Population connectivity and recruitment genetics in two tropical marine invertebrates with contrasting dispersal potential

• Grant number: 13/02003-7
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: May 01, 2014
• End date: August 31, 2015
• Field of knowledge: Biological Sciences - Genetics
• Principal Investigator: Augusto Alberto Valero Flores
• Grantee: Philippe St-Onge
• Host Institution: Centro de Biologia Marinha (CEBIMAR). Universidade de São Paulo (USP). São Sebastião , SP, Brazil

Abstract

The common tropical barnacle Chthamalus bisinuatus and the mottled shore crab Pachygrapsus transversus are two broadcast-spawning marine crustaceans naturally distributed along most of the entire South American Atlantic coast. Although both species share similar distribution patterns, they differ greatly in the amount of time spent developing in the water column as planktonic larvae. C. bisinuatus larvae are known to be fully competent after 12 to 15 days of planktonic life while P. transversus larvae usually remain in the plankton for well over two months before achieving competency and settling onto the benthic substrate. This discrepancy is likely to play an important role in the extent at which larvae are exchanged between populations. Since gene flow between populations occurs mainly through larval dispersal, studies evaluating the genetic structure and connectivity of populations at different temporal and spatial scales would provide useful information as to whether larval duration is a good proxy to predict high dispersal. However, such studies for C. bisinuatus and P. transversus are currently absent from the literature, probably due to the absence of highly polymorphic genetic markers for these species. This project will be separated into three major components: (1) isolation, primer design and characterization of highly polymorphic microsatellite markers for the common tropical barnacle C. bisinuatus and the mottled shore crab P. transversus; (2) genetic population structure of C. bisinuatus and P. transversus across their natural distribution; and (3) temporal monitoring of C. bisinuatus larval cohorts from birth to settlement using genetic parental analyses to assess the overall importance of larval retention in recruitment processes. The first component will be carried out using next-generation sequencing platforms such as Illumina and 454. Sequences will be screened for microsatellite tandem repeats to allow proper design of forward and reverse primers. Each potential microsatellite marker will then be linked with a fluorochrome and tested for polymorphism and frequency of null alleles on a small population of individuals using capillary electrophoresis. For the second component, both crustacean species will be sampled across their natural distribution along the South American coast. Samples will be genotyped and tested for population structure using classical statistical analyses proper to the field of population genetics. It is hypothesized that C. bisinuatus will show more highly structured populations than P. transversus as a result of reduced larval transport, reduced gene flow between populations and increased frequency of larval retention episodes. Finally, the last component will be carried out by monitoring larval cohorts from birth to settlement in a single population. Seawater above adult aggregates will be pumped and sieved using a modified larval trap and a 12V bilge pump. Collected samples will then be brought back to the laboratory to isolate live individual cyprids into ethanol-filled vials. Each larva will be genotyped to infer parental relations and evaluate the overall importance of larval retention. This study will be important for the ecology of broadcast-spawning marine invertebrates as it will increase our understanding of larval dispersal processes and their effects on the genetic population structure at different spatial and temporal scales. (AU)