THE ECOLOGY OF SEED HETEROMORPHISM IN HETEROSPERMA-PINNATUM IN CENTRAL MEXICO
THE ECOLOGY OF SEED HETEROMORPHISM IN HETEROSPERMA-PINNATUM IN CENTRAL MEXICO
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DOI：
10.2307/1938805
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发表时间：
1987-02-01
期刊：
影响因子：
4.8
通讯作者：
ESPINOSA, F
中科院分区：
文献类型：
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作者：
VENABLE, DL;BURQUEZ, A;ESPINOSA, F
瘦果是一种一年生复合体，产生异形瘦果，瘦果的比例因地理而异。通过田间试验、温室试验和实验室试验，研究了异形性的生态后果。根据形态将瘦果分为三种类型。中心的、中间的和外围的形态，以在果头内占据的位置命名，形状从带倒钩芒的细长喙瘦果(中央)到没有喙或芒的短而宽的瘦果(外围)。瘦果和头部特征在种群内和种群间有相当大的表型差异。使用人工分散剂的野外实验表明，中心瘦果最有可能附着在动物身上，而S提出分散的瘦果种群的比例取决于种群中产生的中心瘦果的比例和带有粘性芒的瘦果的比例。瘦果一旦到达地面，平均和中位数的二次扩散距离较短(<；20厘米)。在秋季瘦果产生和夏季雨季开始之间的一段时间里，中央瘦果比外围瘦果更早地丧失先天休眠。萌发受到黑暗的抑制，尽管黑暗在萌发季节开始时变得不那么抑制(中央瘦果较早)。在实验室中，外围瘦果在比中央瘦果稍窄的温度范围内萌发。在田间两次自然萌发事件中，中部瘦果的发芽率高于中间瘦果，中间瘦果的发芽率高于外围瘦果。种子库样本表明，瘦果很少，如果有的话，在多年之间保持休眠。温室内苗木生长速率差异不显著。一项人口统计学实验记录了休眠差异造成的权衡：中央瘦果往往比中间和外围的瘦果更早萌发，早期萌发导致更高的死亡率，但更早萌发的幸存者获得更大的体型和更多的种子。中等瘦果，虽然在所有适合度成分中处于中等水平，但总适合度最高。这是因为它们与外围瘦果相似，发芽较晚，存活率较高，但发芽率较高，与中心瘦果相似。这些实验的结果表明，在单个个体的后代中，瘦果的行为范围从“低风险”(外围瘦果)到“高风险”(中央瘦果)，而个体和种群的后代表现出每种类型行为的比例不同。
Heterosperma pinnatum is an annual composite that produces heteromorphic achenes, with the proportion of achene morphs varying geographically. Field, greenhouse, and laboratory experiments were used to examine the ecological consequences of the heteromorphism. Achenes were classified into three types based on morphology. Central, intermediate, and peripheral morphs, named for the positions occupied within the fruiting head, range in shape from long, thin-beaked achenes with barbed awns (central) to short wide achenes without beaks or awns (peripheral). Considerable within- and between-population phenotypic variation in achene and head characteristics was documented. Field experiments using artificial dispersal agents showed that central achenes are the most likely to adhere to animals and that the proporton of a population''s achenes presented for dispersal that adhere depends on the proportion of central achenes produced in the population and on the proportion of achenes with adhesive awns. Once achenes had reached the ground, mean and median secondary dispersal distances were short (< 20 cm). Central achenes lose innate dormancy earlier than peripheral achenes during the period between autumn achene production and the onset of the summer rainy season. Germination is inhibited by darkness, though darkness becomes less inhibitive at the onset of the germinated season (earlier for central achenes). In the laboratory, peripheral achenes germinated over a slightly narrower range of temperatures than central achenes. Percent germination was greater for central than intermediate achenes, and for intermediate than peripheral achenes, in two natural germination events in the field. Seed bank samples indicated that few if any achenes remain dormant between years. No significant differences in the growth rates of young seedlings were found in the greenhouse. A demographic experiment documented trade-offs resulting from the dormancy differences: central achenes tended to germinate earlier than intermediate and peripheral ones, and early germination resulted in greater mortality, but survivors that had germinated earlier attained greater size and produced more seeds. Intermediate achenes, while intermediate in all components of fitness, had the highest total fitness. This was because they resembled peripheral achenes in germinating late and having high survival, but they resembled central achenes in having higher percent germination. The results of these experiments suggest that achene behavior ranges from "low-risk" (peripheral achenes) to "high-risk" (central achenes) within the progeny of a single individual, while individuals and populations vary in the proportion of offspring exhibiting each type of behavior.