ORIGINALARTICLE

Biogeographical contingency and theevolution of tropical anchovies (genusCetengraulis) from temperate anchovies(genus Engraulis)

W. S. Grant1*, Frederic Lecomte2 and Brian W. Bowen3

1Department of Biological Sciences, University

of Alaska Anchorage, Anchorage, AK 99508,

USA and Alaska Department of Fish and

Game, 333 Raspberry Road, Anchorage, AK

99518, USA, 2INRA-UMR ECOBIOP, Pole

d’Hydrobiologie, Quartier Ibarron, 64310 Saint

Pee sur Nivelle, France, 3Hawaii Institute of

Marine Biology, University of Hawaii, PO Box

1346, Kaneohe, HI, 96744, USA

*Correspondence: Stewart Grant, Department of

Biological Sciences, University of Alaska

Anchorage, Anchorage, AK 99508, USA.

E-mail: phylogeo@yahoo.com

ABSTRACT

Aim Similar regimes of selection in different geographical settings can

deterministically produce similar adaptive morphologies. We tested the

hypothesis that the evolutionary trajectories of fish in upwelling zones can be

altered by biogeographic contingencies in the biological and physical

environment.

Location Eastern Pacific and western Atlantic oceans.

Methods We estimated phylogenetic relationships among eastern Pacific

temperate anchovies (genus Engraulis) and tropical anchovies (genus

Cetengraulis) with neighbour-joining and Bayesian tree analysis of a 521-bp

segment of mitochondrial DNA cytochrome b. Available sequences for five

additional engraulid taxa were included to establish polarity of the tree. Bayesian

estimates (BEAST) of time to most recent common ancestor (TMRCA) for the

nodes in the phylogeny were calibrated with divergence between Cetengraulis

edentulus and Cetengraulis mysticetus precipitated by the rise of the Panama

Isthmus 2.8–3.2 Ma.

Results Neighbour-joining and Bayesian trees indicate that South American

Engraulis anchoita (Argentina) and Engraulis ringens (Chile) together are basal

sister taxa to the California anchovy (Engraulis mordax) and Old World anchovies

(Engraulis japonicas, Engraulis australis, Engraulis capensis and Engraulis

encrasicolus). The two tropical species of Cetengraulis are sister-taxa to

Californian E. mordax, even though their phenotypes and ecologies differ

markedly. A relaxed molecular clock indicates a TMRCA between Californian

E. mordax and Cetengraulis at about 4.2 Ma (3.0–6.3 Ma 95% highest probability

density).

Main conclusions The TMRCA between the California anchovy, E. mordax,

and tropical Cetengraulis coincides with the formation of the Gulf of California,

which provided opportunities for allopatric isolation during climate oscillations.

Mid-Pliocene warming (3.1–2.9 Ma) may have trapped ancestors of Cetengraulis

in the Gulf of California, where they evolved digestive tract morphologies to

exploit inshore tropical habitats with low plankton productivities. While

populations of several other temperate fishes have become isolated in the Gulf

of California, few of these derived species show strong adaptive shifts from

temperate sister taxa or range expansions into the tropical provinces of the

western Atlantic and eastern Pacific.

Keywords

Adaptive shift, Bayesian analysis, determinism, Engraulidae, evolution, Gulf of

California, marine fish, mitochondrial DNA, Panama Seaway, TMRCA.

Journal of Biogeography (J. Biogeogr.) (2010) 37, 1352–1362

1352 www.blackwellpublishing.com/jbi ª 2010 Blackwell Publishing Ltddoi:10.1111/j.1365-2699.2010.02291.x

INTRODUCTION

When similar selective pressures are set into motion, similar

adaptive phenotypes and ecologies may result (Taylor &

McPhail, 2000; MacLean & Bell, 2003; Arendt & Reznick,

2008). These deterministic trajectories, however, can be altered

by contingent shifts in a species’ biological and physical

environment, so that selection pressures under different

circumstances result in a new evolutionary outcome (Gould,

1989, 2002; Luisi, 2003; Vermeij, 2006). Shifts in genetic or

environmental background provide ‘windows of opportunity’

that interact with ecological determinism to produce evolu-

tionary novelty (Taylor & McPhail, 2000; Parmesan & Yohe,

2003). These opportunities can be enhanced by tectonic

or climate-induced barriers to dispersal (Nelson et al., 2000).

The resulting divergence between isolated populations can

contribute to within-species diversity and sometimes to the

evolution of new species.

