Flying for life : wing dimorphism in closely related species of the genus Calathus (Coleoptera: Carabidae)

B. Aukema

Research output: Thesisinternal PhD, WU

Abstract

<p>Factors governing wing dimorphism in ground beetles (Coleoptera: Carabidae) of the <em>Calathus melanocephalus</em> complex have been studied in relation to dispersal by flight. In Western Europe this complex consists of three well-defined species, as was shown by cross-breeding experiments and morphological studies: <em>Calathus cinctus</em> Motschulsky (= <em>C. erythroderus</em> Gemminger & Harold), <em>Calathus melanocephalus</em> (Linnaeus) and <em>Calathus mollis</em> (Marsham). The synonymy of <em>Calathus erythroderus</em> with <em>C.</em><em>cinctus</em> was established. To stabilize the nomenclature of the species involved lectotypes were designated for <em>Carabus melanocephalus</em> Linnaeus and <em>Carabus mollis</em> Marsham. Action undertaken to conserve the specific name of <em>Carabus mollis</em> Marsham was approved by the International Commission on Zoological Nomenclature. Data on morphology, life history and distribution of the three species involved were listed and an identification key is included.<p><em>Calathus cinctus</em> and C. <em>melanocephalus</em> are wing-dimorphic with either strongly reduced wings (short winged or brachypterous) or fully developed wings (long winged or macropterous), whereas <em>C</em> . <em>mollis is</em> always macropterous. Long winged beetles are considered potential flyers, representing the dispersal morph of these species. Populations of C. <em>cinctus</em> and C. <em>melanocephalus</em> showed different proportions of long winged beetles.<p>Wing dimorphism in <em>Calathus cinctus</em> and <em>C</em> . <em>melanocephalus</em> was found to be genetically determined and to be inherited in a simple Mendelian fashion with brachyptery dominant to macroptery. In <em>C.</em><em>cinctus</em> the long winged genotype is always expressed, whereas in <em>C</em> . <em>melanocephalus</em> the expression of the long winged genotype is under environmental control. It was shown that at least temperature and food-supply affected the expression of the long winged genotype in <em>C.</em><em>melanocephalus:</em> more favourable temperatures (i.e. relatively high temperatures) and a higher food-supply resulted in a higher number of long winged beetles compared with less favourable temperatures (i.e. both low and extremely high temperatures) and a lower food-supply.<p>Wing-morph frequencies in populations of wing-dimorphic species may also be affected by differences in fitness between short and long winged beetles. Fecundity (egg production and oviposition period), development time, and growth were studied in this respect.<p>In both <em>Calathus cinctus</em> and <em>C.</em><em>melanocephalus</em> long winged females showed a significantly higher egg production than short winged females, and they also tended to produce eggs during a longer period. Considerable differences in fecundity were observed between the species: the highest egg production was found in <em>Calathus cinctus,</em> a species with a late start and a long oviposition period, and the lowest egg production was found in <em>C</em> . <em>mollis,</em> a species with an early start and a comparably long oviposition period. <em>Calathus melanocephalus</em> showed an egg production intermediate between those of <em>C</em> . <em>cinctus</em> and <em>C.</em><em>mollis,</em> with an early start and a relatively short oviposition period.<p>In all three species development times were generally shorter at higher temperatures and longer at lower temperatures, but in both <em>Calathus cinctus</em> and <em>C</em> . <em>melanocephalus</em> a general relationship between temperature and development time was found neither for wing-morph nor for sex. Development time and growth of long winged genotypes of <em>Calathus melanocephalus</em> were strongly influenced by food- supply: with a higher food-supply shorter development times and higher hatching weights were found. Long winged beetles of both sexes developed faster and were heavier than short winged ones reared under similar conditions, and females weighed more than males.<p>Under laboratory conditions both long winged males and females of the three species studied built up functional flight muscles and were capable of flight. Flight activity in the field, however, was only observed in <em>Calathus cinctus.</em> Building up flight muscles, flight, and subsequent resorption of flight muscles only occurred in the pre- oviposition period, but mating and even ovarian development may occur during the flight period too.<p>The dispersal abilities of the three species studied are supposed to be different because there are large differences in flight potential between the species. In <em>Calathus cinctus</em> and <em>C.</em><em>melanocephalus</em> only part of the individuals is long winged and has flight potential, whereas in <em>Calathus mollis</em> all individuals have this ability. Moreover, in <em>Calathus cinctus</em> the long winged genotype, and so the potential for flight, is always expressed, whereas in <em>C</em> . <em>melanocephalus</em> the expression of the long winged genotype depends on environmental conditions, such as temperature and food- supply, and therefore the flight potential for flight is partly expressed only.<p>Differences in flight potential were clearly associated with differences in life histories and habitat selection. <em>Calathus cinctus</em> occupies temporary habitats, showing a high potential for flight and a high turnover of populations, whereas <em>C</em> . <em>melanocephalus</em> occurs in less temporary habitats, showing a much lower potential for flight and a relatively low turnover of populations. <em>Calathus mollis</em> inhabits coastal dunes and blowing sands, showing a maximum potential for flight, obviously to keep pace with changes in this extreme environment.<p>The higher fecundity of long winged females, closely linked with larger body size and higher weight, is considered to benefit the colonization abilities of the species.<p>The wing-morph determination found in <em>Calathus cinctus</em> and <em>C</em> . <em>melanocephalus</em> fitted the current model, but a trade-off between flightlessness and fecundity was not found. Both flight capability and high fecundity are considered to represent closely linked characters of species adapted to unstable, temporary habitats.<p>Wing dimorphism is supposed to be maintained by a 'balance' between the loss of long winged genotypes by flight activities and the frequency of successful (re)colonizations. In <em>Calathus cinctus</em> both the loss of long winged genotypes and the colonization success is supposed to be high (a short term, opportunistic 'strategy'), whereas in <em>C</em> . <em>melanocephalus</em> both the loss of long winged genotypes and the colonization success is supposed to be low. However, in the latter species the maintenance of wing dimorphism is favoured by the environmental control of the expression of long winged genotypes (a long term, more ensuring 'strategy').
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • van Lenteren, Joop, Promotor
  • den Boer, P.J., Promotor, External person
Award date6 Jun 1995
Place of PublicationS.l.
Publisher
Print ISBNs9789054854074
Publication statusPublished - 1995

Keywords

  • carabidae
  • invertebrates
  • wings
  • polymorphism

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