WTF is w/feminized genetics,

[freefields]

Bah, I'll just set Tom on him if he tries it, Tom is brilliant at putting him in his place! lol

Hempy, your post that Brian quoted is bordering on jibberish in places, had to read it 3 times to understand what you are on about.

This part shows that you don't understand the issue of intersexed plants and feinising one little bit:

Only a few years ago if i had posted which i did saying how a female cannabis plant can produced a single seed and it was a preservation triga i was laft at and told it was a hermaphrodite and told the only good thing i could do with it or any plant like it was to cull it now the same experts are telling me that female seeds are the best thing to cannabis since sliced bread.

Lots of errors in one paragraph. First of all, no cannabis is hermaphroditic, that has been well explained in this thread by Tom and Rick.

Yes, female plants can produce the odd seed as a survival mechanism, but seeds produced in this way are not at all the same thing as feminised seeds, that has been explained in this thread in great detail, quite clearly you are just ignoring the science being presented to you and sticking to your guns, well it's making you ever more stupid and stubborn.

For the record, a seed produced by a female as a survival mechanism is the result of the expression of the intersex gene and will carry that intersex gene, resulting in a female plant with an intersex trait that will more than likely produce staminate flowers, just as it's mother did. This is not at all the same thing as a seed produced by a female plant that has been treated with an ethylene hormone inhibitor such as the silver ion. Yes, if the female that was treated with silver had intersex genes then the seeds produced will have the intersex gene and some of the progeny will express this trait by growing staminate flowers, but this is something that good breeding practices can overcome as has been discussed in this thread.

Quite frankly hempy, until you grasp the science behind this issue (and you keep making it abundantly obvious you haven't grasped it in the slightest) then you have zero of any worth to contribute to the discussion beyond the same old crap you keep spewing.

 

[DocLeaf]

FRT are NOT feminized breeders... neither am I (like Gerrit is).

Painted Lady (fem. x reg. line) is however currently growing all over Europe.. to test fem. seeds for breeding

Brian,, please give us some examples of fem. seeds you've made yourself or worked with during the process of breeding.

Peace
dLeaf

Outside the frame is what we're leaving out...

 

[englishrick]

Bah, I'll just set Tom on him if he tries it, Tom is brilliant at putting him in his place! lol

Lots of errors in one paragraph. First of all, no cannabis is hermaphroditic, that has been well explained in this thread by Tom and Rick.




Yes, female plants can produce the odd seed as a survival mechanism, but seeds produced in this way are not at all the same thing as feminised seeds, that has been explained in this thread in great detail, quite clearly you are just ignoring the science being presented to you and sticking to your guns, well it's making you ever more stupid and stubborn.

For the record, a seed produced by a female as a survival mechanism is the result of the expression of the intersex gene and will carry that intersex gene, resulting in a female plant with an intersex trait that will more than likely produce staminate flowers, just as it's mother did. This is not at all the same thing as a seed produced by a female plant that has been treated with an ethylene hormone inhibitor such as the silver ion. Yes, if the female that was treated with silver had intersex genes then the seeds produced will have the intersex gene and some of the progeny will express this trait by growing staminate flowers, but this is something that good breeding practices can overcome as has been discussed in this thread.

toms not the type to do what hes told,,,thats why hes the leader

id just like to mention;.. when a female member of a dioecious or subdioecious population expresses intersexed traits within a niche enviroment it is deemed monotonous,,,

the outside of the nucleus is effected under certain stress conditions,,,,,,,,,,,sex determining genes on autosomes come into force when the genes controling sex on the sex chromozone become inactive,,,,,,autosomonal factors control the sex type of monoecious offspring,,,,,

crosses between diecious and monoecious hemp give mainly diecious female hemp with a small percentage of monoecious hemp

 

[freefields]

id just like to mention;.. when a female member of a dioecious or subdioecious population expresses intersexed traits within a niche enviroment it is deemed monotonous,,,

Sorry rick, this made me hoot out loud, you made a tiny wee error, monotonous means droning on about the same old sunject, you meant monoecious!

the outside of the nucleus is effected under certain stress conditions,,,,,,,,,,,sex determining genes on autosomes come into force when the genes controling sex on the sex chromozone become inactive,,,,,,autosomonal factors control the sex type of monoecious offspring,,,,,

crosses between diecious and monoecious hemp give mainly diecious female hemp with a small percentage of monoecious hemp

I'm still not well enough read to 100% understand that but thanks for posting it, I know you have done the hard work of reading all the books so I don't doubt your info!

