Bulbophyllum involutum Borba, Semir & F. Barros (Orchidaceae), a New Species from the Brazilian "Campos Rupestres"

Abstract

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Evidence of natural hybridization and introgression in Bulbophyllum involutum Borba, Semir & F. Barros and B. weddellii (Lindl.) Rchb. f. (Orchidaceae) in the Chapada Diamantina, Brazil, by using allozyme markers

“…The morphological uniformity observed in the population of B. weddellii in Mucugê points out to the absence of introgression in this species. The situation found in the sampled populations are at odds with the original findings of Borba & Semir (1998a) at Serra do Cipó. These authors found only one individual of B.…”

“…They also did not find any evidence for introgression into any of the parental species. Borba & Semir (1998a) depicted a series of weak barriers that could constitute a filter system ensuring the rarity of the hybrids and integrity of B. weddellii and B. involutum at Serra do Cipó: 1) the pollinators are the same, but the main pollinator of one species is the secondary of the other; 2) the pollinarium of B. weddellii does not enter on the stigmatic cavity of B. involutum (only the opposite occurs); 3) despite the species being intercompatible, hybrid seeds display low fertility; 4) parental species are sympatric but no syntopic; 5) the hybrid is selfincompatible or sterile and has inefficient pollination system. Similar mechanisms with several individually weak barriers have been observed elsewhere in the Orchidaceae (Romero & Carnevali 1991).…”

“…On the other hand, Borba & Semir (1998a) pinpointed the relativity of self-incompatibility and hybrid sterility in Orchidaceae, since due to the high number of ovules and pollen grains in the flowers and absence of endosperm in the seeds the chance of production of a few viable seeds in self-pollination or backcrosses to the parentals are high, especially in species with vegetative propagation that can live for hundreds of years such as Bulbophyllum (van der Pijl & Dodson 1966). Once the first sterility barriers are broken, complete fertility can be attained in posterior hybrid generations, and could lead to hybrid stability and speciation (Grant 1981, Rieseberg 1995.…”

“…Despite the large differences in flower morphology, they present a relatively high similarity in the chemical composition of floral volatiles (Silva et al 1999) and attract the same species of pollinators (Borba & Semir 1998b). Borba & Semir (1998a) suggested a series of barriers that could lead to the rarity of B. ×cipoense and to the absence of further consequences in the parental species such as introgression or competition with the hybrids.…”

“…The main factors preventing hybridization in Orchidaceae are pre-pollination mechanisms such as pollinator specificity and phenological or mechanic barriers, while genetic barriers (post-pollination) between closely related species are usually weak or absent (van der Pijl & Dodson 1966, Dressler 1981. Borba & Semir (1998a) described the hybrid Bulbophyllum ×cipoense Borba & Semir ( figure 1, 2), between B. involutum Borba, Semir & F. Barros (Bulbophyllum sect. Didactyle) and B. weddellii (Lindl.)…”