Historical biogeography of two cosmopolitan families of flowering plants: Annonaceae and Rhamnaceae

Abstract

Annonaceae are a pantropically distributed family found predominantly in rainforests, so they are megathermal taxa, whereas Rhamnaceae are a cosmopolitan family that tend to be found in xeric regions and may be classified as mesothermal. Phylogenetic analyses of these families are presented based on rbcL and trnL-F plastid DNA sequences. Likelihood ratio tests revealed rate heterogeneity in both phylogenetic trees and they were therefore made ultrametric using non-parametric rate smoothing and penalized likelihood. Divergence times were then estimated using fossil calibration points. The historical biogeography of these families that are species rich in different biomes is discussed and compared with other published reconstructions. Rhamnaceae and most lineages within Annonaceae are too young to have had their distribution patterns influenced by break-up of previously connected Gondwanan landmasses. Contrasts in the degree of geographical structure between these two families may be explained by differences in age and dispersal capability. In both groups, long-distance dispersal appears to have played a more significant role in establishing modern patterns than had previously been assumed. Both families also contain examples of recent diversification of species-rich lineages. An understanding of the processes responsible for shaping the distribution patterns of these families has contributed to our understanding of the historical assembly of the biomes that they occupy.

Introduction and synthesis: plant phylogeny and the origin of major biomes

“…Less attention has been paid to how we might calibrate these phylogenies by assigning ages to individual nodes, but calibration is potentially the largest source of error in the dating of phylogenetic trees. Two principal methods of calibration have been used, taking information from: The high frequency of long-distance dispersal events indicated for many plant groups by authors in this volume (Richardson et al 2004;Plana 2004;Renner 2004;Pennington & Dick 2004; see further discussion in x 6 below) highlights the danger of the use of geological events, especially old ones, as calibration criteria. For example, Renner, Plana and Lavin et al demonstrate that endemic radiations of Melastomataceae sensu stricto, Begonia and Leguminosae (Ormocarpopsis, Indigofera) on Madagascar date only from the Miocene.…”

Annonaceae substitution rates: a codon model perspective

“…The d n and d s trees that we found mirror the branch length patterns that have been found in Annonaceae phylogenetics thus far, regardless of the phylogenetic inference method (CHATROU et al, 2012;COUVREUR et al, 2011;RICHARDSON et al, 2004). It allows eliminating a possible source of error in molecular dating analyses of the family.…”

“…However, the Malmeoideae/Annonoideae sister group relationship has been inferred consistently in previous analyses (e.g. COUVREUR et al, 2008;PIRIE et al, 2006;RICHARDSON et al, 2004), irrespective of whether Meiocarpidium was included. The deviant phylogenetic position of the Ambavioideae could alternatively be explained by the particular reduced character sampling that was employed compared to more extensive phylogenetic analyses of the family -i.e., our focus on coding genes only, to the exclusion of more variable non-coding spacer and intron sequences.…”

“…If they are interpreted at face value as representing real differences in molecular evolutionary rate, it is unclear in what manner (gradual or abrupt) and at what point subsequent to the divergence of their last common ancestor (immediately or more recently) such rate shift might have taken place (PIRIE and DOYLE, 2012). Uncertainty on this point has led to inconsistent age estimates derived from dating analyses using methods that make different assumptions about patterns of rate variation (COUVREUR et al, 2011;PIRIE and DOYLE, 2012;RICHARDSON et al, 2004). Molecular dating analyses assuming autocorrelation of rates among lineages resulted in roughly equal ages for the crown nodes of short and long branch clades (66 Ma and 68 Ma respectively) (PIRIE and DOYLE, 2012).…”

“…The genus Annona belongs to the subfamily Annonoideae, which has also been referred to as the 'long branch clade ' (PIRIE et al, 2005;RICHARDSON et al, 2004). The Annonoideae represents ca 60 % of the species diversity of the family, and are sister to subfamily Malmeoideae (the 'short branch clade') that contains ca 35% of the species diversity.…”