Rethinking glacial retreat and postglacial expansion of the Netropical palm Mauritia

Valentí Rull

This paper presents an unconventional perspective on the glacial retraction and postglacial expansion of the lowland Neotropical palm Mauritia flexuosa during the last glacial cycle. The classical view holds that this palm was confined to multiple wet refugia during the Last Glacial Maximum (LGM), owing to purported Neotropical-wide arid climates. From these refugia, M. flexuosa is thought to have expanded across much of tropical South America in postglacial times in response to a hypothetical increase in moisture. Here, we reconsider the available paleoecological, phylogeographic, paleoclimatic and eustatic evidence to propose an alternative scenario. Paleoecological and phylogeographic data are consistent with widespread glacial refugia; however, paleoclimatic reconstructions indicate that general cooling, rather than the assumption of broad Neotropical aridity, played a greater role in driving M. flexuosa retraction to warm refugia up to ~200 m elevation. Within this framework, the continental shelf—exposed during the LGM—would have represented an unexpected landmass for sustaining glacial Mauritia refugia. Postglacial expansion would have been driven mainly by Holocene warming. This new perspective integrates elements of both the refugial and the divergence–vicariance hypotheses, two classical competing explanations for Neotropical biogeography. The evidence suggests that these hypotheses are best viewed as complementary rather than mutually exclusive.