Download Species Recognition, Dewlap Function and Faunal Size In Rand

AMER., ZOOL., 17:261-270 (1977).
Species Recognition, Dewlap Function and Faunal Size
ERNEST E. WILLIAMS
Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138
AND
A. STANLEY RAND
Smithsonian Tropical Research Institute, Balboa, Canal Zone
SYNOPSIS Although having a number of functions in reproductive, territorial and aggressive behavior, Anolis dewlaps are only one means of intraspecific signaling and they are
always present in small anole faunas (e.g., those of one or two species islands) but here, in
contrast to the situation in large faunas, their color and pattern appear usually very similar
and appear to be unimportant for species (or population) recognition. The latter function
is then performed by such characteristics as adult size and body color and pattern. Where,
however, numerous species abut or overlap, dewlap color and pattern tend to be diverse
and diagnostic (particularly between overlapping forms). Even here, however, adult size,
body shape and body color often redundantly reinforce the species and population
recognition function of even marked dewlap difference. In certain cases in complex faunas,
size and/or body pattern substitute for the species recognition function of reduced or absent
dewlaps.
In Rand and Williams (1970) we argued
that species recognition in anoline lizards
is not based on a single sign stimulus or
releaser but on a complex of stimuli, redundant to each other, which separately
and in various combinations identify the
display animal. Because natural selection
insists that mates be recognizable under a
variety of conditions, we have argued that
selection must favor a system in which
species identity is encoded redundantly.
In the specific case analyzed by us in
1970—species recognition in the eight
species sympatric at a single locality, La
Paltna, on the Greater Antillean island of
Hispaniola—we found that each of the
eight species differed from the rest in
several (average 2-54) characteristics of the
dewlap. Thus the dewlap alone sufficed to
separate these eight species. This redundant use of dewlap characteristics in
species recognition is also largely true in
complex anole faunas of Cuba, such as the
Camaguey fauna studied by Ruibal
(1961a) and by Ruibal and Williams
(1961a, b).
Species identity in anoles, however, can
be encoded redundantly in more ways
than by dewlap color and size.
Even in the Cuban fauna dewlap color
and size by themselves will not adequately
distinguish the eleven species of Camaguey (Table 1). In three species, A.
equestris, A. allisoni and A porcatus, dewlaps
are similar in size (large relative to body
size) and color (pink or pale pink), while in
two others, A. angusticeps and A. isolepis, the
dewlaps differ only slightly in color ("apricot" and "peach").
In these Cuban examples adult male size
or body color and pattern or both are very
different. These then are two additional
ways in which species identity is encoded in
anoles. Climatic niche and perch site are
also important, since these provide part of
the context in which species recognition
occurs. (Body shape is adapted to perch
site and thus correlates with the latter.)
Thanks are due to David Crews, Neil Greenberg The important empirical observation is
and William Haas for constructive comment. This
research was supported by NSF grant GB 3773IX that species similar in dewlaps differ in
some or all of these other characteristics.
and previous grants to E. E. Williams.
261
NO
NO
TABLE 1. Dewlaps m local faunas (Greater Antilles)."
CAMAGUEY, CUBA
Species
equestris
allisoni
porcatus
angusticeps
isolepis
argillaceus
loysiana
lucius
hovwlechis
allogus
sagrei
a
Dewlap color
very pale pink to
almost white
reddish or mauve
reddish or mauve
peach
apricot yellow
yellow, orange-yellow
or red
tan to pink tan to pale
orange red
yellowish at base with white
margin and 2-3 gray stripes
grey or while
yellow to apricot with 3-4
reddish stripes and white
margin
bright red, dark red or
brownish yellow
Body color
bottle green with skin
between scales white
green with head and thorax blue
grey with light and dark
reticulation
greyish
bright green
greyish with reticular and
longitudinal markings
greyish with reticular
markings
greenish blue with nuchal
chevrons
light tan with horizontal
stripes and 4 dark chevrons
reddish brown with yellow
reticulations
tan brown
Size (maximum
snout-vent length)
Ecomorphb
Microclimate
181
crown giant
shade
91
66
trunk crown
trunk crown
sun
52
46
shade
48
twig
twig
trunk
42
trunk
sun
>
6
>
shade
W
73
X
E
»j
w
sun
sun
r
>
70
crevice
shade
58
trunk ground
half shade
62
trunk ground
shade
r
X
60
trunk ground
sun
JO
>
>
Data from Ruibal and Williams (1961a and*), Ruibal (1964) and Schwartz and Garrido (1972).
