Ever since hybrid speciation was discovered, botanists have believed that it plays a constructive part in plants. Recent genetic evidence has shown that hybrid speciation is also common in animals1. Hybrid speciation, one of the evolutionary types, has changed our understanding of the evolution of species.
Natural hybridization happens very rarely but plays a significant role in the evolution of a wide variety of species. Hybrid speciation applies to hybrid species which doubles their chromosome number. Final species initially comprise precisely one genome from each determined, from each parent the contribution is 52%2. This species is new and independent from its parents in terms of reproduction. There are many examples of the nature of hybrid species such as Heliconius butterflies, Passer italiae.
Heliconius is distributed throughout the tropical and subtropical regions of the American continent 3. They have a wide range of colours. Passer italiae, also called the Italian Sparrow, is one of the best-known bird evolutionary intermediates which strays rarely in urban areas. Besides, hybridization has a controversy with Darwin’s thought; because that violates reproductive isolation4. Since species are adapted to their particular niche and hybrid offspring are more or less an intermediate mix of the characters of their parents, hybrids are less suited to the parents’ niche and therefore less likely to survive. As a result, hybrids tend to disappear over time. But in the very rare cases where a hybrid species is more adapted to a particular niche than either parent species, the hybrid may replace one or both parent species or establish its own place5.

The most persistent hybrid strains have the same number of chromosomes as both parent types. This means that both parent types must be closely related to avoiding the genetic and developmental problems associated with unpaired chromosomes in their hybrid offspring. This form of hybridization, known as homoploid hybrid speciation, is most common among animals6. However, the most famous mammalian hybrid, mule, is the offspring of a horse and a donkey with different numbers of chromosomes, thus the hybrids are infertile7. The most complete evidence is the desert sunflowers. Helianthus anomalus, Helianthus deserticola and Helianthus paradoxus are homoploid hybrids between Helianthus annuus and Helianthus petiolaris. Those hybrid species exhibit complementary and favorably interacting gene combinations, making them superior to their parents in extreme habitats8.
Stalvin’s prion of the genus Pachyptila is a small group of closely related seabirds of the same ancestry (“monophletic”). They roam throughout the Antarctic Ocean, and it is noticeable that they all look remarkably alike, especially when seen up close, windswept sub-Antarctic seas. Some research have been carried out by Dr. Masello, Professor Moodley, and colleagues to finally find out exactly how many Pachyptila species there are.

Salvin’s prion differs not only in where and when they breed but also in their beaks. Indeed, the length, width, and height of beaks are crucial to efficient foraging. Therefore, it is possible to distinguish Pachyptila prion species by their appearance alone, by carefully examining their beaks: Three of the six species in the genus have flattened which, like baleen whales, act as a strainer for holding small fishes. Dr. Masello, Professor Moodley, and colleagues measured the size of the beaks of all birds in all six Pachyptila species, they found no overlap between any of the species9. This study shows that interspecies hybridization does not have to be the end of the evolutionary process and that sometimes a new species can arise in this way.
References:
- Mallet, James. “Hybrid speciation.” Nature7133 (2007): 279-283.
- Chapman, Mark A., and John M. Burke. “Genetic divergence and hybrid speciation.” Evolution: International Journal of Organic Evolution7 (2007): 1773-1780.
- Mallet, James, et al. “Natural hybridization in heliconiine butterflies: the species boundary as a continuum.” BMC evolutionary biology1 (2007): 1-16.
- Abbott, Richard, et al. “Hybridization and speciation.” Journal of evolutionary biology2 (2013): 229-246.
- Flegr, Jaroslav. “Microevolutionary, macroevolutionary, ecological and taxonomical implications of punctuational theories of adaptive evolution.” Biology Direct1 (2013): 1-14.
- Schumer, Molly, Gil G. Rosenthal, and Peter Andolfatto. “How common is homoploid hybrid speciation?.” Evolution6 (2014): 1553-1560.
- Short, R. V. “An introduction to mammalian interspecific hybrids.” Journal of Heredity5 (1997): 355-357.
- Nolte, Arne W., and Diethard Tautz. “Understanding the onset of hybrid speciation.” Trends in Genetics2 (2010): 54-58.
- Masello, Juan F., et al. “Additive traits lead to feeding advantage and reproductive isolation, promoting homoploid hybrid speciation.” Molecular Biology and Evolution8 (2019): 1671-1685.
Figure References:
- https://elegantentomology.weebly.com/heliconius-butterfly.html
- https://ebird.org/species/brbpri1?siteLanguage=tr
Inspector: Meryem Melisa KAR