Hermaphroditism in brown shrimp: lessons from field data and modelling |
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Authors: | Marc Hufnagl Axel Temming Andreas Dänhardt |
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Institution: | 1. Institute for Hydrobiology and Fishery Science, Olbersweg 24, 22767, Hamburg, Germany 2. Institute of Avian Research, c/o Research Center Terramare, Schleusenstra?e 1, 26382, Wilhelmshaven, Germany 3. Suerhoper Brunnenweg 13 a, 21244, Buchholz, Germany
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Abstract: | This study was undertaken to further clarify whether the brown shrimp, Crangon crangon (Linnaeus 1758), is a gonochorist, a facultative or an obligate hermaphrodite. Juvenile shrimps were sampled from intertidal
habitats along the German Wadden Sea coast with a push net and from a power plant water inlet to quantify the share of primary
females. Length-based sex ratios were determined for about 27,000 individuals using external characteristics. Observed sex
ratios were mainly female-biased, and also large males occurred regularly in the catch. This indicates that sex at hatch is
not male as would be characteristic for an obligate protandric hermaphrodite and that not all male shrimps change sex. A cohort-based
computer simulation, including sex-specific growth rates, mortality and seasonally varying recruitment, generated sex ratios
comparable to the field. The observed decline in the proportion of males with increasing size can be explained solely by faster
growth of females without involving hermaphroditism. Based on temperature-dependent growth and moult rates as well as length-specific
numbers of eggs per female, the potential egg production of primary and secondary females was modelled, yielding contributions
of secondary females of <1%. Sex change in C. crangon has previously been observed and may be interpreted as an evolutionary relict of this species having evolved in a habitat
characterized by lower population densities, lower predation levels and increased longevity compared to today’s living conditions
in North Sea coastal waters. |
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