REPORT
Connectivity of populations within and between major
biogeographic regions of the tropical Pacific in Conus ebraeus,
a widespread marine gastropod
T. F. Duda Jr ? H. A. Lessios
Received: 20 November 2008 / Accepted: 12 February 2009 / Published online: 3 March 2009

 Springer-Verlag 2009
Abstract Information on genetic connectivity and struc-
ture of populations in the tropical Pacific is critical for
making inferences about the origins and maintenance of
diversity in this region. Sequences of the mitochondrial COI
gene from 92 individuals of the trans-Pacific gastropod
Conus ebraeus from eight localities spanning the tropical
Pacific were analyzed to determine whether populations in
the western, central, and eastern Pacific exhibit genetic
structure, to examine the demographic histories of popula-
tions, and to infer patterns of gene flow. A total of 43 unique
haplotypes were recovered, including a common haplotype
that occurred in six of the eight populations examined.
AMOVA and pairwise F-statistics showed that populations
in the western and central Pacific were significantly dif-
ferentiated from populations in the eastern Pacific, but no
other evidence of structure. Bayesian isolation?migration
(IM) analysis suggested that populations in the western and
central Pacific separated from those in eastern Pacific dur-
ing the Pleistocene. Examination of mismatch distributions
and results from IM revealed that populations in the western
and central Pacific expanded during the Pleistocene. Gene
flow across the East Pacific Barrier appears to occur pre-
dominantly westward.
Keywords Phylogeography 
 East Pacific Barrier 

Conus 
 Gene flow 
 Population structure
Introduction
Distributions of tropical shallow water marine organisms
are generally restricted to four well-defined biogeographic
regions: the Indo-West Pacific, the eastern Pacific, and the
(western and eastern) Atlantic regions (Briggs 1974). These
distributions were presumably strongly influenced by past
vicariant events due to various barriers to dispersal that
separated formerly widespread species. Since the Mesozoic,
numerous geophysical events have shaped marine biotas.
The closure of the Tethys Seaway, the establishment of the
Benguela upwelling, and emergence of the Isthmus of
Panama isolated the Atlantic from the Indo-West Pacific
(defined as the entire Indo-Pacific area, except the eastern
Pacific). The mid-Atlantic and east Pacific barriers (wide
stretches of water, difficult to cross by planktonic larvae)
hindered dispersal of species across the entire width of each
of the two oceans. Phylogenetic relationships among spe-
cies of tropical marine taxa that occur in multiple
biogeographic regions illuminate the importance of these
phenomena in determining broad-scale historic patterns of
divergence (Lessios et al. 1999, 2001, 2003; Colborn et al.
2001; Muss et al. 2001; Meyer 2003; Williams and Reid
2004; Duda and Kohn 2005; Meyer et al. 2005).
The East Pacific Barrier (EPB), a 4,000?7,000 km
stretch of deep water between the easternmost islands of the
central Pacific and the offshore islands of the Americas, is
perhaps the most formidable oceanic barrier to dispersal for
tropical marine organisms. It has presumably been in place
throughout the Cenozoic (Grigg and Hey 1992). Indo-West
Pacific and eastern Pacific shallow-water benthic biotas are
Communicated by Biology Editor Dr. Ruth Gates.
T. F. Duda Jr (&)
Department of Ecology and Evolutionary Biology and Museum
of Zoology, University of Michigan, 1109 Geddes Avenue,
Ann Arbor, MI 48109, USA
e-mail: tfduda@umich.edu
T. F. Duda Jr 
 H. A. Lessios
Smithsonian Tropical Research Institute, Apartado 0843-03092,
Balboa, Ancon, Republic of Panama
123
Coral Reefs (2009) 28:651?659
DOI 10.1007/s00338-009-0485-9
nearly completely distinct, and few benthic and demersal
tropical marine species have disjunct, trans-Pacific distri-
butions (Briggs 1974). These distributions are often
assumed to reflect relatively recent jump dispersals across
this barrier that originated in the Indo-West Pacific (e.g.,
Briggs 1961, 1967; Emerson 1991, but see Robertson et al.
