ArticlePDF Available

Abstract and Figures

The genus Ligia (Ligiidae) has a worldwide distribution and currently includes more than 30 nominal species. Most of the species are littoral, halophilic, and occur on rocky seashores, but seven species are strictly terrestrial. Three species of Ligia have been recorded from the Hawaiian Islands, one introduced, L. exotica, and two edemic, L. hawaiensis and L. perkinsi. Ligia hawaien-sis is a littoral species very common along the rocky coasts of the Hawaiian Islands, and Ligia perkinsi is a montane terrestrial species occurring on Kauai, Oahu, and Hawaii. Morphological and molecular data of the endemic species of Ligia from the Hawaiian Islands are used to test whether the adaptation to the terrestrial environment took place only once or, conversely, it evolved on each island independently. Populations of L. hawaiensis and L. perkinsi from Kauai and Oahu were examined. Four non-Hawaiian species of Ligia (L. italica, L. pallasii, L. vitiensis, and L. ex-otica) and the related ligiid Ligidium hypnorum were included in the molecular analysis as an out-group. All populations of L. hawaiensis were found to be morphologically identical to each other and distinctly different from L. perkinsi. The Kauai populations of L. perkinsi differ slightly from the Oahu one in morphology and ecological habitat. Two regions of mitochondrial DNA were se-quenced: 675 bp of cytochrome c oxidase subunit I and approximately 490 bp of 16S rRNA. The cladogram obtained shows that L. hawaiensis and L. perkinsi belong to the same clade and that L. perkinsi does not constitute a monophyletic unit. The populations of L. hawaiensis show a re-markably high level of geographic structure suggesting that migratory events between the islands are uncommon. Thus, the independent colonization of terrestrial habitat by an ancestral seashore population of Ligia is proposed as the most plausible scenario for the origin of the terrestrial popu-lations.
Content may be subject to copyright.
© Koninklijke Brill NV, Leiden, 2003 Biology of terrestrial isopods, V: 85-102
EVOLUTION OF TERRESTRIALITY IN HAWAIIAN SPECIES OF THE
GENUS LIGIA (ISOPODA, ONISCIDEA)
BY
STEFANO TAITI1,3), MIQUEL A. ARNEDO2,4), STEVE E. LEW2,5)
and GEORGE K. RODERICK2,6)
1) Centro di Studio per la Faunistica ed Ecologia Tropicali del C.N.R., Via Romana 17,
I-50125 Florence, Italy
2) Division of Insect Biology, ESPM, 201 Wellman Hall, University of California-Berkeley,
Berkeley, CA 94720-3112, U.S.A.
ABSTRACT
The genus Ligia (Ligiidae) has a worldwide distribution and currently includes more than 30
nominal species. Most of the species are littoral, halophilic, and occur on rocky seashores, but
seven species are strictly terrestrial. Three species of Ligia have been recorded from the Hawaiian
Islands, one introduced, L. exotica, and two edemic, L. hawaiensis and L. perkinsi. Ligia hawaien-
sis is a littoral species very common along the rocky coasts of the Hawaiian Islands, and Ligia
perkinsi is a montane terrestrial species occurring on Kauai, Oahu, and Hawaii. Morphological and
molecular data of the endemic species of Ligia from the Hawaiian Islands are used to test whether
the adaptation to the terrestrial environment took place only once or, conversely, it evolved on
each island independently. Populations of L. hawaiensis and L. perkinsi from Kauai and Oahu
were examined. Four non-Hawaiian species of Ligia (L. italica, L. pallasii, L. vitiensis, and L. ex-
otica) and the related ligiid Ligidium hypnorum were included in the molecular analysis as an out-
group. All populations of L. hawaiensis were found to be morphologically identical to each other
and distinctly different from L. perkinsi. The Kauai populations of L. perkinsi differ slightly from
the Oahu one in morphology and ecological habitat. Two regions of mitochondrial DNA were se-
quenced: 675 bp of cytochrome c oxidase subunit I and approximately 490 bp of 16S rRNA. The
cladogram obtained shows that L. hawaiensis and L. perkinsi belong to the same clade and that L.
perkinsi does not constitute a monophyletic unit. The populations of L. hawaiensis show a re-
markably high level of geographic structure suggesting that migratory events between the islands
are uncommon. Thus, the independent colonization of terrestrial habitat by an ancestral seashore
population of Ligia is proposed as the most plausible scenario for the origin of the terrestrial popu-
lations.
—————————————————
3) e-mail: taiti@fi.cnr.it
4) e-mail: miquelan@nature.berkeley.edu
5) e-mail: stevelewalready@yahoo.com
6) e-mail: roderick@nature.berkeley.edu
86 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
RIASSUNTO
Il genere Ligia (Ligiidae) è distribuito in tutto il mondo e comprende più di 30 specie nominali.
La maggior parte delle specie sono litorali alofile ed abitano le coste rocciose, mentre sette specie
sono strettamente terrestri. Tre specie di Ligia sono segnalate per le Isole Hawaii, una introdotta,
L. exotica, e due endemiche, L. hawaiensis e L. perkinsi. Ligia hawaiensis è una specie litorale
molto comune lungo le coste rocciose. Ligia perkinsi è una specie terrestre presente nelle isole di
Kauai, Oahu e Hawaii. Viene condotta un’analisi morfologica e molecolare delle specie
endemiche di Ligia delle Isole Hawaii allo scopo di vedere se l’adattamento all’ambiente terrestre
abbia avuto origine una sola volta oppure si sia evoluto indipendentemente su ciascuna isola. Sono
state esaminate diverse popolazioni di L. hawaiensis e L. perkinsi provenienti da Kauai e Oahu.
Nell’analisi molecolare sono state incluse anche altre quattro specie di Ligia (L. italica, L. pallasii,
L. vitiensis e L. exotica) ed una popolazione di Lygidium hypnorum come outgroup. Tutte le
popolazioni di L. hawaiensis esaminate si sono dimostrate morfologicamente identiche, ma
chiaramente distinguibili da quelle di L. perkinsi. In L. perkinsi le popolazioni di Kauai
differiscono da quella di Oahu sia nella morfologia che nell’habitat in cui vivono. Due regioni di
DNA mitocondriale sono state sequenziate: citocromo c ossidasi subunità I e 16S rRNA,
rispettivamente di 675 e circa 490 paia di basi. Il cladogramma ottenuto mostra che L. hawaiensis
e L. perkinsi appartengono allo stesso clade, ma che L. perkinsi non costituisce una unità
monofiletica. Le popolazioni di L. hawaiensis mostrano un alto livello di struttura geografica, che
sembra dimostrare come movimenti migratori fra le diverse isole non siano comuni. La
colonizzazione indipendente dell’ambiente terrestre da parte di una popolazione litorale di Ligia
rappresenta lo scenario più probabile per l’origine delle popolazioni terrestri.
INTRODUCTION
Terrestrial isopods (Oniscidea) are derived from marine ancestors and repre-
sent a very good example of the evolutionary transition of animals from aquatic
environments to terrestrial environments (Warburg, 1968). The group includes
some 4,000 species occurring in all kinds of terrestrial habitats, from the sea-
shores to high mountains and even deserts. At present the Oniscidea are regarded
as a monophyletic unit (Schmalfuss, 1989; Wägele, 1989; Tabacaru &
Danielopol, 1996a, b) and according to Erhard (1998) the family Ligiidae repre-
sents the sister group of all other terrestrial isopods.
The genus Ligia Fabricius, 1798 (Ligiidae) is considered to be transitional be-
tween ancestral marine and fully terrestrial forms (Carefoot & Taylor, 1995).
