SKULL DIVERSITY OF THE GUIANA DOLPHIN Sotalia guianensis (VAN BÉNÉDEN, 1864) ON THE COAST OF THE STATE OF SÃO PAULO - THE USE OF GEOMETRIC MORPHOLOGY IN UNDERSTANDING THE GEOGRAPHIC VARIATION PATTERNS OF THE SPECIES

• Grant number: 24/05304-2
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: September 01, 2024
• Status: Discontinued
• Field of knowledge: Biological Sciences - Zoology - Taxonomy of Recent Groups
• Principal Investigator: Alexandre Reis Percequillo
• Grantee: Helena Micucci Pires Amaral
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

The Guiana dolphin Sotalia guianensis (Van Bénéden, 1864) is one of the Sotalia genus species to inhabit the estuarine-coastal regions of South America, including the Amazon river system (Da Silva & Best, 1996). The effective separation between the species of the genus is relatively recent and occurred via morphology (Borobia, 1989), three-dimensional geometric morphometry (Montero-Filho et al.,2002) and genetic analysis (Cunha et al., 2005; Caballero et al., 2007). As well as other aquatic mammals, especially those of the infraorder Cetacea, the stranding of Guiana dolphins is a relatively common event in nature, however, it has been intensified by the environmental degradation and fishing activities, which overlaps the natural habitat of S. guianensis. São Paulo's coastline has highly anthropic regions, so stranding in this region may be related to human action and may vary according to the progress of these activities. Recently, the distribution area of S. guianensis was divided into 12 Management Units, based on morphological, genetic, and population evidence, which indicated large-scale population structures (Domit et al., 2021), 8 of which are on the Brazilian coast. São Paulo's coast is located between two Management Units, in other words, between two population structures, representing a transition area for the already known and delimited populations of this species. In this context, the question arises as to the relationship between São Paulo's dolphins and the individuals from neighboring states. This study aims to carry out morphological analysis using 3D geometric morphometry of Guiana dolphin's skulls in order to understand age, sex, and size variation of individuals stranded and collected over almost 30 decades, which are currently in mammalogical collections. After the morphometric analysis, a qualitative and quantitative description will be done based on the data obtained in order to relate the stranded specimens from São Paulo to anthropogenic activities in recent decades, as well as relate them to individuals from the northern and souther regions of the state.