Abstract
Extensive ongoing degradation of coral reef habitats worldwide has lead to declines in abundance of coral reef fishes and local extinction of some species. Those most vulnerable are ecological specialists and endemic species. Determining connectivity between locations is vital to understanding recovery and long-term persistence of these species following local extinction. This study explored population connectivity in the ecologically-specialized endemic three-striped butterflyfish (Chaetodon tricinctus) using mt and msatDNA (nuclear microsatellites) to distinguish evolutionary versus contemporary gene flow, estimate self-replenishment and measure genetic diversity among locations at the remote Australian offshore coral reefs of Middleton Reef (MR), Elizabeth Reef (ER), Lord Howe Island (LHI), and Norfolk Island (NI). Mt and msatDNA suggested genetic differentiation of the most peripheral location (NI) from the remaining three locations (MR, ER, LHI). Despite high levels of mtDNA gene flow, there is limited msatDNA gene flow with evidence of high levels of self-replenishment (≥76%) at all four locations. Taken together, this suggests prolonged population recovery times following population declines. The peripheral population (NI) is most vulnerable to local extinction due to its relative isolation, extreme levels of self-replenishment (95%), and low contemporary abundance.
Highlights
Coral reef fishes have evolved in a close relationship with coral reef habitats to produce the most diverse vertebrate communities on earth (Bellwood 1996; Wood 1999; Bellwood and Wainwright 2002; Bellwood et al 2010)
A Minimum Spanning Tree (MST) identified 15 haplotypes in total, one of which was observed at high frequencies representing 82% (n = 80) of all individuals, and 12 of which were unique to single fish only in the sample examined here, nine of which were from the peripheral location (Fig. 2B)
C. tricinctus was found to have (i) sufficient mtDNA gene flow connecting all locations within the western region, but low gene flow and consequent isolation of the peripheral population from the western locations; (ii) low msatDNA gene flow between all locations resulting in populations that are genetically differentiated; (iii) demographic dependence between Lord Howe Island (LHI) and Middleton Reef (MR), yet high levels of inferred self-replenishment at all four locations; (iv) variable genetic diversities: low mtDNA genetic diversity at all three locations within the western region, but not at the peripheral location; and (v) high msatDNA genetic diversity at all four locations
Summary
Coral reef fishes have evolved in a close relationship with coral reef habitats to produce the most diverse vertebrate communities on earth (Bellwood 1996; Wood 1999; Bellwood and Wainwright 2002; Bellwood et al 2010). Coral reef habitats are coming under increasing pressure, facing a multitude of impacts including destructive and excessive fishing, sedimentation, pollution, disease, coral bleaching, ocean warming, and acidification (Hoegh-Guldberg 1999; Hughes et al 2003; Bellwood et al 2004) These disturbances have combined to cause sustained and ongoing declines in the abundance of corals on reefs worldwide (e.g., Gardner et al 2003; Bellwood et al 2004) with approximately 20% of the world’s coral reefs recently destroyed and a further 50% in decline (Wilkinson 2002); whilst coral cover on the Great Barrier Reef has halved in the last 27 years (De’ath et al 2012). Local extinction of coral dependent fishes are likely to increase if major disturbances that cause acute and extensive coral loss, such as coral bleaching, increase in incidence, as predicted (Hoegh-Guldberg 1999; Sheppard 2003)
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