Adder Day

France, British isles

Adder Day

Postby Daniel Kane » Thu Mar 29, 2012 10:05 pm

Today I made a trip to my closest (known) population of Vipera berus. I arrived in fog and no sun which was a big contrast to the previous few days of full sun and high temps but due to this the snakes had not yet had chance to warm up. The first two males emerged from the hibernacula around 9:45 and stayed basking until around 10:30. I had chance to watch them bask, and to take a few photos in this time (all photos are in-situ);

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Individual named 'M7', being the 7th male identified at this site since 2009


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M11


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M7


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I moved on to another area where I have found adders in 2010 and 2009, but none last year. After waiting for a Zootoca to re-emerge (which it did not) I saw this male, a new individual for me; he seemed not to take much notice of me as I took a few more photos. He did slither off but re-emerged 10 minutes later, so I was able to watch him for 30 minutes. Over this time, as he warmed up in the sun, he became more and more restless and progressively moved more of his body into the shade until he was all under.

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M14


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M14


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Almost gone...


At this point I left and photographed a greenish male Zootoca who allowed a very close approach (<10cm).

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Clouds came as I photographed the lizards which allowed M14 to return to basking;

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M14


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M14


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M14


All in all, not a bad morning. I imagine there will be some updates over the next few weeks as I will be following the adders around my area for a final-year university research project.

As you can see the males are already in the sloughing stage (milky eyes) so they should be bright and colourful within a week or so, when I hope to be able to photograph breeding activities; perhaps a bit too ambitious to hope for the dance of the adders again, but you never know!
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Re: Adder Day

Postby Daniel Kane » Thu Apr 05, 2012 4:55 pm

After a few more days of sun (and one of snow) the adders are now mostly into mating mode. All snakes seen have now shed and appear very nice with bright colours, as you would expect. Yesterday I had the fortune to see an individual I had last seen on September the 7th, 2010; he is still in good condition and in the same area of the forest.

Some photos;

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M11 - April 2nd


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M14, recently shed - April 4th


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M15 & F10: April 4th


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Last seen September 7th, 2010: M5 - April 4th
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Re: Adder Day

Postby Jürgen Gebhart » Thu Apr 05, 2012 6:30 pm

Very nice!!

I will change five black males against one of these silver bullets!!!! ;)
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Re: Adder Day

Postby Jeroen Speybroeck » Thu Apr 05, 2012 6:44 pm

Jürgen Gebhart wrote:one of these silver bullets!!!!


Mmmm...!!!
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Re: Adder Day

Postby Daniel Kane » Thu Apr 05, 2012 10:40 pm

Jeroen Speybroeck wrote:
Jürgen Gebhart wrote:one of these silver bullets!!!!


Mmmm...!!!


I am still waiting for the day when I will be fortunate enough to see a nice black adder. It seems you are tripping over them in Holland and Germany!

A quick visit late this evening allowed me to see M5 roughly 40m from where he was last seen yesterday evening - perhaps he has been looking for the girls today (movement is towards a known hibernacula of a large female, although not seen since April 2010...). Also a fresh shed skin of F10 in the heather.

On a side note, is anyone aware of the minimum population size to avoid the effects of inbreeding? 46 recorded observations of 28 individual snakes since May '09 suggests, to me, that the population of breeding adults is quite small. This year I have noticed that the two skins I have found have scale irregularities - some undivided sub-caudal scales, and areas where scales do not cross the ventral surface. I am not sure of this is to be expected in natural (healthy) populations but I have seen that this is often an early indicator of inbreeding. I'd like to hear your thoughts on this.
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Re: Adder Day

Postby Jeroen Speybroeck » Fri Apr 06, 2012 8:59 am

Pfff... I'd take a silver one over a blackie any time...

Daniel Kane wrote:is anyone aware of the minimum population size to avoid the effects of inbreeding?


Talked to a colleague about this...

Hard to fix to a certain number, but there are some general guidelines that allow to assess the probability of inbreeding risks within x generations. Pure coincidence can cause this to be far worse in certain populations in comparison to others. A lot depends on how long that population has been in that state of low numbers.

This is measured by looking at heterozygosity. If very low, things might go bad soon, through combination of unwanted recessive allels. If high, however, you’re still not sure you’re not dealing with “genomic islands” with very low genetic diversity.
(Sometimes, it’s vice versa = very low genomic diversity on average, but with high diversity in places where things really matter for population fitness – like in pike in Ireland. Not very likely in small populations, though)

With a population size of about 28 ind. and an effective population size of probably not more than 10, the inbreeding coefficient increases rapidly (5% loss of heterozygosity within population per generation). After 10 generations (so maybe 50 “adder years”?), this adds up to 0,40. This usually is too much to take for vertebrates.
http://en.wikipedia.org/wiki/Effective_population_size

However, remember that these are merely expected values and in populations with discrete generations. Chance adds a lot of variance in both directions. Selection for heterozygote scan slow down the process (but usually less in small populations of K strategists). Overlapping generations also slow things down (offspring of older cohort has less inbreeding than offspring of younger ones).

In the end, you can be rather sure that an effective populatie size of 10 (or even 28) ind. is unsustainable due to inbreeding. Until when? Hard to tell and depends on how long it’s been going on already. If morphology starts to show actual signs, that means trouble.

As a rule of thumb, Ne=50 is said to suffice to avoid clear effects of inbreeding (1% heterozygosity loss per generation; which is a rate that allows for considerable compensation due to selection for heterozygoten).

The proper way to investigate this is to determine the true effects of fitness on inbreeding by means of experiments in “common garden” with controlled cross-breeding. Or at least long-term monitoring of multiple populations and establishing fitness components (number of offspring per ind. via parent analyses, in connection to its inbreeding coefficient) to get an idea of the link between inbreeding and fitness.
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Re: Adder Day

Postby Daniel Kane » Sat Apr 07, 2012 8:07 pm

Thanks for that Jeroen, a very well-structured answer - just what I was looking for! As far as I am aware the area has remained unchanged, apart from natural succession, for many years; I would imagine the population to be relatively stable. Monitoring the population over a period of x generations and seeing how things go is the most likely thing to be done, although a tutor has mentioned analysing DNA from sloughed skins to asses the genetic diversity of the population. I am not sure how feasible this is though.

An update on the 'silver bullets';

2 hours there today. The sun came through the clouds infrequently but it was warmer today than it has been for the last few days. 4 males observed, only basking (as you can see from their bodies). M5 seemed to be on the move (searching for females maybe) as I was leaving.

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M7


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M5


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M16 - seen for the first time today


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M11 (front) and M7 (back) are often seen basking together
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