Correlates of sexual dimorphism for dry weight and development time in five species of Drosophila

Authors

  • N. Sharmila Bharathi,

    1. Evolutionary Biology Laboratory, Evolutionary & Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, P. O. Box 6436, Jakkur, Bangalore 560 064, India
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  • N. G. Prasad,

    1. Evolutionary Biology Laboratory, Evolutionary & Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, P. O. Box 6436, Jakkur, Bangalore 560 064, India
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    • *

      Department of Biology, Queen's University, Kingston ON K7L 3N6, Canada.

  • Mallikarjun Shakarad,

    1. Behaviour, Ecology and Evolution Laboratory, Department of Biology, Poornaprajna Institute of Scientific Research, 4, Sadashivanagar, Bangalore 560 080, India
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  • Amitabh Joshi

    Corresponding author
    1. Evolutionary Biology Laboratory, Evolutionary & Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, P. O. Box 6436, Jakkur, Bangalore 560 064, India
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†All correspondence to: A. Joshi. E-mail: ajoshi@jncasr.ac.in

Abstract

Pre-adult development time, dry weight at eclosion, and daily fecundity over the first 10 days of adult life were measured in five species of Drosophila from the melanogaster and immigrans species groups. Overall, the three species of the melanogaster group (D. melanogaster, D. ananassae, D. malerkotliana) developed faster, were lighter at eclosion, and produced more eggs per unit weight at eclosion than the two species of the immigrans group (D. n. nasuta, D. sulfurigaster neonasuta). The degree of sexual dimorphism in dry weight was greater than that in development time, but did not vary significantly among species, and was not correlated with fecundity, contrary to expectations that sexual selection for increased fecundity drives sexual size dimorphism in Drosophila. The degree of dimorphism in development time was significantly correlated with dry weight and fecundity, with lighter species tending to be more dimorphic for development time as well as more fecund, both in absolute terms and in terms of fecundity per unit weight. The results suggest that our understanding of the evolutionary forces maintaining sexual size dimorphism in Drosophila will probably benefit from more detailed studies on the correlates of sexual dimorphism within and among Drosophila species, and on the shape of reaction norms for the degree of sexual dimorphism across different levels of ecologically relevant environmental variables.

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