 

[darwinsbulldog]

Sorry rick, this made me hoot out loud, you made a tiny wee error, monotonous means droning on about the same old sunject, you meant monoecious!

lol i was wondering the same thing, got your point though rick thanks for explaining that mate

 

[darwinsbulldog]

Agreed, more Spam.

What would be the correct terminology to describe that cross? it's not an F2, I understand that, but I dunno what the correct term would be?

correct me if i'm wrong but i believe that F1 x F1 is the term to be used

"F generation numbers are to be used cautiously, since misunderstandings may occur. In cases of back cross or out crossing, these numbers are not valid anymore. In general when the fish bred do not belong to the same bloodline or F generation it is better to indicate the two F generations of that particular breeding. For example, if you cross an F2 generation male with an F1 generation female of the same bloodline, it is better to label the fry as F2 x F1. If you cross an F1 parent of one bloodline to an F1 parent from another bloodline, then the fry should be labeled as F1 x F1 and not F2. If you outcross an F1 parent with a wild caught specimen, you should use the F1 x F0 label."

http://www.malawicichlidhomepage.com/aquainfo/mendelian.html

EDIT: i read back and think i may've misunderstood the context. dunno if what's stated above still applies. but using F1xF1 is still an ok label/generation name either way.

 

[BrianBadonde]

Agreed, more Spam.

What would be the correct terminology to describe that cross? it's not an F2, I understand that, but I dunno what the correct term would be?

A fucked polyhybrid I'd say. from what I can gather they took a Spice and pollinated it with Blubbas BBC, then got some F1's of this and just tossed them together. so I'd call it a fucked F2 generation.

 

[freefields]

correct me if i'm wrong but i believe that F1 x F1 is the term to be used

"F generation numbers are to be used cautiously, since misunderstandings may occur. In cases of back cross or out crossing, these numbers are not valid anymore. In general when the fish bred do not belong to the same bloodline or F generation it is better to indicate the two F generations of that particular breeding. For example, if you cross an F2 generation male with an F1 generation female of the same bloodline, it is better to label the fry as F2 x F1. If you cross an F1 parent of one bloodline to an F1 parent from another bloodline, then the fry should be labeled as F1 x F1 and not F2. If you outcross an F1 parent with a wild caught specimen, you should use the F1 x F0 label."

http://www.malawicichlidhomepage.com/aquainfo/mendelian.html

Thanks for that mate, found it very helpful.

A fucked polyhybrid I'd say. from what I can gather they took a Spice and pollinated it with Blubbas BBC, then got some F1's of this and just tossed them together. so I'd call it a fucked F2 generation.

Well yeah, I agree, it's just amateur pollen chucking. I wouldn't be so critical if they weren't spamming it so much and talking about their work like it was top-class breeding when clearly it isn't.

BBC Cheese, hardly something worth breeding with. Spice, a great line but I really don't approve of using other people's hard work.

BBC Cheese is Cheese x Afghan, the original release was an F1, despite BB's BS claims of doing 5 BXes. Dunno if he has worked it anymore since. Spice is an F1 Hawaiian Indica x Hawaiian Sativa.

Neither line has been stabilised to become truebreeding, this means neither is suitable for outcrossing. Crossing two unstable f1s is bad breeding practice to begin with, then doing an f1 x f1 is just going to make things worse. I shudder to think what level of variation would exist within such a line.

My main objection though is people using genetics that were the result of lots of hard work by others, White Widow, Critical Mass, Spice, all created by Shantibaba using very correct breeding practices - large populations, stress testing, Shanti does it all without cutting corners. To go and steal his genes for your own shoddy efforts is plain wrong. Even Shanti wouldn't mind people making crosses of his work as long as it's just for your own (and a few friend's) personal enjoyment, but to use them and then sell the seeds is totally out of order, we should all support shanti, he's a rare diamond in the cannabis scene, many seed companies hack in tents, Shanti does it properly in huge greenhouses.

