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A molecular palaeobiological exploration of arthropod terrestrialization.

Lozano-Fernandez J, Carton R, Tanner AR, Puttick MN, Blaxter M, Vinther J, Olesen J, Giribet G, Edgecombe GD, Pisani D - Philos. Trans. R. Soc. Lond., B, Biol. Sci. (2016)

Bottom Line: Understanding animal terrestrialization, the process through which animals colonized the land, is crucial to clarify extant biodiversity and biological adaptation.While molecular divergence times for Arachnida are consistent with the fossil record, Myriapoda are inferred to have colonized land earlier, substantially predating trace or body fossil evidence.An estimated origin of myriapods by the Early Cambrian precedes the appearance of embryophytes and perhaps even terrestrial fungi, raising the possibility that terrestrialization had independent origins in crown-group myriapod lineages, consistent with morphological arguments for convergence in tracheal systems.This article is part of the themed issue 'Dating species divergences using rocks and clocks'.

View Article: PubMed Central - PubMed

Affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK School of Biological Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.

No MeSH data available.


Results of molecular clock analyses. (a) Divergence times obtained under the CIR autocorrelated, relaxed, molecular clock model. (b) Divergence times obtained using the Uncorrelated Gamma Multipliers model. In both cases, nodes in the tree represent average divergence times estimated using the root prior with 636 Ma mean and 30 Ma SD. Brown bars represent 95% credibility intervals from the considered analysis. Grey bars represent the joint priors (for the considered nodes and analyses). Green bars in figure 2b indicate 95% credibility intervals obtained using the exponential prior of average 636 Ma. Blue branches indicate marine lineages. Brown branches terrestrial lineages. In the timescale, numbers represent Myr before the present.
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RSTB20150133F2: Results of molecular clock analyses. (a) Divergence times obtained under the CIR autocorrelated, relaxed, molecular clock model. (b) Divergence times obtained using the Uncorrelated Gamma Multipliers model. In both cases, nodes in the tree represent average divergence times estimated using the root prior with 636 Ma mean and 30 Ma SD. Brown bars represent 95% credibility intervals from the considered analysis. Grey bars represent the joint priors (for the considered nodes and analyses). Green bars in figure 2b indicate 95% credibility intervals obtained using the exponential prior of average 636 Ma. Blue branches indicate marine lineages. Brown branches terrestrial lineages. In the timescale, numbers represent Myr before the present.

Mentions: Molecular divergence times among arthropod major clades are presented in figure 2 and table 1 and in electronic supplementary material, figures S1–S5. Results obtained using the UGAMMA model are shown in figure 2a, the autocorrelated CIR model in figure 2b. Results obtained using the UGAMMA model but with a more permissive exponential root prior are reported in figure 2a. Using UGAMMA, 95% credibility intervals surrounding the average divergence times were significantly larger than when the autocorrelated CIR model was used. However, it was evident that for the three nodes of interest (those representing Palaeozoic terrestrialization events) the values in the 95% credibility interval obtained under CIR always represented subsets of the values in the 95% credibility interval obtained using UGAMMA. While the two sets of results are thus statistically indistinguishable, they differ in their congruence with the fossil record. While the more permissive UGAMMA analyses did not reject a Late Cambrian to Silurian origin of the three terrestrial arthropod lineages (the upper limit consistent with the fossil evidence), the CIR model rejected an Ordovician origin for the Myriapoda, suggesting a Precambrian origin instead. Under UGAMMA, arachnid terrestrialization happened in the Silurian, whereas CIR suggests an Ordovician colonization of land. In the case of the Hexapoda, UGAMMA analysis suggested an Ordovician origin, whereas CIR suggested a Cambrian origin and statistically rejected an Early Ordovician origin for this group. Thus, in general, CIR results suggest deeper divergence times. The use of the exponential root, while affecting divergence times of the deepest nodes in our tree (e.g. the age of the Deuterostomia–Protostomia split which is not presented in figure 2, but see electronic supplementary material, figures S1–S5), did not have any effect on the divergence times of the nodes of interest (figure 2 and electronic supplementary material, figure S2).Figure 2.


