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found exclusively in the Salamandridae (genera

Salamandra and Lyciasalamandra). Among frogs,

viviparity is known only in the two African bufonid

genera Nectophrynoides and Nimbaphrynoides, and

in the brachycephalid Eleutherodactylus jasperi (see

Wake, 1977; 1989). All viviparous frogs bear fully

metamorphosed young and therefore have no aquatic

larval stage. Viviparous salamanders can bear meta-

morphosed young or (aquatic) larvae. Caecilians of

the genus Typhlonectes are viviparous with aquatic

larvae, whereas other viviparous caecilians have no

larval stage. In pipid frogs of the genus Pipa, the eggs

are embedded in the dorsum of the (aquatic) female

and thus indirectly undergo development in an

aquatic environment; in all other cases, direct-devel-

oping amphibians lay terrestrial eggs.

Direct development has evolved independently in

many amphibian lineages: in salam anders once in the

family Plethodontidae, which contains almost exclu-

sively direct developers; in caecilians, in the family

Caeciliidae; and among anurans in many of the major

lineages: (1) in the basal Leiopelmatidae, genus

Leiopelma from New Zealand; (2) in sooglossids

(genus Sooglossus); (3) in some species of the genus

Pipa (Pipidae); (4) in some genera of myobatrachids;

(5) in brachycephalids; (6) in Hemiphractidae (genus

Hemiphractus); (7) in Cryptobatrachidae (genera

Cryptobatrachus, Stefania); (8) in Amphi-

gnathodontidae (genera Flectonotus, Gastrotheca);

(9) in several genera of bufonids (e.g. Oreophrynella,

Osornophryne, Rhamphophryne); (10) in the genus

Platymantis (Ceratobatrachidae); (11) in Pyxicepha-

lidae (Arthroleptella and related genera); (12) in at

least one dicroglossid species (Limnonectes hasche-

anus); (13) in several species of one genus of

mantellids (Gephyromantis; see Glaw & Vences,

2006); (14) in at least one genus of rhacophorids

(Philautus); (15) in brevicipitids (Breviceps and

related genera); (16) in Australasian microhylids

(subfamily Asterophryinae); (17) in few Neotropical

microhylids (Myersiella, Synapturanus); (18) in sev-

eral arthroleptids (genera Arthroleptis, Schoutedenel-

la). Hence, altogether there are at least 18 independent

evolutionary events towards direct development in

anurans, while this reproductive mode has evolved

only once in salamanders and probably twice in

caecilians. It needs to be emphasi zed that these are

minimum estimates, and especially in frogs it is likely

that more complete phylogenetic data will provide

evidence that direct development evolved even more

commonly in parallel.

Fig. 3 Percentages (rounded) of frog (A), salamander (B) and

caecilian (C) species in categories aquatic, water dependent,

not water related and unknown. Together, the categories

aquatic and water dependent are summed up as ‘Total’ in

Tables 1 and 2

Hydrobiologia (2008) 595:569–580 573

123

Interestingly, some of the direct-developing

amphibian lineages are characterized by a very high

species richness. The Brachycephalidae contain

approximately 800 direct-developing species, and

among salamanders, the largely direct-developing

Plethodontidae encompass by far the largest number

of species (349 out of a total of 514 salamander

species). This may be seen as indication that water-

independence is a particularly successful strategy for

amphibians. It could also be a by-product of a

putative higher fragmentation into isolated demes in

direct developers, which may lead to an increased

rate of species formation (Dubois, 2005). Studies that

apply comparative methods to test against null

models, and population genetic studies of direct

developers are necessary to clarify this question.

Remarkably, recent phylogenetic evidence indi-

cates that in a numb er of groups of predominantly

direct development, some lineages have reversed

their reproductive mode and re-acquired an aquatic

larval stage. This appea rs to be the case in pleth-

odontid salamanders, Desmognathus, as well as in

some amphignathodontid frogs, Gastrotheca, and

possibly in mantellid frogs as well (Duellman &

Hillis, 1987; Vences & Glaw, 2001; Chippindale

et al., 2004). These reversed trends emphasize the

selective advantage, under at least some evolutionary

conditions, of biphasic aquatic-terrestrial life cycles,

and the importance of freshwaters for amphibian

diversity.

