Parallel evolution of arborescent carrots (Daucus) in Macaronesia

Abstract

Premise Despite intensive research, the pathways and driving forces behind the evolution of derived woodiness on oceanic islands remain obscure. The genus Daucus comprises mostly herbs (therophytes, hemicryptophytes) with few rosette treelets (chamaephytes) endemic to various Macaronesian archipelagos, suggesting their independent evolution. To elucidate the evolutionary pathways to derived woodiness, we examined phylogenetic relationships and the habit and secondary xylem evolution in Daucus and related taxa. Methods Sixty taxa were surveyed for molecular markers, life history, and habit traits. Twenty‐one species were considered for wood anatomical characters. A dated phylogeny was estimated using Bayesian methods. The evolution of selected traits was reconstructed using parsimony and maximum likelihood. Results Daucus dispersed independently to the Canary Islands (and subsequently to Madeira), Cape Verde, and the Azores in the late Miocene and Pleistocene. Life span, reproductive strategy, and life form were highly homoplastic; the ancestor of Daucus was probably a monocarpic, biennial hemicryptophyte. Rosette treelets evolved independently in the Canarian‐Madeiran lineage and in Cape Verde, the latter within the last 0.13 Myr. Treelets and hemicryptophytes did not differ in wood anatomy. Pervasive axial parenchyma in wood occurred more often in polycarpic rather than monocarpic species. Conclusions Life span and life form in Daucus are evolutionarily labile and may change independently of wood anatomy, which is related to plant reproductive strategy rather than to life form. Insular woodiness may evolve rapidly (as demonstrated in D. bischoffii), and in Daucus, it does not seem to be an adaptation to lower the risk of xylem embolism.

Leaf functional traits and insular colonization: Subtropical islands as a melting pot of trait diversity in a widespread plant lineage

“…increases in leaf size or tannin content) was consistent across island sublineages. Such parallel patterns are often taken as strong evidence of selective processes driven by island conditions (Baldwin, 2007; Frankiewicz et al., 2020; Givnish, 2010), and may represent a new suite of traits supporting the ‘island syndrome’ (sensu Carlquist, 1974; reviewed in Burns, 2019), at least under conditions similar to those observed in our study system (Mediterranean‐type versus subtropical insular habitats). In summary, we postulate that phenotypic divergence between mainland and island settings is the result of both adaptation to arid conditions in the mainland and an adaptive parallel pattern towards a markedly different phenotype on islands.…”

“…Assuming that selection upon island colonization has a predominant effect on phenotypes (e.g. Clegg et al., 2002), parallel evolution would promote functional similarity among colonizing lineages, but only if environmental pressures in the recipient habitats are similar across islands (Figure 1a; Burns et al., 2012; Frankiewicz et al., 2020). Contrarily, time constraints (Figure 1b) or different selective pressures between island habitats (Figure 1c) may enhance functional variation across islands (Biddick, Hendriks, & Burns, 2019; García‐Verdugo, Caujapé‐Castells, Mairal, & Monroy, 2019).…”

“…Functional similarity across islands associated with multiple colonization events has been often reported (Baldwin, 2007; Foster, McKinnon, Steane, Potts, & Vaillancourt, 2007; Frankiewicz et al., 2020; García‐Verdugo, Forrest, Balaguer, Fay, & Vargas, 2010), but the contribution of biogeographical factors such as colonization time or climatic shifts is still poorly understood in island plant lineages. Having estimates about divergence times from mainland counterparts is crucial to assess the effect of colonization time on phenotypic diversity (Clegg et al., 2002).…”

Derived woodiness and annual habit evolved in African umbellifers as alternative solutions for coping with drought

“…In our earlier research [ 42 , 43 ] on herbaceous and derived woody apioids, we noticed that the entirely fibrous ground tissue was typical for monocarpic taxa irrespectively of their stem architecture, and for polycarpic ones with long internodes, while polycarpic species with shortened internodes (often having leaf rosettes) had parenchymatous ground tissue. This was likely a response to relaxed mechanical requirements of such habit [ 42 , 43 ].…”

“…Interestingly, derived woodiness in other apioid tribes also dates back to the Late Miocene: the arborescent habit of the two carrots from Madeira originated some 7.77 (9.05–6.35) My ago, while shrubby Billburttia from Madagascar and Deverra found mostly in northern Africa were resolved as 9.0 (10.87–7.14) and 9.86 (11.66–8.08) My old, respectively [ 42 , 43 ]. Moreover, 80–90% of the derived woody clades from various plant families in the Canary Islands originated within the last 7 My [ 57 ].…”