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Environ Biol Fish (2011) 92:337349 DOI 10.1007/s10641-011-9844-9
Why protogynous hermaphrodite males are relatively larger than females? Testing growth hypotheses in Mediterranean rainbow wrasse Coris julis (Linnaeus, 1758)
Marta Linde & Miquel Palmer & Josep Als
Received: 27 October 2009 /Accepted: 2 May 2011 /Published online: 25 May 2011 # Springer Science+Business Media B.V. 2011
Abstract Several growth hypotheses have been tested to investigate why males of the sequential hermaphrodite, Mediterranean rainbow wrasse, Coris julis (Linnaeus, 1758), are relatively larger than females of the same age. Individual growth trajectories were estimated to test these hypotheses. A good linear relationship between otolith size and body size was observed (r2=0.71, n=609), thus, past somatic growth of any specific fish can be inferred from the longitudinal data described by the width of annual increments in the otolith. These data were successfully analyzed by a non-linear mixed-effect model (von Bertalanffy growth model) using a Bayesian approach. The results obtained suggest that Mediterranean rainbow wrasse secondary males are relatively larger than females because 1) fish that change sex are already the larger individuals in their age group (specifically those with higher growth rate, ksecondary males=0.199 and kfemales=0.161) and 2) they experience a growth spurt after sex change. The differences in growth observed in this species and in other protogynous hermaphrodites could be related to differences in social organization, which, in turn, are related to differences in the sex change mechanisms.
Keywords Back-calculation . Bayesian approach . Diandric protogyny. Growth curves . Labridae . Sex change
Introduction
Sequential hermaphroditism occurs in a variety of taxa. Fish that are sequential hermaphrodite sexually matures as one sex and change to the opposite sex later in life, either through a male to female sex change (protandry) or a female to male sex change (protogyny). Ghiselin (1969) proposed a model to explain the existence of sequential hermaphroditism, the so-called size advantage model, that has been applied with considerable success (Warner 1988; Charnov and Skuladottir 2000; Linde and Palmer 2008). According to this model, if reproductive potential depends on size (or age), and this potential increases faster for one sex than the other, an organism capable of changing sex could have an advantage over a gonochoristic organism (one not capable of sex change); the hermaphrodite could optimize...