Dr Robert B Angus, Emeritus Reader in Entomology
Taxonomy of Coleoptera
My main interest is in the taxonomy of water beetles, especially the genus Helophorus (now in its own family, Helophoridae, but more familiarly placed in the Hydrophilidae). I work mainly on the fauna of the Palaearctic Region, but have done some work on the Nearctic fauna. I am interested in the biological implications of taxonomic distinctions, and in particular the ecological implications of the separation of species which are morphologically very similar to one another. This means that I investigate details of the life histories of the various species, including details of their larvae and egg cocoons, and their geographical distributions. An example of clear life-history differences between similar species is provided by Helophorus kirgisicus Knisch and H. similis Kuwert. H. similis, as is usual in Helophorus, has three larval instars, but in H. kirgisicus there are only two instars, apparently corresponding with the first and third instars of H. similis. This is apparently an adaptation to shorten the time spent as a larva, possibly to minimise the risk of desiccation in this steppe species. For a fuller account, see Angus (1992a).
||Helophorus aspericollis |
One of the features of particular interest in my work is its relevance to studies of climatic change illustrated by Pleistocene (Ice Age) fossil beetles. Species of Helophorus are numerous in Pleistocene fossil assemblages, and, as with almost all beetles of this age, they are identifiable as species living today, but often with modern distributions far removed from the fossil locations. In some cases the separation of very similar (sibling) species is critical to understanding the results of palaeontological investigations. A case in point is the species pair Helophorus brevipalpis Bedel, very common over most of Europe, and H. aspericollis Angus, confined to eastern Siberia and northern Mongolia. Both species occurred in England during the last glaciation, but while H. aspericollis is characteristic of episodes of cold-continental climate, H. brevipalpis was here during the brief warmer interludes.
A productive aspect of my investigations is the use of chromosomes to help to recognise different species. This work stems from my discovery that it is possible to obtain clear karyotypes from mitotic chromosomes in dividing cells of the mid gut crypts of adult insects. I have used the technique on many species of Helophorus, where discoveries include triploid female H. brevipalpis among Spanish material (Angus, 1992 b). The chromosome techniques are being applied to other groups of beetles, and, more recently, to bugs.
Karyotypes of Helophorus brevipalpis. Figs 1 & 2 are from English embryos, while Figs 3 - 5 are from mid gut. Fig 5 is a Spanish triploid female. The scale line represents 5 µm.
Waller MS, Angus RB. (2005) A chromosomal investigation of the west European species of corixa geoffroy (heteroptera: corixidae). Genetica 125: 17-25 [Abstract on PubMed]
Aradottir GI, Angus RB. (2004) A chromosomal analysis of some water beetle species recently transferred from Agabus Leach to Ilybius Erichson, with particular reference to the variation in chromosome number shown by I. montanus Stephens (Coleoptera: Dytiscidae). Hereditas. 140: 185-192 [Abstract on PubMed]
Angus RB, Kemeny CK, Wood EL. (2004) The C-banded karyotypes of the four British species of Notonecta L. (Heteroptera: Notonectidae). Hereditas. 140: 134-138 [Abstract on PubMed]
Angus, R.B., Brown, R.E., & Bryant, L.J. (2000). Chromosomes and identification of the sibling species Pterostichus nigrita (Paykull) and P. rhaeticus Heer (Coleoptera: Carabidae). Systemic Entomology 25: 325-337
Angus, R. B. (1997). Challenges and rewards in the identification of Pleistocene fossil beetles, with the description of a new species of Hydraena Kugelann (Coleoptera: Hydraenidae) from the Hoxnian Interglacial. Quaternary Procedings 5: 5-14
Angus, R. B. (1992a). Insecta, Coleoptera, Hydrophilidae, Helophorinae. Süsswasserfauna von Mitteleuropa 20/10-2. XI + 144 pp. Gustav Fischer Verlag, Stuttgart, Jena, New York
Angus, R. B. (1992b). A chromosomal investigation of Helophorus brevipalpis Bedel (Coleoptera: Hydrophilidae), with triploid Spanish females a possible source of American parthenogenetic material. The Entomologist 111: 56-60