Distribution and endemicity

Amphibians are in general considered to be poor

dispersers, and the strong phylogeographic structure

encountered in many amphibian species (e.g. Avise,

2000) appears to support this view. Due to their

limited osmotic tolerance, overseas dispersal was

long neglected as dispersal mechanism for amphib-

ians, and their zoogeographic patterns explained

largely by vicariance and dispersal over land con-

nections (e.g. Duellman & Trueb, 1986). Evidence

from molecular clocks and the discovery of endemic

amphibians on oceanic islands, such as Mayotte on

the Comoros, provide strong support that amphibians

are able to colonize landmasses over the sea (e.g.

Hedges et al., 1992; Vences et al., 2003; 2004). This

concerns frogs, but may also apply to salamanders

Table 1 Numbers of water related amphibian species by order

PA NA NT AT OL AU PAC ANT World

Order FW WDpt FW WDpt FW WDpt FW WDpt FW WDpt FW WDpt FW WDpt FW WDpt FW WDpt

Anura 68 0 89 0 1,661 21 816 73 1,001 0 301 35 0 0 0 0 3,978 129

Urodela 92 0 114 48 14 0 0 0 17 0 0 0 0 0 0 0 237 48

Gymnophiona 0 0 0 0 23 0 12 0 44 0 0 0 0 0 0 0 79 0

Total 160 0 203 48 1,698 21 828 73 1,062 0 301 35 0 0 0 0 4,294 177

‘FW’ refers to aquatic plus water dependent species, WDpt to water dependent only (of a total of 5828 amphibian species considered; see text for deﬁnitions). PA : Palearctic; NA

: Nearctic; NT : Neotropical; AT : Afrotropical ; OL : Oriental; AU : Australasian; PAC : Paciﬁc Oceanic Islands, ANT: Antarctic

574 Hydrobiologia (2008) 595:569–580

123

and even caecilians, as indicated by the presence of

an endemic caecilian species, Schistometopum tho-

mense, on the fully volcanic Sa

oTome

island in the

Gulf of Guinea (Measey et al., 2007). Nevertheless, it

remains true that amphibian distributions have cer-

tainly largely been shaped by vicariance, as shown by

relationships of relict forms such as the Seychellean

sooglossid frogs and the Indian Nasikabatrachus

(Biju & Bossuyt, 2003).

At the deep phylogenetic levels, there are clear

distributional trends of salamanders and basal frogs

having their centres of diversity in the Holarctis and

caecilians and modern frogs in the tropics. Since

some phylogenetic reconstructions placed caecilians

as sister group of salamanders, and both basal and

modern frogs (‘‘archaeobatrachians’’ and ‘‘neobatra-

chians’’) as monophyletic groups, the distributional

patterns of these lineages were interpreted by some

phylogeneticists as indicative of vicariance during the

break-up of Pangaea into the Laurasia and Gondwana

supercontinents, with caecilians and ‘‘neobatra-

chians’’ evolving and diversifying on Gondwana,

and ‘‘archaeobatrachians’’ and salamanders diversi-

fying on Laurasia (Feller & Hedges, 1998).

Recent phylogenetic evidence, however, does not

support this hypothesis. Evidence from complete

mitochondrial sequences and nuclear genes indicates

that frogs and salamanders, not salamanders and

caecilians, are sister groups (Meyer & Zardoya, 2003;

San Mauro et al., 2005; Frost et al., 2006). In

addition, phylogenetic reconstructions based on dif-

ferent nuclear genes are concordant in establishing

paraphyly of basal frogs (‘‘archaeobatrachians’’)

relative to the monophyletic ‘‘neobatrachians’’

(Hoegg et al., 2004; San Maur o et al., 2005; Roelants

& Bossuyt, 2005), in accordance with morphological

hypotheses (e.g. Duellman & Trueb, 1986). Further-

more, also the distributional patterns observed leave

room for the assumption that not only causes of

vicariance biogeography, but also of ecological

requirements have shaped the distribution of the

three amphibian orders.

Salamanders are almost exclusi vely distributed on

previous Laurasian landmasses to which 9 of the 10

salamander families are restricted, if the presence of a

few representatives of salamandrids (Salamandra and

Pleurodeles) in nort hern Africa is disregarded. This

pattern is obscured by the fact that one large radiation

of one family, the Plethodontidae, has colonized the

Neotropics and attains a high species diversity in

Mexico and Central America. Indeed, 252 salaman-

der species occur in the Neotropics as deﬁned here,

more than in any other biogeographic region. How-

ever, only few species of two genera, Bolitog lossa

and Oedipina, have penetrated further into South

America, leaving no doubts that northern America

was the initial centre of diversiﬁcation of this family.