Examples of ecological determinism can be found in many

genera of marine fish. These genera include ecologically similar

taxa in widely separated regions around the globe. In some

genera, these taxa are genetically distinct and represent separate

species (e.g. hake, Grant & Leslie, 2001; bonefishes, Bowen et al.,

2007; New World anchovies, Grant et al., 2005). In other

genera, these taxa show only population-level divergences (e.g.

Pacific sardines, Bowen & Grant, 1997; Old World anchovies,

Grant & Bowen, 2006). Anchovies, sardines and mackerel

inhabiting temperate upwelling zones in separate oceans show

strikingly similar diets, and hence digestive tract morphologies

and body shapes (Whitehead et al., 1988). Phenotypes of

individuals in these populations reflect similar selective pres-

sures common to upwelling areas. Over time, these populations

track optimal habitats during ocean–climate shifts and thus

avoid selective pressures (contingencies) that would drive

adaptive change (Crame, 1993; Agostini & Bakun, 2002).

While historical contingencies have been identified in the

evolution of terrestrial (Losos et al., 1998) and freshwater

(Taylor & McPhail, 2000) vertebrates, examples for open-

ocean fishes are rare. Here, we describe an example of

historical contingency in a predominantly pelagic lineage of

globally distributed anchovies (genus Engraulis). Molecular

genetic analyses (Grant et al., 2005) and morphological

comparisons (P. Whitehead in Nelson, 1984) delineate two

groups, one consisting mostly of the Old World taxa found in

Japan (Engraulis japonicus Temminck & Schlegel, 1846),

Australia (Engraulis australis (White, 1790)), southern Africa

(Engraulis capensis Gilchrist, 1913) and Europe (Engraulis

encrasicolus (L.)), but also including the silver anchovy

(Engraulis eurystole Swain & Meek, 1884). The second group

includes three New World taxa occurring in Brazil–Argentina

(Engraulis anchoita Hubbs & Marini, 1935), Peru–Chile

(Engraulis ringens Jenyns, 1842) and California (Engraulis

mordax Girard, 1854). Molecular estimates of genetic diver-

gence reveal separations between Old World taxa of less than

200–300 kyr and only a few thousand years between the

European and southern African populations, but separations

of a few million years between three New World species (Grant

et al., 2005; Grant & Bowen, 2006).

The morphologies of the various species of Engraulis are

strikingly similar, and all the species play the same ecological

role as zooplankton predators in widely separated cold-

temperate upwelling regions (Whitehead et al., 1988; Sch-

wartzlose et al., 1999). However, a study of digestive track

morphology indicates close affinities between New World

species of Engraulis and tropical species of anchovies (genus

Cetengraulis) in the western Atlantic (Cetengraulis edentulus

(Cuvier, 1829)) and eastern Pacific (Cetengraulis mysticetus

Gunther, 1867) (Fig. 1), even though the external morpho-

logies of these genera differ substantially (Nelson, 1984, 1985).

This possible example of ecological–morphological divergence

(contingency) contrasts with demonstrated ecological stasis

(determinism) among Engraulis species isolated from one

another since the Late Miocene.

In the present study we use sequences of mitochondrial

(mt)DNA cytochrome b (cyt b) to test the hypothesis by

Nelson (1984, 1985) of phylogenetic affinities among New

World species of Engraulis and Cetengraulis. A fundamental

requirement for using molecular markers to estimate patterns

of divergence among species is the selective neutrality of the

markers so that they do not directly track adaptive shifts. The

mtDNA cyt b is important for cellular respiration and is

therefore certainly under selection. However, the genes

encoded in cyt b do not have a discernible role in the

morphological and ecological adaptation described here.

Molecular markers can be used to date nodes in a tree, which

can be correlated with palaeoclimatic events. We postulate that

the origin of Cetengraulis was historically contingent on the

formation of the Gulf of California and major ocean–climate

temperature shifts in the mid-Pliocene. We propose that these

environmental changes isolated ancestral populations of

temperate Californian E. mordax and forced an ecological

shift leading to novel adaptations in tropical Cetengraulis.

MATERIALS AND METHODS

Samples of C. mysticetus were collected from the southern

portion of the Gulf of California and from the western shores

of Panama (Table 1, Fig. 1). Samples of western Atlantic C.

edentulus were collected from Trinidad. Specimens were

preserved in 95% alcohol before DNA extraction. A 687-bp

portion of cyt b was amplified with polymerase chain reaction

(PCR) following Lecomte et al. (2004) and the heavy-strand

degenerate primer H15149 (5¢-TTGAGCCCT(C)GCTGGG-

TTA(G)TTAGAT-3¢) and a light-strand primer L 14724

(5¢-CGAAGCTTGATATGAAAAACCATCGTTG-3¢). Negative

PCR controls were used to detect potential DNA contamina-

tion. Dubious sequences were reamplified and resequenced

in the forward direction. Unique sequences are deposited

in GenBank (C. edentulus: accession numbers GU357636–

GU357647; C. mysticetus: GU357648–GU357663).

