Responses of ovaries and testes of Lytechinus variegatus (Echinodermata : Echinoidea) to dietary administration of estradiol, progesterone and testosterone

In many vertebrates, environmental factors influence gamete differentiation and growth of the mature gonad through alteration of sex steroid productio n or action; however, it is unclear how gamete differentiation and gonadal growth are regulated in echinoids. The purpose of this study was to examine the influence of dietary administration of estradiol (E2), progesterone (P 4), testosterone (T) and finasteride (F, a 5 alpha-reductase inhibitor) on the ovaries and testes of mature Lytechinus variegatus (Lamarck) during gon adal growth. Echinoids were fed a formulated diet supplemented with steroid s or steroids in combination with finasteride for 36 d. The effects of diet ary administration of steroids on L. variegatus were both steroid- and sex- specific. The mean ovary index was 54% greater in individuals fed E2 than f rom individuals fed the control (C) diet (10.0 +/- 1.1 vs 6.5 +/- 0.7, resp ectively; P < 0.05). Individuals fed E2, P4, E2/P4, and P4 in combination w ith F had significantly smaller oocytes (P < 0.005) than individuals fed C. The volume fraction occupied by nutritive phagocytes in ovarian tubules fr om individuals fed E2/P4 or P4 were significantly larger than the volume fr action occupied by nutritive phagocytes from individuals fed C, indicating that E2 and 5 alpha-reduced progestins may promote nutrient allocation to n utritive phagocytes. Although oocytes from the individuals fed T alone were significantly smaller than those fed T in combination with F, oocytes from individuals in both treatments were significantly larger compared to oocyt es from individuals fed C. These data suggest that upon removal of 5 alpha- reduced androgens, T is able to promote an increase in oocyte diameters. In contrast, the mean testis index was 56% greater in individuals fed P4 than in individuals fed C (8.9 +/- 0.6 vs 5.7 +/- 0.9, respectively; P < 0.05); the testis index did not increase in individuals fed P4/F, suggesting that 5 alpha-reduced progestins stimulate testicular growth. Testes growth in t he presence of 5 alpha-reduced progestins was accomplished by significant i ncreases in the volume fraction occupied by nutritive phagocytes and by a s ignificant reduction in the volume fraction occupied by spermatogenic colum ns in testicular tubules. These data further indicate that 5 alpha-reduced progestins (or 5 alpha-reduced androgens) may inhibit spermatogenic column formation. In conclusion, E2 stimulated ovarian growth but inhibited oocyte growth, whereas T had no affect on ovarian growth but promoted oocyte grow th in L. variegatus. We hypothesize that the E2 (or E2 metabolites) and/or 5 alpha-reduced androgens in combination with T regulate oocyte growth in t he echinoid L. variegatus. In addition, 5 alpha-reduced progestins promoted nutrient accumulation in nutritive phagocytes within the ovaries and the t estes. Furthermore, 5 alpha-reduced progestins stimulated growth of the tes tes and inhibited spermatogenic column formation, suggesting that 5 alpha-r educed progestins regulate nutrient accumulation into nutritive phagocytes and spermatogenic column formation in L. variegatus. The differences in est rogen effects between echinoids and asteroids may be related to differences in gonad morphology and, ultimately, the differences in cellular signallin g pathways (paracrine vs endocrine).