Global Phylogeography of the Critically Endangered Hawksbill Turtle (Eretmochelys imbricata)

Introduction

• Global Study of Migratory Species: Rarely conducted comprehensively; leads to fragmented info on evolutionary history.
• Sea Turtles: Cosmopolitan, migrate across ocean basins.
  • Structured nesting populations vs. diverse foraging stocks.
• Phylogeographic Studies: Use genetic/distribution data for insights into origin, distribution, dynamics.
  • Important for structuring sea turtle populations, estimating gene flow, and understanding migrations.
• Mitochondrial DNA Markers: Common in sea turtle studies; control region (D-loop) used for analysis.
  • Data often limited to local populations; need for global data integration.
• Hawksbill Turtle: Critically endangered, threatened by human activities and coral reef degradation.

Material and Methods

Data Collection

• Compilation of mtDNA haplotypes from GenBank and Atlantic Ocean database.
• Focused on haplotypes with population frequency data.
• Populations with small sample sizes grouped by proximity.
• Standardized nomenclature: EiA (Atlantic) and EiIP (Indo-Pacific).

Phylogenetic Analysis

• Used BEAST software for lineage divergence times.
• Model: TrN+G+I with gamma shape and invariable proportion.
• Assumed rate homogeneity (strict molecular clock).
• Conducted runs for 200 million generations.

Genetic Diversity and Population Structure

• Estimated haplotype diversity, nucleotide differences, and population structure using DnaSP and PopART.
• Pairwise FST for population differentiation.
• SAMOVA used for grouping populations based on genetic variance.

Results

• Haplotype Distribution: 1983 individuals analyzed; 88 haplotypes in rookeries, 79 in foraging aggregations.
• Haplotype Ambiguities: Found and standardized nomenclature discrepancies.
• Lineage Divergence: Identified nine major mtDNA clades with divergence times from Pliocene and Pleistocene epochs.
• Genetic Diversity: Higher in Indo-Pacific than Atlantic populations.
• Population Structure: Significant differentiation in Indo-Pacific vs. Atlantic; complex regional groupings.

Discussion

Genetic Stocks

• Phylogeographic Patterns: Higher diversity in Indo-Pacific, no shared haplotypes between major oceanic basins.
• Complex Connectivity: Weak isolation by distance, influenced by ocean currents.
• Regional Grouping Challenges: Different tests suggest varied groupings.

Migration Patterns

• Foraging Aggregations: Mixed stocks; evidence of transoceanic movements.
• Unknown Origins: Many haplotypes without known source rookeries.
• Conservation Implications: Need for more sampling and tracking to understand migrations.

Phylogenetic History and Divergence Time

• Major Lineage Divergence: Atlantic and Indo-Pacific split in early Pliocene.
• Impact of Climate: Pleistocene climate cycles influenced genetic divergence.
• Recent Expansions: Lineages expanded during warmer periods.

Conclusions

• Divergent Lineages: Two major lineages split in early Pliocene, with population movements influenced by climate and currents.
• Data Standardization: Importance of comprehensive global data and collaboration.
• Conservation Needs: Highlighted need for international efforts and standardized data collection.

Acknowledgments

• Thanks to contributors and supporting organizations like CAPES, CNPq, FAPEMIG, and specific individuals for data and assistance.