Hi Cassandra,

Several factors can lead to sympatric speciation and there is a bunch of literature on this. Working mainly on fish, I can only think of the "Sebastes" complex both in North Atlantic and Pacific, where it has been shown that depth, in these cases, lead to sympatric speciation. But I'm pretty sure there are other examples.

Hi!

If you come to sympatric speciation, new species evolve from single ancestral species that are inhabiting same geographic area. Further it is divided into two types allopatric and parapatric

Main factor that leads to sympatric specification is Resource Polymorphism (RP) or Trophic polymorphism that means polymorphism related to diet. It is predominantly observed in fish, amphibians and birds.

Mechanisms that generate and maintain RP provides insight into the role of natural selection driving phenotypic, behavioral, life history diversification which ultimately leads to speciation.

Factors that leads to resource polymorphism are differences of prey utilization and structurally contrasting habitats. RP can be induced by phenotypic plasticity or genetic differences or both.

Fish are the best examples for resource polymorphism. These fish are common in the lakes of glaciated areas of northern hemisphere (10,000-15,000 yrs). The best example what I studied is arctic charr (Salvelinus alpinus) occur in lake Thingavallavatn, Reykjavik, Iceland, a system reflecting rapid changes in the last 10 thousand years. Where you see 4 morphs. Cichlids also the best example.

I am attaching one article for your information.

Evolutionary Significance of Resource Polymorphisms in Fishes, Amphibians, and Birds

vast literature is available

SS Snorrason et.al. Bio. Journal of Linn. Society 1994, 52:1-18

HJ Malmquist Oecologia 1992, 92:354-361

Odd Terje Sandlund et.al. Oikos 64:305-351 Copenhagen 1992

Skulason et.al. Bio. Jourl.of Linn.Society 1989, 38:281-301

Genetic and developmental basis of cichlid trophic diversity, Heredity (2006) 97, 211–221

Polymorphism and speciation in Arctic charr, Journal of Fish Biology (2001) 58, 605–638 etc.etc.

Much of the research on sympatric speciation has also taken place in insects, particularly species of herbivores associated with particular plants and species of parasitoids associated with particular insects. I agree with Jetty that it is primarily associated with resource partitioning with a genetic basis (I haven't heard of resource polymorphisms before). Because of that ecological association and our inability to go back in time to know whether the ancestral divergent populations were in the same location or not, "sympatric speciation" has fallen out of favor to instead refer to "ecological speciation".

Hi Cassandra

Among others I want to stress upon two very important factors influencing the occurrence of sympatric speciation. These are:

1. Intense mate selection is basic to bring about sympatric speciation.

2. Resource distribution is bimodal and competition is less among the phenotypes.

Please see

1. H. D. Rundle, L. Nagel, J. W. Boughman, and D. Schluter, “Natural selection and parallel speciation in sympatric sticklebacks,” Science, vol. 287, no. 5451, pp. 306–308, 2000.

2. http://www.hindawi.com/journals/ijeco/2012/235010/

3. A. P.Michel, S. Sim, T. H. Q. Powell,M. S. Taylor, P. Nosil, and J. L. Feder, “Widespread genomic divergence during sympatric speciation,” Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 21, pp. 9724–9729, 2010.

Best

Dola