Selection effects, example and question?

[Tom]

Alberta does not have a full curl restriction on hunting rams.
This article shows the decline in weight and horn size resulting from this in the last 30 years.

Its a research article in the very prestigious, International weekly journal of science, nature 11DEC2003, p655-658 and on the cover.

A conclusion is that Alberta should consider the full curl restriction before the herd further declines its gene pool.

Mean horn length has gone down about 20 cm in 30 years and harvest of only 57 or so rams, or a little over 1 inch per 4 years. Pretty neat, eh, they figured that out? Scientists from UK, Canada, and the US are authors of the paper.

Rams are pretty sensitive, I've heard. Anybody know of genetic selection effects in deer? Like if we shot all the little young bucks, could we expect the herd antlers to get bigger.

 

[pawclaws]

Tom I'm by no means knowledgeable on this subject. I have heard though that antler/horn mass is nutrition related rather than genetic. I would think that Pops, Yukon Hunter, Ray Vincent, and possibly Elkchaser, or Elkhunter might be of some help to you on this one.

 

[Tom]

Its related to nutrition, age, and genetics, all of them, I know that part some. I'm asking if there is info. out there on the selection effect on the quantitative characteristics of the antlers. They are definitely inherited, but what conditions are needed to expect a reasonable effect, if we select for antlers.

It didn't take much to get a pretty big effect on those rams.

 

[BuzzH]

Tom, theres a huge difference between sheep and deer.

For starters, I think genetics are the most important thing for producing B&C sized rams, bulls, or bucks. There is a very, very, very, small percentage of bucks, bulls, rams, etc. that are genetically capable of ever reaching B&C size, in spite of nutrition, habitat, etc.

If you dont believe genetics are a big part of record book quality animals, look at Montanas sheep. Montanas genetic stock for most of the transplants has come from the Sun River herd, which has awesome genetics, always has. Montana has dominated the record book entries for the last 20 years or so. The main reason is because of excellent genetics that came from the source of nearly all the rams transplanted in MT.

Now check out Wyoming and Colorado for the size of their rams. The habitat (nutrition) is similar to that of MT, but its rare to find a ram in either state that makes the record book. The sheep in Wyoming are healthy, get plenty of age on them, but they just dont have the genetics. They're still beautiful rams, just dont have the 16+ inch bases and 37 inch horns at 6 years like many of the sheep in MT.

With deer its the same way, there are areas that have better genetics than other areas. Evidenced by looking at record books. Dont just look at the total number of record book animals from a state/province, but look at how many they get in relation to the total deer population.

As far as managing deer like sheep, you cant. Heres why. Its almost impossible to tell the age of deer with respect to their antler size, or any other method, short of killing it. Whitetail typically reach their maximum antler growth potential at age 6 (or so). Some are B&C sized at ages significantly lower than that. If I remember right the Hansen #1 typical WT was aged at 4 1/2 years.

Sheep on the other hand typically just get better with age, as they grow until they die. Its also a fair statement that rarely will you get a record book ram much under 6 years. Most record book rams are 8+.

Its easy to manage sheep because age and horn length (full curl) are something a hunter and an agency can identify. Even further, with good glass at close range you can count annuli on the rams horns to know the age. Deer, on the other hand are about impossible to select based on an age. Young whitetail bucks can have B&C sized antlers pretty easily.

I think the best management style you can hope for with free-ranging whitetail is to manage for a distribution of age classes with the total herd number at about 80% of the carrying capacity.

 

[pawclaws]

Tom one place you might try checking is with the US Forest Service. Buzz can help you there. Next go to the library and look up the records in the Commerce Business Daily to find out if there have been any studies contracted which cover the subject. Then run a global search using the sheep as your largest parameter then the topics of horn mass, curl, genetics, nutrition, herd characteristics, etc as your finite parameters. Sounds like a fun project. Best of luck!!

 

[pawclaws]

Peredicting changes among variables is a function of correlation regression analysis or what many call the "least squares" method. The idea is to identify the elements that are believed to affect the aspect of interest, in this case horn mass, and by using math develop a formula or set of formulae that can interpret and predict the degree of influence each variable has with given mathematic precision. You should be looking for research or studies that use this approach.

 

[Tom]

People down here judge the age of bucks all the time using body characteristics, more before the rut than after it though as the older ones trim up and look younger at the end of the rut. The new book, Observing and Evaluating Whitetails, available from qdma.com gives a great set of pictures and text on how they do it.

There's studies showing the heritability of antlers in whitetail bucks I know, I just don't know what the expected gain is for selection. That would be a way to see what you could expect to get for some selection procedure.

Texas Parks and Wildlife advocates selection by taking out the yearling spikes at least, maybe 3 and 4 pointers also, and they have data to show why. Even Harry Jacobson, the guy from Miss. who said spikes get big advocates a reverse selection. He advocates protecting the biggest of the young bucks for their whole life, i.e. never shoot them, so they breed. He's moved to Texas in his retirement and manages some ranches that way. I just went to a set of talks on this and heard these guys present their arguments and management strategies.

