Abstract
BackgroundAs one of largest angiosperm families, orchids have long fascinated evolutionary biologists with their staggering diversity in floral design and display to promote outcrossing. Two of the most intriguing aspects of orchid pollination that promote cross-pollination are pollinarium reconfiguration (PR) and deceptive pollination. PR and generalized food deception employ virtually antagonistic methods of promoting cross-pollination: PR occurs through delayed pollination, involving the relatively long visitation periods that are typically observed for the pollinators of one flower or inflorescence; conversely, generalized food deception leads to reductions in the visitation periods of pollinators to one flower or inflorescence. Thus, it is logical to hypothesize that PR is unnecessary or PR happens soon in generalized food-deceptive orchids in the promotion of cross-pollination. Using Doritis pulcherrima as a model, the aim of this study was to understand the following: (1) the pollination and breeding system of D. pulcherrima; (2) the morphological interactions between orchids and their pollinators; and (3) whether PR is necessary in the promotion of cross-pollination in D. pulcherrima.ResultsOur observations indicated that Doritis pulcherrima is pollinated almost exclusively by Amegilla nigritar (Hymenoptera: Apidae) and possesses pollinia that are deposited on the “occiputs” (cervical membranes) of these insects. All of evidences are indicated that D. pulcherrima is a generalized food-deceptive orchid. Our morphometric measurements of the flowers and pollinators show that the heights of the “occiputs” with un-oriented pollinaria were equal to the distances between stigmas and surfaces of the middle lobes, suggesting that pollinarium reconfiguration is not necessary in Doritis pulcherrima.ConclusionsOur observation and analyses supported the hypothesis that pollinarium reconfiguration is unnecessary in generalized food-deceptive orchids, such as Doritis pulcherrima, for the promotion of cross-pollination. This conclusion was indirectly supported by the abundance of deceptive orchids that do not exhibit pollinarium reconfiguration. There are two mechanisms (i.e. clone-growing characteristics and a long flowering season) that promote fruit sets in the epiphytic food-deceptive orchids in tropical regions.
Highlights
As one of largest angiosperm families, orchids have long fascinated evolutionary biologists with their staggering diversity in floral design and display to promote outcrossing
pollinium shrinking (PS) was reported in two species of Bulbophyllum [5] and Trigonidium [6], whereas anther cap retention (ACR) has been recorded in several genera, including Eulophia [3] and Tipularia [7]
Using Doritis pulcherrima as a model, the aims of this study are to understand the following: (1) the pollination and breeding system of D. pulcherrima; (2) the morphological interactions between orchids and their pollinators; and (3) whether pollinarium reconfiguration (PR) is necessary in the promotion of cross-pollination in D. pulcherrima
Summary
As one of largest angiosperm families, orchids have long fascinated evolutionary biologists with their staggering diversity in floral design and display to promote outcrossing. Two of the most intriguing aspects of orchid pollination that promote cross-pollination are pollinarium reconfiguration (PR) and deceptive pollination. It is logical to hypothesize that PR is unnecessary or PR happens soon in generalized food-deceptive orchids in the promotion of cross-pollination. As one of largest plant families with approximately 19,500 species [1], orchids have long fascinated evolutionary biologists with their staggering diversity in floral design and display to maximize outcrossing. It is estimated that approximately one-third of orchids, approximately 6500 species, are pollinated through deception [8,9,10,11,12]. In contrast to PR, deceptive pollination promotes cross-pollination by reducing the visitation period of pollinators and/or discouraging repeat visits to one flower or one inflorescence [9,14,15]
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