The small genetic world of Seriatopora hystrix

The exchange of genetic information among coral reefs, through the transport of larvae, is critical to the function of Australia’s Great Barrier Reef because it influences recruitment rates and resilience to disturbance. For many species the genetic composition is not homogeneous and is determined, in part, by the character of the complex dispersal pathways that connect the populations situated on each coral reef. One method of measuring these genetic connections is to examine the microsatellite composition of individual corals and then statistically compare populations across the region. We use these connection strengths, derived from a population similarity measure, to create complex networks to describe and analyse the genetic exchange of the brooding coral, Seriatopora hystrix. The network, based on determining the putative parental origin of individual coral colonies, involved sampling 2163 colonies from 47 collection sites and examining 10 microsatellites. A dispersal network was created from the genetic distance DLR values that measure the genetic similarity of each population (defined by the local sampling effort) to every other sampled population based on the microsatellite composition. Graph theory methods show that this network exhibited infrequent long distance links and population clustering which is commonly referred to as small world topology. Comparison with a hydrodynamic based network indicates that the genetic population network topology is similar. This approach shows the genetic structure of the S. hystrix coral follows a small world pattern which supports the results derived from previous hydrodynamic modelling.