Liu Xiaoyuan, Pitchford Jonathan W, Constable George W A
Cancer Research UK Scotland Institute, Glasgow, Scotland, United Kingdom.
Department of Mathematics, University of York, York, North Yorkshire, United Kingdom.
PLoS Comput Biol. 2025 Apr 8;21(4):e1012418. doi: 10.1371/journal.pcbi.1012418. eCollection 2025.
In unicellular organisms, sexual reproduction typically begins with the fusion of two cells (plasmogamy) followed by the fusion of their two haploid nuclei (karyogamy) and finally meiosis. Most work on the evolution of sexual reproduction focuses on the benefits of the genetic recombination that takes place during meiosis. However, the selection pressures that may have driven the early evolution of binary cell fusion, which sets the stage for the evolution of karyogamy by bringing nuclei together in the same cell, have seen less attention. In this paper we develop a model for the coevolution of cell size and binary cell fusion rate. The model assumes that larger cells experience a survival advantage from their larger cytoplasmic volume. We find that under favourable environmental conditions, populations can evolve to produce larger cells that undergo obligate binary cell fission. However, under challenging environmental conditions, populations can evolve to subsequently produce smaller cells under binary cell fission that nevertheless retain a survival advantage by fusing with other cells. The model thus parsimoniously recaptures the empirical observation that sexual reproduction is typically triggered by adverse environmental conditions in many unicellular eukaryotes and draws conceptual links to the literature on the evolution of multicellularity.
在单细胞生物中，有性生殖通常始于两个细胞的融合（质配），随后是它们两个单倍体细胞核的融合（核配），最后是减数分裂。大多数关于有性生殖进化的研究都集中在减数分裂过程中发生的基因重组的益处上。然而，对于二元细胞融合早期进化的选择压力关注较少，二元细胞融合通过将细胞核聚集在同一个细胞中为核配的进化奠定了基础。在本文中，我们建立了一个细胞大小和二元细胞融合率共同进化的模型。该模型假设较大的细胞因其较大的细胞质体积而具有生存优势。我们发现，在有利的环境条件下，种群可以进化出产生较大细胞的能力，这些细胞会进行 obligate 二元细胞分裂。然而，在具有挑战性的环境条件下，种群可以进化出随后产生较小细胞的能力，这些较小细胞在二元细胞分裂时仍通过与其他细胞融合而保持生存优势。因此，该模型简洁地重现了一个实证观察结果，即在许多单细胞真核生物中，有性生殖通常由不利的环境条件触发，并与多细胞性进化的文献建立了概念上的联系。