Almost all plethodontids are characterized by direct

development, and are therefore less relevant in the

present survey of freshwater diversity , most species

not being included in Table 1. Salamanders have

almost not penetrated into tropical areas of Asia,

although there are salamandrids occurring as far to

the south as Laos and Vietnam.

Caecilians have a distribution fully restricted to the

tropics. They are found in the Neotropical, Afrotrop-

ical and Oriental regions. Interestingly, although

endemic caecilians are pres ent on the Seychelles,

they are absent from Madagascar. Caecilians do not

occur in southernmost South America, or in southern

Table 2 Numbers of amphibian genera including aquatic and water dependent species according to the deﬁnitions used herein by

order

Order PA NA NT AT OL AU PAC ANT World

Anura 8 9 119 85 64 20 0 0 294

Urodela 18 18 1 0 4 0 0 0 40

Gymnophiona 0 0 7 4 3 0 0 0 14

Total 26 27 127 89 71 20 0 0 348

For the subfamily Hylinae, the classicatory scheme of Faivovich et al. (2005) is followed. However, all other numbers in genera have

not been updated and refer to a taxonomy prior to the publication of Frost et al. (2006). Therefore, some genera were supposed to

occur in more than one biogeographic region and thus the sums of all regional numbers are higher than the total numbers. PA :

Palearctic; NA : Nearctic; NT : Neotropical; AT : Afrotropical; OL : Oriental; AU : Australasian; PAC : Paciﬁc Oceanic Islands,

ANT: Antarctic

Hydrobiologia (2008) 595:569–580 575

123

Africa, indicating that the limiting factor for their

distribution is indeed the presence of tropical-humid

environments. Apart from climate which obviously

triggers the current distribution of caecilians, it has

been assumed that radiation in caecilians largely took

place before Gondwana split into sub-continents.

Some families like the South American Rhinatremat-

idae and the Asian Ichthyophiidae are supposed to

represent relict distributions of formerly widespread

Gondwanan ancestors (Duellman & Trueb, 1986),

whereas some Neotropical members of the Caecilii-

dae (e.g. Typhlonectes) possibly are the product of

subsequent radiations on the already isolated South

American continent (Himstedt, 1996).

Basal frog lineages (‘‘archaeobatrachians’’, de-

ﬁned as a paraphyletic group of all extant frogs not

belonging to the modern frogs or ‘‘neobatrachians’’)

are mainly distributed in the Holar ctis, with four

notable exceptions, however. (1) Pipids, the only

frogs which are fully aquatic also in their adult stage,

have a clearly Gondwanan distribution, with genera

in Africa (Xenopus, Silurana, Pseudhymenochirus

and Hymenochirus; 23 species) and in South America

(Pipa; 7 species). (2) Leiopelmatidae: the genus

Leiopelma (4 species) occurs in New Zealand,

although its closest relative, Ascaphus, is restricted

to the Nearctis. (3) The discoglossid genus Barbour-

ula occurs on Borneo and the Philippines, whereas its

closest relatives, the genus Bombina, has a Palearctic

distribution. And (4) the Megophryidae, with 72

species by far the largest ‘‘archaeobatrachian’’ fam-

ily, has radiated in the Oriental region and is common

in tropical environments. Based on a robust molec-

ular phylogeny and molecular clock dating, Roelants

& Bossuyt (2005) found evidence for three major

cladogenetic events between a Laurasia- and a

Gondwana-associated lineage, represented by Asca-

phus and Leiopelma, Rhinophrynidae and Pipidae and

Pelobatoidea and ‘‘Neobatrachia’’, respectively, all

these splits being very close to the onset of Pangaean

break-up at 180 mya. Although this pattern substan-

tiates a high-biogeographic relevance of ‘‘archaeoba-

trachians’’, they altogether make up only a negligible

part of overall frog diversity, with a total of 191 of

the total of 5,146 frog species (including non-water

related taxa).