b
Ecomorphs (Williams, 1972) differ characteristically in body shape, size, microhabitat and often in color. They are convergent phenotypes adapted
to the specific stations in the vegetation (trunk-crown, trunk-ground, bush-grass) that they usually inhabit.
o
263
SPECIES RECOGNITION, DEWLAPS AND FALNAL SIZE
In faunas smaller and simpler than
those of Cuba and Hispaniola, dewlaps
quite often are of similar size and color. A
comparison of dewlap colors and sizes at
Mona on the Liguanea Plain in Jamaica
shows that A. garmani, A. grahami and A.
opalinus, all occurring in tree crowns, all
have bright orange dewlaps (Table 2).
(These differ radically in size.) At El Verde
Luquillo Mt., Puerto Rico,/4. evermanni (an
anole of the tree crowns) and krugi (an
anole living in bushes or grasses) have
orange dewlaps and the dewlap of A.
gundlachi (a trunk-ground anole living in
deep shade below A. evermanni) is dull
orange (Table 3). (These are separated by
perch site and correlated body shape.)
In the still smaller faunas of the Lesser
Antilles (only one or two anole species per
island), the similarity in dewlaps within
and between islands is still more striking.
One set of colors—yellow to yellow-orange, darker or lighter—occurs almost
throughout both on the one and two
species islands (Tables 4 and 5). Extreme
variants are whitish or grey or with some
hint of green. The minor variations, however, only emphasize the general regularity of dewlap color in the Lesser Antilles,
which contrasts markedly with the very
striking body color and pattern differences
between and within Lesser Antillean
species. Thus A. marmoratus on Guadeloupe has a series of races all with very
similar dewlaps, in one of which males
have an apple green body and a blue-grey
head with brilliant orange marbling, while
in another males are plain green in ground
color but anteriorly and dorsally have dark
blotches tending to run together and set
off by pale cream borders. In yet another
race males are pale grey-green with brown
heads, and there are still other remarkably
different patterns within this one species
on a complex island (see Figure 5, Crews
and Williams, 1977). Similar differences in
body pattern occur within A. roquet (Martinique) and A. oculatus (Dominica). (See
Lazell, 1972, for more complete data on
these and other species and color plates.)
Yellow to yellow-orange are common
dewlap colors also on other small (one to
two species) islands in the Caribbean. Red
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ERNEST E. WILLIAMS AND A. STANLEY RAND
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to red-orange may be the darker extreme
of this spectrum (A. concolor—orange to
red-orange in San Andres; A. pinchoti —
red to dusky red in Providencia; Corn and
Dalby, 1973). It is to be remembered that
the anoles of these small faunally depauperate islands all had ancestors that lived
in the complex faunas of the Greater Antilles or in the equally or even more complex
faunas of the continental mainland. The
dewlaps of the small island anoles are
clearly not a random sample of the wide
diversity of dewlaps found in the anoles of
complex faunas.
The small island anoles come from several phyletic stocks, and the islands they
inhabit include both low arid islands and
high wet ones and a diversity of types in
between. Clearly there is not a simple phyletic explanation for the relative uniformity
of dewlaps in small island anoles nor a direct ecological correlation.
