Variação morfológica da concha de bivalves do gênero Donax (Bivalvia : Donacidae) do Nordeste Brasileiro

• Autor(a) principal: Castro, Juliano Guerra de
• Data de Publicação: 2023
• Tipo de documento: Trabalho de conclusão de curso
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/jspui/handle/riufs/19308
• topic: Ciências biologicas; Ensino superior (UFS); Donacídeos; Morfometria geométrica; Taxonomia; Donacids; Geometric morphometrics; Taxonomy; CIENCIAS BIOLOGICAS::ZOOLOGIA

The genus Donax L., 1778 comprises bivalves inhabiting intertidal regions of tropical beaches. The genus has 90 described species, four of them occurring on the Brazilian coast, Donax denticulatus L., 1758, from the state of Pará to Alagoas, D. striatus L., 1767, from Maranhão to Rio Grande do Norte, D. hanleyanus Philippi, 1847 and D. gemmula Morrison, 1971 both present in the southern and southeastern regions from Espírito Santo to Rio Grande do Sul. D. gemmula is also documented in the Northeast region, specifically in the state of Ceará. D. vellicatus Reeve, 1855 has one record for the Brazilian coast, for Rio Grande do Norte, in 1971. The Donax species found along the coast of Sergipe have never undergone taxonomic investigation. Consequently, we performed a conchological analysis and geometric morphometric approaches to compare the morphology of donacids in Sergipe with Donax gemmula from São Paulo, species with which they resembled the most, aiming to identify the taxa present in Sergipe. We analyzed shells from 88 specimens of the Donax genus deposited at the Coleção de Zoologia da Universidade Federal de Sergipe, collected at three distinct location along the Aracaju coast, at Atalaia’s Beach (AT), southern part of Mosqueiro (SM) and northern part of Mosqueiro (NM). Additionally, we examined 59 specimens of Donax gemmula from Coleção de Malacologia do Museu de Zoologia da Universidade de São Paulo, originating from Santos-SP (SA) and São Sebastião-SP (SB) Brazil. Our analysis initially focused on shell characteristics, followed by a subsequent geometric morphometric analysis of the left valve. The conchological analysis revealed that individuals from the southern Mosqueiro population belong to the Donax gemmula species. However, the specimens from AT and NM could not be conclusively identified due to the absence of known diagnostic features for the described species. The statistical results from the morphometric analysis aligned with those from the conchological study. In the Principal Components Analysis (PCA), we observed a significant overlap between specimens from southern Mosqueiro and D. gemmula from São Paulo. However, the specimens from the AT and the NM exhibited minimal to no overlap with other populations, respectively. The Procrustes and Malahanobis distances between all population pairs were notably disticnt. Regression analysis of Procrustes coordinates against centroid size revealed an allometric relationship between size and shape. K-means analysis indicated the presence of two or three distinct morphotypes among all populations, effectively distinguishing the Atalaia Beach and northern Mosqueiro from the majority of other individuals, for both k = 2 and k = 3. Consequently, we deduce that D. gemmula is also present in another location along the northeastern coast, reinforcing the hypothesis that its distribution is continuous along the Brazilian coast. The specimens from AT and NM region exhibit striking morphological diferences from other Donax species and may potentially represent a significant latitudinal phenotypic plasticity within D. vellicatus or belong to a new species. Further research, including the study of Caribbean species, is imperative to validate these hypotheses.