If asexual reproduction survives at all, conditions must sometimes favor it, even in competition for a niche with sexually reproducing species. Some insects, like aphids, are both asexual and sexual reproducers. Though rare, those species that reproduce asexually tend to persist.

Efficiency, for one thing, is on the side of asexual organisms: Without the need for males, every clonal individual passes a full set of identical genes onto the next generation. In addition, a single female can establish a new population. This gives asexual creatures on the fringes of a habitat an edge in colonizing a new one.

Clonal organisms with tolerance for a broad range of conditions also exist. Even if they do not vary much genetically, they possess what scientists have dubbed "general-purpose genotypes." One example is a type of minnow found in Minnesota that tolerates both highly oxygenated and poorly oxygenated waters. Able to survive in an unpredictable environment, this minnow outlasts more specialized strains.

Asexual animals arose from diversified sexually reproducing ancestors. Often they are hybrids between two different species, and may possess two complete sets of chromosomes.

One such asexual organism is the whiptail lizard in the U.S. Southwest, Mexico, and South America, which consists only of females who reproduce by parthenogenesis. They appear to be the only known unisexual reptile.

Clones generally hit a dead end, going extinct when their limited variation collides with changing environmental conditions or with better-surviving sexual reproducers. With their unusual way of reproducing, they continue to fascinate scientists because they are natural experiments in interactions between fixed genotypes and varying environments.

Can sex earn its keep?

It would seem best to reproduce asexually or be a hybrid of some sort. However, some scientists have come up with a theory about why sexual reproduction is still needed from an evolutionary standpoint. Rather than correcting mutations or diversity that occurs during sexual reproduction, it may be better to allow those mistakes to occur, then "remove" them later - like through natural selection.

However, the problem is the speed at which asexual individuals reproduce. A sexually reproducing population could inevitably be driven extinct by the asexual organism's productivity in producing offspring. A new hypothesis has come out - the Red Queen Hypothesis - coined from Alice In Wonderland: "It takes all the running you can do, to keep in the same place."

This describes the never-ending interaction between hosts and disease, or predator and prey. As species that live at each other's expense continue to evolve, they are engaged in a constant struggle for survival advantage as their environment is constantly changing. So, this means sexual reproduction is needed. Those mutations or the genetic diversity from the mixing of the gametes allows new traits to appear that could help fight disease or evade predators.

Think about our example of sickle cell in humans - this is a detrimental disease that, according to evolution by natural selection, should have died out. But, it persists, as this is the method by which humans have to fight off malarial infections in certain regions of the world. If organisms only reproduce asexually and did not have the sickle cell allele, they would all die from malarial infection.

So, each type of strategy is useful from the context of evolution and natural selection. As we've seen repeatedly, this is mostly dependent on the environmental conditions of the organism and how their traits allow them to either survive in that environment, or die.

From:http://www.pbs.org/wgbh/evolution/library/01/5/l_015_01.html

Asexual Reproduction Use the information and data provided to answer the question. You will also need to refute (reject) the alternative claim given using information from your initial background reading at the beginning of the lesson. The Deepwater Horizon drilling unit in the Gulf of Mexico exploded on April 20, 2010, leading to the blowout of one of the wells. This resulted in the release of 50,000 to 70,000 barrels of oil and natural gas per day into the water from April 20 to June 4. Oil and natural gas are primarily made up of hydrocarbons, which are molecules composed of hydrogen and carbon. As oil was released, large hydrocarbon plumes formed in the deep waters of the gulf. On June 4, the oil flowing from the well was partially captured, reducing the leak rate to about 60% of the original rate. After 83 days, the well was completely shut in, halting the leak. The plumes stimulated the growth of naturally occurring bacteria that use hydrocarbons as fuel to grow and reproduce. In the process, they break down the hydrocarbons into smaller molecules, thereby degrading the hydrocarbons into components that in turn feed other microbe communities. Researchers observed the succession of the enriched bacteria populations using data from before, during and after the 83-day spill. Relative abundance of bacterial taxa (groups) over time was used to determine microbial response and the potential for biodegradation of the oil spill. The graph and chart below describes the populations over time, and some of the roles of each of the bacterial taxa (groups) studied.partial capture of oil well shut-in Oceanospirillaceae Pseudomonas Colwellia Cycloclasticus Pseudoalteromonas Methylomonas Piscirickettsiaceae Alteromonadaceae Flavobacteriaceae Rhodobacteraceae Saprospiraceae 7-Jul 5-Jun 15-Jul 23-Jul 31-Jul 8-Aug 13-Jun 29-Jun 21-Jun 16-Aug 24-Aug 28-May Caption: The bacterial taxa that were overabundant in oil plumes during and after the Deepwater Horizon oil spill in the Gulf of Mexico. The gray bars indicate the time periods when the abundance of bacterial taxa was "enriched" (> 2 times the prespill abundance in that area). The time period between the green and blue lines is when oil was being partially captured, reducing oil inputs by over 50%. The time period after the blue line is when the oil well was completely shut in and the flow of oil into the gulf ceased. Microbe Consumes/breaks down Oceanospirillales, Pseudomonas linear-chain hydrocarbons (6 or more carbons) Colwellia, Cycloclasticus, and Pseudoalteromonas cyclic hydrocarbons (harder to break down than linear bonds) Methylomonas methane (most abundant hydrocarbon released in spill) Piscirickettsiaceae methanol and/or formaldehyde (produced by Alteromonadaceae) Flavobacteriaceae, Alteromonadaceae, and complex organic matter (e.g., bacteria) RhodobacteraceaeExplanation Tool Question: What is the scientific question you are investigating? How do different types of reproductive strategies influence evolution? Evidence Scientific Reasoning What are the science observations or data that How can you explain the evidence you have address/relate to your question? observed/collected to answer the question? Alternative Claim Evidence to Refute Claim Sexual reproduction is the best strategy for organisms to survive. Claim What claim can you make that answers the question, based on your evidence, reasoning and science concept(s)? Single sentence without using the word "because" in your sentence. Construct a Scientific Explanation Using the information in the boxes you have completed, write a scientific explanation that includes: The scientific question Your Claim - and the alternative claim you are refuting/rejecting Relevant evidence that supports your claim - and evidence that refutes the alternative claim Scientific reasoning that links the evidence to your claim and explains how the evidence answers the question Scientific Explanation