Pleistocene shaping of genetic diversity in a monsoon-affected environment: the case of <Emphasis Type="Italic">Gymnosporia</Emphasis> (Celastraceae) in the southern Arabian Peninsula

The Gymnosporia dhofarensis complex (Celastraceae) consists of the closely related taxa G. dhofarensis (Sebsebe) Jordaan and G. parviflora (Vahl) Chiov. and occurs in the fragmented and isolated monsoon-affected refugia of the coastal mountains in a vegetation of relics of (semi-)evergreen Afro-montane woodland and drier habitats (deciduous woodland, open dry scrub) of the southern Arabian Peninsula. To study the phylogeography of the complex, 536 individuals from 31 populations were analysed using cpDNA-RFLP, while a subset of 320 individuals from 20 populations was analysed using AFLP fingerprinting. Additionally, for 46 accessions from populations throughout the distribution range of the complex and 10 individuals of G. senegalensis (Lam.) Exell. s.l. sequences of nrDNA ITS were established to infer ribotype variation and allow dating of diversification events. Phylogeographical reconstructions based on six detected chloroplast haplotypes show a distinct haplotype distribution pattern with a main split between western (Northern Yemen/Jabal Eraf/Jabal Al Aghbar/Jabal Urays; G. parviflora) and eastern populations (Ras Fartak/Hawf Mts/Dhofar Mts; G. dhofarensis). The results of AFLP fingerprinting are congruent with chloroplast data but offer an even more detailed view into the intra-regional population differentiation. The analysis of nrDNA ITS variants shows that G. dhofarensis s.l. is well separated from other Gymnosporia representatives in the study (i.e. G. senegalensis s.l. and G. aff. divaricata). Based on nrDNA ITS sequence variation, the main inter-regional split between western (G. parviflora) and eastern populations (G. dhofarensis) is dated to 0.9–2.2 Ma before present.