How do sex chromosomes evolve in the transition to asexuality? So far, species that depart from canonical sexual reproduction-for example, parthenogens with rare sex or species where the paternal genome is set aside-have been found to carry either no sex chromosomes or sex chromosomes but no male-specific sex chromosome (i.e. no Y). Here we reveal that, in Mesorhabditis nematodes, a new Y chromosome evolved once, from sexual ancestors, in species that have transitioned into an unconventional mode of reproduction called autopseudogamy. In this reproductive system, females produce clonal females plus rare (∼10%) males that are needed for fertilization but that do not contribute to the female genome. Analyzing the Y chromosomes of two autopseudogamous species, we found high levels of degeneration, most likely due to loss of recombination, and two additional conserved features: (i) they accumulated male-beneficial genes, and (ii) they display a strong fertilization drive, in that mainly Y-bearing sperm fertilize female oocytes. Both features are likely evolutionarily favorable in the context of autopseudogamy. Our results suggest that male-specific chromosomes can still be maintained in systems with rare, and possibly "genetically useless," males.
SN - 0737-4038
SN - 1537-1719
ER -