Haplotype (h) and nucleotide (hp) diversities were estimated

with arlequin 3.1 (Excoffier et al., 2005). Haplotype networks

Biogeographical contingency and evolution of tropical anchovies

Journal of Biogeography 37, 1352–1362 1353ª 2010 Blackwell Publishing Ltd

for C. edentulus and C. mysticetus were estimated with tcs 1.21

using the 95% criteria for network links (Clement et al., 2000).

Sister-group relationships were estimated with a dataset

consisting of 97 unique sequences for 11 taxa, including C.

edentulus, C. mysticetus, E. mordax, E. encrasicolus, E. japonicus,

E. anchoita, E. ringens, Anchovia clupleoides (Swainson, 1839),

Anchoviella lepidentostole (Fowler, 1911), Coilia brachygnathus

Kreyenberg & Pappenheim, 1908 and Coilia nasus Temminck

& Schlegel, 1846. This 521-bp sequence corresponded to

positions 14385–14905 in the GenBank sequence NC009581 of

E. encrasicolus. Net sequence divergence (dnet) between taxa

was estimated with mega 4.0 (Tamura et al., 2007). A

neighbour-joining (NJ) tree was constructed with mega using

the Tamura–Nei model of substitution (TrN; Tamura & Nei,

1993), and with 10,000 bootstraps to estimate statistical

support for nodes. A Bayesian tree was produced with beast

1.4.7 (Drummond et al., 2002; Drummond, 2003) and with

the TrN+I+G model with invariant sites (I = 0.603) and site

heterogeneity (shape a = 1.438), as determined with the

Akaike information criterion (Akaike, 1974) in modeltest

3.06 (Posada & Crandall, 1998). Trees were produced with 15

million Markov chain Monte Carlo (MCMC) steps (effective

sample sizes � 200) with the Yule model of lineage births

under a lognormal relaxed clock. A maximum credibility tree

was selected by TreeAnnotator 1.4.8 and visualized with

FigTree 1.2 (A. Rambaut, http://tree.bio.ed.ac.uk/). Nodes in

this tree were calibrated by the separation between Cetengraulis

edentulus (Caribbean) and C. mysticetus (eastern Pacific) at

3.0 Ma with a prior normal distribution with a standard

deviation of 0.1 (2.8–3.2 Ma). This period marks the closing of

the Panama Seaway (Bartoli et al., 2005; Coates et al., 2005;

Lessios, 2008). The two species of Coilia served as outgroups.

RESULTS

Mitochondrial DNA variability

In tropical Atlantic C. edentulus, 13 substitutions (11 transition

(ti), 2 transversion (tv)) defined 12 haplotypes among 25 cyt b

sequences (521 bp). In tropical Pacific C. mysticetus, 29

(a)

(b)

Figure 1 Map showing distributions of New

World Engraulis anchovies and two tropical

species of Cetengraulis. Locations of Ceten-

graulis mysticetus samples in the eastern

Pacific and of Cetengraulis edentulus in the

Caribbean are indicated with solid circles.

Also included are 95% networks of cyto-

chrome b haplotypes in C. edentulus and

C. mysticetus. Numbers below the open

circles indicate haplotype number, and closed

circles represent intermediate, but unob-

served, haplotypes. For C. edentulus, haplo-

type numbers 1–12 correspond to GenBank

accession numbers GU357636–GU357647,

respectively. For C. mysticetus, haplotype

numbers 1–16 correspond to GenBank

accession numbers GU357648–GU357663,

respectively.

Table 1 Mitochondrial DNA summary statistics for major populations of Cetengraulis and Engraulis.

Taxon Abbreviation Location n A h hp

C. edentulus Ced Western Atlantic 25 12 0.853 0.0046

C. mysticetus Cmy Eastern Pacific 24 16 0.928 0.0143

E. mordax Emo California–Mexico 14 8 0.890 0.0064

E. anchoita Ean Argentina 19 4 0.450 0.0009

E. ringens Eri Peru–Chile 17 5 0.427 0.0009

E. japonicus Eja Japan 22 15 0.944 0.0101

E. encrasicolus Een Europe 17 13 0.949 0.0138

n, sample size; A, number of haplotypes; h, haplotype diversity; hp, nucleotide diversity.

W. S. Grant et al.

1354 Journal of Biogeography 37, 1352–1362ª 2010 Blackwell Publishing Ltd

substitutions (27 ti, 2 tv) defined 16 haplotypes among 24

sequences. Haplotype diversities were h = 0.853 and 0.928 and

nucleotide diversities were hp = 0.0046 and 0.0143, respectively

(Table 1). A 95% confidence network of haplotypes showed

two closely related clusters in C. edentulus, and two haplotype

clusters separated by eight mutations in C. mysticetus (Fig. 1).

One of these clusters (A) consisted of five closely related

haplotypes with a mean sequence divergence of 0.6% Myr)1,

but the second cluster (B) consisted of divergent haplotypes

with a mean sequence divergence of 1.2% Myr)1 (Table 2).

Net sequence divergence between Cetengraulis and E.

mordax was dnet = 11.8–14.5% Myr)1, and between C. edent-

ulus and C. mysticetus dnet = 11.4% Myr)1. The topology of

the NJ tree placed A. lepidentostole as a sister taxon to the

South American anchovies, E. anchoita and E. ringens (Fig. 2),

and these, along with Coilia species, as sister taxa to the

remaining engraulids included in this study. Anchovia clupeo-

ides was a sister taxon to the Old World anchovies, E. japonicus

and E. encrasicolus. These three species were sister taxa to the

California anchovy, E. mordax, and tropical C. edentulus

and C. mysticetus. Engraulis mordax was a sister taxon to

Cetengraulis with bootstrap support of 56%.

A similar topology appeared in the Bayesian tree (Fig. 3).

Sister-group status between the two species of Cetengraulis and

E. mordax was supported by a posterior probability of 1.0. The

nodes in this tree were calibrated by the separation of C.

edentulus and C. mysticetus by the formation of the Isthmus of

Panama at 3.0 (prior: 2.8–3.2 Ma). This molecular clock

calibration placed the time to most recent common ancestor

(TMRCA) of Cetengraulis and E. mordax at 4.20 Ma (95%

highest posterior density (HPD): 3.03–6.26 Ma), and the

TMRCA of this group and a group consisting of E. japonicus,

E. encrasicolus and A. clupeoides at 4.82 Ma (95% HPD: 3.32–

7.52 Ma).

DISCUSSION

The nominal members of ‘Engraulis’ occur in upwelling areas

across the northern and southern temperate regions. Our tests

of biogeographical hypotheses have to be tempered by the

recognition that the reconstruction of the ‘Engraulis’ phylog-

eny and evolutionary history remains incomplete. Estuarine

and freshwater engraulid species of the Americas may also fall

within the ‘Engraulis’ family tree (Lovejoy et al., 2006; Wilson

et al., 2008). The absence of many of these taxa in the

phylogeny presented here, however, does not detract from the

following biogeographical scenario for the origin of Ceteng-

raulis. The evolution of Cetengraulis from ancestral E. mordax

is a robust conclusion based on mtDNA and morphology. This

event probably provided the first step in a remarkable chain of

evolutionary events leading from cold-temperate oceans to

freshwater ecosystems of the Amazon Basin.

Phylogeny of Engraulis and Cetengraulis anchovies

The NJ and Bayesian molecular trees demonstrate that the

two tropical species of Cetengraulis fall within the phylogeny

of temperate upwelling Engraulis species and are sister taxa

with the California anchovy, E. mordax. This polyphyletic

relationship was predicted by Nelson (1985) on the basis of

feeding and gut morphology, and is now confirmed with

molecular markers. The polarized mtDNA phylogeny places

the species of Cetengraulis in a derived position in the

phylogeny and indicates an adaptive shift from temperature-

upwelling areas into tropical inshore habitats. Here, we

provide a zoogeographical scenario based on a time-cali-

brated molecular tree and the tectonic history of the eastern

Pacific.

The separation of the two Cetengraulis species by the

Isthmus of Panama provides a unique opportunity to calibrate

sequence divergences within the Engraulis phylogeny. Strati-

graphically dated sediments from the western Atlantic indicate

that uplift and volcanic activity led to the closure of the

Panama Seaway 2.8–3.2 Ma (Coates et al., 2005; Lessios,

2008). The rising isthmus, however, may have become an

ecological barrier much earlier (Knowlton et al., 1993; Marko,

2002). Hence, we used an earlier estimate of separation at

3.3 Ma to provide a calibration of sequence divergence

Table 2 Net sequence divergence (Tamura–Nei) between cytochrome b (521 bp) haplotypes in the engraulids Cetengraulis, Engraulis,

Anchovia, Anchoviella and Coilia. The diagonal is mean within-group sequence divergence.

1. C. edentulus 0.0114

2. C. mysticetus-A 0.1135 0.0055

3. C. mysticetus-B 0.1152 0.0155 0.0119

4. E. mordax 0.1448 0.1201 0.1179 0.0077

5. E. japonicus 0.1721 0.1601 0.1685 0.1553 0.0120

6. E. encrasicolus-A 0.1737 0.1529 0.1531 0.1482 0.0199 0.0062

7. E. encrasicolus-B 0.1742 0.1641 0.1706 0.1554 0.0134 0.0148 0.0086

8. Anchovia clupeoides 0.1646 0.1852 0.1920 0.1531 0.1561 0.1578 0.1610 –

9. E. anchoita 0.2191 0.2237 0.2193 0.1894 0.2474 0.2392 0.2485 0.2223 0.0029

10. E. ringens 0.2270 0.2162 0.2142 0.1924 0.2216 0.2187 0.2198 0.2414 0.0670 0.0031

11. Anchoviella lepidentostole 0.2204 0.2095 0.2103 0.2299 0.2211 0.2123 0.2369 0.2052 0.2052 0.2102 –

12. Coilia spp. 0.2438 0.2442 0.2255 0.2526 0.2126 0.2300 0.2147 0.2463 0.2200 0.2476 0.2200 0.0019

1 2 3 4 5 6 7 8 9 10 11 12

Biogeographical contingency and evolution of tropical anchovies

Journal of Biogeography 37, 1352–1362 1355ª 2010 Blackwell Publishing Ltd

between lineages of 1.9% Myr)1. This calibration places the

separation between ancestral California anchovy and Ceten-

graulis at about 3.6–4.5 Ma, and the separation between

California anchovy and Old World anchovies at about 4.5–

4.8 Ma. The approximate ages of these separations set the stage

for testing biogeographic and speciation models.

Figure 2 Neighbour-joining bootstrap tree of mitochondrial (mt)DNA haplotypes and Tamura–Nei sequence divergences between

engraulid species. Bootstrap support (10,000 pseudo-replicates) appears at the nodes. GenBank sequences: Engraulis encrasicolus phylogroup

A: AF472579, EF427558–9, EF439526, EU224052, EU492081–2, EU553563–4; E. encrasicolus phylogroup B: DQ197948, EF439527,

EU224051, EU264006–7; E. japonicus: AB374208–22, AY923785–97; E. anchoita: AY923766–9; E. ringens: AY923770–4; Coilia brachygnathus:

EU694410; C. nasus: EU694405–6, NC009579.

W. S. Grant et al.

1356 Journal of Biogeography 37, 1352–1362ª 2010 Blackwell Publishing Ltd

Selective determinism of feeding ecologies in regional

populations

Adaptive shifts in a lineage can often be identified by

superimposing ecological traits on a molecular phylogeny

(e.g. Bowen et al., 1993; Block & Finnerty, 1994; Streelman

et al., 2002). In the case of anchovies, mouth and digestive tract

morphologies are similar among upwelling populations

(Appendix 1), even though Old World and New World species

show an early Pliocene divergence (Grant et al., 2005). While

tropical Cetengraulis is deeply embedded in the Engraulis

phylogeny, the morphologies and ecologies of these fishes

contrast markedly with the ecologies of oceanic anchovies. The

morphological shifts in Cetengraulis generally include the

evolution of a more complex intestinal and gill-raker morphol-

ogy that allows these fish to inhabit less productive habitats.

Three factors may contribute to the morphological and

ecological parallelism among Engraulis populations and species.

First, the remarkable similarities in the ecologies, diets and

morphologies of fish in the various populations are likely to

reflect deterministic selection pressures common to upwelling

systems. Anchovies in upwelling areas feed largely on calanoid

copepods and euphausids (Hayasi, 1966; James, 1988; Plounevez

& Champalbert, 1999; Capitanio et al., 2005; Espinoza &

Bertrand, 2008). Although prey species differ between upwelling

zones, prey size and abundances are similar, so that the shared

anchovy morphology most efficiently exploits this resource.

The deep molecular divergences between upwelling taxa are

coupled with a lack of morphological and ecological divergence,

reflecting the long-term stability of selection pressures in

upwelling zones.

Second, the lack of barriers to migration and dispersal

within an upwelling area produces high levels of gene flow that

swamp adaptive genotypes in marginal populations (Lecomte

et al., 2004; Bridle & Vines, 2007). Numerous studies of

genetic population structure with neutral molecular markers

indicate that populations of anchovies in upwelling areas show

remarkably low levels of differentiation, with values of FST

generally less than 0.002. Virtually no genetic structure has

been observed among populations of E. anchoita in the south-

west Atlantic (Grant et al., 2005), E. mordax in the north-east

Pacific (Hedgecock et al., 1989; Lecomte et al., 2004),

E. japonicus in the north-west Pacific (Liu et al., 2006) and

E. capensis off southern Africa (Grant, 1985).

Exceptions to this generalization are found among popula-

tions of E. encrasicolus, partially isolated by complex shorelines

in the Mediterranean, Strait of Gibraltar, and north-east

Atlantic (Bembo et al., 1995, 1996a,b; Magoulas et al., 1996,

2006). Opportunities for allopatric isolation in the Mediter-

ranean have prompted an apparent adaptive shift into

estuarine environments (Borsa, 2002). Collectively, the results

from linear continental coastlines indicate that unrestricted

gene flow inhibits locally adaptive forms within open-ocean

upwelling zones.

Figure 3 Bayesian highest credibility tree of mitochondrial DNA cytochrome b haplotypes (521 bp) in Engraulis and Cetengraulis based on

the Tamura–Nei substitution model with gamma and invariant sites. Posterior probabilities appear at the nodes. The time-scale was

estimated by divergence between Cetengraulis edentulus and Cetengraulis mysticetus across the Isthmus of Panama. Grey bars indicate

Bayesian 95% highest probability densities for the positions of the nodes.

Biogeographical contingency and evolution of tropical anchovies

Journal of Biogeography 37, 1352–1362 1357ª 2010 Blackwell Publishing Ltd

Third, the morphological and ecological similarities between

populations in some upwelling areas may be due to recent

shared ancestries. For example, phylogeographic analyses of

populations off southern Africa and Australia indicate that

these populations are recently derived from Northern Hemi-

sphere populations in Europe and Japan, respectively. Southern

populations appear to suffer periodic climate-driven extinc-

tions followed by recolonization from northern populations

(Grant & Bowen, 2006). The lack of morphological divergence

in these southern populations may, therefore, be due to a

shallow evolutionary history. Nevertheless, Old World popu-

lations still show strong ecological and morphological similar-

ities to New World anchovies after about 5 Myr of isolation.

Plate tectonics and climate variability

The development of shoreline complexity in the north-east

Pacific, together with long-term cycles of climate variability,

appear to have been the driving forces that prompted adaptive

change in ancestral Cetengraulis. Shoreline topographies in this

region have changed considerably over the timeframe of

anchovy evolution in the New World. Molecular coalescences

place the deepest nodes of the Engraulis phylogeny in the

mid-Miocene, 10–15 Ma (Grant et al., 2005). At 15 Ma, a

deep-water seaway separated Central America from the north-

western shores of South America and connected the eastern

tropical Pacific and the Caribbean (Coates & Obando, 1996).

The Neogene (22.5 Ma to present) was marked by a long-

term decline in global temperatures, with precipitous drops in

the mid-Miocene and late Pliocene (Zachos et al., 2001). This

decline in temperature produced changes in the geographical

distributions of Miocene molluscs in coastal California (Hall,

2002). At several times over the late Miocene to early Pliocene,

the cool California Current reached deeply into the Panama

province (Duque-Caro, 1990), as evidenced by the appearance

of California Province fishes in Pliocene fossils in Ecuador

(Landini et al., 2002). These episodic incursions of cool water

into the equatorial eastern Pacific may have permitted periodic

range expansions of Engraulis to the south, but would not

necessarily have driven an adaptive shift into warm tropical

waters.

The mid-Miocene (15 Ma) collision of the Pacific and

Caribbean plates produced uplift and volcanism that led to the

closure of the Panama Seaway. The closing seaway restricted

first the movements first of deep-water species, then of inshore

species (Knowlton et al., 1993). The initial severance occurred

at 3.5 Ma, physically subdividing a once continuous biogeo-

graphical province into two tropical provinces. The appearance

of the Panama Isthmus probably isolated ancestral populations

of C. edentulus and C. mysticetus, but this separation does not

explain the earlier appearance of Cetengraulis.