 

[darwinsbulldog]

A fucked polyhybrid I'd say. from what I can gather they took a Spice and pollinated it with Blubbas BBC, then got some F1's of this and just tossed them together. so I'd call it a fucked F2 generation.

lol "fucked F2 generation" is that the correct term? i can't find it in my genetics text book... haha

 

[darwinsbulldog]

My main objection though is people using genetics that were the result of lots of hard work by others, White Widow, Critical Mass, Spice, all created by Shantibaba using very correct breeding practices - large populations, stress testing, Shanti does it all without cutting corners. To go and steal his genes for your own shoddy efforts is plain wrong. Even Shanti wouldn't mind people making crosses of his work as long as it's just for your own (and a few friend's) personal enjoyment, but to use them and then sell the seeds is totally out of order, we should all support shanti, he's a rare diamond in the cannabis scene, many seed companies hack in tents, Shanti does it properly in huge greenhouses.

i dunno, i don't think there's anything wrong with using other people's stuff, i mean some people don't have the time or the means of reinventing the wheel when getting involved in breeding. that said though, you should always ask permission if you plan on selling it yourself and pay full respect to those who have put the majority of hard work into the girls you've used. but i'd agree with you guys that if you want real respect, use landraces and make a name for yourself with something 100% yours and unique.

 

[englishrick]

with all respect you have only just learnt this yourself.

Ps. sig removed by friggin admin, this place is worse the fucking N Korea. thats it I'm done, Tom you are a gent and good man.

actualy Brian,,,i was previously assuming that 1 of Hillig`s biotypes was confirmed to be hemaphrodite,,,,,when tom mentiond "no cannabis is hemaphrodite", i whent and checked every book i have access too,,,,an low and behold tom was spoton,,go figure,,,fukin tyipical

when i relized i was actualy shocked,,,,everytime i hear the word hemaphrodite on this site its not only being missused but as far as every biotype in cannabis is conserned the word hemaphrodite is simply not aplicable

@Darwins bulldog,,,,,we cant perpetuate inaccuracys bro, no matter how easy it is to make the mistake ourselvs....i am 100% sure the word Hermi is missleading new growers and especialy young polen chuckers,,,the word Hermi is ammo to the people that fear feminized seeds,,,,,we need to be more strict in future,,,,imo ,,,,

im not gona buy into coined terms,,,

im gona learn ,,then re-learn,

 

[freefields]

actualy Brian,,,i was previously assuming that 1 of Hillig`s biotypes was confirmed to be hemaphrodite,,,,,when tom mentiond "no cannabis is hemaphrodite", i whent and checked every book i have access too,,,,an low and behold tom was spoton,,go figure,,,fukin tyipical

when i relized i was actualy shocked,,,,everytime i hear the word hemaphrodite on this site its not only being missused but as far as every biotype in cannabis is conserned the word hemaphrodite is simply not aplicable

@Darwins bulldog,,,,,we cant perpetuate inaccuracys bro, no matter how easy it is to make the mistake ourselvs....i am 100% sure the word Hermi is missleading new growers and especialy young polen chuckers,,,the word Hermi is ammo to the people that fear feminized seeds,,,,,we need to be more strict in future,,,,imo ,,,,

im not gona buy into coined terms,,,

im gona learn ,,then re-learn,

Rick mate, you never cease to amaze me with the degree of learning you have done in the last year or so, keep it up mate!

I agree that we should start being strict about the use of terminology, it does no-one any good to perpetuate false info.