2004), but the direction of the initial dispersal event and of
subsequent gene flow has only been extensively examined
in fishes (Lessios and Robertson 2006).
Among prosobranch gastropods, 33 species are known
to occur in both the Indo-West Pacific and eastern Pacific
(Emerson 1991). All 33 trans-Pacific species possess
planktotrophic larvae, and their populations in the eastern
Pacific are assumed to represent ephemeral sink popula-
tions, which depend for their long-term persistence on
recruitment from Indo-West Pacific populations (Emerson
1978, 1991; Emerson and Chaney 1995). Because most
transpacific species [including gastropods (Emerson 1991)]
have much wider distributions west of the EPB, the eastern
Pacific populations are thought to have resulted from range
expansion initiated in the Indo-West Pacific (Briggs 1974).
However, reconstruction of phylogenetic relationships of
members of the gastropod genus Conus revealed several
historic breaches of the EPB that may have occurred in
either direction during at least the past 10 million years
(my) (Duda and Kohn 2005). Moreover, there is little
reason for assuming that the initial introduction occurred in
the same direction as subsequent gene flow. Phylogeo-
graphic analyses of 20 trans-Pacific fish species showed
that directionality of gene flow across this barrier is not as
universal as had been assumed; while some fishes exhibit
bidirectional gene flow, others show predominant patterns
of migration in either westward or eastward directions
(Lessios and Robertson 2006). These results challenge the
long assumed view (Ekman 1953; Briggs 1974; Dana 1975;
Vermeij 1978; Glynn et al. 1983; Rosenblatt and Waples
1986; Vermeij 1991) that initial colonization and sub-
sequent gene flow across the EPB occur exclusively in an
eastward direction and call for further investigations of
patterns of genetic exchange of populations separated by
this barrier.
Understanding patterns of divergence of tropical marine
organisms within biogeographic regions is also critical for
making inferences about the origins of biodiversity. These
patterns are best illuminated through comparison of the
distributions of genotypes of populations of widespread
species. For example, even though a number of unrelated
taxa show concordant genetic breaks between Indian and
Pacific populations, presumably caused by historical iso-
lation of the two basins during times of low sea level stands
(Benzie and Stoddart 1992; Mcmillan and Palumbi 1995;
Lavery et al. 1996a; Miya and Nishida 1997; Williams and
Benzie 1997, 1998; Duke et al. 1998; Benzie 1999; Duda
and Palumbi 1999b; Lessios et al. 1999, 2001; Williams
et al. 2002; Bay et al. 2004; Teske et al. 2005; Reid et al.
2006; Crandall et al. 2008), there is no equivalent con-
cordance in breaks between the western and central Pacific
areas of the Indo-West Pacific, or between localities within
either of these areas. Vicariant events that could have
influenced the genetic divergence between populations in
the western and the central Pacific are not apparent in
geologic history. Some species, including clams (Benzie
and Williams 1997), sea urchins (Palumbi et al. 1997;
Lessios et al. 1999, 2001), lancelets (Kon et al. 2006), and
fishes (Winans 1980; Bernardi et al. 2001; Planes and
Fauvelot 2002; Bay et al. 2004; Ravago-Gotanco and Jui-
nio-Men?ez 2004), exhibit patterns of genetic differentiation
between these two regions that suggest isolation by dis-
tance. However, there is no obvious consistency among
species in patterns of gene flow among populations. Other
species, including gastropods (Crandall et al. 2008), crus-
taceans (Williams et al. 2002), and echinoderms (Lessios
et al. 2001), show evidence of limited structure between
these areas. The lack of concordance in the distributions of
genotypes and patterns of gene flow of species in the wes-
tern and central Pacific implies that differences in species
traits, possibly related to life history, dispersal ability, or
other aspects of their biology, or unique demographic
histories have affected their current genetic population
structures.
Three Conus species currently exhibit trans-Pacific dis-
tributions: C. chaldaeus, C. ebraeus, and C. tessulatus
(Emerson 1991). In the Indo-West Pacific these species
range from the eastern shores of Africa to the easternmost
islands of the central Pacific, although C. chaldaeus and
C. tessulatus have not been reported from Easter Island, and
C. tessulatus does not occur in the Hawaiian Archipelago
(Ro?ckel et al. 1995). These three species also occur at off-
shore islands in the eastern Pacific, including Clipperton
Atoll (all three species), Isla del Coco (all three species), the
Galapagos Islands (C. chaldaeus and C. ebraeus), the
Revillagigedo Islands (C. tessulatus only), as well as at
several nearshore islands off of the coast of Central America
(Emerson 1991). The phylogeography of one of these three
trans-Pacific Conus species, C. ebraeus, was examined to
interpret levels of differentiation and patterns of gene flow of
this species in the tropical Pacific. The range of C. ebraeus
is summarized in Fig. 1 based on data presented in
Ro?ckel et al. (Ro?ckel et al. 1995). Planktotrophic larvae of
C. ebraeus have a minimum pelagic period of 25?27 days
(Kohn and Perron 1994) and thus have the potential to dis-
perse relatively large distances. The following questions
were addressed: Do populations of C. ebraeus show evi-
dence of genetic subdivision within the western and central
Pacific? Are populations of C. ebraeus in the eastern Pacific
and the Indo-West Pacific genetically differentiated from
652 Coral Reefs (2009) 28:651?659
123
each other? Is gene flow between eastern Pacific and Indo-
West Pacific populations occurring and, if so, is it direc-
tionally biased?
Methods
Sequences of a fragment of the mitochondrial cytochrome
oxidase subunit I (COI) gene were obtained from 92 indi-
viduals of C. ebraeus from locations spread through the
tropical Pacific (Fig. 1). Although C. ebraeus occurs in the
eastern Pacific, it is not particularly abundant in some
locations, so only two specimens were obtained from
islands in the Gulf of Chiriqu?? in western Panama and 10
specimens from Clipperton Island. Tissues were preserved
in 75?95% ethanol. All specimens that were specifically
collected for this work were deposited in the collections of
the Mollusk Division of the University of Michigan
Museum of Zoology (UMMZ). Tissues from specimens
from Enawetak and Clipperton Island were acquired from
collections of the UMMZ and the Santa Barbara Museum of
Natural History, respectively. While most specimens were
from recent collections and were preserved and stored in
75?95% ethanol, specimens from Enawetak were collected
in 1960 and initially preserved in propylene phenoxetol.
Previously unpublished sequence data were deposited in
GenBank under accession numbers EF547559-EF547649.
DNA was extracted from approximately 25 mg of foot
tissue using methods described in Duda and Palumbi
(1999a), or with the E.Z.N.A.TM Mollusc DNA Kit (Omega
Bio-Tek, Doraville, Georgia, USA). Tissues from speci-
mens from Enawetak that were originally preserved in
propylene phenoxetol had a gelatin-like consistency;
extractions of these tissues were also performed with the
Omega Bio-Tek kit; amplifications from the resultant DNAs
from these samples were by and large successful. Amplifi-
cation of a fragment of the mitochondrial COI gene was
accomplished using universal COI primers LCO1490 and
HCO2198 (Folmer et al. 1994). Unincorporated dNTPs and
primers were removed from amplified sequences with
the Qiaquick PCR Purification Kit (Qiagen, Valencia,
California, USA). Approximately 611 bases of the ampli-
fied fragments were sequenced in both directions.
Chromatograms were analyzed, and sequences were aligned
to a sequence previously determined from an individual of
C. ebraeus from American Samoa (GenBank accession
number AY588175, Duda and Rola?n 2005) with Sequen-
cher 4.6 (Gene Codes Corporation, Ann Arbor, Michigan,
USA).
The most appropriate model for nucleotide substitution
was determined with Modeltest 3.7 (Posada and Crandall
1998). Sequences were inspected to identify haplotypes that
are shared among individuals with MacClade 4.0 (Maddison
and Maddison 2000). To examine the distribution of
haplotypes among populations, a haplotype network was
constructed with TCS version 1.21 (Clement et al. 2000).
Arlequin version 2.0 was used (Schneider et al. 2000) to
calculate haplotype frequencies, haplotype diversity statis-
tics, Analysis of Molecular Variance (AMOVA) (Excoffier
et al. 1992), and pairwise UST statistics using Tamura and
Nei (1993) distances. Although hierarchical likelihood ratio
tests in Modeltest selected the HKY model (Hasegawa et al.
1985) as the most appropriate model for nucleotide substi-
tution, this model is not available in Arlequin and so
Tamura-Nei distances were used; HKY and Tamura-Nei
distances differ at most at the fifth decimal place. About
10,010 permutations were used to assess the degree to which
obtained estimates were different than those obtained from a
random assignment of haplotypes to populations. Arlequin
was also used to examine mismatch distributions (Rogers
and Harpending 1992; Rogers 1995) to investigate the
demographic history of populations.
To distinguish whether genetic similarity between pop-
ulations from the eastern Pacific and from the rest of the
Pacific is due to recent separation or to recurrent gene flow
after initial separation, and to determine the direction of
gene flow, a Bayesian procedure, developed by Nielsen and
Wakeley (2001); Hey and Nielsen (2004) was employed.
This isolation?migration (IM) method uses coalescence to
estimate effective population size of ancestral and daughter
Fig. 1 Map of the Indian and
Pacific Oceans with the range of
Conus ebraeus (delimited by
thick lines), collection locations
and sample sizes (n)
Coral Reefs (2009) 28:651?659 653
123
populations, the time since their initial separation (i.e., the
time since vicariance or the last massive invasion), and the
migration rate in each direction. Specifically, the algorithm
estimates the time of separation t (number of generations,
scaled by mutation rate, l) between populations, h = Nel
(where Ne is the effective population size of the ancestral
and the two daughter populations, each estimated sepa-
rately), and the scaled migration rate m = m/l in each
direction. Analyses were implemented by pooling sequen-
ces from the eastern Pacific in one sample, those from the
rest of the Pacific in another, using the HKY (Hasegawa
et al. 1985) model of nucleotide substitutions, and assuming
constant population size. From the results of IM, twice the
number of females moving through the barrier per genera-
tion (M) was calculated as M = 2Nemf = hm/2 (where mf is
the female migration rate).
To perform the IM analysis, wide limits for prior values
for each parameter were selected, then multiple runs were
carried out, starting from simple unheated runs with burn-
in intervals of 105 steps, and continuing by increasing the
number of steps, the burn-in time, and the complexity of
the heating scheme until complete (or nearly complete)
posterior likelihood curves were obtained for each param-
eter. Runs were initiated with different random seeds. The
final run, from which estimates are shown here, involved
geometric heating of 20 Markov chains, a burn-in period of
5 9 106 steps, continuous calculations of 2.85 9 108 steps
beyond the burn-in, and a minimum effective sample size
(ESS) of 907.
Results
Sequences and haplotypes
Among the 92 individuals sequenced, 43 unique COI
haplotypes were detected. These sequences differed by a
maximum of 12 out of a total of 61 variable sites. Of these,
31 haplotypes were unique to single individuals, another
occurred in more than one individual but was unique to a
single location (haplotype 38, Fig. 2) and the remaining 11
occurred in more than one individual from more than one
location (haplotypes 1?11). Haplotype diversity in western
and central Pacific sites with N [ 6 ranged from 0.93 to 1.
Clipperton in the eastern Pacific and combined eastern
Pacific sites had lower haplotype diversity (Table 1).
The haplotype network constructed from the COI
sequences (Fig. 2) reveals that the most common, presum-
ably ancestral, haplotype (no. 3) occurred at all locations
except for Guam and Panama. The distribution of this
haplotype thus extends from the Philippines and Okinawa,
all the way to the Clipperton Atoll, a distance of approxi-
mately 13,500 km. Many other haplotypes in the western
Pacific differ by one or two mutations from this common
haplotype. Several other haplotypes differ by more than
four sites from the ancestral haplotype.
Analysis of molecular variation within and between
regions
AMOVA comparison of genetic variation within and
between the eastern Pacific samples versus the western and
central Pacific ones revealed that nearly 74% of the vari-
ance in COI was within localities, and only 1% between
localities within regions (Table 2). Approximately one-
fourth (25.2%) of the variance was between regions.
Pairwise F-statistics
As is to be expected given the AMOVA results, pairwise UST
values among localities show evidence of significant genetic
separation between eastern Pacific and western ? central
Pacific samples (Table 3). Within the western and central
Pacific, samples from each site show no evidence of struc-
ture, and pairwise UST values are considerably smaller than
those observed between western ? central Pacific site and
the Clipperton Island samples; none of the comparisons
within the western ? central Pacific are significantly dif-
ferent from zero (Table 3).
Historical demography of populations
The mismatch distribution of haplotypes from the entire
western and central Pacific was not significantly different
Fig. 2 Statistical parsimony (Templeton et al. 1992) network of COI
haplotypes joining 92 individuals of Conus ebraeus from the tropical
Pacific at the 95% confidence level. The ancestral haplotype
according to ??outgroup weight?? (Castelloe and Templeton 1994) is
depicted as a rectangle. Numbers inside the shapes are designating
individual haplotypes. The area of each shape is proportional to the
frequency of each haplotype (haplotype 1: n = 6, 2:4, 3:19, 4:4, 5:3,
6:5, 7:4, 8:4, 9:2, 10:2, 11:5 and 38:3). Hypothetical haplotypes are
indicated with empty small circles. Localities are shown in the legend
654 Coral Reefs (2009) 28:651?659
123
from the unimodal distribution expected from recent
expansion (P = 0.249) (Fig. 3). Similar results were also
obtained when samples from sites in the western and
central Pacific were examined individually by location.
Estimates of initial and current h following population
expansion (h0 and h1, respectively, where h = 2Nel, Ne is
the effective population size and l is the mutation rate) of
the combined western and central Pacific sites are
h0 = 2.752 (95% confidence interval = 0.000?8.400) and
h1 = 1062.5 (95% confidence interval = 20.994?7586.3).
The estimated value of s (the number of generations
scaled by mutation rate) for the combined data from
samples in the western and central Pacific is 1.399 (95%
confidence interval: 0.352?5.500). On the other hand, the
mismatch distribution for data from the two sites in the
eastern Pacific is bimodal, and the least squares fit is
significantly different than one determined for a simulated
recently expanded population (P = 0.005). Nonetheless,
because the sample size from this region is small this
result is not robust.
Table 1 Sample sizes and
haplotype diversity of
Conus ebraeus from several
sites in the Pacific
Standard errors are indicated in
parentheses
Number of
individuals
Number of
haplotypes
Haplotype
diversity (SE)
Eastern Pacific
Clipperton 10 4 0.778 (0.091)
Panama 2 1 0.000 (0.000)
Combined 12 4 0.712 (0.105)
Central and western Pacific
Hawaii 17 13 0.963 (0.033)
American Samoa 20 14 0.947 (0.034)
Enawetak 9 9 1.000 (0.052)
Guam 10 9 0.978 (0.054)
Philippines 6 2 0.333 (0.215)
Okinawa 18 12 0.935 (0.041)
Combined 80 41 0.942 (0.018)
Table 2 Analysis of molecular variance (AMOVA) and U-statistics of populations of Conus ebraeus from the eastern Pacific and
western ? central Pacific
Category Observed partition
Variance % explained U-statistics P df
Among regions 0.631 25.2 UCT = 0.252 \0.00001 1
Among populations within regions 0.026 1.0 USC = 0.014 0.244 6
Within populations 1.845 73.7 UST = 0.263 \0.00001 84
Table 3 Pairwise UST values for all populations of Conus ebraeus in the tropical Pacific with n [ 5
Eastern Pacific Central and western Pacific
Clipperton Hawaii American Samoa Enawetak Guam Philippines Okinawa
Eastern Pacific
Clipperton ?
