Lasiodora parahybana

[m0lsx]

Feeding the other evening we realised that the only female Lasiodora parahybana's we have, we have brought as females. All those we have acquired as slings have been sexed as males. Which left me wondering. Are Lasiodora parahybana's like Theraphosa blondi & stirmi, do the majority of slings become males?

What are other people's experiences? We have had 5 slings, over the past few years & all have been sexed as males.

 

[Enn49]

I bought 2 1" slings 9 years ago and was lucky enough to get a male (matured and passed on) and a female (still with me).

 

[Stan Schultz]

Feeding the other evening we realised that the only female Lasiodora parahybana's we have, we have brought as females. All those we have acquired as slings have been sexed as males. Which left me wondering. Are Lasiodora parahybana's like Theraphosa blondi & stirmi, do the majority of slings become males?

What are other people's experiences? We have had 5 slings, over the past few years & all have been sexed as males.

First, as far as I have ever known (note that important qualification), the genetics of sex inheritance among tarantulas follows the same rules as that of most other animals on planet Earth. (Aphids and alligators, among others, are distinct exceptions however.) That is, approximately equal numbers are produced during normal reproduction. (More qualifiers!) But, if any of you have reliable references to literature discussing tarantula genetics, especially with specific reference to genetic determination of sex, I would appreciate being sent an E-mail pointing me to your reference source. (My E-mail appears in my sig, below.)

But this seems to refute my theory of equality between tarantulas' sexes! The following story may shed a little light on the matter. A dealer I knew several decades ago by the name of John (all names are fictitious to avoid my being sued for defamation of character or a visit by the "Boys from Detroit!") had a major portion of his house turned into a warehouse for all manner of creepy-crawlies. Arachnids occupied what used to be the master bedroom (the "tarantularium") filled with an assortment of shelves, bookcases, and tables. (John slept on a couch in one corner of the living room. A sacrifice by a true devotee!) And each kind of tarantula had its own assigned space somewhere in this labyrinth. A local high school kid (I'll call him Bill) would come in about every second evening and search through the hundreds to thousands of various vials, bottles, and deli cups, looking for freshly molted tarantulas. He'd collect these containers, with their inhabitants, placing them on the end of a small desk near the room's entrance. John had also supplied him with an inexpensive, binocular, dissecting microscope, and the various tools and supplies required for the job of sexing these tarantulas. And Bill would spend several hours going through the containers, shed skin by shed skin, looking for proven females, and marking each such container with the symbol for female with a felt tipped marker.

At the end of each session, all the containers with their tarantulas would be returned to the shelves from whence they came. (This is an important datum!)

During the course of filling various orders for tarantulas, John would go back into the tarantularium, grab the appropriate number of vials, bottles, and/or deli cups of the required kinds. If no sex designation was given in the order, John grabbed the unmarked containers. However, if a female had been ordered (at an appropriately higher price), he grabbed a container specifically marked as female.

Now, think about this for a moment. If I am correct in that tarantulas come into this world with approximately equal numbers of males and females (notice that qualifier again), and if John had 100 tarantulas, then there should be very close to 50 males and 50 females on that shelf. And if you ordered a dozen of them, on average you should get 6 of each sex, right? (But see the note at the end of this posting.)

But, if someone places an order for five guaranteed females, after filling that order, there would be only 45 females left on the shelf, plus the original 50 males. Hence, if you walked in immediately thereafter to buy a tarantula of any random sex, the probability of you getting a female was lessened by a fraction, and skewed in favor of you getting a male. (See an explanation for this in the footnote at the end.) And each time this scenario recurs, the relative number of females continues to diminish until John has little or nothing but males to sell! In which case, eventually, you're almost 100% guaranteed that you're going to get a male unless you specifically request that you want a female.

And thus, around the world, I'm seeing dozens, if not hundreds of light bulbs blinking on over tarantula enthusiasts' heads. It's a glorious sight indeed!

Stan

Footnote:
Before the transaction noted above, your probability of getting either sex would be 50 out of 100 = 50/100 = 50%.

