Crabs, lobsters and shrimp now have a family tree dating 500 million years

Researchers have for the first time traced the roots of crabs, lobsters and shrimp to create the family tree of crustaceans.

Representatives of major decapod lineages. (a) Lucifer sp. (Southeast Florida, USA)(Dendrobranchiata); (b) Stenopus
hispidus (Komodo, Indonesia) (Stenopodidea); (c) Procaris chacei (Bermuda) (Procarididea); (d) Arctides regalis
 (Maui, Hawaii, USA) (Achelata); (e)Cherax quadricarinatus (aquarium specimen) (Astacidea); (f) Thor amboinensis
 complex (Ternate, Maluku Islands, Indonesia) (Caridea); (g) Axiopsis serratifrons (Bali, Indonesia) (Axiidea);
(h) Stereomastis sculpta (specimen ULLZ 8022) (Polychelida); (i) Upogebia cf.pusilla (Arcachon Bay, France)
 (Gebiidea); (j) Emerita talpoida (Westerly, Rhode Island, USA) (Anomura); (k) Pachygrapsus crassipes
(Catalina Island, California, USA) (Brachyura) [Credit: Wolfe et al. 2018]

The tree shows the 450-million-year evolution of these 10-legged decapods, when lobsters and crabs each diversified from a single evolutionary origin. Groups of shrimp evolved earlier.
The findings are part of a massive family tree project where researchers resolved the deep evolutionary relationships between crabs, shrimp and lobsters. The discoveries made by analyzing more than 400 genes from 94 species could also inform conservation policies to ensure their longevity.

«Understanding the origins of biodiversity across half a billion years in groups that are extremely ecologically and economically important is fascinating,» said FIU marine sciences professor Heather Bracken-Grissom, the anchor author of the study. «This is extremely important since studying and preserving biodiversity needs to be at the forefront of our efforts in the biological sciences and across humanity»

Phylogenetic hypothesis for Decapoda based on the topology from the Bayesian CATGTR + G analysis.
Unlabeled nodes are considered strongly supported. Nodes where at least one analysis rejected the depicted
topology are illustrated with rug plots showing the support values from each analysis. In rug plots, the illustrated
topology is first row, first column. All alternative topologies are available in Dryad. Species used for probe
 design by shotgun whole genome sequencing in bold text. For clarity, the branch leading to the outgroup
 Branchinecta sp.(Anostraca) has been shortened, and the real length is indicated. Organism silhouettes
 are from PhyloPic (phylopic.org) or created by J.M. Wolfe. [Credit: Wolfe et al. 2018]

The boom of diversification for crabs, lobsters and shrimp may coincide with the spread of modern reef-building corals, Bracken-Grissom said. It is possible the emergence of reef-building corals provided new habits for decapods to colonize and diversify, leading to the emergence of several new lineages after the mass extinction of life on Earth 250 million years ago.
While the study produced the largest amount of genetic information about decapods, more work remains to be done including the addition of more species to better understand species-level relationships. The researchers hope the newly generated genomic resources will be used by others interested in decapod crustaceans for years to come.

«When we started this work in 2013, most studies that looked at the evolutionary relationships of decapods were based on physical traits, and the genetic work that had been done was very limited in scope,» said lead author Jo Wolfe, a post-doctoral researcher at Harvard University and former Gerstner Scholar at the American Museum of Natural History. «It was challenging to jump into this project on such an ancient and species-rich lineage without relying on the experience of others.»

Divergence time estimates for Decapoda based on the topology in Figure 2. Posterior ages were estimated
in PhyloBayes using the CAT-GTR + G substitution model, the CIR clock model, and a gamma distributed
 root prior of 440 Ma ± 20 Myr. Horizontal shaded bars represent 95% confidence intervals.
Numbered circles represent nodes with fossil calibrations [Credit: Wolfe et al. 2018]

The study was published in the journal Proceedings of the Royal Society B.

The work is part of the Decapod Tree of Life project, an initiative aimed at uncovering the relationships of crab, lobster and shrimp across their hundreds of millions of years on the planet.

Author: Chrystian Tejedor | Source: Florida International University [April 24, 2019]

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