RESULTS

RESULTS View in CoL

We compiled 125 papers that included cytogenetic data on Loricariidae species. These studies comprised a diversity of 234 species, here included those identified as “sp.”, prope, “aff.”, “cf.”, “n.sp.”, and “L” as distinct species, from 48 genus. Hypostominae was the subfamily most represented with 142 species karyotyped, followed by Loricariinae (54 spp.), Hypoptopomatinae (34 spp.), and Delturinae and Rhinelepinae with 2 spp. each, with absence of data for Lithogeninae . The Hypostomus genus was the most represented with 26 valid species karyotyped, in a total of 159 records when including all populational data and those identified as “sp.”, prope, “aff.”, “cf.”, “n. sp.”, and “L”. The geographical coordinates plotted into maps show a distribution of species cytogenetically investigated in Brazil, Argentina, and Paraguay, comprising six distinct river basins ( Fig. 2 View FIGURE 2 ). Although species from Ecuador and Venezuela were also compiled, those papers do not present geographical coordinates of the sample sites.

Diploid number varied from 2n = 33 in males of Rineloricaria teffeana (Steindachner, 1879) ( Marajó et al., 2022) to 2n = 96 in Hemipsilichthys sp. ( Kavalco et al., 2004, 2005). The fundamental number ranged from 34 in R. teffeana ( Marajó et al., 2022) to 142 in Hypostomus topavae (Godoy, 1969) ( Kamei et al., 2017) , and the simple distribution of Ag-NOR/18S rDNA was the most common with 269 records, against 110 records of multiple sites. Seven sex chromosomes systems were described for 31 Loricariidae species, the simple XX/XY, XX/X0, and ZZ/ZW, and the multiples X 1 X 1 X 2 X 2 /X 1 X 2 Y, XX/XY 1 Y 2, ZZ/ZW 1 W 2, and Z 1 Z 1 Z 2 Z 2 /Z 1 Z 2 W 1 W 2. B chromosomes were found in five species, varying from 1B (e.g., de Souza et al., 2009) to 3B chromosomes (e.g., Porto et al., 2010). Complete results were compiled in Tab. 1 View TABLE 1 .