Both of these management practices assume there is going to be some effect of the genetic selection/protection they are using, but was it the magnitude of the effect? I heard their is a way to estimate the expected size of the gain, but I don't know an animal geneticist to ask right off. I'm looking for an estimate method on that, the expected gain.

Heck, if the rams are sensitive and it took 30 years, maybe a ranch wouldn't see an effect in whitetails for 60 years, if heritability is smaller? By that time, the guy that started the program would be dead. Maybe it could happen faster though?

Heritability of ram horns must be a pretty high number, I think that's the first study that showed such an effect, but is it?

 

[BuzzH]

Tom,

I also think there is a big difference between attempting to manage whitetails in the North than in the South.

For starters, with all the public land, you cant really demand that hunters only shoot certain age classes or spikes or 3-4 points.

It wouldnt be very easy for you to see the effects of point restrictions, etc. on public lands open to public hunting.

You'd be better off trying to find data in a more controlled environment...like those found in Texas.

I just think you have to focus on the deer and the management style in Texas as the situation is so different from whats found in the wild in MT, WY, etc.

 

[Tom]

I don't know, Alberta is farther north and there was an effect on the big horn sheep in the wild there.

Deer antlers would have to be a lot less heritable than ram horns for there not to be an effect of selection.

Genetic selection is genetic selection, if something is heritable, there are selection effects, you can select for it. I want to learn how to compute the expected gains from selection to quantify it, but I never studied that stuff.

 

[pawclaws]

Tom I suppose I can teach you; but, as I had to do with Algebra I'll ask that if you do not understand an aspect simply accept it and follow the rules until it clicks in. Nothing will frustrate one more than head banging against something that simply isn't ready to sink in yet. If you are willing to give it a go I'll walk you through the process two or three steps at a time. Be prepared though, the data collection effort alone will take at least a full year at a minimum. What is your current level of competence with statistics? Do you know what the term standard deviation means?

 

[Tom]

I got a PhD in statistics pawclaws. Just tell me the reference for selection effects in quantitative heritable traits. Hopefully, it will have a worked example?

You think its just regression, what's the reference, give me an example?

 

[pawclaws]

Super!! Yes I would approach the thing that way Tom, Ergo identify each variable within a defined strata. For genetics I suppose you might consider things like: Territorial parameters, constrained size, weight,color, etc characteristics. I think that you might find the colleges dealing with zoology, biology, etc interested in putting grad students on the data collection effort once the variables are defined. Lots of kids out there looking for Thesis Topics you know. Using the defined variables bounce them against the mass, length, curl, etc characteristics of the rack and see which appear to have the greatest influence and whether or not a pattern manifests. Where is the example? Beats the hell out of me! I guess you are building it!! I'll nose around and see what I can find though. This one sounds like real fun!!

 

[Tom]

I see why you're thinking regression. The bighorn sheep example demonstrates the effect with a regression line.

There's a way to predict the effect ahead of time though, I heard someone say. That's what I want to learn about. There's some genetic model where you put in your selection strategy, then you compute what the expected gain will be in the future.

That would be a way to test out different harvest strategies. I guess biologists put point restrictions for deer or full curl restrictions for rams, etc. expecting an effect of letting animals age some before they are shot. But, the Alberta ram example demonstrates an effect on the gene pool, I think, if you read the paper in Nature.

Dr.Coors from Wisconsin, just e-mailed me some texts to learn about it! They look pretty introductory, but he says there's worked examples.

"Falconer, D. S., and Trudy F. C. Mackay. 1996. Introduction to quantitative genetics. Longman Essex, England.

Hartl, D. L. and A. G. Clark. 1997. Principles of Population Genetics. Sinauer Associates, Inc., Sunderland, MA.

These texts provided several worked examples."

 

[pawclaws]

Oh No!! I was preparing to build the model!! If one exists then all this leg work stuff has already been done! Still might be a good idea to validate the significance measures. So let us go forth and find this model!

 

[Tom]

Falconer has a chapter on selection, the response, and its prediction. It outlines it. The library here has the old edition, I need to go accross town to see what the new edition adds if anything.

Its a regression like you said, but with other stuff too.

Response difference from the mean of a quantitative trait
is heritability times
selection difference from the mean of a quantitative trait.

He gives ways to see how this is a function of selection intensity (i.e. how many are shot or die), how many for males and/or females seperately, how the phenotypic variance is reduced from selection, and how the expected gain (or loss if its negative selection) is changed at first but then stabilizes.

A guy at work here told me some recessive traits can pop up with intense selection, that's what stops some people from taking this too far.

I'm learning about it. I figure everytime we pull the trigger we change the gene pool, so we might as well learn to be smart about it.

 

[nmtaxi]

huh-huh. What if c-a-t really spelled dog?

 

[nmtaxi]

Just so there's no more confusion by you intellectual types, that was just a little joke from a movie. Get it... like you guys were talking over my head, so I pretend like I'm making an intellectual statement. Get it...it's funny. You know... a joke. It wasn't serious.... I swear.