Phylogeography of the Trumpetfishes (Aulostomus): Ring Species Complex on a Global Scale

Abstract

The distribution of circumtropical marine species is limited by continental boundaries, cold temperate conditions, and oceanic expanses, but some of these barriers are permeable over evolutionary time scales. Sister taxa that evolved in separate ocean basins can come back into contact, and the consequences of this renewed sympatry may be a key to understanding evolutionary processes in marine organisms. The circumtropical trumpetfishes (Au-lostomus) include a West Atlantic species (A. maculatus), an Indian-Pacific species (A. chinensis), and an East Atlantic species (A. strigosus) that may be the product of a recent invasion from the Indian Ocean. To resolve patterns of divergence and speciation, we surveyed 480 bp of mitochondrial DNA cytochrome b in 196 individuals from 16 locations. Based on a conventional molecular clock of 2% sequence divergence per million years, the deepest partitions in a neighbor-joining tree (d 0.063-0.082) are consistent with separation of West Atlantic and Indian-Pacific species by the Isthmus of Panama, 3-4 million years ago. By the same criteria, trumpetfish in the East Atlantic were isolated from the Indian Ocean about 2.5 million years ago (d 0.044-0.054), coincident with the advent of glacial cycles and cold-water upwelling around South Africa. Continental barriers between tropical oceans have only rarely been surmounted by trumpetfishes, but oceanic barriers do not appear to be substantial, as indicated by weak population partitioning (ST 0.093) in A. chinensis across the Indian and Pacific Oceans. Finally, morphological and mito-chondrial DNA data indicate hybridization of A. strigosus and A. maculatus in Brazil. After 3-4 million years and a globe-spanning series of vicariant and dispersal events, trumpetfish lineages have come back into contact in the southwest Atlantic and appear to be merging. This ring species phenomenon may occur in a broad array of marine organisms, with clear implications for the production and maintenance of biodiversity in marine ecosystems.

Evidence of a human–mediated invasion of the tropical western Atlantic by the ‘world's most common brittlestar’

“…Although this tropical species is highly unlikely to be able to disperse around Cape Horn (South America) due to the cold waters of the circum-Antarctic current, dispersal around the Cape of Good Hope (South Africa) may be more probable, as warm waters of the Agulhas current travelling south along the eastern side of South Africa are able tō ow into the southeastern Atlantic (Briggs 1974;Gordon 1985;de Ruijter et al 1999). However, the Benguela cold current, and upwelling off southwestern Africa, present a major barrier to the dispersal of even highly vagile tropical Indian Ocean taxa into the Atlantic (Bowen et al 2001). The Benguela current originated in the Miocene period but has experienced¯uctuations in its intensity ever since the beginning of the Pleistocene period (Shannon 1985) and may have allowed dispersal of tropical taxa into the Atlantic during times of minimal strength.…”

Surgeons and suture zones: Hybridization among four surgeonfish species in the Indo-Pacific with variable evolutionary outcomes

“…Each site (and species) was also fitted with the population parameter  in order to estimate the time since the most recent population expansion ( = 2μt; Rogers and Harpending, 1992), where t is the age of the population in generations and μ is the mutation rate per generation for the sequence (μ = number of bp · divergence rate within a lineage · generation time in years). We used a range of approximate cyt b mutation rates available from previous fish studies (1% per million years [MY] to 1.55% per MY within lineages; Bowen et al, 2001;Lessios, 2008;Reece et al, 2010) and a generation (replacement) time of 12 years for all species based on existing life-history information (i.e. age-at-maturity ~ two years, longevity ~ 27 to 36 years; J.H.…”

“…japonicus, A. leucosternon and A. nigricans based on mitochondrial DNA (cytochrome b) sequence data. Time since the most recent population expansion was calculated using a range of mutation rates (1% to 1.55% per million years within lineages; Bowen et al, 2001, Lessios, 2008, Reece et al, 2010 and a generation time of 12 years for all species (see Materials and Methods). 2 2 n/a c n/a n/a n/a Johnston Atoll (JON) 3 2 n/a n/a n/a n/a Hawaiian Islands (HAW) 2 2 n/a n/a n/a n/a Acanthurus leucosternon Socotra, Yemen (SOC) 5 n/a n/a n/a n/a n/ Table 1).…”

“…Nonetheless, fishes with a long pelagic larval stage tend to have extensive dispersal, broad ranges and dominate communities on isolated islands (Horne et al, 2008;Reece et al, 2011;. Some of the most dispersive reef fishes are those that can stay in the water column after transforming from larva to juvenile (or pre-juvenile), including trumpetfishes (Bowen et al, 2001), squirrelfishes (Craig et al, 2007) and (most relevant) other surgeonfishes (Thresher, 1984). The sister species surveyed here provide additional examples of highly dispersive fishes, a trait that may be a general feature of the genus Acanthurus (Eble et al, 2011).…”

High population connectivity across the Indo-Pacific: Congruent lack of phylogeographic structure in three reef fish congeners

“…In contrast, however, an increasing number of phylogeographic studies are also providing evidence of widespread reef fishes in which geographic population structure is minimal or altogether lacking. Some examples of reef fishes with little genetic population structure include holocentrids ), scarine labrids (Bay et al 2004), aulostomids (Bowen et al 2001) and acanthurids (Klanten et al, 2007). Such studies suggest that the larvae of some reef fishes readily cross very large open ocean barriers that impede dispersal in other species (Lessios and Robertson 2006) and that larval movement across oceanic barriers may be highly variable among different reef fish taxa.…”