Karyotypic Diversity and Evolution in a Sympatric Assemblage of Neotropical Electric Knifefish

Abstract

Chromosome changes can perform an important role in speciation by acting as post-zygotic reproductive barriers. The Neotropical electric fish genus Brachyhypopomus (Gymnotiformes, Hypopomidae) has 28 described species, but cytogenetic data are hitherto available only for four of them. To understand karyotype evolution and investigate the possible role of chromosome changes in the diversification of this genus, we describe here the karyotype of eight species of Brachyhypopomus from a sympatric assemblage in the central Amazon basin. We analyzed cytogenetic data in the context of a phylogenetic reconstruction of the genus and known patterns of geographical distribution. We found a strong phylogenetic signal for chromosome number and noted that sympatric species have exclusive karyotypes. Additional insights into the role of chromosome changes in the diversification of Brachyhypopomus are discussed.

First chromosomal analysis of Gymnorhamphichthys britskii: the remarkable lowest diploid value within the family Rhamphichthyidae (Gymnotiformes)

“…Compared to other rhamphichthyids that have 2n = 50, the karyotype of G. britskii suggested a reduction in the 2n, indicating that chromosome rearrangements, such as centric fusions that can alter the chromosome number may have occurred during the diversification of this group. Chromosome fusions were identified as important events in the diversification of Hypopomidae (the sister group of Rhamphichthyidae), in which the diploid number varies between 36 chromosomes, as in B. brevirostris, and 48 chromosomes, as in M. bilineatus (de Jesus et al, 2016;Batista et al, 2017;Cardoso et al, 2018). In Rhamphichthyidae, the chromosomic data of G. britskii alter the paradigm of karyotype evolution characterized by 2n conservation (50 chromosomes) and chromosome inversions (Cardoso et al, 2011;Mendes et al, 2012;Silva et al, 2013).…”

“…Among the other Rhamphichthyidae, cytogenetic information is available only for Hypopygus lepturus Hoedeman, 1962(Almeida-Toledo, 1978, Steatogenys duidae (La Monte, 1929), S. elegans (Steindachner, 1880) (Cardoso et al, 2011), Rhamphichthys hahni (Meinken, 1937), R. pantherinus Castelnau, 1855 (cited as R. marmoratus) and R. rostratus (Linnaeus, 1766) (Mendes et al, 2012;Silva et al, 2013). Among the Hypopomidae, it is available for Hypopomus artedi (Kaup, 1856) (Almeida-Toledo, 1978, eight Brychyhypopomus species (Almeida-Toledo, 1978;Mendes et al, 2012;Cardoso et al, 2018) and Microsternarchus bilineatus Fernández-Yépez, 1968(de Jesus et al, 2016Batista et al, 2017).…”

“…In Rhamphichthyidae all species had 2n = 50 chromosomes but differed in their karyotypes (Almeida-Toledo, 1978;Cardoso et al, 2011;Mendes et al, 2012;Silva et al, 2013). Among the Hypopomidae, the diploid number ranged from 36 (Brachyhypopomus brevirostris (Steindachner, 1868)) to 48 (M. bilineatus) chromosomes (de Jesus et al, 2016;Batista et al, 2017;Cardoso et al, 2018).…”

Anatomy and homology of the accessory electric organs of the toothless knifefishes (Rhamphichthyoidea: Gymnotiformes)

“…(). This method has been used to evaluate macroevolutionary patterns and character transitions within other studies of the Neotropical ichthyofauna (Cardoso et al ., ; Crampton et al ., ; Guisande et al ., ). The ultrametric tree was generated with the chronopl tool (Paradis et al ., ) by applying a crosschecked validated smoothing parameter ( λ = 10) for the penalized likelihood method (Sanderson, ).…”

“…We estimated discrete binary character state transitions under two different models of character transition rates (equal rates (ER) and all rates different (ARD)) using the ape package in R (Paradis et al, 2004; www.r-project.org) on an ultrametric tree from the total evidence analysis of Tagliacollo et al (2016). This method has been used to evaluate macroevolutionary patterns and character transitions within other studies of the Neotropical ichthyofauna (Cardoso et al, 2018;Crampton et al, 2016a;Guisande et al, 2012). The ultrametric tree was generated with the chronopl tool (Paradis et al, 2004) by applying a crosschecked validated smoothing parameter (λ = 10) for the penalized likelihood method (Sanderson, 2002).…”