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Systematics, Historical Biogeography and
Ecological Phylogenetics
in a clade of water striders1
J. DAMGAARD
Abstract: I hereby review the current knowledge about systematics, historical biogeography and ecolo-
gical phylogenetics in the three principal northern temperate genera of water striders LimnoporusSTÅL
1868, AquariusSCHELLENBERG1800 and GerrisFABRICIUS1794. Most of the discussion is based on com-
parison of a recently published combined analysis tree involving four genetic markers and a morpholo-
gical data set with older phylogenetic trees primarily based on manual cladistic optimization of mor-
phological characters.
Key words: DNA-barcodes, Gerrinae, phylogeography, simultaneous analyses.
Introduction nally, water striders show great variation in
mating strategies, and morphological and
Water striders (Hemiptera-Heteroptera,
behavioral adaptations to accomplish or
Gerromorpha, Gerridae) are familiar inhab-
avoid multiple mating (ANDERSEN 1994,
itants of aquatic habitats throughout the
1996; ARNQVIST 1997). The striking diver-
Worlds temperate, subtropical, and tropical
sity in habitat selection, wing polymorphism
regions comprising approximately 640 de- and mating strategies – along with the prac-
scribed species in 72 genera (ANDERSEN & tically two dimensional habitat, has made
WEIR 2004). Most water striders are found water striders popular objects in studies of
in freshwater habitats, such as rivers, behavior, ecology and evolution (SPENCE&
streams, lakes and ponds, but a few genera ANDERSEN 1994; ROWE et al. 1994; FAIR-
are found in marine – even oceanic – habi- BAIRNet al. 2003; ABEet al. 2004; BERTIN&
tats, and still others have become semi-ter- FAIRBAIRN2005).
restrial (ANDERSEN1982). Being Hemipter-
The late Dr. Andersen (1940-2004)
ous insects, water striders use their rostrum
from the Zoological Museum in Copen-
to immobilize and suck out prey, which of-
hagen, Denmark, was an expert in extant
ten comprises dead or drowning insects
and fossil Gerromorpha, and a pioneer in
caught in the surface film. Water striders are
studies of historical biogeography and eco-
particularly variable with respect to wing re-
logical phylogenetics (e.g. ANDERSEN 1982,
duction, and often display striking patterns
1998; SPENCE& ANDERSEN1994; ANDERSEN
of wing polymorphism (ANDERSEN 1993b, & WEIR 2004). By mapping different traits
1997, 2000). Populations often comprise in question upon a cladogram, he recon-
both long-winged (macropterous) and structed ancestral states and inferred the
short-winged (brachypterous/micropterous) number and sequence of evolutionary tran-
or wingless (apterous) individuals, but the sitions between states. Andersen thereby of-
situation may be even more complicated by fered new hypotheses about the evolution of
macropterous individuals mutilating their water striders that were not purely specula-
wings and/or histolyzing flight muscles, tive but testable, and by dating the events
thereby becoming secondarily flightless. Fi- with fossils he furthermore established a
Denisia 19, zugleich Kataloge
1This paper is dedicated to Dr. Ernst Heiss on the occasion of his 70thbirthday and in recognition of his considera- der OÖ. Landesmuseen
ble contribution to the study of aradids and their allies. Neue Serie 50 (2006), 813–822
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potheses. As a student of Andersen, I was
given the opportunity to participate in stud-
ies of the molecular phylogeny of water
striders, and after working with the subject
for a decade, I find it appropriate to synthe-
size the results and outline some of the prob-
lems that still prevail about the systematics,
ecology, behavior, and distribution of this
fascinating group of insects.
