Marine Biosystems Research Center, Chiba University , Kamogawa 299-5502, Japan.
Department of Evolution, Ecology and Behaviour, University of Liverpool , Liverpool L69 7ZB, UK.
Biol Lett. 2024 Oct;20(10):20240489. doi: 10.1098/rsbl.2024.0489. Epub 2024 Oct 9.
In eukaryotes, gamete size difference between the two sexes (anisogamy) evolved from gametes of equal size in both mating types (isogamy). The gamete dynamics (GD) model for anisogamy evolution combines gamete limitation and competition and predicts that if gametes of both mating types can develop parthenogenetically (i.e. without fusing with the opposite mating type), large isogamy can evolve under gamete-limited conditions. Ulvophycean marine green algae that have been claimed to exhibit various gametic systems from isogamy to anisogamy are important models for testing such theories. However, in most previous papers, whether a species is isogamous or anisogamous has not been examined statistically. Caution is necessary regarding claims of slight anisogamy because of gamete size variation. We reveal (i) that the gametic system of is large isogamy using a generalized linear mixed model, which accounted for the variation of gamete size among individual gametophytes, and (ii) that gametes of this alga can actually develop parthenogenetically, contrary to a previous report. Its habitat environments and protracted duration of gamete release suggest that this alga might experience gamete-limited conditions. seems to produce large parthenogenetic isogametes following GD model predictions, as an adaptation to deep waters.
在真核生物中，两性配子大小的差异（雌雄配子大小不同，即雌雄配子异型）是由两种交配类型配子大小相等（雌雄配子同型）进化而来的。雌雄配子异型进化的 GD 模型结合了配子限制和竞争，并预测如果两种交配类型的配子都可以进行孤雌生殖（即不与相反的交配类型融合），那么在配子限制条件下，大型雌雄配子同型可以进化。具有从雌雄配子同型到雌雄配子异型等各种配子系统的绿藻门海洋绿藻一直是检验这些理论的重要模型。然而，在大多数先前的论文中，并没有对物种是雌雄配子同型还是雌雄配子异型进行统计检验。由于配子大小的变化，对于轻微的雌雄配子异型的说法需要谨慎。我们揭示了（i）使用广义线性混合模型，该模型考虑了配子大小在个体配子体之间的变化， 是大型雌雄配子同型，（ii）该藻类的配子实际上可以进行孤雌生殖，这与之前的报告相反。其生境环境和配子释放的漫长时间表明，该藻类可能经历了配子限制条件。 似乎根据 GD 模型的预测，产生了大型的孤雌生殖雌雄配子同型，这是对深海环境的一种适应。
