Effects of herkogamy and inbreeding on the mating system of <Emphasis Type="Italic">Mimulus luteus</Emphasis> in the absence of pollinators |
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Authors: | Gastón O Carvallo Rodrigo Medel |
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Institution: | 1.Departamento de Ciencias Ecológicas, Facultad de Ciencias,Universidad de Chile,Santiago,Chile |
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Abstract: | Self-pollination mechanisms are often invoked to explain plant reproduction in environments devoid of pollinators. However,
populations may evolve a diverse variety of strategies depending on the ecological context of pollination. In this study we
examined the pollination environment, inbreeding depression, and herkogamy of Mimulus luteus (Phrymaceae) in two consecutive years in an attempt to evaluate the extent to which these factors determine the current level
of autogamy in this population. Results indicate that pollinators were almost absent in the study site in 2005 and 2006. Likewise,
no evidence of significant inbreeding depression for seed production and seed germination was detected in the 2 years. Because
M. luteus presents hermaphrodite flowers with ‘movement herkogamy’ (touch-sensitive stigmata that close upon contact), and anther–stigma
separation, we evaluated the role of these traits in self-fertilization. First, we assessed the effects of pollen source (self-
and xenogamous pollen, and control solution) on stigmata dynamics after pollen deposition, and seed production. We observed
that stigmata that received pollen (self- and xenogamous hand-pollinated) remained closed for a longer time than flowers that
received no pollen (control flowers). Seed production, however, was unaffected by pollen source, indicating that movement
herkogamy does not prevent self-fertilization in this population. Second, a phenotypic selection analysis revealed that seed
production increased with a reduction of anther–stigma separation in absence of pollinators (bagged flowers), suggesting that
low herkogamy levels are promoted in this population. Our results indicate that lack of inbreeding depression, ineffective
movement herkogamy, and selection against anther–stigma separation are factors that may contribute to the prevalence of autogamous
reproductive mechanisms when M. luteus faces environments with scarce mating opportunity. |
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