‘‘Neobatrachians’’, with 4,955 species, do not only

form the most speciose anuran subgroup, but also

include by far more species than all other amphibian

groups together. Monophyly of these ‘‘modern frogs’’

is well established by molecular and morphological

characters (Duellman & Trueb, 1986; Hoegg et al.,

2004; Roelants & Bossuyt, 2005; San Mauro et al.,

2005). Their largest diversity belongs into two

subgroups, the hyloids, with a centre of diversity in

the Neotropics, and the ranoids, with a centre of

diversity in Africa and Asia.

Ranoids, according to the scheme of Frost et al.

(2006), include families restricted to Africa and/or

Madagascar, such as the Arthroleptidae, Hemisotidae,

Hyperoliidae, Mantellidae, Phrynobatrachidae, Pty-

chadenidae and Pyxicephalidae; two mainl y Asian

families with few African representati ves, the Rhac-

ophoridae and Dicroglossidae; two South Asian

families, the Nyctibatrachidae and Microxalidae;

one South-East Asian family, the Ceratobatrachidae;

one family present in Africa and Asia, and that

succeeded to colonize also North and South America,

the Microhylidae; and the species-rich Ranidae that

colonized Europe as well as North and South

America. The Pedropeditae sensu Frost et al. (2006)

contain African and South Asian species, although

these relationships require further corroboration.

Hyloids include several families restricted to the

Neotropics, such as the Amphignathodontidae,

Brachycephalidae, Ceratophryidae, Centrolenidae,

Cryptobatrachidae, Cycloramphidae, Dendrobatidae,

Hemiphractidae, Leptodactylidae, Thoropidae; one

family, the Bufonidae, common in the Neotropis with

also many repr esentatives in the Palearctic, Nearctic,

Oriental, and Afrotropical regions, including genera

endemic to the main biogeographical regions; and

one family, the Hylidae, with many species in the

Neotropis, which has representatives also in the

Nearctic, Palearctic and Australian region.

Besides hyloids and ranoids, a number of further

‘‘neobatrachian’’ families exist. Into this assemblage

belong the sooglossids from the Seychelles and

southern India, as well as heleophrynids from South

Africa, limnodynastids and myobatrachids from

Australia and New Guinea and the Batrachophryni-

dae from South America.

While providing a general zoogeographic picture

for amphibians or discussing the possible prevalence

of vicariance vs. dispersal hypotheses, is clearly

beyond the scope of this article, a number of general

patterns can still be discerned from the distributions

outlined above:

576 Hydrobiologia (2008) 595:569–580

123

(1) At a very fundamental level, the inﬂuence of

vicariance is very clearly visible in a number of

amphibian distributions. Although salamanders

and caecilians are certainly limited in their

distribution by adaptations to temperate vs.

tropical environments, their general patterns of

geographic occurrence and the restriction of

salamanders to temperate regions of the north-

ern hemisphere make it likely that the basal

diversiﬁcation of salamanders occurred on

Laurasia and that of caecilians on Gondwana

(Feller & Hedges, 1998). ‘‘Archaeobatrachians’’

are separated in a number of lineages of

alternatingly Laurasian or Gondwanian distri-

bution (Roelants & Bossuyt, 2005). The distri-

bution of basal neobatrachians in the southern

hemisphere indicates that they initially had a

Gondwanan distribution. And the diversity

centres of hyloid vs. ranoid neobatrachian frogs

in the New World vs. the Old World (and here,

especially Africa) are likely to correspond to the

separation of South America and Africa, which

also roughly agrees with molecular clock

calculations (e.g. San Mauro et al., 2005;

Roelants & Bossuyt, 2005).

(2) The initial pattern originated by vicariance has

been modiﬁed extensively by dispersal. The

occurrence of some endemic amphibians on

oceanic islands is a clear evidence for the

possibility of overseas dispersal also in this

group. The phylogenetic split of several lin-

eages like the reed frogs, Hyperoliidae, are so

young according to molecular clocks that their

occurrence in Madagascar and on the Seychelles

can only be seen in colonization by ancestors

rafting on ﬂotsam over the sea (Vences et al.,

2003). The few genera occurring in more than

one biogeographic region and continent provide

further evidence for the possibility and potential

speed of amphibian dispersal. The genus Hop-

lobatrachus has a number of species in Asia,

and has one Afrotropical species that colonized,

out of Asia, vast areas of the African savannas

in short time spans, as to judge from the low

molecular differentiation among Asian and

African Hoplobatrachus species (Kosuch

et al., 2001). Similar examples can be found in

other genera and families as well. The coloni-

zation of South America by plethodontid sala-

manders and ranid frogs, and the colonization of

the Palearctis by hylid frogs, almost certainly

represent such instances. At the interface

between dispersal and vicariance, the hylid

subfamilies Pelodryadinae (Australian) and

Phyllomedusinae (N eotropical) are sister groups

(Hoegg et al., 2004; Frost et al., 2006), and

probably are witne sses of a vaster distribution of

these tree frog s while South America and

Australia were connected over Antarctica in

the Early Cenozoic. During this time, probably,

the ancestor of these frogs dispersed from South

America to Australia, and the two groups

evolved in vicariance after the continental

connections were severed.