 

[darwinsbulldog]

actualy Brian,,,i was previously assuming that 1 of Hillig`s biotypes was confirmed to be hemaphrodite,,,,,when tom mentiond "no cannabis is hemaphrodite", i whent and checked every book i have access too,,,,an low and behold tom was spoton,,go figure,,,fukin tyipical

when i relized i was actualy shocked,,,,everytime i hear the word hemaphrodite on this site its not only being missused but as far as every biotype in cannabis is conserned the word hemaphrodite is simply not aplicable

@Darwins bulldog,,,,,we cant perpetuate inaccuracys bro, no matter how easy it is to make the mistake ourselvs....i am 100% sure the word Hermi is missleading new growers and especialy young polen chuckers,,,the word Hermi is ammo to the people that fear feminized seeds,,,,,we need to be more strict in future,,,,imo ,,,,

im not gona buy into coined terms,,,

im gona learn ,,then re-learn,

very fair point you have there englishrick, i agree with you, it can just be irritating constantly having to define monoecious/bisexual and why hermaphroditism isn't correct when speaking with people on here who use the incorrect word in discussion. though laziness isn't a legitimate reason not to. i'll try and be a bit more of a stickler for truth in the future then mate.

darwin

 

[BrianBadonde]

actualy Brian,,,i was previously assuming that 1 of Hillig`s biotypes was confirmed to be hemaphrodite,,,,,when tom mentiond "no cannabis is hemaphrodite", i whent and checked every book i have access too,,,,an low and behold tom was spoton,,go figure,,,fukin tyipical

when i relized i was actualy shocked,,,,everytime i hear the word hemaphrodite on this site its not only being missused but as far as every biotype in cannabis is conserned the word hemaphrodite is simply not aplicable

@Darwins bulldog,,,,,we cant perpetuate inaccuracys bro, no matter how easy it is to make the mistake ourselvs....i am 100% sure the word Hermi is missleading new growers and especialy young polen chuckers,,,the word Hermi is ammo to the people that fear feminized seeds,,,,,we need to be more strict in future,,,,imo ,,,,

im not gona buy into coined terms,,,

im gona learn ,,then re-learn,

Rick the Biotypes have nothing to do with weather the Genus Cannabis is Dioecious or Sub Dioecious, unless there is a specific group of Hermaphrodite plants that know one knows about within the genus Cannabis! Wide leaf is a biotype, as is Narrow leaf. Saddens me but I have seen the likes of Simon from serious use the word Hermaphrodite with regards to this plant species.

 

[BrianBadonde]

lol

this is so funny,,,,,peoples hatered for hermis is like racism,,,dont be afraid of it,,,dont try and kill racizm or hermis,,love everything,,,thats the bigger power

odd you were using the word yourself here? (but dont sweat it I'm as guilty as anyone of doing the same, so my apologies for that.) Edit 18.06.10

 

[darwinsbulldog]

odd you were using the word yourself here?

lol he's got you there englishrick!

 

[freefields]

Er, Brian, it just detracts from your otherwise excellent points and info to go nitpicking like that. If you replace the word 'hermis' in that post rick made then he is absolutely correct.

I know you got a lot of good stuff to offer mate, would be much better if you stuck to the good stuff and left the pointless nitpicking and hatred to those who don't have anything else to contribute and god knows there are plenty of those types in this thread.

 

[BrianBadonde]

Er, Brian, it just detracts from your otherwise excellent points and info to go nitpicking like that. If you replace the word 'hermis' in that post rick made then he is absolutely correct.

I know you got a lot of good stuff to offer mate, would be much better if you stuck to the good stuff and left the pointless nitpicking and hatred to those who don't have anything else to contribute and god knows there are plenty of those types in this thread.

Point Taken, but I have taken umbridge with rick about posts to Gerrit.

(and yes I've swallowed a dictionary)

 

[englishrick]

i agree with you Brian,,,,i have been guilty,,,,,i have been at fault!!,,,,,,,,but now im ready for redemption,,,,,yeha

comon man ,,,show me some love??

i read a paper you droped where it explains the "Gynodioecy pathway to dioecy" ,,,and ,,,"Androdioecy pathway to hermaphroditism",,,,,,but when noticed ALL of Hillig`s 7 biotypes are ALL dioecious,,,,the words "domestication syndrome" comes to my mind,,,,,canna is playing a form of gametheory and it takes its cues from the enviroment,,,,the bitch knows when to lay down all her chips,,,


i have thrown the term around myself,,,,,,,but now im convinced its doing more harm than good,,,,

i think we need to stop them hemikids and say,,,,"hay hemikid!!,,,stop being a hermikid!!,,,ya fuking hermikid,,,,wise up and smell the monocious specimine"

 

[Dalaihempy]

Here do some reading.

