Molecular evidence for multiple origins of woodiness and a new world biogeographic connection of the Macaronesian island endemic Pericallis (Asteraceae: senecioneae)

Abstract

The prevalence of woody species in oceanic islands has attracted the attention of evolutionary biologists for more than a century. We used a phylogeny based on sequences of the internal-transcribed spacer region of nuclear ribosomal DNA to trace the evolution of woodiness in Pericallis (Asteraceae: Senecioneae), a genus endemic to the Macaronesian archipelagos of the Azores, Madeira, and Canaries. Our results show that woodiness in Pericallis originated independently at least twice in these islands, further weakening some previous hypotheses concerning the value of this character for tracing the continental ancestry of island endemics. The same data suggest that the origin of woodiness is correlated with ecological shifts from open to species-rich habitats and that the ancestor of Pericallis was an herbaceous species adapted to marginal habitats of the laurel forest. Our results also support Pericallis as closely related to New World genera of the tribe Senecioneae.

Figure 1

One of the 214 equally parsimonious ITS trees from unweighted Fitch parsimony analysis (593 steps; consistency index = 0.607, without autapomorphies; retention index = 0.775). The two branches that collapse in the strict consensus tree are indicated by dashed lines. Numbers above and below branches represent number of steps and bootstrap values (>50%), respectively. This tree is identical to the strict consensus trees obtained after transversions are weighted over transitions by factors of 1.3:1, 1.4:1, 1.5:1, and 1.6:1 and also after gaps of the sequence alignment are incorporated as binary characters. Geographic distribution on continental or island areas also is shown. Taxa included in the maximum- likelihood search are identified by arrows. Sequences obtained after cloning of PCR products are marked below with ¶. All voucher specimens are deposited at ORT, except where indicated below. ^¶Cineraria alchemilloides: South Africa, Watson and Panero 94-30 (TEX); ^¶Dendrosenecio cheranganiensis: Kenya, Knox 3 (MICH); Dendrosenecio kilimanjari subsp. cottonii: Tanzania, Knox 50 (MICH); ^¶Dorobaea pimpinellifolia: Nordenstam and Lundin 158 (S); ^¶Euryops pectinatus: ex hort., The University of Texas, Panero 98-DNA-1 (TEX); ^¶Gynura formosana: Taiwan, Panero, and Hsiao 6457 (TEX); Othonna parviflora: South Africa, Watson and Panero 94–14 (TEX); Packera obovata: Travis Co., Texas: Panero-7386 (TEX); Phaneroglossa bolusii: South Africa, Watson and Panero 94–62 (TEX); Pericallis appendiculata: ^¶La Gomera, JFO 98–150 (FTG); La Palma, ASG 97–4, ASG 97–5; ^¶Tenerife, JFO 98–3 (FTG); P. aurita: Madeira, ex hort., Botanical Garden of La Orotava material from seed collection of O (1997–530); ^¶P. cruenta: Tenerife, JFO 98–60 (FTG); P. echinata: Tenerife, ASG 97–6; P. hadrosoma: Gran Canaria ex hort., Jardín Botánico Viera y Clavijo; ^¶P. hansenii: La Gomera, ASG 97–7; ^¶P. lanata: Tenerife, ASG 97–8; species nova: JFO 98–152 (FTG); P. malvifolia: Azores, ex hort., Botanical Garden of La Orotava, material from seed collection of Botanical Garden of Faial (1998–10); P. multiflora: Tenerife, ASG 97–9; P. murrayi: El Hierro, ASG 97–10; P. papyracea: La Palma, ASG 97–11; P. steetzii, La Gomera, ASG 97–15; P. tussilaginis, Tenerife, ASG 97–12, ASG 97–13; Gran Canaria, ASG 97–14; P. webbii: Gran Canaria, Panero et al. 7130; ^¶Pseudogynoxys chenopodioides, ex hort., from local nursery at Austin, Panero 98-DNA-2 (TEX); Senecio glaucescens, ex hort. from seeds provided by Kirstenbosch Botanical Garden, South Africa. *, Distribution extends into northern Siberia; **, Distribution extends into Arabia and Socotra island.

Figure 2

One of the 214 equally parsimonious ITS trees from unweighted Fitch parsimony analysis (further details on tree topology are shown in Fig. 1). This is the same tree shown in Fig. 1 but indicating the ecological zones and habit of Pericallis and continental species. Solid circles, herbaceous species; shaded circles, woody species; open circles, genera with both woody and herbaceous species. Bootstrap values (>50%) are indicated along each branch.

Figure 3

Evolution of woodiness in Pericallis (Fig. 1) assuming that the ancestor of Pericallis was herbaceous (A) or woody (B and C). Numbers of steps of each tree and number of changes to woodiness also indicated. Solid branches indicate a herbaceous condition, and shaded branches indicate the woody habit. Bootstrap values are indicated along each branch.