Spatial-temporal evolution of Macaranga ant-plant lineages (Euphorbiaceae) in Southeast Asia
Final Report Abstract
One of the fundamental aims in evolutionary biology is a deeper understanding of the factors that determine the evolution and diversity of organisms. The species-rich palaeotropic genus Macaranga (Euphorbiaceae) is an excellent model system to analyze evolutionary processes associated with myrmecophytism, that is the obligate association between plants and ants. Using next-generation-sequencing techniques (genotyping-by-sequencing, GBS) we were able to reconstruct for the first time a comprehensive and highly resolved phylogeny of Macaranga ant-plants and their close relatives in Southeast-Asian Sundaland. This enabled us to draw various conclusions on the spatial-temporal evolution of the group and to elaborate on the role that myrmecophytism played during diversification processes. Contrary to earlier investigations, our analysis provided clear evidence that myrmecophytism evolved only once in Macaranga, approximately 18 million years ago (mya) on the island of Borneo. Given the variation in domatia types and the fact that domatia, as the central trait of myrmecophytes, were lost at least 4-6 times during evolution of Macaranga ant-plants, suggest that traits associated with myrmecophytism are prone to phenotypic plasticity and are not stable in time. Additionally, diversification rate analyses yielded no support for the earlier hypothesis that myrmecophytism may have enhanced diversification rates in Macaranga. Coupled with the observation that Macaranga ant-plants exhibit varying degrees of antpartner specificity, with more basal host plant lineages exhibiting a stronger degree of specialization, we conclude that while myrmecophytism undoubtedly acts as a key innovation with regard to the enlargement of ecological niches, it does not seem to act as a primary driver of speciation in Macaranga. Instead, we suggest that in overly specialized cases it might even represent an evolutionary dead end. Biogeographic inferences obtained from dated phylogenies and ancestral area reconstruction suggest that geological events and geographic settings rather than the association with ants were the main drivers of biodiversity evolution in Macaranga. Diversification of three major myrmecophytic lineages in the genus line up at ~ 9 mya, coinciding with volcanic activity and the rapid uplift of Mt. Kinabalu in northern Borneo. Similarly, some extrinsic factor is likely to have acted as a driving force promoting dispersal and diversification in Macaranga section Pruinosae. Diversification between eastern and western Sundaland lineages in widely distributed species of this section concentrated around 1.4 mya, suggesting that dispersal across the Sunda shelf, which acted as a barrier to gene flow throughout most of the past, was facilitated at that time. The two islands of Bangka and Belitung, which are located between Borneo and Sumatra, obviously played an important role as stepping stones for dispersal across the shelf at least in some species.
Publications
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An NGS approach to unraveling the phylogeny and biogeography of section Pruinosae within the SE Asian ant-plant genus Macaranga. Meeting of the Section Biodiversity and Evolution, German Society for Plant Sciences. 5th October 2021, online
Dixit, N. M. & Guicking, D.
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An NGS-based approach to investigating the spatial and temporal evolution of myrmecophytism in Southeast Asian Macaranga (Euphorbiaceae) lineages. SFE² GfÖ EEF Joint meeting, International Conference on Ecological Sciences "Ecology and Evolution: New perspectives and societal challenges". 21-25 November 2022, Metz (France)
Dixit, N. M. & Guicking, D.
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NGS based approach to investigating systematics and biogeography of myrmecophytic Macaranga (Euphorbiaceae). 23rd Annual Meeting of the Society of Biological Systematics. 21st – 24th March 2022, online
Dixit, N. M. & Guicking, D.
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An NGS-based approach to investigate the evolutionary dynamics of myrmecophytism in the Southeast Asian Macaranga (Euphorbiaceae) ant-plant lineages. 52. Jahrestagung der GfÖ, 12. - 16. September 2023, Leipzig
Dixit, N. M. & Guicking, D.
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Biogeography of the Sunda Shelf revisited: Insights from Macaranga section Pruinosae (Euphorbiaceae). Frontiers in Ecology and Evolution, 10.
Dixit, Nadi M.; Zirpel, Malte; Slik, J. W. Ferry; Jamsari, J.; Weising, Kurt & Guicking, Daniela
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Myrmecophytism as a driver of macroevolutionary patterns: perspectives from the Southeast AsianMacarangaant-plant symbiosis. Cold Spring Harbor Laboratory.
Dixit, Nadi M. & Guicking, Daniela
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Understanding the macroevolutionary dynamics of myrmecophytism through the Southeast Asian Macaranga-Crematogaster ant-plant symbiosis. DBG, Meeting of the Section Biodiversity & Evolutionary Biology, 23rd - 26th Aug. 2023, Gießen
Dixit, N. & Guicking, D.
