Population structure in Banggai cardinalfish, Pterapogon kauderni, a coral reef species lacking a pelagic larval phase

Previous studies on two reef fish lacking a pelagic larval phase (Acanthochromis polyacanthus and Embiotoca jacksoni) revealed features that may be characteristic of their lifestyle: (1) low levels of gene flow, (2) frequent population bottlenecks, and (3) strong phylogeographic breaks, all within their over 1,000 km coastal geographic ranges. The present study tested the predictive nature of these three characteristics in another species lacking a pelagic larval stage, but with a very restricted distribution (<10,000 km). The Banggai cardinalfish, Pterapogon kauderni Koumans, 1933, is a mouthbrooding species occurring in the Banggai Archipelago (eastern Indonesia). Fish were captured in January and February (2001, 2002). The mitochondrial control region of 122 individuals from 22 locations was sequenced. P. kauderni individuals clustered in two reciprocally monophyletic clades corresponding to a southwestern population (restricted to the southwest of Bangkulu Island) and all northern and eastern populations, which included all the remaining samples. Data were compatible with reduced gene flow and the presence of severe bottlenecks; however, small sample sizes and limited genetic variability in P. kauderni prevented a definitive conclusion. Further studies using larger samples and more rapidly evolving molecular markers may provide enough power to conclusively test our hypotheses. Introduction The great diversity of fish species found on coral reefs is often considered a paradox (Shulman 1998). Indeed, the vast majority of reef fishes exhibit a bipartite life history that includes a dispersive pelagic larval phase, which in turn results in high levels of gene flow (Doherty et al. 1985; Leis 1991; Palumbi 1992, 1994; Leis and McCormick 2002; Taylor and Hellberg 2003). Such high gene flow is presumed to counteract population genetic drift and ultimately speciation (Scheltema 1986; Palumbi 1992, 1994); yet, coral reefs are rich in species, and very poor in species that lack a pelagic larval stage. Thus, there must be high evolutionary or ecological costs in lacking a pelagic larval stage, such as increased vulnerability to environmental changes. Among the 335 species of damselfishes (Pomacentridae), only 3 species are known to lack a pelagic larval phase: Acanthochromis polyacanthus, Altrichthys azurelineatus, and Altrichthys curatus (Robertson 1973; Allen 1999). Among the 250 species of cardinalfishes (Apogonidae) (Nelson 1994; Allen and Morrison 1996), only 1 species mouthbroods its young until settlement, the Banggai cardinalfish (Pterapogon kauderni) (Allen and Steene 1995; Vagelli 1999; Allen 2000). In temperate reefs, all 24 members of the surfperch family (Embiotocidae) give birth to fully developed young. Other examples are few and in some cases questionable (Leis 1991; Leis and McCormick 2002). In-depth genetic studies have focused on only two of these species, the spiny damselfish A. polyacanthus (Doherty et al. 1994; Planes and Doherty 1997a, 1997b; Planes et al. 2001) and the black surfperch Embiotoca jacksoni (Bernardi 2000). These two species share the following characteristics: (1) low levels of gene flow, (2) a propensity for population fluctuations resulting in frequent bottlenecks, and (3) the presence of strong phylogeographic breaks. Acanthochromis polyacanthus and E. jacksoni have very large geographic ranges, which cover >1,000 km of coastline. In contrast, the two damselfish species in the genus Altrichthys and the Communicated by J.P. Grassle, New Brunswick G. Bernardi (&) Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060, USA E-mail: bernardi@ biology.ucsc.edu Tel.: +1-831-4595124 Fax: +1-831-4593383 A. Vagelli New Jersey State Aquarium, 1 Riverside Drive, Camden, NJ 08103, USA Marine Biology (2004) 145: 803–810 DOI 10.1007/s00227-004-1355-1