Phylogeny
Until quite recently, Limnoporus,Aquar-
ius and Gerris were treated as subgenera of
Gerris, but in a series of papers, ANDERSEN
(1975, 1990, 1993b) and ANDERSEN &
SPENCE (1992) re-established their generic
ranks, and organized their members into
presumed monophyletic subgenera and
species groups. In his most recent checklist
of gerrine water striders, ANDERSEN (1995)
listed six species of Limnoporus, 15 species
and two subspecies of Aquarius, and three
subgenera, 42 species and five subspecies of
Gerris. Today, four new species can be added
to this assemblage: Aquarius liliPOLHEMUS&
POLHEMUS 1994, A. remigoides GALLANT &
FAIRBAIRN 1996, A. philippinensis ZETTEL &
RUIZ 2003, and Gerris kobaishanus LIN-
NAVUORI 1998, and there are furthermore
indications of several yet undescribed
species (ANDERSEN 1990, 1993b; ZIMMER-
MANN & SCHOLL 1993; MURAJI 2001;
DAMGAARD 2005). Andersen never pub-
lished a global phylogenetic analysis for the
three genera, but his most exhaustive analy-
Fig. 1: Phylogenetic relationships among time frame for the evolution of such traits. sis (ANDERSEN1993b), includes 63 morpho-
species, species and subgenera of logical characters scored for two species of
Such hypotheses of course rely heavily on
Limnoporus, Aquariusand Gerrisbased on
Limnoporus, seven species of Aquarius, and
ANDERSEN(1990, 1993b) and ANDERSEN& correct observations and a robust phyloge-
19 species of Gerris. His preferred topology
SPENCE(1992). netic reconstruction, and most studies
from this analysis (ANDERSEN 1993b: Fig.
therefore address a clade comprising the
23), however, was a manual correction of a
three principal northern temperate genera,
strict consensus of two equally parsimonious
LimnoporusSTÅL1868, AquariusSCHELLEN-
trees obtained by a successive approxima-
BERG 1800 and Gerris FABRICIUS 1794. By
tion weighting of 102 trees. Later he manu-
comparing extant and extinct taxa, Ander-
ally expanded and corrected this phyloge-
sen found that members of the three genera
netic reconstruction (e.g. ANDERSEN 1994:
exhibited a strong structural stasis in some
Fig. 2, 1997: Fig. 4) for inferring evolution-
characters, but abundant convergences in ary trends, but the cladograms were never
others, probably due to evolutionary and based on computer-based parsimony analy-
ecological constraints associated with the ses. In order to summarize Andersen´s hy-
life on water surfaces, and realized that mor- potheses of the phylogenetic relationships
phological characters alone would not suf- within and between the three genera, the
fice for providing robust phylogenetic hy- results from ANDERSEN (1990) and SPENCE
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& ANDERSEN (1992) are therefore inferred
onto his preferred tree (Fig. 1).
The phylogenetic hypotheses outlined
above have been tested repeatedly in simul-
taneous analyses of genetic and morpholog-
ical characters (SPERLING et al. 1997;
DAMGAARD et al. 2000; DAMGAARD &
SPERLING 2001; DAMGAARD & COGNATO
2003), and recently DAMGAARD& COGNA-
TO (2005) summarized these studies in a
study of 53 species and five subspecies com-
prising all species of Limnoporusand Aquar-
iusand a dense taxon sampling of Gerrisin-
cluding representatives of all subgenera and
species groups. The character matrix com-
prised 66 morphological characters and
DNA sequence data from the mitochondri-
al protein coding genes for cytochrome c oxi-
dase subunit I+II(COI+II 1349 characters);
the ribosomal gene encoding the large mito-
chondrial ribosomal subunit (16SrRNA 426
characters), and the nuclear protein coding
gene for elongation factor 1 alpha(EF-1α515
characters), adding to a total of 2356 char-
acters. A parsimony analysis of this data set
gave 8 equally parsimonious trees, and Fig. 2
shows a reduced version of the strict con-
sensus tree (DAMGAARD& COGNATO2005:
Fig. 2).
By comparison, the tree based on earlier,
morphological studies (Fig. 1) and the com-
bined analysis tree (Fig. 2) give somewhat
different conclusions about the phylogenet-
ic relationships within and among the three
genera. The most notable differences are (1)
Aquariusis monophyletic in Fig. 1 but poly-
phyletic in Fig. 2 because the A. remigis
Morphological versus Fig. 2: Phylogenetic relationships among
group is sister group to Gerris, and A. chilen-
species, species and subgenera of
sis (BERG 1881) is placed unresolved at the molecular characters Limnoporus, Aquariusand Gerrisbased on
basis of the tree; (2) the Limnoporus canalic- DAMGAARD& COGNATO(2005).
