Final Report Summary - GEN-RESP (Evaluation of the genetic response to climatic changes: the demographic history of the cottoid fish flock from Baikal)
The Lake Baikal, the world's oldest and deepest body of fresh water, is located in Siberia (Russia). The common ancestor of the 33 endemic species of cottoid fishes (Scorpaeniformes) present in the lake might have existed as recently as 2.5 million years ago. This age is puzzling as the lake may be at least 25 million years old. Cataclysmic events are expected to leave an imprint on the genetic architecture of organisms therefore a better understanding of Baikal's evolutionary radiations may help understanding the Lake environmental fluctuations.
In this project, we aimed at testing the role of climate changes and of Lake Baikal's more recent physical past on the evolution of the endemic sculpin species complex. Through comprehensive phylogeographic and demographic analyses of several endemic target species present all over the Lake we wanted to test several hypotheses concerning the biotic response to geological or climatic events.
Two mitochondrial markers, the control region and the Cytochromme Oxidase I sequenced for 3 deep-water species (L.godlewski B.multiradiatus A.korotneffi) and 2 shallow-water species (L.kesslerii P.knerii) were previously sequenced for a total of 412 individuals. We did a population genetic analyses on these data through the construction of haplotype networks, population genetic indices calculations (i.e. Fst) and demographic analyses (using mismatch distribution, Bayesian skyline plots and ABC methodologies).
As a general picture, we could see that the genetic diversity was extremely low for each studied species. This does not confirm our hypothesis that deep-living species should be more stable and less sensitive to climate changes than shallow water ones and therefore display a higher genetic diversity.
The shallow water species have a completely different genetic structure depending on their biology. L. kessleri, which has pelagic larvae, did not display any population structure. Conversely, P. knerii lives on rocky shores and its strong genetic structure seems to be the consequence of interruptions of rocky habitats by sand stretches.
Concerning the deep-water species, their genetic structuring is variable and seems to be related to the depth at which they occur. Indeed the Baikal Lake is made of three basins directed North-east / South-West. The northern and central basins are separated by the Academic Ridge with a level of around 300 meters bellow water level, while the central and southern basins are separated by the Selenga delta. At the location of the Selenga delta (east side of the Lake) the water level is very low and may represent an important barrier to population expansion. On the west side, the depth is around 300 m below water level. Therefore species living under 300m will have more difficulties to migrate from a basin to another. A. korotneffi that can be found from 300 to 1600 meters displays a strong structuration pattern with very few haplotypes shared between the 3 basins. Conversely L. godlewskii living between 100 and 1300m display a pattern with shared haplotypes between basins and with the highest haplotype diversity found in the Central basin.
In all cases, the colonisation of the Baikal Lake seem to have happened from the Northern side, which does not reflect the impact of glaciations, more probably stronger in the north of Baikal than in the South. This does not indicate that the Southern basin has been used as a refuge.
Demographic analyses display an extremely recent diversification period for each species. We could not yet date these diversification events and test their probability to have happened concomitantly, driven by the same climatic or geological event. At this point of the study, the patterns of genetic diversity displayed by the cottoid fishes seem to be more dependents on specific life history traits than on environmental events. Data from nuclear markers are definitely needed to allow further investigation.
In this project, we aimed at testing the role of climate changes and of Lake Baikal's more recent physical past on the evolution of the endemic sculpin species complex. Through comprehensive phylogeographic and demographic analyses of several endemic target species present all over the Lake we wanted to test several hypotheses concerning the biotic response to geological or climatic events.
Two mitochondrial markers, the control region and the Cytochromme Oxidase I sequenced for 3 deep-water species (L.godlewski B.multiradiatus A.korotneffi) and 2 shallow-water species (L.kesslerii P.knerii) were previously sequenced for a total of 412 individuals. We did a population genetic analyses on these data through the construction of haplotype networks, population genetic indices calculations (i.e. Fst) and demographic analyses (using mismatch distribution, Bayesian skyline plots and ABC methodologies).
As a general picture, we could see that the genetic diversity was extremely low for each studied species. This does not confirm our hypothesis that deep-living species should be more stable and less sensitive to climate changes than shallow water ones and therefore display a higher genetic diversity.
The shallow water species have a completely different genetic structure depending on their biology. L. kessleri, which has pelagic larvae, did not display any population structure. Conversely, P. knerii lives on rocky shores and its strong genetic structure seems to be the consequence of interruptions of rocky habitats by sand stretches.
Concerning the deep-water species, their genetic structuring is variable and seems to be related to the depth at which they occur. Indeed the Baikal Lake is made of three basins directed North-east / South-West. The northern and central basins are separated by the Academic Ridge with a level of around 300 meters bellow water level, while the central and southern basins are separated by the Selenga delta. At the location of the Selenga delta (east side of the Lake) the water level is very low and may represent an important barrier to population expansion. On the west side, the depth is around 300 m below water level. Therefore species living under 300m will have more difficulties to migrate from a basin to another. A. korotneffi that can be found from 300 to 1600 meters displays a strong structuration pattern with very few haplotypes shared between the 3 basins. Conversely L. godlewskii living between 100 and 1300m display a pattern with shared haplotypes between basins and with the highest haplotype diversity found in the Central basin.
In all cases, the colonisation of the Baikal Lake seem to have happened from the Northern side, which does not reflect the impact of glaciations, more probably stronger in the north of Baikal than in the South. This does not indicate that the Southern basin has been used as a refuge.
Demographic analyses display an extremely recent diversification period for each species. We could not yet date these diversification events and test their probability to have happened concomitantly, driven by the same climatic or geological event. At this point of the study, the patterns of genetic diversity displayed by the cottoid fishes seem to be more dependents on specific life history traits than on environmental events. Data from nuclear markers are definitely needed to allow further investigation.