Subfamily/ Genus Species Locality Ximbaúva Latitude Longitude Basin 2n NF AgNOR - 18S Multiple KF 8m + 10sm + 18sm + 32a SCS Reference/ Observation Hypostomus ancistroides stream, Ourizo- IvaÍ 68♀ ♂ Endo et al. (2012) ancistroides Piquiri River, Brazil 68♀ ♂ Multiple 14m + 14sm + 8st + 32a Bueno et al. (2013) ancistroides Água Boa stream, Mundo Novo, MS, Brazil 68♀ ♂ 116 Multiple 14m + 24sm + 10st + 20a Fernandes et al. (2012) ancistroides Dourado stream, Mundo Novo, MS, Brazil 68♀ ♂ 116 Multiple 10m + 22sm + 16st + 20a Fernandes et al. (2012) ancistroides Dourado stream, Mundo Novo, MS, Brazil 68♀ ♂ 120 Multiple 14m + 16sm + 22st + 16a Traldi et al. (2013) ancistroides Hortelã stream, Botucatu, SP , Brazil 22°56'28.9"S 48°35' 03.2"W 68♀ ♂ Multiple 10m + 20sm + 10st + 28a Pansonato-Alves et al. (2013) ancistroides Piquiri River , Nova Laranjeiras, Brazil 24°56'54.0"S 52°35' 49.0"W 68♀ ♂ Multiple 14m + 14sm + 8st + 32a Bueno et al. (2014) ancistroides Monjolinho River, São Carlos, SP, Brazil 68♀ ♂ 102 Multiple 16m + 18sm + 34st/a Lorscheider et al. (2015) cf. heraldoi Zawadzki, Weber & Pavanelli, 2008 Mogi Guaçu River, Pirassununga, SP, Brazil Mogi Guaçu 72♀ ♂ Simple 6m + 6sm + 26st + 34a Martinez et al. (2011) cf. plecostomus (Linnaeus, 1758) Severo stream, Brazil 9°54' 30.8"S 56°03'33.9"W Amazon 68♀ ♂ 120/ 121 Multiple 14m + 24sm + 14st + 16a ♂, 15m + 24sm + 14st + 15a ♀ ZZ/ZW Oliveira et al. (2015) cf. topavae Carrapato stream, Penápolis, SP, Brazil Paraná 80♀ ♂ Multiple 6m + 8sm + 42st + 24a Martinez et al. (2011) cf. wuchereri (Günther, 1864) Mutum River, Jequié, BA, Brazil 13°43'18.0"S 39°51'20.0"W Contas 76♀ ♂ 104 Simple 10m + 18sm + 48st/a Bitencourt et al. (2011b) cf. wuchereri Una River , Valença, BA, Brazil 13°21'55.0"S 39°04'35.0"W Recôncavo Sul 76♀ ♂ 104 Simple 10m + 18sm + 48st/a Bitencourt et al. (2011b) cochliodon Kner, 1854 Iguaçu River, Brazil 64♀ ♂ Simple 12m + 16sm + 16st + 20a Bueno et al. (2014) cochliodon Iguaçu River, Foz do Iguaçu, PR, Brazil 25°38'53.0"S 54°27' 28.0"W 64♀ ♂ Simple 12m + 16sm + 16st + 20a Rubert et al. (2016) cochliodon Piraputanga River, Cáceres, MT, Brazil 16°03'33.0"S 57°40'33.0"W Paraguai 64♀ ♂ 100 Multiple 16m + 20sm + 28st/a Rubert et al. (2016) commersoni Valenciennes, 1836 Iguaçu River, Brazil 68♀ ♂ Multiple 12m + 14sm + 14st + 28a Bueno et al. (2013) commersoni Lake of Ney Braga hydroeletric plant, Mangueririnha, PR, Brazil 68♀ ♂ 100 Multiple 12m + 12sm + 8st + 36a Maurutto et al. (2012) commersoni Piquiri River, Nova Laranjeiras, Brazil 24°56'54.0"S 52°35'49.0"W 68♀ ♂ Multiple 12m + 14sm + 14st + 28a Bueno et al. (2014) commersoni Iguaçu River, Foz do Iguaçu, PR, Brazil 25°38'53.0"S 54°27' 28.0"W 68♀ ♂ Multiple 12m + 14sm + 14st + 28a Bueno et al. (2014) commersoni Iguaçu River, PR, Brazil 26°15'01.1"S 51°06'10.7"W Paraná 68♀ ♂ 106 Multiple 12m + 12sm + 14st + 30a Lorscheider   GoogleMaps et al. (2018) derbyi (Haseman, 1911) Iguaçu River, Curitiba , PR, Brazil 66♀ ♂ 82 Multiple 6m + 10sm + 20st + 30a Maurutto et al. (2012) derbyi Iguaçu River, PR, Brazil 26°15'01.1"S 51°06'10.7"W Paraná 68♀ ♂ 102 Simple 12m + 12sm + 10st + 34a Lorscheider   GoogleMaps et al. (2018) faveolus Zawadzki, Birindelli & Lima, 2008 Taquaralzinho River, MT, Brazil 64♀ ♂ Simple 18m + 8sm + 22st + 16a Bueno et al. (2013) faveolus Taquaralzinho River, Barra do Garças, MT, Brazil 15°40'42.0"S 52°17'52.0"W 64♀ ♂ Simple 18m + 8sm + 22st + 16a Bueno et al. (2014) goyazensis (Regan, 1908) Vermelho River, GO, Brazil 72♀ ♂ Simple 10m + 16sm + 10st + 36a Alves et al. (2006) hermanni (Ihering, 1905) Piquiri River, PR, Brazil 72♀ ♂ Multiple 10m + 8sm + 32st + 22a Bueno et al. (2013) hermanni Piquiri River, Nova Laranjeiras, Brazil 24°56'54.0"S 52°35' 49.0"W 72♀ ♂ Multiple 10m + 8sm + 32st + 22a Bueno et al. (2014) hermanni Piracicaba River, Piracicaba, SP, Brazil 22°43'07.0"S 47°39' 19.0"W 72♀ ♂ 98 Simple   GoogleMaps 8m + 18sm + 46st/a Rubert et al. (2016)

