Ratio of Males to females

Bengal21

Arachnopeon
Joined
Nov 4, 2010
Messages
42
When T's or other spiders for that matter have babies, is the ratio of males to females 50/50, or relatively close to it, like in several other species? Or are there 5 males for every female. Just curious. Tried to find the answer in a search before I posted but no luck.
 

captmarga

Arachnobaron
Joined
Mar 31, 2010
Messages
340
What animals have a 50/50 ratio?
Most animals with parents contributing x and y chromosomes have a ratio of approximately 50/50. Those numbers are based on counting in groups of 100 at the VERY least.

Reptiles may have all-male or all-female clutches based on temperature, but in mammals, the numbers stay fairly close to the 50/50.

As for Ts, one would have to keep track of the majority of the young and verify their sex. Or, one might be able to randomly sample 25 out of the clutch, and see how the numbers looked. Again, it would depend on the total number of hatchlings.

Just my input, having done a lot of equine genetic research and crunched a lot of numbers.

Marga
 

Chris_Skeleton

Arachnoprince
Old Timer
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Jan 31, 2010
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Hmm.. I did not know that.

I think a study into that would be very interesting. Someone should do a sample of 15-25 slings or more if they can and do it with species from the same genus to start out with. And do that a couple times. Then they can move on and study the subfamilies. I think breeders on here could get this study done pretty well.
 

2oCHEVYo0

Arachnosquire
Joined
Aug 29, 2010
Messages
67
IDK for sure, i've heard that you are 5x more likely to get a L. Violaceopes male than a female. Again though, that's just what I heard.
 

pok2010

Arachnopeon
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Oct 12, 2010
Messages
30
IDK for sure, i've heard that you are 5x more likely to get a L. Violaceopes male than a female. Again though, that's just what I heard.
that is correct mate, L.violaceopes have a hell of alot more males than females, so if bought 2 slings, the chances are you may have 2 male's, so best to grab a girl if you can find one with these :}
 

captmarga

Arachnobaron
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Mar 31, 2010
Messages
340
that is correct mate, L.violaceopes have a hell of alot more males than females, so if bought 2 slings, the chances are you may have 2 male's, so best to grab a girl if you can find one with these :}
In this case, I would wonder about temperature and incubation (as with some reptiles). Again, records of the temperature that the female and egg sac were kept in would be vital to determining this.

Marga
 

Titandan

Arachnopeon
Joined
Jul 17, 2004
Messages
19
Paul Becker told me that King Baboon spiderlings are more the opposite. He said most of the slings end up being females!

I guess it depends on the species. But for the most part, I think males end up growing a lot faster.
 

Bill S

Arachnoprince
Old Timer
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Oct 2, 2006
Messages
1,404
Most animals with parents contributing x and y chromosomes have a ratio of approximately 50/50. Those numbers are based on counting in groups of 100 at the VERY least.

Reptiles may have all-male or all-female clutches based on temperature, but in mammals, the numbers stay fairly close to the 50/50.

Just my input, having done a lot of equine genetic research and crunched a lot of numbers.
Not all animals have X and Y chromosomes. Reptiles, for example, do not. Your X/Y ratio sounds like just basic Mendellian genetics, which has limited application. Would work fairly well in equine genetics, but not in all animals.

In many animals sex is determined or at least influenced by factors other than direct genetics. Temperatures at incubation can shift male/female ratios in some animals, and some species (some fish, for example) can start life as one sex and shift to the other under certain conditions.

To come up with valid predictions in tarantulas, I think we'd need to start by directly observing tarantulas. And even then it may vary a lot according to species and conditions.
 

Bengal21

Arachnopeon
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Nov 4, 2010
Messages
42
I guess it's a good question when your answers only lead to more questions...
 

captmarga

Arachnobaron
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Mar 31, 2010
Messages
340
Not all animals have X and Y chromosomes. Reptiles, for example, do not. Your X/Y ratio sounds like just basic Mendellian genetics, which has limited application. Would work fairly well in equine genetics, but not in all animals.

In many animals sex is determined or at least influenced by factors other than direct genetics. Temperatures at incubation can shift male/female ratios in some animals, and some species (some fish, for example) can start life as one sex and shift to the other under certain conditions.