Central and western Pacific
Hawaii 0.189*** ?
American Samoa 0.210**** -0.025 ?
Enawetak 0.194** -0.021 -0.009 ?
Guam 0.157** -0.019 0.006 -0.015 ?
Philippines 0.248* -0.011 -0.010 -0.047 0.039 ?
Okinawa 0.112* 0.017 0.034 0.039 -0.021 0.085 ?
Probabilities that observed UST values deviate from a null hypothesis of no difference between populations were determined from the proportion
of 10,100 permutations of haplotypes between populations that gave UST values greater than or equal to the observed UST (* P \ 0.05,
** P \ 0.01, *** P \ 0.005, **** P \ 0.001)
Coral Reefs (2009) 28:651?659 655
123
Despite IM run durations longer than 1 year, it proved
impossible to obtain a distinct inflection point in the pos-
terior probability density curve of h for the populations
from the western and central Pacific, indicating that the
data from this single locus did not contain the information
necessary for the estimation of this parameter. The curve of
posterior probability density for this parameter rose from a
low value to a plateau, such that all estimates of h greater
than 2,000 had the same approximate probability, and so it
is reasonable to consider 2,000 as a minimum estimate of h
(see Hey 2005). Convergence was reached for all other
parameters. Based on these results, h for combined data
from the western and central Pacific (hW?CP [ 2000) was
considerably larger than estimates of h for the eastern
Pacific [hEP = 0.045 (highest posterior probability interval
HPPI): 0.045?1.04)] and of the ancestral population
(hA = 11.11, HPPI: 0.027?69.09). These results were
consistent with those from analyses of mismatch distribu-
tions in which the population from the western and central
Pacific appears to have undergone recent population
expansion while the population from the eastern
Pacific has not. While the scaled probability of migration
into the eastern Pacific was higher (mEP = 40.2,HPPI:
0.25?394.25) than that into the western and central Pacific
(mW?CP = 0.05, HPPI: 0.05?8.68), the number of female
propagules (M = 2Nem = hm/2) that the western and
central Pacific has received (MW?CP [ 50.0) was much
higher than the number that the eastern Pacific has received
(MEP = 0.92) if the estimation of hW?CP is reasonable.
Also, the proportion of time during the IM run that MW?CP
was greater than MEP was 0.99. The estimated scaled time
of divergence of populations (t = g/u, g is number of
generations) was 0.315 (HPPI: 0.075?3.375).
Discussion
Connectivity among western and central Pacific
populations
Even though all samples of C. ebraeus in the western and
central Pacific included haplotypes unique to particular
sites, the majority of these haplotypes were only a few
mutational steps removed from the most common haplo-
type. Many other haplotypes were shared among
populations (Fig. 2). Thus, COI in C. ebraeus indicates
high levels of on-going gene flow among populations west
of the EPB, including those from Hawaii, or else that
C. ebraeus recently expanded in these regions. Pairwise
estimates of UST between populations in this region also
reveal an overall lack of structure among these populations
(Table 3). No UST value between any pair of populations
from the western and central Pacific was significant.
Analysis of molecular variance further demonstrates that
the majority of the genetic variation occurs within popu-
lations and only approximately 1% of the variation is
partitioned among populations within regions when con-
sidering populations from the western ? central and
eastern Pacific (Table 2).
The genetic structure of C. ebraeus in the western and
central Pacific perhaps best resembles that of several
other Indo-West Pacific species: the nerite gastropods
Nerita albicilla and N. plicata (Crandall et al. 2008) and the
sea urchins Tripneustes gratilla (Lessios et al. 2003) and
Diadema savignyi (Lessios et al. 2001). As in C. ebraeus,
several mitochondrial haplotypes are shared among popu-
lations throughout the range of each species. Pairwise
estimates of UST are generally low, though in Tripneustes
some are significant. Larvae of Diadema and Tripnuestes
have planktonic phases that last from one to three months,
and so, similar to C. ebraeus, they may achieve high rates of
gene flow due to great dispersal abilities of their planktonic
larval stage.