The sex expression of plants appears to be a function of hormonal control; there seems to be evidence that dioecious plants (male and female reproductive organs on separate plants) are potentially bisexual and that a delicate internal hormonal balance results in one sex "over-riding" the other. A traumatic incident might, therefore, act by temporarily upsetting this balance which is later restored in a way which leads to the opposite sexual character being manifested. Another pointer in this direction is the fact that a variety of artificially applied chemical substances has been shown to affect the sexual expression of a significant number of different plants. Jan Ceuns, working in Belgium, believes that the class of chemicals known as the steroid hormones might be a major key to the sex expression lock. All this indicates that it might be possible to "create" a female E. woodii by either a physical shock or a controlled chemical process.



Tackling the diversity of sex determination

A workshop on ‘The evolution of sex determination systems’ was held at a remote place in the Swiss Alps from 17 to 20 June 2009. It brought together theoreticians and empiricists, the latter ranging from molecular geneticists to evolutionary ecologists, all trying to understand key aspects of sex determination. The topics discussed included the evolutionary origins of sex determination, the diversity of sex determination mechanisms in different taxa, and the transition from genotypic to environmental sex determination and vice versa.

1. Introduction

The genetics, ecology and evolution of sex determination have always fascinated evolutionary biologists. Among the many important questions still puzzling researchers today is a very basic one: why is there such a diversity of sex determination mechanisms? Mammals and birds (and most dioecious plants) have only genotypic sex determination (GSD); that is, their sex is established at fertilization by genetic factors. Other vertebrates have environmental sex determination (ESD), which is also widespread in plants and other animals. In ESD, sex development is under the control of environmental cues (temperature, pH, social factors and so on) and is usually determined within a discrete period after conception. Many organisms, including many fish and amphibians, have a mixture of GSD and ESD, for example, when environmental sex reversal creates a mismatch between genotypic and phenotypic sex. (Such mismatches can have interesting consequences, for example, on the future demographics of a population.)

The following is another basic question that remains challenging: how do sex determination mechanisms evolve? Obviously, each sexually produced offspring has a father and mother, so we expect strong frequency-dependent selection on the production of sons and daughters. Meiotic separation of sex chromosomes ensures a 1∶1 sex ratio, but ESD can lead to biased sex ratios. ESD may, however, be favoured over GSD under some sex-specific selection pressures, for example, if male fitness improves more with increasing size than female fitness and ESD allows males to grow larger than females (Bull 1983). These first thoughts set the stage, but cannot yet explain the diversity of sex determination mechanisms we see in the wild.

2. From data to theory and back again

Separate sexes in plants have probably, and often recently, evolved many times. Deborah Charlesworth (University of Edinburgh) opened the meeting with an overview of the similarities and differences between plant and animal sex chromosomes. She reviewed genetic data on questions such as: (i) When did sex chromosomes evolve in different species? (ii) Why does this usually result in a loss of recombination? (iii) What are the consequences of the latter? It is now evident for several model systems that recombination ceased at different times on different parts of the sex chromosomes, that is, there is no single age of such chromosomes. Charlesworth also reviewed the argument that it needs at least two interacting sex determination genes on a chromosome, and selection for reduced recombination between these, to set off the evolution of sex chromosomes. Furthermore, sexually antagonistic genes may be added later to a system, leading to selection for reduced recombination in new regions. An important consequence of reduced recombination is genetic degeneration, that is, poorer gene function, loss of genes and sometimes the evolution of dosage compensation. It is not yet clear how much time is required for this process (Bergero & Charlesworth 2009).

