Some cryptic species are well studied and are definitely distinct. Often they have different behavior or habitat, if not morphology.
4 Likes
I think I get what you’re saying, but I wouldn’t word it this way.
In order reliably identify species, it is critically important to be aware of aspects of morphology that are independent of the qualities used to distinguish species. I also would not say that they are “not genetically based” as there is a degree to which all morphology is influenced by genetics. It’s more that they’re “not based in the aspects of genetics that differ between species”. But of course that’s a mouthful so I get why you worded it the way you did.
An example of this would be how, on oaks, there can be great differences in leaf shape between shade-grown leaves low to the ground, especially of seedlings, and leaves high up on a tree exposed to full sun. Often these differences are greater, at a glance, than the differences from one species to another. For example, both Quercus velutina and Quercus rubra will have deeper sinuses between lobes at the top of a tree and broad, full leaves with very shallow sinuses on shade-grown seedlings. So, you need to look for other aspects of the leaf in order to tell them apart.
So this stuff is relevant to species identification to the extent that you need to be aware of it and able to filter it out or ignore it.
3 Likes
I unfortunately can’t find the article at the moment, but at some point over the past year I found an analysis of some oaks in a hybrid swarm, which had been trying to settle the question of the genetic composition. The researchers ended up concluding that the genetic analysis reinforced, but added nothing new to the conclusions reached by morphological examination of the individuals alone: i.e. that morphologically-intermediate individuals showed similarly intermediate genetics, and that examining the morphology was a reliable way of predicting the genetic relationships, like whether a particular individual was closer to one species or the other.
It is all sort of intuitive to me.
I think this reinforces that, at least with our current technology where genetic analysis is costly and labor intensive, examining morphology is still far more useful.
There may be some exceptions though, on species that are clearly distinct and do not hybridize, but are very hard to tell apart by morphology. I mostly focus on plants though and don’t often encounter them. It still seems harder and more involved to analyze the genetics in every case.
1 Like
For identification DNA is used in birds from poop or feathers/blood.
3 Likes
Which is a sort of roundabout way of saying that you need to be aware that an observed variation is not relevant to species identification, I think.
Morphological (or behavioural or physiological etc.) variation that is not heritable is noise not information if the context is differentiating between species. Heritability is (with maybe some exceptions related to things like maternal effects, depending on how you define these things) about genetics.
The barcode tech is not prohibitively expensive and it is a useful tool in a bunch of contexts. It is one of a suite of DNA technologies that have emerged as tools for ecological and environmental work.
1 Like
If you are analysing DNA from faeces, how can you be sure the sequence you are looking at has come from the target organism and not from the gut microbes or the semi-digested food? I suppose you select a sequence that is unique to the target species, but doesn’t that rely on a huge knowledge of the genetics of all the other organisms that could be in the sample?
I’ve asked the same question of an archaeologist who was looking at neanderthal DNA, and his answer was that he didn’t know.
Yeah, it fully should rely on knowing what you’re looking for, but actually they look for fresh feces so there shouldn’t be much more han hwat is living inside the bird.
Currently most DNA sequencing methods do not look at one strand of DNA but many strands of DNA with the same sequence. To go from environmental DNA (with lots of random DNA from many different sequences) to one short sequence with many repeats a method called PCR is used. This amplifies specific segments of DNA by selectively binding a preselected primer. These primers are where the specificity of PCR comes from. Primers are between 15-30 base pairs long and because each base pair can be one of four options the specificity of the primer is very high (4^length of the primer).
For a gene to be interesting it has to be variable but the primer has to start in a conserved region. This is where primer design comes in. By using known sequences and sequences of closely related species primers can be designed to only amplify the desired sequence. On top of that if a read happens and DNA is amplified that has no relationship to what is expected it will be noticed, and attempts can be made to amplify the desired section by redesigning primers.
You know you’re sequencing the right sequence because PCR primers are highly specific and well designed, and because the read can be compared to existing reads from related organisms.
4 Likes
Thanks very much.
John
2 Likes
The interbreeding/unable to interbreed distinction isn’t all that relevant any more. There are far too many cases of hybridization between species, including some widely divergent. An extreme example of this is with American Paddlefish and Russian Sturgeon that have been separated for 184 million years, yet can still hybridize.
The current summary when it comes to species definitions is basically, “Well, it’s complicated.” As a result there are a number of different classifications schemes being used, not all of which include reproductive isolation as the primary distinguishing marker.
-
A brief overview of 26 different ways to define a species - not paywalled
-
Zachos 2016 An Annotated List of Species Concepts - paywalled
4 Likes
Well, sturddlefish seem to be sterile, and usually the biological species concept is more fully defined as “…interbreed and produce fertile offspring”. But I agree that the BSC is much more of a good general guide than an iron law.
2 Likes
I was using that specific example mainly to show that even things separated by large amounts of time that are in different branches of their biological tree can have enough critical similarities remaining to be cross-fertile.
For similar examples that result in reproductively fertile offspring, plants would be the way to go as hybridization resulting in fertile offspring is not unusual. I’m not as familiar with specific examples in the case of plants though.
In primates we see fertile offspring often with macaque hybrids. This is actually a problem where I work, we have fertile hybrids that are Rhesus Macaque x Long-tailed Macaque crosses, and Pig-tailed Macaque x Rhesus Macaque fertile hybrids are known from further south. Within langurs there appear to be fertile hybrids between species, but to my knowledge that hasn’t been studied all that much.
2 Likes
Thanks for destroying my last contact with certainty in non human life forms 
. “It’s complicated” is probably the best way to describe things. I know of two moth species which are so closely related, that only Pheromones - sent out at different times - prevent them from mating in the wild. They will in captivity, and I don’t know if their offspring are fertile or not. I guess I was just wondering how long we could look at something and say ‘it’s x or y’, or whether genetics will take over that aspect.
2 Likes
So even their genitals are ok for each other? Sounds like pretty close species, wonder in which circumstances they split up.
2 Likes
No clue. I didn’t look into it much at the time. Chance? I personally believe that chance - contingency, to quote Stephen Jay Gould - plays a larger role in Life than we recognize.
2 Likes
This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.