It seems probable that some of this near
uniformity in dewlap color has been
evolved after arrival on the small islands. It
is true that the orange dewlaps of sagrei
(Little Cayman, Roatan) are derived from
the ancestral populations of this species on
Cuba, and the pink to red dewlaps of the
carolinensis complex on the Bay Islands,
Half Moon Cay off Belize and the Bahamas are to be regarded as directly derived
from their Cuban ancestors (Williams,
1969). But the dewlaps of the distinctive
long-headed species of the carolinensis
complex, A. longiceps (Navassa) and A.
maynardi (Little Cayman) are modified toward orange rather than pink or red
(Thomas, 1966) and the sagrei relatives on
Swan Island and on Cayman Brae (A.
nelsoni and A. luteogularis) have changed
toward yellow. In these cases convergence
toward the yellow or orange of the Lesser
Antilles may reflect longer periods of residence on these islands.
If we consider only the small oceanic
islands, the only truly anomalous cases are
A. conspersus on Grand Cayman and A.
lineatus on the arid island of Curacao, both
"solitary" anoles. A. lineatus has no close
mainland relatives and has a bicolor (black
and orange) dewlap quite unlike anything
anywhere on the mainland. A. conspersus,
SPECIES RECOGNITION, DEWLAPS AND FAUNAL SIZE
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265
on the other hand, is an obvious derivative
of the Jamaican A. grahami, close enough
to have been considered a subspecies of
the latter, but it differs radically in its blue
rather than orange dewlap.
It is possible that these species have
evolved their aberrant dewlaps as the result of "failed invasions" (Baskin and Williams, 1966; Williams, 1969). A. lineatus
occurs on Aruba, which is on the continental shelf, as well as on Curacao, and both
populations are close to mainland South
American faunas. The species most likely
to have made contact with lineatus are A.
(Tropidodactylus) onca (red-orange dewlap)— but this is ordinarily a solitary anole
wherever it occurs (Collins, 1971; Williams, 1974)—and A. auratus (black or
blackish dewlap). A. lineatus is amply distinguished from these (even beyond any
evident need; perhaps still other species
were in contact in the past). A. conspersus is
on an island in the direct line of drift from
Jamaica. A critical frequency of failed invasions may provide the threshold for
evolution of character displacement in
these cases.
In the two species islands of the Lesser
Antilles, the species differ greatly in size as
well as body shape, color and pattern
(Schoener, 1970; Williams, 1972). The two
species on a two species island do not differ
in these respects as much as do the two most
different species living together on a large
multispecies island, but they do differ very
much more in these characters than do the
most similar species on such an island. The
Lesser Antillean species pairs differ in at
least the three ways mentioned above and
we are suggesting that such differences in
simple faunas permit species recognition
with an adequate level of redundancy
without dewlap differences.
The long ignored experimental results
of Greenberg and Noble (1944) are relevant here. They report that female A.
carolinensis (an anole without sympatric
congeners over most of its range within the
United States) respond equally readily to
males with normally pink or with green
painted dewlaps. These results have been
confirmed and extended recently by Crews
(1975). (There are in fact green dewlap
266
ERNEST E. WILLIAMS AND A. STANLEY RAND
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These many examples make clear that
while, as at La Palma, the dewlap may in
complex faunas be the major signal, or at
least a signal, for species recognition, this is
often not true and is in fact very unlikely to
be true in simple faunas. Clearly, dewlaps
in simple faunas must be serving some
other function than species recognition,
since species on one species islands or alone
on the mainland characteristically not only
retain but actively use their dewlaps. It is on
Cuba, in a very complex fauna (more than
25 species), that two species {A. bartschi and
A. vermiculatus) have totally lost their dewlaps (i.e., in a very complex fauna where
there are many differences in one kind of
signal—dewlap color—it is one additional
kind of signal to omit the dewlap entirely).
