Taxonomy & Evolution

Diversification in Mediterranean firs occurred much earlier than expected

Mediterranean firs appeared millions of years earlier than was supposed, and likely through a single colonization event from Asia.

Extant gymnosperms have relatively low species diversity, a fact attributed to high extinction and low speciation rates. The perception of the group as a whole is that it is very old and not very variable. However, some gymnosperm groups show evidence of recent pulses of radiation, highlighting how little is known about the factors influencing their evolution. Reconstructing the evolutionary history of gymnosperm groups is key in deciphering the drivers and patterns of their diversification. Firs (genus Abies) are the second most species-rich group of gymnosperms with more than 50 species. In one of their major areas of distribution, the Mediterranean Basin, the fir phylogeny remains debated and not fully resolved.

In a recent study published in Annals of Botany, Francisco Balao and colleagues used restriction site-associated DNA sequencing to produce a dated species tree of all Circum-Mediterranean firs (CMFs). They also conducted the first formal test of species delimitation within the group.

Sampling map for the Mediterranean firs used in this study. Source Balao et al. 2019.

The researchers successfully produced the first fully resolved species tree for the CMFs. The phylogeny supported all previously recognized species with the exception of A. tazaotana and A. marocana, which appear to be a single species. Dating of the tree revealed that the speciation pulse that produced the CMFs occurred at the Oligocene-Miocene boundary, millions of years prior to previous estimates, predating even the establishment of the Mediterranean climate. The ancestor of CMFs is thought to have come from Asia and spread westward. “The global climate cooling down through the Eocene–Oligocene period could have favoured the geographical expansion of firs,” write the authors. “In a relatively short time, as supported by the fossil records, the CMF ancestor could have reached the westernmost region of the Mediterranean Basin (i.e. the Iberian Peninsula).”

The clarification of CMF taxonomy will provide a useful tool for focussing conservation efforts in the region, particularly in the case of Moroccan and Turkish firs. “Due to a high degree of endemism, geographically scattered distribution and fragmentation by human activities, four CMF taxa are currently included in the IUCN red list as critically endangered or endangered,” the authors write. “Hence, the clarification and accurate assessment of species status has important conservation implications.”