Ecological speciation involves divergent natural selection where isolation occurs in prezygotic or postzygotic from drive divergence in phenotypic traits through to reinforcement. The proximate basis of reduced hybrid fitness takes the form of ecological selection, genetic incompatibility, and sexual incompatibility while, in other non-ecological speciation mechanisms, the process occurs from genetic incompatibility to sexual incompatibility.
Reinforcement is the process through which ecological speciation takes place, for instance; it can occur indirectly as a result of natural selection on morphological, behavioral, or physiological traits. It can also take place through direct selection on pre-mating isolation.
Direct speciation occurs through direct selection on pre-mating isolation, as opposed to consequential of natural selection on behavioral, morphological, or physiological traits.
From the figure, it is clearly evident that the divergent selection generates body size differences that result in predation of larger agents on the smaller species. The evolution of behavioral defenses in these smaller species reduces the frequency of possible crossbreeding as a by-product. This acts as a possible basis for enhanced pre-mating isolation in which females of the larger species start preying upon eggs guarded by the males of, the smaller species.
Ecological speciation processes occur when reproductive isolation evolves ultimately as a result of divergent selection on traits between environments and interactions with other species. Ecological speciation that is driven by sexual selection is ecological when it comes about as a result of divergent selection on traits between environments such as resources and physical structures and non-ecological when it is brought about by interactions with other species, for example, predation and resource competition.
Populations can be distinguished by unique combination of ecotypes and mating types. Males and females mating types match with one another through evolutionary dynamics.
Through divergent agents, selection evolution of reproductive isolation in populations strengthens selection through secondary contact. Other agents of selection that develop from interactions between drive reproductive isolation to completion. For instance, the competition for resources between the sympatric populations could lead to exaggerated divergence among phenotypes, and further enhance the reproductive isolation like a by-product.
Studies have demonstrated that negative epistasis between host microbiome and host genes accelerate the evolution of hybrid sterility and lethality. This follows the idea that phylosymbiotic gut microbiome within the species breaks down in hybrids via epistatic interactions between the nuclear and microbiome leading to hybrid lethality. Laboratory experiments of hybrids that would be expected to show severe lethality under conventional conditions indicate a striking increase in survival. Again, 39.7% of immune genes were underexpressed by the twofold in germ-free hybrids relative to inoculated and conventional hybrids while 4.9% were overexpressed.
This type of speciation is non-ecological. This is because ecological speciation that is driven by sexual selection is ecological when it comes about as a result of divergent selection on traits between environments such as resources and physical structures and non-ecological when it is brought about by interactions with other species, for example, predation and resource competition.
Sequential radiation is the chain of reactions of speciation events across the different trophic levels brought about by the emergence of new species which create new niches for other species to exploit.
Gene flow among Rhagoletis flies is subject to critical ecological barrier resulting from the diapauses life-history differences. The differences in the timing of eclosion of sympatric blueberry, hawthorn, and apple flies as adults at different times in the summer or spring which also matches the timing of the ripening of host plant fruits can isolate the flies. This is also made possible by the fact that the Rhagoletis flies have one generation per year and live for a period of one month in the field. Similar occurrences exist for the D. alloeum especially in apple, hawthorn, and blueberry wasps. The only one not found to have similar results was the late fruiting apple from Dowagiac MI site where the apple wasps have relatively late mean eclosion time of 112.9 days. The mean longevity of the adult D. alloeum was as less than 2 weeks in the laboratory. Eclosion time differences, based on the assumption that wasps have a similar lifespan, seasonal overlap and opportunities for mating between the apple and blue apple wasps at the sympatric Fennville site by 28.9%, between hawthorn and apple by 29.8%, and between hawthorn and blueberry wasps by 74.5%.