Global Phylogeography of the lemon sponge Leucetta chagosensis: from the Indian to the Pacific Oceans
Aim: In general, phylogeographic patterns for marine species in the Indian Ocean (IO) are poorly understood and globally, there remains a paucity of studies focussing on marine sponges. The sponge Leucetta chagosensis Dendy (1913) has a wide distribution throughout the Indo-Pacific (IP) region, with previous studies focussing primarily on the western Pacific Ocean.  In order to increase our knowledge of the spatial variation of genetic diversity throughout the IP, we constructed a global phylogeny for L. chagosensis to assess evolutionary patterns for this species, in particular reconstructing relationships between individuals collected from the IO to elsewhere globally and assess if there is an overlap between biogeographic and phylogeographic breaks. Location: Indo-Pacific regionMethods: 188 sequences were generated from L. chagosensis collected throughout the IP and were used to construct Maximum Likelihood and Bayesian Inference trees using mitochondrial cytochrome oxidase subunit 3 gene (cox3) and nuclear ribosomal RNA gene (28S) markers. The spatial variation of genetic diversity of L. chagosensis was assessed using a phylogeographic approach, including haplotype networks. Results: Results suggest that L. chagosensis is composed of six cryptic lineages confined to different biogeographic regions. Genetic divergence was high (cox3 AMOVA Fst = 0.89, P < 0.00; 28S AMOVA =0.70, P <0.00), with a low nucleotide diversity but high haplotype diversity for most lineages. Main conclusions: In addition to six divergent lineages, L. chagosensis found in the IO differ significantly from those found in the rest of the IP region. The low nucleotide diversity may indicate a rapid expansion of the populations after a period of low population density. This study highlights the need for a sustained effort in resolving sponge biodiversity globally