Other species in which dewlaps are greatly
reduced are A. poncensis on Puerto Rico in
a fauna of 10 species and the A. hendersoni
complex, and to a lesser degree A. aliniger
and A. singularis, on Hispaniola in a fauna
of more than 20 species. The single very
striking exception—the sole instance of
reduction of the dewlap on a one anole
island — is Anolis agassizi on the bare and
very isolated Malpelo Id in the Pacific, a
highly special case which is discussed below.
Gorman (1968) and Rand (in preparation) have analyzed the use of the dewlap
in the single species islands of the Lesser
Antilles. Here dewlaps are used in
stereotyped displays in both aggressive encounters and in courtship. Dewlaps serve
in these situations (1) to identify the sex of
the displaying animal; (2) to distinguish
between juveniles and adults; (3) to indicate the size of the displaying animal; (4) to
discriminate territory holders from wandering or subordinate animals; (5) to signal the mood (aggressive, sexual, etc.) of an
animal; (6) to call attention to an animal by
increasing its conspicuousness.
In such single species islands we suggest
that it is the change in shape of the displaying animal which dewlap extension produces rather than the color displayed that
is the social signal (see also Crews, 1975).
The color of the dewlap in this situation
SPECIES RECOGNITION, DEWLAPS AND FAUNAL SIZE
,
¥
would primarily be affected by selection
pressures enhancing visibility. From the
prevalence of yellow-orange in the dewlaps in single species faunas, it would
seem probable that this is the most visible
dewlap color against most backgrounds. It
is a color that, as mentioned above, also
occurs regularly in the complex faunas of
the large West Indian islands and it is also
common on the mainlands of Central and
South America.
The social uses of dewlap displays are, of
course, not confined to Lesser Antillean
anoles. They are retained in most anoles of
complex faunas, both on islands and on
the continental mainlands. Wherever dewlap remains a distance signal, color should
also be retained. Echelle, Echelle and Fitch
(1971), for example, remark on the conspicuousness provided by the flashing of
the red dewlap in A. pentaprion in Costa
Rica. Here the flashing of a conspicuously
colored dewlap appears to permit A. pentaprion to signal its presence to conspecific
and congeners without revealing itself to
predators more than momentarily. In contrast, in another environment Ecuadorian
A. gemmosus has a large but greenish dewlap (Williams, personal observation).
Since this species lives in relatively dense
wet forest vegetation, it is hard to believe
that the dewlap can be a distance signal.
The dewlap is more likely to be useful in
increasing apparent size in close agonistic
contacts between males.
Quite another situation is seen in the
case of A. agassizi on Malpelo Id. Because
this bare rock provides an extraordinarily
rigorous environment (Rand et al., 1975)
A. agassizi has not adopted (most probably
has lost) the strategy of territoriality, and
instead social facilitation is an important
phenomenon. The reduction of the dewlap is understandable in such a situation.
In general it would appear that as long
as species are sufficiently different in general appearance to preclude confusion,
dewlaps, particularly dewlap colors, are
not important in species recognition but
are important in social signaling. However,
in more complex faunas the coexisting
species include many that are similar in
size and general appearance—much more
267
similar than the species pairs on two
species islands (Schoener, 1970; Williams,
1972). (See especially the colors of the
dewlaps in the trunk-ground series in
Cuba [Table 6].) The grass-bush series in
Puerto Rico contains only three species,
but the differences in dewlap are extremely sharp: A. krugi, orange; A. pulchellus, crimson; A. poncensis, white; (Schmidt,
1926). Although size difference in adults is
a ready species recognition character, because of the species-packing on the large
islands, ecological constraints reduce the
possibility of marked size differences ("the
crowded middle"—Williams, 1972). In the
absence of size differences other characters
must be used. Some species have evolved
elaborate body color patterns (Lazell,
1972) but, except in the giant species of the
two largest islands, this is not common on
the large islands. Instead, dewlap differences are the rule. One of the exceptions,
the A. hendersoni complex, comprises small
species with striking body patterns and
colors and very reduced dewlaps. This is
concordant with the reciprocal relationship we are suggesting between body pattern and dewlap.
