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In regards to 'species'

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In regards to 'species'

Postby Deflare » Wed Jan 26, 2005 6:58 am

So far, my understanding of the definiton of 'species' is that it means a classification of organisms (animals, in this case) that are only able to create reproductively viable offspring with other members of its species. However, well-known concepts in zoology and, presumably, other life sciences disprove this.

Grey wolves (Canis lupus) are, as far as I'm aware, capable of creating reproductively viable offspring with other canine species (ex. Canis familiaris and Canis rufus). In addition, in another post on this forum it says that a lion/tiger hybrid was capable of producing offspring with another hybrid or a lion or tiger (too lazy to check the details).

So, what's the answer? At this rate, it seems like genus is the cutoff point for reproductively viable offspring. Is this the case, or is it a different issue entirely?
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Postby biostudent84 » Thu Jan 27, 2005 12:04 am

For the most part, species is the cutoff for viable species cutoff. However, in biology, exceptions are more constant than rules are. =)

You've listed a number of exceptions.
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Postby Deflare » Thu Jan 27, 2005 12:06 am

Ah, thank you. However, if these species are capable of producing viable offspring, then doesn't that beg the question of whether or not they should be categorized as seperate species?
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Postby biostudent84 » Thu Jan 27, 2005 3:59 pm

Ability to reproduce is just one of the variables that make up a species. Remeber that when we humans categorize nature, there are always gray areas. Biology is more overlap than not, and we could never make a perfect system of classification.
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Postby Deflare » Fri Jan 28, 2005 12:34 am

Thank you for your help; this issue had been irritating me for a while. I will now continue along my merry way.
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Postby mith » Fri Jan 28, 2005 8:39 pm

also note that sometimes it's not ethically or practically possible to test breed. Plants, bacteria or even humans cause some problems if we're only looking for a sexual reproduction cutoff.
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Postby biostudent84 » Thu Feb 03, 2005 9:45 pm

Agreed, Mithrilhack. One of the darkest parts of biology is the source of the majority of knowledge of human genetics. Expirements on humans during the Holocaust taught us more about ourselves than anyone cares to admit.

Today, we take a more ethical approach. When we study the effects of genetics, we primarily examine twins. While they are genetically identical, they are enviornmentally different. Even before birth, the twins' enviornments are different...one is on the left, the other is on the right. Twin Studies, as they are called, have given us a great deal of knowledge over what genetics effect combined with what enviornment effects.
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Postby Canaduck_89 » Sat May 07, 2005 8:15 am

Biostudent...
I think what you're talking about is really interesting. Do you think you could elaborate for the sake of my curiosity? :P
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Re: In regards to 'species'

Postby clarence » Thu May 19, 2005 12:07 pm

Deflare wrote:So far, my understanding of the definiton of 'species' is that it means a classification of organisms (animals, in this case) that are only able to create reproductively viable offspring with other members of its species. However, well-known concepts in zoology and, presumably, other life sciences disprove this.

Grey wolves (Canis lupus) are, as far as I'm aware, capable of creating reproductively viable offspring with other canine species (ex. Canis familiaris and Canis rufus). In addition, in another post on this forum it says that a lion/tiger hybrid was capable of producing offspring with another hybrid or a lion or tiger (too lazy to check the details).

So, what's the answer? At this rate, it seems like genus is the cutoff point for reproductively viable offspring. Is this the case, or is it a different issue entirely?


Species are expected often to have fuzzy and imprecise boundaries because evolution is ongoing. Some species are in the process of forming; others are recently formed and still difficult to interpret. The complexities of biology add further complications. Many pairs of species remain distinct despite a small amount of hybridization between them. Some groups are asexual or frequently produce asexual strains, so how many species to split them into becomes problematical.

There are different species definitions used by biologists, none of them mutually exclusive. The most used is the Biological Species Concept that you have just said. Another one is the Phenetic (or Morphological) Species Concept. Cronquist, one of the famous contemporary plant taxonomists, defines this as "... the smallest groups that are consistently and persistently distinct and distinguishable by ordinary means.", "ordinary means" includes any techniques that are widely available, cheap and relatively easy to apply, relative to the organism. Still another one is the Phylogenetic Species Concept. Species is defined as the smallest cluster of organisms that possesses at least one diagnostic character, may be morphological, biochemical or molecular and must be fixed in reproductively cohesive units. Each of these species concepts has its own criticisms. For example, the biological species concept is problematic because of interspecific hybridization between clearly delimited species, as you have just said. These different definitions of species serve different purposes. Species concepts are used both as taxonomic units, for identification and classification, and as theoretical concepts, for modeling and explaining. There is a great deal of overlap between the two purposes, but a definition that serves one is not necessarily the best for the other. Furthermore, there are practical considerations that call for different species criteria as well. Species definitions applied to fossils, for example, cannot be based on genetics or behavior because those traits do not fossilize. The biological species concept has been very successful as a theoretical model for explaining most species differences. This can lead us to glibly assert its universal applicability, despite its irrelevance to many groups. We need to always ask the question which species definition is the most reasonable for a group of organisms in question.

I hope this helps.
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Re: In regards to 'species'

Postby Shaun » Mon May 23, 2005 2:28 pm

I will read forum rule #5
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Postby clarence » Sat May 28, 2005 6:15 pm

Here's more information on the red wolf, Canis rufus.

Wayne and Jenks, in a recent Nature, present a study of the mtDNA(mitochondrial DNA) of the endangered red wolf, Canis rufus. This species, once extending over a large range in the southeast, is now extinct in the wild. The authors examined the mtDNA sequence of red wolves (zoo animals and from DNA obtained from museum pelts from 1905 to 1930) as well as grey wolves and coyotes. (The red wolf occurred only in regions where grey wolves and coyotes were.)

When they analysed the red wolf sequences, they found that the mtDNA was either of grey wolf type or coyote type. This (along with the geographic information) lead them to conclude that the "species" red wolf is (was) actually a hybrid of the grey wolf and the coyote.

It is also found out that Grey wolves and coyotes have overlapping ranges in the northern US, but the red wolf phenotype is not present in hybrids in the north. The red wolf phenotype is not only a product of the hybridization, but of environment as well.

Source:

Wayne and Jenks, 1991, Mitochondrial DNA analysis implying extensive hybridization of the endangered red wolf Canis rufus, Nature 351: 565 - 567
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