Despite the more exhaustive taxon sam-
ulatus-group from Fig. 1 is paraphyletic in
pling in DAMGAARD & COGNATO (2005)
Fig. 2 because L. canaliculatus(SAY1832) is
compared to earlier studies, all additional
sister species to the L. rufoscutellatus-group
species are nested within species groups al-
and not to L. esakii(MIYAMOTO1958); and
ready represented, and therefore probably
(3) within Gerris, both the “G. marginatus-”
do not contribute much to the overall phy-
and “G. thoracicus-groups” from Fig. 1 are
logenetic resolution. What matter instead is
polyphyletic in Fig. 2, and the G. odonto-
gaster-group is nested more basal within the addition of molecular characters com-
Gerriss.str. prising almost 95 % of the total Partition
Branch Support (PBS) (BAKER & DESALLE
1997), which summarizes nodal support
from each data partition on the simultane-
ous analysis tree. Because the morphological
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Fig. 3: Species-area cladogram for
Aquariusbased on DAMGAARD&
COGNATO(2005).
data comprise less than 3 % of the total With the new phylogenetic relationships
number of characters, it could look as if the several clades are left without convincing
morphological characters are simply morphological synapomorphies. This is most
“swamped“ by the molecular data, but when problematic for clades that have been given
morphological characters were optimized formal names, such as the genus Aquarius
upon the combined analysis tree a posteriori and the subgenus Macrogerris (ANDERSEN
(DAMGAARD & COGNATO 2005: Fig. 3) it 1993a) even though both clades may be di-
became evident that many synapomorphies agnosed on basis of unique combinations of
suggested by earlier studies were still diag- homoplasious characters. ANDERSEN
nostic. An inspection of the homoplastic (1993b) used the relative length of the an-
characters revealed that several of these tennal segments as his character 3 and gave
were poorly defined, or even incorrectly it two states: (1) antennal segments 2+3
scored. As examples are characters in the longer than antennal segment 1 and (2)
shape of the male ventral segments 7 and 8 shorter than antennal segment 1. He used
in Aquarius which ANDERSEN (1990) used the relatively long segment 1 to diagnose
for assigning A. paludum (FABRICIUS 1794) Aquarius, even though MATSUDA (1960)
and A. adelaidis (DOHRN 1860) as sister stated that in A. remigis(SAY1832) and re-
species, and A. distanti(HORVÁTH1899) as lated species, this segment was subequal to
sister species to this clade but, as pointed the remaining antennal segments. By using
out by DAMGAARD & ZETTEL (2003), these the current, incorrect character states,
characters are difficult to score and probably Aquariusis left without synapomorphies but,
functionally related. The color of the prono- by giving a third character state for the A.
tal disc is another poorly defined character, remigis-group (antennal segments 2+3 sube-
which ANDERSEN (1993b) gave only two qual to 1), DAMGAARD& COGNATO(2005)
states, but which DAMGAARD & COGNATO gave new diagnostic states for both Aquarius
(2005) found should either be ignored or and for the A. remigis-group. Whether diag-
broken op into several new states. nostic morphological characters can be
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found for the remaining clades still need to
be investigated. Unique nucleotide substitu-
tions of a <1kb strand of COI, a.k.a. “DNA-
barcodes“, have been used successfully to di-
agnose clades in other groups of organisms
(e.g. HEBERT et al. 2003). Also DAMGAARD
& ZETTEL (2003) found that species of the
A. paludum-group were monophyletic in
their mitochondrial DNA, and that they
each could be diagnosed by unique substitu-
tions. However, in the much denser popula-
tion sampling of the two sibling species
Aquarius najas (DEGEER 1773) and A.
Fig. 4: Neighbor-joining tree showing
cinereus (PUTON 1869), DAMGAARD (2005) genetic distances within and between
showed that these two species were not re- members of the Aquarius najas-group after
ciprocally monophyletic in their mitochon- DAMGAARD(2005).
drial DNA (Fig. 4) Whether this is due to
cryptic species, hybridization, incomplete
lineage sorting, or something else, still needs
to be worked out, but it calls for caution
when trying to identify species via a tree-
building algorithm, especially when based on
a single character system.
The conclusion is that molecular char-
acters have provided abundant information,
thus leading to new and better supported
phylogenetic hypotheses of water strider re-
lationships, and that simultaneous analyses
of molecular and morphological characters
have offered far better phylogenetic esti-
mates than analyses of individual data sets.
However, there are major problems also in
using molecular data sets. First of all it is
very difficult to obtain DNA sequences from
museum material that is more than a few
years old, unless it has been preserved in
strong (96-100 %) ethanol. This is even
more so for single copy nuclear genes, such
as EF-1α, which only exists in two copies
per cell, compared to mitochondrial and/or
ribosomal genes, which exists in hundreds
or perhaps thousands of copies per cell. Al-
though museum material of many species
were available due to the earlier studies, it
preting the results. It is therefore important
has taken long time and involved numerous
to keep a close collaboration with foremost
collaborators all over the World to get the
the traditional morphologically based tax-
taxon sampling used in DAMGAARD& COG-
onomy, in order to evaluate results from mo-
NATO(2005), and additional work is needed
in order to obtain fresh material of the Ger- lecular studies.
risspecies that have not yet been sequenced.