Similarly consistent with this relationship is the situation in A. poncensis in which
the male dewlap is reduced. Here there is
much stronger sexual dimorphism in body
color than in its relatives {A. pulchellus and
A. krugi) in which there is a strong sexual
dimorphism in dewlap size.
Probably the emphasis on dewlaps
rather than body patterns when it occurs is
the result of predation pressures. The
Greater Antilles have unquestionably
greater number of kinds of visually hunting predators, both snakes and birds, than
do the smaller islands of the Lesser Antilles (Bond, 1971; Underwood, 1962; Maglio, 1970). Where visual predators are
common, there may be a strong advantage
in being cryptic and therefore in a dewlap
that is usually kept retracted and inconspicuous and will be displayed conspicuously only when needed.
In contrast, when predators are fewer or
less important, there is obvious social advantage in keeping display characteristics
continuously in evidence. A lizard that is
268
ERNEST E. WILLIAMS AND A. STANLEY RAND
TABLE 6. Dewlap within ecomorph series.*
Cuba—
The trunkground series
Dewlap color
Body color
homolechis
white or grey
jubar
yellow to orange with a variable
white margin
yellow with red stripes or
light tan with a white-margined
orange-yellow
dark ocellus above shoulder"
dark red basal spot with two
light grey usually with a greenish
orange-yellow stripes and wide
cast
white margin
yellow to apricot with 3-4 reddish reddish brown with yellow
stripes and a white margin
reticulations
large red spot surrounded by a
tan with a greenish cast and
broad yellow white area
"salt and pepper" speckling
4-5 thin red lines on deep
pale grey with "salt and pepper"
yellow ground and a white margin speckling or vertical black bands
brown
[indistinct crossbandsp
variable but with orange or
tan with sometimes yellow vertical
reddish tints
stripes and dots
brownish yellow with maroon
tan with yellow markings
markings
quadriocelhfer
meslrei
allogus
ahli
rubribarbus
tmias
sagrei
bremeri
light tan with 4 dark chevrons on
dorsum and horizontal stripes
on flanks
light tan
Size (maximum 6
snout-vent length)
70 mm
62 mm
55 mm
56 mm
62 mm
58 mm
62 mm
64 mm
60 mm
71 mm
a
Data from Ruibal (1964).
Note that species which are closest in dewlap color (jubar, quadriocelhfer and allogus, rubribarbus) differ in
body color.
c
Only known from the type and paratype. The collector, P. J. Darlington, noted dewlap color in life but not
body color.
b
are otherwise similar in size and general
appearance which differ strikingly in dewlap color. When West Indian anoles have
similar ecological adaptations, they usually
have the same size and body form and
even color, i.e., they are ecomorphs in the
sense of Williams, 1972. They usually have
differently colored dewlaps, particularly if
they are not allopatric. (Again see the
trunk-ground ecomorphs in Cuba, Table
6.) We predict that the exceptions will be
found to differ in display much more
strikingly than do species that are more
different in appearance.
Our contention that complexly colored
dewlaps and striking body patterns may be
alternative and equivalent solutions to the
problem of species recognition is supported by an examination of intraspecific
mentioned, A. equestris, A. porcatus, A. alli- variation—both inter- and intrapopulasoni, A. angusticeps and A. isolepis in the tional—in these characters.
Camaguey local fauna are similar in dewIn the Lesser Antilles, as we have seen,
lap color but sharply different in color or the variation between populations on the
pattern or size or all three.
same island or bank tends to be striking
In the large faunas it is the species which only in body color and pattern (see spe-
boldly and conspicuously marked is in a
very real sense displaying much of the time
without the energetic cost of dewlap display. Thus bold body patterns are utilized
both by species in the Lesser Antilles
where there are few predators and by
giants such as those of the A. equestris
complex of Cuba, which as adults must be
invulnerable to most island predators. The
apparent counterexamples—e.g., such a
species or species complex as A hendersoni,
which in the complex fauna of Hispaniola
can show a male body pattern of startling
beauty and brilliance—have also very dull
cryptic color phases.