(3) A third factor that should not be underestimated

is (natural) extinction. There is impressive

evidence in current amphibian distributions for

formerly larger distribution areas of groups of

today relictual occurrence. Among the examples

are the relationships between Ascaphus and

Leiopelma (Leiopelmatidae), the most basal of

the extant anurans, and with two and four

species restricted to the Western North Amer-

ica, and to New Zealand respectively. Pleth-

odontid salamanders are today most diverse in

the Nearctis and Neotropis, but one genus,

Speleomantes, is known from Italy and France.

The very recent discovery of the ﬁrst Asian

plethodontid Karsenia by Min et al. (2005)

clearly demonstrates that this group had a wider

distribution in Asia and Europe before, and

probably went extinct over most of its Palearctic

distribution area. Again, also the relictual dis-

tribution of the basal ‘‘neobatrachian’’ frogs in

southern South America, Australia, South Afri-

ca, the Seychelles and India probably witnesses

a previous, much wider Gondwanian distribu-

tion. Probably, and especially in frogs, succes-

sive waves of radiation of more modern groups

have largely replaced the more basal groups

which survived, if at all, as species-poor relicts

in very restricted and fragmented distribution

areas.

Due to their relatively limited dispersal ability, by

far most amphibian genera, and almost all amphibian

species, are endemic to single continents or biogeo-

graphic units. These units largely correspond to the

Hydrobiologia (2008) 595:569–580 577

123

biogeographic regions used here. Some additional

subdivisions are obvious (of course not considering

introductions): In the Afrotropical region, all species

and all genera but one occurring in Madagascar are

endemic to the island (with two genera of mantellid

frogs also having one species each endemic to the

Comoro island of Mayotte); and all genera and

species of Seychellean caecilians and frogs are

endemic to the archipelago. Sub-Saharan Africa

shares no amphibian species with Asia or Europe,

and the species-level of endemism of Australia is

above 90%. Further islands with a degree of ende-

mism of 100% at the species level are Jamaica, Sa

Tome

and Principe, New Zealand, Fiji and Palau

(percentages based on analyses including non-water

related amphibian species; see http://www.globalam-

phibians.org/patterns.htm for a more detailed analysis

based on the data from the Global Amphibian

Assessment).

Most of the few genera with distributions extend-

ing over more than one of the main zoogeographic

regions, all of them frogs, were classical ‘‘dump bin’’

genera which were recently split into various genera

after comprehensive revisi ons (Faivovich et al., 2005;

Frost et al., 2006). For example, the formerly 340

species of Hyla with representatives in the Neotropis,

Orientalis, Nearctis and Palearctis have recently been

taxonomically revised and were split into 15 genera,

with the genus Hyla now being restricted to few

species in the Nearctic and Palearctic regions

(Faivovich et al. 2005). In addition, only the frog

genera Hoplobatrachus (Orientalis with four and

Afrotropis with one species) and Ptychadena (one

species in Palaearctis as deﬁned herein, all others in

Afrotropis) have a distribution across biogeographic

regions, and the salamander genus Ambystoma has 15

Nearctic and 14 Neotropical representatives; how-

ever, the Neotropical species are restricted to Mexico

and the genus did not further disperse into Central or

South America.

Human related issues: global amphibian declines

More new amphibian species are being discovered

every year than ever, but at the same time, amphib-

ians are paradoxically declining at a very fast rate

(Hanken, 1999). Multi-causal declines have been

recorded worldwide. The most obvious and immedi-

ate threat to most amphibians in a threatened IUCN

category is habitat destruction, and for some species

overexploitation (as pets or food) constitutes an

imminent danger as well.

