Burning Phylogenies: Fire, Molecular Evolutionary Rates and Diversification.
Verdú, M.; Pausas, J.G.; Segarra-Moragues, J.G.; Ojeda, F.. Burning Phylogenies: Fire, Molecular Evolutionary Rates and Diversification.. Evolution. 2007, Vol. 61(9), p. 2195-2007.
Mediterranean-type ecosystems are among the most remarkable plant biodiversity “hot spots” on the earth, and fire has traditionally
been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants
of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are
only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters,
particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their
diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than
resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa
from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification
was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and
Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular
rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters—
which did not agree with theoretical predictions—may occur if (1) the timing of the switch from seeding to resprouting (or vice
versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters
suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of
mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence
of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary
rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger
diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems
Mediterranean-type ecosystems are among the most remarkable plant biodiversity “hot spots” on the earth, and fire has traditionally
been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants
of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are
only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters,
particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their
diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than
resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa
from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification
was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and
Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular
rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters—
which did not agree with theoretical predictions—may occur if (1) the timing of the switch from seeding to resprouting (or vice
versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters
suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of
mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence
of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary
rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger
diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems