reproductive barriers between marine species can occur in less than 1.6 million
years (McCartney et al. 2000).
A global molecular phylogeny of Diadema (including D. antillarum and
D. mexicanum from Panama) was published by Lessios (2001) and Lessios et al.
(2001). This molecular study showed that Diadema is composed of reciprocally
monophyletic mtDNA clades, and that the eastern Atlantic D. antillarum
(D. antillarum-b) from Madeira, Canary Islands, Cape Verde and Sao Tome is
genetically distinct from the western Atlantic D. antillarum. These species are
separated by the long stretch of deep water separating the eastern from the western
Atlantic. Diadema antillarum ascensionis Mortensen, 1909 from the central
Atlantic islands of Ascension and St. Helena was found to be genetically isolated,
but nested within the Brazilian clade of the western Atlantic D. antillarum. Lessios
suggests that the biogeographic barrier between the Caribbean and Brazil may be
caused by the outflow from the Amazon and Orinoco Rivers. High levels of gene
flow were reported among populations of D. mexicanum in the eastern Pacific,
with D. mexicanum from the Galapagos and Cocos Island belonging to the same
population as sea urchins from Panama and Mexico (Lessios et al. 2001).
A study of the phylogeography of the pantropical sea urchin Tripneustes by
Lessios et al. (2003) showed that based on morphology, COI, and bindin data,
T. depressus A. Agassiz, 1863 from the eastern Pacific is in fact the same species
as T. gratilla (Linnaeus, 1758) from the western Pacific. The formation of the
Isthmus of Panama, the deep water separating the eastern and western Atlantic,
and the freshwater plume of the Orinoco and Amazon rivers between the
Carribbean and the coast of Brazil were shown to be important barriers to the
evolution of Tripneustes. However, the Eastern Pacific Barrier (5,000 km of deep
water) between the central and eastern Pacific was unimportant in the subdivision
in the genus.
A phylogeographic study of the genus Lytechinus by Zigler and Lessios (2004)
using mitochondrial COI, and the entire molecule of nuclear bindin shows that the
genus Lytechinus is paraphyletic (using Toxopneustes and Tripneustes as outgroups), with Sphaerechinus granularis (Lamarck, 1816) coming out as the sister
species to L. euerces Clark, 1912 . The authors propose that L. euerces should be
moved into the monotypic Sphaerechinus, rather than placing Sphaerechinus in
Lytechinus which would increase the range of the genus to the temperate eastern
Atlantic and Mediterranean (Mortensen 1943a). Lytechinus semituberculatus
(Valenciennes in L. Agassiz, 1846) and L. panamensis formed a clade with no
distinction between the two species, while L. anamesus and L. pictus were also
phylogenetically indistinguishable. A well supported Atlantic clade was formed of
L. williamsi and the three subspecies of L. variegatus (L. variegatus variegatus,
L. variegatus atlanticus, L. variegatus carolinus). Lytechinus williamsi from the
Caribbean was found to share mtDNA haplotypes with L. variegatus variegatus,
however, their bindin was shown to be distinct and to coalesce within each
morphospecies. A small private clade of mtDNA was found in some L. williamsi
from Panama and Belize. Zigler and Lessios (2004) suggest that this may be
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S. E. Coppard and J. J. Alvarado
years (McCartney et al. 2000).
A global molecular phylogeny of Diadema (including D. antillarum and
D. mexicanum from Panama) was published by Lessios (2001) and Lessios et al.
(2001). This molecular study showed that Diadema is composed of reciprocally
monophyletic mtDNA clades, and that the eastern Atlantic D. antillarum
(D. antillarum-b) from Madeira, Canary Islands, Cape Verde and Sao Tome is
genetically distinct from the western Atlantic D. antillarum. These species are
separated by the long stretch of deep water separating the eastern from the western
Atlantic. Diadema antillarum ascensionis Mortensen, 1909 from the central
Atlantic islands of Ascension and St. Helena was found to be genetically isolated,
but nested within the Brazilian clade of the western Atlantic D. antillarum. Lessios
suggests that the biogeographic barrier between the Caribbean and Brazil may be
caused by the outflow from the Amazon and Orinoco Rivers. High levels of gene
flow were reported among populations of D. mexicanum in the eastern Pacific,
with D. mexicanum from the Galapagos and Cocos Island belonging to the same
population as sea urchins from Panama and Mexico (Lessios et al. 2001).
A study of the phylogeography of the pantropical sea urchin Tripneustes by
Lessios et al. (2003) showed that based on morphology, COI, and bindin data,
T. depressus A. Agassiz, 1863 from the eastern Pacific is in fact the same species
as T. gratilla (Linnaeus, 1758) from the western Pacific. The formation of the
Isthmus of Panama, the deep water separating the eastern and western Atlantic,
and the freshwater plume of the Orinoco and Amazon rivers between the
Carribbean and the coast of Brazil were shown to be important barriers to the
evolution of Tripneustes. However, the Eastern Pacific Barrier (5,000 km of deep
water) between the central and eastern Pacific was unimportant in the subdivision
in the genus.
A phylogeographic study of the genus Lytechinus by Zigler and Lessios (2004)
using mitochondrial COI, and the entire molecule of nuclear bindin shows that the
genus Lytechinus is paraphyletic (using Toxopneustes and Tripneustes as outgroups), with Sphaerechinus granularis (Lamarck, 1816) coming out as the sister
species to L. euerces Clark, 1912 . The authors propose that L. euerces should be
moved into the monotypic Sphaerechinus, rather than placing Sphaerechinus in
Lytechinus which would increase the range of the genus to the temperate eastern
Atlantic and Mediterranean (Mortensen 1943a). Lytechinus semituberculatus
(Valenciennes in L. Agassiz, 1846) and L. panamensis formed a clade with no
distinction between the two species, while L. anamesus and L. pictus were also
phylogenetically indistinguishable. A well supported Atlantic clade was formed of
L. williamsi and the three subspecies of L. variegatus (L. variegatus variegatus,
L. variegatus atlanticus, L. variegatus carolinus). Lytechinus williamsi from the
Caribbean was found to share mtDNA haplotypes with L. variegatus variegatus,
however, their bindin was shown to be distinct and to coalesce within each
morphospecies. A small private clade of mtDNA was found in some L. williamsi
from Panama and Belize. Zigler and Lessios (2004) suggest that this may be
126
S. E. Coppard and J. J. Alvarado