80 percent of eggsack male?

[Andrea82]

So I was grumbling about my G.iheringi being male, and that most of my slings turn out as male on Facebook and I got a reaction from someone that claimed that 'since 80 percent of eggs are male, chances of getting a male is very high.'
On my asking if he had some science to back that up he referred me to Google, but Google doesn't seem to understand my question.

What do you think of this claim? Anybody got a paper or something on this subject? I know some species have a high male 'rate' but not all right?

 

[MetalMan2004]

Sounds like you found another facebook genius! If they can’t produce the scientific evidence themself its probably because they don’t know what they’re talking about.

Like you, I’m interested to see if anyone her does have scientific or anecdotal evidence on this. I’ve heard plenty about it varying by species but nothing specific.

 

[weibkreux]

Documenting is hard since you need not only one egg sac (which contains hundreds of spooders), for data collected to be relevant. Imagine the effort of raising all of those. While it may be fun, not everyone have the luxury of time. Unless its done by a dedicated group of individuals of course.

 

[Greasylake]

I haven't seen any real evidence of this yet, just people saying they bought a handful of slings that came out one way or another. This could be put to rest if someone raised a whole sack to maturity but I don't think anyone has the time or patience for that, I know I don't.

 

[antinous]

Sounds like you found another facebook genius! If they can’t produce the scientific evidence themself its probably because they don’t know what they’re talking about.

Like you, I’m interested to see if anyone her does have scientific or anecdotal evidence on this. I’ve heard plenty about it varying by species but nothing specific.

This. I’ve always heard people saying that egg saves are anywhere from 60-70% male and that for every female in a egg sac there are at least 1-2 males.

 

[Andrea82]

Hmz. So while it is not unequivocally true, it's not fully false either..
Calling in the big guys...
@advan, @cold blood @EulersK, @viper69
Do you guys have any ideas on this? Thanks in advance for any and all information!

Edit: the guy claiming this is obnoxious and a pita and got put on ignore and block from me right after this.

 

[cold blood]

Well for one, all species will not produce the same...we dont need much scientific evidence as we as a hobby, see vast differences with certain species...so no one percentage would be at all viable across the board.

That said, to know a species percentages, one would need to raise entire sacs until every one could be sexed...thats not happening...on top of that, just one sac wouldnt be enough, you would need to do this repearedly, sac after sac until some concrete evidence can be understood...and one would need to do this with every individual species....again, not happening.

Are some 80% male? Perhaps...but not all are and no one can say for certain with any species what the actual percentages are of any species...but to say all are 80% male, well we can say difinitively that this does not apply to all species across the board by any means....so its just not a correct statement to boldly make with one's face book muscles.

 

[Teal]

Am I the only one who has the desire to keep an entire sac? LOL.

Maybe this is something I should work on...

 

[fleetwoodmcc]

Sex ratio biologically in sexually reproducing species (as adults) tends to skew towards 1:1. This obviously makes sense, 1 male is needed to mate with 1 female to produce offspring. This isn't the case in some arthropod species, as the ratio sometimes skews towards females. There are several publications about sex ratios in spiders.

Some social spiders are observed to carry more XX offspring in a study of embryonic chromosomes, producing female dominated societies.: http://www.americanarachnology.org/JoA_free/JoA_v19_n2 /JoA_v19_p126.pdf
The application of this to tarantula is shaky at best, but it is interesting to see skewed sex-ratio in populations of spiders. Other social species produce 1:1 sex ratios.

This article discusses that male spiders can increase the production of XX offspring 'strategically' rather than on the Mendellian 1:1: https://www.ncbi.nlm.nih.gov/pubmed/29563266
Again, this primarily relates to social spiders, but specifically cites that subsocial species produce 54% X-sperm. Not tarantulas, of course, but supports the idea of non-social spiders producing 1:1 sex ratio.