Ligia has a worldwide distribution and currently includes over 30 nominal spe-
cies. Most of the species are halophilic forms occurring in the supralittoral zone
of rocky seashores, just above the water line, where they feed on seaweed. Seven
species are strictly terrestrial and occur in montane habitats in tropical regions,
mostly cloud forests on island mountain ridges. These species are: Ligia simoni
(Dollfus, 1893) from Colombia and Venezuela, L. perkinsi (Dollfus, 1900) from
the Hawaiian islands, L. platycephala (Van Name, 1925) from Venezuela,
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 87
Guiana, and Trinidad, L. latissima (Verhoeff, 1926) from New Caledonia, L.
philoscoides Jackson, 1938 from the Austral Islands, L. boninensis Nunomura,
1979 from the Bonin Islands, Japan, and L. taiwanensis Lee, 1994 from Taiwan.
The terrestrial species of Ligia are believed to be derived from littoral forms,
which has led to the suggestion that Ligia provides a good model of colonization
of terrestrial biotopes by isopods (Schmalfuss, 1978). On the basis of morphologi-
cal similarities, a sister species relationship may be hypothesized between some
terrestrial species of Ligia and species occurring on nearby coasts, e.g., L. perkinsi
and L. hawaiensis Dana, 1853 in the Hawaiian Islands, L. taiwanensis and L. exot-
ica Roux, 1828 in Taiwan, and L. philoscoides and L. rugosa Jackson, 1938 in the
Austral Islands (S. Taiti, pers. obs.). However, nothing is known about the phy-
logenetic relationships of these species. In the present study we analyse the possi-
ble phylogenetic relationships of Ligia species occurring in the Hawaiian Islands.
The Hawaiian Archipelago is the most isolated major archipelago in the world,
lying in the middle of the Pacific Ocean 4,000 km from the nearest major land
masses (North America and Japan) and the nearest comparable island groups (the
Marquesas). The islands are the emerged summits of submarine volcanoes and are
progressively younger proceeding from northwest to southeast (Carson & Clague,
1995): Kauai, Waialeale 5.1 Myr; Oahu, Waianae Range 3.7 Myr, Koolau Range
2.6 Myr; Molokai, Puu Nana 1.9 Myr, Kamakaou, 1.76 Myr; Maui, Puu Kukui
1.32 Myr, Haleakala 0.75 Myr; and Hawaii, Kohala 0.43 Myr, Mauna Kea 0.38
Myr, Mauna Loa and Kilauea 0.4 Myr to present.
Three species of Ligia occur on the Hawaiian Islands, two littoral (L. exotica
and L. hawaiensis) and one terrestrial (L. perkinsi). Ligia exotica has a pantropi-
cal distribution and has been recorded from the Hawaiian Islands by Dollfus
(1893) and Richardson (1905). This species is certainly introduced to Hawaii
since it occurs only on the docks of the harbours of Honolulu, Oahu, and Hilo,
Hawaii (S. Taiti, pers. obs.) (fig. 1). Ligia hawaiensis is endemic to the Hawai-
ian Islands, where it is very common along the rocky coasts. It has been re-
corded from almost all the major islands (fig. 1), and also from the northwestern
Hawaiian Islands (Taiti & Ferrara, 1991; Taiti & Howarth, 1996; Taiti, unpubl.
data). Ligia perkinsi is also endemic to the Hawaiian islands. It was first re-
corded by Dollfus (1900) from Kauai and Hawaii, and more recently (Taiti &
Howarth, 1996) from Oahu (fig. 1). On Hawaii Island this species seems to be
no longer present, since it has not been reported since 1896, and numerous at-
tempts to recollect it in recent years have been unsuccessful. This is a montane
species living on wet mossy tree trunks, wet vertical rocky cliffs, rheocrenes,
and stream margins.
88 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
Fig. 1. Recorded distribution of Ligia species from the Hawaiian Archipelago (northwestern islands
not included). The numbers refer to the populations used in the present study: 1, Honolulu Harbour;
2, Kauapea Beach; 3, Kapaa; 4, Lihue; 5, Kukuiula; 6, Pupukea; 7, Coconut Island; 8, Pouhala
Marsh; 9, Ala Wai Canal; 10, Makaleha Mts; 11, Mt. Kahili; 12, Haupu Range; 13, Nuuanu Pali.
Fig. 2. Alternative hypotheses of the evolution of terrestrial lifestyle (closed boxes) in Hawaiian Ligia.
A, independent evolution of terrestrial lifestyle; B, single origin of adaptation to terrestrial habitats.
In the present study a morphological analysis of several populations of the two
Hawaiian endemic species of Ligia (L. hawaiensis and L. perkinsi) from the islands
of Kauai and Oahu is undertaken to detect intra- and interspecific differences. Mo-
lecular data are used to test whether these species are the result of a single coloniza-
tion to the archipelago and whether the adaptation to the terrestrial environment
took place independently on the two islands (i.e., whether L. perkinsi is not mono-
phyletic) (fig. 2A) or only once (i.e., L. perkinsi is monophyletic) (fig. 2B).
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 89
MATERIALS AND METHODS
Eight populations of Ligia hawaiensis and four of L. perkinsi were sampled
from the islands of Kauai and Oahu (fig. 1, table I) for both morphological and
molecular analyses.
Adult male and female specimens from each population have been considered
in the morphological analysis. The following characters were compared using a
stereomicroscope and a compound microscope for micropreparations: body size,
cephalon structure and eye dimensions, shape of antennule, antenna, buccal
pieces, pleotelson, pereopods, and pleopods.
Four additional Ligia species were included in the molecular analysis (table
I): L. exotica, L. pallasii Brandt, 1833, L. vitiensis Dana, 1853, and L. italica
Fabricius, 1798. The species Ligidium hypnorum (Cuvier, 1792) in the family
Ligiidae was used as an outgroup. Two to four pereopods from live specimens
collected in the field and fixed in 95% ethanol (in a few cases specimens pre-
served in 75% ethanol from museum collections) were used for DNA extrac-
tions, and the rest of the specimen kept as a voucher (stored at Essig Museum of
Entomology at University of California, Berkeley, U.S.A.).
Total genomic DNA was extracted following the phenol/chloroform protocol
of Palumbi et al. (1991) or using QIAGEN DNeasy Tissue Kits. Partial frag-
TABLE I
Species and populations sampled in the present study
Species Populations
Ligidium hypnorum (Cuvier, 1792) Austria: Tirol, Ziller Tal, near Fügen
Ligia italica Fabricius, 1798 Italy: Tuscany, Giannutri Island
Ligia vitiensis Dana, 1853 Madagascar: Nosy-Be
Ligia pallasii Brandt, 1833 Canada: British Columbia, Sepping Island
Ligia exotica Roux, 1828 U.S.A.: Hawaiian Is, Oahu, Honolulu Harbour
Ligia hawaiensis Dana, 1853 U.S.A.: Hawaiian Is, Kauai, Kauapea Beach
U.S.A.: Hawaiian Is, Kauai, Lihue
U.S.A.: Hawaiian Is, Kauai, Kapaa
U.S.A.: Hawaiian Is, Kauai, Kukuiula
U.S.A.: Hawaiian Is, Oahu, Pouhala Marsh
U.S.A.: Hawaiian Is, Oahu, Coconut Island
U.S.A.: Hawaiian Is, Oahu, Ala Wai Canal
U.S.A.: Hawaiian Is, Oahu, Pupukea
Ligia perkinsi (Dollfus, 1900) U.S.A.: Hawaiian Is, Kauai, Mt Kahili
U.S.A.: Hawaiian Is, Kauai, Mt Kahili
U.S.A.: Hawaiian Is, Kauai, Makaleha Mts
U.S.A.: Hawaiian Is, Kauai, Haupu Range
U.S.A.: Hawaiian Is, Oahu, Nuuanu Pali
U.S.A.: Hawaiian Is, Oahu, Nuuanu Pali
90 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
ments of the mitochondrial genes cytochrome c oxidase subunit I (CO1) and 16S
rRNA (16S) were amplified using the primer pairs C1-J-1490 and C1-N-2198
(Folmer et al., 1994) (675 bp) and LR-N-13398 (Simon et al., 1994) and LR-J-
12864 (5’-CTCCGGTTTGAACTCAGATCA-3’) (Hsiao, pers. comm.) (approx.