Size and shape, in addition to body color, can, we emphasize, substitute for dewlap color in species recognition even in the
largest of the Greater Antilles. As already
SPECIES RECOGNITION, DEWLAPS AND FAUNAL SIZE
269
Most anoles also show variability within
populations in dewlap colors and in body
colors and patterns. Such variability certainly contradicts any hypothesis that a
single character is a simple sign stimulus
acting as a releaser. However, this variability fits rather well with our suggestion that
a lizard encodes its species identification in
several different ways and that redundancy itself is selected for because it is
important in allowing species recognition
under a variety of circumstances. If no one
character is by itself necessary in recognition, then variation in display characA. equestris, A. ricordii and A. hendersoni, ters— and even individual recognition
interpretation has recently shifted from (Rand, in preparation) — is possible withthat of geographic races of single species to out destroying the system. Note that such
allopatric species. In at least the A. equestris individual difference in dewlap characcomplex in Cuba, instances of sympatry teristics is the indispensable prerequisite
have been discovered (Schwartz and Gar- for evolution of geographic and interspecific evolution of dewlap differences.
rido, 1972; Garrido, 1975).
There do exist, however, in the Greater
Thus while throughout the genus Anolis
Antilles very remarkable examples of cor- the dewlap functions in intraspecific sigrelated geographic variation of dewlaps naling, encoding information about size,
and body color within species {A. distichus sex, and in association with characteristic
in Hispaniola and the Bahamas [Schwartz, display behavior, reproductive condition
1968, see the color plates], A. lineatopus in and motivational state (see also Crews,
Jamaica [Underwood and Williams, 1959; 1975), in simple faunas species recognition
see the diagrams of pattern difference is achieved by characteristics of size, color
between populations; there is more varia- and pattern with little involvement of dewbility than the color plates or diagrams lap color. It is only in more complex and
indicate, but the vivid nature of the differ- larger anole faunas that the color and
ences is still very real].)Such variation in a pattern of the dewlap are important in
characteristic presumed important in species recognition. In these cases, the use
species recognition and mate selection of the dewlap as a distinguishing character
could be the result of such factors as 1)
environmental differences that result in between otherwise similar anoles may be
different colors or patterns having differ- one significant factor explaining the
ent visibilities; 2) sympatry with different coexistence of so many sympatric species.
species thus requiring changes to facilitate
REFERENCES
recognition (this explanation, very improbable or impossible for A. lineatopus,
has been documented for the contact Baskin, J. N. and E. E. Williams. 1966. The Lesser
Antillean Ameiva (Sauria, Teiidae). Re-evaluation,
zones of three sibling species of the A.
zoogeography and the effects of predation. Studies
dally marmoratus on Guadeloupe and Les
Saintes and oculatus on Dominica, Lazell,
1962, 1964, 1972), and dewlap color varies
only slightly. In the Greater Antilles very
striking variation is seen in body pattern in
the giant Anolis of Cuba (Schwartz and
Garrido, 1972—at least six species) and
Hispaniola (Schwartz, 1974—three species) and in the hendersoni complex in Hispaniola (three allopatric forms, probably
three species - Williams, 1963). In the case
of marmoratus, intergradation between the
several populations on Guadeloupe is
abundantly demonstrated. In the case of
distichus-related brevirostris complex, Webs-
ter and Burns, 1973); 3) geographic variation selected to promote mating with close
neighbors, reduce interdeme gene flow,
thus allowing closer genetic adaptation to
local conditions (Williams, in preparation;
see also Crews and Williams, 1977). (For
the last, note the parallel with bird dialects.)
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Crews, D. 1975. Effects of different components of
male courtship behaviour on environmentally in-
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