Phylogeography and population differentiation in the Psittacanthus calyculatus (Loranthaceae) mistletoe: a complex scenario of climate–volcanism interaction along the Trans‐Mexican Volcanic Belt

Abstract

Aim: The formation of the Trans-Mexican Volcanic Belt (TMVB) played an important role in driving inter-and intraspecific diversification at high elevations. However, Pleistocene climate changes and ecological factors might also contribute to plant genetic structuring along the volcanic belt. Here, we analysed phylogeographical patterns of the parrot-mistletoe Psittacanthus calyculatus to determine the relative contribution of these different factors. Location: Trans-Mexican Volcanic Belt. Methods: Using nuclear and chloroplast DNA sequence data for 370 individuals, we investigate the genetic differentiation of 35 populations across the species range.We conducted phylogenetic, population and spatial genetic analyses of P. calyculatus sequences along with ecological niche modelling and Bayesian inference methods to gain insight into the structuring of genetic variation of these populations.Results: Our analyses revealed population structure with three genetic groups corresponding to individuals from Oaxaca and those from the central-eastern and western TMVB regions. A significant genetic signal of demographic expansion, an eastto-west expansion predicted by species distribution modelling, and approximate Bayesian computation analyses strongly supported a scenario of habitat isolation and invasion of TMVB by P. calyculatus during the late-Pleistocene.Main conclusions: The genetic differentiation of P. calyculatus may be explained by the combined effects of (1) geographical isolation linked to the effects of the glacial/interglacial cycles and environmental factors, driving genetic differentiation from congeners into more xeric vegetation and (2) the invasion of TMVB from east to west, suggesting a role for both colonization and glacial/interglacial cycles models.

Phylogeography and climate-associated morphological variation in the endemic white oakQuercus deserticola(Fagaceae) along the Trans-Mexican Volcanic Belt

“…Therefore, it is possible that the populations to the north and the east of the TMVB were more recently colonized than the populations to the south D r a f t and the west. Interestingly, a recent phylogeographic study of the mistletoe Psittacanthus calyculatus (Loranthaceae) which frequently uses Q. deserticola as a host (Pérez-Crespo et al 2017), found evidence of a south to north expansion and colonization of the TMVB from the Sierra Madre del Sur during the late Pleistocene; but afterwards the direction of the expansion within the TMVB was from east to west. However, this parasitic plant has a broad host range and seems to follow its own ecological niche rather than closely tracking its hosts (Ramírez-Barahona et al 2017).…”

Hybridization and differential introgression associated with environmental shifts in a mistletoe species complex

“…Accordingly, the most accepted explanation of mistletoe diversification is that of ‘host-race formation’ 12 , 34 – 36 , where genetic differentiation, and eventually host-race formation, is acquired through isolation-by-distance or by ecological adaptation following the ‘invasion’ of a different host species (‘host-switching’ hypothesis 12 ). In addition, the geographic structuring of genetic variation in some mistletoe species has been explained as the result of past climate changes 31 , 32 , 37 , 38 , landscape fragmentation 39 , emergence of biogeographic barriers 30 – 32 , 38 , and by the parasites’ own climatic niche preferences 40 , 41 .…”

“…schiedeanus ( c . 2.5–1.8 Ma 32 , 38 ) can be found infecting different host tree species under distinct environmental conditions along their wide geographical distributions 29 , 41 , 58 – 60 . Kuijt 21 reported that these species are distributed, more or less sympatrically, from Mexico to Panama, but recent molecular data suggest that these are allopatric and restricted to Mexico 41 .…”

“…schiedeanus parasitizes cloud forest trees, mainly Liquidambar styraciflua (Altingiaceae) in eastern Mexico 32 , 38 , 41 . Patterns of genetic structure in chloroplast DNA (cpDNA) sequences and nuclear microsatellites showed two main lineages within the species complex 32 , 38 , 41 , with further genetic structuring of populations and evidence of genetic admixture in particular regions 41 . However, the presence of highly admixed individuals within particular populations has not been explored or discussed further 41 .…”

Floral anatomy of the plant Psittacanthus schiedeanus (Loranthaceae)

“…The species parasitizes over 20 different hosts Cocoletzi, Angeles, Ceccantini, Patrón, & Ornelas, 2016) and it is considered part of a species complex involving P. calyculatus (DC.) G. Don, P. breedlovii Kuijt, and P. angustifolius Kuijt (Diaz-Infante, Lara, del Coro Arizmendi, Eguiarte, & Ornelas, 2016;Pérez-Crespo et al, 2017). This robust mistletoe can reach 3 m in diameter, has large leaves (up to 20 cm long), and a terminal inflorescence consisting of three to five pairs of triads.…”