Finally, a publication that discusses sex ratio of adult E. weijenberghi (a tarantula species): https://www.researchgate.net/public...orell_1894_Evidences_of_monandry_and_polygyny
Adults are noted as having a heavily female-skewed sex ratio, as males perish after several months once reaching sexual maturity. The females are monoandrous and mate infrequently (once every 2 years, per this study) while males mate several times (two copulations per sperm production), lowering the operational sex ratio (9:1 skewed toward females without these advantages). To me, this says a heavily skewed male sac is a pretty unlikely thing. A 9:1 operational sex ratio won't exist if the sacs are 8:1 skewed males at birth. I believe, like other non-social spider species cited here, that the sex ratio in the sacs are 1:1, as males have other advantages to lower the operational sex ratio rather than a skewed ratio from birth. Sorry if some of the publications are inaccessible, I know everyone isn't a student...

 

[viper69]

Hmz. So while it is not unequivocally true, it's not fully false either..
Calling in the big guys...
@advan, @cold blood @EulersK, @viper69
Do you guys have any ideas on this? Thanks in advance for any and all information!

Edit: the guy claiming this is obnoxious and a pita and got put on ignore and block from me right after this.

If someone knows this for a fact with this species, it's not published in a scientific journal.

 

[boina]

Spiders have an X0 system of sex determination or a variation thereof. That's like XY, just without any Y. The overwhelming majority of species with chromosomal sex determinatination show a more or less even sex ratio. There are a few known mechanisms however, that can skew that ratio. It is not known if any of those mechanism are used in spiders.

I am highly skeptical of anecdotal reports of some species producing consistently more males. That's simply not how statistics work. Statistically, you can have 10 males in a row and still have an overall even sex ratio. Ever played Roulette? If you have, you'll know you can have 10 times red in a row. Statistics mean that even improbable things will happen once in a while. So, statistically, one egg sac wouldn't even be enough to clear up that question - it could always be the statistical outlier.

Now, I'm not saying it's impossible that some species have a skewed sex ratio. There are claims that Asian arboreals produce more males that females. I've also heard that 60-70% males claim for Brachys. I've also heard that African terrestrials produce more females...

What I'm saying is that none of this has ever been proven, or even researched in any controlled and reproducible way. All you hear are personal impressions that get repeated over and over. I don't know the true sex ratio - nobody does.

 

[AphonopelmaTX]

90% of all statistics you hear or read about are made up.

 

[aphono]

On my asking if he had some science to back that up he referred me to Google, but Google doesn't seem to understand my question.

That was a huge, blazing red flag. Person making the claim needs to back it up, not turn around and place the burden on the questioner. It would have been more than fair to dismiss that claim outright for this reason. Always good to know though- search it by yourself or asking credible sources without further response to that person. Or explain back how backing up claims are supposed to roll.

 

[BobDuB]

The idea has been planted in my head now. Its interesting, but daunting the thought of keeping an entire clutch for this purpose.

 

[cold blood]

The idea has been planted in my head now. Its interesting, but daunting the thought of keeping an entire clutch for this purpose.

No, you would need to keep several clutches of each species....It would take a long time...like dedicate the next decade to this experiment...lol.

Keeping one sac to sexable size though would be a start though.

 

[SonsofArachne]

So I was grumbling about my G.iheringi being male, and that most of my slings turn out as male

Sounds like you have same luck as I do. I've sent four 2 inch molts to Kelly swift to sex.
Results:
B. vagans - tore too much to tell
P. carpenteri - male
D. diamantinensis - male
C. hainanus - male

So, maybe, one female out of four. The D. diamantinensis really hurts as it's the only one I have.

 

[BobDuB]

No, you would need to keep several clutches of each species....It would take a long time...like dedicate the next decade to this experiment...lol.

Keeping one sac to sexable size though would be a start though.

Correct. Never meant to imply I would solve the problem with one sac. More possibly provide a small amount of information towards a collective goal.

Plus I have a tendency to like odd projects.

 

[The Grym Reaper]

Am I the only one who has the desire to keep an entire sac? LOL.

I'd happily raise an entire sac of iheringi, I bloody love my girl.

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[Teal]

I'd happily raise an entire sac of iheringi, I bloody love my girl.

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She is gorgeous!
Mine would be Pterinochilus. I kept a third of my last OBT sac LOL

 

[Andrea82]

I'd happily raise an entire sac of iheringi, I bloody love my girl.

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Since my G.iheringi turned out male I don't think I get to raise a sack. Would love to as well!

@everyone else;
Thanks so much for the helpful posts!