Banca de DEFESA: MARSILIO SECUNDO PEREIRA DA ROCHA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : MARSILIO SECUNDO PEREIRA DA ROCHA
DATE: 22/07/2022
TIME: 09:00
LOCAL: Google meet: https://meet.google.com/tme-zhha-ayz
TITLE:

CYTOGENOMIC DIVERGENCE IN DAMSELFISHES OF THE GENUS Stegastes Jenyns, 1840 (POMACENTRIDAE) FROM THE ATLANTIC: INTER AND INTRASPECIFIC VARIATION AND HYBRID ZONE ANALYSIS

KEY WORDS:

Fish cytogenetics, karyotypic evolution, cytotaxonomy, pericentric inversions, rDNA

PAGES: 58
BIG AREA: Ciências Biológicas
AREA: Genética
SUBÁREA: Genética Animal
SUMMARY:

Pomacentridae (damselfishes) constitute an extremely diverse and abundant group of fishes in rocky areas and coral reefs of tropical and subtropical oceanic regions. In the western South Atlantic, the genus Stegastes is the most representative. Variations in coloration and overlapping meristic characters make the taxonomy of the Atlantic species of this genus in some cases imprecise. In this regard, the taxonomic status, and relationships of insular nominal forms, such as S. rocasensis, S. sanctipauli, and S. fuscus trindadensis, have received increasing attention. Previous cytogenetic data for Stegastes, have indicated remarkable structural karyotypic variation. However, population cytogenetic comparisons, aspects of the organization of repetitive sequences of chromosomes, which can help in understanding the taxonomy and phylogenetic relationships of these species, are still incipient. Thus, in the current study, we performed population and interspecific cytogenetic analyses, including the patterns of rDNA sequence organization, of Stegastes species endemic to the Western Atlantic coast, Atol das Rocas (AR), and the regions of São Pedro e São Paulo Archipelagos (SPSPA) and Trindade Island (TI). Additionally, the karyotypic patterns of S. fuscus and S. variabilis were investigated in a probable hybridization zone on the coast of Rio Grande do Norte, Northeast region of Brazil. The species presented 2n=48, with high NC values (chromosome arms; 88-90). Heterochromatin showed similar interspecific distribution, with conspicuous blocks in the centromeric and pericentromeric regions. The Ag-RONs loci are unique, except for S. variabilis, which showed multiple sites. Samples of S. rocasensis from AR and SPSPA (previously S. sanctipauli), showed similar karyotypes and rDNA site arrangements. Stegastes fuscus from TI showed a syntenic arrangement of the 18S and 5S rDNA sites, in contrast to the S. fuscus population from the coast, whose sites occur on different chromosomes. This conspicuous karyotypic variation indicates an Evolutionarily Significant Unit (ESU) status for this island population. Stegastes variabilis showed transcriptionally active 18S and 5S syntenic rDNA arrangements, demonstrating that such organization does not impede its gene functionality. Added to molecular and morphological data, S. rocasensis/S. sanctipauli also share the same cytogenetic patterns, supporting that it is the same species. Population analyses of S. variabilis and S. fuscus in a hybridization zone did not reveal intermediate karyotypes, suggesting that hybridization in this region may be sporadic, rare, or time-limited events. Karyotypic evolution in Stegastes revealed conspicuous differentiation, with clear cytotaxonomic distinctiveness, markedly shaped by multiple pericentric inversions. Analyses of the dynamics of repetitive sequences in these species will contribute to elucidating the high level of chromosomal differentiation in this group of reef fishes.

COMMITTEE MEMBERS:
Presidente - 1199139 - WAGNER FRANCO MOLINA
Externo à Instituição - GIDEÃO WAGNER WERNECK FELIX DA COSTA
Externa à Instituição - KARLLA DANIELLE JORGE AMORIM