Signatures of volcanism and aridity in the evolution of an insular pine (Pinus canariensis Chr. Sm. Ex DC in Buch)

Abstract

Oceanic islands of volcanic origin provide useful templates for the study of evolution because they are subjected to recurrent perturbations that generate steep environmental gradients that may promote adaptation. Here we combine population genetic data from nuclear genes with the analysis of environmental variation and phenotypic data from common gardens to disentangle the confounding effects of demography and selection to identify the factors of importance for the evolution of the insular pine P. canariensis. Eight nuclear genes were partially sequenced in a survey covering the entire species range, and phenotypic traits were measured in four common gardens from contrasting environments. The explanatory power of population substrate age and environmental indices were assessed against molecular and phenotypic diversity estimates. In addition, neutral genetic variability (F ST ) and the genetic differentiation of phenotypic variation (Q ST ) were compared in order to identify the evolutionary forces acting on these traits. Two key factors in the evolution of the species were identified: (1) recurrent volcanic activity has left an imprint in the genetic diversity of the nuclear genes; (2) aridity in southern slopes promotes local adaptation in the driest localities of P. canariensis, despite high levels of gene flow among populations.

Plasticity in Vulnerability to Cavitation of Pinus canariensis Occurs Only at the Driest End of an Aridity Gradient

“…In accordance, Canary Island pine populations from the windward slopes of Tenerife and El Hierro were more vulnerable than populations from the leeward slopes of Tenerife and Gran Canaria. Although constant plasticity (i.e., similar plasticity of different populations), as shown for most traits in our study, reduces the strength of diversifying selection and can alter the impact of gene flow on local adaptation in heterogeneous environments ( Crispo, 2008 ), volcanism and aridity could have exerted selective pressures strong enough in traits related to drought resistance as to counteract for the homogenizing effect of an extensive gene flow ( López de Heredia et al, 2014 ). This seems to be the case of genetic variation in cavitation resistance and other drought adaptive traits at the leaf level: sclerophylly, osmotic adjustment and leaf anatomy ( López et al, 2009 , 2010 , 2013 ) whereas for other such K l, K s or growth most of the variation resides within populations ( López et al, 2013 ; the present study).…”

“…The six populations included in this study, out of 21 growing in the provenance trials (more details about the establishment and populations included in these provenance trials can be found in López et al, 2007 ) were selected to cover both the range of the climatic envelope of the species and populations with different ages based on the chronostratigraphy of the substrate where they occur (more details in López de Heredia et al, 2014 ).…”

A novel dendroecological method finds a non-linear relationship between elevation and seasonal growth continuity on an island with trade wind-influenced water availability

“…Pinus canariensis is a palaeo-endemic pine species (Pinaceae) of the Canary Islands (Wieser et al 2016) that shows adaptation to a wide range of climatic conditions (López de Heredia et al 2014). Pinus canariensis grows up to 60 m high, has long needles (up to 25 cm) enabling it to comb out water from passing clouds, thick bark (up to 7 cm), which can resist fire, serotinous cones allowing a regeneration after fire and it is one of the very few species of Pinaceae which can resprout from epicormic shoots after severe fire (Climent et al 2004).…”

Proliferation of axial parenchymatic xylem cells is a key step in wound closure of girdled stems in Pinus canariensis

“…This pine, with a comparatively abundant xylem parenchyma, is a suitable model species to study wound response in conifers, since it shows an extraordinary healing and even resprouting ability, highly uncommon among gymnosperms, particularly in the adult stage [ 29 , 30 ]. These features could be linked to P. canariensis evolutionary history, driven by the successive volcanic eruptions and subsequent re-colonizations in the Canary Islands [ 31 ]. We have used younger plants than previous works, analyzing the response not only in the xylem or phloem but also in the cortical parenchyma, and have performed both fenestration wounds and complete girdling.…”