A Tale of Two Aggregations: Kinship and Population Genetics of Whale Sharks (Rhincodon typus) at Shib Habil, Saudi Arabia, and Mafia Island, Tanzania.

Abstract

In a recent global study of whale shark population genetics, aggregations were found to belong to either the Indo-Pacific or Atlantic population. This overview included an aggregation found within the Red Sea near Al Lith, Saudi Arabia, however the Mafia Island, Tanzania, aggregation was not part of the study. Both aggregations have unique aspects with the Saudi Arabian individuals showing sexual parity with no segregation, while recent acoustic results have revealed cryptic residency at Mafia Island. Genetic analysis using 11 microsatellite markers was performed on whale sharks from both locations. A combination of primers sourced from previous studies and newly designed primers were used to compare both aggregations and the individuals within. Samples were collected in the Red Sea for 5 seasons spanning 6 years, and for 2 seasons in Tanzania. Analysis with STRUCTURE showed a lack of significant genetic differences between the two aggregations, confirming that whale sharks in Tanzania are part of the Indo-Pacific population. Kinship analysis using COLONY found two potential pairs of full siblings in Tanzania. One pair had a high probability (.993) of being a full sibling dyad while the other had a lower probability (.357). There were no sibling pairs identified from the Red Sea aggregation. Genetic diversity was investigated using allelic richness over the 6 seasons at Al Lith, with values showing no significant change. This is in contrast to results that showed a decline in genetic diversity at Western Australia’s Ningaloo reef. These differences, however, only highlight the need for genetic diversity studies over longer time periods and at other aggregations within the Indo-Pacific.