na, PR, Brazil

Subfamily/ Genus Species Locality Latitude Longitude Basin 2n NF AgNOR - 18S KF SCS Reference/ Observation Hypostomus tapijara Oyakawa, Akama & Zanata, 2005 Ribeira de Iguape River, Registro, SP, Brazil 66♀ ♂ 118 Multiple 14m + 24sm + 14st + 14a Traldi et al. (2013) tietensis (Ihering, 1905) PiraÍ River, Brazil 23°22' 22.0"S 47°22' 13.0"W Paraná 72♀ ♂ 108 Simple   GoogleMaps 8m + 8sm + 20st + 36a Anjos et al. (2020) tietensis PiraÍ River, Brazil 23°22' 22.0"S 47°22' 13.0"W Paraná 72♀ ♂ 109 Simple 8m + 8sm + 20st + 36a Paula et al. (2022) Mogi Guaçu topavae (Godoy, 1969) River, Pirassununga, SP, 80♀ ♂ 104 Multiple 8m + 16sm + 56st/a Artoni, Bertollo (1996). Reported as Hypostomus sp. E Brazil Mogi Guaçu topavae River, Pirassununga, SP, 80♀ ♂ 104 Multiple 8m + 16sm + 56st/a Lorscheider et al. (2015) Brazil topavae Piquiri River , Nova Laranjeiras, PR, Brazil 80♀ ♂ 14m + 10sm + 26st + 30a Bueno et al. (2012) topavae Piquiri River, PR, Brazil 80♀ ♂ Simple 14m + 10sm + 26st + 30a Bueno et al. (2013) topavae Piquiri River, Nova Laranjeiras, PR, Brazil 24°56'54.0"S 52°35' 49.0"W Paraná 80♀ ♂ Simple 14m + 10sm + 26st + 30a Bueno et al. (2014) topavae Keller River, Brazil 23°38' 25.9"S 51°51' 32.8"W 80♀ ♂ 142 Multiple 14m + 30sm + 18st + 18a Kamei et al. (2017) unae (Steindachner, 1878) 76♀ ♂ 10m + 20sm + 46st/a Anjos et al. (2020) Lasiancistrus schomburgkii (Günther, 1864) Massangana River, Brazil 9°80′48″S* 63°08′90″W* Amazon 54♀ ♂ 108 Simple 28m + 16sm + 10st Mariotto et al. (2019) sp. Cachoeira River, Brazil 14°64′66″S* 52°35′50″W* Tocantins-Araguaia 54♀ ♂ 108 Simple 28m + 16sm + 10st Mariotto et al. (2019) Megalancistrus sp. Cuiabá River , Brazil 15°62′90″S* 56°08′70″W* Paraguai 52♀ ♂ 104 Simple 28m + 16sm + 8st Mariotto et al. (2019) parananus (Peters, 1881) Piquiri River , Nova Laranjeiras, PR, Brazil 52♀ ♂ Simple 18m + 24sm + 10st Bueno et al. (2018) Camarapi River, Panaqolus sp. Portel, PA, 52♀ ♂ Simple 24m + 18sm + 10st/a Ayres-Alves et al. (2017) Brazil tankei Cramer & Sousa, 2016 Xingu River, Brazil 52♀ ♂ 104 Simple 6m + 38sm + 8st Ferreira et al. (2021) armbrusteri Lujan, Hidalgo & Stewart, 2010 Xingu River, Panaque Altamira, PA, 52♀ ♂ Simple 26m + 20sm + 6st/a Ayres-Alves et al. (2017) Brazil Gorgulho da armbrusteri Rita, Altamira, 52♀ ♂ Simple 26m + 20sm + 6st/a Ayres-Alves et al. (2017) PA, Brazil Araguaia River, cf. nigrolineatus Barra do Garças, 52♀ ♂ Simple 26m + 20sm + 6st/a Artoni, Bertollo (2001) Peckoltia cavatica Armbruster & Werneke, 2005 PA, Brazil 52♀ ♂ Simple 38m /sm + 14st Pety et al. (2018) multispinis (Holly, 1929) PA, Brazil 52♀ ♂ Simple 28m /sm + 24st Pety et al. (2018) oligospila (Günther, 1864) PA, Brazil 52♀ ♂ Multiple 38m /sm + 14st Pety et al. (2018) sabaji Armbruster, 2003 PA, Brazil 52♀ ♂ Multiple 38m /sm + 14st Pety et al. (2018) sp. 1 Jari river   GoogleMaps Jari River, Monte Dourado, PA, Brazil 03°18'14.9"N 52°03'29.3"W 52♀ ♂ 102 Multiple 44m /sm + 6st + 2a + 1B Souza et al. (2009) Jari River, sp. 2 Jari river   GoogleMaps Monte Dourado, 03°18'14.9"N 52°03'29.3"W 52♀ ♂ 102 32m /sm + 18st + 2a Souza et al. (2009) PA, Brazil sp. 3 Jarumã Abaetuba, PA, Brazil 1°42'41.9"S 48°51'45.9"W 52♀ ♂ Simple 46m /sm + 6st Silva et al. (2021) sp. 4 Caripetuba Abaetuba, PA, Brazil 1°37' 23.5"S 48°55'33.0"W 52♀ ♂ Multiple 40m /sm + 12st Silva et al. (2021) vittata (Steindachner, 1881) Xingu River , Altamira, PA, Brazil 03°12'4"N 52°12' 41.7"W 52♀ ♂ 102 Simple 16m + 20sm + 14st + 2a Souza et al. (2009) vittata PA, Brazil 52♀ ♂ Simple 32m /sm + 18st + 2a Pety et al. (2018) Pseudacanthicus leopardus (Fowler, 1914) Xingu River, Brazil Xingu - Amazon 52♀ ♂ 104 Simple 18m + 34sm Santos da Silva et al. (2022b) sp. Xingu River, Brazil Xingu - Amazon 52♀ ♂ 104 Simple 18m + 34sm Santos da Silva et al. (2022b) spinosus (Castelnau, 1855) Tocantins River, Brazil Tocantins-Araguaia 52♀ ♂ 104 Simple 18m + 34sm Santos da Silva et al. (2022b) Pterygoplichthys ambrosettii (Holmberg, 1893) Preto River, Mirassolândia, SP, Brazil 52♀ ♂ Simple 16m + 24sm + 8st + 4a Artoni et al. (1999 b). Reported as Liposarcus anisitsi ambrosettii Tietê River, Botucatu, SP, Brazil 52♀ ♂ Simple 28m + 12sm + 8st + 4a Alves et al. (2006). Reported as Liposarcus anisitsi

MT, Brazil

DISCUSSION

The origin of the chromosomal diversity of Loricariidae is attributed to both ecological and molecular factors. Small and isolated populations, in addition to the low vagility, are the main ecological characteristics that have allowed the fixation of chromosomal rearrangements in Loricariidae , as suggested for Farlowella ( Marajó et al., 2018) , Harttia ( Sassi et al., 2023) , and Rineloricaria ( Rosa et al., 2012) . The diploid number 2n = 54 is often considered the ancestral diploid number for the family, since it is observed in most Loricariidae subfamilies and present in other Siluriformes ( Artoni, Bertollo, 2001) . However, there is no consensus on the matter particularly considering the new karyotypic description of basal taxa within subfamilies. Takagui et al. (2020) in a review of Loricariinae karyotypes argue that although predominant, 2n = 54 should not be considered the basal diploid number for the family because multiple divergences in the microstructure of karyotypes within the same 2n are recurrently seen throughout the family. Notably, the 2n range in Loricarioidei suggest that other numbers rather than 2n = 54 can be considered the plesiomorphic ones, as Astroblepidae presents 2n = 52–54, Scoloplacidae 2n = 50, Callichthyidae 2n = 40–134, and Trichomycteridae 2n = 32–62 (reviewed by Conde-Saldaña et al., 2018). Beyond that, the Diplomystidae (Siluroidei) presents 2n = 56 chromosomes ( Campos et al., 1997; Oliveira, Gosztonyi, 2000), which might also suggest that as the ancestral 2n.

We plotted the 2n range per subfamily into the main molecular phylogenetic reconstructions of Loricariidae ( Fig. 3 View FIGURE 3 ) and 2n = 54 is the most widespread, being conserved in Rhinelepinae and present in all other subfamilies. Regardless matter whether 2n = 54 or 2n = 56 is the ancestral diploid number, it is noteworthy that chromosomal evolution in Loricariidae is complex. Considering the lower number of karyotyped species when compared to the valid richness, 234 spp. with cytogenetic data against 1,051 valid species ( Fricke et al., 2023), it is difficult to establish the evolutionary pathways that led to the observed variability. Notably, while the stability is restricted to 2n in some genera, with high divergence in karyotype structure, as the 2n = 58 in Farlowella , 2n = 54 in Corumbataia , and 2n = 52 in Pterygoplichthys , stable 2n and karyotype is also observed, as the 2n = 52 (26m +20sm+6st/a) in two species of Panaque . Our compilation reveals that processes of ascending and descending dysploidy (i.e., the increase or decrease of 2n while preserving the genomic content) were frequent in most subfamilies but Rhinelepinae, which may exhibit the constant 2n = 54 as a symplesiomorphic trait.

Despite the 2n conservation in Rhinelepinae, variations in the karyotype structure are observed within and between species. Populations of Rhinelepis aspera Spix & Agassiz, 1829 from the same river differ in the karyotype formula ( Artoni, Bertollo, 2001; Endo et al., 2012), suggesting that pericentric inversions played an important role in the chromosomal evolution of the species. Such mechanism is not restricted to Rhinelepinae but also observed in other loricariids, such as Ancistrus ( Mariotto et al., 2009) , Loricariichthys ( Takagui et al., 2014) , and Rineloricaria ( Rosa et al., 2012; Primo et al., 2018). In addition, the multiple Ag-NOR observed in Pogonopoma wertheimeri (Steindachner, 1867) ( Artoni, Bertollo, 2001) when compared to the simple distribution in other Rhinelepinae species suggest that other mechanisms are also important for the chromosomal evolution in the group. Notably, numeric and structural polymorphisms are frequently observed in loricariids, for example in the multiple karyomorphs of Rineloricaria pentamaculata Langeani & de Araujo, 1994 ( Glugoski et al., 2023), and the presence of B chromosomes in Harttia longipinna Langeani, Oyakawa & Montoya-Burgos, 2001 ( Blanco et al., 2012). This chromosomal diversity was probably generated by a combination of rearrangements that include Robertsonian fusions and fissions, paracentric and pericentric inversions, and translocations ( Artoni, Bertollo, 2001; Kavalco et al., 2004; Ziemniczak et al., 2012).

Although rare in most fish species, being observed in only about 5% of Teleostei species ( Arai, 2011; Sember et al., 2021), our compilation shows that Loricariidae species carry seven out of the nine known sex chromosome systems observed among fishes. Ancistrus was demonstrated to harbor the largest diversity of sex chromosomes with six of the seven recognized systems for the family distributed in 18 species, corresponding to about 23% of the valid species (Neuhaus et al., 2023). The simple XX/XY was the most predominant in the genus, recorded in A. maximus de Oliveira, Zuanon, Zawadzki & Rapp Py-Daniel, 2015 ( Oliveira et al., 2010; Favarato et al., 2016), Ancistrus cf. dubius ( Mariotto et al., 2011) , Ancistrus sp. 1 Quianduba River ( Silva et al., 2022, 2023), Ancistrus sp. 1 Maracapucú River ( Santos da Silva et al., 2023), Ancistrus sp. 1 Ilha do Capim ( Santos da Silva et al., 2023), Ancistrus sp. Catalão ( Favarato et al., 2016), Ancistrus sp. L2 ( Prizon et al., 2017), Ancistrus sp. L3 ( Prizon et al., 2017), and Ancistrus sp. Purus ( Oliveira et al., 2010; Favarato et al., 2016). Additionally, two multiple sex chromosome systems that were not observed in any other Loricariidae are recorded in Ancistrus : ZZ/ZW1 W 2 in A. clementinae Rendahl, 1937 ( Nirchio et al., 2023), and Z 1 Z 1 Z 2 Z 2/Z1 Z 2 W 1 W 2 ( Oliveira et al., 2008; Favarato et al., 2016). On other hand, Harttia harbor the highest number of multiple sex chromosome systems when compared to the number of valid species, with six occurrences representing about 25% of valid species (compiled in Sassi et al., 2021): XX/XY1 Y 2 in H. carvalhoi Miranda Ribeiro, 1939, H. intermontana Oliveira & Oyakawa, 2019 , and Harttia sp. 1 ( Centofante et al., 2006; Deon et al., 2020); X1X1X2X2/X1X2Y in H. duriventris Rapp Py-Daniel & Oliveira, 2001 , H. punctata Rapp Py-Daniel & Oliveira, 2001 , and H. villasboas Oyakawa, Fichberg & Rapp Py-Daniel, 2018 ( Blanco et al., 2014; Sassi et al., 2020), in addition to putative simple XX/XY in H. rondoni Oyakawa, Fichberg & Rapp Py-Daniel, 2018 and H. torrenticola Oyakawa, 1993 ( Deon et al., 2020; Sassi et al., 2020). The Loricariidae diversity of sex chromosomes was originated by rearrangements that include translocations ( Blanco et al., 2014), centric fissions ( Sassi et al., 2023); centric fusions ( Centofante et al., 2006), and pericentric inversions ( Artoni et al., 1998), including the combination of distinct rearrangements especially in the origin of multiple sex chromosome systems ( Oliveira et al., 2008; Deon et al., 2022). Sex chromosomes in Loricariidae seems to have independent origins, but further research is required to explore the genomic content of those sex chromosomes and its origin. Indeed, there is a recognized lack of information regarding the effects of environmental cues and molecular/gene mechanisms in sex determination of Neotropical fishes ( Fernandino, Hattori, 2019).

