Abstract
The relationship between growth and sexual maturation is central to understanding the dynamics of animal populations which exhibit indeterminate growth. In sequential hermaphrodites, which undergo post-maturation sex change, the size and age at which sex change occurs directly affects reproductive output and hence population productivity. However, these traits are often labile, and may be strongly influenced by heterogenous growth and mortality rates. We analysed otolith microstructure of a protandrous (i.e., male-to-female) fish (barramundi Lates calcarifer) to examine growth in relation to individual variation in the timing of sex change. Growth trajectories of individuals with contrasting life histories were examined to elucidate the direction and extent to which growth rate influences the size and age individuals change sex. Then, the relationships between growth rate, maturation schedules and asymptotic maximum size were explored to identify potential trade-offs between age at female maturity and growth potential. Rapid growth was strongly associated with decreased age at sex change, but this was not accompanied by a decrease in size at sex change. Individuals that were caught as large females grew faster than those caught as males, suggesting that fast-growing individuals ultimately obtain higher fitness and therefore make a disproportionate contribution to population fecundity. These results indicate that individual-level variation in maturation schedules is not reflective of trade-offs between growth and reproduction. Rather, we suggest that conditions experienced during the juvenile phase are likely to be a key determinant of post-maturation fitness. These findings highlight the vulnerability of sex-changing species to future environmental change and harvest.
Highlights
The relationship between growth and sexual maturation is central to understanding the dynamics of animal populations which exhibit indeterminate growth
Growth in most fishes is indeterminant and the size and age at sexual maturation is strongly influenced by growth rate and mortality risk[19,20]
We investigated the relationship between age-specific growth rates in barramundi and age-at-sex change and size-at-sex change
Summary
The relationship between growth and sexual maturation is central to understanding the dynamics of animal populations which exhibit indeterminate growth. In sequential hermaphrodites, which undergo post-maturation sex change, the size and age at which sex change occurs directly affects reproductive output and population productivity. These traits are often labile, and may be strongly influenced by heterogenous growth and mortality rates. Individuals that were caught as large females grew faster than those caught as males, suggesting that fast-growing individuals obtain higher fitness and make a disproportionate contribution to population fecundity These results indicate that individual-level variation in maturation schedules is not reflective of trade-offs between growth and reproduction. Such life-history divergences among individuals may be shaped by a wide range of factors, such as differences in individual physiology or morphology, local environmental conditions, and intra-specific social interactions[25,26,27]
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