Abstract
Understanding the processes that cause speciation is a key aim of evolutionary biology. Lineages or biomes that exhibit recent and rapid diversification are ideal model systems for determining these processes. Species rich biomes reported to be of relatively recent origin, i.e., since the beginning of the Miocene, include Mediterranean ecosystems such as the California Floristic Province, oceanic islands such as the Hawaiian archipelago and the Neotropical high elevation ecosystem of the Páramos. Páramos constitute grasslands above the forest tree-line (at elevations of c. 2800–4700 m) with high species endemism. Organisms that occupy this ecosystem are a likely product of unique adaptations to an extreme environment that evolved during the last three to five million years when the Andes reached an altitude that was capable of sustaining this type of vegetation. We compared net diversification rates of lineages in fast evolving biomes using 73 dated molecular phylogenies. Based on our sample, we demonstrate that average net diversification rates of Páramo plant lineages are faster than those of other reportedly fast evolving hotspots and that the faster evolving lineages are more likely to be found in Páramos than the other hotspots. Páramos therefore represent the ideal model system for studying diversification processes. Most of the speciation events that we observed in the Páramos (144 out of 177) occurred during the Pleistocene possibly due to the effects of species range contraction and expansion that may have resulted from the well-documented climatic changes during that period. Understanding these effects will assist with efforts to determine how future climatic changes will impact plant populations.
Highlights
The processes by which lineages diverge into new species are still poorly understood but are more likely to be determined in lineages that have recently speciated or are undergoing incipient speciation (Rieseberg and Willis, 2007)
The average diversification rate of the Páramo lineages sampled (Tables 1, 2) is 1.36 speciation events per million years (Myr-1; n = 13; we report values for a pure-birth model of diversification, one with a constant rate and no extinction r (Kendall, 1949; Moran, 1951; Magallón and Sanderson, 2001); rates factoring in extinction are reported in Table S1) compared with 1.07 Myr1 in the Mediterranean Basin (n = 8), 0.76 Myr-1 in Succulent Karoo (n = 9), 0.73 Myr-1 in Hawaii (n = 9), 0.58 Myr-1 in Cerrado (n = 10), 0.40 Myr-1 in the Cape Floristic Region (n = 13), 0.39 Myr-1 in the California Floristic Province (n = 6)
We demonstrate that Páramos have had a rapid diversification rate but those radiations have been more recent than in other hotspots
Summary
The processes by which lineages diverge into new species are still poorly understood but are more likely to be determined in lineages that have recently speciated or are undergoing incipient speciation (Rieseberg and Willis, 2007). The great majority of the plant species found in the Páramos are endemic to this ecosystem, with close relatives in lowland-tropical or northand south-temperate regions (van der Hammen and Cleef, 1986) (Figure 2). These ecosystems may be considered the “water towers” of South America as they provide large reservoirs that serve www.frontiersin.org
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