Evolution of sympatric species: a case study of the coral reef fish genus Pomacanthus (Pomacanthidae)

Aim To establish a spatial and temporal framework within which we can begin to investigate the role of geography in the evolution of Pomacanthus species. This study examines the phylogenetic relationships among Pomacanthus species, tests whether the degree of sympatry among sister taxa correlates with their age, and explores potential modes of diversification. Location Pan-tropical coral reef systems. Methods Three gene regions (12S rRNA, 16S rRNA and nuclear S7) from all 13 Pomacanthus species were used in conjunction with fossil calibration to reconstruct a chronogram. IUCN maps were used to evaluate geographical range overlap. Various age-range correlation (ARC) analyses were used to test for a correlation between range overlap and node age. Range-size symmetry and node age were also examined. Results Biogeographical splits within the phylogeny corroborated key biogeographical events well, suggesting a potential role for allopatric speciation in the evolutionary history of the genus. ARC analyses suggested that speciation leading to sympatry is widespread in Pomacanthus, with 80% of sister species showing complete or substantial (> 85%) range overlap. No significant relationship between degree of sympatry and node age was recovered, which demonstrates that, for this group, exceptional sympatry is not necessarily a result of relatively old lineages. Range-size symmetry analysis was consistent with models of peripatric speciation within a finite area. Main conclusions We present evidence consistent with allopatric speciation, while our ARC results are consistent with simulations of sympatric speciation, with the possibility of peripheral budding having led to the richness of sympatric species in the West Indian Ocean. We discuss how these processes can affect the interpretation of temporal and spatial analyses, and provide a basis for future investigations into the processes driving speciation.