Q.-T. Jo, H. Laufer, W.J. Biggers, H.S. Kang
Abstract:
To stimulate reproduction of Crustacea that are difficult to reproduce, eystalk ablation or X-organ sinus gland removal is commonly utilized in commercially important species such as shrimp. We have investigated the effect of unilateral and bilateral eyestalk ablation on methyl farnesoate (MF) production by mandibular organs (MOs) and effects on vitellogenesis of female Libinia emarginata, as a useful model since these animals are in a terminal molt, and are devoid of a functional Y-organ.
Non-reproductive, overwintering female spider crabs, Libinia emarginata, were induced to be reproductive by feeding and increasing the holding temperature to stimulate the endocrine system to reproductive maturation. In addition, we removed X-organ sinus glands, by eyestalk ablation, either unilaterally (UA) or bilaterally (BA) to further stimulate methyl farnesoate (MF) synthesis by MOs. Endogenous MF in the hemolymph was purified and quantified by means of HPLC and in some casees by GC/MS. Oocyte growth and egg quality were studied simultaneously to determine how thay were related to MF levels found during vitellogenesis.
The initial MF concentration in unablated controls was low, 0.31 ng/ml of hemolymph, and increased to about 1 ng/ml by 2 weeks remaining at about that level for the remainder of the experiment. Eystalk ablation significantly stimulated MF concentrations by week 1 to nearly 2- and 3.5 ng/ml in the UA and BA animals, respectively (p<0.01). Oocytes appeared to respond to increased MF levels, oocyte growth was initiated from the point at which MF increased (p<0.01). Thereafter, growth continued, with initial elevations of MF in a concentration-dependent manner (p<0.01). The gonad-somatic index (GSI=gonad weight/body weight x 100) of controls at the start was about 1.5 and increased to 6.5 by week 4. Mature oocytes were reached at a GSI around 7. The times the crabs had mature oocytes were at week 2 in BA, week 3 in UA, and later than week 4 in controls. After maturation, oocytes started to degrade in some ablated animals, particularly in the bilaterally ablated ones where the highest MF concentrations were observed.
These data indicate that MF elevations are required for stimulating oocyte growth and vitellogenesis of Crustacea. MF appears to accelerate gonad development, during the vitellogenic process, but may be deleterious at high concentrations.
These results have significant and important application and implications for aquaculture.
(The research was supported in part by the Sea Grant College Program NOAA).
(Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06268, USA)