490 bp), respectively. In a few cases, a shorter CO1 fragment was amplified with
primer pair C1-J-1751 and C1-N-2191 (Simon et al., 1994) (421 bp). The Perkin
Elmer 9700, Perkin Elmer 9600, or the BioRad i-Cycler were used to perform 25
iterations of the following cycle: 30 s at 95°C, 45 s at 42-45°C (depending on the
primers) and 45 s at 72°C, beginning with an additional single cycle of 2 min at
95°C and ending with another one of 10 min at 72°C.
The PCR reaction mix contained primers (0.48 µM each), dNTPs (0.2 mM
each) and 0.6 U Perkin Elmer AmpliTaq® DNA polymerase (for a 50 µl reac-
tion) with the supplied buffer and, in some cases, adding an extra amount of
MgCl2 (0.5 to 1.0 mM). PCR products were cleaned using Geneclean® II (Bio
101) or QIAGEN QIAquick PCR Purification Kits following the manufacturer’s
specifications. DNA was directly sequenced in both directions using the dye
terminator cycle sequencing method (Sanger et al., 1977) and the ABI PRISM
BigDyeTM Terminator Cycle Sequencing Ready Reaction with AmpliTaq® DNA
Polimerase FS kit. Sequenced products were cleaned using Princeton Separa-
tions CentriSep columns and run out on an ABI 377 automated sequencer. Se-
quences were edited using the Sequencher 3.1.1 software package (Gene Codes
Corporation). Sequences were subsequently exported to the program GDE 2.2
(Smith et al., 1994) running on a Sun Enterprise 5000 Server, and manual align-
ments were constructed taking into account secondary structure information from
secondary structure models available in the literature. These initial alignments were
used to identify fragments of well-supported homology (i.e., fragments of identical
or well-conserved flanking regions), which were subsequently used as input files
for the analysis after their gaps were removed. All sequences obtained in the pre-
sent study are available from Genbank under accession numbers: AY051319-
AY051337 (CO1) and AY051338-AY051356 (16S).
Partial and combined sequence data sets were analysed using the direct optimi-
zation method (Wheeler, 1996) as implemented in the computer program POY
(Wheeler & Gladstein, 2000). This method circumvents problems inherent in a
priori alignment by incorporating the search for the most parsimonious optimiza-
tions of insertion/deletion events into the evaluation of candidate topologies. The
heuristic search strategy used combined 100 iterations of random addition of taxa,
each of the iterations followed by additional rounds of tree-fusing and tree-drifting
(Goloboff, 1999). Sensitivity of the results to changes in parameter values was in-
vestigated by running analyses with different combinations of gap and transver-
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 91
sion/transition costs. Gap costs of 1, 2, 4, and 8 times the base transformations
were combined with transversion/transition costs of 1, 2, 4, and 8 (only combina-
tions with gap cost equal to or higher than transversion/transition cost were as-
sayed). Congruence across data partitions as measured by the ILD (Mickevich &
Farris, 1981) has been proposed as an objective criterion to choose among differ-
ent parameter combinations. However, these measurements do not seem to be in-
dependent of the actual parameter values considered (Faith & Trueman, 2001).
Equal weighting is usually rendered as just another type of character weighting.
However, equal or uniform weighting differs epistemologically from other weight-
ing schemes, because it neither adds any extra information to the background
knowledge nor reduces the empirical content of the resulting cladograms. There-
fore, equal weighting maximizes the explanatory power of the characters (Kluge,
1997; Frost et al., 2001). Results obtained from the analysis under uniform costs
were considered to represent the best current estimate of the phylogenetic relation-
ships of the taxa sampled in the present study.
Pair-wise uncorrected genetic distances (p-values) were calculated from the
implied alignment derived from the preferred tree under equal parameter costs.
Clade support was assessed by means of heuristic calculations of Bremer support
(Bremer, 1988), as implemented in POY, and bootstrap proportions, as calcu-
lated with the computer programs Winclada (Nixon, 1999) and NONA
(Goloboff, 1998), using 1000 iterations of an heuristic search of 15 random addi-
tions of taxa holding a maximum of 20 trees per iteration and up to 1000 total
trees (calculated from the implied alignment). Support of data for alternative to-
pologies was examined using constrained searches.
RESULTS
Morphological analysis
The comparison of the eight populations of the littoral Ligia hawaiensis from
the islands of Kauai and Oahu showed that they are all morphologically homo-
geneous and no remarkable differences were observed. The terrestrial Ligia
perkinsi shows clear differences from Ligia hawaiensis, and some minor differ-
ences are found also between the populations of L. perkinsi from Kauai and that
from Oahu. No differences were observed among the three populations of L.
perkinsi from Kauai.
Size. — The maximum sizes observed are: for Ligia hawaiensis from both
Kauai and Oahu, 22 × 10 mm, 13 × 5 mm; for L. perkinsi from Kauai, 13
× 5 mm, 17 × 8 mm; for L. perkinsi from Oahu, 15 × 6 mm, 17 × 8.5 mm.
92 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
Fig. 3. A-B, Ligia hawaiensis Dana, 1853, 18 mm long from Pouhala Marsh, Oahu: A, cephalon;
B, pleotelson. C-D, L. perkinsi (Dollfus, 1900), 13 mm long from Mt. Kahili, Kauai: C, cephalon;
D, pleotelson. E-F, L. perkinsi, 15 mm long from Nuuanu Pali, Oahu: E, cephalon; F, pleotelson.
Ligia hawaiensis is larger than L. perkinsi, and in L. hawaiensis males are larger
than females while in L. perkinsi females are larger than males.
Cephalon. — The distance between the eyes is proportionally smaller in L.
hawaiensis (ratio distance between eyes/eye width = ca. 3/5) (fig. 3A) than in L.
perkinsi (ratio ca. 1/1) (fig. 3C, E).
Pleotelson. — The shape of the pleotelson is identical in both L. perkinsi from
Kauai (fig. 3D) and Oahu (fig. 3F). In L. hawaiensis, the pleotelson is very simi-
lar to that of L. perkinsi, only the lateral posterior points are slightly more pro-
truding (fig. 3B).
Pereopods. — The dactylus of the sixth and seventh pereopod in both sexes has
a tuft of very long thin setae on the tergal margin in Ligia hawaiensis (fig. 4A), in
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 93
Fig. 4. A, Ligia hawaiensis Dana, 1853, 18 mm long from Pouhala Marsh, Oahu: pereopod 7 dac-
tylus; B, L. perkinsi (Dollfus, 1900), 13 mm long from Mt. Kahili, Kauai: pereopod 7 dactylus;
C, L. perkinsi, 15 mm long from Nuuanu Pali, Oahu: pereopod 7 dactylus.
L. perkinsi from Kauai there are some short setae (fig. 4B), and in L. perkinsi
from Oahu (fig. 4C) there is an intermediate condition with some setae shorter
and thicker than in L. hawaiensis but longer than in L. perkinsi from Kauai.
Male characters. — The major differences are found in the male characters.
Ligia species usually possess fields of papillae on the male first three pereopods
which function as anti-slide structures during copulation (Schmalfuss, 2003). In
Ligia hawaiensis, the papillar fields on carpus and merus of the first pereopod are
large (fig. 5A), while they are reduced in both populations of L. perkinsi from
Kauai (fig. 5C) and Oahu (fig. 5E). The propodus of the first pereopod is propor-
tionally shorter and thicker in L. hawaiensis than in L. perkinsi and shows a pro-
truding triangular process on the distal part. This process is typical of the Indo-
Pacific species belonging to the exotica-group, and can be considered as a syn-
apomorphic character of the species belonging to this group. This process is miss-
ing in both the two island populations of L. perkinsi. In the second and third pere-
opods, the papillar field is large on the carpus and small on the merus of L.
hawaiensis (fig. 5B), reduced on carpus and lacking on merus of both L. perkinsi
from Kauai (fig. 5D) and Oahu (fig. 5F). Distinct differences are found also in the
endopod of the male second pleopod: in L. hawaiensis it is enlarged in the distal
part with an obliquely truncate apex (fig. 6A), in L. perkinsi from Kauai the apical
part is not enlarged and the apex is rounded, slightly bilobed (fig. 6B), while in L.
perkinsi from Oahu the distal part is not enlarged and apically truncate (fig. 6C).
