Could coastal plants in western Amazonia be relicts of past marine incursions?

Abstract

The rainforests of Amazonia comprise some of the most biologically diverse ecosystems on Earth. Despite this high biodiversity, little is known about how landscape changes that took place in deep history have affected the assembly of its species, and whether the impact of such changes on biodiversity can still be observed. Here, we present a hypothesis to explain our observation that plants typical of Neotropical coastal habitats also occur in western Amazonia, in some cases thousands of kilometres away from the coast. Evidence on their current distribution, dispersal biology and divergence times estimated from molecular phylogenies suggest that these plants may be the legacy of the large marine‐influenced embayment that dominated the area for millions of years in the Neogene. We hypothesize that coastal plants dispersed along the shores of this embayment and persisted as inland relicts after the marine incursion(s) retreated, probably with the aid of changes in soil conditions caused by the deposition of marine sediments. This dispersal corridor may also have facilitated the colonization of coastal environments by Amazonian lineages. These scenarios could imply an unexpected coastal source that has contributed to Amazonia's high floristic diversity and led to disjunct distributions across the Neotropics. We highlight the need for future studies and additional evidence to validate and shed further light on this potentially important pattern.

Biogeography of the neotropical freshwater stingrays (Myliobatiformes: Potamotrygoninae) reveals effects of continent‐scale paleogeographic change and drainage evolution

“…Amazon, Guiana Shield, marine incursions, Orinoco, Paleogeography, Parana-Paraguay, Pebas Wetlands, South America F I G U R E 1 Map of South America during the middle Miocene showing position of the Pebas Wetlands (adapted from Hoorn, Wesselingh, Ter Steege, et al, 2010. using shapefiles from Cao et al, 2017 (Aleman & Ramos, 2000;Brea & Zucol, 2011), while others argue that it extended only as far as present-day Bolivia (Bernal et al, 2019;Wesselingh & Hoorn, 2011). The giant wetlands of the Pebas experienced oscillating levels of marine influence, as evidenced by sediments characteristic of both freshwater and tidal conditions (Hovikoski et al, 2010) and a rich fossil record of freshwater to marine-associated lineages, ranging from invertebrates (Wesselingh et al, 2006;Wesselingh & Ramos, 2010) and plants (Bernal et al, 2019;Hoorn, 2006), to crocodylians (Salas-Gismondi et al, 2015).…”

“…The Pebas Mega‐Wetland System (hereafter Pebas wetlands or system) was an epicontinental marine/freshwater system covering more than one million km 2 , spanning from the Caribbean to southern South America (Figure 1; Bernal et al, 2019; Hoorn, Wesselingh, Hovikoski, et al, 2010; Hoorn, Wesselingh, Ter Steege, et al 2010; Shephard et al, 2010; Wesselingh & Hoorn, 2011). This system covered the western Amazon region during most of the Miocene (23–10 Ma) (Bernal et al, 2019; Hoorn, Wesselingh, Hovikoski, et al, 2010), but its southernmost boundary is uncertain. Some authors have suggested it extended as far as southern Argentina, connecting to the Paranaense Sea (Aleman & Ramos, 2000; Brea & Zucol, 2011), while others argue that it extended only as far as present‐day Bolivia (Bernal et al, 2019; Wesselingh & Hoorn, 2011).…”

“…Some authors have suggested it extended as far as southern Argentina, connecting to the Paranaense Sea (Aleman & Ramos, 2000; Brea & Zucol, 2011), while others argue that it extended only as far as present‐day Bolivia (Bernal et al, 2019; Wesselingh & Hoorn, 2011). The giant wetlands of the Pebas experienced oscillating levels of marine influence, as evidenced by sediments characteristic of both freshwater and tidal conditions (Hovikoski et al, 2010) and a rich fossil record of freshwater to marine‐associated lineages, ranging from invertebrates (Wesselingh et al, 2006; Wesselingh & Ramos, 2010) and plants (Bernal et al, 2019; Hoorn, 2006), to crocodylians (Salas‐Gismondi et al, 2015). Complex salinity gradients would have offered an ideal setting for the evolution of marine to freshwater transitions, and the connection of the Pebas system to the Caribbean region would have offered proto marine‐derived lineages a portal to the upper Amazon (Bernal et al, 2019; Bloom & Lovejoy, 2017; Lovejoy et al, 2006; Nuttal, 1990).…”

Mesoamerica is a cradle and the Atlantic Forest is a museum of Neotropical butterfly diversity: Insights from the evolution and biogeography of Brassolini (Lepidoptera: Nymphalidae)

“…2). The Pebas wetland might in fact have increased opportunities for dispersal and diversification of some typical coastal plants (Bernal et al 2019), including many of the butterflies’ hostplants in the region: mainly Aracaceae (palms), Poaceae (bamboo) and Zingiberales such as Marantaceae (Beccalconi et al 2008, Janzen et al 2009). Therefore, the evolutionary consequences of the Miocene marine incursions in western Amazonia might have been mixed, restricting dispersal and diversification in some lineages while providing ecological opportunities for others, such as Brassolini butterflies.…”

“…This wetland system was occasionally affected by marine flooding events, which were probably short-lived, and at least two dated events at ∼13.7 and ∼17.8 Mya (Jaramillo et al ., 2017a) were concurrent with the early and rapid cladogenesis events of major Brassolini clades in Amazonia. The Pebas wetland might in fact have increased opportunities for dispersal across Amazonia and diversification of some typical coastal plants (Bernal et al ., 2019), including many of the Brassolini’s hostplants in the region: Arecaceae (palms), Poaceae (bamboos), and Zingiberales such as Marantaceae (Beccaloni et al ., 2008; Janzen et al ., 2009). It is plausible that the evolutionary consequences of the Miocene marine incursions in western Amazonia might have been mixed and rather ephemeral (Musher et al ., 2019), restricting dispersal and diversification in some butterfly lineages such as Ithomiini (Chazot et al ., 2019b) while providing ecological opportunities for diversification of others, such as Brassolini.…”