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Fishery Bulletin 111(2) 
water off Central America originally identified as S. po- 
eyi (Sy nodus poeyi lineage 2 in Fig. 1). That lineage is 
17.9% divergent from S. poeyi specimens from the Gulf 
of Mexico (Sy nodus poeyi lineage 1 in Fig. 1). 
A comprehensive study of S. poeyi from throughout 
its range, similar to this study conducted for S. inter- 
medius and S. foetens, should help clarify the taxonomy 
of that species and likely will result in the recogni- 
tion of a new species or one resurrected from synony- 
my. Preliminary investigation of Synodus synodus and 
Saurida brasiliensis from Cape Verde (not included in 
Fig. 1) reveal approximately 5-6% divergences in COI 
from western Atlantic Synodus synodus and Saurida 
brasiliensis, indicating deep population structure or 
potential cryptic species in those lizardfish lineages. 
Initial investigation of some Pacific lizardfish species 
(genetic data not included in this article) indicates that 
Trachinocephalus my ops from the Philippines is highly 
divergent in COI from western Atlantic T. myops — a 
finding that sheds doubt on the current circumtropical 
distribution of T. myops and the monotypy of Trachi- 
nocephalus. Further investigation of this genus world- 
wide is needed to evaluate species diversity. 
The intrageneric genetic variation in COI in western 
Atlantic Synodus and Saurida is high compared to the 
variation observed for other marine fishes that have 
been analyzed. Ward et al. (2005) found the average in- 
trageneric variation in 207 species of Australian fishes 
to be 9.93%, and Hubert et al. (2008) found an average 
8.30% intrageneric distance for 193 species of Cana- 
dian freshwater fishes. Average intrageneric divergence 
in western Atlantic synodontids (20.5%) exceeds even 
the average intergeneric distance of 16.6% calculated 
by Kartavtsev (2011) for animal species in general. 
Interspecific and intergeneric distances are similar in 
western Atlantic synodontids (Table 1). Large diver- 
gences likely reflect older speciation events, but the 
factors that drive lizardfish evolution are unknown. 
Geographic and population variation 
Although a species phylogeny for synodontids is need- 
ed to hypothesize sister-group relationships and ex- 
amine patterns of speciation in this family, we note 
that morphologically and genetically similar species, 
such as S. foetens and S. bondi or S. intermedius and 
S. macrostigmus, exhibit different geographical and, 
sometimes, depth distributions. Synodus foetens and S. 
bondi have nearly distinct geographical distributions 
(Fig. 6). Synodus foetens occurs off the East Coast of 
the United States, in the Gulf of Mexico, and in the 
central Caribbean; S. bondi occurs in coastal Central 
and South America northward to Haiti. The distribu- 
tion for these species overlaps in Belize and eastward 
to Jamaica and Haiti (Fig. 6). 
Having largely disjunct distributions that overlap 
in the central Caribbean is a pattern congruent with 
distributions observed in other predatory fish genera, 
such as Scomberomorus (mackerels) and Rhizoprion- 
odon (sharpnose sharks). In Scomberomorus, S. macu- 
latus occurs off the East Coast of the United States, 
in the Gulf of Mexico, and in the northern and north- 
western Caribbean, whereas S. brasiliensis occurs in 
the southern and central Caribbean (Collette et al., 
1978; Banford et al., 1999). These 2 species overlap off 
northern Central America and potentially in the south- 
ern Gulf of Mexico. Similarly, Rhizoprionodon terrae- 
novae (Atlantic Sharpnose Shark) inhabits the Gulf 
of Mexico, northern Caribbean, and East Coast of the 
United States, whereas the closely related species, R. 
porosus (Caribbean Sharpnose Shark), occurs off South 
and Central America. These 2 species may overlap in 
the central Caribbean (Springer, 1964; Compagno et 
al., 2005). Synodus foetens and S. bondi do not appear 
to have different depth preferences because both spe- 
cies inhabit depths between the surface and 95 m. 
The geographic distributions of Synodus macrostig- 
mus and S. intermedius overlap (Fig. 4). S. macrostig- 
mus is known from the eastern and southern Gulf of 
Mexico and East Coast of the United States, whereas 
S. intermedius inhabits the eastern Gulf of Mexico, 
East Coast of the United States, Bermuda, Bahamas, 
and the Caribbean. These overlapping distributions 
are similar to the distributions observed in 2 genetic 
lineages of the goby, Bathygobius soporator (Frillfin 
Goby), by Tornabene et al. (2010). Those authors did 
not describe the lineages as separate species because 
no morphological differences were found to corroborate 
the genetic data, but Tornabene and Pezold (2011) not- 
ed that the B. soporator lineages could represent re- 
cent divergence and ongoing speciation in the western 
Atlantic. However, because the genetic divergence was 
observed in mitochondrial DNA alone, they could not 
rule out the possibility of deep coalescence. 
Unlike the gobies, S. intermedius and S. macrostig- 
mus are morphologically distinct, and they exhibit dif- 
ferent depth preferences. Although S. macrostigmus 
primarily inhabits depths below 28 m (mean 96.5 m), 
S. intermedius is found typically at shallower depths 
(mean 49.3 m). However, S. intermedius has a broad 
depth distribution and has been collected in deep water 
along with S. macrostigmus (i.e., UF29818). Further in- 
vestigation is needed to ascertain possible reproductive 
barriers in the evolutionary history of these species 
and whether or not ecological speciation (e.g., Rocha et 
al., 2005) could have played a role. 
The neighbor-joining tree (Fig. 1) also reveals evi- 
dence of population structure in some species. For ex- 
ample, S. foetens specimens from the Gulf of Mexico 
differ in COI by 1.2% from a specimen in Belize, and 
Caribbean specimens of Trachinocephalus myops differ 
genetically by 1.6% from 2 deepwater Gulf of Mexico 
specimens. Finally, within Saurida normani, specimens 
from the Gulf of Mexico differ from Central American 
specimens by 1.7%. Additional material and genetic 
analyses are needed to describe the population struc- 
ture of western Atlantic lizardfishes. 
