A phylophysiological evaluation of osmotic and ionic regulatory mechanisms in Fiddler Crabs (Brachyura, Ocypodidae: Gelasiminae e Ocypodinae) from the Neotropical Coasts of Equador and Mexico

• Grant number: 22/14344-2
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: October 01, 2023
• End date: January 31, 2027
• Field of knowledge: Biological Sciences - Physiology - Compared Physiology
• Principal Investigator: Samuel Coelho de Faria
• Grantee: Luiza Grassi Villela
• Host Institution: Centro de Biologia Marinha (CEBIMAR). Universidade de São Paulo (USP). São Sebastião , SP, Brazil

Abstract

The zoogeographical distribution of fiddler crabs has changed extensively over evolutionary time, with environmental salinity likely driving their dispersal. Those inhabiting the Indo-Pacific Ocean constitute a monophyletic group of six genera and 46 species while those from Neotropical America are divided into two large clades of three and a single genus, respectively containing 48 and 10 species, distributed along both coasts. This project aims to phylogenetically compare the osmoregulatory physiology of selected species from riverine, mangrove and semi-terrestrial habitats from the shores of the eastern Pacific and western Atlantic Oceans of Neotropical America. We will investigate three groupings of four genera including 34 species that are part of three biogeographical areas: (i) the Pacific coast of Ecuador and (ii) Baja California, Mexico [Eastern Pacific Ocean]; and (iii) the Yucatán Peninsula, Mexico [Western Atlantic Ocean]. Area (i) already has been explored, hemolymph samples obtained, and analyses are currently in progress. For domains (ii) and (iii), after a 5-day exposure of the crabs to different salinities, their lower (LI50) and upper (LS50) lethal salinity limits will be established, and their hemolymph osmotic and ionic (Cl- and Na+) regulatory curves, isosmotic and ionic points, hyper- and hypo-regulatory capabilities, and hemolymph osmolality, [Cl-] and [Na+] at the LI50 and LS50 will be generated for the three groupings. We will also investigate the molecular basis of osmoregulatory ability, including enzyme activity, gene and protein expression and immunocytochemical localization of ion transporters like the Na+/K+- and V(H+)-ATPases and Na+-K+-2Cl symporter in the posterior gills. By including existing data for the ten species of fiddler crabs inhabiting the eastern coast of South America, these findings will enable a better understanding of the evolution of osmoregulatory mechanisms in semi-terrestrial crabs and allow assessment of adaptability from a phylophysiological point of view. (AU)