The Phylogeny of the Pentaschistis Clade (Danthonioideae, Poaceae) Based on Chloroplast Dna, and the Evolution and Loss of Complex Characters

Abstract

We construct a species-level phylogeny for the Pentaschistis clade based on chloroplast DNA, from the following regions: trnL-F, trnT-L, atpB-rbcL, rpL16, and trnD-psbA. The clade comprises 82 species in three genera, Pentaschistis, Pentameris, and Prionanthium.We demonstrate that Prionanthium is nested in Pentaschistis and that this clade is sister to a clade of Pentameris plus Pentaschistis tysonii. Forty-three of the species in the Pentaschistis clade have multicellular glands and we use ancestral character state reconstruction to show that they have been gained twice or possibly once, and lost several times. We suggest that the maintenance, absence, loss, and gain of glands are correlated with leaf anatomy type, and additionally that there is a difference in the degree of diversification of lineages that have these different character combinations. We propose that both glands and sclerophyllous leaves act as defense systems against herbivory, and build a cost/benefit model in which multicellular glands or sclerophyllous leaves are lost when the alternative defense system evolves. We also investigate the association between leaf anatomy type and soil nutrient type on which species grow. There is little phylogenetic constraint in soil nutrient type on members of the Pentaschistis clade, with numerous transitions between oligotrophic and eutrophic soils. However, only orthophyllous-leaved species diversify on eutrophic soils. We suggest that the presence of these glands enables the persistence of orthophyllous lineages and therefore diversification of the Pentaschistis clade on eutrophic as well as oligotrophic soils.KEY WORDS: Ancestral, correlated evolution, Danthonioideae, gland evolution, Pentaschistis, phylogeny, Poaceae.Interest in the evolution of complex structures and their influence upon the success of organisms has a long history. Classic examples include orchid flowers (Darwin 1862) and the evolution of eyes (Fernald 2004). Part of their fascination lies in the very low probability that such structures should evolve at all (Dawkins 1986). However, their (often) unique evolution makes it difficult to tease apart the adaptive aspects from other factors, including chance. In contrast, the loss of such complex structures presents us with an opportunity to explore their function. Losses tend to be more numerous than gains in many complex structures or traits (e.g., heterostyly [Kohn et al. 1996;Schoen et al. 1997]; secondary xylem in aquatic plants [Sculthorpe 1967]; wings in insects [Whiting et al. 2003]; or the chlorophyll producing function of chloroplasts, in holoparasites [Judd et al. 2002;APG 2003;Bungard 2004]; Nickrent et al. 2004]). This makes them more tractable to investigation than gains. For example, if the losses of a particular structure within a clade are nonrandom with respect to other morphological characters or habitat, these losses can be used to investigate Peculiar multicellular glands (see Fig. 1A, B) exist on the inflorescences and/or leaves in 43 species of Pentaschistis and of P...

The Great Escarpment of southern Africa: a new frontier for biodiversity exploration

“…Such research is not hypothesis driven and thus perhaps unfashionable (and even non-fundable by some funding agencies), but it is fundamental to accurate floristic, faunistic and biogeographical analysis, systematic studies, taxonomy, and conservation planning (Kruckeberg and Rabinowitz 1985;Huntley and Matos 1994;Kahindo et al 2007). The compilation of a complete (and accurate) Escarpment flora would be a major step in firmly determining plant diversity and endemism, and provide an opportunity for detailed floristic analysis between (Nekola 1999), for which there is often little evidence (Kruckeberg and Rabinowitz 1985), and migration routes and refugia (Poynton 1983;Griffin 1998;Simmons et al 1998;Prendini 2005;Galley and Linder 2007;Devos et al 2010). Creation and interpretation of such phylogenies will add greatly to the debate regarding Escarpment connections (past and present) with the CFR and other highland areas in Africa (Galley and Linder 2007;Bergh and Linder 2009;Clark 2010), as well as with the adjacent southern African coastal lowlands and the significance of intervals along the Escarpment.…”

“…The compilation of a complete (and accurate) Escarpment flora would be a major step in firmly determining plant diversity and endemism, and provide an opportunity for detailed floristic analysis between (Nekola 1999), for which there is often little evidence (Kruckeberg and Rabinowitz 1985), and migration routes and refugia (Poynton 1983;Griffin 1998;Simmons et al 1998;Prendini 2005;Galley and Linder 2007;Devos et al 2010). Creation and interpretation of such phylogenies will add greatly to the debate regarding Escarpment connections (past and present) with the CFR and other highland areas in Africa (Galley and Linder 2007;Bergh and Linder 2009;Clark 2010), as well as with the adjacent southern African coastal lowlands and the significance of intervals along the Escarpment. Phylogenies obtained can provide valuable data on genetic diversity, cryptic species (Bickford et al 2006), the effect of past climates and tectonic events (Midgley et al 2001;Jetz et al 2004;Bergh et al 2007;Linder 2008), and the role of various parameters on Escarpment speciation (Jetz et al 2004;Nosil et al 2009).…”

A Generic Classification of the Danthonioideae (Poaceae)1

“…TAXA, DATA, AND ANALYSIS Morphological descriptions were based on the study of herbarium collections in AD, B, BM, BOL, C, CANB, CHR, CONC, GRA, HO, K, L, MEL, NBG, NSW, NU, P, PRE, S, US, Z, and ZT over the past 15 years and were generated in the process of preparing revisions or flora accounts (Baeza, 1990(Baeza, , 1996aLinder & Ellis, 1990a;Barker, 1993Barker, , 1995Linder, , 1999Linder, , 2005Linder & Davidse, 1997;Verboom & Linder, 1998;Galley & Linder, 2006). The original observations were reported in these publications.…”

A plastid tree can bring order to the chaotic generic taxonomy of Rytidosperma Steud. s.l. (Poaceae)

“…There is an increasing trend toward the use of nucleotide sequence data in taxonomic studies at the generic rank . Danthonioideae is no exception: a string of recent molecular phylogenetic studies have addressed generic delimitation of certain groups (Cortaderia: Barker et al, 2003; African members of the Rytidosperma clade: Verboom et al, 2006; Pentaschistis and allies: Galley and Linder, 2007) or have assessed generic limits in the subfamily as a whole (Pirie et al, 2008). However, none of these studies has provided resolution of the Rytidosperma clade that is informative enough to serve as a guideline for a generic classification.…”