Fig. 3 Mismatch distributions of COI haplotypes of populations of
Conus ebraeus from a the western and central Pacific and b the
eastern Pacific. Curves depicting frequency distributions of pairwise
sequence differences simulated under a model of population expan-
sion are illustrated for each set of haplotypes
656 Coral Reefs (2009) 28:651?659
123
Results from analysis of F-statistics are incapable of
distinguishing between low levels of gene flow among
recently derived populations and higher levels of gene flow
among long separated populations. The mismatch distribu-
tion of combined haplotype sequences of western and
central Pacific populations of C. ebraeus (Fig. 3) is con-
sistent with a model of recent expansion within this region.
COI sequences of a pair of transisthmian Conus, C. gladiator
and C. mus, given by Duda and Rola?n (2005) and an esti-
mated time of divergence of these species at 6.9 my (Duda
and Kohn 2005) provides a mutation rate of 3.7 substitutions
per million year for the amplified fragment of COI. Based on
this rate and the estimated value of s, expansion of western
and central Pacific populations presumably took place dur-
ing the last 190 thousand years; the 95% confidence interval
for the timing of the expansion is 50?740 thousand years.
Accordingly, fossils of C. ebraeus are known from Pleis-
tocene deposits in the Seychelles (Braithwaite et al. 1973),
Australia (Kohn 1997), and Hawaii (Kosuge 1969) but have
not been reported from earlier deposits. The coconut crab,
Birgus latro (Lavery et al. 1996b), and the sea urchin
T. gratilla (Lessios et al. 2003) also show similar mismatch
distributions as those of C. ebraeus and apparently also
recently expanded in the western Pacific during the Pleis-
tocene. Based on a variety of Bayesian analyses, the nerites
N. albicilla and N. plicata also appear to have recently
expanded in the Pacific during the Pleistocene (Crandall
et al. 2008). Few other phylogeographic studies have spe-
cifically examined the demographic histories of species
in the western and central Pacific, but gene trees of sev-
eral, including some echinoderms, such as D. savignyi,
D. setosum and D. paucispinum (Lessios et al. 2001) and a
fish (Chlorurus sordidus, Bay et al. 2004), exhibit a star-like
pattern that is suggestive of recent population expansion.
Thus, the limited degree of genetic differentiation of popu-
lations of these species may simply reflect recent expansion,
rather than current levels of gene flow and this pattern
appears to be shared by many other western and central
Pacific marine taxa.
History and origins of populations in the eastern Pacific
Trans-Pacific distributions of tropical prosobranch gastro-
pod species that are widely distributed and abundant in the
Indo-West Pacific are often assumed to indicate relatively
recent range expansions from these areas into the eastern
Pacific (e.g., Emerson 1991). However, if speciation is
often peripatric (Mayr 1970), there is also the possibility
that a new species would arise in the margins of the
ancestral distribution, then spread into the center. In
C. ebraeus the ancestral haplotype is found in the western,
central and eastern Pacific, so it provides no information
regarding the direction of invasion across the East Pacific
Barrier. In 13 out of 20 trans-Pacific fishes examined by
Lessios and Robertson (2006) source populations were not
obvious for the same reason.
