Conservation implications of complex population structure: lessons from the loggerhead turtle (Caretta caretta)

Abstract

Complex population structure can result from either sex-biased gene flow or population overlap during migrations. Loggerhead turtles (Caretta caretta) have both traits, providing an instructive case history for wildlife management. Based on surveys of maternally inherited mtDNA, pelagic post-hatchlings show no population structure across the northern Atlantic (phi(ST) < 0.001, P = 0.919), subadults in coastal habitat show low structure among locations (phi(ST) = 0.01, P < 0.005), and nesting colonies along the southeastern coast of the United States have strong structure (phi(ST) = 0.42, P < 0.001). Thus the level of population structure increases through progressive life history stages. In contrast, a survey of biparentally inherited microsatellite DNA shows no significant population structure: R(ST) < 0.001; F(ST) = 0.002 (P > 0.05) across the same nesting colonies. These results indicate that loggerhead females home faithfully to their natal nesting colony, but males provide an avenue of gene flow between regional nesting colonies, probably via opportunistic mating in migratory corridors. As a result, all breeding populations in the southeastern United States have similar levels of microsatellite diversity (H(E) = 0.70-0.89), whereas mtDNA haplotype diversity varies dramatically (h = 0.00-0.66). Under a conventional interpretation of the nuclear DNA data, the entire southeastern United States would be regarded as a single management unit, yet the mtDNA data indicate multiple isolated populations. This complex population structure mandates a different management strategy at each life stage. Perturbations to pelagic juveniles will have a diffuse impact on Atlantic nesting colonies, mortality of subadults will have a more focused impact on nearby breeding populations, and disturbances to adults will have pinpoint impact on corresponding breeding populations. These findings demonstrate that surveys of multiple life stages are desirable to resolve management units in migratory marine species.

Population structure and conservation implications for the loggerhead sea turtle of the Cape Verde Islands

“…While North Atlantic and Mediterranean loggerhead turtles are a relatively well-studied systems in population genetics and connectivity research Encalada et al 1998;Laurent et al 1998;Bowen et al 2004Bowen et al , 2005Carreras et al 2006Carreras et al , 2007Lee 2008), key gaps in sampling still remain. The second largest nesting aggregation of the globally endangered loggerhead sea turtle (IUCN 2007) in the Atlantic Ocean is found at the Cape Verde Islands, which is also the only major rookery in Western Africa for this species.…”

“…Samples from most major loggerhead turtle rookeries, albeit with significant exceptions such as the Cape Verde Islands, have been sequenced at the mitochondrial DNA control region Bowen et al 2005;Carreras et al 2007;Reis et al in press), revealing significant genetic differentiation among most rookeries. More recent control region research identified five rookery groups in the Western Atlantic (Bowen et al 2005). In the eastern Mediterranean, Carreras et al (2007) found four independent units, most of them characterized by one exclusive haplotype.…”

“…In sea turtles, the contrast between mitochondrial (mtDNA) and nuclear (nDNA) results and among different life stages highlights the complex population structure of these organisms and the need to examine multiple genetic markers and life stages (Bowen et al 2005). Samples from most major loggerhead turtle rookeries, albeit with significant exceptions such as the Cape Verde Islands, have been sequenced at the mitochondrial DNA control region Bowen et al 2005;Carreras et al 2007;Reis et al in press), revealing significant genetic differentiation among most rookeries.…”

Sea Turtles in Florida's Atlantic Waters

“…As sea turtles approach maturity, they move to waters in closer proximity to nesting beaches (Bowen et al, 2005) and commence migratory breeding cycles every one to nine years depending on the species and ocean basin (Carr and Ogren, 1960;Miller, 1997). During nesting season, adult turtles temporarily reside in neritic waters along the continental shelf, just off nesting beaches (Stoneburner, 1982;Mortimer and Porter, 1989;TEWG, 2009).…”

Genetic fingerprinting reveals natal origins of male leatherback turtles encountered in the Atlantic Ocean and Mediterranean Sea

“…Like the seals and birds described above, they are highly migratory, traveling great distances between reproductive sites and foraging grounds . While breeding areas are relatively discrete geographically and genetically, foraging areas for marine turtles may comprise individuals from multiple populations and geographic locations (Bowen et al 2005;Murphy et al 2006;Bolker et al 2007;Doyle et al 2008;López-Mendilaharsu et al 2009;Wallace et al 2010;Tucker et al 2014). Their broad distribution makes them vulnerable to a variety of anthropogenic threats including interactions with fishing gear (Stewart et al 2016), entanglement, and marine debris ingestion at varying spatial scales, which are important to understand for management purposes because certain populations (especially small ones) may be differentially affected by these threats (Stewart et al 2016).…”