高榕的3类雌花形态及其繁殖特征

榕树(Ficus spp.)及其传粉榕小蜂(Agaonidae)之间经过长期的协同进化, 已形成了高度专一的互惠共生关系。在雌雄同株的榕树中, 同一个榕果内既繁殖种子, 又繁殖榕小蜂, 雌花资源在繁殖种子和榕小蜂之间是怎样分配的?该研究选择广泛分布于西双版纳地区的高榕(F. altissima)及其传粉榕小蜂系统来回答这个问题。高榕果内的雌花柱头形态变异较大, 有3种类型的柱头——球型、弯钩型和火炬型, 它们分别占到雌花总量的54.00%、36.93%和9.07%。3种类型柱头的雌花分别具有不同长度的花柱, 球型柱头雌花的平均花柱长度最短, 火炬型柱头次之, 弯钩型柱头雌花的平均花柱长度最长。在高榕果内, 有传粉者Eupristina altissima和欺骗者Eupristina sp.两类小蜂进入榕果内繁殖, 前者的产卵器长度比96.01%以上的雌花花柱长, 后者的产卵器也要长于85.73%的雌花花柱, 从产卵器长度和雌花花柱长度的匹配情况看, 它们应该可以利用绝大多数雌花产卵繁殖后代。然而, 繁殖榕小蜂的雌花主要是短花柱的雌花, 其中60.64%是球型柱头的雌花; 而繁殖种子的主要是花柱较长的弯钩型柱头和火炬型柱头的雌花。显然, 繁殖榕小蜂和种子的雌花不仅花柱长度有差异, 柱头也分化出了不同的形态, 变异的柱头形状也是调节榕树-榕小蜂繁殖平衡的手段之一。

Reproductive characteristics of three different shaped stigma in flowers of the fig tree Ficus altissima

Aims Conflicts of interest can be seen in the mutualism between fig trees and their species-specific fig wasp pollinators, where tree reproduction depends on pollen-carrying wasps whereas wasp fitness depends only on the latter. The factors that influence the balance of seed and fig wasp production are still debated. We have found flowers with three different shaped stigmas in the monoecious fig tree Ficus altissima at Xishuangbanna, China, and our objectives were to investigate whether these differences are related to the production of either seeds or fig wasps. Methods Flowers with different stigmal shapes were identified and counted using a dissecting microscope. We measured the style lengths associated with each stigma type and also the ovipositor length of the fig wasps Eupristina altissima and Eupristina sp. that attempt to lay their eggs down the styles. We identified the fate of flowers with each type of stigma using ovule differences after wasp entry and their style lengths. Important findings Based on their shape, we refer to the three types of stigma as globular, hook-like and torch-like. They accounted for 54.00%, 36.93% and 9.07% of the total female flowers, respectively. The style lengths of flowers with globular stigmas were significantly shorter than the others, but 85.73% and 96.01% of the styles were shorter than the lengths of the ovipositors of E. altissima and Eupristina sp., respectively. Most of their eggs were laid in short styled flowers, with globular stigmas (60.64%), whereas most of the seeds were produced by flowers with long styles and hook-like or torch-like stigmas. Flowers producing seeds therefore tend to have a different shaped stigma to those that produce wasps, and stigma shape reflects specialization for either male (pollen-carrying wasp) or female reproductive function. Consequently, it may be one of the factors that influence the balance between fig and fig wasp reproduction in F. altissima.