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A molecular dating approach for Canary Island lineages

Generate sequences for additional herbaceous lineages and ancestrally woody lineages and their closest continental relatives to assess the niche pre-emption hypothesis. This hypothesis states that earlier colonisers have greater chance to diversify compared to later colonisers due to the availability of niches that become increasingly occupied by species over time.

Supervisor and contact:

Dr. Frederic Lens (Naturalis Biodiversity Center, frederic.lens@naturalis.nl)

Dr. Vincent Merckx (Naturalis Biodiversity Center, vincent.merckx@naturalis.nl)

Dr. Steven Jansen (Botanic Garden Meise, Belgium, steven.janssens@br.fgov.be)

 

Period and duration:

Ca. 6 months, project can start now

 

Study and level:

MSc project

 

Background and context:

The Canary Islands harbour a unique flora with about 1300 native species of flowering plants of which 40% are endemic. Insular floras often include species with a remarkable degree of woodiness. This so-called insular woodiness was described by Darwin who assumed that at least some woody island species have continental herbaceous ancestors (Fig. 1), an hypothesis that has been supported by more recent molecular analyses [1]. An ongoing study, focusing on the time of origin and the palaeoclimate in which these insular woody lineages have originated, supports the link between wood development and drought stress. The present study wants to build on the existing molecular database and provide dating estimates for the colonisation of a wide array of additional Canary lineages including only one to many species in order to find out whether the older lineages have more species compared to the more recent ones (niche pre-emption hypothesis).

Fig. 1: Based on molecular phylogenies, we know that herbaceous Echium species of the European continent have reached the Canary Islands about 3 million years ago, followed by a rapid speciation into ca. 26 woody species.

Objectives and goals:

This MSc proposal wants to build on an ongoing Canary Island study, where we have dated 25 insular woody lineages and six herbaceous lineages and linked the time of origin of these lineages with palaeoclimatic conditions. The student will generate rbcL and matK sequences for additional herbaceous lineages and ancestrally woody lineages and their closest continental relatives to assess the niche pre-emption hypothesis. This hypothesis states that earlier colonisers have greater chance to diversify compared to later colonisers due to the availability of niches that become increasingly occupied by species over time [2]. Our ongoing dataset based on 31 lineages does not seem to support niche pre-emption hypothesis, however, but many more lineages need to be dated in order to confirm this. The dating estimates of the non-insular woody lineages can also be linked to the palaeclimatic conditions to know whether most insular and non-insular woody lineages on the Canaries originated at the same or a different time.

 

Material, tasks and approach:

Fossils are scarce and often unreliable on the Canaries, which sometimes force authors to use the geological age of specific islands to calibrate nodes in the molecular phylogeny of endemic Canary Island groups [3]. This may lead to inaccurate divergence times, because plant groups can arrive long after islands have originated. To overcome this problem, we have been establishing a broad-scale molecular dating approach at the flowering plant level including rbcL and matK sequences of over 30.000 species and calibrated with over fifty fossil calibration points [Janssens et al., unpublished]. This broad-scale approach enables us to use credible fossil calibrations outside the Canary Island clades, and makes it possible to date a wide variety of Canary Island groups simultaneously.

Due to the large size of the rbcL - matK database, a maximum likelihood (ML) based method (RAxML) will be performed using the Cipres scientific portal (200 independent runs). The phylogenetic relationships of all species in the aligned dataset are constrained at the family level before the RAxML ML analysis. This taxon constraining is necessary because the discriminatory power of matK and rbcL at the genus and species level comes at the cost of correct “deep” phylogenetic reconstruction. Furthermore, constraining until family level reduced computational time for the RAxML method. Molecular dating will be completed using TreePL version 1.0.

 

Requirements:

Experience with evolutionary techniques and sequencing is recommended.

 

References:

[1] Lens F, Davin N, Smets E, del Arco M. 2013. Insular woodiness on the Canary Islands: a remarkable case study of parallel evolution. Int J Plant Sci 174: 992-1013. [2] Silvertown J, Francisco-Ortega J, Carine M. 2005. The monophyly of island radiations: an evaluation of niche pre-emption and some alternative explanations. J Ecol 93: 653-657. [3] Kim SC, McGowen MR, Lubinsky P, Barber JC, Mort ME, Santos-Guerra A. 2008. Timing and tempo of early and successive adaptive radiations in Macaronesia. Plos One 3: e2139.