Indirect detection of genetic dispersal (movement and breeding events) through pedigree analysis of dugong populations in southern Queensland, Australia

Abstract

Understanding the patterns of movement and breeding within and between wildlife populations is important for the assessment of conservation status of endangered species, the development of conservation management strategies and priorities, and the prediction of population behaviour based on future threats. Methods for determining long term gene flow and dispersal are well researched, but analysis of recent movement is more difficult, typically relying on real-time tracking of individuals using telemetry, or through identification of marked individuals at multiple locations. These methods are limited by the considerable sampling effort required over time periods sufficient to recapture individuals in multiple locations. In contrast, we can infer recent movement from a reconstructed pedigree based on genetic and ancillary biological data, by identifying parent-offspring relationships in which the parent and offspring may be found in different locations. Hence, this method can use a single sampling period to identify movement and possibly associated breeding events over the last one or two generations. This study demonstrates the utility of reconstructed pedigrees in inferring recent movements in a dugongs distributed across a number of spatially distinct foraging locations in southern Queensland, Australia. Dugongs, which are classified as vulnerable to extinction, have long lifespans and protracted breeding cycles and give birth to single offspring at irregular intervals, implying a complex pedigree without distinct generational structure or large sibling groups. A pedigree was constructed for 1002 different dugongs across four locations in southern Queensland: Moreton Bay (n=630), the Great Sandy Straits (n=281), Hervey Bay (n=59) and Shoalwater Bay (n=27) using PR-genie software. PR-genie is a pedigree reconstruction system designed specifically for complex multigenerational wildlife pedigrees based on genetic identity (microsatellite DNA) and including ancillary biological data (sex and body size-class). Movements of genetically tagged individuals between locations were detected as parent-offspring links found across locations. Approximately 30% of assigned parents had at least one offspring found in a different location, implying recent movement of the parent or offspring. Where multiple individuals in a family are present, parsimonious explanations of movement indicate that male dugongs move between populations more frequently than females. Markedly more movement between locations was found than has been previously possible to detect through repeated direct sampling of individuals or through telemetry.