Uncertain about Indo-pacific bottlenose dolphin populations - Geneland identifies 4 but migration detected between 3

[jessica.m.dasilva]

In preparation for a Red List meeting on marine mammals, I came across a situation where I was uncertain of the number of populations for the species in South Africa.

It seems to show bioregional structure (Agulhas and Natal bioregions), and further substructure within the Natal bioregion (weak but significant differentiation), at least according to Geneland analyses. Therefore the study identified 4 genetic clusters/populations for the species in South Africa. However, bidirectional migration was detected between the 3 populations within the Natal bioregion, believed to be associated with sardine runs. 

Given the presence of migration, I am inclined to place the three Natal biogregion clusters in a single metapopulation, making the number of populations in SA 2. 

Would others support this?

[Isa-Rita Russo]

Morning all,

 

I agree with your assessment Jessica. It sounds like a Natal ESU with 3 MUs so I will go for 2 populations overall. Having said this, I just had a look at Figure 5. There seems to be migration between the two populations of Agulhas and Natal so this is a difficult one. I can’t see this in the paper, maybe supplementary, but do they report the probability values for the 4 populations as identified in Geneland?

 

Isa-Rita

 

School of Biosciences   Sir Martin Evans Building              Museum Avenue                    Cardiff CF10 3AX                  Wales, UK                           Tel: +44 29 2087 6036

Ysgol y Biowyddorau Adeilad Syr Martin Evans Rhodfa'r Amgueddfa Caerdydd CF10 3AX Cymru, y DU Ffôn: +44 29 2087 6036

 

 

 

From: <genetic-indic...@googlegroups.com> on behalf of "jessica.m.dasilva" <jessica....@gmail.com>
Reply to: "genetic-indic...@googlegroups.com" <genetic-indic...@googlegroups.com>
Date: Tuesday, 11 July 2023 at 08:11
To: Genetic indicators project <genetic-indic...@googlegroups.com>
Subject: Uncertain about Indo-pacific bottlenose dolphin populations - Geneland identifies 4 but migration detected between 3

 

External email to Cardiff University - Take care when replying/opening attachments or links.

Nid ebost mewnol o Brifysgol Caerdydd yw hwn - Cymerwch ofal wrth ateb/agor atodiadau neu ddolenni.

 

--
You received this message because you are subscribed to the Google Groups "Genetic indicators project" group.
To unsubscribe from this group and stop receiving emails from it, send an email to genetic-indicators-...@googlegroups.com.
To view this discussion on the web, visit https://groups.google.com/d/msgid/genetic-indicators-project/8427415f-ef21-4fa1-973d-8009f550839en%40googlegroups.com.

[Joachim Mergeay]

If we look at how strong that genetic structure is across the entire region (Agulhas and Natal), it is rather weak. The highest neutral FST, representing gene flow and drift interacting, is 0.036, which suggests that there has always been considerable gene flow in the past, in spite of adaptive differences.  

Unless something has changed dramatically in these populations over the past decades (which could cause them to drift apart genetically due to a disruption of gene flow patterns or just due to lower Ne), I would consider them to be part of a single metapopulation, not even two. 

Since it seems the numbers have been declining recently (see https://www.frontiersin.org/articles/10.3389/fmars.2020.542675/full), you could err on the side of caution and indeed consider two populations. 

Clustering shows 4 populations, but what does that mean? That there are genetic discontinuities, and detecting them depends on sampling strategy and statistical power. If you look hard enough, you nearly always find structure. It says nothing on whether those are subpopulations of a well-connected metapopulation (the unit we should be focusing on for Ne>500).

 

If you run simulations with 6-7 MPG (which is the lowest value expected here across the least connected populations), you see nicely correlated genetic drift across replicate populations. But given the declines, the FST of 0.03 may overestimate connectivity at present), and I'd remain cautious and consider 2 populations. 

Joachim 

To view this discussion on the web, visit https://groups.google.com/d/msgid/genetic-indicators-project/6F83E83B-B8D0-405C-9969-8D9E75E6280C%40cardiff.ac.uk.

--

Joachim Mergeay (he/him)

Research Institute for Nature and Forest - Belgium                                  

Associate Professor KULeuven Ecology Evolution and Biodiversity Conservation

Tel: +32 499 942 942

Meldpunt wolven Vlaamse overheid : wo...@inbo.be

///////////////////////////////////////////