Abstract:Background
Quaternary climate fluctuations are an engine of biotic diversification. Global cooling cycles, such as the Last Glacial Maximum (LGM), are known to have fragmented the ranges of higher-latitude fauna and flora into smaller refugia, dramatically reducing species ranges. However, relatively less is known about the effects of cooling cycles on tropical biota.
Results
We analyzed thousands of genome-wide DNA markers across an assemblage of three closely related … Show more
“…However, due to the Massenerhebung effect 19 , temperature drops more quickly with increasing altitude in the isolated Moluccan islands than in New Guinea, and both systems encompass environmental extremes from sweltering lowland swamps to chilly mountain cloud forests. Finally, while the geological history has affected the Indo-Pacific biota significantly, dramatic climatic oscillations during the Pleistocene are also expected to impact diversity build-up in the region 20 , 21 . Fig.…”
Tropical mountains harbor exceptional concentrations of Earth’s biodiversity. In topographically complex landscapes, montane species typically inhabit multiple mountainous regions, but are absent in intervening lowland environments. Here we report a comparative analysis of genome-wide DNA polymorphism data for population pairs from eighteen Indo-Pacific bird species from the Moluccan islands of Buru and Seram and from across the island of New Guinea. We test how barrier strength and relative elevational distribution predict population differentiation, rates of historical gene flow, and changes in effective population sizes through time. We find population differentiation to be consistently and positively correlated with barrier strength and a species’ altitudinal floor. Additionally, we find that Pleistocene climate oscillations have had a dramatic influence on the demographics of all species but were most pronounced in regions of smaller geographic area. Surprisingly, even the most divergent taxon pairs at the highest elevations experience gene flow across barriers, implying that dispersal between montane regions is important for the formation of montane assemblages.
“…However, due to the Massenerhebung effect 19 , temperature drops more quickly with increasing altitude in the isolated Moluccan islands than in New Guinea, and both systems encompass environmental extremes from sweltering lowland swamps to chilly mountain cloud forests. Finally, while the geological history has affected the Indo-Pacific biota significantly, dramatic climatic oscillations during the Pleistocene are also expected to impact diversity build-up in the region 20 , 21 . Fig.…”
Tropical mountains harbor exceptional concentrations of Earth’s biodiversity. In topographically complex landscapes, montane species typically inhabit multiple mountainous regions, but are absent in intervening lowland environments. Here we report a comparative analysis of genome-wide DNA polymorphism data for population pairs from eighteen Indo-Pacific bird species from the Moluccan islands of Buru and Seram and from across the island of New Guinea. We test how barrier strength and relative elevational distribution predict population differentiation, rates of historical gene flow, and changes in effective population sizes through time. We find population differentiation to be consistently and positively correlated with barrier strength and a species’ altitudinal floor. Additionally, we find that Pleistocene climate oscillations have had a dramatic influence on the demographics of all species but were most pronounced in regions of smaller geographic area. Surprisingly, even the most divergent taxon pairs at the highest elevations experience gene flow across barriers, implying that dispersal between montane regions is important for the formation of montane assemblages.
“…P ast climate changes have often been invoked as important drivers of population demographic dynamics, species distribution, and genomic diversity patterns, as species directly respond to environmental changes and to changes in resource availability 1 . Mainly studied in temperate regions [2][3][4][5] , such dynamics remain much less explored and more debated in the tropics 6,7 , which are characterized by a very high biodiversity richness. Among tropical regions, Madagascar, with its long history of isolation, high rates of endemism 8,9 , and no significant human impact until the late Holocene 10 , is a key model area to understand how natural climate changes impacted evolutionary trajectories.…”
Quaternary climatic changes have been invoked as important drivers of species diversification worldwide. However, the impact of such changes on vegetation and animal population dynamics in tropical regions remains debated. To overcome this uncertainty, we integrated high-resolution paleoenvironmental reconstructions from a sedimentary record covering the past 25,000 years with demographic inferences of a forest-dwelling primate species (Microcebus arnholdi), in northern Madagascar. Result comparisons suggest that climate changes through the African Humid Period (15.2 – 5.5 kyr) strongly affected the demographic dynamics of M. arnholdi. We further inferred a population decline in the last millennium which was likely shaped by the combination of climatic and anthropogenic impacts. Our findings demonstrate that population fluctuations in Malagasy wildlife were substantial prior to a significant human impact. This provides a critical knowledge of climatically driven, environmental and ecological changes in the past, which is essential to better understand the dynamics and resilience of current biodiversity.
“…S9). We find that the downslope expansion of montane forest habitat during the Pleistocene (Hewitt 2000, Garg et al 2020) did not connect different populations on the same island (e.g. Mindanao, Greater Sundas, New Guinea) sufficiently to erase relatively deep genetic structure among them (Fig.…”
Tropical islands are renowned as natural laboratories for evolutionary study. Lineage radiations across tropical archipelagos are ideal systems for investigating how colonization, speciation, and extinction processes shape biodiversity patterns. The expansion of the island thrush across the Indo-Pacific represents one of the largest yet most perplexing island radiations of any songbird species. The island thrush exhibits a complex mosaic of pronounced plumage variation across its range, and is arguably the world’s most polytypic bird. It is a sedentary species largely restricted to mountain forests, yet it has colonized a vast island region spanning a quarter of the globe. We conducted comprehensive sampling of island thrush populations and obtained genome-wide SNP data, which we used to reconstruct its phylogeny, population structure, gene flow, and demographic history. The island thrush evolved from migratory Palearctic ancestors and radiated explosively across the Indo-Pacific during the Pleistocene, with numerous instances of gene flow between populations. Its bewildering plumage variation masks a biogeographically intuitive stepping stone colonization path from the Philippines through the Greater Sundas, Wallacea and New Guinea to Polynesia. The island thrush’s success in colonizing Indo-Pacific mountains can be understood in light of its ancestral mobility and adaptation to cool climates; however, shifts in elevational range, degree of plumage variation and apparent dispersal rates in the eastern part of its range raise further intriguing questions about its biology.
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