Males growing faster than females? - Myth?

[KenTheBugGuy]

I have never encountered males growing faster than females. I think this myth grew from the fact that males mature faster than females in the long run. This does not mean they grow faster just that they will mature at a younger age. If you have encountered this for real and not just going off of myth please chime in as I would like to know what species this is specific too. As far as I have witnessed with MANY species is they all grow at an equal pace and the males just mature out before the females are full grown.

Same type of myth is that females are fatter than the males. Funny thing is about this one is it kinda of counterdicts the last one. This is sometimes true with full adults but when it comes to slings, once again its a myth based on adults.

The funniest part of this is I have seen many long term hobbyist and even dealers that believe this myth....it holds true for real life though when it comes to myths

I have learned some myths about child rearing this year and find it funny some of the things we all hold to heart when it comes to life. We really should do our research before just believing a rumour or even what we were told through life by others.

Couple of fun ones most parents worry about(as did I )....how many kids really die on plastic bags? Drown in buckets? You will be suprised that they are more likely to be hit by a car, drown in your pool, be hit by lightning or far more!

 

[Formerphobe]

Of the groups of sac mates I've raised, individuals would go off on dramatically different molting schedules, but for the most part, the males and females grew at about the same rate. I've noted some size difference between individuals, but gender didn't seem to have anything to do with it. By the time they're subadults, the males of some species seem to start looking leggier, and the females a bit 'stockier', but that may be subjective observation, too.

You're probably correct, Ken. More appropriate terminology would be males mature faster than females, not grow faster.

In this day and age kids are definitely more likely to be hit by a car, drown in the pool, be hit by lightning, etc than suffocate in a plastic bag or drown in a bucket (or toilet). But, the risk is there and it does happen. More amazing to me are the cases where the parent forgets the child in the car seat in the back of the car on a hot summer day... or forgets the infant that they set on top of the car while they loaded groceries, then they get in the car and drive away... A little common sense goes a long way.

 

[freedumbdclxvi]

Good observations.

 

[Tarac]

I have a handful of P. regalis that exhibited faster increase in size with males than females. They're sac mates and two others that are unrelated. I'm sure you (Ken) have reared vast numbers more than I have by orders of magnitude, but within the set that I have it is statistically significant. Wasn't noticeable until they were 1.5-2" or so, but by then the males were easy to pick out as they had molted more often and had thus gained more in the same span of time.

On the other hand I have others where development seems to be in tandem (P. cancerides, Brachys, etc.) or even reversed- I was wondering if it may be due to OW v. NW or something like that, where the truncated relative lifespan may play a role. The gain for shorter lived species would be more dramatic and therefor easier to quantify at smaller sizes in some cases. I was able to guess very accurately just by molt rate and size for the regalis but had to wait for molts of decent stature for the others.

The detail I place emphasis on is- what plays a role in sexual maturation for a tarantula? More or less positively correlated number of instars, not necessarily size. More instars in less time could possibly equal more rapid gain in terms of mass, remembering that there are other factors involved of course. May be that with some species it is evident sometimes because the ultimate mature sizes of males and females are not so dramatically different in contrast to those with significantly smaller adult males.

You are right that it most certainly is not a universal rule, but I do think that common sense you mention would suggest that if gain is directly related to molts and males molt more frequently early on then a comparably sized male and female adult would have staggered juvenile sizes with males gaining more rapidly- probably not linear gain so likely more noticeable where the growth curve is most steep (point of greatest sensitivity). Important in my mind to note if the final adult stature is similar enough and that they aren't maturing over a century where changes are not that noticeable from instar to instar anyway.

Good question, interested to hear what other people think. Tarantulas are fun for these kinds of reasons- get to figure things out through observation and discourse since so few people are working with them outside the hobby. Thanks Ken, you are invaluable for many reasons!

 

[jayefbe]

I'm so glad this was posted. I personally have seen no difference in growth rate between the sexes. But then again, I haven't paid particularly close attention to large numbers of each sex for multiple species. Once I get some sacs, I might.

