Abstract
Background and aims – Conserving threatened biodiversity needs a robust knowledge and delineation of the taxonomical entities targeted for in or ex situ conservation. In the genus Armeria (Plumbaginaceae), the frequent correlation between geographical isolation and morphological differentiation led to the delineation of some taxa consisting of few populations. Armeria belgenciensis is a narrow endemic represented by one population in southern France, which recently experienced a strong demographic decline caused by repeated disturbances of its habitat and was the object of a demographic rescue. Within two kilometres of A. belgenciensis, the presence of A. arenaria subsp. peirescii, also represented by one small population, poses the question whether the two populations are genetically isolated and should be considered as separated taxa for conservation.Material and methods – The genetic structure of Armeria belgenciensis and the geographically close populations of Armeria arenaria were analysed based on 328 AFLP markers using model-based and model-free clustering methods. In addition, flowering phenology was estimated to address the possibility of pre-zygotic isolation between A. belgenciensis and A. arenaria subsp. peirescii. Key results – The genetic structure supported a close relationship between A. belgenciensis and A. arenaria subsp. peirescii, compared to other populations of A. arenaria. Despite its recent decline, the genetic diversity of A. belgenciensis was not particularly low compared to the other studied populations or other rare species in this genus. The existence of gene flow between these two populations is likely given their moderate differentiation and the detection of admixture by one of the clustering methods. The phenological study showed that cross-pollination is possible during a short time period. Conclusion – We propose to place these two populations under the name A. belgenciensis, but to keep them as two different management units until there is no evidence of a harmful effect due to small effective sizes.
Highlights
Conserving threatened species requires to properly design conservation units
Since the Mediterranean Basin hotspot includes many rare and vulnerable narrow endemic plant species, the number of available molecular systematic studies is not sufficient to understand the complexity of the evolution of many groups and to properly design conservation units (Médail & Baumel 2018)
The main result of this study based on 328 Amplified Fragment Length Polymorphism (AFLP) markers is that different methods of clustering revealed a close relationship between Armeria belgenciensis (BEL) and A. arenaria subsp. peirescii (PER) as suggested by a previous morphometric study (Baumel et al 2009)
Summary
Conserving threatened species requires to properly design conservation units. Delineating conservation units is never straightforward, and it often requires the judicious use of available data. In the case of incipient species, insufficient isolation and divergence may have precluded the formation of morphologically discrete and reciprocally monophyletic entities for the molecular loci considered. In such cases, combining systematics with population genetic approach is crucial to consider the balance between recognizing ongoing diversification (Moritz 2002; Daïnou et al 2014) and the risk of over-splitting taxa into populations that may compromise both management and rescue, and their long-term persistence (Frankham et al 2012)
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