Any biologists out there?

[TillEulenspiegel]

I remember reading and being exposed to ??Film maybe? About spontainious gender reassignment in frogs and fish due to environmental pressures ( overcrowding, ect.), or even flooding the environment with certain chemicals/hormone precursers/hormones. Anyone here fimiliar whith that?

 

[Fade]

Yes. There are quite a few species out there that can change their gender "at will" (use the term very loosely, it's more a necessity thing) and quite a few species that are simultaneously male and female.

 

[Jim_MDP]

Odd, must be the night for Michael Crichton references.

This makes two.

 

[Eos of the Eons]

Wrasse (Labridae): Some wrasses which form social groups can change gender. Most wrasses are born female and mature into females. The dominant fish in a wrasse group is a male and he has a harem of females. If he dies, the dominant or largest female becomes a male and breeds with the other "wives". In some (like the Cleaner Wrasse), the change to male is quick: within hours 'she' looks like a 'he' although it takes about 10 days before 'his' reproductive organs are functional.

Angelfish (Pomacanthidae) are highly territorial and their bright colours help identify each other; group members versus outsiders. Body markings on a juvenile (right) are often very different from those of a mature adult (left). This is believed to protect the young fish from aggression by older adults. But both genders look similar. They can change gender. In some, the largest in the group is a male and the other females his harem. If he is killed, the largest female becomes a male. Or if the harem becomes too large, they will split and the largest female becomes a male.

Grouper/Sea Bass and Basslets (Serranidae)...Many can change gender. They are born female, change to male. Some may change back to female. Others are both genders at the same time! One species schools in harems of females led by a spectacularly coloured dominant male.

http://www.szgdocent.org/ff/f-reef3a.htm


External events trigger a hormonal change.


Although this may be normal in some, people are finding that some changes aren't so normal because they are caused by pollution:

http://news.bbc.co.uk/2/hi/science/nature/3071549.stm

 

[TillEulenspiegel]

Yes scary stuff.. read in a news article and a paper ( Nature I believe) a while back indicating what seems to be psudo-hemorphic changes in adult frogs and true hermaphroditic sex assignment in tadpoles in the US because of a runoff of the pesticide atrazine.

Canary in a coal mine or hysteria?


Ahh forgot to say Thanks

 

[athon]

In evolutionary terms, sex determination via chromosomes is quite advanced. Many organisms still have their sex determined by environmental factors.

It has its advantages. For instance, if the environment is favourable for more offspring - more water, food, etc., then it would be of advantage to have more females. One guy can inseminate a lot of females.

If the environment is changing, then you want more variation. This would favour more males.

Athon

 

[TillEulenspiegel]

My questions revolve around a discussion I am engaged in with in regards to Human sexuality, homosexuality to be specific. There is one side that says nurture and another that says nature ( and environment). I am aware of hormonal flooding having an impact on humans at a critical junture that relates to sex assignment, but don't seem to be able to find the pertinent studies. ( many are published under the aegis of professional societies, which in turn require standing to access that information.) I rememberd accessable studies concerening frogs and fish, so thought I'd start there. So the specific information I seek is really about human biology, with examples of this phenom in other spices.

 

[Eos of the Eons]

Okay.

1. Why would someone 'choose to be that way' if they aren't hard wired for it. Children brought up by gay parents should then be gay if it is 'nurture'. They aren't. It has no effect on the kids' sexual orientation. It only affects how they view gay people-they learn homosexuals are caring and normal people.

2. If it was 'nurture' it would be 'reversible'.

3. There is a higher rate of homosexuality in families if a family member is gay...among brothers of homosexual men 13.5% are also gay, which is higher than the general population.

http://www.google.ca/custom?q=cache...omeronasal+lobe,+homosexuality&hl=en&ie=UTF-8[/url]

4. If it was 'nurture', then gay people should react to the opposites sex's pheremones. A perfume company did a study on human pheremones. When a person detects pheremones (they aren't smelly, you can't smell them) with the VNO lobe, the body reacts only if it is the opposite sex's pheremones, unless you are gay. When you don't react to the opposite sex's pheremones, you can't get 'turned on' physically. Instead, you get 'turned on' by the same sex. You can still love people of the opposite sex if you are gay, but you aren't attracted to them.

I saw this particular study on TV. The long name of VNO is Vomero Nasal Organ. If you could 'smell' pheremones, then we wouldn't need the VNO. The VNO "picks up" on the pheremone, and an area of the brain is stimulated.

Vomeronasal organ: (VNO)

-Small chemosensory organ in nose
Detects chemical signals that mediate sexual and territorial behavior

Human:
Male VNO responds to estrogens
Females VNO responds to androgens
Females: Synchronization of menstrual cycles
More then 100 genes code for receptors
Different receptors mediate different behavioral responses
Example: Sexual arousal, aggression
Signals bypass brain higher cognitive centers and stimulate subconcious responses that we are not aware of....

http://www.biosci.ohio-state.edu/~microbio/class_notes/bsz/biol102n.html

Given the genetically predisposed nature of mammalian olfactory_genetic_neuronal-hormonal_behavioral interaction in both males and females, it then appears that, minimally, there are three models (e.g., Samama & Aron, 1989; Bakker, Baum, & Slob, 1996; Perkins, et. al, 1995) leading to the tentative conclusion that pheromones and olfaction are involved both in mammalian heterosexual and in mammalian homosexual receptivity and proceptivity. Given this mammalian model, perhaps further research will help to explain variations in human sexual orientation. [para 59]

http://cas.bellarmine.edu/tietjen/images/human_pheromones.htm

4. Some people are coming up with theories on the hypothalmus and the homosexual orientation. This would explain why homosexuals react to the 'wrong set' of pheremones.


There are similar theories on bisexuality.

 

[TillEulenspiegel]

Wow A little vehement aren't we? =)

I am aware of a few studies , didn't know about the Pheremone one, The ones I am aware of ( and have reference posted in the discussion) are
The Hypothalimus studies, CAT scan studies of size and function in "normal" males VS "Homosexual" males. LeVay's pronouncements have been questioned as he is an advocate of the biological view. There are a plurality of this type of study tho so...
The "Twin" studies, again a plurality.
The hormone flooding studies on the gestating fetus excess' or scarcity of hormones that reinforce gender development during and after genital assignment.

Another class of study that I read about in live PET and NMR data documenting areas of the brain that are most active during arousal ( hard finding documentation on this one , Nuro stuff is pretty rarified)

I do not want to turn this thread into another discussion of the causality or behavioral details of homosexuality as I am engaged in one now. This was mearly a quest for information, and as there appeares to be experts from many fields on the board , I thought I'd try here first.

 

[Eos of the Eons]

What do you mean vehement? Those are the main points I've ever found for the 'nature' side. And the fact that there are homosexuals animals.

Where is the other thread on " do not want to turn this thread into another discussion of the causality or behavioral details of homosexuality as I am engaged in one now." If it's not on these boards, I won't bother with it I guess.

I hope you get some better answers from people who know more about this area and gender reassignment.