Jackson Robert C, Mistry Hitesh B
Pharmacometrics Ltd., Cambridge, United Kingdom.
Division of Pharmacy, University of Manchester, Manchester, United Kingdom.
PeerJ. 2020 May 11;8:e9073. doi: 10.7717/peerj.9073. eCollection 2020.
A mechanism is proposed by which speciation may occur without the need to postulate geographical isolation of the diverging populations. Closely related species that occupy overlapping or adjacent ecological niches often have an almost identical genome but differ by chromosomal rearrangements that result in reproductive isolation. The mitotic spindle assembly checkpoint normally functions to prevent gametes with non-identical karyotypes from forming viable zygotes. Unless gametes from two individuals happen to undergo the same chromosomal rearrangement at the same place and time, a most improbable situation, there has been no satisfactory explanation of how such rearrangements can propagate. Consideration of the dynamics of the spindle assembly checkpoint suggest that chromosomal fission or fusion events may occur that allow formation of viable heterozygotes between the rearranged and parental karyotypes, albeit with decreased fertility. Evolutionary dynamics calculations suggest that if the resulting heterozygous organisms have a selective advantage in an adjoining or overlapping ecological niche from that of the parental strain, despite the reproductive disadvantage of the population carrying the altered karyotype, it may accumulate sufficiently that homozygotes begin to emerge. At this point the reproductive disadvantage of the rearranged karyotype disappears, and a single population has been replaced by two populations that are partially reproductively isolated. This definition of species as populations that differ from other, closely related, species by karyotypic changes is consistent with the classical definition of a species as a population that is capable of interbreeding to produce fertile progeny. Even modest degrees of reproductive impairment of heterozygotes between two related populations may lead to speciation by this mechanism, and geographical isolation is not necessary for the process.
本文提出了一种物种形成机制，该机制无需假定分化种群的地理隔离。占据重叠或相邻生态位的近缘物种通常具有几乎相同的基因组，但因染色体重排而有所不同，从而导致生殖隔离。有丝分裂纺锤体组装检查点通常发挥作用，防止具有不同核型的配子形成有活力的合子。除非来自两个个体的配子碰巧在同一时间和地点发生相同的染色体重排，而这是极不可能的情况，否则对于这种重排如何传播一直没有令人满意的解释。对纺锤体组装检查点动力学的思考表明，可能会发生染色体裂变或融合事件，从而允许在重排核型和亲本核型之间形成有活力的杂合子，尽管其育性会降低。进化动力学计算表明，如果由此产生的杂合生物在相邻或重叠的生态位中比亲本菌株具有选择优势，那么尽管携带改变核型的种群存在生殖劣势，但这种情况可能会充分积累，以至于纯合子开始出现。此时，重排核型的生殖劣势消失，一个单一的种群被两个部分生殖隔离的种群所取代。将物种定义为通过核型变化与其他近缘物种不同的种群，这与将物种定义为能够杂交产生可育后代的种群的经典定义是一致的。即使两个相关种群之间的杂合子生殖能力仅有适度受损，也可能通过这种机制导致物种形成，而且这一过程并不需要地理隔离。
