males/females percentage

[Thoroughbred]

so,what do you think? how many males and how many females come out from a sac? ever since i'm in this hobby,i was wondering...

 

[jayefbe]

I've asked this question myself, and have done a lot of research while essentially getting nowhere. I've read in multiple places that Lampropelma species have something like a 7:1 male:female ratio, but it's all hearsay.

It does make sense for a heavy male:female ratio to evolve in tarantulas. Given the much longer lifespans of females (a male has a single breeding season, a female has potentially 10 or more), and the predilection for females to try to eat males, would mean that mature males are always in a shortage. Whether or not certain clades of tarantulas have evolved this capacity to produce a skewed sex ratio (some species of animals have) is unknown to me. I haven't seen any reliable indication (ie scientific papers) that give any clear evidence one way or the other.

 

[Thoroughbred]

I've asked this question myself, and have done a lot of research while essentially getting nowhere. I've read in multiple places that Lampropelma species have something like a 7:1 male:female ratio, but it's all hearsay.

It does make sense for a heavy male:female ratio to evolve in tarantulas. Given the much longer lifespans of females (a male has a single breeding season, a female has potentially 10 or more), and the predilection for females to try to eat males, would mean that mature males are always in a shortage. Whether or not certain clades of tarantulas have evolved this capacity to produce a skewed sex ratio (some species of animals have) is unknown to me. I haven't seen any reliable indication (ie scientific papers) that give any clear evidence one way or the other.

yeah that makes sense,i agree...i heard that male/female ratio is about 70/30...

so if i want at least 1 female p.metallica i should buy 4-5 slings

here's something interesting =>

 

[LisaD]

That table assumes a 50:50 ratio of male to female. You can use a version of this calculation with a skewed sex ratio. If females were the scarcer sex, you would have to buy more slings in order to have similar chances to obtain a female.

For example, if the ratio is 25% female, 75% male, then you would have to buy 4 slings to have a 50% chance of getting a female (I think, it's been a while since I had to think like this). I think with every sling you got, there would be a 1/8 probability that it would be female:

1/4 - frequency in population x 1/2 - probability that an individual will be female = 1/8

 

[Thoroughbred]

That table assumes a 50:50 ratio of male to female. You can use a version of this calculation with a skewed sex ratio. If females were the scarcer sex, you would have to buy more slings in order to have similar chances to obtain a female.

For example, if the ratio is 25% female, 75% male, then you would have to buy 4 slings to have a 50% chance of getting a female (I think, it's been a while since I had to think like this). I think with every sling you got, there would be a 1/8 probability that it would be female:

1/4 - frequency in population x 1/2 - probability that an individual will be female = 1/8

yep...that's sad isn't it...

 

[Teal]

Ack.. math?! This is a tarantula forum, people.. keep it clean! LOL

I agree that having the ratio skewed towards males sounds very probable, and seems to be the case (without having done any study, and just speaking from the number I've times I've seen "It's a boy!" on sling sexing threads lol).

It would be interesting if a breeder could really do a long term study on this sort of thing... the average number of eggs in a sac, the average number to survive to sling-hood, and then the ratio of male/female when they mature. But, that would require keeping in touch with hundreds of people for years - unless they kept all the slings themselves

 

[jayefbe]

I've actually thought about keeping the slings from an entire eggsac long enough to actually sex them all out. It's definitely my science background coming into play. Couple issues 1) who would actually buy the males and 2) picking a species that may actually have a skewed ratio.

I do have a sub-adult pair of Lampropelma violaceopes, so I may give it a shot. But I doubt I'll have time when I enter graduate school this fall.

 

[billopelma]

In my experience of mostly buying a diverse mix of unsexed slings and growing them up to sex-able size my records indicate a ratio very close to 50:50. I've heard similar reports from other hobbyists. My collection now has a higher ratio of female adults as many of the males have reached maturity and are no longer around.

It does make sense for a heavy male:female ratio to evolve in tarantulas. Given the much longer lifespans of females (a male has a single breeding season, a female has potentially 10 or more), and the predilection for females to try to eat males, would mean that mature males are always in a shortage.

On the other hand as juveniles all those extra males would be competing for food/shelter with their female counterparts, which wouldn't seem too productive...

Bill

 

[Rabid538]

The ratio is 50:50 just like all other species. I read about it in a genetics book by Richard Dawkins. Regardless of males having a shorter life span there is always one male and one female parent. Neither is favored. It will always come out to a 50:50 ratio.

