Mitochondrial DNA Variation Reveals a Sharp Genetic Break within the Distribution of the Blue Land Crab Cardisoma guanhumi in the Western Central Atlantic.

Maria Amaral,Alan Mckinley,Fabio Diniz,Severino Cavalcante De Sousa,Marc Albrecht,Adriana De Carvalho

doi:10.3390/molecules200815158

Abstract

The blue land crab Cardisoma guanhumi is widely distributed throughout tropical and subtropical estuarine regions in the Western Central Atlantic (WCA). Patterns of population genetic structure and historical demographics of the species were assessed by mtDNA control region sequence analysis to examine the connectivity among five populations (n = 97) within the region for future conservation strategies and decision-making of fishery management. A total of 234 polymorphic nucleotides were revealed within the sequence region, which have defined 93 distinct haplotypes. No dominant mtDNA haplotypes were found but instead a distribution of a few low-frequency recurrent haplotypes with a large number of singletons. A NJ-tree and a median-joining haplotype network revealed two distinct clusters, corresponding to individuals from estuaries located along the Caribbean Sea and Brazilian waters, respectively. AMOVA and FST statistics supported the hypothesis that two main geographic regions exists. Phylogeographical discontinuity was further demonstrated by the Bayesian assignment analysis and a significant pattern of isolation-by-distance. Additionally, tests of neutral evolution and analysis of mismatch distribution indicate a complex demographic history in the WCA, which corresponds to bottleneck and subsequent population growth. Overall, a sharp genetic break between Caribbean and Brazilian populations raised concerns over the conservation status of the blue land crab.

Highlights

The blue land crab Cardisoma guanhumi Latreille 1825 (Decapoda: Brachyura: Gecarcinidae) is a nearly terrestrial species widely distributed throughout tropical and subtropical estuarine regions in the Western Central Atlantic, ranging from southeast Florida, Central America and the Bermudas, through the Gulf of Mexico and parts of the Caribbean Islands, to Brazil [1,2,3,4,5]
High values of haplotype diversity and of nucleotide diversity were observed (Table 1), which is similar to a previous report based on the same investigated species from populations distributed along the Brazilian coast using the mitochondrial DNA
The extensively high values for haplotype and nucleotide diversity could be attributed to the complex and variable nature of C. guanhumi population distribution in the Western Central Atlantic [40] with deep evolutionary history, a combination of a high mutation rate in the study fragment and the large population size of the species [41,42]. This result indicates to some extent that the genetic diversity of the blue land crab is characterized by high genetic variability distributed homogeneously within each main geographical region (Caribbean Sea and the Brazilian coast), as observed in a previous study within Brazilian mangroves exclusively [31], and on other crab species (e.g., [43,44])

Summary

Introduction

The blue land crab Cardisoma guanhumi Latreille 1825 (Decapoda: Brachyura: Gecarcinidae) is a nearly terrestrial species widely distributed throughout tropical and subtropical estuarine regions in the Western Central Atlantic, ranging from southeast Florida, Central America and the Bermudas, through the Gulf of Mexico and parts of the Caribbean Islands, to Brazil (from Ceará to São Paulo) [1,2,3,4,5]. The species is intensively exploited as a food resource in many countries along the Atlantic coast of Central and South America, Puerto Rico, the Bahamas, Honduras, Columbia, Venezuela, and Northeast Brazil [7,8,9,10], which has led to increase pressure on overfishing, and contributing to unsustainable fisheries throughout its distribution range. The species is currently listed as “threatened, over-exploited, or threatened with overexploitation” in Brazil [14] and as “biologically vulnerable” by the Florida Fish and Wildlife Conservation Commission [15] in USA. This current fishing status has revealed the need for developing and implementing effective management strategies for the conservation of their wild stocks

Results

Discussion

Conclusion