94 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
Fig. 5. A-B, Ligia hawaiensis Dana, 1853, 18 mm long from Pouhala Marsh, Oahu: A, pereopod 1;
B, pereopod 2. C-D, L. perkinsi (Dollfus, 1900), 13 mm long from Mt. Kahili, Kauai: C, pereopod 1;
D, pereopod 2. E-F, L. perkinsi, 15 mm long from Nuuanu Pali, Oahu: E, pereopod 1; F, pereopod 2.
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 95
Fig. 6. A, Ligia hawaiensis Dana, 1853, 18 mm long from Pouhala Marsh, Oahu: pleopod 2; B, L.
perkinsi (Dollfus, 1900), 13 mm long from Mt. Kahili, Kauai: pleopod 2; C, L. perkinsi, 15 mm
long from Nuuanu Pali, Oahu: pleopod 2.
Moreover, the two island populations of L. perkinsi differ also in the habitat
where they occur: on Kauai the species is common in wet moss on indigenous
trees of montane rain forests above 600 m, while on Oahu it occurs on a wind-
ward wet rocky cliff at approximately 300 m on Koolau Range.
Molecular analysis
Partitioned analyses of the two gene fragments under equal weights resulted
in two trees of 632 steps for the CO1 and two trees of 592 steps for the 16S (not
shown). The simultaneous analysis of the two genes yielded one tree of length
1238 (fig. 7). Results from the partitioned as well as the combined analyses were
very similar, and differences were mostly restricted to the non-Hawaiian species
(16S) and the relationships of the L. hawaiensis haplotypes from Oahu. Parti-
tioned and combined analyses agree in supporting the monophyly of the Hawai-
ian species, the monophyly of the sampled haplotypes of L. hawaiensis, and the
monophyly of populations of L. perkinsi within each island. However, L.
perkinsi is shown to be paraphyletic with respect to L. hawaiensis, with the Oahu
population splitting first and the Kauaian haplotypes forming the sister clade of
L. hawaiensis. The Oahu populations of L. hawaiensis are shown to be para-
phyletic with respect to the monophyletic Kauaian lineage.
The effect of different parameter combinations analysed on specific topologi-
cal hypotheses is summarized in fig. 8. The monophyly of the Hawaiian species,
the monophyly of the L. hawaiensis haplotypes, and the paraphyly of L. perkinsi
96 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
Fig. 7. Single most parsimonious tree obtained by simultaneous direct optimization of the CO1 and
16S fragments, with heuristic Bremer supports (below branches) and bootstrap proportions (above
branches) of the Ligia populations examined in this study.
island populations are recovered regardless of the gap cost and transversion
weighting considered. The monophyly of the Oahu haplotypes of L. hawaiensis
is only supported under particular parameter cost schemes (fig. 8). The branch-
ing pattern of the island populations of L. perkinsi is also sensitive to
gap/transformation costs, although most of the parameter combinations suggest
that the Oahu populations of L. perkinsi were the first offshoots of Hawaiian
Ligia, in contrast to what we might expect due to the older age of Kauai. Forcing
monophyly of L. perkinsi under equal costs increases tree length by 13 steps,
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 97
Fig. 8. Summary of the results of parameter sensitivity analyses. Ten different parameter combinations
were analysed: gap cost equal, twice, four times, or eight times base transformations (indicated in the
x-axis) combined with transversion (TV) cost equal, twice, four times, or eight times transitions (TS)
(indicated in y-axis). Only combinations with gaps equal to or higher than transversions were assayed.
Black boxes denote support of all trees obtained under this particular parameter combination, grey
boxes indicate partial support (only some of the obtained trees support the specified group) and white
boxes indicate complete lack of support (none of the obtained trees supports the specified group).
while constraining monophyly of the island populations of L. perkinsi and L.
hawaiensis results in 21 extra steps.
Uncorrected genetic distances across taxa are shown in table II. Divergence
values between the island population of L. perkinsi average 0.12 ± 0.003 and be-
tween L. perkinsi and L. hawaiensis 0.11 ± 0.006. The larger divergences ob-
served across L. hawaiensis haplotypes are 0.10 ± 0.002, between haplotypes of
Oahu (Ala Wai Canal excluded) and Kauai, and 0.08 ± 0.001 and 0.09 ± 0.002,
between the haplotype from Ala Wai and the rest of Oahu haplotypes and the
Kauai ones, respectively.
DISCUSSION
The cladistic patterns obtained from the sampled populations of Ligia perkinsi
and L. hawaiensis are compatible with both of the proposed hypotheses (fig. 2)
98 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 99
Fig. 9. Alternative scenarios of the evolution of terrestrial lifestyle in Hawaiian Ligia. A, inde-
pendent evolution of terrestrial lifestyle (closed boxes), with extinction of sister island populations
of Ligia hawaiensis Dana, 1853 (crossed branches); B, single origin of adaptation to terrestrial
habitats (closed box) and subsequent reversal to primitive littoral, halophilic habitat (open box).
for the adaptation to terrestrial habitats. However, the reconciliation of the pre-
ferred topology with either of these hypotheses requires different sets of assump-
tions. The plausibility of the two alternative scenarios can thus be evaluated
through the comparison of the required assumptions. On the one hand, the inde-
pendent evolution towards a terrestrial lifestyle would involve the extinction of
both island lineages of L. hawaiensis sister to the respective L. perkinsi island
population (fig. 9A). However, if the Oahu populations of L. hawaiensis are mo-
nophyletic, as suggested by some of the parameter combinations, it would be
sufficient to invoke only the extinction of the sister lineage of L. hawaiensis
from Oahu and a subsequent recolonization of the island by a L. hawaiensis
lineage from Kauai. On the other hand, the single origin of adaptation to the ter-
restrial habitat would require a reversal event to the primitive seashore dwelling
condition (fig. 9B) in the ancestor of the current lineages of L. hawaiensis.
Therefore, selection of one scenario over the other requires deciding what is
more plausible, the extinction of haplotype lineages or the back adaptation to a
seashore habitat from a terrestrial dwelling state. Extinction of haplotype line-
ages or replacements of old lineages by more recently evolved lineages are regu-
lar processes of the dynamics of a population (Avise, 2000). The shift from a
seashore habitat to a mist forest (or the other way around) involves important
physiological changes, mostly related to osmotic regulation (Tsai et al., 1997).
Although adaptation to hypotonic, terrestrial freshwater environments from a
marine littoral environment has been hypothesized in Ligia (cf. Schmalfuss,
1978), there is no evidence to date of a shift in the opposite direction. Therefore,
at this point we consider the independent adaptation to terrestrial habitats in Ha-
waiian Ligia as the most plausible explanation for the origin of L. perkinsi popu-
lations in Oahu and Kauai.
If this hypothesis is correct, then some morphological characters present in
both Oahu and Kauai populations of L. perkinsi must be due to convergence, i.e.,
100 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
the reduction of papillar fields on the carpus and merus of the male first three
pereopods and the reduction of a triangular process on the propodus of the male
first pereopod. According to Schmalfuss (2003), large papillar fields in male an-
terior pereopods and the size of males larger than females indicate a mate-
guarding behaviour prior to copulation. This behaviour is probably present in L.
hawaiensis and lost in L. perkinsi from both Kauai and Oahu.
