Male/Female ratio butterflies

[wollastoni]

Dear members,

Male/Female ratio for human beings is about 50%/50%.
What is this ratio for butterflies ? Is it the same for all species.

I know some species where males are very easy to find and females found at only 2 or 3 exemplaires during more than one century because females never leave the canopy. But is the ratio between male and female equal ?

Thanks for your help.

[bobw]

Observation in the wild will tell you very little as males are nearly always far more visible than females. Males are always on the look-out for females, whether it be by patrolling, perching or hilltopping, so usually make themselves pretty obvious. Females tend to wait for males to find them so don't fly very much, or only for short distances. Once they're paired they usually stay in the vicinity of the foodplant and fly no more than is necessary, in the case of forest species this is often in the treetops, rendering them even less visible. That's why so few are seen.

The only way to tell for sure is to rear them. In this case, even for species where far more males than females are seen, the results of large samples over time are as near to 50-50 as makes no statistical difference. I have occasionally had broods that consist of all, or nearly all, one sex; this has often happened due to high larval mortality at a specific point in time which has killed either all the more advanced (male) or less advanced (female) larvae. Male larvae grow at a faster rate than females so that they are out and sexually mature when the females emerge; sometimes the difference is as little as a day or two but sometimes it can be weeks.

I have also had broods, usually late in the year, that consist of only one sex - usually female; I've particularly noticed it with Lycaena phlaeas. I have no idea why this happens.

Bob

[wollastoni]

OK thank you bob for confirming that the ratio is 50/50, also for butterflies.

[nomihoudai]

If you look at the problem more theoretically the first question is how is male and female defined? This is to be answered by the two different sets of chromosomes that we call X and Y.

The next question is at what point is the chromosome set of a being decided? This happens when the egg gets fertilized.

Next question, which one of the two genders does have an influence what chromosomes are present and how will this affect the sex? In humans you have XX/XY for female/male and after checking the almighty google most lepidoptera do have "XY/XX" for female/male.

Now it doesn't matter which Y, or X makes female or male but the essence is that 1 gender has the influence during the generation of his sexual reproductary cells. For humans this is the man and his spermatogenesis in which of 1 diploid cell with the X and the Y turns into 2 cells with each X or Y and then those split again to two X sperms and 2 Y sperm cells. So the ratio is in theory 50/50 from the starting moment.

I could not verify now but I guess that the system of 1 diploid (2 chromosomes XY) cell -> 4 haploid ( 1 chromosome each, X,X,Y,Y) cells should be the same in lepidoptera as this is a basic progress that developped as soon as sexual reproduction had evolved. Given this there also should be 50/50 ratio.

Now for the human ratio, why is it different from 50/50? This happens when the sperms are on their way to the egg cell, as sperm containing the double sized X chromosome are much heavier than those with the Y they have problems advancing to the egg and the sex ratio will depend upon the distance to travel to the egg cell prior to fecondation.

In Lepidoptera you have of course similar things, if you just check "lepidoptera sex ratio" on the internet you get many articles like "explaining sex-ratio bias by bacteria affecting male/female eggs/caterpillars/whatever" and similar things that affect the sex posteriory to reproductary cell developpment.

I hope what I wrote now isn't too far from reality and does explain the thing theoretically.

[wollastoni]

Thanks a lot Claude, very interesting.

[africaone]

in all my breedings (a lot in many families) i always obtainrd a ratio around 50/50 except in one case : a parthenogenesis (in teh saturniidae Goodia kuntzei)
what is strange is that this "species" is parthegentic only in SE Congo around Lubumbashi.
There are 2 possible reasons for that
- the pollution (it is probably one of the most polluated area in this part of africa), not my favorite hypothesis
- the systematic. It apperas with barcode results that a lot of species seems to be involved under this name. may be one of this is restricted to this area and is parthenogenetic (then it is probably not a parthenogenetis relied to geography what was first thought without recent genetic discoveries). the most reliable for me.

I had another interesting breeding experience with Epitola adolfifrederici ( a big African lycaenidae). It has gregarious caterpillars (in "herd" like some gregarious lymantrid) and clusters of pupas of the same "family" may be also found on bark tree. In all cases all the female borned one day and males another day (I don't remember which sex born first). This is probably to minimise the chance of an interbreeding inside the family.

[jackblack]

All very intersting discussion , I have bred butterflies many years in the past commercially and genarally found 50/50 .An interesting observation breeding phasmids for years recent is although species accept a huge range of host plant like some Lepidoptera I note that with Phasmids many will turn to male on a particular unsuitable host and I think that rather than die and not be able to produce offsping it struggles on becomes a male which are geneaerally winged and then can at least fly off and procreate rather than die on an unsuitable host.
More food for thought .

