MARETEC, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal.
CCMAR, Center of Marine Science, University of Algarve, Campus Gambelas, 8005-139, Faro, Portugal.
BMC Evol Biol. 2018 Nov 20;18(1):174. doi: 10.1186/s12862-018-1285-z.
Conditional differentiation is one of the most fundamental drivers of biodiversity. Competitive entities (usually species) differ in environmental or ecological niche enabling them to co-exist. Conditional differentiation of haploid and diploid generations is considered to be a requirement for the evolutionary stability of isomorphic biphasic life-cycles and the cause for the natural occurrence of both phases at uneven abundances. Theoretically, stage dependent survival rates are the most efficient way to explain conditional differentiation.
We tested for conditional differentiation in survival rates among life stages (haploid males, haploid females, and diploids) of Gracilaria chilensis, an intertidal red alga occurring along the Chilean shores. Therefore, the fate of individuals was followed periodically for 3 years in five intertidal pools and, for the first time in isomorphic red algae, a composite model of the instantaneous survival rates was applied. The results showed the survival dependency on density (both competition and Allee effects), fertility, age, size, season and location, as well as the differentiation among stages for the survival dependencies of these factors. The young haploid females survived more than the young of the other stages under Allee effects during the environmentally stressful season at the more exposed locations, and under self-thinning during the active growth season. Furthermore, fertile haploid females had a higher survival than fertile haploid males or fertile diploids.
Here, we show a survival advantage of haploids over diploids. The haploid females probably optimize their resource management targeting structural and physiological adaptations that significantly enhance survival under harsher conditions. In a companion paper we demonstrate a fertility advantage of diploids over haploids. Together, the survival and fertility differentiation support the evolution and prevalence of biphasic life-cycles.
条件分化是生物多样性最基本的驱动力之一。有竞争力的实体（通常是物种）在环境或生态位上存在差异，使它们能够共存。单倍体和二倍体世代的条件分化被认为是同形二相生活史进化稳定性的要求，也是导致两个阶段不均匀丰度自然发生的原因。从理论上讲，依赖于阶段的存活率是解释条件分化的最有效方法。
我们测试了智利江蓠（Gracilaria chilensis）生活阶段（单倍体雄性、单倍体雌性和二倍体）存活率的条件分化，智利江蓠是一种沿智利海岸生长的潮间带红藻。因此，我们在五个潮间带水池中定期跟踪个体的命运长达 3 年，并首次在同形红藻中应用了瞬时存活率的综合模型。结果表明，存活率依赖于密度（竞争和阿利效应）、繁殖力、年龄、大小、季节和位置，以及这些因素的生存依赖性在不同阶段之间的分化。在环境压力较大的季节和活跃的生长季节，处于阿利效应下的年轻单倍体雌性比其他阶段的年轻个体存活率更高，在自疏作用下也是如此。此外，有繁殖力的单倍体雌性比有繁殖力的单倍体雄性或有繁殖力的二倍体存活率更高。
在这里，我们展示了单倍体相对于二倍体的生存优势。单倍体雌性可能通过针对结构和生理适应的资源管理来优化其生存，这些适应在更恶劣的条件下显著提高了生存能力。在一篇相关的论文中，我们证明了二倍体相对于单倍体的繁殖优势。总之，生存和繁殖分化支持了二相生活史的进化和流行。