Because of the morphological uniformity, the close proximity of the islands,
and the coastal habitat of L. hawaiensis, we expected to find that L. hawaiensis
represented a single, archipelago-wide, panmictic population. However, our re-
sults show deep genetic divergences both between and within (Oahu’s Ala Wai
haplotype) island populations of L. hawaiensis, well above the mitochondrial di-
vergences reported between species, or even genera, of other Hawaiian inverte-
brates (Gillespie et al., 1994; Shaw, 1996; Thacker & Hadfield, 2000). These re-
sults could point towards a long-time presence of Ligia in the Hawaiian Islands.
However, high levels of molecular divergence in 16S have been reported in
other oniscidean species (Michel-Salzat & Bouchon, 2000), which may be in-
dicative of an accelerated rate of evolution in the mitochondrial genes of these
organisms. Ligia hawaiensis also displays a remarkable geographic structure,
with most of the island populations forming exclusive clades, suggesting that in-
ter-island dispersal events have been rare throughout the history of the lineage.
This seems to contradict the hypothesis that littoral species have a great facility
of dispersal as commonly supposed (Vandel, 1960: 63).
CONCLUSIONS
In conclusion, the genus Ligia provides an excellent model to test hypotheses
regarding the evolution of ecological shifts. Although the obtained population
cladogram is compatible with both proposed hypotheses, we conclude that the
independent colonization of the terrestrial habitats of Kauai and Oahu by an an-
cestral seashore population of Ligia is the most plausible scenario for the origin
of terrestrial populations. Thus, considering also their morphological differences,
the two terrestrial populations of Ligia from Kauai and Oahu should be regarded
as belonging to distinct species. Ligia hawaiensis populations display a remark-
able genetic divergence and geographic structure, suggesting that inter-island
colonization events are rare. More work is required to clarify the evolutionary
significance of the patterns found in the present study. More specifically, a more
thorough sampling that includes all the Hawaiian Islands inhabited by Ligia is
necessary for testing further the independent origin of the terrestrial populations
Taiti et al., TERRESTRIALITY IN HAWAIIAN LIGIA 101
and to look for the presence of the phylogeographic patterns observed in Kauai
and Oahu populations of L. hawaiensis on the remaining islands.
ACKNOWLEDGEMENTS
We would like to express our most sincere thanks to Dr. F.G. Howarth and Mr
D.J. Preston, Bernice P. Bishop Museum, Honolulu, and Dr. A. Asquith, U.S.
Fish and Wildlife Service, Kauai, for their invaluable help in collecting part of
the material examined. The whole staff of the Entomology Department of the
Bishop Museum is particularly acknowledged for their kind help and hospitality
during S.T.’s visits to the Hawaiian Islands. We wish to thank Leo Shapiro and
two anonymous reviewers who provided valuable comments on the manuscript.
M.A. was supported by a fellowship from the Spanish Ministerio de Educación y
Cultura (EX-99-46630819).
REFERENCES
AVISE, J. C., 2000. Phylogeography: the history and formation of species: 1-447. (Harvard Univer-
sity Press, Cambridge, Mass.).
BREMER, K., 1988. The limits of amino acid sequence data in angiosperm phylogenetic reconstruc-
tion. Evolution, 42: 795-803.
CAREFOOT, T. H. & B. E. TAYLOR, 1995. Ligia: a prototypal terrestrial isopod. Crust. Issues, 9: 47-60.
CARSON, H. L. & D. A. CLAGUE, 1995. Geology and biogeography of the Hawaiian islands. In:
W. L. WAGNER & V. A. FUNK (eds.), Hawaiian biogeography: 14-29. (Smithsonian Institu-
tion, Washington, D.C.).
DOLLFUS, A., 1893. Sur la distribution du genre Ligia Fabr. Feuille jeun. Nat., 24: 23-26.
— —, 1900. Crustacea Isopoda. Fauna Hawaiiensis, 2: 521-526, pl. 20.
ERHARD, F., 1998. Phylogenetic relationships within the Oniscidea (Crustacea, Isopoda). Israel
Journ. Zool., 44: 303-309.
FAITH, D. P. & J. W. H. TRUEMAN, 2001. Towards an inclusive philosophy for phylogenetic infer-
ence. Syst. Biol., 50: 331-350.
FOLMER, O., M. BLACK, W. HOEH, R. LUTZ & R. VRIJENHOEK, 1994. DNA primers for amplifica-
tion of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates.
Molec. mar. Biol. Biotechnology, 3: 294-299.
FROST, D. R., M. T. RODRIGUES, T. GRANT & T. A. TITUS, 2001. Phylogenetics of the lizard genus
Tropidurus (Squamata: Tropidurinae): direct optimization, descriptive efficiency, and sensi-
tivity analysis of congruence between molecular data and morphology. Mol. Phylogenet.
Evol., 21: 352-371.
GILLESPIE, R. G., H. B. CROOM & S. R. PALUMBI, 1994. Multiple origins of a spider radiation in
Hawaii. Proc. nat. Acad. Sci. U.S.A., 91: 2290-2294.
GOLOBOFF, P. A., 1998. NONA ver. 2.0. (Program and documentation available at www
.cladistics.com).
— —, 1999. Analyzing large data sets in reasonable times: solutions for composite optima. Cladis-
tics, 15: 415-428.
102 CRM 002 – Sfenthourakis et al. (eds.), BIOLOGY TERRESTRIAL ISOPODS, V
KLUGE, A. G., 1997. Sophisticated falsification and research cycles: consequences for differential
character weighting in phylogenetic systematics. Zool. Scr., 26: 349-360.
MICHEL-SALZAT, A. & D. BOUCHON, 2000. Phylogenetic analysis of mitochondrial LSU rRNA in
oniscids. C. R. Acad. Sci., Paris, (3, Sci. Vie) 323: 1-11.
MICKEVICH, M. F. & J. S. FARRIS, 1981. The implications of incongruence in Menidia. Syst. Zool.,
30: 351-370.
NIXON, K. C., 1999. Winclada (BETA) ver. 0.9.9. (Published by the author, Ithaca, New York;
available at www.cladistics.com).
PALUMBI, S. A., S. MARTIN, S. ROMANO, W. O. MCMILLAN, L. STICE & G. GRABOWSKI, 1991.
The simple fool’s guide to PCR, version 2.0: 1-25. (Dept. Zool. Univ. Hawaii, Honolulu).
RICHARDSON, H., 1905. A monograph on the isopods of North America. Bull. U. S. natn. Mus.,
54: i-liii, 1-727.
SANGER, F., S. NICKLEN & A. R. COULSEN, 1977. DNA sequencing with chain terminating inhibi-
tors. Proc. natn. Acad. Sci. U.S.A., 74: 5463-5468.
SCHMALFUSS, H., 1978. Ligia simoni: a model for the evolution of terrestrial isopods. Stuttgarter
Beitr. Naturk., (A) 317: 1-5.
— —, 1989. Phylogenetics in Oniscidea. Monitore zool. italiano, (n. s.) (Monogr.) 4: 3-27.
—, 2003. Leg structure and mate-guarding in the Ligiidae (Isopoda, Oniscidea). Crustaceana
Monogr., 2: 53-68. [This volume.]
SHAW, K. L., 1996. Sequential radiations and patterns of speciation in the Hawaiian cricket genus
Laupala inferred from DNA sequences. Evolution, 50: 237-255.
SIMON, C., F. FRATI, A. BECKENBACH, B. CRESPI, H. LIU & P. FLOOK, 1994. Evolution, weighting,
and phylogenetic utility of mitochondrial gene sequences and a compilation of conserved
polymerase chain reaction primers. Ann. ent. Soc. America, 87: 651-701.
SMITH, S. W., R. OVERBEEK, C. R. WOESE, W. GILBERT & P. M. GILLEVET, 1994. The genetic data
environment an expandable GUI for multiple sequence analysis. Computer Applics Biosci.,
10: 671-675.