But what bothers me, is that anytime there's some variability in growth rate among sac mates, everyone's first reaction is that they are different genders, to the point that some people even sell the slower growers as females, despite no other corroborating evidence. There are SO MANY other possibilities that affect growth rate. Feeding, temperature, slight microhabitat differences that we don't even notice. Oh yeah, there's a big one, GENETICS! Sac mates only share fifty percent of their genes. While only a tiny portion of the genome controls sex (albeit a very important genomic region) there's still half of the genome that varies between siblings that can conceivably still affect growth rate! The ONLY way to provide evidence that one gender grows faster than another is to look at hundreds of individuals from dozens of sacs from dozens of species. Even then, if there IS a difference (there might be) it will only be seen as a difference in average growth rate across hundreds of individuals. If you have 5 slings and one grows slower than the rest, to say that it's a female shows a complete inability to grasp the simplest of statistical concepts!

Growth rate varies for a number of different reasons. If I had to bet my worldly possessions on it, sex is very very low on that list. Stop assuming that your slow growers are females and the fast are males!

 

[wesker12]

My fastest growing P.cambridgi was female (.5 inches to 4+ in less than 5 months) - out of 7.

 

[billopelma]

I've done a half dozen or so P. rufilata communals with anywhere from 3 to 20 something individuals. One thing that has been relatively consistent is that there are usually (only) one or two females that outpace all the others in size by a big margin. Noticeable even at an inch or so. By the time they're adult size the smaller ones catch up. I've also heard the same about other poec species (specific to communal rearing) but haven't experienced it myself.


Bill

 

[captmarga]

I have a number of sacmates of various species I'm monitoring right now for those very details. I've marked the N chromatus slings as Tiny or Huge at 2nd instar, those I will keep until they are big enough to sex via molt/microscope. The same with several OBTs. There is a marked difference in size already in the juvies. They are also fed on the same schedule and the same amount of food (ie they all get small crickets or they all get large crickets that week). I have two pulchripes slings I was photographing yesterday. They are sacmates that I got at .5". One is barely an inch, the other is 1.5". Again, same temps (they are in the same room, in similar habitats) and same feeding schedule.

We shall see...

Marga

 

[Stan Schultz]

I have never encountered males growing faster than females. I think this myth grew from the fact that males mature faster than females in the long run. This does not mean they grow faster just that they will mature at a younger age. If you have encountered this for real and not just going off of myth please chime in as I would like to know what species this is specific too. As far as I have witnessed with MANY species is they all grow at an equal pace and the males just mature out before the females are full grown. ...

About 10 or 12 years a go, while Marguerite and I were still selling tarantulas out of our living room, we had an eggsac of Brachypelma albopilosum (curlyhair tarantulas) release several hundred babies. Note that we had both parents in our possession, and knew the exact dates of mating, egg laying and eclosion.

One of our friends got three of the babies a few weeks after eclosion. About 9 months later he called back and wanted to bring them over for us to see. I was astounded! There were 2 females and 1 male. The females had DLS of something in the close neighborhood of 1.5". The male had a DLS of 5+ inches and was sexually mature! I double checked my records. He was about 9 months 2 weeks out of the eggsac!

Thinking that he had gotten our tarantulas confused with someone else's, I questioned him closely. No, we were the only people he'd bought any tarantulas from, much less albopilosum.

He had built a small constant environment chamber, fixed it up with a thermostatically controlled heater, and kept it at about 90° F. He had kept all 3 babies in it, and kept baby crickets (later larger crickets for the male) with the tarantulas literally 24/7. For all intents and purposes he almost force fed them! This was power feeding to the extreme.

Could I trust this guy? I'd known him on and off for a number of years and had found no reason to distrust him previously. He was in his early 20s, so one would presume he'd gotten beyond the "Teenage Credibility Gap"*, and was a devout Mormon who was trying very hard to get into Seminary. (I think. Since I'm not Mormon, I'm not sure.) Yeah. I trust him.

(Doug? Are you out there, big guy? You want to chime in on this one? Bail me out? I said nice things about you. Please?) :biggrin:

So based on an "n" of one, I do think that under some circumstances, some males of some kinds will grow somewhat to significantly faster than their sisters. (But, notice all the modifiers, each a potential "back door escape route.") As with most things "tarantulaic," we need more research!

