Morphology vs Genetics: the hybrid origin of a sea turtle disproved by DNA

Abstract

A putative hybrid sea turtle juvenile was evaluated with discriminant DNA markers. When compared with standard values for sea turtles, the general morphological features assigned the specimen to Caretta caretta, while the shape and coloration of the head and the beak profile fell within the Eretmochelys imbricata range; the front flippers were instead like those of a Chelonia mydas. Moreover, prefrontal scale number was outside the putative parental species’ ranges. The mitochondrial D-loop sequence was from C. caretta, and matched haplotype CC-A2.1, the most common in the Mediterranean. Sequence profiles at three nuclear loci withspecies-specific substitutions (Cmos, BDNF and R35) revealed only C. caretta variants, thus excluding that the individual wasan F1 hybrid. This study highlights the importance of integrating different methodological approaches to understand reproductive animal biology and to set the boundaries for specific morphological traits. In particular, we propose the genetic analysis of a new combination of mitochondrial and nuclear markers as a standard procedure which can be adopted in the identification of sea turtlehybrids.

Integrating morphological, molecular and cytogenetic data for F2 sea turtle hybrids diagnosis revealed balanced chromosomal sets

“…Morphological analysis of sea turtles is an essential filter for determining when to execute genetic analysis for hybrids recognition (Garofalo et al, 2012; Seminoff et al, 2003). Our results from hybrids A and B showed mixed morphological traits of the parental sea turtle species.…”

“…The hybrid B's carapace demonstrated a non‐modal scute pattern and alterations in plastron and flipper claw patterns (Pritchard & Mortimer, 1999; Wyneken, 2001). These traits are known for their natural variability at an individual level in sea turtle species (Garofalo et al, 2012; Pritchard & Mortimer, 1999; Wyneken, 2001). Still, these alterations, combined with the phenotypic similarity of hybrid B 's head and carapace to those of olive ridleys, can indicate a crossbreeding between C. caretta and L. olivacea .…”

“…First, the number of prefrontal and postorbital scales was counted, followed by the count of vertebral, lateral, nuchal, marginal and supracaudal carapace scutes. Then, some secondary characteristics were evaluated, such as the general shape of the head and carapace of the individuals, patterns of scutes on the plastron and the number of claws in flippers (Garofalo et al, 2012; Pritchard & Mortimer, 1999; Sim et al, 2014; Wyneken, 2001).…”

“…Sea turtles exhibit significant phenotypic variability in the number and shape of carapace scutes and head scales (Mast & Carr, 1989; Ozdemir & Turkozan, 2006; Pritchard & Mortimer, 1999; Sim et al, 2014; Wyneken, 2001). However, this variability can also occur due to hybridization, making the analysis of morphological parameters one of the first steps to identify potentially hybrid sea turtles and thus screen them for further genetic analysis (Garofalo et al, 2012; Hart et al, 2019; Kelez et al, 2016; Sim et al, 2014). Studies of hybrids with molecular markers allow the analysis of hybridization events with better precision than morphology‐based approaches, constituting a tool for identifying the parental lineages (Seminoff et al, 2003; Vilaça et al, 2012).…”

Mitochondrial diversity and inter-specific phylogeny among dolphins of the genus Stenella in the Southwest Atlantic Ocean

“…Although intermediate morphology is strong evidence of hybridization, it should not be considered as a diagnostic. There is a possibility that hybrids (fertile cases) will backcross with one of the parental species and exhibit the dominant morphology of this species and, therefore, be "camouflaged" within these populations [ 67 ].…”