Combined use of mitochondrial and nuclear genetic markers further reveal immature marine turtle hybrids along the South Western Atlantic.

Cíntia Brito,Maíra Carneiro Proietti,Rodrigo Maggioni,Ana Luzia Lacerda,Maria Ângela Marcovaldi,Sibelle Torres Vilaça,Gabriela Vélez-Rubio

doi:10.1590/1678-4685-gmb-2019-0098

Abstract

Marine turtle hybridization is usually sporadic and involves reports of only a few individuals; however, Brazilian populations have high hybridization rates. Here we investigated the presence of hybrids in morphologically identified immature hawksbills (Eretmochelys imbricata) along the South Western Atlantic (SWA). We sequenced one mitochondrial (D-Loop) and three nuclear DNA (RAG1, RAG2, and CMOS) markers to better understand the patterns and characteristics of hybrids. We identified 22 hybrids (n = 270), 11 of them at the extreme South of the SWA. Uruguay had the highest hybrid frequency in the SWA (~37.5%) followed by southern Brazil with 30%. These are common areas for loggerheads (Caretta caretta) but uncommon for hawksbills, and these hybrids may be adopting the behavior of loggerheads. By analyzing nuclear markers, we can infer that 50% of the sampled hybrids are first generation (F1) and 36% are the result of backcrosses between hybrids and pure E. imbricata (> F1). We also report for the first time immature E. imbricata x Lepidochelys olivacea hybrids at the Brazilian coast. Considering the high frequency of hybrids in the SWA, continuous monitoring should be performed to assess the fitness, genetic integrity, and extent of changes in the gene pools of involved populations.

Highlights

Hybridization can be defined as the production of offspring by the crossbreeding between genetically different populations or species (Harrison, 1990)
Through the combined analysis of mtDNA and nDNA (RAG1, RAG2 and CMOS) markers, we evaluated if: 1) the use of multiple markers enhances the detection of immature hybrids; 2) immature hybrid turtles present preference for certain foraging areas; and (3) the identified immature hybrid turtles are first generation (F1), the result of crossing between hybrids (F2), or of introgression between hybrids and pure parent species (>F1)
Our study shows the importance of the combined use of mtDNA and nDNA markers in the evaluation of hybridization among marine turtles

Summary

Introduction

Hybridization can be defined as the production of offspring by the crossbreeding between genetically different populations or species (Harrison, 1990). At least 25% of plant species and 10% of animal species are involved in hybridization processes and potential introgression (Mallet, 2005). According to Rieseberg and Wendell (1993), introgression can be defined as “the incorporation of genes from one set of different populations into another, i.e. the incorporation of external alleles into a new, reproductively integrated population system”. These processes are considered natural in evolution, and continuous events of interspecific and intergeneric hybridization may lead to the appearance of new species (e.g. 50-70% of angiosperms; Whitham et al, 1991). It is possible that this interbreeding occurs due to the lack of reproductive barriers (Seminoff et al, 2003) and a chromosomal compatibility between the different species (Karl et al, 1995)

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