The Global Amphibian Assessment (Stuart et al.,

2004) classiﬁed 1856 amphibian species (32.5%) into

one of the IUCN threat categories (Vulnerable,

Endangered or Critically Endangered), many more

than in other groups such as mammals (23%) or birds

(12%). About 43% of all species were recorded to

experience some sort of population decline. A total of

32 amphibian species have become extinct , and 122

species were considered to be ‘‘possibly extinct’’,

with no recent sightings.

Most alarmingly, so-called enigmatic declines

have also been reported from unaltered and largely

undisturbed habitats, especially in South America and

Australia, but also in North America and Europe

(Blaustein et al., 1994). Furthermore, it has been

shown that the absence of aquatic larvae in declining

anuran populations may signiﬁcantly alter freshwater

ecosystems (Ranvestel et al. 2004). Most likely,

emerging infectious diseases, especially chyt ridiomy-

cosis, play a key role in these declines which in many

cases apparently have led to full extinctions already

(Daszak et al., 2003). The chytrid fungus Batracho-

chytrium dendrobatidis especially affects species that

are ecologically predisposed in that their natural

history (high-altitude occurrence, stream breeding)

coincides with the preferences of the pathogen, and if

combined with low fecundity and habitat specializa-

tion, a species can quickly be driven to extinction

(Daszak et al., 2003), and this process may be

furthered by climatic change (Pounds et al., 2006).

Interestingly, despite high degrees of chytrid infec-

tion in the wild, no African frogs have yet been

reported to have enigmatically declined, which led

Weldon et al. (2004) to hypothesi ze that the disease

may have originated in Africa and spread to other

continents by exported clawed frogs, Xenopus,as

carriers.

The important role of chytridiomycosis in amphib-

ian declines has been asserted, and obvious measures

include the control of amphibian introductions into

unaffected areas as well as the disinfection of ﬁshing

gear and similar equipment by limnologists working

on different continents. However, the inﬂuence of

other agents such as pesticides or increased UV

radiation should not be disregarded, and multi-causal

578 Hydrobiologia (2008) 595:569–580

123

hypotheses may well be most powerful to explain

declines in some cases. Certainly, the simultaneous

dependence of many amphibian species from both

aquatic and terrestrial environments make them

especially vulnerable to a multitude of factors. The

importance of the freshwater environment for the

survival of amphibian populations is paramount, and

more studies on the speciﬁc requirements of amphib-

ians in their aquatic, mostly larval phase are neces-

sary to develop integrated conservation strategies.

Acknowledgements We are grateful to Francisco Hita

Garcı

a for his help with updating our amphibian species

database, and to Frank Glaw for numerous discussions and

comments.

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FRESHWATER ANIMAL DIVERSITY ASSESSMENT

Global diversity of lizards in freshwater

(Reptilia: Lacertilia)

Aaron M. Bauer Æ Todd Jackman

 Springer Science+Business Media B.V. 2007

Abstract No lizards are strictly aquatic, but at least

73 species in 11 different families can be considered to

regularly utilize freshwater habitats. There are no

aquatic lizards in the Nearctic or Palearctic regions,

whereas the Neotropics, Southeast Asia, and the Indo-

Australian Archipelago support the greatest diversity of

freshwater forms, particularly in the families Gymno-

phthalmidae, Scincidae and Varanidae. A number of

larger aquatic lizards are harvested for food and for the

reptile skin trade and several are CITES listed.

Keywords Lizards  Distribution  Natural history 

Scincidae  Varanidae  Gymnophthalmidae

Introduction

Approximately 5,000 species of lizards (including

amphisbaenians) are distributed between the Arctic

Circle and Tierra del Fuego, with most species

occuring in the tropics and subtropics. Most are

arboreal, saxicolous, terrestrial, or fossorial. Many

tropical li zards prefer or require mesic environments

and, as a consequence, some are largely or entirely

restricted to habitats bordering streams, rivers, or

pools (e.g., agamids of the genus Gonocephalus). A

much smaller subset of lizards regularly utilize

freshwater habitats. No lizards are known to be

strictly aquatic in that they must remain submerged

for extended periods or depend exclusively on aquatic

prey. Those lizards here considered to be aquatic

typically retreat to water when alarmed and regularly

include aquatic prey in their diets. Many are also

partly arboreal and perch in branches overhanging

water bodies. The designation ‘‘aqua tic’’ is necessar-

ily subjective, however, as some individuals of many

other lizard species may retreat to or feed in

freshwater at some time.

