Evolution of the mantle margin in Pteriomorphia (Mollusca: Bivalvia): insights into the macroecology of the marine benthos

Author(s)

Jorge Alves Audino

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2019-05-31

Examining board members

José Eduardo Amoroso Rodriguez Marian; Daniel José Galafasse Lahr; Fabrizio Marcondes Machado; Flávio Dias Passos; Marcello Guimarães Simões

• Advisor: José Eduardo Amoroso Rodriguez Marian

Abstract

The mantle margin in bivalve mollusks typically comprises three folds, being considered a key element in the evolutionary radiation of the class and occupancy of novel ecological niches. In the subclass Pteriomorphia, which includes oysters, scallops, and mussels, the mantle margin is significantly diverse. In addition, several lines of evidence suggest the association between mantle structures and diversification of lifestyles, making the mantle margin a suitable anatomical region for studies focused on adaptations and phenotype-environment correlations. The present investigation evaluated the morphological diversity of the mantle margin in Pteriomorphia, by means of comparative and functional approaches, to infer the evolution of this anatomical region, and test hypotheses of homology, convergence and correlation. The methodology included: (1) phylogenetic inference of Pteriomorphia based on 187 taxa and up to five genes; (2) comparative morphology of 209 species based on observations of archived specimens, survey of key mantle traits and subsequent use of phylogenetic comparative methods; and (3) detailed anatomy of the mantle margin in representatives of 12 species from the most diverse pteriomorphian families, which were collected and analyzed by means of histology, scanning electron microscopy and confocal microscopy. Phylogenetic analyses of Pteriomorphia corroborate its monophyly and indicate it is comprised of four orders divided in two main clades (Arcida+Pectinida and Ostreida+Mytilida). The inferred evolution of the mantle margin suggests the origin of five types of photoreceptor organs in independent epifaunal lineages, with subsequent loss of eyespots mostly in groups that became infaunal. Evolutionary convergences were pervasive in pteriomorphian radiation, as illustrated by multiple gains of mantle tentacles. Some convergences are correlated with transitions to infaunal lifestyles, as demonstrated by the hypertrophy of the inner mantle fold in lineages within Arcida and Mytilida. In addition, the detailed investigation of musculature, innervation, secretory activity and cilia of the mantle margin permitted inferring possible functions performed by mantle folds, eyespots, tentacles, glands and further associated structures. Altogether, the results shed light on the evolution of the mantle margin in Pteriomorphia in association with lifestyle shifts, therefore providing bases to explore macroecological questions in the evolutionary radiation of bivalves and the marine benthos as a whole (AU)

• FAPESP's process: 15/09519-4 - Evolution and functional anatomy of the mantle margin in the Pteriomorphia (Mollusca, Bivalvia)
• Grantee: Jorge Alves Audino
• Support Opportunities: Scholarships in Brazil - Doctorate