HETEROSPORY - THE MOST ITERATIVE KEY INNOVATION IN THE EVOLUTIONARY HISTORY OF THE PLANT KINGDOM
HETEROSPORY - THE MOST ITERATIVE KEY INNOVATION IN THE EVOLUTIONARY HISTORY OF THE PLANT KINGDOM
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DOI：
10.1111/j.1469-185x.1994.tb01276.x
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发表时间：
1994-08-01
影响因子：
10
通讯作者：
DIMICHELE, WA
中科院分区：
文献类型：
--
作者：
BATEMAN, RM;DIMICHELE, WA
[1]总的来说，过去关于异孢子生殖及其在世代交替中的作用的讨论充满了模糊性，反映了术语和概念的重叠。如果将Heterosporysensu lato分成一系列更容易定义的进化创新，则可以更有效地分析Heterosporysensu lato：严格的Heterosporysensu stricto（孢子大小的双峰性），二分体，异孢子囊，内孢子，单大孢子，内孢子囊，整合，lagenostomy，原位授粉，原位受精，花粉管形成和管花受精（表1，2，图1，13）。目前的证据表明，最后五个特征仅限于种子植物。2化石记录证明了异形孢子谱系从异形同孢祖先的重复进化。然而，由于化石孢子体的分离，在自由孢子蕨类植物中将同种但物理上独立的孢子体和配子体世代联系起来的困难，无法直接观察个体发育，以及保存短暂和/或微观生殖现象（如合婚和管婚）的罕见性，阻碍了解释。不幸的是，很少保存的现象往往比相应的容易保存的现象具有更大的生物学意义（例如异孢子生殖与二孢子生殖，异孢子囊与内孢子生殖）。3在大多数化石中，配子体性别只能通过孢子体的形态，特别是孢子的形态外推。当两种孢子性别在大小、形态、超微结构和发育行为上有很大差异时，这对于具有高水平异孢子生殖的物种很容易实现。然而，最有可能在陆生植物的早期化石记录中阐明的异孢子生殖进化的最早阶段也显示出最少的孢子发生分歧。在同时期的同孢子种中，很难将大的小孢子和小的大孢子与大的等孢子区分开来（图3-6a，g）。通过对孢子囊内孢子种群的定量分析，可以最好地在化石中鉴定出异孢子生殖。4大孢子和小孢子差异表达的空间尺度从在单个孢子囊（异孢子生殖）中共存到在不同孢子体（异孢子生殖）中共存不等（图6-8）。对孢子体上两种孢子形态的相对位置以及发育异常畸胎的研究（图9）表明，性别在孢子体和配子体中都表现为表观遗传。激素控制通过营养渐变群进行，营养丰富的微环境有利于雌性;大孢子和小孢子竞争孢子体资源。外部环境也可以影响性别，特别是在自由生活的外生孢子配子体中。起源的数量是最好的评估，通过分支图，但没有目前的系统发育，包括足够的相关的维管植物物种。此外，几个现存的异孢子物种与其最近的亲属由于高度的生态专业化和/或跳跃进化差异很大;将需要广泛的分子数据来确定其正确的系统发育位置。目前的证据表明，至少有11个异孢子生殖的起源，在Zosterophyllopsida（1：上泥盆统），石松（1：上泥盆统），楔（？2：下石炭统）、Pteropsida（？4：上白垩统/古近纪）和前裸子植物纲（？3：上泥盆统/石炭纪）。可以说单系的裸子植物纲可能从它们的裸子植物科祖先那里继承了异孢子生殖（表3.
1In aggregate, past discussions of heterospory and its role in the alternation of generations are riddled with ambiguities that reflect overlap of terms and concepts. Heterosporysensu latocan be analyzed more effectively if it is fragmented into a series of more readily defined evolutionary innovations: heterosporysensu stricto(bimodality of spore size), dioicy, heterosporangy, endospory, monomegaspory, endomegasporangy, integumentation, lagenostomy,in situpollination,in situfertilization, pollen tube formation, and siphonogamy (Tables 1, 2, Figs 1, 13). Current evidence suggests that the last five characters are confined to the seed‐plants.2The fossil record documents repeated evolution of heterosporous lineages from anisomorphic homosporous ancestors. However, interpretation is hindered by disarticulation of fossil sporophytes, the difficulty of relating conspecific but physically independent sporophyte and gametophyte generations in free‐sporing pteridophytes, the inability to directly observe ontogeny, and the rarity of preservation of transient and/or microscopic reproductive phenomena such as syngamy and siphonogamy. Unfortunately, the rarely preserved phenomena are often of far greater biological significance than corresponding readily preserved phenomena (e.g. heterospory versus dioicy, heterosporangy versus endospory).3In most fossils gametophyte gender can only be inferred by extrapolation from the morphology of the sporophyte and especially of the spores. This is readily achieved for species possessing high‐level heterospory, when the two spore genders have diverged greatly in size, morphology, ultrastructure and developmental behaviour. However, the earliest stages in the evolution of heterospory, which are most likely to be elucidated in the early fossil record of land‐plants, also show least sporogenetic divergence. It is particularly difficult to distinguish large microspores and small megaspores from the large isospores of some contemporaneous homosporous species (Figs 3–6a,g). Heterospory is best identified in fossils by quantitative analysis of intrasporangial spore populations.4The spatial scale of the differential expression of megaspores and microspores varies from co‐occurrence in a single sporangium (anisospory) to different sporophytes (dioecy) (Figs 6–8). Studies of the relative positions of the two spore morphs on the sporophyte, and of developmentally anomalous terata (Fig. 9), demonstrate that gender is expressed epigenetically in both the sporophyte and gametophyte. Hormonal control operates via nutrient clines, with nutrient‐rich microenvironments favouring femaleness; megaspores and microspores compete for sporophytic resources. External environments can also influence gender, particularly in free‐living exosporic gametophytes.5The evolution of heterospory was highly iterative. The number of origins is best assessed via cladograms, but no current phylogeny includes sufficient relevant tracheophyte species. Also, several extant heterosporous species differ greatly from their closest relatives due to high degrees of ecological specialization and/or saltational evolution; extensive molecular data will be needed to ascertain their correct phylogenetic position. Current evidence suggests aminimumof 11 origins of heterospory, in the Zosterophyllopsida (1: Upper Devonian), Lycopsida (1: Upper Devonian), Sphenopsida (?2: Lower Carboniferous), Pteropsida (?4: Upper Cretaceous/Palaeogene) and Progymnospermopsida (?3: Upper Devonian/Carboniferous). The arguably monophyletic Gymnospermopsida probably inherited heterospory from their progymnospermopsid ancestor (Table 3 …