Abstract
Bird pollination in Asia is regarded as an uncommon phenomenon and, therefore, only a few investigations on mating pattern and paternity in fruits of Asian bird-pollinated plants have been conducted. Here, we examined spatial genetic structure, pollen dispersal, and multiple paternity in a natural population of Bombax ceiba (B. ceiba) (Malvaceae) in Hainan Island, South China, using simple sequence repeat (SSR) markers. A low genetic diversity (He = 0.351 ± 0.0341 and 0.389 ± 0.043, respectively, for adults and offspring) and bottleneck effects were observed. Genetic kinship was significant within 400 m or in 1,800–3,800 m. Both the mating pattern and paternity analysis confirmed obligate xenogamy and a low multiple paternity in B. ceiba. There was a strongly negative relationship between the frequency of matings and the distance between mating pairs. The average pollen dispersal distance was 202.89 ± 41.01 m (mean ± SE) and the farthest distance of > 1 km was recorded. Realized mating events showed an extremely leptokurtic distribution within 1,200 m, suggesting that the pollen dispersal distance was consistent with the optimal foraging theory of generalist birds such as Zosterops spp. and Pycnonotus spp. Paternity per tree ranged from two to six and the average effective number of pollen donors per maternal plant was 3.773, suggesting a low level of paternity diversity as compared to other bird-pollinated plants. We concluded that optimal foraging behavior by generalist birds could explain the leptokurtic pollen dispersal distribution and predominantly near-neighbor matings in B. ceiba. The limited pollen dispersal distance and low multiple paternity were consistent with low fruit setting rate (3.27 ± 0.93%) in this self-incompatible tree, which was caused mainly by the restricted flight distance of birds and human disturbances. Low genetic diversity and significant spatial genetic structure might have largely resulted from logging and human collection of fruits.
Highlights
Birds are one of the most diverse group of ecosystem service providers
Our findings show that near-neighbor mating is common in generalist-pollinated B. ceiba and that the pollen dispersion pattern follows a leptokurtic distribution, which is in accordance with the optimum foraging theory of animals (Pyke, 1984)
Our result indicated that B. ceiba possesses strict self-incompatibility with limited pollen dispersal distance and low level of paternity, together with low levels of genetic diversity and a significant spatial genetic structure, which may be consequences of near-neighbor mating caused by restricted flight distance of birds and human disturbances
Summary
Birds are one of the most diverse group of ecosystem service providers. More than 900 bird species pollinate members of ca. 500 of the 13,500 vascular plant genera, making bird pollination an essential component of the ecosystem (Sekercioglu, 2006). (Bombacoideae, Malvaceae) is an umbrella species in dry and hot forest areas of Asia because they can provide food, shelter, roosting, and breeding sites to a large number of birds as well as insects and form the major structural and functional basis of forest ecosystems (Jain et al, 2011) It is found in temperate and tropical regions of Asia such as India, China-Indochina Peninsula, Indonesia, Malaysia, Philippines, Sri Lanka, and Northern Australia. The flowering of B. ceiba peaks during late February and early March, which is the dry season in southern China, especially in Hainan Island (data from National Meteorological Information Center).1 At this time, there are only limited number of plants that are flowering in southern China and the copious dilute nectar of B. ceiba acts as the main food and a safe water resource for generalist birds. This study addresses the following two questions: (i) What is the mating system and pollen dispersal of B. ceiba? and (ii) How do generalist birds affect genetic diversity and mating patterns? We hypothesize that: (i) limited-distance pollen dispersal and low paternal diversity may be due to high density of B. ceiba individuals and bird habits such as the restricted flight distance of birds and optimum foraging behavior of birds and (ii) pollination by generalist birds may result in high outcrossing rate, but low genetic diversity in B. ceiba due to human disturbances
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