The formation of the Gulf of California began about

13 Ma and produced a long narrow sea with a latitudinal

traverse of about 9�. A slip collision of the Pacific Plate

against what is now Mexico captured a sliver of the continent

and produced a proto Gulf of California at 8 Ma (Atwater,

1998; Oskin et al., 2001). The captured portion of the North

American Plate moved obliquely northward opening the

entire Gulf of California basin 6.5–6.3 Ma (Atwater, 1998;

Oskin & Stock, 2003). These events produced a north–south

oriented Gulf of California open to the Pacific only at its

southern boundary, where temperature oscillations limit

access to the Gulf (Bernardi et al., 2003). We postulate here

that as the southern boundary of ancestral populations of the

California anchovy retreated northward during ocean–climate

warming, a population was trapped in the Gulf of California.

In isolation from oceanic populations, ancestral Cetengraulis

adapted to warm-water near-shore habitats and subsequently

invaded southern tropical waters before the closure of the

Panama Isthmus.

Biogeographical contingency and adaptive shifts

The adaptive shift from a temperate upwelling ecology in

ancestral Engraulis to tropical inshore Cetengraulis represents a

shift from a plankton-rich to a plankton-poor environment.

A fundamental response to this environmental shift requires a

greater efficiency in extracting nutrients from plankton. The

importance of feeding efficiency is illustrated by rapid changes

in the digestive tract in response to food quality and quantity

in unstable environments (Stearns, 1989; Starck, 1999). In

Cetengraulis, greater feeding efficiency has been achieved by

more elaborate gill rakers to filter plankton and bottom

sediments, an extension of the intestine to increase absorptive

surfaces (Nelson, 1984) and a deeper body to accommodate

the larger intestine.

The Gulf of California has traditionally been viewed as a

hotspot of species diversity (Hubbs, 1960; but see Simison,

2006) and, hence, is associated with speciations promoted by

climate-driven allopatric isolations (Jacobs et al., 2004).

Several species inhabiting the temperate coast of California

are also represented as isolated populations in the Gulf of

California, or have closely related sister taxa in the Gulf

(Present, 1987; Terry et al., 2000; Huang & Bernardi, 2001;

Stepien et al., 2001; Bernardi et al., 2003; Bernardi & Lape,

2005). While the isolated taxa have diverged from parental taxa

to various degrees, as indicated by molecular divergences, none

of the other isolated taxa show a major adaptive shift into

tropical habitats. Hence, the adaptive shift and penetration

into tropical habitats by Cetengraulis is unusual among these

diverging pairs of taxa.

CONCLUSIONS

Species of temperate anchovies (genus Engraulis) respond to

climate change by shifting their geographical distributions so

that populations remain in optimal habitats. These popula-

tions can avoid selective pressures that would prompt an

adaptive shift. Alternatively, the lack of a suitable coastline for

population displacement can prevent populations from track-

ing optimal habits and can thus lead to local or regional

extirpations (Grant, 2005; Grant & Bowen, 2006). These

W. S. Grant et al.

1358 Journal of Biogeography 37, 1352–1362ª 2010 Blackwell Publishing Ltd

vacated areas are often recolonized by fish from other

upwelling areas. In both cases, selection for upwelling habitat

deterministically maintains a common ecology and similar

phenotypes, even among populations separated by thousands

of kilometres and millions of years.

We have described an example of a major adaptive shift in

a globally distributed lineage with otherwise remarkable

ecological and morphological stasis. This adaptive shift

appears to have been prompted by the contingencies of

climate warming and allopatric isolation in the Gulf of

California. Isolations of the California anchovy, E. mordax,

have undoubtedly occurred numerous times since the

formation of the Gulf of California about 6 Ma. Genetically

undifferentiated populations of the California anchovy cur-

rently inhabit the gulf (Lecomte et al., 2004). However, none

of these other isolation events has led to a new species. A

major adaptive shift, based on selection of quantitative traits,

may not occur readily. Alternatively, a shift may be contin-

gent on fortuitous chromosomal rearrangements or genome

reorganizations.

Superficially, an evolutionarily younger taxon situated in the

tropics between two older taxa supports a deterministic centre-

of-origin model in which competitive exclusion pushes

parental taxa into higher latitudes (Briggs, 1987, 1999).

However, the molecular phylogeny of New World Engraulis

does not provide support for this hypothesis. In this case, the

tropical Cetengraulis clearly originated from temperate popu-

lations of E. mordax and are not the progenitors of temperate

Californian and Peruvian anchovies.

