EVIDENCE OF A BIOGEOGRAPHIC BREAK BETWEEN POPULATIONS OF A HIGH DISPERSAL STARFISH - CONGRUENT REGIONS WITHIN THE INDO-WEST PACIFIC DEFINEDBY COLOR MORPHS, MTDNA, AND ALLOZYME DATA
St. Williams et Jah. Benzie, EVIDENCE OF A BIOGEOGRAPHIC BREAK BETWEEN POPULATIONS OF A HIGH DISPERSAL STARFISH - CONGRUENT REGIONS WITHIN THE INDO-WEST PACIFIC DEFINEDBY COLOR MORPHS, MTDNA, AND ALLOZYME DATA, Evolution, 52(1), 1998, pp. 87-99
Both mtDNA variation and allozyme data demonstrate that geographic gro
upings of different color morphs of the starfish Linckia laevigata are
congruent with a genetic discontinuity between the Indian and Pacific
Oceans. Populations of L. laevigata sampled from Thailand and South A
frica, where an orange color morph predominates, were surveyed using s
even polymorphic enzyme loci and restriction fragment analysis of a po
rtion of the mtDNA including the control region. Both allozyme and DNA
data demonstrated that these populations were significantly genetical
ly differentiated from each other and to a greater degree from 23 popu
lations throughout the West Pacific Ocean, where a blue color morph is
predominant. The genetic structure observed in L. laevigata is consis
tent with traditional ideas of a biogeographic boundary between the In
dian and Pacific Oceans except that populations several hundreds kilom
eters off the coast of north Western Australia (Indian Ocean) were gen
etically similar to and had the same color morphs as Pacific populatio
ns. It is suggested that gene flow may have continued (possibly at a r
educed rate) between these offshore reefs in Western Australia and the
West Pacific during Pleistocene falls in sea level, but at the same t
ime gene flow was restricted between these Western Australian populati
ons and those in both Thailand and South Africa, possibly by upwelling
s. The molecular data in this study suggest that vicariant events have
played an important role in shaping the broadscale genetic structure
of L. laevigata. Additionally, greater genetic structure was observed
among Indian Ocean populations than among Pacific Ocean populations, p
robably because there are fewer reefs and island archipelagos in the I
ndian Ocean than in the Pacific, and because present-day surface ocean
currents do not facilitate long-distance dispersal.