Mexican origins for the Texas green turtle foraging aggregation: A cautionary tale of incomplete baselines and poor marker resolution

Abstract

The green turtle (Chelonia mydas) foraging aggregation along the Texas coast has increased dramatically in recent years, but the source populations for these turtles have not been adequately resolved. Previous mixed stock analysis (MSA) based on 490 base pair (bp) mitochondrial control region haplotypes suggested a large Florida contribution, but widespread sharing of common haplotypes among potential source populations and incomplete source population baseline data precluded precise assessment. To test the hypothesis that Texas turtles may represent proximal western Gulf of Mexico (GoM) nesting populations, we analyzed novel rookery samples from Rancho Nuevo, Tamaulipas, Mexico (RNMX) and conducted oceanic connectivity simulations. The RNMX samples yielded haplotypes CM-A1.1 and CM-A3.1 in frequencies not significantly different from those of the central eastern Florida nesting population. However, mitogenomic sequencing identified a diagnostic mitochondrial SNP (mtSNP) variant that is fixed in RNMX relative to the Florida CM-A1.1 lineage. Pairwise comparisons indicate that the Tamaulipas rookery represents a discrete population relative to those previously described in the northern Greater Caribbean, warranting recognition of a western GoM management unit (MU). Contrary to previous findings, the Florida populations were ruled out as major contributors to the Texas aggregation through screening of the mtSNP. Mixed stock analysis incorporating the mtSNP data suggested a western GoM origin for approximately 70% of the Texas foraging aggregation, with Quintana Roo contributing the majority of the remainder. Backtracking

Predicted distributions and abundances of the sea turtle ‘lost years’ in the western North Atlantic Ocean

“…6B) also appears consistent with existing data on the genetic structure of green turtles. For instance, the mitogenomics of stranded green turtles in Texas point toward origins from Mexico and Costa Rica, rather than Florida (Shamblin et al 2017) and our model's predictions of juvenile inputs to Texas from nesting beaches across Mexico and Costa Rica (but not Florida) are closely related to green turtle strandings (Supplementary material Appendix 1 Table A4). For the eastern Gulf of Mexico, genetic analyses of green turtles indicate inputs from populations in Mexico, Costa Rica and Florida, though proportions may vary over time or sub-regionally (Foley et al 2007, Naro-Maciel et al 2017, Shamblin et al 2018.…”

Fibropapillomatosis prevalence and distribution in green turtles Chelonia mydas in Texas (USA)

“…The fact that FP tumors were first detected in green turtles at neritic foraging areas in southern Florida in 1937 (Hirama & Ehrhart 2007) and in the Hawaiian Islands in 1958(Balazs & Pooley 1991, but not in Texas until nearly half a century later, is compelling evidence and could provide clues regarding how the disease spreads to new areas. The Texas neritic foraging juvenile green turtle population is genetically distinct, indicating isolation of these western Gulf of Mexico juvenile green turtles (Shamblin et al 2017). Thus, the late appearance and increasing prevalence of FP in Texas green turtles could be due to novel incursion of the virus into an immunologically naive population.…”

Advances in the Application of Genetics in Marine Turtle Biology and Conservation

“…This marker demonstrated that turtles nesting in Florida and Tamaulipas represented distinct populations. Subsequent MSA including the mtDNA SNP excluded Florida as a source of Texas foraging juveniles, and established the strong connectivity between this foraging aggregation and the newly proposed western Gulf of Mexico MU (Shamblin et al, 2017).…”

“…An MSA of juvenile green turtles in Texas foraging grounds suggested a large Florida rookery contribution based on the presence of these haplotypes at high frequencies (Anderson et al, 2013). Yet later analysis of the green turtle rookery at Rancho Nuevo, Tamaulipas, Mexico found CM-A1 and CM-A3 in the same frequencies as the central Florida MU, so the source of the majority of juveniles foraging in Texas remained unresolved using standard markers (Shamblin et al, 2015a(Shamblin et al, , 2017. However, mitogenomic sequencing of the CM-A1 females nesting in Rancho Nuevo and Florida identified a single diagnostic mtDNA SNP between the two rookeries.…”

“…This is particularly important for identifying population "units to conserve" (see Box 2) and for conducting meaningful MSA and individual assignments that require a comprehensive rookery baseline dataset of potential natal stock sources. Lack of this information can significantly limit MSA and assignment inferences, and in some cases can lead to inaccurate interpretation of results (Shamblin et al, 2017). In the case of oceanic juvenile loggerheads foraging in the North Atlantic, baseline 817 bp haplotype data were initially lacking for several potentially contributing rookeries, preventing robust MSA.…”