[wingedwishes]

While I do know that some reptile species genders can be influenced by temperature, I wonder if this has been observed in insects. Have there been any studies on pollutants or other stresses influencing gender percentages?

[starlightcriminal]

One other thing that relates to gender composition that Claude explained is that in butterflies, females would be more "fragile" gender due to their being heterogametic. In humans males are the more fragile embryo because they have only one X and one Y so if a defect is on either one it can cause catastrophic developmental problems. In Lepidoptera, females are ZW so a problem affecting one chromosome would like wise be more detrimental than it would to a male that is ZZ, especially when considering recessive genetic diseases that cause termination of the fetal organism- of course many genetic diseases are recessive or they would by nature breed themselves out. This plays a role in the slight female bias of surviving human embryos so probably similarly Lepidoptera.

[wollastoni]

Very interesting, thank you starlight.

[Deleted]

In humans males are the more fragile embryo because they have only one X and one Y

yes but human females lack the gene that enables them to drive a car properly or look where they are going.

[starlightcriminal]

Embryo, dunc. I've never met an embryonic driver, though I have met quite a few with a smaller brain capacity. I tell my wife that she doesn't lack anything- it's the estrogen added into the equation that makes her mind clouded, lol. Then I go sleep on the couch.

[wingedwishes]

Oct 20, 2011 10:45:23 GMT -8 starlightcriminal said:

Then I go sleep on the couch.

And then sleep with one eye open.

[krupten]

"While I do know that some reptile species genders can be influenced by temperature, I wonder if this has been observed in insects. Have there been any studies on pollutants or other stresses influencing gender percentages?

Well - here is a story ABOUT what may be interpreted and an OTHER STRESS:

SPECIES - LOEPA SIKKIMA

about 4 years ago I took some wild larvae and reared them thru in my room and upon emergence - the all related adults- bred immediately - and of the 9 larvae the 4 females all laid fertile ova. The average was about 130 ova (+/- about 7%) which then resulted in F2 and the resultant parents - again were quite happy to mate for another subsequent 5 generations IN MY ROOM.

HERE IS THE KICKER- The last generation produced about 80 ova and a considerable less number of pupae - and were about 20 % smaller than the original parent stock (all siblings from the outset by the way). From this I had about 45 pupae. OF THEM only about 5 or 6 emerged in the NORMAL duration or cycle (about one month) the others became dormant.

Three months past - and some emerged - but PREDOMINATELY MALE - of these 8 - 7 were boys. 1 female - and she subsequently bred - and her children were very weak and of 55 - 60 0va more than 80% perished or were infertile. The remaining pupae - remained in stasis for another 3 - 4 months then another emergence - but again 8 - 10 and this time MOSTLY FEMALES emerged - and the boys were too weak to do anything serious to harass the ladies. More dormancy then the rest emerged over a 2 month period and the sporadic emergences were the same - MOSTLY ONE GENDER - either male or females but ONE IN MAJORITY. EARLY Generations were almost 50/50 at all time and hardly any remained for more than a month in the pupa. IN fact once they started to emerge - it was insane as up to 45 - 65 would come out each night.

So - there is some grist for those of you who like to ponder puzzles. for me I interpret this as a case for survival and to ensure genetic health. ONCE the inbreeding became so predominate - the species I suggest have a mechanism that causes them to go into a diapause if you will and they come out in such a fashion that will almost certainly result in breeding with moths of diffenent lineage thus ensuring the genetic strength of the species and thus SURVIVAL OF THE SPECIES.

OH - here in Tanah Rata the species flies with and concurrently with Loepa megacore and HYBRIDS have not been recorded. I reared both - together and they do not HYBRIDIZE and females will call and a male megacore will NOT ANSWER even in the same room with about a dozen female sikkima. You would think that the phermones would be so overwhelming that the males would be COMPELLED but not so. POSSIBLE REASONS: The species use two different hosts - sikkima is on 4 species of trees (I believe related) here and megacore uses a vine (I have not had the time to get the trees identified sorry) but sikkima will take the same vine as megacore (cissus) and loves it but the female will NOT OVIPOSIT ON THE VINES - ever. TREES ONLY. NO more that 27 ova on any tree. (that is the max I found so far). Megacore lays on vines and no more than 12 - 14 ova on a large vine. (the neonate larvae by they way - DISPERSE at a rate I cannot describe and they do not stop for anything. The sikkima on the other hand emerge then become a nice little family group in the first and second instars.) I believe the chemical composition of the hosts plants is a significant factor in keeping the gene pools of two very closely related speces from interbreeding.

If anyone can shed some light - OR opinions I am pleased to gain more insight - but I guess I should write the notes up and send them to Wolfgang, Richard or Stefan for them to work out.

[wingedwishes]

Thank you for relating that situation. I envy that you get to raise my favorite group of moths - Loepa.