It is my ongoing goal to explain, in common terms, what it is that I'm doing with this half-decade in graduate school. To that end, I'm hoping to make everyone familiar with certain terms; once you understand them, they're no longer over-your-head jargon! So every so often at the Gametophyte Junction we'll hop on the definition train. First up: sympatry.
Sympatry, like many biology terms, is a word derived from Greek: sym/syn- (meaning same), -patry (meaning fatherland). Two species are therefore sym-patric when they share the same fatherland; they have ranges which overlap. The opposite of sympatry is allopatry, meaning different-fatherland, and describes two species which have non-overlapping ranges. In between is parapatric, meaning adjacent-fatherland, and implying that the ranges of two species share a border (like two countries), or sometimes they have a narrow overlap range.
The concept of sympatry is important because of gene flow and speciation (the formation of new species). Initially, new species start out as populations, freely exchanging genes throughout the generations. The principles of population genetics have taught us that when a population has free gene flow, it is very tough to have different varieties. When a new variety emerges, three things usually happen: 1) The new variety is more adapted to the environment, and spreads quickly, wiping out the older varieties. 2) The new variety is less adapted to the environment, and vanishes quickly. 3) The new variety is neutral with respect to how adapted to the environment it is, and these varieties fluctuate until they are eventually lost or adopted by the whole population.
Species, meanwhile, under the Biological Species Concept, are not just observed by their separate and discontinuous variety. To achieve this discontinuity, there must be some barrier to gene flow between the population with the new variety and the other populations. Typically, this is done in allopatry- some geographic barrier (like a mountain or a body of water) separates two populations for an extended period of time. During this time, the two populations adapt to environments that are almost certainly different. These different adaptations may also change the organism in such a way that if the barrier were removed (a gap in the mountain, land bridge over the body of water), the two populations may have trouble mating. This creates the barrier to gene flow.
You'll notice that when the barrier is removed, the two populations are now in sympatry. It is usually at this point that species are truly formed- when two populations have reduced gene flow among them in sympatry. On a practical level, this manifests usually as "hybrid breakdown." Most people are familiar with the mule- it is an offspring of a horse and a donkey, but the mule itself is sterile. Because the horse and donkey adapted to different environments, they evolved genes that are slightly incompatible; enough to create a live child but one that is sterile. Having sterile offspring is definitely a barrier to gene flow. It is also a waste of resources, and natural selection typically leads such populations to methods of avoiding creating these bad hybrids. Animals recognize members of their own species through sight and sound; plants change pollinators or chemicals on the surfaces of gametes in an effort to only use precious reproduction resources on making good children.
What does this have to do with me? Well, by and large most of the work on mosses has not been under the Biological Species Concept. Bryologists over the years have been guided by the principles of taxonomy, grouping organisms in to species and genera and families based on similar characteristics. Whether two moss species have any barriers to gene flow is largely unknown. So it is entirely possible that the two species I'm studying, Funaria hygrometrica and Funaria flavicans, actually exchange genes. If so, then they are, in my opinion, one species. I'm bringing this up in part because of the following picture:
This was from my field trip, taken near Dillwyn, Virginia. The green capsules are F. hygrometrica and the smaller red capsules are F. flavicans. They are growing right next to each other, sympatrically. This is not a unique finding, my advisor wrote a paper in 1992 describing a mine site which had both species and what appeared to be intermediates. However, no DNA work was done to determine if there were hybrid plants. Some of the questions that intrigue me include:
Do the two species hybridize? If not, what barrier to gene flow separates them?
If hybrids form, are they less "fit" than their parents?
What genes control the separation of the species? Are there many genes or just a few?
For example, the F. flavicans in the picture above are red because they matured earlier than F. hygrometrica. Timing in plant matings are very important; if hybrids between the species were to mature at some intermediate time, they may not find many mates. That would make them less "fit" because "number of offspring" is the definition of fitness.
That's all for now; as always, feel free to ask questions if there's something unclear. I'm always willing to find new ways to explain things!
Sympatry, like many biology terms, is a word derived from Greek: sym/syn- (meaning same), -patry (meaning fatherland). Two species are therefore sym-patric when they share the same fatherland; they have ranges which overlap. The opposite of sympatry is allopatry, meaning different-fatherland, and describes two species which have non-overlapping ranges. In between is parapatric, meaning adjacent-fatherland, and implying that the ranges of two species share a border (like two countries), or sometimes they have a narrow overlap range.
The concept of sympatry is important because of gene flow and speciation (the formation of new species). Initially, new species start out as populations, freely exchanging genes throughout the generations. The principles of population genetics have taught us that when a population has free gene flow, it is very tough to have different varieties. When a new variety emerges, three things usually happen: 1) The new variety is more adapted to the environment, and spreads quickly, wiping out the older varieties. 2) The new variety is less adapted to the environment, and vanishes quickly. 3) The new variety is neutral with respect to how adapted to the environment it is, and these varieties fluctuate until they are eventually lost or adopted by the whole population.
Species, meanwhile, under the Biological Species Concept, are not just observed by their separate and discontinuous variety. To achieve this discontinuity, there must be some barrier to gene flow between the population with the new variety and the other populations. Typically, this is done in allopatry- some geographic barrier (like a mountain or a body of water) separates two populations for an extended period of time. During this time, the two populations adapt to environments that are almost certainly different. These different adaptations may also change the organism in such a way that if the barrier were removed (a gap in the mountain, land bridge over the body of water), the two populations may have trouble mating. This creates the barrier to gene flow.
You'll notice that when the barrier is removed, the two populations are now in sympatry. It is usually at this point that species are truly formed- when two populations have reduced gene flow among them in sympatry. On a practical level, this manifests usually as "hybrid breakdown." Most people are familiar with the mule- it is an offspring of a horse and a donkey, but the mule itself is sterile. Because the horse and donkey adapted to different environments, they evolved genes that are slightly incompatible; enough to create a live child but one that is sterile. Having sterile offspring is definitely a barrier to gene flow. It is also a waste of resources, and natural selection typically leads such populations to methods of avoiding creating these bad hybrids. Animals recognize members of their own species through sight and sound; plants change pollinators or chemicals on the surfaces of gametes in an effort to only use precious reproduction resources on making good children.
What does this have to do with me? Well, by and large most of the work on mosses has not been under the Biological Species Concept. Bryologists over the years have been guided by the principles of taxonomy, grouping organisms in to species and genera and families based on similar characteristics. Whether two moss species have any barriers to gene flow is largely unknown. So it is entirely possible that the two species I'm studying, Funaria hygrometrica and Funaria flavicans, actually exchange genes. If so, then they are, in my opinion, one species. I'm bringing this up in part because of the following picture:
This was from my field trip, taken near Dillwyn, Virginia. The green capsules are F. hygrometrica and the smaller red capsules are F. flavicans. They are growing right next to each other, sympatrically. This is not a unique finding, my advisor wrote a paper in 1992 describing a mine site which had both species and what appeared to be intermediates. However, no DNA work was done to determine if there were hybrid plants. Some of the questions that intrigue me include:
Do the two species hybridize? If not, what barrier to gene flow separates them?
If hybrids form, are they less "fit" than their parents?
What genes control the separation of the species? Are there many genes or just a few?
For example, the F. flavicans in the picture above are red because they matured earlier than F. hygrometrica. Timing in plant matings are very important; if hybrids between the species were to mature at some intermediate time, they may not find many mates. That would make them less "fit" because "number of offspring" is the definition of fitness.
That's all for now; as always, feel free to ask questions if there's something unclear. I'm always willing to find new ways to explain things!
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