Search

Author(s): Banerjee, Shreya M; Frey, Amy; Kurle, Carolyn M; Perrault, Justin R; Stewart, Kelly R | Abstract: Understanding species’ mating systems provides important information about their ecology, life history, and behavior. Direct observations of mating behaviors can be challenging, but molecular techniques can reveal information about mating systems and paternal identity in difficult-to-observe species such as sea turtles. Genetic markers can be used to assess the paternity of a clutch and to assign hatchlings to a father. Leatherback turtles Dermochelys coriacea sometimes mate with multiple individuals, resulting in clutches with mixed paternity; however, the effects of multiple paternity on hatchling quality are unclear. Leatherback hatchlings at Sandy Point National Wildlife Refuge, St. Croix, US Virgin Islands, exhibit visible variation in individual body size, sometimes within the same clutch. We collected morphometrics and tissue samples from hatchlings across multiple nesting seasons (2009, 2012, 2013, 2015, and 2016) and found that hatchlings exhibited small but statistically significant differences in morphometrics between years. We used maternal and hatchling microsatellite genotypes to reconstruct paternal genotypes, assigning fathers to each hatchling. We found multiple paternity in 5 of 17 clutches analyzed and compared differences in morphometrics between full-siblings with differences between half-siblings. We found no significant differences between morphometrics of hatchlings from the same mother but different fathers. We compared within-clutch variances in morphometrics for clutches with and without multiple paternity and found no significant difference in morphological variation between them. Therefore, we could not attribute differences in hatchling size within a clutch to paternal contribution. Understanding other factors affecting hatchling morphology, and other possible fitness metrics, may reveal insights into the benefits, or lack thereof, of polyandry in sea turtles.

Assessing population connectivity and identifying conservation units are critical to formulating effective management plans for marine turtles. We combined a multiplexed targeted enrichment capture technique and high-throughput sequencing to discover single nucleotide polymorphisms (SNPs) and to genotype hawksbill turtles (Eretmochelys imbricata) to examine population structure. Our approach discovered 455 potential informative SNPs for hawksbill turtles. We optimized 25 of the 455 SNPs discovered and used them to identify preliminary evidence of hawksbill population structure, suggesting that these markers will be informative in discerning conservation units when applied to larger sample sizes in future studies.

BackgroundTranscriptomic data has demonstrated utility to advance the study of physiological diversity and organisms’ responses to environmental stressors. However, a lack of genomic resources and challenges associated with collecting high-quality RNA can limit its application for many wild populations. Minimally invasive blood sampling combined with de novo transcriptomic approaches has great potential to alleviate these barriers. Here, we advance these goals for marine turtles by generating high quality de novo blood transcriptome assemblies to characterize functional diversity and compare global transcriptional profiles between tissues, species, and foraging aggregations.ResultsWe generated high quality blood transcriptome assemblies for hawksbill (Eretmochelys imbricata),loggerhead (Caretta caretta), green (Chelonia mydas), and leatherback (Dermochelys coriacea) turtles. The functional diversity in assembled blood transcriptomes was comparable to those from more traditionally sampled tissues. A total of 31.3% of orthogroups identified were present in all four species, representing a core set of conserved genes expressed in blood and shared across marine turtle species. We observed strong species-specific expression of these genes, as well as distinct transcriptomic profiles between green turtle foraging aggregations that inhabit areas of greater or lesser anthropogenic disturbance.ConclusionsObtaining global gene expression data through non-lethal, minimally invasive sampling can greatly expand the applications of RNA-sequencing in protected long-lived species such as marine turtles. The distinct differences in gene expression signatures between species and foraging aggregations provide insight into the functional genomics underlying the diversity in this ancient vertebrate lineage. The transcriptomic resources generated here can be used in further studies examining the evolutionary ecology and anthropogenic impacts on marine turtles.

Mapping vertebrate incompatibility alleles Deleterious gene interactions may underlie the observed hybrid incompatibilities. However, few genes underlying hybrid incompatibilities have been identified, and most of these involve species that do not hybridize in natural conditions. Powell et al. used genome sequencing to map genes likely responsible for incompatibilities that reduce fitness in naturally occurring hybrid swordtail fish. These gene combinations result in malignant melanoma, which is found in naturally hybridizing populations but is not present in the parental populations (see the Perspective by Dagilis and Matute). Using genome and population resequencing, the authors performed a genome-wide association study to identify potentially causative mutations. Using an admixture mapping approach that assessed introgression between multiple swordtail fish species, the authors suggest that lineages carry different genes that interact with the same candidate gene, resulting in the observed melanomas and providing insight into convergent hybrid incompatibles that arise between species. Science , this issue p. 731 ; see also p. 710

Urban coastal ecosystems are unique intersections of human development and biodiversity, and monitoring populations in these areas is critical to understanding ecosystem health and function. Three highly urbanized estuary systems, San Diego Bay, San Gabriel River, and Seal Beach National Wildlife Refuge (all in California), are the northernmost foraging habitats for green turtles (Chelonia mydas) in the Eastern Pacific. Here, we report blood biochemistry and morphological parameters for these Southern California green sea turtle foraging aggregations to investigate the current health status of these animals and provide baseline values for future work. Morphometric and blood biochemistry parameters for green turtles captured in this study (n = 39) were clinically reasonable and were generally consistent with previously reported parameters for green turtles.