TABACARU, I. & D. L. DANIELOPOL, 1996a. Phylogénie des isopodes terrestres. C. R. Acad. Sci.
Paris, (3) 319: 71-80.
— & — —, 1996b. Phylogenèse et convergence chez les isopodes terrestres. Vie Milieu, 46:
171-181.
TAITI, S. & F. FERRARA, 1991. Terrestrial isopods (Crustacea) from the Hawaiian Islands. B.P.
Bishop Mus. occ. Pap., 31: 202-227.
TAITI, S. & F. G. HOWARTH, 1996. Terrestrial isopods from the Hawaiian Islands (Isopoda: Onis-
cidea). B.P. Bishop Mus. occ. Pap., 45: 59-71.
THACKER, R. W. & M. G. HADFIELD, 2000. Mitochondrial phylogeny of extant Hawaiian tree
snails (Achatinellinae). Molec. Phylogenet. Evol., 16: 263-270.
TSAI, M.-L., C.-F. DAI & H.-C. CHEN, 1997. Responses of two semiterrestrial isopods, Ligia exot-
ica and Ligia taiwanensis (Crustacea) to osmotic stress. Comp. Biochem. Phys., (A)
118:141-146.
VANDEL, A., 1960. Isopodes terrestres (Première partie). Faune France, 64: 1-416.
WÄGELE, J. W., 1989. Evolution und phylogenetisches System der Isopoda. Stand der Forschung
und neue Erkenntnisse. Zoologica, Stuttgart, 140: 1-262.
WARBURG, M. R., 1968. Behavioral adaptations of terrestrial isopods. American Zool., 8: 545-559.
WHEELER, W. C., 1996. Optimization alignment: the end of multiple sequence alignment in phy-
logenetics? Cladistics, 12:1-9.
WHEELER, W. C. & D. S. GLADSTEIN, 2000. POY: the Optimization of Alignment Characters.
(Program and documentation available at ftp://amnh.org/pub/molecular).
... Past studies on terrestrial isopods (Crustacea, Oniscidea) have revealed high genetic divergence at species or genus level, among individuals distributed at geographically close areas, including isolated islands and islets (Bidegaray-Batista et al., 2015;Kamilari et al., 2014;Klossa-Kilia et al., 2006;Parmakelis et al., 2008;Poulakakis and Sfenthourakis, 2008;Santamaria, 2019;Santamaria et al., 2013;Taiti et al., 2003). Nevertheless, none of the aforementioned studies has addressed diversification patterns within islands. ...
Article
Full-text available
Understanding intra-island patterns of evolutionary divergence, including cases of cryptic diversity, is a crucial step towards deciphering speciation processes. Cyprus is an oceanic island isolated for at least 5.3 Mya from surrounding continental regions, while it remains unclear whether it was ever connected to the mainland, even during the Messinian Salinity Crisis. The terrestrial isopod species Armadillo officinalis, that is widespread across the Mediterranean, offers the opportunity to explore intra-island divergence patterns that might exhibit geographical structure related also to the region’s known paleogeography. Genome-wide ddRADseq, as well as Sanger sequencing for four mitochondrial and three nuclear loci data were generated for this purpose. In total, 71 populations from Cyprus, neighbouring continental sites, i.e., Israel, Lebanon and Turkey, and other Mediterranean regions, i.e. Greece, Italy, and Tunisia, were included in the analysis. Phylogenetic reconstructions and population structure analyses support the existence of at least six genetically discrete groups across the study area. Five of these distinct genetic clades occur on Cyprus, four of which are endemic to the island and one is widely distributed along the circum-Mediterranean countries. The sixth clade is distributed in Israel. The closest evolutionary relationship of endemic Cypriot populations is with those from Israel, while the evolutionary clade that is present in countries all around the Mediterranean is very shallow. Cladochronological analyses date the origin of the species on the island at ∼6 Mya. Estimated f4 and D statistics as well as FST values indicate the genetic isolation between the populations sampled from Cyprus and surrounding continental areas, while there is evident gene flow among populations within the island. Species delimitation and population genetic metrics support the existence of three distinct taxonomic units across the study area, two of which occur on the island and correspond to the endemic clade and the widespread circum-Mediterranean one, respectively, while the third corresponds to Israel’s clade. The islands’ paleogeographic history and recent human activities seem to have shaped current patterns of genetic diversity in this group of species.
... Rivera et al. (2002) used mtDNA markers to address relationships among Hawaiian cavernicolous isopods and found no support for a vicariant mode of speciation but support for an adaptive shift from a marine littoral to a terrestrial subterranean habitat in Littorophiloscia. Charfi-Cheikhrouha (2003) explored genetic diversity in Armadillidium pelagicum using 16S rDNA, while Taiti et al. (2003) used mtDNA markers and morphological evidence to show that terrestrial forms of Ligia evolved independently from littoral ones on different Hawaiian islands. Molecular phylogenetic methods have also been applied on Ligia species to explore the effects of environmental factors (Eberl et al. 2013) and dispersal ) on distribution patterns. ...
Chapter
Among crustaceans, only Amphipoda, Isopoda, and Decapoda have invaded truly terrestrial environments, but only two groups show full adaptations to live on land: the family Talitridae among the Amphipoda and the suborder Oniscidea among the Isopoda. The Talitridae occur primarily in forest leaf litter, but a number of other habitats, including caves, are recorded. Talitrids are important ecological contributors to the litter fauna, often occurring in high densities. Their adaptations to a terrestrial way of life include the retention of the mitten-shaped second gnathopods, a neotenic condition among males; the first article of antenna 2 greatly enlarged and fixed to the side of the head; and enlarged gills and pleopods often reduced, sometimes to vestigial stumps. Talitrids have a skewed world distribution being at their most diverse in New Zealand, Tasmania, and Japan/Taiwan. They occur in the Caribbean and Central America but are absent from South and North America except as introduced taxa. Their distribution is largely a result of tectonic activity during the past 150 million years and of extinctions during the Tertiary due to increasing aridity of the climate. The Oniscidea (terrestrial isopods) are the only crustaceans that have managed to adapt to almost all habitat types on land and have become the most species-rich suborder of Isopoda. Although monophyly of the Oniscidea is generally accepted, current taxonomy, based almost entirely on morphological characters, needs extensive revision. Terrestrial isopods present a number of unique adaptations to life on land, some of which result from what can be considered as pre-adaptations of ancestral marine isopods, such as egg development in a marsupium, being dorso-ventrally oblate and having a pleopodal respiration. Other crucial adaptations of Oniscidea include the water-conducting system, the structure of their cuticle, and the “covered” type of pleopodal lungs, all of which are responses to the acute problem of desiccation. They are also among the most speciose taxa in caves, some species have even returned to an aquatic life, and a few species have evolved social behavior. Oniscidea are increasingly being used in biogeographical, phylogeographical, ecological, and evolutionary research and can become model organisms for a broad range of biological studies.
... It takes about 5wk from egg deposition to release . Further details of their biology, including types, habitats, reproduction, food, growth, physiology et al can be found in an academic website A Snail's Odyssey (Carefoot, 2020), andTaiti et al. 2003; Renate Eberl, 2012. Ligia isopods are omnivorous detrivores and feed by chewing on organic debris on the shore. ...
