Families in the Sea: Understanding the kinship relationships of dusky dolphins in Patagonia, Argentina

Methods

Summary

Samples collection and data recording

The study area will be navigated randomly until a dolphin group is sighted, which is defined as a conjunction of nearby individuals (<10 meters) among themselves, moving together and showing similar behaviours. Then, the GPS position will be taken, the size and type of group will be classified, and the activity of the focal group will be reported. At the same time the photography of dorsal fins will be taken to photo-identification process. All the registers will be incorporated into the data base of Laboratorio de Mamíferos Marinos (LAMAMA-CESIMAR-CONICET). Finally, the skin samples will be obtained through biopsy following the methodology proposed by Loizaga de Castro et al. (2013). The samples will be conserved to -20° Celsius since being processed for the genetic and stable isotopes analyses.

Social structure analysis

The photographs will be classified and processed using the FinBase program. The group structure will be analysed through the Average Weight Index. A temporal analysis of the associations will be explored, and then the coefficients of association between different sizes and types of groups will be compared. For these analyses of social structure, the 'assoc' module from the SOCPROG v2.9 program will be used.

Stable isotopes analysis

For this analysis, small tissue samples are required. The skin of cetaceans integrates a period of 2-3 months. Because of this, biopsy collections throughout the year will allow us to explore changes between the warm and cold seasons. All samples will be treated with chloroform/methanol (2:1) for lipid extraction and subsequently lyophilized for isotopic analysis. To estimate the isotopic niche width of each group and the isotopic overlap between the dolphin groups, the Standard Ellipse Area Bayesian (SEAB) will be calculated using the Stable Isotope Bayesian Ellipse in R (SIBER) package. The isotopic analyses will be performed in collaboration with Dr. Seth Newsome (UNM, USA).

Genetic analyses

The extraction of genetic material from all individuals will be conducted using commercial kits (QIAGEN, https://www.qiagen.com/us). The 800bp fragment of the control region from mitochondrial DNA will be amplified using PCR techniques following standard protocols. More than 20 loci of variable microsatellites will be analysed, based on loci designed for this species. The software KINGROUP v2 will be used to estimate all values of kinship between individuals (R) as a single population (using all biopsies of the individuals to define allelic frequencies). R is estimated from the similarity of genotypes between two individuals, which implies a common ancestry (identity by descent). For all kinship analyses, the CERVUS 3.0.7 and COLONY 2.0.6.2 software will be used. The molecular analysis will be carried out in the GenMol lab at CCT-CENPAT-CONICET.