The Dispersal Barrier in the Tropical Pacific: Implications for Molluscan Speciation and Extinction

Abstract

Abstract. -Stretches ofdeep ocean constitute barriers to the dispersal ofmany shallow-water marine species in the tropical Pacific. The purpose ofthis study was to assess the selectivity ofthese barriers with respect to the habitat characteristics, adult size, and predation-related shell architecture of gastropods, and to explore the implications of this selectivity for macroevolutionary patterns of extinction and speciation. The dispersal barrier between continental islands (represented in my collections by species from eastern Indonesia, the southern Philippines, and the north coast of New Guinea) and the nearby oceanic Palau Islands was studied by evaluating the percentage of each architectural and habitat category that is present on the continental islands but missing in Palau. The barrier is significantly more effective against sand-dwelling species than against rock-dwellers, and among rock-dwellers it is most effective against aperturally unarmored taxa. Barriers between Palau and Guam, Guam and the Hawaiian Islands, and the Line Islands and the tropical Eastern Pacific are generally unselective with respect to substratum type and architecture. The fact that narrow-apertured species are less affected by the barrier between the continental islands and Palau than are other rock-dwelling gastropods is consistent with the interpretation that this group has been unusually resistant to extinction and highly susceptible to founder speciation when oceanic circulation is altered. These patterns of susceptibility and geographical distribution may explain why armored gastropods have increased in numbers relative to unarmored ones in the tropical Pacific during the Cenozoic.Received June 9, 1986. Accepted March 10, 1987 It is now widely appreciated that the evolutionary success of adaptive traits of individual organisms depends not only on the outcome of natural selection, but is also contingent on population-level processes of sorting among species (

Regional Environmental Breadth Predicts Geographic Range and Longevity in Fossil Marine Genera

“…Geographic ranges of species and higher taxa vary through space and time in response to environmental perturbations, local biological interactions, and the formation and destruction of physical barriers to dispersal [1]–[4]. Geographic range is an important attribute of taxa because the durations of many marine organisms in the fossil record are positively correlated with geographic range [5]–[13].…”

“…However, the advantage of studying time-averaged geographic ranges is that high frequency variations (e.g., seasonal, decadal) in areal extent are averaged out [21]. The time dimension of the fossil record, of course, allows geographic ranges to be incorporated into macroevolutionary theory (e.g., [1], [5]–[7], [10], [13], [15], [22]). …”

ALLOPATRIC DIVERGENCE AND SPECIATION IN CORAL REEF FISH: THE THREE-SPOT DASCYLLUS,DASCYLLUS TRIMACULATUS,SPECIES COMPLEX

“…A number of taxa in various families have widespread ranges of distribution coupled with genetic homogeneity (Randall 1998; McMillan et al 1999; Planes and Fauvelot 2002; Horne et al 2008). (2) Besides the permanent hard continental barriers that have led to separation between ocean basins (e.g., the rise of the Isthmus of Panama between the Atlantic and Pacific Oceans, Lessios 2008), only a few barriers to coral reef fish dispersal such as oceanic currents (Lessios et al 1999; Barber et al 2000), open‐ocean distances (Vermeij 1987; Lessios and Robertson 2006), and freshwater outflows (Rocha 2004; Floeter et al 2008; Beldade et al 2009) have been identified as important factors in marine speciation (but see Connolly et al 2003 for critical assessment). (3) Barriers that are currently recognized have changed over time.…”

First Evidence of Inbreeding, Relatedness and Chaotic Genetic Patchiness in the Holoplanktonic Jellyfish Pelagia noctiluca (Scyphozoa, Cnidaria)

“…According to classical genetic theory, a marine species with high pelagic dispersal potential is expected to have no clear genetic structure at least below the minimum dispersal distance of individuals [95]–[98] and previous phylogeographic studies on P. noctiluca confirmed this expectation. Indeed, Miller et al [15], in a phylogeographic study performed using mitochondrial cytochrome oxidase subunit I (COI) and two nuclear internal transcribed spacers (ITS1 and ITS2) genes, found high and statistically significant genetic differences (at two out of three markers: COI: Φ ST  = 0.72, P<0.001; ITS2: Φ ST  = 0.023, P<0.001) only between Southern and Northern Atlantic samples, geographically very far from each other (≈10.000 km), whereas no genetic difference was found at a smaller geographic scale.…”