Abstract
Reproductive investment generally involves a trade-off between somatic growth and energy allocation for reproduction. Previous studies have inferred that jumbo squid Dosidicus gigas support growth during maturation through continuous feeding (an “income” source). However, our recent work suggests possible remobilization of soma during maturation (a “capital” source). We used fatty acids as biochemical indicators to investigate energy acquisition and allocation to reproduction for female D. gigas. We compared the fatty acid profiles of the ovary to those of the mantle muscle (slow turnover rate tissue, representing an energy reserve) and the digestive gland (fast turnover rate organ, reflecting recent consumption). For each tissue, the overall fatty acids among maturity stages overlapped and were similar. The changes with maturation in fatty acid composition in the ovary consistently resembled those of the digestive gland, with the similarity of fatty acids in the mantle muscle and the ovary increasing during maturation, indicating some energy reserves were utilized. Additionally, squid maintained body condition during maturation regardless of increasing investment in reproduction and a decline in feeding intensity. Cumulatively, D. gigas adopt a mixed income-capital breeding strategy in that energy for reproduction is mainly derived from direct food intake, but there is limited somatic reserve remobilization.
Highlights
Reproductive investment generally involves a trade-off between somatic growth and energy allocation for reproduction
Twenty-eight fatty acids were found in female D. gigas, of which 19 had relative mean values greater than 0.5% and in total made up 92–98% of total fatty acids (Table 1)
The total fatty acid content was higher for functionally mature animals in all tissues analysed, with the highest values consistently observed in the digestive gland (Supplementary Tables 1–3)
Summary
Reproductive investment generally involves a trade-off between somatic growth and energy allocation for reproduction. The purpleback squid Sthenoteuthis oualaniensis apparently supports reproduction using energy acquired directly from food intake, leading to multiple spawning events and continuous growth before death[4] The former is referred to as a capital breeder, and the latter as an income breeder[8]. The digestive gland is important for digestion and absorption[37,38], and has a fast turnover of dietary fatty acids, reflecting more recent food intake (10–14 days39,40), and is considered a good indicator of nutritional status due to the high lipid concentration[41] Tissues such as the mantle muscle are considered the most important energy reserve, with a slower fatty acid turnover rate, that reflects diet over a longer period of time (~4 weeks or longer[39]). The results of this work will lead to a better understanding of the breeding strategy of D. gigas, and further support the use of fatty acids to study energy allocation to reproduction for oceanic squid and other species
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