Sussmann A V, Dewreede R E
Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4 Canada.
Am J Bot. 2001 Sep;88(9):1535-44.
This study establishes the phenology of the alternate life history phases of the green alga Acrosiphonia in British Columbia, Canada. Free-living, filamentous plants are seasonal, March-July, with peak percent cover (10%) in April. Plants are fertile immediately after establishment. The unicells, previously identified as Chlorochytrium inclusum and Codiolum petrocelidis, are the sporophyte phase of Acrosiphonia. 'Chlorochytrium,' spherical and 160-280 μm in diameter, colonizes the foliose red alga Mazzaella splendens 1 mo after filamentous Acrosiphonia plants appear. Maximum density (53 'Chlorochytrium' cells/cm(2) of blade) was recorded in May. 'Codiolum,' on the other hand, is stalked (the vesicle measures 150 × 50 μm) and colonizes the red algal crust Petrocelis. Peak density (22 400 'Codiolum' cells/cm(2) of crust) was recorded 2 mo after 'Chlorochytrium' density peaked. The endophytes survive high summer temperatures, which correlate with death of the free-living plants, and overwinter in their hosts. Zoospore release in late winter corresponds to decreased host abundance, suggesting the endophytes have evolved a strategy whereby duration in the host is synchronized with host seasonality. A bet-hedging strategy is proposed for Acrosiphonia's life history: two morphologically different phases have adapted to a seasonally variable environment, with the sporophyte phase capable of colonizing two different hosts.
本研究确定了加拿大不列颠哥伦比亚省绿藻顶管藻交替生活史阶段的物候特征。自由生活的丝状植物具有季节性，出现在3月至7月，4月覆盖率达到峰值（10%）。植物在形成后立即具有繁殖能力。以前被鉴定为包囊绿藻和石氏双鞭藻的单细胞是顶管藻的孢子体阶段。“包囊绿藻”呈球形，直径为160 - 280μm，在丝状顶管藻植物出现1个月后定殖于叶状红藻灿烂节荚藻上。5月记录到最大密度（每平方厘米藻体有53个“包囊绿藻”细胞）。另一方面，“双鞭藻”有柄（囊泡大小为150×50μm），定殖于红藻壳状石氏藻上。在“包囊绿藻”密度达到峰值2个月后记录到最大密度（每平方厘米藻壳有22400个“双鞭藻”细胞）。内生植物在夏季高温下存活，这与自由生活植物的死亡相关，并在其宿主中越冬。冬末游动孢子的释放与宿主丰度的下降相对应，这表明内生植物已经进化出一种策略，使其在宿主中的持续时间与宿主的季节性同步。针对顶管藻的生活史提出了一种风险对冲策略：两个形态不同的阶段适应了季节性变化的环境，孢子体阶段能够定殖于两种不同的宿主。
