Adaptive aspects of bioenergetics in sexual and asexual species of fresh-water triclads

Beveridge, Malcolm C.M. (1981) Adaptive aspects of bioenergetics in sexual and asexual species of fresh-water triclads. PhD thesis, University of Glasgow.

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The effects of temperature and starvation on 3 species of freshwater triclad with contrasting life cycles, distribution and methods of reproduction were investigated, to examine the relative merits of each species' strategy in relation to its environment. The 3 species - Polycelis tenuis (Iijima), Polycelis felina (Dalyell) and Dugesia tigrina (Girard) - were cultured at 5°, 10°, 15° and 20°C, under fed and starved conditions. Food intake, respiration, growth and reproductive rates, were measured for each species under each set of conditions. A study of a population of P. felina was also undertaken to seek information on field conditions. The results from fed triclads show that in general food intake, and growth and respiration rates, increase with temperature. At low temperatures (below 15°C), D. tigrina ingests little food, and growth and respiration rates are much lower than in the 2 other species. Similarly tigrina does not reproduce below 15°C, confirming its thermophilic nature. P. tenuis is more temperature sensitive than P. felina. In P. tenuis, food intake, and growth and respiration rates, reach a maximum at 20°C, whereas they are greatest in P. felina at 15°C. These differences between the 2 species are reflected in the higher Q10 values observed in P. tenuis. During starvation, the exponential rates of degrowth increase with temperature. Except for D. tigrina at 5°, 10° and 15°C, respiration rates are significantly lower in starved than in fed individuals. The respiration rates also increase with temperature, although this is less pronounced in P. felina than in P. tenuis or D. tigrina. In all 3 species, reproduction ceased soon after the onset of starvation. The field study of P. felina identified seasonal changes in temperature and food supply. An examination of potential mortality factors demonstrated that predation was likely to be negligible, and that death was most likely to occur through being washed away. In conclusion, it was suggested that the indigenous asexual reproducer (P. felina) was successful because it was eurytolerant, and because it occurred in streams where biotic stress (i.e. competition and predation) was low. Under such circumstances, the adoption of a low cost method of reproduction such as fission, was argued to be prudent. In contrast, D. tigrina, the immigrant asexual reproducer, could compete successfully with indigenous populations of lake-dwelling triclads such as P. tenuis by growing and reproducing at a very high rate.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Calow, Dr. P.
Date of Award: 1981
Depositing User: Ms Anikó Szilágyi
Unique ID: glathesis:1981-82360
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jul 2021 15:31
Last Modified: 30 Jul 2021 15:31
Thesis DOI: 10.5525/gla.thesis.82360
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