Halobates - Oceanic Insects
Phylogeny and Evolution
Ó Copyright, N. M. Andersen & Zoological Museum, University of
There has been much speculation about the origin and evolution of sea skaters, particularly how, when and where the oceanic species achieved their unique way of life. In his monographic revision of Halobates, Herring (1961) recognized several species groups and depicted relationships between them in a "phylogenetic diagram". However, some of these groups were explicitly based on "primitive" (plesiomorphic) characters and may therefore not be monophyletic in the strict sense. Herring grouped the five open-ocean species together, implying that the oceanic way of life only have arisen once within Halobates.
Andersen (1991) presented the first attempt to reconstruct the phylogeny of Halobates using cladistic methods applied to a suite of morphological characters, with emphasis on male and female genital structures. Until recently, the sister group of Halobates was thought to be the likewise marine genus Asclepios (with three species in South and East Asia). However, the recently described, limnic halobatine Austrobates rivularis Andersen & Weir (1994a) from northern Australia, has proven to be even more closely related to Halobates. All three genera constitute the tribe Halobatini. The other halobatine tribe, Metrocorini, comprises about 100 species living in lotic freshwater habitats throughout the Afrotropical and Oriental regions.
recently, Damgaard et al. (2000) tested Andersen's (1991) phylogeny of Halobates and allied taxa by comparing it with a phylogeny based on
sequence data obtained from the mitochondrial gene COI. The molecular and
morphological data sets were also combined in a single “total evidence”
analysis. The resulting phylogeny offers alternative hypotheses about the
evolution of the marine way of life in Halobates,
in particular the oceanic habit of some species.
The COI mtDNA sequence data support the monophyly of a group composed by the oceanic species Halobates sobrinus, H. splendens, and H. micans, the relationship between the two latter species also being supported by evidence from translated amino acid sequences. Another well supported group is composed by the oceanic species H. germanus and H. sericeus, and the coastal species H. hayanus. Finally, the molecular data strongly support the hypothesis proposed by Andersen (1991), that H. flaviventris (and its sibling species H. hawaiiensis) is more closely related to some open ocean species than to other nearshore Halobates.
Establishing a reliable phylogeny for sea skaters helps answer important questions about the evolution of sea skaters and, in particular, of the oceanic way of life in some species. We believe that a phylogenetic reconstruction based on both molecular and morphological data is reliable enough to justifies such generalisations. The phylogeny (above) supports the scenario proposed by Andersen (1991) and Andersen & Weir (1994a) in which ancestral Halobatini lived in both limnic and marine habitats. Asclepios adopted a preference for coastal marine habitats whereas Austrobates and Halobates evolved from their euryhaline ancestors into species preferring only limnic and marine habitats, respectively.
The oceanic way of life in some Halobates species probably evolved at least twice.
First, in the clade composed by the oceanic species H. germanus and H. sericeus
and the nearshore species H. hayanus
(and a few other coastal species). Second, in the clade composed by the oceanic
species H. sobrinus, H. splendens, and
H. micans and the coastal species H.
flaviventris and H. hawaiiensis.
This hypothesis is at least more parsimonious than one
including only one basal transition to the open ocean, and two
independent reversals to coastal habitats.
Andersen NM. 1982. The Semiaquatic Bugs (Hemiptera, Gerromorpha). Phylogeny, adaptations, biogeography, and classification. Entomonograph 3: 1-455.
Andersen NM. 1991. Marine insects: genital morphology, phylogeny and evolution of sea skaters, genus Halobates (Hemiptera: Gerridae). Zool. J. Linn. Soc. 103: 21-60.
Andersen NM, Weir TA. 1994. Austrobates rivularis, gen. et sp. nov., a freshwater relative of Halobates (Hemiptera: Gerridae), with a new perspective on the evolution of sea skaters. Invertebrate Taxonomy 8: 1-15.
Andersen NM, Weir TA. 1994. The sea skaters, genus Halobates Eschscholtz (Hemiptera: Gerridae), of Australia: taxonomy, phylogeny and zoogeography. Invertebrate Taxonomy 8: 861-909.
Damgaard J, Andersen NM, Cheng L, Sperling FAH. 2000. Phylogeny of sea skaters, Halobates Eschscholtz (Hemiptera, Gerridae), based on mtDNA sequence and morphology. Zool. J. Linn. Soc. 130: 511-526.
Herring JL. 1961. The genus Halobates (Hemiptera: Gerridae). Pacific Insects 3(2-3): 223-305.
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Last update: 04 september 2002