Even though molecular systematics is a
highly promising discipline, it is still in a
premature phase in terms of output, quality,
and homologizing of the data, and in inter-
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Taxonomic consequences species, it is evident that the majority of
taxa is confined to the Palaearctic Region,
Based on the results from DAMGAARD&
and that only a few species groups are re-
COGNATO (2005) Aquarius obviously needs
stricted to the Nearctic Region, or are
to be redescribed and restricted to the A.
shared between the Palaearctic and Nearc-
paludum- and A.conformis-groups and west-
tic Regions. However, the relatively species
ern Palaearctic members of the A. najas-
poor genus Aquarius deserves special atten-
group. In such a revision it will be important
tion because it – according to the new phy-
to determine if A. nebularis (DRAKE &
logenetic relationships – is represented by
HOTTES 1925) should be synonymized with
geographically highly disjunct species in the
A. conformis (UHLER 1878), since the two
Palaearctic, eastern Nearctic, Afrotropical,
species are very much alike both in terms of
Oriental, and Australian regions, including
morphology and molecules (ANDERSEN
several island endemics, such as A. lilifrom
1990; DAMGAARDet al. 2000), and whether
Timor, A. philippinensisfrom the Philippines,
A. najasand A. cinereushave unrecognized
and A. paludum amamiensis from Amami-
sibling species in the Mediterranea as indi-
Oshima and the Ryukyu Islands south of
cated by ZIMMERMANN & SCHOLL (1993)
Japan (Fig. 3). Only a single fossil, A. lunap-
and DAMGAARD (2005). The A. remigis
olaensis(LIN1981) from Miocene Tibet, has
group probably needs to be erected to a new
been assigned to Aquariuswith any certain-
generic level and diagnosed on basis of the
ty, and was even placed in the A. najas-
unique male genitalia and in the relative
group on basis of striking similarities (AN-
length of antennal segments as compared to
Aquarius and Gerris. Also the four species DERSEN1998). If this is true then the present
distribution of the A. najas group in the
currently assigned to this clade need to be
western Palaearctic region is likely to be re-
revised because their taxonomy and exact
lictual. The distribution of the three extant
distributions are poorly known (ANDERSEN
species with A. cinereus in the western
1990; GALLANT & FAIRBAIRN 1996;
DAMGAARDunpublished). Finally, the enig- Mediterranea, A. ventralis (FIEBER 1861) in
the eastern Mediterranea, and A. najas
matic “A. chilensis“ shows a mixture of char-
throughout the western Palaearctic Region
acters that on one side points to the A. na-
jas-group, and on the other side to more (ANDERSEN 1990: Fig. 73) could indicate
speciation in situ, perhaps following isola-
basal members of Gerrinae as originally dis-
tion in different refugia during the Pleis-
cussed by ANDERSEN (1990). Aquarius
tocene glaciations, but this view is contra-
chilensis probably needs to be erected to a
dicted by the deep molecular divergence be-
new, monotypic genus, but is left unresolved
tween A. ventralis and A. najas + A.
until an investigation of gerrine water strid-
cinereus, which suggests a basal divergence
ers have been carried out following the
well before the onset of the glaciations
guidelines laid out by MURAJI& TACHIKAWA
(2000) and DAMGAARDet al.(2005) for the (DAMGAARD 2005) (Fig. 4). The disjunct
superfamily Gerroidea. geographical relationship between the east-
ern Palaearctic A. elongatus (UHLER 1896)
and the eastern Nearctic A. conformis/A.
