Fish and Wildlife Service's Forensics Laboratory. Her lab is responsible for identifying any animal remains or products that are suspected to have been illegally traded or harvested.
Since adopting DNA sequencing techniques more than 20 years ago, the lab has been able to make identifications much more rapidly, and increase the number of species it can reliably recognize by the hundreds.
The lab receives slabs of unidentified meat, crafted decorative items or even the stomach contents of other animals. Identifying these unusual items is usually out of the reach of taxonomic experts using body shape, hair identification and other physical characteristics. Still, Curtis, who previously studied fishes, doesn't discount the importance of traditional taxonomists.
Experienced taxonomists can often quickly identify recognizable cases, leaving the more expensive DNA sequencing for the situations that really need it. Not all ecologists are sold on these advances. Some express concerns about " taxonomic inflation ," as the number of species identified or reclassified continues to skyrocket.
They worry that as scientists draw lines based on the narrow shades of difference that DNA technology enables them to see, the entire concept of a species is being diluted. Wilting had proposed condensing tigers into just two subspecies , from the current nine. Other scientists are concerned about the effects that reclassifying once-distinct species can have on conservation efforts. In , the endangered dusky seaside sparrow, a small bird once found in Florida, missed out on potentially helpful conservation assistance by being reclassified as a subspecies of the much more populous seaside sparrow.
Less than two decades later, the dusky seaside sparrow was extinct. But he does expect that DNA technology will have a significant impact on disrupting and reshaping the work of those fields. This uncertainty is in many ways reflective of the definition of species today too, Hilton-Taylor says.
Subtle differences in appearance led to the designation of nine different sub species instead. Interbreeding is key to the biological species concept, which defines a species as members of populations that can interbreed with each other to produce viable offspring. The offspring of different giraffe mixes were viable, so everyone assumed giraffes were all members of the same species. The problem is that hybridization between species is quite common. In response, some researchers define species on the basis of morphological differences.
Exhaustive physical analysis of a specimen is required before an organism is officially a new species. Even then there is wiggle room. In a debate dating back to botanist and Darwin contemporary Joseph Hooker , taxonomists argued about the murky criteria for a new species.
Conservative lumpers, like Hooker and Darwin, were far more hesitant to identify new species. Splitters had no such reticence and were willing to assign species based on slight differences. A group of plants, for example, might be 10 species according to lumpers and 50 according to splitters. Privacy Policy Contact Us You may unsubscribe at any time by clicking on the provided link on any marketing message. DNA sequencing has brought us the genetic species concept.
In this model, species are defined by genetic isolation rather than reproductive isolation. Species may be more or less identical morphologically but differences in DNA determine if a population is a separate species or not. The rest of the genetic hereditary information is passed on through the autosomes. When the researchers mapped the factors that cause hybrid males to become sterile, they found that there were many more incompatibility factors on the X allosome compared to the autosomes.
This means that sex chromosomes become functionally different between species much faster than non-sex chromosomes, Presgraves says.
But what is it that makes sex chromosomes accumulate genetic incompatibility faster than the rest of the genome? The researchers found that a class of "selfish genes" called meiotic drive elements are responsible for making sex chromosomes genetically incompatible at a faster rate.
In general, selfish genes are parasites of the genome—they propagate themselves at the expense of other genes. Meiotic drive elements in particular sabotage the rules of typical inheritance: in normal Mendelian inheritance, a gene is transmitted to half the offspring. Meiotic drive elements, however, manipulate reproduction so they can transmit themselves to more than their fair share of the genome. In hybrid male fruit flies, meiotic drive elements usually kill any sperm that don't carry them, leaving only or mostly sperm that do carry the meiotic drive elements.
In a twist, however, the researchers also found that if meiotic drive elements are able to experience gene flow, they can also help bring species together. During early speciation, when two different species are just beginning to break away from one another, reproductive incompatibility can be incomplete and "leaky"—some part of the genome may still be compatible and exchangeable.
If the species interbreeds and this selfish gene is able to be passed down, instead of becoming incompatible, "that part of the genome will become perfectly exchangeable.
In some cases a selfish gene will basically erase the build-up of incompatibilities for a part of the genome. That is, meiotic drive elements can cause incompatibilities between species if they do not experience gene flow, or they can cause a convergence of the species, if they species does experience gene flow. A major factor in determining whether or not a species is compatible hinges on whether or not there is gene flow between the species , Presgraves says.
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