 

[LisaD]

Not sure what you mean here. I never read that from Richard Dawkins. Are you referring to his book "The Selfish Gene"?

There definitely are animals with skewed sex ratios. Even though you have one male and one female mating, the offspring does not have to be 50:50.

Sex is determined genetically, and there is more than one method (besides X and Y chromosomes) for sex determination in animals. And besides genetics, sex can be controlled by development. For example, some reptiles will develop more of one sex in response to incubation temperature of the eggs.

In addition, some animals (not Ts, I don't think) can actually change their sex as they mature. This happens often in marine fish. In some bees and wasps, almost all offspring are female, and males come only from unfertilized eggs.

With all the variety there is in nature, it seems very possible that there might be skewed sex ratios in some tarantula species.

I'm hoping it's more like 50/50, though.

 

[Noexcuse4you]

IME, at least with pokies, its 50/50.

 

[Rabid538]

Not sure what you mean here. I never read that from Richard Dawkins. Are you referring to his book "The Selfish Gene"?

There definitely are animals with skewed sex ratios. Even though you have one male and one female mating, the offspring does not have to be 50:50.

Sex is determined genetically, and there is more than one method (besides X and Y chromosomes) for sex determination in animals. And besides genetics, sex can be controlled by development. For example, some reptiles will develop more of one sex in response to incubation temperature of the eggs.

In addition, some animals (not Ts, I don't think) can actually change their sex as they mature. This happens often in marine fish. In some bees and wasps, almost all offspring are female, and males come only from unfertilized eggs.

With all the variety there is in nature, it seems very possible that there might be skewed sex ratios in some tarantula species.

I'm hoping it's more like 50/50, though.

It was from the book River Out of Eden. And yes, you are correct, the ratio is different for animals that can change their gender over the course of their lifetime as well as bees whose queen can actually determine the sex of the offspring.
Tarantulas do not fall under any of those categories though. Still, I don't know for certain that they have a 50:50 ratio. I am just going by what I have read. Experiments could be done, but more than one sac will have to be used and that is a lot of spiders to raise and sex.

 

[sharpfang]

I wanted to Raise my 1st Sack up too...Avics

But, I gave-away most the slings Instead......I bet outta 80...I woulda got around 50 Males, I'll NEVER know now

Maybe we should start giving I.D. #'s to Sold Tarantulas :?
{tracking #'s} Tag them, in a sense.

A "slightly" skewed sex-ratio I feel, is Obvious and makes sense.

Great Question :clap: could they be Temp sex Dependant ?

- Jason

 

[jayefbe]

It was from the book River Out of Eden. And yes, you are correct, the ratio is different for animals that can change their gender over the course of their lifetime as well as bees whose queen can actually determine the sex of the offspring.
Tarantulas do not fall under any of those categories though. Still, I don't know for certain that they have a 50:50 ratio. I am just going by what I have read. Experiments could be done, but more than one sac will have to be used and that is a lot of spiders to raise and sex.

The 50:50 standard sex ratio is largely due to something similar to density dependent selection. Basically, more females means less competition between males and selection will benefit the production of more males and vice versa. End result, 50:50 sex ratio.

However, skewed sex ratios have evolved multiple times in many different groups (more than just bees and fish that can change sexes). Also, given the vast differences in life history traits between male and female tarantulas, they would theoretically benefit from a skewed sex ratio. Whether or not that has actually occurred is circumspect, but casual observations seem to show that Lampropelma species have a male-heavy sex ratio in offspring. Whether or not this is actually true is still unclear, but it is definitely possible.

 

[Rabid538]

The 50:50 standard sex ratio is largely due to something similar to density dependent selection. Basically, more females means less competition between males and selection will benefit the production of more males and vice versa. End result, 50:50 sex ratio.

However, skewed sex ratios have evolved multiple times in many different groups (more than just bees and fish that can change sexes). Also, given the vast differences in life history traits between male and female tarantulas, they would theoretically benefit from a skewed sex ratio. Whether or not that has actually occurred is circumspect, but casual observations seem to show that Lampropelma species have a male-heavy sex ratio in offspring. Whether or not this is actually true is still unclear, but it is definitely possible.

Okay. That makes sense. I guess there are many variables that might cause the standard ratio to change.