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Table 2 Many of the documented examples of speciation in natural species fit the proposed model.

From: The existence of species rests on a metastable equilibrium between inbreeding and outbreeding. An essay on the close relationship between speciation, inbreeding and recessive mutations

Species Nature of the phenotype associated to speciation Population structure and mutation load
Fish   
Salmonidae   Highly philopatric
Studies on MHC give conflicting results suggesting optimal outbreeding model
Cichlids Bright colours typical of species are recessive (disappear in hybrids) Close preference for kin, with no detectable inbreeding depression
Sticklebacks EDA mutation (armour plate loss) is completely recessive
Pitx1 mutation (loss of pelvic structures) is recessive
Studies on MHC support optimal outbreeding model
Panmictic species (cod, macquerel, tuna...)   Susceptible to large and unpredictable fluctuations in numbers
Birds   Migrating birds are highly philopatric
Quail   Preferential mating among cousins (led to Bateson's optimal oubreeding)
Darwin's finches   High inbreeding coefficient due to small size of the niche
Mammals   Rate of speciation inversely related to the effective size of populations
Mice and rats   Very fragmented populations correlates with capacity to inbreed
Pikas   Optimal outbreeding
Insects   
Haplodiploids (bees, ants, termites)   Very low mutations loads correlate with very high species richness, and global ecological success
Drosophila Mating preferences are recessive (disappear in F1) Assortative mating, and chromosomal rearrangements are more prominent between populations that are in close contact in the wild.
H. Carson highlighted the correlation of speciation with small populations based mostly on data from drosophila.
Apple maggot fly Fruit preference is recessive (disappears in F1)  
Heliconius mimetic butterflies Sexual preference of the males is asymmetric, and linked to the recessive yellow colour  
Plants   Selfing plants undergo more speciation, but the species go extinct more quickly
Monkey flowers The red derived phenotype is recessive to the pink ancestral one  
  1. Please refer to text in section V for relevant bibliographic references