To come up with valid predictions in tarantulas, I think we'd need to start by directly observing tarantulas. And even then it may vary a lot according to species and conditions.
Correct, which is why I specifically said animals with parents contributing x and y USUALLY have 50/50. In chickens, the genes are opposite what you expect. Mammals traditionally have a 50/50 ratio. Reptiles do not. Insects do not - look at bees and ants. The gender of the bees is controlled by the way the larvae are raised, not only with genetic but with environmental influence.

Again, one would have to take either a completely random sampling from the egg sac (ie, keep 25 3rd instars to maturity or be able to sex the microscopic molts) or raise an entire brood and check gender. To make it valid scientifically, the female should be mated to a different male for three or more sacs, and the gender ratio of the offspring recorded.

Now, if anyone has confirmed male/female from Sac number 1234 from the pairing of So-and-so's female named Whatever, then you have the start of a study.

Marga
 

Bill S

Arachnoprince
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Correct, which is why I specifically said animals with parents contributing x and y USUALLY have 50/50.
Even then the idealized 50/50 can be shifted. For example, I remember years ago there was speculation that the reason that in humans more males tend to be born (Not far from 50/50, but still consistently leaning toward the male side) is that the sperm carrying the Y chromosome is a tiny bit lighter than the one carrying the X chromosome and can therefore swim faster, giving a slight advantage to fertilization by male chromosomes.
 

captmarga

Arachnobaron
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Mar 31, 2010
Messages
340
Even then the idealized 50/50 can be shifted. For example, I remember years ago there was speculation that the reason that in humans more males tend to be born (Not far from 50/50, but still consistently leaning toward the male side) is that the sperm carrying the Y chromosome is a tiny bit lighter than the one carrying the X chromosome and can therefore swim faster, giving a slight advantage to fertilization by male chromosomes.
Not entirely true, but it has been proven that one is faster and one longer lived... so again environmental factors (time factor of conception, temperature and Ph of the womb, etc) can effect which sperm make it where and when. Such as the old wives tale of eating bananas to produce a male... actually has some truth.

Marga
 

Scoolman

Arachnolord
Joined
Feb 9, 2010
Messages
613
4 slings (G pulchra) from the same sac; 2 males 2 females. I am keeping detailed records on the G pulchra I am raising and breeding. So,in about 5-10 years I will let you know what I find out about gender probability in the species. ;)
 

KoffinKat138

Arachnoknight
Old Timer
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Nov 21, 2008
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I've had 5 Brachypelma smithi slings, and crazy enough all five of them turned out to be female. I've always had more luck getting Brachypelma SP Female's than any other species.
 

Terry D

Arachnodemon
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Nov 21, 2009
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It appears I'm lucky, too- at least on B boehmei. I finally was able to get an unshredded exuvia and see the spermatheca on the biggest one I'd previously thought was male. :)
 

Protectyaaaneck

Arachnoking
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IDK for sure, i've heard that you are 5x more likely to get a L. Violaceopes male than a female. Again though, that's just what I heard.
Source?

that is correct mate, L.violaceopes have a hell of alot more males than females, so if bought 2 slings, the chances are you may have 2 male's, so best to grab a girl if you can find one with these :}
Source?

Sounds like a conspiracy theory to me. :rolleyes:
 

Lorum

Arachnosquire
Joined
Jun 10, 2010
Messages
111
IDK for sure, i've heard that you are 5x more likely to get a L. Violaceopes male than a female. Again though, that's just what I heard.
A friend of mine had 3 spiderlings of Lampropelma violaceopes, and we now know that two of them are males and one is a female.

I bought myself two spiderlings of the same species (with another dealer), and I now have one male and one female.
 

AgentD006las

Arach-how about..NO
Old Timer
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Jan 30, 2010
Messages
590
I think the only way to make a conclusion as to the ratio of males to females would to take an entire egg sac, raise them up and sex them all. If you took 50 out of a 100 eggs you could very well take 50 males and leave 50 females. (that is if its 50/50) IMO thats the only correct way to find out the ratio.

I brought up the temperature vs male/female ratio and i believe Schoolman volenteered to do an experiment. Raising a sac at room temp and one at elevated temps.
 
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