Historical biogeography
nebularis likewise points to a characteristic
Even though Limnoporus, Aquarius and pattern following habitat fragmentation and
Gerrisare the dominant water strider genera isolation of populations following orogeny
in northern temperate regions, only Limno- and climatic changes on the northern
porus is strictly Holarctic, while the Gerris Hemisphere during the late Miocene
swakopensis-group is found throughout the (DAMGAARD & ZETTEL 2003). However,
Afrotropical region (incl. Madagascar), and such palaeoclimatic events probably can not
Aquarius was – until the possible exclusion solely be used to explain the distribution of
of A. chilensis– considered the only cosmo- the geographically disjunct species in the A.
politan genus of water striders (ANDERSEN paludum-group, since sister species relation-
1982, 1990, 1993b, 1995, DAMGAARD & ships here often are found among geograph-
COGNATO2005). When comparing the dis- ically highly disjunct species. POLHEMUS &
tribution of subgenera, species groups and POLHEMUS (1994) were the first to suggest
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much older divergences since the newly de- loss of flight ability and maintenance of
scribed Timorese A. liliwas not sister species wing polymorphism is undoubtedly a conse-
to the geographically proximate A. fabricii quence of adaptation through natural selec-
ANDERSEN 1990 from northern Australia, tion as first proposed by DARWIN (1872),
but instead to the widespread Oriental A. and is probably somehow linked to the
adelaidis, even though no geographically in- “flight-oogenesis“ syndrome (JOHNSON
termediate populations are known from the 1969) whereby the female divert energy
region. DAMGAARD & ZETTEL (2003) and normally used in wing and wing muscle de-
DAMGAARD& COGNATO(2005) confirmed velopment to the production of more eggs,
the close relationship between A. lili, A. which would increase the female’s fitness
adelaidis and the newly described A. philip- more than the advantages associated with
pinensis from ancient crater lakes in the the ability to fly. Even though a growing
Philippines (ZETTEL & RUIZ 2003), and amount of studies is becoming available, our
found that the Afrotropical A. distanti was knowledge of the frequency and determina-
sister species to this clade instead of the tion of wing morphs in many species is still
trans-Palaearctic A. paludum suggested by highly insufficient. VEPSÄLÄINEN (1974)
ANDERSEN (1990). The relatively small ge- suggested that A. najasprobably has geneti-
netic divergences between A. lili, A. philip- cally determined wing-dimorphism, and
pinensis and A. adelaidis seem to contradict long-winged specimens are certainly rare in
an ancient diversification of this clade, most northern areas, but may be more com-
while the sister group relationship with A. mon in southern latitudes. However,
distantisupport an ancient vicariance event, AHLROTHet al. (1999) were able to induce
probably following the break-up sequence of a high frequency of the long winged morph
the southern super-continent Gondwana. from several apparently monomorphic wing-
less Finnish populations by rearing nymphs
under high temperature and short day-
Ecological phylogenetics
length, thereby simulating more southern
ANDERSEN (1993b) hypothesized that latitudes. It was further noticed that popula-
the ancestor of the three genera was a wing tions from southern Finland gave a higher
dimorphic species, which lived in relatively frequency of the long-winged morph than
stable, lentic water bodies with a high de- northern populations, but also that no long-
gree of seasonal predictability, and that from winged specimens survived during winter.
this ancestral type of ecology, evolution Another particularly well-studied species is
went in two directions: (1) species of some the likewise eastern Palaearctic Gerris tho-
lineages adapted themselves to lotic habi- racicus, which has two long-winged adult
tats, and (2) species of other lineages be- morphs differing in their ability to fly during
came adapted to increasingly unstable lentic the reproductive period: “non-flyers“ (with
habitats (temporary ponds, water-filled flight muscles histolyzed) that live in the
ditches, etc.). Examples of the first category most permanent habitats and “flyers“ (with
were the primarily wingless species belong- functional flight muscles) that are able to
ing to the Aquarius najas and A. remigis colonize new and temporary habitats during
groups, and examples of the second category the breeding season (KAITALA1988, 1991).
were species belonging to the Limnoporus ru-
This altogether indicates that the inter-
foscutellatus-,Gerris thoracicus-,G. lacustris-,
play between genes, development of flight
G. marginatus-, and G. odontogaster-groups.
muscles and wings, and environment is con-
These species are either permanently or sea-
siderably more complicated than previously
sonally wing-dimorphic or monomorphic
believed, and calls for more attention before
long-winged, and the most versatile species
any general evolutionary trends can be re-
were the larger Limnoporusspecies and Ger-
vealed.