In a second opening talk, theoretician Mark Kirkpatrick (University of Texas) reviewed ideas and models for evolutionary changes and turnover of sex chromosomes. In ‘homogametic transitions’, a pair of autosomes becomes a new pair of X and Y chromosomes replacing the old X and Y, whereas ‘heterogametic transitions’ change an XY system (with males heterogametic) to a ZW (with females heterogametic) or vice versa. Such transitions are feasible if Y or W are not considerably degenerated. They can be a result of random drift, pleiotropic effects favouring new sex determination alleles, selection on sex ratio, transmission distortion or sexually antagonistic selection. Kirkpatrick elaborated on the idea that an autosomal gene under sexually antagonistic selection can cause the spread of new sex determination genes linked to it, and that this is a likely cause for homo- or heterogametic transitions (van Doorn & Kirkpatrick 2007), which can in turn lead to the origin of new sex determination loci, the transposition of an ancestral sex determination gene to an autosome, or the maintenance of multiple sex determination factors in species that lack heteromorphic sex chromosomes.

Fishes generally seem to be excellent models in which to study changes in sex determination. Jean-Francois Baroiller (CIRAD, Montpellier) provided an overview of piscine sex determination mechanisms, which seem to vary continuously from different forms of GSD to different forms of ESD, including, for example, temperature-dependence (TSD) (Baroiller et al. in press). Additive genetic variation for reaction norms is sometimes found within a single species. Sex reversal is often possible and is routinely used in aquaculture to produce single-sex populations. Subsequent breeding and sex reversal can lead to YY females. These are viable in many species, suggesting that the male-determining regions evolved too recently to undergo significant genetic degeneration. As a consequence, environmental sex reversal could be used in population management to control, for example, introduced exotic species (Cotton & Wedekind 2008). Delphine Galiana-Arnoux (Institut de Génomique Fonctionnelle, Lyon) described duplications, insertions, deletions and transposable elements in the sex determination region of the platyfish, and argued that there is no shared synteny to other fish sex chromosomes. Helena D'Cotta (CIRAD, Montpellier) reviewed molecular work aimed at discovering genes involved in the sex determination cascade in tilapia. In lizards, however, Martina Pokorná (Charles University, Prague) showed, using phylogenetic analysis, that transitions between different sex determination mechanisms are infrequent.

The significance of sexually antagonistic selection and genomic conflict was further elaborated in talks by William Rice (University of California) and Leo Beukeboom (University of Groningen). Beukeboom reviewed the genetic conflicts that are likely to influence the evolution of sex determination mechanisms and that emerge from conflicts between cytoplasm and nucleus, sex chromosomes, parents and offspring, and mothers and fathers (Werren & Beukeboom 1998). He supported some of his arguments with new simulations and suggested experiments on species with natural sex determination polymorphism, such as the house fly (Musca domestica). Rice explained in detail how a ‘green beard effect’, that is, a particular form of cooperation that is theoretically predicted, but has not often been demonstrated, can drive the evolution of sex chromosomes by sib competition for parental care. In this context, offspring sex is a tag (like a ‘green beard’). Selection in the heterogametic sex can thus cause ‘zygotic drive’, a previously overlooked form of sexual genomic conflict that may be especially common in birds. Green-beard effects may occur if the opposite sex is more likely to be killed in siblicide, or if parental provisioning or epigenetic effects are sex specific. Genomic conflict may lead to chromosomes modifying gene expression on other chromosomes. Indeed, the Drosophila melanogaster Y has 12 known coding genes, but expression levels of hundreds of genes are affected by the Y (Lemos et al. 2008). Autosomes and new sex chromosomes are expected to evolve counterstrategies such as early inactivation of sex chromosomes during spermatogenesis. Such counterstrategies can ultimately lead to adaptations that reduce the fitness of the organism, for example, by disruption of sex-specific pathways, increased rate of spontaneous abortions or homosexuality (Rice et al. 2008).

