BackgroundInterspecific interactions have long been assumed to play an important role in diversification. Mutualistic interactions, such as nursery pollination mutualisms, have been proposed as good candidates for diversification through co-speciation because of their intricate nature. However, little is known about how speciation and diversification proceeds in emblematic nursery pollination systems such as figs and fig wasps. Here, we analyse diversification in connection with spatial structuring in the obligate mutualistic association between Ficus septica and its pollinating wasps throughout the Philippines and Taiwan.Results Ceratosolen wasps pollinating F. septica are structured into a set of three vicariant black coloured species, and a fourth yellow coloured species whose distribution overlaps with those of the black species. However, two black pollinator species were found to co-occur on Lanyu island. Microsatellite data on F. septica indicates the presence of three gene pools that broadly mirrors the distribution of the three black clades. Moreover, receptive fig odours, the specific message used by pollinating wasps to locate their host tree, varied among locations.Conclusions F. septica and its black pollinator clades exhibited similar geographic structuring. This could be due originally to geographic barriers leading to isolation, local adaptation, and finally co-structuring. Nevertheless, the co-occurrence of two black pollinator species on Lanyu island suggests that the parapatric distribution of the black clades is now maintained by the inability of migrating individuals of black pollinators to establish populations outside their range. On the other hand, the distribution of the yellow clade strongly suggests an initial case of character displacement followed by subsequent range extension: in our study system, phenotypic or microevolutionary plasticity has allowed the yellow clade to colonise hosts presenting distinct odours. Hence, while variation in receptive fig odours allows specificity in the interaction, this variation does not necessarily lead to coevolutionary plant-insect diversification. Globally, our results evidence evolutionary plasticity in the fig-fig wasp mutualism. This is the first documentation of the presence of two distinct processes in pollinating fig wasp diversification on a host species: the formation of vicariant species and the co-occurrence of other species over large parts of their ranges probably made possible by character displacement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-1034-8) contains supplementary material, which is available to authorized users.
The obligate mutualism of figs and fig-pollinating wasps has been one of the classic models used for testing theories of co-evolution and cospeciation due to the high species-specificity of these relationships. To investigate the species-specificity between figs and fig pollinators and to further understand the speciation process in obligate mutualisms, we examined the genetic differentiation and phylogenetic relationships of four closely related fig-pollinating wasp species (Blastophaga nipponica, Blastophaga taiwanensis, Blastophaga tannoensis and Blastophaga yeni) in Japan and Taiwan using genome-wide sequence data, including mitochondrial DNA sequences. In addition, population structure was analysed for the fig wasps and their host species using microsatellite data. The results suggest that the three Taiwanese fig wasp species are a single panmictic population that pollinates three dioecious fig species, which are sympatrically distributed, have large differences in morphology and ecology and are also genetically differentiated. Our results illustrate the first case of pollinator sharing by host shift in the subgenus Ficus. On the other hand, there are strict genetic codivergences between allopatric populations of the two host-pollinator pairs. The possible processes that produce these pollinator-sharing events are discussed based on the level and pattern of genetic differentiation in these figs and fig wasps.
Although species specificity between fig trees and their pollinators has been considered a classic example of obligate mutualism, increasing exceptions to the one-to-one relationship suggest that multiple pollinator species per fig host species may be a pervasive phenomenon. Based on both mitochondrial DNA and microsatellite analyses, we found three putative pollinator species (Ceratosolen spp.) associated with Ficus spetica in southern Taiwan, two of which, that differ in color, routinely coexist within single figs. These three pollinators are substantially divergent from the pollinator of F. spetica in New Guinea, implying that wasp diversity may be highly underestimated when the one-to-one rule is assumed. Our findings not only provide the first case of coexistence of pollinators within single figs on a shared dioecious Ficus host, but also an ideal system to investigate interspecific competition and sex allocation, especially when coexisting pollinators are visually distinguishable by their colors. Abstract in Chinese is available at
The nocturnal distribution and resource use by Ryukyu flying foxes was studied along 28 transects, covering five types of habitats, on Iriomote Island, Japan, from early June to late September, 2005. Bats were mostly encountered solitarily (66.8%) or in pairs (16.8%), with a mean linear density of 2.5 ± 0.6 bats/km of transect/night. Across the island, however, bat densities were distributed non-randomly among transect-nights, not correlated with transect length, and showed a slightly clumped distribution (variance/mean = 3.3). Outskirt trails contributed higher values to the relative importance of bat abundance, but the highest mean abundances occurred mostly at village sites on the west coast, which on average devoted only a quarter of their land area to agriculture/husbandry compared to those on the east coast. This supports our prediction that higher bat abundances are found in areas with less anthropogenic interference and more forest. Among habitats, the mean total abundance and density were lower in cultivated areas than in villages and inland forests. Bat perches in cultivated areas were also lower, and were in correspondence with lower shrub and canopy heights, and less canopy coverage. Flying fox abundance was correlated moderately with the heterogeneity of the tree composition, and strongly with the density of major fruiting trees. Thirty-nine species of plants and some animal items were used by Ryukyu flying foxes, including at least 31 species of fruits, 13 species of flowers, and leaves of seven species, with 14 species new to the record. Ficus septica and F. variegata were the most frequently encountered and dominant items in both fecal and rejecta/dropped samples, followed mostly by other figs and mulberries in the former, but by larger-seed non- Moraceae plants in dropped samples. Our results suggest that for conservation of flying foxes undisturbed forests providing an adequate resource basis are of major importance.
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