Past climate changes facilitated homoploid speciation in three mountain spiny fescues (Festuca, Poaceae)

Abstract

Apart from the overwhelming cases of allopolyploidization, the impact of speciation through homoploid hybridization is becoming more relevant than previously thought. Much less is known, however, about the impact of climate changes as a driven factor of speciation. To investigate these issues, we selected Festuca picoeuropeana, an hypothetical natural hybrid between the diploid species F. eskia and F. gautieri that occurs in two different mountain ranges (Cantabrian Mountains and Pyrenees) separated by more than 400 km. To unravel the outcomes of this mode of speciation and the impact of climate during speciation we used a multidisciplinary approach combining genome size and chromosome counts, data from an extensive nuclear genotypic analysis, plastid sequences and ecological niche models (ENM). Our results show that the same homoploid hybrid was originated independently in the two mountain ranges, being currently isolated from both parents and producing viable seeds. Parental species had the opportunity to contact as early as 21000 years ago although niche divergence occurs nowadays as result of a climate-driven shift. A high degree of niche divergence was observed between the hybrid and its parents and no recent introgression or backcrossed hybrids were detected, supporting the current presence of reproductive isolation barriers between these species.

New prospects in the detection and comparative analysis of hybridization in the tree of life

“…While the impacts of both niche evolution and climate change on hybridization are poorly understood, more study has been devoted to the latter question, with many qualitative hypotheses that hybridization in various plant groups was enabled by increased geographic range contact under Pleistocene glacial conditions. One extreme situation where this situation arises is in putative ancestral hybridization events where the descendants are allopatric and highly disjunct, a phenomenon observed in several plant lineages (Klein and Kadereit, ; Marques et al., ; Folk et al., ).…”

“…Alpine taxa that have been examined under Pleistocene cool conditions (e.g., Waltari and Guralnick, ; Espíndola et al., ; López‐Alvarez et al., ; Marques et al., ) have typically shown a very distinct pattern from lowland taxa, greatly increasing geographic range due to more suitable habitat, not necessarily with any southern migration. These results, primarily based on ecological modeling and paleoclimate data, are consistent with the fossil record, which has long suggested the existence of forested dispersal corridors in what are currently desert regions (e.g., Gugger et al., ).…”

“…These results, primarily based on ecological modeling and paleoclimate data, are consistent with the fossil record, which has long suggested the existence of forested dispersal corridors in what are currently desert regions (e.g., Gugger et al., ). These diverse range dynamics could add to the instability of geographic relationships among taxa, potentially creating some of the unusual distributions observed in ancestral hybridization events (Klein and Kadereit, ; Marques et al., ; Folk et al., ). Of course, these observations are not limited to Pleistocene scenarios; the accumulation of more ancient hybridization events will create opportunities for testing the association of hybridization with other periods of elevated disturbance.…”

Advances in the systematics and evolution of western Mediterranean representative species of the Pentanema conyzae clade through genetic fingerprinting

“…This hypothesis would be reinforced if the putative descendants (MO6146 and MO6147) had a level of 2 n = 8 x = 64. On the other hand, if the ploidy level of these populations corresponded to 2 n = 4 x = 32, a homoploid hybridization process could not be ruled out (Mameli et al, ; Marques et al, ; Nieto‐Feliner et al, ). However, another types of data are necessary (i.e., karyological, cross‐over studies) to understand the biology of these intermediate forms and to interpret them correctly.…”

Geographic range dynamics drove ancient hybridization in a lineage of angiosperms

“…The detection of hybridization has largely been an exercise in molecular data analysis, 9,[24][25][26][27][28][29] with few exceptions 8 . This assertion is strictly true of studies assessing ancestral hybridization (that is, gene flow among species that are not extant).…”