Department of Biology, The University of Alabama at Birmingham, 1300 University Blvd, Birmingham, Alabama, 35924, USA.
J Phycol. 2020 Aug;56(4):1114-1120. doi: 10.1111/jpy.13011. Epub 2020 May 23.
Worldwide, macroalgae have invaded near-shore marine ecosystems. However, their haplodiplontic life cycles have complicated efforts to predict patterns of growth and spread, particularly since most theoretical predictions are derived from diplontic taxa (i.e., animals). To complete one revolution of the life cycle, two separate ploidy stages, often including separate haploid sexes, must pass through development and reproduction. In the case of the invasive, red macroalga Agarophyton vermiculophyllum, during the invasion of soft-sediment estuaries throughout the Northern Hemisphere, diploid tetrasporophytes came to dominate all free-floating populations and haploid gametophytes were consistently lost. The ecological hypothesis of nutrient limitation might contribute to an explanation of this pattern of tetrasporophytic dominance in free-floating populations. Under this hypothesis, gametophytes should outperform tetrasporophytes under nutrient limited conditions, but tetrasporophytes should be better able to exploit optimal or even abundant nutrient conditions, such as in eutrophic estuaries. We sampled tetrasporophytes, male gametophytes, and female gametophytes from two sites each located on either side of the Delmarva Peninsula that separates the Chesapeake Bay from the Atlantic Ocean. We subjected apices excised from multiple thalli from each life cycle stage to a nutrient-enriched and a nutrient-poor seawater treatment and assessed growth and survival. While nutrient addition increased growth rates, there was no significant difference among ploidies or sexes. Gametophytes did, however, suffer higher mortality than tetrasporophytes. We discuss how nutrient-dependent differences in growth and survival may contribute to observed patterns of tetrasporophytic dominance in soft-sediment A. vermiculophyllum populations.
全球范围内，大型藻类已经入侵近岸海洋生态系统。然而，它们的单双倍体生活史使得预测其生长和扩散模式变得复杂，特别是因为大多数理论预测都是基于双倍体分类单元（即动物）得出的。为了完成一个生命周期的循环，两个独立的倍性阶段，通常包括独立的单倍性性别，必须经历发育和繁殖。在入侵性的红色大型藻类 Agarophyton vermiculophyllum 的情况下，在其入侵整个北半球的软泥质河口的过程中，二倍体四分孢子体逐渐占据了所有自由漂浮种群的主导地位，而单倍体配子体则持续丢失。营养限制的生态假说可能有助于解释这种自由漂浮种群中四分孢子体优势的模式。根据这一假说，在营养有限的条件下，配子体应该比四分孢子体表现更好，但四分孢子体应该更能利用最佳甚至丰富的营养条件，例如在富营养化的河口。我们从位于切萨皮克湾和大西洋之间的特拉华半岛两侧的两个地点，每个地点都采样了二倍体四分孢子体、雄性配子体和雌性配子体。我们将取自每个生活史阶段多个藻体的顶端部分分别置于富营养化和贫营养化海水中进行处理，并评估了它们的生长和存活情况。虽然营养添加增加了生长速度，但在倍性或性别之间没有显著差异。然而，配子体的死亡率却高于四分孢子体。我们讨论了生长和存活的营养依赖性差异如何有助于解释软泥质 A. vermiculophyllum 种群中观察到的四分孢子体优势模式。