ris thoracicusSCHUMMEL1832Andersen fur-
ther inferred, that there were two kinds of In water striders, the most common
short-winged gerrids, probably as the result mating system is “scramble competition
of different mechanisms of morph determi- polygyny (SPENCE& ANDERSEN1994; “Type
nation (genetic versus environmental). The 1 matings“ of ARNQVIST 1997) where the
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male simply lunge at any female within his ics on water striders, and to Dr. Herbert
reach, grasps her thorax with his fore legs, Zettel and Dr. Anthony I. Cognato for con-
and attempts to insert his phallus into her tributing important ideas in recent joint
genital opening. After the copulation prop- projects. Finally I want to thank everybody
er has terminated, males usually exhibit who contributed with specimens of water
post-copulatory guarding, staying in close striders for my studies, and without whom I
contact with the female. Members of the would not have accomplished to get an al-
Aquarius remigis-group are unique among most complete taxon-sampling: P. Ahlroth,
northern temperate water striders in that G. Arnqvist, C. Askenmo, M. Caterino, M.
they stay in genital contact with the female Cherkassova, D. Currie, V. Diaz, H. Dreisig,
after the actual mating has taken place. In D.J. Fairbairn, T. Harada, R. Hauser, K.
other species the male simply rides the fe- Hayashi, J. Juste, F.E. Klausen, P. Kment, G.
males back after copulation, and this post- Koelch, P. Kotlic, D. Kovac, M. Holmen, R.
copulatory guarding may last from several Hosseini, M. Itov, O. Karsholt, J.J. Krupa,
hours to days in Aquarius najas (ARNQVIST H. Levente, P. Magnien, O. Martin, V.
1997). Because superfluous mating is costly Michelsen, L.G. Nersting, E.S. Nielsen, P.
to females (e.g. in terms of increased ener- Nielsen, J. Örnborg, B. Pedersen, B.V. Ped-
getic expenditure, reduced mobility, and in- ersen, X. Sá Pinto, D.A. Polhemus, J.T. Pol-
creased predation risk), females usually re- hemus, R. Preziosi, A.R. Rasmussen, I. Rib-
spond to males by vigorous struggling and era, L. Rowe, R.B. Ruiz, T.J. Simonsen, N.
often succeed in dislodging him. Such a sex- Simov, J. Turcinaviciene, C. Villagra, J. Vil-
ually antagonistic co-evolution has resulted imova, L.J. Wang & C.M. Yang. This study
in the evolution of morphological adapta- was supported by grants from the Danish
tions in males that increase their ability to Natural Science Research Council, the
grasp females efficiently and distinct mor- Carlsberg Foundation, and the Villum Kann
phological adaptations in females that in- Rasmussen Foundation.
crease the efficiency with which females dis-
lodge males during these struggles (ARN-
Zusammenfassung
QVIST & ROWE 2002a, b; ROWE & ARN-
QVIST2002). Die Arbeit gibt einen Überblick über
den aktuellen Kenntnisstand der System-
Even though the phylogeny of
atik, historischen Biogeographie und ökolo-
Limnoporus, Aquarius and Gerris – and
gischen Phylogenetik der drei nordtemper-
therefore the interpretation of their evolu-
aten Wasserläufergattungen Limnoporus
tionary trends – has changed considerably
with the inclusion of new molecular data, STÅL 1868, Aquarius SCHELLENBERG 1800
Andersen and others certainly deserves und Gerris FABRICIUS 1794. In der Diskus-
sion wird ein aktuell publizierter kom-
credits for synthesizing a broad range of in-
binierter Stammbaum aus vier genetischen
dividual observations into testable hypothe-
Markern und einem morphologischen
ses. Whether these hypotheses still hold or
Datenset mit älteren, kladistischen Stamm-
not will, however, have to await both more
bäumen morphologischer Merkmale ver-
studies of ecology, ontogeny, adaptation and
glichen.
selection, as well as a more robust resolution
of gerrine water strider relationships as men-
tioned above.
Acknowledgements
I sincerely want to thank the late Dr.
Nils Møller Andersen for introducing me to
the wonderful world of water striders. I also
want to thank Drs. Felix A. H. Sperling,
John R. Spence, Masahiko Muraji and Shu-
ji Tachikawa for establishing the fundamen-
tal framework for doing molecular systemat-
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ANDERSENN.M. & T.A. WEIR(2004): Australian Wa-
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AHLROTHP., ALATALOR.V., HYVÄRINENE. & J. SUHONEN tification. — Entomonograph Vol. 14, Apollo
(1999): Geographical variation in wing poly- Books, Denmark, 344 pp.
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Address of the Author:
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coevolution in a mating system: Combining Dr. Jakob DAMGAARD
experimental and comparative approaches to Department of Evolutionary Biology,
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