A molecular palaeobiological exploration of arthropod terrestrialization.

Lozano-Fernandez J, Carton R, Tanner AR, Puttick MN, Blaxter M, Vinther J, Olesen J, Giribet G, Edgecombe GD, Pisani D - Philos. Trans. R. Soc. Lond., B, Biol. Sci. (2016)

Results of molecular clock analyses. (a) Divergence times obtained under the CIR autocorrelated, relaxed, molecular clock model. (b) Divergence times obtained using the Uncorrelated Gamma Multipliers model. In both cases, nodes in the tree represent average divergence times estimated using the root prior with 636 Ma mean and 30 Ma SD. Brown bars represent 95% credibility intervals from the considered analysis. Grey bars represent the joint priors (for the considered nodes and analyses). Green bars in figure 2b indicate 95% credibility intervals obtained using the exponential prior of average 636 Ma. Blue branches indicate marine lineages. Brown branches terrestrial lineages. In the timescale, numbers represent Myr before the present.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920334&req=5

RSTB20150133F2: Results of molecular clock analyses. (a) Divergence times obtained under the CIR autocorrelated, relaxed, molecular clock model. (b) Divergence times obtained using the Uncorrelated Gamma Multipliers model. In both cases, nodes in the tree represent average divergence times estimated using the root prior with 636 Ma mean and 30 Ma SD. Brown bars represent 95% credibility intervals from the considered analysis. Grey bars represent the joint priors (for the considered nodes and analyses). Green bars in figure 2b indicate 95% credibility intervals obtained using the exponential prior of average 636 Ma. Blue branches indicate marine lineages. Brown branches terrestrial lineages. In the timescale, numbers represent Myr before the present.
Mentions: Molecular divergence times among arthropod major clades are presented in figure 2 and table 1 and in electronic supplementary material, figures S1–S5. Results obtained using the UGAMMA model are shown in figure 2a, the autocorrelated CIR model in figure 2b. Results obtained using the UGAMMA model but with a more permissive exponential root prior are reported in figure 2a. Using UGAMMA, 95% credibility intervals surrounding the average divergence times were significantly larger than when the autocorrelated CIR model was used. However, it was evident that for the three nodes of interest (those representing Palaeozoic terrestrialization events) the values in the 95% credibility interval obtained under CIR always represented subsets of the values in the 95% credibility interval obtained using UGAMMA. While the two sets of results are thus statistically indistinguishable, they differ in their congruence with the fossil record. While the more permissive UGAMMA analyses did not reject a Late Cambrian to Silurian origin of the three terrestrial arthropod lineages (the upper limit consistent with the fossil evidence), the CIR model rejected an Ordovician origin for the Myriapoda, suggesting a Precambrian origin instead. Under UGAMMA, arachnid terrestrialization happened in the Silurian, whereas CIR suggests an Ordovician colonization of land. In the case of the Hexapoda, UGAMMA analysis suggested an Ordovician origin, whereas CIR suggested a Cambrian origin and statistically rejected an Early Ordovician origin for this group. Thus, in general, CIR results suggest deeper divergence times. The use of the exponential root, while affecting divergence times of the deepest nodes in our tree (e.g. the age of the Deuterostomia–Protostomia split which is not presented in figure 2, but see electronic supplementary material, figures S1–S5), did not have any effect on the divergence times of the nodes of interest (figure 2 and electronic supplementary material, figure S2).Figure 2.

Bottom Line: Understanding animal terrestrialization, the process through which animals colonized the land, is crucial to clarify extant biodiversity and biological adaptation.While molecular divergence times for Arachnida are consistent with the fossil record, Myriapoda are inferred to have colonized land earlier, substantially predating trace or body fossil evidence.An estimated origin of myriapods by the Early Cambrian precedes the appearance of embryophytes and perhaps even terrestrial fungi, raising the possibility that terrestrialization had independent origins in crown-group myriapod lineages, consistent with morphological arguments for convergence in tracheal systems.This article is part of the themed issue 'Dating species divergences using rocks and clocks'.

View Article: PubMed Central - PubMed

Affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK School of Biological Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.

No MeSH data available.