Most Loricariidae species present a single 18S rDNA/Ag-NOR site, which is also considered a plesiomorphic character in the group ( Artoni, Bertollo, 2001; Kavalco et al., 2004), and the standard distribution in most vertebrates ( Sochorová et al., 2018). Notably, such region in loricariids is involved in several chromosomal rearrangements, including the origin and differentiation of sex chromosomes, being considered evolutionary breakpoint regions in Ancistrus , Harttia , and Rineloricaria ( Glugoski et al., 2018; Deon et al., 2022). Size heteromorphism in the Ag-NOR site is also common, probably because of unequal crossing-over between homologs ( Takagui et al., 2020). According to our review, some genus conserved the simple Ag-NOR locus in all analyzed species to date (here included only those genera with more than one species karyotyped), namely as Baryancistrus , Corumbataia , Farlowella , Harttia , Hisonotus , Lasiancistrus , Loricaria , Loricariichthys , Neoplecostomus , Panaqolus , Panaque , Pareiorhina , Pseudacanthicus , Pterygoplichthys , and Scobinancistrus . On other hand, the multiple distribution of Ag-NOR seems to be conserved only in Hypancistrus , while other genus as Ancistrus , Hypostomus , and Rineloricaria present both simple and multiple distributions on chromosomes.

Although distributed throughout the Neotropical region, there is a predominance of cytogenetic studies in Loricariidae species from Brazil ( Fig. 2 View FIGURE 2 ). Few studies were conducted in other countries that includes Argentina, Ecuador, Paraguay, and Venezuela. Notably, those in Argentina and Paraguay were mostly restricted to the frontier region with Brazil. When accounting the Brazilian territory, is also notable that some regions are poorly represented in cytogenetic studies, especially the northeast in which at least nine states have not been included in the cytogenetic samplings. In addition, the Guianas Shield and Western Amazon regions are largely recognized as neglected regions in biogeographical and evolutionary studies ( Cassemiro et al., 2023), also with little or absent cytogenetic information for Loricariidae . Despite the regional sampling gap problem, Loricariidae diversity is still insufficiently represented by cytogenetic studies. Our compilation recorded 234 species assessed by cytogenetic studies, that in comparison to the 1,051 valid species ( Fricke et al., 2023), represents 22.26% of the family species richness. The diversity of genus assessed by cytogenetic studies was the highest in Hypoptopomatinae (42.1%), followed by Rhinelepinae (28.5%), Hypostominae (27.2%), Loricariinae (24.4%), Delturinae (20%), and Lithogeninae (0%). Besides Lithogeninae that do not have any species karyotyped to date, the subfamily Delturinae has only one genus and two unidentified species karyotyped: Hemipsilichthys sp. Paraitinga River ( Kavalco et al., 2004, 2005), and Hemipsilichthys n. sp. Patos River ( Alves et al., 2005). We suggest that further cytogenetic studies focus on expand the sampling in the northeast Brazil, the Western Amazon, the Guianas Shield, and other Neotropical countries, in addition to evaluate a more representative portion of the diversity.