Larval morphology in caridean shrimps: applied microscopical key tools for a new perspective in taxonomy and systematics

• Grant number: 24/01947-6
• Support Opportunities: Regular Research Grants
• Duration: July 01, 2024 - June 30, 2026
• Field of knowledge: Biological Sciences - Zoology - Morphology of Recent Groups
• Principal Investigator: Fernando Jose Zara
• Grantee: Fernando Jose Zara
• Host Institution: Faculdade de Ciências Agrárias e Veterinárias (FCAV). Universidade Estadual Paulista (UNESP). Campus de Jaboticabal. Jaboticabal , SP, Brazil
• Associated research grant: 18/13685-5 - Integrative analysis of the Brazilian fauna of decapod crustaceans: taxonomy, phylogenetic systematics, spermiotaxonomy, morphology of post-embryonic development, ecology and conservation, AP.BTA.TEM
• Associated scholarship(s): 24/13154-0 - Larval morphology of carid shrimps: application of different microscopic tools for taxonomy and systematics, BP.JD

Abstract

The morphological description of the larval stages of Decapoda crustaceans contribute to the classification of new species in an integrated manner along with molecular biology and adult morphology, contemplating the requirements of modern taxonomy. Furthermore, larval studies assist in the identification of species, the description of new taxa, as well as ecological, behavioral and distribution and dispersal studies across the plankton. The identification of larval stages can be a complex task, since many taxa still contain a deficiency regarding the different larval forms, with only a brief description of their morphology, few illustrations and a low number of parental individuals identified at the species level. Traditionally, studies related to the larval morphology of decapods use light microscopy (LM), and for shrimp from the Caridea infraorder, few studies are found using different microscopic techniques. The application of scanning electron microscopy (SEM) has already been used in combination with LM for carideans describing mainly hard structures of mouth appendages or just details of appendages, setae or spinules. It is possible to correlate this deficiency in an integrated study with SEM due to the variability of techniques for fixing/preserving samples. Although there are comparative processes demonstrating that using an ascending graded series of ethanol (30%, 50%, 70%) can result in less shrinkage of the structures, there is still a wide variety of preparation methods applied to caridean larvae, with the use of the aforementioned graded series of ethanol; 2.5% glutaraldehyde (in seawater); 4% formaldehyde; or 10% formaldehyde. Therefore, determining a specific standard for preparing caridean larvae for SEM is necessary to guarantee the quality of the data generated, so that they are consistent and reproducible, guaranteeing scientific validation for comparison of results. In addition, the application of phase differential interference contrast (DIC) microscopy and confocal fluorescence can also complement information obtained by combining LM and SEM. Using DIC microscopy, combined with image stacking techniques in different focal planes (confocal), it is possible to observe the morphological structures of the larvae in three dimensions, with contrasts or marked by endogenous or artificial fluorescein, for example, highlighting setae positions on appendages. To test the integration of microscopy techniques, the species of Lysmata Risso, 1816, widely distributed in tropical and subtropical regions and which have high value for ornamental aquarium farming, will be used as a model. Its species are grouped into different clades, with lineages defined considering molecular phylogeny, "Tropical American", "Cleaner", "Cosmopolitan" and "Morphovariable", or by morphological characters of adults, following the active branch of the antennule, "long accessory branch" (LAB), "short accessory branch" (SAB) and "ungiform branch" (UB). Larval morphology can also contribute to the definition of lineages in Lysmata, in which species that hatch in zoea I with the presence of the fifth pair of pereopods are part of LAB, and those that hatch without this appendage are part of SAB or UB. Despite this, currently only 10 species, among the approximately 50 described for the genus, present information on larval morphology. Therefore, a morphological analysis will be applied using integrative microscopy techniques (LM, SEM, DIC and confocal) to describe the zoea objectives of three species of Lysmata, and the morphological characteristics of their appendages will be compared and grouped to ascertain the contribution of the larval morphology in separating the different clades described for the genus. (AU)