Pollination ecology and breeding system of Xylopia championii (Annonaceae): curculionid beetle pollination, promoted by floral scents and elevated floral temperatures

Data on the reproductive biology of the Annonaceae are rather fragmentary, particularly for paleotropical species. The pollination ecology and breeding system of the Sri Lankan endemic Xylopia championii (Annonaceae) are described in detail. The pollination ecology was investigated using a diverse range of approaches, including (1) observations of flower-level and population-level phenology, (2) assessments of floral visitors and effective pollinators, (3) monitoring of floral temperature in situ using a digital data logger, and (4) analysis of scent chemistry using solid-phase microextraction sampling and gas chromatography-mass spectrometry identification of volatiles. The breeding system was evaluated using pollen/ovule ratios and field-based controlled-pollination experiments. Intrafloral dichogamy (protogyny) occurs over a 2-d period, with a reproductively inactive phase between the pistillate and staminate phases, although there is no evidence of interfloral dichogamy. The inner petals close to form a pollination chamber during the reproductively active phases. The flowers are pollinated by a species of Endaeus weevil (Coleoptera: Curculionidae). Floral chamber temperatures are elevated to 8°C above ambient levels. The floral scent contains a combination of volatiles that have previously been observed in fruits and other flowers and that possibly mimic insect pheromones. Xylopia championii has an essentially xenogamous breeding system, promoted by protogyny. Although X. championii possesses numerous clear adaptations for cantharophily, there is no evidence for a species-specific interaction. The beetles are attracted to the flowers by strong scents; rewards offered to the beetles include heat energy and protection from predators. Low levels of fruit set in natural conditions suggest that pollinator availability may be a limiting factor. © 2007 by The University of Chicago. All rights reserved.published_or_final_versio

Reproductive biology of two sympatric species of Polyalthia (annonaceae) in Sri Lanka. I. Pollination by curculionid beetles

The pollination biology of two sympatric species, Polyalthia coffeoides and Polyalthia korinti (Annonaceae), is described in detail. An Endaeus species (Coleoptera: Curculionidae) is shown to be the major pollinator of both species, with Carpophilus plagiatipennis (Coleoptera: Nitidulidae) as the secondary pollinator of P. coffeoides. Both Polyalthia species show intrafloral dichogamy (protogyny) with a reproductively inactive phase between the pistillate and staminate phases, although there is no evidence of interfloral dichogamy. A pollination chamber is formed by the inner petals throughout the reproductively active phases. Thermogenesis occurs in P. korinti, with internal floral temperatures up to 6°C above ambient levels. The heat is presumably an energy reward for the beetles. Although most pollination systems are regarded as diversified and opportunistic, specialized pollination systems are typical of the Annonaceae. Although P. coffeoides and P. korinti have overlapping distributions, habitats, and flowering seasons and share the same pollinators, the extent of competition for pollinators is likely to be lessened due to the abundance and nonspecificity of the beetles. © 2006 by The University of Chicago. All rights reserved.published_or_final_versio

Reproductive biology of two sympatric species of Polyalthia (annonaceae) in Sri Lanka. II. Breeding systems and population genetic structure

The breeding systems of two sympatric species, Polyalthia coffeoides and Polyalthia korinti (Annonaceae), are assessed using a range of approaches, including controlled pollination experiments and analysis of inter-simple sequence repeat markers within and between populations. Natural (open) pollination resulted in similar levels of fruit formation as artificial cross-pollination, suggesting that pollinator availability is not a limiting factor in reproduction. Both species possess facultatively xenogamous breeding systems, with 33%-36% fruit formation in artificially crossed experiments and 17%-19% fruit formation following geitonogamy. Reduced fruit set following geitonogamy suggests partial self-incompatibility; this is supported by index of self-incompatibility values of ca. 0.5 in both species. Analysis of population genetic structure supports the hypothesis of a mixed but largely xenogamous mating system. Genetic diversity within populations was estimated to be ca. 80% and 66% of total genetic diversity for P. coffeoides and P. korinti, respectively. The levels of gene flow between populations were moderate (Nm = 2.033 for P. coffeoides and 0.970 for P. korinti), and genetic identity (I) values between populations within species were high. This possibly reflects the fragmentation of a previously more extensive population, correlated with the historical deforestation associated with crop cultivation and irrigation in Sri Lanka. © 2006 by The University of Chicago. All rights reserved.published_or_final_versio