Intragenus F1-hybrids of African weakly electric fish (Mormyridae: Campylomormyrus tamandua ♂ × C. compressirostris ♀) are fertile

Abstract

Hybridization is widespread in fish and constitutes an important mechanism in fish speciation. There is, however, little knowledge about hybridization in mormyrids. F1-interspecies hybrids between Campylomormyrus tamandua ♂ × C. compressirostris ♀ were investigated concerning: (1) fertility; (2) survival of F2-fish and (3) new gene combinations in the F2-generation concerning the structure of the electric organ and features of the electric organ discharge. These F1-hybrids achieved sexual maturity at about 12–13.5 cm total length. A breeding group comprising six males and 13 females spawned 28 times naturally proving these F1-fish to be fertile. On average 228 eggs were spawned, the average fertilization rate was 47.8%. Eggs started to hatch 70–72 h after fertilization, average hatching rate was 95.6%. Average mortality rate during embryonic development amounted to 2.3%. Average malformation rate during the free embryonic stage was 27.7%. Exogenous feeding started on day 11. In total, we raised 353 normally developed larvae all of which died consecutively, the oldest specimen reaching an age of 5 months. During survival, the activities of the larval and adult electric organs were recorded and the structure of the adult electric organ was investigated histologically.

Transcriptome-wide single nucleotide polymorphisms related to electric organ discharge differentiation among African weakly electric fish species

“…A complementary approach could be a co-segregation analysis among EOD phenotypes and genetic variants among F2-species hybrids. Indeed, hybridization of our species is possible [ 74 ] and some F1 hybrids are fertile [ 75 ], but so far no F2 hybrids could be brought to a stage where they exhibit an adult EOD. Consequently, we can so far not proof a direct link between the inferred candidate genes and processes and the actual electric organ/electrocyte features.…”

Intergenus F1-hybrids of African weakly electric fish (Mormyridae: Gnathonemus petersii ♂ × Campylomormyrus compressirostris ♀) are fertile

“…The AR experiments in the mormyrid fish (Kirschbaum et al 2016;Korniienko et al 2020;this paper) have documented a high potential in mormyrid fish to generate fertile hybrids, such that postzygotic isolation seems weak or even absent. In contrast, natural hybrids seem to be rare (see above), pointing towards effective prezygotic isolation.…”

“…This feature correlates with the presence of an initial head negative phase in the EOD (Bass 1986;Gallant et al 2011). In contrast, in the four species C. compressirostris, C. tshokwe, C. numenius and C. rhynchophorus there is no initial head negative phase in the EOD; the main stalk is found on the caudal face of the electrocyte and penetrations are absent (Paul et al 2015;Nguyen et al 2020).…”

“…To find out, if this characteristic is related to the genetic inventory of G. petersii, an additional hybrid between another Campylomormyrus species (C. compressirostris) and G. petersii was produced (Kirschbaum et al 2016), but so far only the first steps of the ontogeny of this hybrid, concerning the EO, were described. The aim of the current study, therefore, is a detailed description of the ontogeny of the EO and, in addition, to unravel whether these intergenus hybrids are fertile, as has been observed in intragenus Campylomormyrus (C. tamandua × C. compressirostris) hybrids (Kirschbaum et al 2016;Korniienko et al 2020).…”

“…200 µs (as in C. compressirostris) to ca. 25 ms as in C. rhynchophorus and C. numenius (Feulner et al 2008(Feulner et al , 2009a(Feulner et al , 2009bNguyen et al 2020). In addition, there are basic differences in the anatomy of the electrocytes of the EO concerning the organisation and location of the stalk system, which consists of numerous small specialised protrusions of the electrocyte that fuse to form the main stalk, which receives the innervation by electromotor neurons.…”