Rapid in situ diversification rates in Rhamnaceae explain the parallel evolution of high diversity in temperate biomes from global to local scales

Abstract

Summary The macroevolutionary processes that have shaped biodiversity across the temperate realm remain poorly understood and may have resulted from evolutionary dynamics related to diversification rates, dispersal rates, and colonization times, closely coupled with Cenozoic climate change. We integrated phylogenomic, environmental ordination, and macroevolutionary analyses for the cosmopolitan angiosperm family Rhamnaceae to disentangle the evolutionary processes that have contributed to high species diversity within and across temperate biomes. Our results show independent colonization of environmentally similar but geographically separated temperate regions mainly during the Oligocene, consistent with the global expansion of temperate biomes. High global, regional, and local temperate diversity was the result of high in situ diversification rates, rather than high immigration rates or accumulation time, except for Southern China, which was colonized much earlier than the other regions. The relatively common lineage dispersals out of temperate hotspots highlight strong source‐sink dynamics across the cosmopolitan distribution of Rhamnaceae. The proliferation of temperate environments since the Oligocene may have provided the ecological opportunity for rapid in situ diversification of Rhamnaceae across the temperate realm. Our study illustrates the importance of high in situ diversification rates for the establishment of modern temperate biomes and biodiversity hotspots across spatial scales.

Radiating diversification and niche conservatism jointly shape the inverse latitudinal diversity gradient of Potentilla L. (Rosaceae)

“…It is pervasive for species to retain the climatical preferences of their ancestors [ 18 , 19 ]. An increasing number of studies have found that niche conservatism play a major role in shaping various distribution patterns, including LDGs [ 15 , 58 ], inverse LDGs [ 3 , 5 , 8 , 10 ], and others [ 59 , 60 ]. However, the influence of evolutionary time and diversification rates on driving species distribution patterns varies greatly across lineages, regardless of whether these distribution patterns conform to LDGs or inverse LDGs [ 3 , 6 , 9 , 10 , 12 ].…”

“…An increasing number of studies have found that niche conservatism play a major role in shaping various distribution patterns, including LDGs [ 15 , 58 ], inverse LDGs [ 3 , 5 , 8 , 10 ], and others [ 59 , 60 ]. However, the influence of evolutionary time and diversification rates on driving species distribution patterns varies greatly across lineages, regardless of whether these distribution patterns conform to LDGs or inverse LDGs [ 3 , 6 , 9 , 10 , 12 ]. Generally, the lineages with ancient origins tend to favor the time-for-speciation hypothesis, such as Cycadaceae (stem age: ca.…”

“…However, there are also some taxonomic lineages that exhibit inverse LDGs, in which species richness reaches its zenith in extratropical regions and decreases toward the tropical regions. Such inverse LDGs have been observed in insects [ 3 , 4 ], amphibians [ 5 ], birds [ 6 , 7 ], mammals [ 6 ], angiosperms [ 8 – 10 ], and gymnosperms [ 11 , 12 ]. For example, the stenammine ants species are most diverse in the 35°N to 40°N range and decrease towards the equator [ 3 ], and the Rhamnaceae species diversity is markedly higher in temperate than in tropical regions, resulting in a bimodal latitudinal diversity gradient [ 10 ].…”

“…Such inverse LDGs have been observed in insects [ 3 , 4 ], amphibians [ 5 ], birds [ 6 , 7 ], mammals [ 6 ], angiosperms [ 8 – 10 ], and gymnosperms [ 11 , 12 ]. For example, the stenammine ants species are most diverse in the 35°N to 40°N range and decrease towards the equator [ 3 ], and the Rhamnaceae species diversity is markedly higher in temperate than in tropical regions, resulting in a bimodal latitudinal diversity gradient [ 10 ]. Determining the driving forces behind these less common richness patterns is helpful in deepening our understanding of the regular LDGs.…”