Facultative sex change in the brown shrimp Crangon crangon L.

Project proposed by Dr Chiara Benvenuto, School of Environment & Life Sciences

One of the most striking and under-investigated phenomena in the evolution of mating systems in animals is sequential hermaphroditism, more commonly referred to as sex change or sex reversal. As the name suggest, sequential hermaphrodites change their sex during their life: individuals reproduce initially as males and then change to females (protandrous hermaphrodites) or vice versa (protogynous hermaphrodites). Sex change has been reported in numerous plants, invertebrates and fishes.

Sex change has intrigued evolutionary biologists for decades. Several studies have investigated the proximate causes of sex change, i.e., the genetic, neurological, physiological, endocrinological, behavioural and social control of sex determination and sexual lability. Some of these mechanisms have been elucidated, but not all. Moreover, we are still lacking a good understanding of the ultimate, adaptive causes of sex change. Many theoretical models have been proposed, mainly based on sexual allocation theories and the differential advantage of body size on the reproductive success of each sex: sex changers should increase their fitness becoming large males (in protogyny) or large females (in protandry), as proposed initially by Ghiselin in 1969. Nevertheless, field and laboratory studies are still challenging for many species.

Among invertebrates, sequential hermaphroditism is common in crustaceans. Crustaceans can be easily observed in the field and reared and manipulated under laboratory conditions. The brown shrimp Crangon crangon L. (Decapoda, Caridea) is an interesting candidate for studies of sex reversal. Its sexual mode of reproduction is still debated, being described as gonochoristic (fixed separate sexes), but also as obligate protandric (male to female sex change) or facultative protandric (some but not all individuals change sex). This may suggest a degree of sexual plasticity that can be investigated in different populations, under different environmental conditions.

This project will involve:

• Field sampling of C. crangon in the UK and in the Mediterranean;
• Analysis of sex ratios of natural populations;
• Rearing shrimps in aquaria;
• Use of morphological, morphometric and histological tools to assess sex reversal;
• Manipulative laboratory experiments in aquaria (changing density, sex ratio, etc…) to evaluate changes in the rate of sex reversal;
• Use of the empirical data collected to model sex change in this system.

The brown shrimp is abundant in shallow coastal and estuarine waters. It is a key species with a major role in ecosystem functioning. It is also commercially valuable. The importance of crustaceans as model organisms in the study of evolutionary questions has often been underlined. Few studies so far have attempted a targeted and empirical investigation on sex change in a sexually plastic species. This project can help us to gather new perspectives and a better understanding of the adaptive causes of sex change, coupling field studies, manipulative lab experiments and ecological modelling in a common species, easily reared in aquaria. Moreover, a better knowledge of the life cycle, behavioural ecology and mating strategies of a commercially exploited species can bring valuable insights for conservation and management in marine areas.

For further information, please contact: C.Benvenuto@salford.ac.uk

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