Biological Journal of the Linnean Society , 2003, 78 , 149–154. With 1 figure © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78 , 149–154 149 Blackwell Science, LtdOxford, UKBIJBiological Journal of the Linnean Society0024-4066The Linnean Society of London, 2003 78 Original Article SPERM COST IN A HERMAPHRODITE POLYCHAETE WORMG. SELLA and M. C. LORENZI *Corresponding author. E-mail: gabriella.sella@unito.it Increased sperm allocation delays body growth in a protandrous simultaneous hermaphrodite GABRIELLA SELLA* and MARIA CRISTINA LORENZI Dipartimento di Biologia Animale e dell’Uomo, Università di Torino, Italy Received 31 July, 2001; accepted for publication 31 October, 2002 Sex allocation theory for simultaneous hermaphrodites predicts that hermaphrodites have a fixed amount of repro- ductive resources to allocate to both sex functions and that they trade off their allocation to both sexes depending on environmental conditions. Ophryotrocha diadema is a simultaneous hermaphroditic polychaete worm which has a protandrous phase prior to the hermaphroditic phase. The ability of adolescent males to compete with mature her- maphrodites for egg fertilization and the costs of an increase in male expenditure during the protandrous phase were tested in experiments where adolescent males had the possibility to fertilize hermaphrodites’ eggs. Results document that adolescent males were able to compete with hermaphrodites for egg fertilization and caused the hermaphrodites fitness losses of 31.4%. Adolescent males which fertilized hermaphrodites’ eggs had a slower growth rate than males which had no possibility to fertilize eggs. This result indicates that an increased male expenditure is a cost for ado- lescent males and that, during the protandrous phase, resources are allocated to reproduction at the expense of somatic development. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 149–154. ADDITIONAL KEYWORDS: male expenditure – Ophryotrocha diadema – Polychaeta – protandry – simulta- neous hermaphroditism – sperm cost – trade-off. INTRODUCTION Most research on simultaneous hermaphrodite resource allocation is focused on how sex allocation is partitioned between male and female functions: sex allocation theory predicts that hermaphrodites have a fixed amount of reproductive resources to allocate to both sexual functions; moreover, they allocate resources to either sex function based on environmen- tal conditions (Charnov, 1982; Fischer, 1984; Angeloni, Bradbury & Charnov, 2002). Theory predicts that within such a fixed amount, allocation to male func- tion (which may be very costly, Dewsbury, 1982; Greeff & Michiels, 1999; Wedell, Gage & Parker, 2002) increases as mating group size increases. Empirical evidence from Raimondi & Martin (1991) supports this statement: barnacles allocate proportionally more of their reproductive resources to female function when they occur in small mating groups than when they are in large ones. Similar findings were described by Trouvé et al . (1999) and by Schärer & Wedekind (2001) in platyhelminth parasites. Little is known about other life-history trade-offs in hermaphrodites. Reproductive investment may limit other life functions. For example, increased sperm production reduces lifespan in Caenorhabditis ele- gans (Van Voorhies, 1992) and may also lead to a delay of the onset of oogenesis and hence to an increase in minimum generation time and a decrease in population growth (Hodgkin & Barnes, 1991; Barker, 1992). In the colonial ascydian Botryllus schlosseri , a cyclical hermaphrodite with sexual and asexual reproduction, a negative correlation has been demonstrated between asexual growth and sexual investment (Yund, Marcum & Stewart-Sevage, 1997). A trade-off between growth and male reproductive success was also shown in two gonochoric fish species (reviewed by Taborsky, 1994). Evidence of a relationship between reproduction and growth rate in hermaphrodites is lacking. De Visser, Ter Maat & Zonneveld (1994) showed that Downloaded from https://academic.oup.com/biolinnean/article/78/1/149/2639884 by guest on 17 July 2022