Vicariance and adaptation in a common temperate ophiuroids

Congratulations to Emilie (and her colleagues) for their new paper in Molecular Ecology. It has just been accepted. Find below the details of this nice paper.


Title: Did vicariance and adaptation drive cryptic speciation and evolution of brooding in Ophioderma longicauda (Echinodermata: Ophiuroidea), a common atlanto-mediterranean ophiuroid?


Authors: Emilie Boissin, Sabine Stohr and Anne Chenuil

Abstract: Over the last decade, cryptic speciation has been discovered in an increasing number of taxa. Species complexes are useful models for the understanding of speciation processes. Motivated by the discovery of brooding specimens in the common Atlanto-Mediterranean broadcast spawning brittle star, Ophioderma longicauda, a recent study revealed the occurrence of divergent mitochondrial lineages. We analysed 218 specimens from 23 locations spread over the geographic range of the species with partial Cytochrome c Oxidase subunit I (COI) sequences. A subset of this sample was also surveyed with the internal transcribed spacer of the ribosomal DNA cluster (nuclear ITS-1). Our study revealed six highly divergent mitochondrial lineages and the ITS-1 data confirmed that they most likely represent a species complex. Geographic ranges, abundances and genetic structures are contrasted among the putative cryptic species. Lineages in which brooding specimens have been found form a monophyletic group and are restricted to the Eastern Mediterranean basin, an oligotrophic zone. A phylogeny-trait association analysis revealed a phylogenetic signal for low  ‘chlorophyll a’ values (our proxy for oligotrophy). An ecological shift related to the hyper oligotrophy of the Eastern Mediterranean region is therefore likely to have played a role in the evolution of brooding. This study revealed that a complex mixture of vicariance, population expansion, adaptive divergence and possibly high local diversification rates resulting from brooding has shaped the evolution of this species complex. The dating analysis showed that these events probably occurred in the Pleistocene epoch.

Brooded juvenile (SEM image) and adult (picture) of Ophioderma longicauda 

JC_29.08.11_minutes

In our journal club from last Monday, we discussed an interesting paper by McGovern and co-workers: “Divergence genetics analysis reveal historical population processes leading to contrasting phylogeographic patterns in co-distributed species” (Molecular Ecology, 2010, 19, 5043–5060).

The paper emphasizes the importance of taking into consideration the historical perspective when studying any spatial genetic pattern. A phylogeographic break does not necessarily means that the gene flow is currently restricted (that’s what is happening in the bat star across QCS). The contrary is also true a more subtle differentiation at this break is not equals to a greater contemporaneous gene flow (instead it can be due to a more recent divergence time, this is what is happening in the snail).

Contrary to the extrapolation of gene flow from traditional Fst, the software IMa does not make assumptions of equilibrium (genetic drift/mutation/migration) and allows disentangling between ancestral polymorphism and ongoing gene flow. A good paper to read about this topic is the paper accessible in the September edition of TREE from Marko & Hart (The complex analytical landscape of gene flow inference, Trends in Ecology and Evolution September 2011, Vol. 26, No. 9).

We also discussed the extirpation of the snail and the recolonization range. Why was the snail extirpated if it is the cold species of the two? And when did it recolonize this entire range? Indeed, the date of divergence between north and south populations does not approximate the recolonization but just the population split. The recolonization of the north by the snails could have happened any time between 282000 and 11000-17000 years ago.

We discussed the possible causes explaining the fact that the older event in the bat star (282000) was visible by AMOVA but not the more recent one (100000). Maybe a difference in the duration of the separation is the explanation, given that gene flow seems homogeneous across the range of the bat star.

We also discussed the problems of using a single gene. We talked about selection and the difference of informativeness/variability between nuclear and mitochondrial markers.

We discussed about the choice of the markers, particularly tRNAs, and the importance of the calibration in the dating of divergence time.

Journal Club Sessions (Aug-Nov)

Date	Speaker	Field
29-Aug	Emilie	Phylogeography
05-Sep	Tim	Phylogeny
12-Sep	Ilkser	Population genetics
19-Sep	Catherine	Phylogeny
26-Sep
03-Oct	Amanda	Phylogeography
10-Oct	Carel	Population genetics
17-Oct	Kerry	Phylogeography
24-Oct	Sarita	Population genetics
31-Oct	Miekie	Phylogeny
07-Nov	Paulette	Phylogeography
14-Nov	Sam	Population genetics
21-Nov	Thierry	Phylogeny

Does the geography alone can trigger life history adaptation?

Here the geography represent vicariance events that correspond to a rupture of gene flow of an ancestral single population/species. Does anyone can think of any processes by which such vicariance event alone (without change in habitats or ecology) can induce changes in life history traits such as reproductive startegy, dispersal ability etc.
Any ideas?

How scientists see each other ?

You are more than welcome to share your views ;)

Zanclus samples from Anse des Cascades - 19 July 2011

Because the sea was very rough during the two weeks in Reunion and because we could not be sampling in the marine reserve, this was the only site where we could go to search for the Moorish idol: Anse des Cascades.

And here are the 15 samples we collected with my brother ...

Sampling trip July - Reunion

The past two weeks, Emilie and I have been in holidays in Reunion. But as everyone knows, none of us as biologist can be in real holidays. So, we kept this statement true and we went snorkeling to see cucumber ;). Anyway, here are some pictures we took while "working".

Here is the culprit sea cucumber, Synapta maculata (on right hand side), with its nice tentacles around its mouth. The urchin Diadema setosum with its five characteristic white dots and peacock worm in the top left.

Then we saw some fish like this trumpet fish and this Picasso trigger fish.

This puffer fish that Emilie hunted for a while to get this nice picture!

Also some beautiful fish and others not very nice.

Emilie picked up some ophiuroids also. This one was probably Ophionereis porrecta as you can see.

Who's who? who can say which one is moorish idol and which one is the bannerfish?

And then when we left, we got a very nice surprise (thanks to Emilie's piercing eyes!). Look in the water close to the fishing boat, there are two dark roundish shapes. Who guessed?

Two juveniles of rays at only 3m from the beach!

That was our snorkeling in the reserve area at Etang Sale