Preprint
Full-text available
Background: The semiterrestrial isopod, Ligia exotica represents one of the oldest documented species introductions of marine organisms and is known as an intermediate form between marine and strictly terrestrial isopods. In order to explore the practical value for food & feed of Ligia, this study focused on growth rate under laboratory rearing conditions and detailed analysis of the overall nutrient content of the species in comparison to two other aquatic food media (krill and fish meal). Results: Evaluation of the growth rate of juveniles suggests it is a relatively fast-growing species of the Ligiidae family. The essential amino acids content Ligia meal is the lowest but the proportion of flavor amino acids was higher. In particular, the content of taurine was much higher. Amino acid score and chemical score show that the most restricted amino acids of isopod meal are methionine and cysteine. The extremely unbalanced amino acid composition may affect the absorption and utilization by consumers. In terms of fatty acids, the total polyunsaturated fatty acids in isopod is very low. A total of 12 vitamins were examined. The VK1, VE, VB2, VB3, VB5 content of isopod meal were significantly higher than those of krill meal and fish meal. Similarly, most of the 11 mineral elements are the highest in isopod meal. Conclusions: Ligia offers potential as an alternative natural food source especially in aquaculture given the growth rate under culture and the overall nutrient content. But Ligia collected in most of the field would be deemed unfit for human consumption because of the relatively low nutritional value and heavy metal content exceeding the provided standard. Ligia isopods offer some potential to become a crustacean model animal for commercial aquaculture crustaceans, further study is warranted to elucidate its biological characteristics.
Article
Full-text available
The semiterrestrial isopod, Ligia exotica represents one of the oldest documented species introductions of marine organisms and is known as an intermediate form between marine and strictly terrestrial isopods. In order to explore the potential value of Ligia as an animal food source, this study focused on the growth rate under laboratory rearing conditions and conducted a detailed analysis of the overall nutrient content of the species in comparison to two other marine food media (krill and fish meal). Evaluation of the growth rate of juveniles suggests it is a relatively fast-growing species of the Ligiidae family. The essential amino acids content Ligia meal is the lowest amongst the three studied media but the proportion of flavor amino acids, and in particular taurine, was higher. The most restricted amino acids of isopod meal are methionine and cysteine. The significantly unbalanced amino acid composition of Ligia meal may affect the absorption and utilization by consumers. In terms of fatty acids, the total polyunsaturated fatty acids in the isopod is very low. A total of 12 vitamins were examined. The VK 1, VE, VB 2 , VB 3 , VB 5 content of isopod meal were significantly higher than those of krill meal and fish meal. Similarly, most of the 11 mineral elements are highest in the isopod meal. Ligia therefore offers potential as an alternative natural food source in animal given the growth rate under culture and the overall nutrient content. But Ligia collected in most of the field would be deemed unfit for human consumption because of the relatively low nutritional value and heavy metal content exceeding the provided standard. Further study is warranted to elucidate the biological characteristics of isopods and how its diet is reflected in its nutritional value to consumers.
Preprint
Full-text available
The extensive coastlines of South Africa and Namibia extends from the Atlantic to the Indian Ocean and encompass several major biogeographic provinces, each characterized by unique faunal and floral assemblages. Recent biogeographic studies have led to competing biogeographic models of the southern African coastline. This has stimulated phylogeographic work to determine whether the distribution of genetic diversity within coastal invertebrate species match the proposed biogeographic regions. The lack of congruence between studies and the discovery of cryptic diversity indicating the possible existence of cryptic species in coastal isopods in the region underscore the need for additional phylogeographic research in southern Africa, particularly for organisms that have been shown to both harbor cryptic diversity and to retain signatures of past geological and oceanographic processes in their phylogeographic patterns. Isopods in the genus Ligia exhibit several biological traits that suggest they may be informative on phylogeographic patterns. They inhabit patchy rocky beaches, are direct developers, avoid the open water, and exhibit several biological traits that severely constrain their dispersal potential (e.g. poor desiccation resistance). These traits are thought to lead to long term isolation of populations, the retention of geological and oceanographic signatures in phylogeographic patterns of Ligia , and the presence of cryptic lineages. In this study, we used mitochondrial and nuclear markers to characterize Ligia collected in 18 localities across Namibia to the KwaZulu-Natal region of South Africa. We report the presence of cryptic lineages within Ligia species in the region, as well as distributional patterns that differ from those reported from other coastal taxa, but that broadly matches a widely used biogeographic model for the region.
Preprint
Full-text available
Ligia isopods are conspicuous inhabitants of rocky intertidal habitats exhibiting several biological traits that severely limit their dispersal potential. Their presence in patchy habitats and low vagility may lead to long term isolation, allopatric isolation and possible cryptic speciation. Indeed, various species of Ligia have been suggested to represent instead cryptic species complexes. Past studies; however, have largely focused in Eastern Pacific and Atlantic species of Ligia , leaving in doubt whether cryptic diversity occurs in other highly biodiverse areas. The Seychelles consists of 115 islands of different ages and geological origins spread across the western Indian Ocean. They are well known for their rich biodiversity with recent reports of cryptic species in terrestrial Seychellois organisms. Despite these studies, it is unclear whether coastal invertebrates from the Seychelles harbor any cryptic diversity. In this study, we examined patterns of genetic diversity and isolation within Ligia isopods across the Seychelles archipelago by characterizing individuals from locations across both inner and outer islands of the Seychelles using mitochondrial and nuclear markers. We report the presence of highly divergent lineages of independent origin. At Aldabra Atoll, we uncovered a lineage closely related to the Ligia vitiensis cryptic species complex. Within the inner islands of Cousine, Silhouette, and Mahé we detected the presence of two moderately divergent and geographically disjunct lineages most closely related to Ligia dentipes . Our findings suggest that the Seychelles may harbor at least three novel species of Ligia in need of description and that these species may have originated independently.
Preprint
Full-text available
The extensive coastlines of South Africa and Namibia extends from the Atlantic to the Indian Ocean and encompass several major biogeographic provinces, each characterized by unique faunal and floral assemblages. Recent biogeographic studies have led to competing biogeographic models of the southern African coastline. This has stimulated phylogeographic work to determine whether the distribution of genetic diversity within coastal invertebrate species match the proposed biogeographic regions. The lack of congruence between studies and the discovery of cryptic diversity indicating the possible existence of cryptic species in coastal isopods in the region underscore the need for additional phylogeographic research in southern Africa, particularly for organisms that have been shown to both harbor cryptic diversity and to retain signatures of past geological and oceanographic processes in their phylogeographic patterns. Isopods in the genus Ligia exhibit several biological traits that suggest they may be informative on phylogeographic patterns. They inhabit patchy rocky beaches, are direct developers, avoid the open water, and exhibit several biological traits that severely constrain their dispersal potential (e.g. poor desiccation resistance). These traits are thought to lead to long term isolation of populations, the retention of geological and oceanographic signatures in phylogeographic patterns of Ligia , and the presence of cryptic lineages. In this study, we used mitochondrial and nuclear markers to characterize Ligia collected in 18 localities across Namibia to the KwaZulu-Natal region of South Africa. We report the presence of cryptic lineages within Ligia species in the region, as well as distributional patterns that differ from those reported from other coastal taxa, but that broadly matches a widely used biogeographic model for the region.
Preprint
Full-text available
The native ranges and invasion histories of many marine species remain elusive due to a dynamic dispersal process via marine vessels. Molecular markers can aid in identification of native ranges and elucidation of the introduction and establishment process. The supralittoral isopod Ligia exotica has a wide tropical and subtropical distribution, frequently found in harbors and ports around the globe. This isopod is hypothesized to have an Old World origin, from where it was unintentionally introduced to other regions via wooden ships and solid ballast. Its native range, however, remains uncertain. Recent molecular studies uncovered the presence of two highly divergent lineages of L. exotica in East Asia, and suggest this region is a source of nonindigenous populations. In this study, we conducted phylogenetic analyses (Maximum Likelihood and Bayesian) of a fragment of the mitochondrial 16S ribosomal (r)DNA gene using a dataset of this isopod that greatly expanded previous representation from Asia and putative nonindigenous populations around the world. For a subset of samples, sequences of 12S rDNA and NaK were also obtained and analyzed together with 16S rDNA. Our results show that L. exotica is comprised of several highly divergent genetic lineages, which probably represent different species. Most of the 16S rDNA genetic diversity (48 haplotypes) was detected in East and Southeast Asia. Only seven haplotypes were observed outside this region (in the Americas, Hawai’i, Africa and India), which were identical or closely related to haplotypes found in East and Southeast Asia. Phylogenetic patterns indicate the L. exotica clade originated and diversified in East and Southeast Asia, and only members of one of the divergent lineages have spread out of this region, recently, suggesting the potential to become invasive is phylogenetically constrained.
