The shaping of genetic variation in edge-of-range populations under past and future climate change

Razgour et al.. Ecology Letters (early view). DOI: 10.1111/ele.12158. The shaping of genetic variation in edge-of-range populations under past and future climate change

Plecotus austriacus; photo by Branko Karapandža

Plecotus austriacus; photo by Branko Karapandža (via EuroBats)

Will Pearse

Will Pearse

This is an extremely impressive set of analyses that did make me think. The authors examine the genetic structure of these bats, find that glacial refugia contain a lot of its genetic diversity, and then show that under climate change a lot of this diversity will be lost.

It had never occurred to me that hiding from glaciers and hiding from climate change involve species moving in opposite directions, and so what was a refuge before is now a death-trap with nowhere to run to. We know that species’ traits can vary (often adaptively) within their ranges, and we know that species’ past selective pressures can leave an imprint on species today (phylogenetic signal/inertia) and can cause sub-optimal phenotypes. Thus I think it’s entirely plausible that the progeny of the colonists that survived the last great climate-shift on Earth are the ones that will be worst-hit by the next, and so might do badly in it. Of course, you could invert this and say that the descendants of those who dispersed after glaciation are now in the safest spot, and so maybe we’ll be OK. Anyway, my point is to expose my own ignorance, and to wonder whether this could help us figure out a null expectation for what intraspecific variation should look like when looking at lots of species, and improve the fit of species distribution models. Perhaps this has already been done, in which case please let me know!

I like bats (I worked with them one summer as work experience), and while I’m no expert, I feel safe saying they’re very sociable animals. I wonder what effect this will have on their ability to disperse in the face of climate change, because while they are quite choosy in where they roost, they (surely) choose a new roost as a group and as such they’re more likely to find a suitable habitat. Indeed, they must also be less sensitive to allee effects because an entire group is moving at once, and in species where males roost together they’re always having to hunt around for females anyway. I must emphasise I know very little about bats, and so if any/all of the above is nonsense please call me on it right now!

A final thought: I like this paper very much, and love the story it tells, but what will the consequences be of losing these populations of diversity? Are these differences all just drift, or are there adaptations? In other words, what would we be losing? I imagine the authors know the answer to these questions, but I’d quite like to know what they are!

Lynsey McInnes

Lynsey McInnes

Wow, this paper has a bit of everything,and, weirdly, incorporates elements of most of my interests in one, pretty impressive, whole! Niche conservatism, rane shifts, climate change, barriers to movement and my persistent pet interest genetic diversity within the range and the need to consider intraspecific variation and not just treat the range as one big, homogeneous whole. Neat.

The authors do a fine job of integrating the results from a whole host of analyses to suggest that this bat species is most genetically diverse in Iberia (the site of one of its refugia in the LGM) and is showing signs of movement north westerly into England where there is evidence of decreasing population size despite conditions here seemingly spot on for population persistence. The authors emphasise that such results underline the need to conserve edge of the range populations (Iberia for diversity, England for suitable conditions for driving forth any range shift necessitated through shifting climates). Sounds reasonable.

To be cynical, I’m actually not sure how novel such advice is. In a world where extensive range shifts to track climate are predicted (and have been observed), it seems intuitive to focus on range edges as these are the populations that are most likely to lead the movements. To be less cynical, the authors try to show this really is the case. Similarly, a whole host of studies have shown that genetic diversity is often greatest in glacial refugia, if, for no other reason, because these populations are the oldest. Nevertheless, this study is still one of the few that sample range wide populations to show this, and also find that not all refugia are similarly diverse.

The authors also take a pragmatic approach to finding evidence for niche conservatism, arguing that their ecological niche models probably are capturing the fundamental niche and not the realised niche such that their observation of temporal continuity is valid because the species already exists in sympatry with members of its genus (ie not limited by species interactions) and is absent from more arid regions adjacent to its range despite the ability to get there (if it wanted to). While these arguments seem reasonable and are better elaborated than many similar studies, I do wonder whether there are any more conclusive ways to test this assumption. Probably heating the bat on hot plates would be one way forward (dessicating it as well to test further niche axes perhaps).

I remain on the fence over the validity of ABC analyses, but really appreciated the thought that went into defining populations and models to test. I just worry a lot about the sheer amount of simulations necessary to implement such analyses. In this case, the conclusions wrought were interesting and seemed reasonable. Just out of curiousity, I wonder at what stage the ABC analysis was implemented and how much the authors had a feeling for the results already…

I’ll end this with a plea of – watch this space – our lab is working on ways to obtain analytical solutions to similar questions of demographic history and phylogeography such that there will be no need for the simulation quagmire of ABC.

In short, I was really impressed with this study, bringing together a lot of data and analyses to underline the necessary route forward to successful protection of a species. How do we now make this macro- and roll it out for more species, either across a whole clade or a whole community? Exciting times.


About will.pearse
Ecology / evolutionary biologist

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