I'm glad to see this thread. I'm going to be watching the results of the postings very closely.

Enjoy your little, 8-legged King Kong!


* "You know when teenagers [are] lying? When their mouths are moving." -- Judge Judith Sheindlin

 

[Lopez]

Hi Stan.

I had a similar experience with male B.albopilosum to your friend Doug - under a year to mature a B.albopilosum after "force feeding". I'll see if I still have the pics somewhere!

 

[BrettG]

T.gigas--Females got the jump on the males for the first 5 molts,then the males caught up and surpassed the females.Males are now 2.75ish,while the females are 2.5.I expect the gap to grow even greater with the upcoming molts.***All spiders kept at same temp/feeding interval.***
T.violaceus--See above
I.hirsutum--See above
We are also monitoring 12 A.minatrix that we held back from our last sack.Some are 4th instar,while others are still 2i and still feeding,not even close to a molt.Same temps,same feeding.After a few more molts I will see if the larger individuals are indeed male and the smaller female.We are doing this with A.laeta as well,so hopefully in about 6 months I can update this thread.

 

[kristinnandbenn]

My Brachypelma vagans, which are supposed to be slow growers, went from a 1/4 inch DLS to a 4.5 inch DLS in about 14 months. Sexed as female.

 

[BrettG]

My Brachypelma vagans, which are supposed to be slow growers, went from a 1/4 inch DLS to a 4.5 inch DLS in about 14 months. Sexed as female.

B.vagans are actually one of the faster growing Brachypelma.

 

[Tmobo]

I wonder if some grow faster than others is because in the wild they need some fast growers to have a higher survival rate? Maybe something in genetics just chooses which t's get it at random?

 

[le-thomas]

AHe was in his early 20s, so one would presume he'd gotten beyond the "Teenage Credibility Gap"*

* "You know when teenagers [are] lying? When their mouths are moving." -- Judge Judith Sheindlin

I take this personally and am offended
Since growth rate can vary so greatly between individuals, we may just be misinterpreting it as a difference in growth between the sexes. Of course, every genus and/or species may be in a different situation regarding the male to female growth rates. I'm sure I'm just reiterating this point, but I still think it's worth saying.

 

[BrettG]

Honestly,Ken brings up a very interesting question.I know there are quite a few other members that have had some successful breeding projects the past couple of years,and hopefully if they have held back stock they can chime in with their experience.Maybe a few other breeders/hobbyists that are breeding can put aside a certain amount of offspring from each sack and just start taking notes,treating them all equally feeding and temperature-wise.
We are going to keep setting aside 15+ of each Genus/sp we produce and go from there.The T.gigas from our first sack were a surprise to us,we thought that with such a fast growing sp it really would be themales growing faster. I wonder if it happens with them due to the fact that by the time the males mature,the females would be sexually mature,as T.gigas has been known to become sexually mature at very small sizes.Who knows.I would love to hear others thoughts on the matter.

 

[apophysis]

I agree with Ken here. I keep all my TS at same temps and they all get fed pretty much once a week. I have wondered many times if this is really true (males grow faster then females) because I keep a lot of TS and brother and sister are growing at same pace, many even molt on the same week when still young.


TRUE -> "As far as I have witnessed with MANY species is they all grow at an equal pace and the males just mature out before the females are full grown"

 

[poisoned]

I have a number of sacmates of various species I'm monitoring right now for those very details. I've marked the N chromatus slings as Tiny or Huge at 2nd instar, those I will keep until they are big enough to sex via molt/microscope. The same with several OBTs. There is a marked difference in size already in the juvies. They are also fed on the same schedule and the same amount of food (ie they all get small crickets or they all get large crickets that week). I have two pulchripes slings I was photographing yesterday. They are sacmates that I got at .5". One is barely an inch, the other is 1.5". Again, same temps (they are in the same room, in similar habitats) and same feeding schedule.

We shall see...

Marga

I would really love to see results from this project, but I highly suggest you name them (#1, #2, ...) and record molt dates and sizes after every molt, these records can show much more information to us.