ACKNOWLEDGEMENTS

We thank the editor, Robert McDowall, and two anonymous

referees for insightful comments and helpful suggestions, and

M. Soerse and R. Castilho for discussions on determinism and

contingency in evolution. M. Grant edited various drafts of the

manuscript. D. R. Robertson, C. Quinonez-Velazquez and B.

Marin kindly provided samples of Cetengraulis. This study was

funded by a National Science Foundation grant (DEB-9727048

to B. W. B.) jointly awarded by the Population Biology and

Biological Oceanography Divisions. F. L. was supported by a

PhD Internship grant from Fonds pour la Formation des

Chercheurs et l’Aide a la Recherche, Quebec, Canada. B. W. B.

is supported by National Science Foundation Grant OCE-

0929031. This is contribution no. 1381 from the Hawaii

Institute of Marine Biology and contribution no. 7874 from

the School of Ocean and Earth Science and Technology at the

University of Hawaii.

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BIOSKETCHES

W. Stewart Grant is an affiliate professor at the University

of Alaska Anchorage, and has investigated the evolution and

biogeography of marine fishes for several decades using

biochemical and molecular methods. His present focus is on

the biogeographies of small pelagic and north Pacific subpolar

marine fishes.

Frederic Lecomte is a research associate interested in the use

of molecular markers to study various aspects of fish biology

and genetic population structure.

Brian W. Bowen is a research professor at the Hawaii Institute

of Marine Biology, University of Hawaii. He studies the

evolution and conservation genetics of marine vertebrates, with

an emphasis on how biodiversity is generated and maintained.

Editor: Robert McDowall

APPENDIX 1

Presence (1) or absence (0) of morphological character states among species of Engraulis and Cetengraulis.

Trait Cmy Ced Emo Eri Ean Eja Reference

Symmetrically coiled intestine 1 1 0 0 0 0 A

Laterally compressed body 1 1 0 0 0 0 A

Large number of gill rakers 1 1 0 0 0 0 E

Long branchiostegal rays 1 1 0 0 0 0 A

Broadly united branchiostegal membrane 1 1 0 0 0 0 A

Long and pointed snout 1 1 0 0 0 0 A

Prominent flange behind base of gill rakers on first three arches 1 1 0 0 0 0 A

Gizzard-like stomach (loss of the diverticulum) 1 1 0 0 0 0 B

No gill rakers on posterior face of the third epibranchial 1 1 1 1 1 0 C

Maxilla tip pointed (projecting posteriorly beyond tip of the second supramaxilla) 0 0 1 1 1 0 A

Single (but paired) series of spines on gill rakers 1 1 1 1 1 0 A

Additional series of paired spines on gill rakers 0 0 0 0 1 0 B

Number of gill rakers increasing with age 1 1 0 0 0 0 B

Tooth plate 0 0 1 1 ND ND D

Tooth plate overlying basibranchial 3 0 0 1 1 ND ND D

Tooth plate overlying fifth ceratobranchial 0 0 1 1 ND ND D

Tooth plate fused with infrapharyngobranchials 1 (1 = fused with first epibranchial) 0 0 1 1 ND ND D

Tooth plate fused with infrapharyngobranchials 3 (1 = fused) 0 1 1 1 ND ND D

Tooth plate fused with infrapharyngobranchials 4 (1 = tooth plate independent;

0 = toothless plate)

0 0 1 1 ND ND D

Tooth plate primitively supported by infrapharyngobranchials 5 0 0 1 1 ND ND D

ND, no data.

Species: Cmy, Cetengraulis mysticetus; Ced, Cetengraulis edentulus; Emo, Engraulis mordax; Eri, Engraulis ringens; Ean, Engraulis anchoita; Eja,

Engraulis japonicus.

References: A = Nelson (1984, citing Whitehead, 1973); B = Nelson (1984); C = Nelson (1984, citing Hubbs, 1952); D = Nelson (1970); E = Hil-

debrand (1964).

Data for the three New World species, E. mordax, E. ringens and E. anchoita, provide comparisons to species of Cetengraulis. Data for E. japonicus are

included to represent Old World populations inhabiting the north-west, north-east and south-east Atlantic and the south-west Pacific. Despite wide

separations, species of Old World Engraulis, including Engraulis eurystole, show only population-level genetic divergences from one another (Grant

et al., 2005; G. Silva, W.S. Grant & R. Castilho, unpublished) and are morphologically indistinguishable (Whitehead et al., 1988).

W. S. Grant et al.

1362 Journal of Biogeography 37, 1352–1362ª 2010 Blackwell Publishing Ltd