Abstract
Andean uplift and the concomitant formation of the Diagonal Arid of South America is expected to have promoted species diversification through range expansions into this novel environment. We evaluate the evolution of Argylia, a genus belonging to the Bignoniaceae family whose oldest fossil record dates back to 49.4 Ma. Today, Argylia is distributed along the Andean Cordillera, from 15°S to 38.5°S and from sea level up to 4,000 m.a.s.l. We ask whether Argylia’s current distribution is a result of a range expansion along the Andes Cordillera (biological corridor) modulated by climatic niche conservatism, considering the timing of Andean uplift (30 Ma – 5 Ma). To answer this question, we reconstructed the phylogenetic relationships of Argylia species, estimated divergence times, estimated the realized climatic niche of the genus, reconstructed the ancestral climatic niche, evaluated its evolution, and finally, performed an ancestral range reconstruction. We found strong evidence for climatic niche conservatism for moisture variables, and an absence of niche conservatism for most of the temperature variables considered. Exceptions were temperature seasonality and winter temperature. Results imply that Argylia had the capacity to adapt to extreme temperature conditions associated with the Andean uplift and the new climatic corridor produced by uplift. Ancestral range reconstruction for the genus showed that Argylia first diversified in a region where subtropical conditions were already established, and that later episodes of diversification were coeval with the of Andean uplift. We detected a second climatic corridor along the coastal range of Chile-Peru, the coastal lomas, which allowed a northward range expansion of Argylia into the hyperarid Atacama Desert. Dating suggests the current distribution and diversity of Argylia would have been reached during the Late Neogene and Pleistocene.
Highlights
Southern South America exhibits a wide range of climates that results in an extraordinary diversity of biomes including forest, grassland, steppe, alpine, and desert (Ortega et al, 2012)
The results show that Argylia is a monophyletic group with an estimated minimum date of origin of ∼38.21 Ma (Figure 4)
It diverged ∼28.04 Ma to further subdivide into two subclades: SC I, formed by the two ChileanArgentinean taxa A. uspallatensis and A. bustillosii, with a Mean Annual Temperature (MAT) Temperature Seasonality (TS) maxTWaM minTCM mTWaQ mean Temperature of the Coldest Quarter (mTCQ) Annual Precipitation (AP) Precipitation of the Driest Month (PDM) Precipitation Seasonality (PS) Precipitation of the wettest Quarter (PWeQ) Precipitation of the Driest Quarter (PDQ) AUC
Summary
Southern South America exhibits a wide range of climates that results in an extraordinary diversity of biomes including forest, grassland, steppe, alpine, and desert (Ortega et al, 2012). One of the most defining features of South America biogeography is a large arid region with annual rainfall below 500 mm that crosses the western side of the continent diagonally from northwest to southeast, beginning at coastal equatorial latitudes (4◦S) and culminating on the Atlantic coast at latitude 55◦S. This region has been defined as the South American Arid Diagonal (SAD, Veit and Garleff, 1995; Villagrán and Hinojosa, 1997; Garreaud et al, 2010; Figure 1). The coeval emergence of the Humboldt Current during the Neogene further intensified aridity leading to the development of the current hyperarid Atacama Desert on the Pacific coast, a region considered one of the most arid in the world (Hinojosa and Villagrán, 1997; Latorre et al, 1997; Hartley et al, 2005; Garreaud et al, 2010)
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