Evolution of Myrmecophytism in Western Malesian Macaranga (Euphorbiaceae)

Abstract

Plants inhabited by ants (myrmecophytes) have evolved in a diversity of tropical plant lineages. Macaranga includes approximately 300 paleotropical tree species; in western Malesia there are 26 myrmecophytic species that vary in morphological specializations for ant association. The origin and diversification of myrmecophytism in Macaranga was investigated using phylogenetic analyses of morphological and nuclear ITS DNA characters and studies of character evolution. Despite low ITS variation, the combined analysis resulted in a well-supported hypothesis of relationships. Mapping myrmecophytism on all most parsimonious trees resulting from the combined analysis indicated that the trait evolved independently between two and four times and was lost between one and three times (five changes). This hypothesis was robust when tested against trees constrained to have three or fewer evolutionary transformations, although increased taxon sampling for the ITS analysis is required to confirm this. Mapping morphological traits on the phylogeny indicated that myrmecophytism was not homologous among lineages; each independent origin involved a suite of different specializations for ant-plant association. There was no evidence that myrmecophytic traits underwent sequential change through evolution; self-hollowing domatia evolved independently from ant-excavated domatia, and different food-body production types evolved in different lineages. The multiple origins of myrmecophytism in Macaranga were restricted to one small, exclusively western Malesian lineage of an otherwise large and nonmyrmecophytic genus. Although the evolution of aggregated food-body production and the formation of domatia coincided with the evolution of myrmecophytism in all cases, several morphological, ecological, and biogeographic factors appear to have facilitated and constrained this radiation of ant-plants.

Timing of butterfly parasitization of a plant–ant–scale symbiosis

“…However, we did not investigate the geographical context of the lycaenid diversification because the lycaenid sampling locations were insufficiently widespread for phylogeographic inferences. Further sampling throughout the distribution area of myrmecophytic Macaranga (Sumatra, the Malay Peninsula, and Borneo; Fiala et al 1999;Davies et al 2001) would be necessary to clarify the postglacial biogeography of the lycaenids.…”

An ancient tripartite symbiosis of plants, ants and scale insects

“…Upon the inspection of the COI sequences, it was discovered that a pseudogene had been amplified in the out-group C. celatus (as indicated by a frame-shift mutation with an ensuing stop codon near the 5 0 end) and thus it was removed from analyses. (c) Phylogenetic analyses Maximum-likelihood (ML) analyses were performed with PHYML (Guindon & Gascuel 2003) Davies et al 2001). Five thousand Monte Carlo simulations of the sampling distribution were also performed to assess the observed sample against the null distribution.…”

“…If so, the ants may have relied on extrafloral nectaries (EFNs) in place of coccoids or they may have relied only Davies et al (2001) showed that myrmecophytism evolved only in Macaranga lineages in which EFNs on mature leaf surfaces had been lost and in which leaf margin (as opposed to leaf surface) EFNs became enlarged, suggesting a role for carbohydrate-rich plant exudates, whether in the form of EFNs or homopteran honeydew, in the evolution of myrmecophytism. The single-locus dataset used here does not lend itself to inferring species boundaries, which can conflict with mitochondrial lineages due to introgression or incomplete lineage sorting (Avise 1994;Sota & Vogler 2001;Shaw 2002;Linnen & Farrell 2007).…”

Taxonomic Revision of the Obligate Plant-Ants of the Genus Crematogaster Lund (Hymenoptera, Formicidae, Myrmicinae), Associated with Macaranga Thouars (Euphorbiaceae) on Borneo and the Malay Peninsula

“…All obligately Macaranga-associated Crematogaster (Crematogaster borneensis-group) colonize host species belonging to the sections Pachystemon and Pruinosae within the genus Macaranga (Blattner et al, 2001;Davies et al, 2001). The section Winklerianae that is endemic to Borneo is exclusively colonized by a species that we had named Crematogaster morphospecies 8 in former publications by our group (Fiala et al, 1999).…”