Abstract: The likelihood ratio (LR) method is commonly used to determine kinship in civil, criminal, or forensic cases. For the past 15 years, our research group has also applied LR to ancient STR data and obtained kinship results for collections of graves or necropolises. Although we were able to reconstruct large genealogies, some pairs of individuals showed ambiguous results. Second-degree relationships, half-sibling pairs for example, were often inconsistent with detected first-degree relationships, such as parent/child or brother/sister pairs. We therefore set about providing empirical estimations of the error rates for the LR method in living populations with STR allelic diversities comparable to that of the ancient populations we had previously studied. We collected biological samples in the field in North-Eastern Siberia and West Africa and studied more than 800 pairs of STR profiles from individuals with known relationships. Because commercial STR panels were constructed for specific regions (namely Europe and North America), their allelic makeup showed a significant deficit in diversity when compared to European populations, replicating a situation often faced in ancient DNA studies. We assessed the capacity of the LR method to confirm known relationships (effectiveness) and its capacity to detect those relationships (reliability). Concerns over the effectiveness of LR determinations are mostly an issue in forensic studies, while the reliability of the detection of kinship is an issue for the study of necropolises or other large gatherings of unidentified individuals, such as disaster victims or mass graves. We show that the application of LR to both test populations highlights specific issues (both false positives and false negatives) that prevent the confirmation of second-degree kinship or even full siblingship in small populations. Up to 29% of detected full sibling relationships were either overestimated half-sibling relationships or underestimated parent-offspring relationships. The error rate for detected half-sibling relationships was even higher, reaching 41%. Only parent-offspring pairs were reliably detected or confirmed. This implies that, in populations that are small, ill-defined, or for which the STR loci analyzed are inappropriate, an examiner might not be able to distinguish a pair of full siblings from a pair of half-siblings. Furthermore, half-sibling pairs might be overlooked altogether, an issue that is exacerbated by the common confusion, in many languages and cultures, between half-siblings and full siblings. Consequently, in the study of ancient populations, human remains of unknown origins, or poorly surveyed modern populations, we recommend a conservative approach to kinship determined by LR. Next-generation sequencing data should be used when possible, but the costs and technology involved might be prohibitive. Therefore, in potentially contentious situations or cases lacking sufficient external information, uniparental markers should be analyzed: ideally, complete mitochondrial genomes and Y-chromosome haplotypes (STR, SNP, and/or sequencing).

Abstract: La faune marine antarctique adaptée à des conditions de température extrêmement basses et stables depuis des millions d'années, constitue un modèle sténotherme particulièrement intéressant pour l'étude de l'évolution du climat et de ses conséquences sur la biodiversité. Pour évaluer l'impact du réchauffement climatique chez ces animaux au niveau moléculaire, nous avons réalisé l'étude de l'expression des HSP70 (Heat Shock Proteins), marqueurs de stress thermique, chez deux espèces clés de l'écosystème marin antarctique : le krill des glaces Euphausia crystallorophias et la crevette Chorismus antarcticus. La caractérisation préliminaire d'une forme du gène hsp70 chez la crevette et de plusieurs formes chez le krill, a permis de générer des sondes moléculaires pour suivre leurs variations d'expression en PCR quantitative chez des individus « choqués » thermiquement. Chez E. crystallorophias bien que les résultats en PCR quantitative ne soient pas exploitables, les premiers résultats en PCR semblent indiquer qu'il existe une réponse au choc thermique, tandis que chez la crevette C. antarcticus, la quantification du niveau de transcrits indique une absence de réponse à ce type de stress. Cette étude comparée de la réponse moléculaire au stress thermique chez deux espèces antarctiques tend à démontrer qu'il pourrait exister une corrélation entre capacité thermique, disponibilité de formes variées d'Hsp70 et milieu de vie.
Encadrement : J-Y. Toullec

Abstract: Communication at the Krill in Changing Ocean WOrkshop: Texel May 2011