After this specific transaction, the probability of getting a female would be 45 out of 95 = 45/95 = 47.3%. And the probability of getting a male would be 50 out of 95 = 50/95 = 52.6%. Thus you have about a 5% better chance of getting a male than a female! (52.6% - 47.3% = 5.3%)

If the same transaction happened a second time in succession, the probability of getting a female would be 40 out of 90 = 40/90 = 44.4%. And the probability of getting a male would be 50 out of 90 = 50/90 = 55.6%. AND, you now have an 11% better chance of getting a male than a female! (55.6% - 44.4% = 11.2%)

Your homework assignment is to repeat this process until there are no more females left.

Hint: Remember that probabilities are never hard facts, but rather chaotic approximations, and therefore highly variable. In reality, after some number of instances for each such transaction, the percentages would only mark the center point for the results of all similar tests (instances). [Probability and Statistics 101 ]

 

[m0lsx]

Stan, there is certainly an accepted (within the hobby,) higher instance of male to female among Theraphosa blondi & stirmi.

The problem with academic research into % of male to female is that it would be long term & involve a significant number species & a large number of egg sacks per species to be conclusive. And it would probably not gain financial backing, as what use is it to academics, unless they know the logic behind what they see?

It would need to look at what happens with say a T blondi with a small egg sack of around 100- 150. As opposed to something like an LP that produces as many as 2000 per egg sack. It would also need to find out if being terrestrial, fossorial or arboreal make a difference & what about continent or the weather within the T's geographic area. Does that make a difference? Would for example, the extreme heat & flooding of Arizona produce a different need for reproduction among Arizona Blondes from Arizona, as opposed to an Aphonopelma, from states with more stable weather? Both would be Aphonopelma, both from the same general geographic area, but different local conditions could produce different needs.

I know in Australia, a species of snake living on an island, has evolved into what is accepted to be a different species, due to it needs within that environment. Could % of male to female per egg sack be an evolutionary need? Or is the number of males to females we get from sling purchases just down to luck?

I have seen several LP's from different sources, gained across a few years all turn out male & I wondered if others were seeing a similar pattern.

 

[m0lsx]

It is also worth noting that T's are different to many other creatures. Many male T's do not even get to successfully mate once, due to the female killing them. Whilst Swans pair for life & most herd animals have a hierarchy of males, with the strongest male being able to mate with multiple females per year. T's probably have a need for more males than many other species, as males get to mate once, if they are lucky & have to travel to find a female once mature. With all the risks that produce & what happens if they fail to find a female? Surely the fact a female tarantulas lives so much longer & will be capable of mating so many more times decrees a need for more males, than females? Or do females statistically only mate once, at best, in the wild? And that would be the case if tarantula egg sacks produced a 50/50 male to female statistic.

 

[tarantula ramblings]

I can only say that over here in the UK the largest shop has females and young females listed but never seems to have any males listed .
So I wouldn't buy a juvenile from them for the reasons you listed above . Also I expect mystery boxes are a great way to shift the extra males they pretend they have not sexed.

 

[m0lsx]

Also I expect mystery boxes are a great way to shift the extra males they pretend they have not sexed.

All I can say is that the mystery boxes that I have brought from UK suppliers have always had a fair share of male & female. When we could buy from Europe, there was one supplier I would not buy anything but slings off, as even their alleged females were not female on more than one occasion. But UK wise, I have used all the main suppliers here & would trust any of them.

 

[tarantula ramblings]

I have not got any reason to not trust the seller from the North other than I had already come to the same type of conclusion you had . If the females are getting cherry picked that leaves more males and more chances of getting a male if the seller sells juvenile females but not males.
That just seems Logical to me .
Some sellers like Portsmouth tarantulas list an equal amount of juvenile males and females in fact I need to get a juvenile male obt and male bumba horrida from them.
I also know someone who has grown four lp's up from slings all male .

 

[Stan Schultz]

Stan, there is certainly an accepted (within the hobby,) higher instance of male to female among Theraphosa blondi & stirmi.

But has anybody published accurate specific counts per eggsac to verify this "accepted" cottage wisdom? If so, where can I get a copy of the publication (even if it's only in a hobbyist magazine or forum report)?