Preprint
Full-text available
The native ranges and invasion histories of many marine species remain elusive due to a dynamic dispersal process via marine vessels. Molecular markers can aid in identification of native ranges and elucidation of the introduction and establishment process. The supralittoral isopod Ligia exotica has a wide tropical and subtropical distribution, frequently found in harbors and ports around the globe. This isopod is hypothesized to have an Old World origin, from where it was unintentionally introduced to other regions via wooden ships and solid ballast. Its native range, however, remains uncertain. Recent molecular studies uncovered the presence of two highly divergent lineages of L. exotica in East Asia, and suggest this region is a source of nonindigenous populations. In this study, we conducted phylogenetic analyses (Maximum Likelihood and Bayesian) of a fragment of the mitochondrial 16S ribosomal (r)DNA gene using a dataset of this isopod that greatly expanded previous representation from Asia and putative nonindigenous populations around the world. For a subset of samples, sequences of 12S rDNA and NaK were also obtained and analyzed together with 16S rDNA. Our results show that L. exotica is comprised of several highly divergent genetic lineages, which probably represent different species. Most of the 16S rDNA genetic diversity (48 haplotypes) was detected in East and Southeast Asia. Only seven haplotypes were observed outside this region (in the Americas, Hawai’i, Africa and India), which were identical or closely related to haplotypes found in East and Southeast Asia. Phylogenetic patterns indicate the L. exotica clade originated and diversified in East and Southeast Asia, and only members of one of the divergent lineages have spread out of this region, recently, suggesting the potential to become invasive is phylogenetically constrained.
Preprint
Full-text available
Ligia isopods are conspicuous inhabitants of rocky intertidal habitats exhibiting several biological traits that severely limit their dispersal potential. Their presence in patchy habitats and low vagility may lead to long term isolation, allopatric isolation and possible cryptic speciation. Indeed, various species of Ligia have been suggested to represent instead cryptic species complexes. Past studies; however, have largely focused in Eastern Pacific and Atlantic species of Ligia , leaving in doubt whether cryptic diversity occurs in other highly biodiverse areas. The Seychelles consists of 115 islands of different ages and geological origins spread across the western Indian Ocean. They are well known for their rich biodiversity with recent reports of cryptic species in terrestrial Seychellois organisms. Despite these studies, it is unclear whether coastal invertebrates from the Seychelles harbor any cryptic diversity. In this study, we examined patterns of genetic diversity and isolation within Ligia isopods across the Seychelles archipelago by characterizing individuals from locations across both inner and outer islands of the Seychelles using mitochondrial and nuclear markers. We report the presence of highly divergent lineages of independent origin. At Aldabra Atoll, we uncovered a lineage closely related to the Ligia vitiensis cryptic species complex. Within the inner islands of Cousine, Silhouette, and Mahé we detected the presence of two moderately divergent and geographically disjunct lineages most closely related to Ligia dentipes . Our findings suggest that the Seychelles may harbor at least three novel species of Ligia in need of description and that these species may have originated independently.
Article
Full-text available
The phylogenetic relationships among oniscids (Crustacea, Isodopa) remain contradictory despite numerous morphological studies. We have investigated them using molecular data. Partial sequences of the mitochondrial LSU rRNA gene were obtained from 42 species of aquatic and terrestrial crustaceans from 31 genera. This gene provided well-supported information, notwithstanding the high taxonomic level of this study, indicating a useful amount of variation despite the noise due to multiple substitutions. The phylogenetic inferences demonstrated that a) Crinocheta and Synocheta sections are monophyletic and sister-groups, b) Ligiidae and Tylidae representatives are in a basal position compared to other oniscids, c) Helleria brevicornis, the only representative of the Helleriinae subfamily, has undergone different evolution , d) the relationships between aquatic isopods and ancient groups of Oniscidea are not resolved, probably due to fast radiation not discriminated by the molecular phylogeny.
Article
Full-text available
An X-Windows-based graphic user interface is presented which allows the seamless integration of numerous existing biomolecular programs into a single analysis environment. This environment is based on a core multiple sequence editor that is linked to external programs by a user-expandable menu system and is supported on Sun and DEC work stations. There is no limitation to the number of external functions that can be linked to the interface. The length and number of sequences that can be handled are limited only by the size of virtual memory present on the workstation. The sequence data itself is used as the reference point from which analysis is done, and scalable graphic views are supported. It is suggested that future software development utilizing this expandable, user-defined menu system and the I/O linkage of external programs will allow biologists to easily integrate expertise from disparate fields into a single environment.
Article
Amino acid sequence data are available for ribulose biphosphate carboxylase, plastocyanin, cytochrome c, and ferredoxin for a number of angiosperm families. Cladistic analysis of the data, including evaluation of all equally or almost equally parsimonious cladograms, shows that much homoplasy (parallelisms and reversals) is present and that few or no well supported monophyletic groups of families can be demonstrated. In one analysis of nine angiosperm families and 40 variable amino acid positions from three proteins, the most parsimonious cladograms were 151 steps long and contained 63 parallelisms and reversals (consistency index = 0.583). In another analysis of six families and 53 variable amino acid positions from four proteins, the most parsimonious cladogram was 161 steps long and contained 50 parallelisms and reversals (consistency index = 0.689). Single changes in both data matrices could yield most parsimonious cladograms with quite different topologies and without common monophyletic groups. Presently, amino acid sequence data are not comprehensive enough for phylogenetic reconstruction among angiosperms. More informative positions are needed, either from sequencing longer parts of the proteins or from sequencing more proteins from the same taxa.
Article
Practicing phylogenetic systematics as a sophisticated falsification research program provides a basis for claiming increased knowledge of sister species relationships and synapomorphies as evidence for those cladistic propositions. Research in phylogenetic systematics is necessarily cyclic, and the place where the positive shift in understanding occurs is subsequent to discovering the most parsimonious cladogram(s). A priori differential character weighting is inconsistent with seeking the maximally corroborated cladogram (sensu Popper), because weighting adds to background knowledge, the evidence being then less improbable than it would be otherwise. Also, estimating weights from character state frequencies on a cladogram is inconsistent with the view that history is unique. Sophisticated falsification provides the place in the cycle of phylogenetic systematic research where weight of evidence can be evaluated and these inconsistencies do not apply. On balance, phylogenetic systematics appears to achieve greater coherence and generality as a result of focusing on the foundations for claiming increased knowledge and avoiding efforts to differentially weight characters.
Article
In their response to environmental stimuli, terrestrial isopods show various trends that are correlated with their ecology and physiology. With the transition from sea to the littoral zone (Ligia), orientation to light changes from positive to negative. Yet, since these isopods are positively hygrokinetic even at very high humidities, their hygroreaction is of greater significance than their photoreaction. In isopods from mesic habitats (Oniscus, Porcellio, Armadillidium) photoreaction becomes of less significance than in littoral species, until in some species it reverts to positive (Armadillidium). Sometimes the positive photoreaction occurs only at high temperatures (Porcellio), a pattern of behavior correlated with thermoregulation by evaporative cooling. Similarly, in mesic species the response to humidity becomes less significant than in littoral species, resuming importance mainly when the isopods become dehydrated (Armadillidium). Finally, in isopods from xeric habitats in semi-arid and desert regions (Armadillo, Venezillo), photoreaction is strongly negative except in Hemilepistus at lower temperatures. All of these isopods are positively hygrokinetic only at low humidities and are strongly negatively thermoactive, indicating a drop in activity at high temperatures. The photonegative response in these isopods is stronger than the hygroreaction.