I wonder whether hybrids actually retain both maternal and paternal COI, and if it is the case, are both genes expressed simultaneously? I mean- if we use COI for the species identification - whether the hybrid be allocated as belonging to one of the parental species or to be identifiable as a hybrid?
If the mitochondrial inherance is exclusively matrilinear, your hybrids barcodes should match the mother species, not the father. Here, I attach you and example of what happen with a nemertean species which only can reproduce by fissiparity and has an hybrid origin: barcodes only matched one of the species.
Fernando is absolutely correct: for mammals, and most animals, mitochondrial DNA is inherited maternally. If only COI is being sequenced, then a hybrid should assign to the species of its mother. With mtDNA alone, there is no way to identify a "hybrid": it will just assign to one of the two parental species.
Now, if you can determine it is a hybrid based on phenotype, then mtDNA can reveal the maternal species. Nuclear markers are required to determine whether an individual is a hybrid and the relative contributions of each species.
Here is some literature on the subject.
Article An efficient method for screening fecal DNA genotypes and de...
Article Assessing the prevalence of hybridization between sympatric ...
https://doi.org/10.1577/1548-8659(2002)131%3C0772:EOIHBB%3E2.0.CO;2
Article DNA barcoding: promise and pitfalls. PLoS Biol 2:28-39
Article Hybridization relics complicate barcode-based identification...
Except for rare cases (some bivalves for instance) mitochondria are inherited in a matrilinear way and haybrids have the mitochondrial DNA of the "mother species". This fact has been used to show that hybridization frequently (mostly) is unidirectional. See this pdf.
As mentioned, mtDNA inheritance is usually uniparental, far mostly matrilineal, and this is achieved by diverse mechanisms. Nonetheless, some organisms (including some humans) are heteroplasmic as result of the sperm mtDNA leakage, and hybridization increases the probability of the paternal mtDNA leakage into the new zygote (see Article Extensive mitochondrial heteroplasmy in hybrid water frog ( ...
).So, it depends on the organism, and the particular question you're interested in.
For example, in our study of fish hybrid zone, we assumed the matrilineal mtDNA inheritance.
Article Rare and asymmetrical hybridization of the endemic Barbus ca...
Zdeněk Lajbner Thank you Zdenek. I am interested in how it might happen in cephalopods. To my best knowledge cephalopod hybrids are not known. Am I wrong?
there are very few examples of supposed cephalopod hybrids, both recent and extinct
These are:
- Illex (O’Dor, Lipinski, 1998; Roper et al., 1998)
O’Dor R.K., Lipinski M.R. The genus Illex (Cephalopoda; Ommastrephidae): Characteristics, distribution and fi sheries // In: P. Rodhouse, E. Dawe & R. O’Dor (eds). Squid recruiment dynamics. The genus Illex as a model, the commercial Illex species and infl uences on variability. FAO Fisheries Techn. Pap. 1998. № 376. P.1–8.
Roper C. F., Lu C.C., Vecchione M. A revision of the systematics and distribution of Illex species (Cephalopoda: Ommastrephidae) // Smithson. Contrib. Zool. 1998. № 586. P.405–423.
- Nautilus (Saunders, Ward, 1987; Saunders et al., 1987)
Saunders W.B., Ward P.D. Sympatric occurrence of living Nautilus (N. pompilius and N. stenomphalus) on the Great Barrier Reef, Australia // The Nautilus. 1987. V. 101. P. 188–193.
Saunders W.B., Davis L.E., Knight R.L. Sympatric species of Nautilus (N. pompilius and N. scrobiculatus) in the Admiralty Islands, Papua New Guinea // The Nautilus. 1987. V. 101. P. 93–99.
some ammonites:
- scaphitids (Machalski M., Jagt J. W., Landman N.H., Motochyrova-Dekova N. The highest records of North American scaphitid ammonites in the European Maastrichtian (Upper Cretaceous) and their stratigraphic implications // Acta Geol. Pol. 2007. V. 57. № 2. P. 169–185.)
- craspeditids (Rogov, 2018, pp. 113-115 here: http://ginras.ru/materials/files/cephalopod_meeting2018.pdf)
belemnites (Remin Z. Fusiteuthis polonica – an intergeneric belemnite hybrid; proofs and discussion // 8th Intern. Symp. Cephalopods – Present and Past (Dijon – France 2010) August 30 – September 3, 2010. Abstr. vol. Dijon: University of Burgundy & CNRS, 2010. P. 143)
I am glad you find my response helpful, Vlad :)
There is a signature of mtDNA recombination in squids, and paternal mtDNA leakage is a likely cause: https://academic.oup.com/mbe/article/21/12/2319/1071059
There were ~18 interspecific hybrid cephalopod records in 2008:
https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.2008.0055
Unfortunately, these records are mostly based on morphological characters that might be misleading.
I found an extensive record of squid natural hybrid zone studied by molecular genetic markers, but the two ESU are formally considered as a single species (Sepioteuthis australis), despite of a reproductive barrier.
http://www.publish.csiro.au/mf/Fulltext/MF03157#R23
Healey et al. reported molecular signatures of hybridization within Sepia officinalis complex (Sepia officinalis, Sepia hierredda, and Sepia vermiculata) on their CIAC2018 poster.
It seems that interspecific hybridization in cephalopods is quite rarely detected (insufficiently studied and/or rarely occurring). I think it's relatively safe to assume the common matrilineal mtDNA inheritance. In case of finding a heteroplasmic individual, I would double check in order to exclude a contamination, and get nuclear markers involved, if possible. In heteroplasmic individuals, both variants can be expressed simultaneously, but there are often large differences in their copy numbers.
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