Patterns of gene flow between western ? central
Pacific and eastern Pacific populations
The results of the IM analysis are tentative, not only
because it proved impossible to obtain a good estimate of
effective population size for the western ? central Pacific,
but also because a single locus does not necessarily provide
good estimates of population history. Nevertheless, the
estimate that more larvae cross the EPB in a westerly
direction and contribute genes to populations in the western
and central Pacific is similar to results recently obtained for
a variety of fishes (Lessios and Robertson 2006). Out of 15
comparisons of trans-Pacific populations of fishes across the
EPB in which directionality of migration could be deter-
mined, Lessios and Robertson (2006) found that 11 showed
a higher rate of gene flow westward. They attributed this
trend to the higher probability that migrants across this large
oceanic stretch would successfully mate and leave their
genes behind when they arrived at the denser and more
widespread populations in the west. The time of separation
between eastern and western ? central Pacific populations
of C. ebraeus estimated by IM, when calibrated with the
same substitution rate of Conus as the estimates obtained
from the mismatch analysis, is approximately 84 thousand
years. If this estimate is correct, there was a large pulse of
migration, obliterating any genetic differences that might
have existed between populations within the last millen-
nium. Given that the sample from the eastern Pacific is
composed almost entirely of C. ebraeus collected at the
Clipperton Atoll, the westernmost island in the eastern
Pacific, the fauna of which is a mixture of eastern and
central Pacific species (Emerson 1994; Robertson and Allen
1996), this scenario is not entirely implausible.
Sample sizes, geographic coverage and single locus
analysis
Because of the difficulty of obtaining C. ebraeus from many
places, sample sizes from some localities are small, and
geographic coverage, albeit widespread within the Pacific, is
not dense. Nonetheless, the inclusion of COI data from
additional individuals or localities would not be likely to
produce results that contradict the main interpretations
concerning the lack of structure within the western ? cen-
tral Pacific and distinctiveness of the eastern Pacific
population even if inferences of demographic histories are
more tentative. For example, despite low sample sizes from
some sites, pairwise UST values estimated between sites
in the western and central Pacific are consistently not
Coral Reefs (2009) 28:651?659 657
123
significant, whereas those estimated between sites in the
western ? central Pacific and eastern Pacific are consis-
tently significant. These interpretations are also based solely
on examination of a single mitochondrial gene. Presumably
variation in the marker is effectively neutral, but if this were
not the case (e.g., if a recent selective sweep of mitochon-
drial DNA had occurred), then the inferences on
demographic histories would be in error. Examination of
additional loci would be useful in evaluating these
interpretations.
The phylogeography of C. ebraeus contrasts greatly with
that of another gastropod, Astralium rhodostomum (Meyer
et al. 2005). Like C. ebraeus, A. rhodostomum has a wide
distribution (from Thailand to Polynesia) and possesses a
planktonic larva. But unlike the planktonic larvae of Conus,
those of Astralium are unable to feed, and thus spend less
time in the plankton. Possibly due to this difference,
A. rhodostomum displays a high degree of fine-scale ende-
mism, with 30 separate clades, many of them geographically
isolated from each other. Meyer et al. suggest that such
??species?? that are morphologically uniform but genetically
differentiated between archipelagos are common among
gastropods. C. ebraeus definitely does not fit this pattern,
and its phylogeography is more similar to that of other
marine taxa than it is to Astralium. Thus, each marine spe-
cies, independently of its phylogenetic affinities, has its own
unique history and its own biological characteristics that can
affect its phylogeographic history. Many more studies of
widespread species will be needed before the factors that
contribute to modern-day patterns can be elucidated.
Acknowledgments Dan Lindstrom, Laura Geyer, Alan Kohn, Steve
Vollmer, Kirstie Kaiser, and Hank Chaney assisted in obtaining or
aided in access to specimens. Don Barclay and family greatly assisted
in fieldwork and collections in American Samoa. Mike Hadfield and
members of the Kewalo Marine Lab (University of Hawaii) facilitated
collections on Oahu. The crew of the R/V Urraca? (STRI) assisted with
obtaining specimens from Panama. We are extremely grateful for
access to specimens from the Invertebrate Zoology collections at the
Santa Barbara Museum of Natural History. We also appreciate
comments on this manuscript from Diarmaid O? Foighil, Evan Bra-
swell and several anonymous reviewers. Aspects of this work were
initiated while TFD was a Tupper Fellow at STRI and completed with
support from NSF (0718370) and start-up funds from the University
of Michigan Museum of Zoology and Department of Ecology and
Evolutionary Biology.
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