Habitat-specific divergence of procyanidins in Protium subserratum (Burseraceae)

Abstract

In Amazonian Peru, the neotropical tree Protium subserratum Engl. (Burseraceae) occurs as distinct ecotypes on low nutrient white-sand (WS), intermediate fertility brown-sand (BS), and nutrient-rich clay (CS) soils. Genetic analysis indicates that these ecotypes are undergoing incipient speciation. Possible drivers of this divergence are habitat-specific herbivore faunas and differing resource availabilities. Protium subserratum, therefore, provides an ideal opportunity to investigate how defense chemistry evolves during lineage divergence. WS and BS races of P. subserratum are host to largely nonoverlapping herbivore communities and they differ in chlorogenic acid, flavonoid, and oxidized terpene chemistry. Here, we investigate how another important class of anti-herbivore chemicals, procyanidins (PCs), varies among the ecotypes. We isolated the PCs from leaves of juvenile and adult trees from each ecotype and used spectroscopic and chemical techniques to characterize the chemical structures of their component monomers. We found that WS, BS, and CS ecotypes accumulate ca. 17 % of leaf dry weight as PCs. Within ecotypes, we found very little difference in PC type, neither by site nor by life stage.Among ecotypes, however, we observed a marked divergence in PC composition that arose at least in part from differences in their terminal and extension subunits. In addition, the average polymer length of BS and CS PCs was significantly greater than in WS ecotypes. We conclude that phenotypic differences in PCs in the WS versus BS and CS ecotypes of P. subserratum are consistent with selection by herbivores in different soil types that differ strongly in nutrient availability and may contribute to the evolution of habitat specialization.

Ode to Ehrlich and Raven or how herbivorous insects might drive plant speciation

“…, Lokvam et al. ) provide the best evidence for postzygotic mechanisms. Here Protium varieties differ markedly in defensive chemistry, they grow on soils that differ in nutrient availability and herbivore communities, and the impacts of these herbivores on plant growth vary by soil type and plant variety.…”

“…, Misiewicz and Fine ), in which there are three different chemical ecotypes, each found on a different soil type (Lokvam et al. ). Differences in soil chemistry on the three soil types are associated with differences in herbivore communities and different leaf defensive chemistry.…”

“…As a result they cannot invade clay soils even if herbivores are absent because clay soil species invest less in defense and thus can grow faster. Incipient speciation is occurring in Protium subserratum (Burseraceae; Fine et al 2013, Misiewicz andFine 2014), in which there are three different chemical ecotypes, each found on a different soil type (Lokvam et al 2015). Differences in soil chemistry on the three soil types are associated with differences in herbivore communities and different leaf defensive chemistry.…”

Habitat Endemism in White‐sand Forests: Insights into the Mechanisms of Lineage Diversification and Community Assembly of the Neotropical Flora

“…, Lokvam et al . ) with these differences corresponding to white‐sand or terra firme soils. Misiewicz and Fine () used nuclear microsatellite markers to show that populations of ecotypes found in adjacent and divergent soil types (<3 km apart) exhibited extremely low levels of gene flow compared to populations of ecotypes that were from the same soil type 100 km distant, even though all populations overlapped considerably in their flowering times and pollinators (Misiewicz , Misiewicz et al .…”

“…, Lokvam et al . ), suggesting that selection by natural enemies may be a very important factor driving habitat specialization. Because these ecotypes have similar flowering times and share many insect pollinators (Misiewicz , Misiewicz et al .…”