As a bit of a scientist, I'm much more interested in facts and numbers than casual observations. Please don't misunderstand me, I value such casual observations almost as much as I do reports in the scientific literature, principally because they point us to new avenues of investigation. But since we're answering a troublesome question, and implying, if not inferring, that a segment of our hobby may be conducting business in an ignorant or unfair manner, we should have some solid facts to go on. Plus, anyone reading my former dissertation might be convinced to change their buying habits as a result. I'd like to be able to give them hard facts on which to base their decisions, rather than the "word on the street." Hence, my call for any, even faintly believable, published data.

Secondly, even if a given kind of tarantula produced significantly more males per eggsac then females, that fact wouldn't negate the deeper meaning of my story: For whatever reason, it is possible that the probability of getting the tarantula of your hoped for sex may be disadvantageously altered by the dealer's business practices, whether the dealer is being dishonest or merely ignorant.

The problem with academic research into % of male to female is that it would be long term & involve a significant number species & a large number of egg sacks per species to be conclusive. And it would probably not gain financial backing, as what use is it to academics, unless they know the logic behind what they see?

No, no, no! A question (some might accuse me of making an allegation) has been made. The next stage is a "Proof of Concept." All that would be required is for one hobbyist who may already be breeding tarantulas (not necessarily the most difficult kinds on the market today) to set aside the offspring of one or two eggsacs (not necessarily those producing "hatches" of several thousand at a time). Once these babies reached a size where visually determining their sex by examining their shed exuvia with a dissecting microscope became practical, the collection of such data would be almost boring. And, if a little intelligence were used in picking the kind of tarantula, that stage might be reached in two to five years. So far, none of this is terribly out of the ordinary or terribly difficult.

The third stage involves using the data from stage two to apply for support from some granting entity. This would require our budding researcher to write up a research proposal and submit it for consideration. Partially because I believe that our crusade is more likely to be of interest to academia (as you suggest), and partially because I am more familiar with the academic process, I'll confine my further comments to that milieu, leaving someone else to discuss applying for grants to the other agencies such as charitable or business entities.

Some research biologist (e.g., an arachnologist or animal behaviorist) might be interested in answering our questions by setting up a small breeding attempt in the corner of a much larger lab. At first, the care and breeding of one or two kinds of tarantulas would only require a few hours of technician time every week to bring the adults into breeding condition, initiate the breeding, hatch the eggs, and care for the babies. (After all is said and done, how much time do you spend actually caring for a half dozen or dozen tarantulas?) At sometime before sex determination becomes possible, a prospective graduate student might be identified to use this stage for the acquisition of a masters degree, thus freeing up the technician's time for other matters. The counts would be made, statistical analyses performed, the results written up and published, and submitted as part of the masters dissertation. But, take note: If you think it's all going to be that simple, cut, and dried, do I ever have a shock for you!

All the other aspects of the case that you discussed are PHD level or higher matters that would use the data developed above to go on to further study. Ideally they would eventually consume a senior scientist's entire life's efforts to answer. (If any of you are interested, start perusing the arachnological research publications to identify those research scientists who might be interested in such a project.)

And while these researches would doubtlessly produce very interesting results, they would not necessarily answer our seminal questions, "Did either or both of the one or several kinds of tarantulas that were first considered produce offspring of approximately equal numbers, or not?" And, "Does that suggest an answer to the question of, 'What strategy or strategies would be best for an enthusiast to use when purchasing new tarantulas for their collection?' "

May all the holes in your path hold large fuzzy spiders!

Stan

 

[m0lsx]

No, no one has ever conducted research into egg sack statistics as far as I know & I would assume for the sort of reasons, that I gave above. Hence, why I give accepted hobby knowledge, as it is all we seem to have. To be taken seriously & to seen as scientific & thus something reliable & worth quoting as a figure. As I said above such research would need to check multiple egg sacks to find an average male to female number for each species.

Looking at one egg sack, even two or three, is not scientific & would not give any form of reliable average figure. Or not unless we already knew that egg sacks produced very similar results across multiple species & even then it would still only be an educated guess.

Using your pseudoscientific methodology, we could look at Fred Phelps from the Westboro Baptist Church & conclude that all families are like his. Or how about families who have twins or triplets, are they typical of human birth numbers? I worked as part of a team of 6 people at one point, & 2 colleges were born as part of triplets. Provable statistics shows that the chance of triplets is 1 in 62,500 birth. Your pseudoscientific methodology could easily have concluded, from my former work place, that it was 2 in 6.