Martin Hasselmann (University of Düsseldorf) presented details of the genetics of sex determination in the honeybee (Apis mellifera), a haploid–diploid system with complementary sex determination (heterozygotes develop into females, hemizygotes and homozygotes into males). He explained the regulatory interactions between the recently duplicated complementary sex determiner gene (csd), the feminizer gene (fem, the ancestrally conserved progenitor from which csd arose) and Am-dsx (a conserved sex-specific transcription factor). RNA interference-induced knockdowns confirmed that csd affects sex through allelic combination, whereas fem induces sex-specific splicing, producing a functional protein only in females. Comparison between the sex determination pathways of A. mellifera, Ceratitis capitata and D. melanogaster suggests that the fem/dsx pathway is ancestral, and that rather simple evolutionary steps of gene duplication and neo-functionalization can yield radically different sex determination systems. Interestingly, the data from insects suggest that the plasticity of sex regulatory proteins may have facilitated the recruitment of upstream signals to take over sex determination function. Furthermore, a comparative analysis of fem- and csd-coding sequences from five bee species provides evidence for a recent origin of csd in the honeybee lineage, followed by positive selection at csd and accompanied by purifying selection at fem (Hasselmann et al. 2008). Hasselmann speculated that gene duplication and positive selection at csd may be consistent with selection for a novel sex determination pathway, resulting from deleterious mutations accumulating on the initial sex determination locus, due to recombination reduction and an erosion of gene function. These findings offer a potential explanation for the stunning diversity of genetic sex determination factors observed in insects.

Fredric Janzen (Iowa State University) identified the interplay between sex ratio selection and sex determination mechanisms as one of the most powerful drivers of population dynamics in species with ESD. The existence of organisms with multifactorial sex determination (such as GSD plus environmental effects) poses a problem for sex ratio theory, because it predicts the production of widely varying, unstable sex ratios. Janzen opined that if we are to understand the persistence of multifactorial systems and the seemingly infinite combinations of genotypic and environmental sex factors in nature, we need to tackle the issue from several angles. He recommended phylogenetic comparative methods, as well as field and laboratory experiments, that integrate different study areas and different levels of biological organization. As general explanations for the adaptive significance or persistence of ESD, Janzen listed phylogenetic inertia, group adaptation, inbreeding avoidance and sex-specific selection pressures (Janzen & Phillips 2006). He then reviewed some of the latest work on reptiles with TSD suggesting that the fitness of each sex is maximized by the incubation temperature producing that sex, as predicted by Charnov & Bull (1977). Janzen concluded that TSD is a classic case of phenotypic plasticity, that it is likely to have multiple evolutionary origins, and that it may be adaptive in turtles with seasonally shifting differential fitness for males and females. On a related note, Christine Grossen (University of Lausanne) explored the influence of stochastic effects and environmental variance on the spread of new sex determiners using an individual-based model with sex determination as an additive quantitative trait. The model gave three potential outcomes: population extinction, the evolution of ESD (and then new GSD) or a direct transition to another GSD system. Her analyses suggest that ESD and GSD are two extremes of a continuum.

Nicolas Perrin (University of Lausanne) asked the following question. Why do sex chromosomes not decay in lower vertebrates as they do in higher ones? Perrin suggested possible mechanisms that may have led to a low decay of Y chromosomes specifically in amphibia. The high evolutionary turnover rates of sex determination systems found in some species groups may partly explain the observations. But if this were the only reason, it would appear that >90 per cent of all amphibian species must have experienced a recent turnover. This seems unlikely, and we are left with another exciting problem that still needs to be solved.

3. Possible future directions

Fundamental organismic traits like sex determination mechanisms may rarely be amenable to experimental evolution. Many talks (including those that were not mentioned for lack of space) suggested that we can learn much about the evolution of sex determination from studying genetics and molecular pathways, using phylogenetic comparisons (e.g. to identify changes between sex determination mechanisms), as well as from extending theoretical analyses and combining them with field and laboratory studies on real populations. We may soon, for example, have a greater understanding of genetic degeneration and be able to estimate the divergence time between homologous X and Y sequences if we can identify specific genes involved in sex determination, and the genes linked to these. Models for the stable coexistence of ESD and GSD, as often observed in the wild, should be elaborated on and tested. There are further unanswered questions to be investigated. Why are some sex determination systems stable in some taxa but not in others? How did recombination between sex chromosomes cease in the heterogametic sex? What is the significance of genotype × environment interactions, and are sexually antagonistic loci involved in transitions in sex determination systems? Can species with ESD adapt quickly enough to changing environments? Several promising systems have been identified for studying such questions and exciting breakthroughs can be expected within the next few years.

http://rsbl.royalsocietypublishing.org/content/6/1/7.full