Floral mimicry between two desert annuals, mohavea confertiflora (scrophulariaceae) and mentzelia involucrata (loasaceae)
Claremont, Calif., Claremont Graduate Univ., Diss., 1980
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| Sprache: | eng |
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Tag hinzufügen | Zusammenfassung: | Claremont, Calif., Claremont Graduate Univ., Diss., 1980 A case of deceptive floral mimicry involving two desert annuals, Mohavea confertiflora and Mentzelia involucrata, was investigated. A set of categories was established to provide a framework by which situations of putative deceptive floral mimicry could be studied and analyzed. These were based in part on the tripartite system for classifying mimetic phenomena. The type of mimicry investigated appears based upon food deception since the model produces abundant pollen and nectar in open, actinomorphic flowers which are visited by several species of bees and beetles. In contrast, the mimic produces a minute amount of nectar but this and its pollen are 'hidden' within the closed floral tube of its zygomorphic corolla. The potential food resources of Mohavea blossoms are not exploited as they are in Mentzelia involucrata. Evidence for floral mimicry is based upon morphological similarities of the flowers of model (M. involucrata) and mimic (M. confertiflora) and from observations of pollinator activity in relation to them. Analysis of ethological behavior was emphasized. A series of categories was established for analyzing pollinator behavior. These were grouped according to (a) minimal requirements which are necessary for deceptive mimicry systems to be operative, (b) additional considerations of pollinator behavior, and (c) similarities that may exist in floral and plant morphology in deceptive mimicry systems. The primary pollinators of both model and mimic are two closely related species of Xeralictus and two closely related species of Hesperapis bees. These bees exhibited a high level of constancy to the model and are the only known pollinators of the mimic. Analysis of every category of pollinator behavior showed that the model consistently had a higher rate of activity (e.g. visits and pollinations) than the mimic. In no case did the mimic outcompete the model for pollinator service even in locations where the model was greatly outnumbered by the mimic. The mimic is pollinated when the bee pollinators 'mistake' it for the model. Pollinations of the mimic by Hesperapis female bees appear entirely the result of chance mistakes. Pollinator activity by Xeralictus and Hesperapis males in relation to the mimic is more difficult to analyze but shows that these bees also prefer the model to the mimic. Estimations of the number of mistakes made by these bees are obtained by noting the number with Mohavea pollen attached to their thorax. The pollination mechanism of Mohavea confertiflora appears highly efficient and adapted to 'take advantage' of occasional 'mistakes' by the otherwise oligolectic pollinators of the model (i.e. Hesperapis and Xeralictus bees). For example, (a) the physical movements by which bees gain entry into a Mentzelia flower are identical with the movements required to enter the narrow floral tube of Mohavea flowers; (b) pollen deposition is nototribic and Mohavea pollen is spatially separated on the bees from Mentzelia pollen; (c) Mohavea pollen is cohesive and sticks to the thorax of bees, where it accumulates, 'ready' for another 'mistake', which may result in pollination of another Mohavea flower; and (d) bees which carry Mohavea pollen need enter the floral tube of a Mohavea flower for only a split second in order to effect pollination. Morphological evidence for the existence of floral mimicry consisted of comparing characters of model and mimic which were considered important for attracting visually orienting bees, such as plant height, size and degree of dissection of their flowers. A high degree of similarity was found in the morphological characters examined; strong evidence was obtained for convergence in petal length; a remarkable convergence occurs in pollen morphology. Floral spectral reflectance patterns are also quite similar. Corollas of model and mimic are UV absorptive and highly reflective at higher wavelengths. |
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| Beschreibung: | 191 S. |