Post by starlightcriminal on Aug 26, 2011 9:59:08 GMT -8
The fertility of offspring of an inter-specific hybrid does not necessarily disqualify their classification as species. What do you do with inter-generic hybrids then? We see them frequently, especially in things like Orchidaceae that have complicated and diverse chromosomal states. We see examples listed here on Insectnet even. That alone wouldn't preclude the possiblity of two or three distinct species here.
That said, I think the major problem with this study in my mind is the limited number of characters being used to distinguish species. It's really the major taxonomic dilemma of modern genomics I think- how do you decide which characters are enough to separate a species? How do you know which are important and which are not and when do you decide to tighten or loosen criteria? Some of this has to do with the size of the genome for each specific case but some of it is due to our limited understanding of the various genetic conditions within a set of organisms, as is the case with most insects beside Drosophila or something. It sounds to me like a subspecies or even form still, at best a naturally occurring hybrid that might be on its way to speciation. The obvious problem which was not addressed is "how do you know there aren't crosses between 'appalachiensis' and glaucus?" We can't say yet that they are distinct, only that they have a striking number of shared genetic markers which is not convincing evidence for re-classification. And now it is being called its own genus too? Lofty aspirations I think.
We know that eclosure patterns, tonality, subtle differences in shape, etc. are all on a curve with a peak that would define the norm but without a necessitated end or beginning, thus you must prove the absence of existing intermediates before you declare one condition genetically distinct from the other. Otherwise you could just as easily have a subspecies that exhibits a few distinct qualities which we happen to rely heavily on for taxonomy, but that may or may not be in the process of being re-absorbed completely by one of the two parent species, in this case glaucus. Could be why the distribution is so limited, in fact- why would an otherwise well-adapted set of parent species produce a new species of hybrid origin that is apparently so unsuited to the parent's habitat that it has all but disappeared over the past 100,000 years (if that is correct)? Hard to notice an intermediate between the two species if we can barely distinguish the two anyway. I still would reserve judgement until more complete data are available.
The last paragraph from Harvard:
"Since appalachiensis largely overlaps with glaucus and still remains a distinct species, and given its specific combination of traits from the two parental species that is clearly under selection, it appears that appalachiensis is maintained as a hybrid species due to natural selection for mimicry and traits necessary to survive in a cold thermal habitat. Overall, it represents a telling example of hybrid species that informs us on the dynamics of hybrid speciation in animals."
"Natural selection" for traits exactly like those of the parents? Come on, even the conclusions are hastily drawn and not well thought out. What exactly is "clearly under selection?" They're trying to say it is mimicking the parent species when what the really should've said is that it is derived from the parents so by default they will look very much the same in some combination. You can't make chicken cordon bleu out of chocolate chip cookies, what else would you expect? Their study only shows that these three organisms are very closely related but does not put forward conclusive evidence for breaking this hybrid off from the parent species yet (rather it might suggest what Hypantria put forward- maybe the parents are barely unique species by virtue only of their geography which is not that separate either). That's not to say it won't ever happen, but it sounds to me like someone wanted a big discovery for their resume so we got a little carried away. It's not uncommon in taxonomy though- if you don't hurry up and describe something yourself you can rest assured that someone else will and probably is already in the process of it. Much easier to re-organize if you are wrong than it is to find something equally as impressive to name.
That said, I think the major problem with this study in my mind is the limited number of characters being used to distinguish species. It's really the major taxonomic dilemma of modern genomics I think- how do you decide which characters are enough to separate a species? How do you know which are important and which are not and when do you decide to tighten or loosen criteria? Some of this has to do with the size of the genome for each specific case but some of it is due to our limited understanding of the various genetic conditions within a set of organisms, as is the case with most insects beside Drosophila or something. It sounds to me like a subspecies or even form still, at best a naturally occurring hybrid that might be on its way to speciation. The obvious problem which was not addressed is "how do you know there aren't crosses between 'appalachiensis' and glaucus?" We can't say yet that they are distinct, only that they have a striking number of shared genetic markers which is not convincing evidence for re-classification. And now it is being called its own genus too? Lofty aspirations I think.
We know that eclosure patterns, tonality, subtle differences in shape, etc. are all on a curve with a peak that would define the norm but without a necessitated end or beginning, thus you must prove the absence of existing intermediates before you declare one condition genetically distinct from the other. Otherwise you could just as easily have a subspecies that exhibits a few distinct qualities which we happen to rely heavily on for taxonomy, but that may or may not be in the process of being re-absorbed completely by one of the two parent species, in this case glaucus. Could be why the distribution is so limited, in fact- why would an otherwise well-adapted set of parent species produce a new species of hybrid origin that is apparently so unsuited to the parent's habitat that it has all but disappeared over the past 100,000 years (if that is correct)? Hard to notice an intermediate between the two species if we can barely distinguish the two anyway. I still would reserve judgement until more complete data are available.
The last paragraph from Harvard:
"Since appalachiensis largely overlaps with glaucus and still remains a distinct species, and given its specific combination of traits from the two parental species that is clearly under selection, it appears that appalachiensis is maintained as a hybrid species due to natural selection for mimicry and traits necessary to survive in a cold thermal habitat. Overall, it represents a telling example of hybrid species that informs us on the dynamics of hybrid speciation in animals."
"Natural selection" for traits exactly like those of the parents? Come on, even the conclusions are hastily drawn and not well thought out. What exactly is "clearly under selection?" They're trying to say it is mimicking the parent species when what the really should've said is that it is derived from the parents so by default they will look very much the same in some combination. You can't make chicken cordon bleu out of chocolate chip cookies, what else would you expect? Their study only shows that these three organisms are very closely related but does not put forward conclusive evidence for breaking this hybrid off from the parent species yet (rather it might suggest what Hypantria put forward- maybe the parents are barely unique species by virtue only of their geography which is not that separate either). That's not to say it won't ever happen, but it sounds to me like someone wanted a big discovery for their resume so we got a little carried away. It's not uncommon in taxonomy though- if you don't hurry up and describe something yourself you can rest assured that someone else will and probably is already in the process of it. Much easier to re-organize if you are wrong than it is to find something equally as impressive to name.