Aquatic lizards vary signiﬁcantly in size and body

form and few generalizations can be made as to

morphological features indicative of an aquatic

lifestyle; even within the genus Anolis, the seven

aquatic forms share few features in common (Leal

et al. 2002). A laterally compressed tail, however, is

common to most aquatic lizards (Bedford & Christian

1996) and rugose or keeled body scalation is

exhibited by many (e.g., Lanthanotus, Neusticurus,

Tropidophorus, and Cophoscincopus). A series of

rectangular toe fringes characterizes two of the

lineages (Basiliscus, Hydrosaurus) capable of run-

ning on the water surface (Luke 1986). Given the lack

of reliable morphological markers, only natural

Guest editors: E. V. Balian, C. Le

que, H. Segers &

K. Martens

Freshwater Animal Diversity Assessment

A. M. Bauer (&)  T. Jackman

Department of Biology, Villanova University,

800 Lancaster Avenue, Villanova, PA 19085, USA

e-mail: aaron.bauer@villanova.edu

T. Jackman

e-mail: todd.jackman@villanova.edu

123

Hydrobiologia (2008) 595:581–586

DOI 10.1007/s10750-007-9115-0

history data can reveal if a lizard species is a

freshwater-dweller. We present a summary of lizards

which, on the basis of literature records and our own

observations, appear to be partly dependent on

freshwater habitats or resources for their existence.

Species diversity and distribution

Utilization of freshwater habitats and resources has

evolved numerous times within lizards, occurring in 11

families (Tables 1, 2), chieﬂy in the tropics (Fig. 2).

Higher order relationships of these families to one

another are discussed by Townsend et al. (2004) and

Lee (2005). Information on freshwater lizard systemat-

ics, distribution and natural history may be found in the

works of Pianka and Vitt (2003) (World), Blanc (1967),

Glaw & Vences (1994), Bo

hme et al. (2000) (Afrotrop-

ical), Beebe (1945), Howland et al. (1990), Avila-Pires

(1995), Vitt & Avila-Pires (1998), Leal et al. (2002),

Doan & Castoe (2005) (Neotropical), Sprackland

(1972), Ma

gdefrau (1987), Darevsky et al. (2004),

Honda et al. (2006) (Oriental), Shine (1986), Daniels

(1987), and Greer (1989) (Australasian).

Palearctic region

No aquatic lizards occur in Europe, North Africa, or

Palearctic Asia.

Nearctic region

Lizard diversity in the Nearctic is heavily biased

toward arid and semi-arid adapted species. No

aquatic lizards are known or are likely to occur in

this region.

Afrotropical region

Five mainland African lizards, the Nile monitor,

Varanus niloticus, and the ornate monitor, V. ornatus,

as well as all three species of the west African skink

genus Cophoscincopus, are semi-aquatic. Another

four water-associated species: the gerrhosaurid

Zonosaurus maximus and three skinks, Amphiglossus

astrolabi, A. waterloti, and A. reticulatus, are ende-

mic to Madagascar.

Neotropical region

The most striking Neotropical aquatic lizards are the

members of the corytophanid genus Basiliscus.

Although none are restrict ed to aquatic habitats, all

possess fringed toes, which help to support the body

when the animal runs bipedally across the water

surface, as part of its spectacular escape behavior. A

total of 7 out of 358 species of Anolis lizards (two in

Table 1 Global distribution of freshwater lizard species by biogeographic region

SP: Species number PA NA NT AT OL AU PAC ANT World Aquatic Species World species in family

Lizards

Agamidae 4 2 5 395

Corytophanidae 4 4 9

Gerrhosauridae 1 1 32

Gymnophthalmidae 7 7 204

Lanthanotidae 1 1 1

Polychrotidae 7 7 395

Scincidae 6 21 4 1 32 1,320

Teiidae 3 3 123

Tropiduridae 1 1 317

Varanidae 2 1 8 1 11 62

Xenosauridae 1 1 7

Total 0 0 22 9 28 14 2 0 73

Note that totals may be lower than the sum of all cells because some species are shared between regions

PA: Palaearctic; NA: Nearctic; NT: Neotropical; AT: Afrotropical; OL: Oriental; AU: Australasian; PAC: Paciﬁc Oceanic Islands;

ANT: Antarctic

582 Hydrobiologia (2008) 595:581–586

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