QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online April 23, 2004
Journal of Experimental Biology 207, 1843-1853 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00954

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Quintana, L. Articles by Macadar, O. Search for Related Content PubMed PubMed Citation Articles by Quintana, L. Articles by Macadar, O.

Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators in Brachyhypopomus pinnicaudatus from a temperate climate

Laura Quintana^1,*, Ana Silva^1,2, Nibia Berois³ and Omar Macadar¹

¹ Depto de Neurofisiología, Instituto de Investigaciones Biológicas Clemente Estable, Unidad Asociada de Facultad de Ciencias–Universidad de la República, Avda, Italia 3318, Montevideo, Uruguay
² Depto de Fisiología, Facultad de Ciencias-Universidad de la República, Montevideo, Uruguay
³ Sección de Biología Celular, Facultad de Ciencias-Universidad de la República, Montevideo, Uruguay

View larger version (98K): [in a new window]   Fig. 1. Germ cell features (A,C,E) and panoramic views of ovaries (B,D,F). (A) Small aggregation of oogonia. Note the large, pale nucleus, single nucleoli and scarce cytoplasm. Scale bar, 10 µm. (B) Ovary in the resting stage from a fish captured in July. Previtellogenic oocytes show a very basophilic cytoplasm and various perinuclear nucleoli. It is possible to observe oocytes in different sizes, some may be in very early stages of vitellogenesis. Scale bar, 50 µm. (C) Oocyte in lipid yolk stage. Note the lipid droplets, the numerous perinuclear nucleoli and the chorion. Scale bar, 50 µm. (D) Ovary in the recovering stage from a fish captured in October. Oocytes are mainly previtellogenic and lipid yolk. Scale bar, 100 µm. (E) Two oocytes in the protein yolk stage. The protein yolk has pushed the lipid droplets to the periphery. The chorions are wide. Note the follicular cells between the oocytes. Scale bar, 50 µm. (F) Mature ovary from a fish captured in December. It is possible to observe oocytes in all stages of development. Fully grown oocytes, others in process of protein yolk deposition, lipid yolk oocytes and previtellogenic oocytes. Scale bar, 100 µm.. The maturing ovary, present in October and November is not shown. (G) Cell-type distribution represented by relative area of four different types of oocytes in ovaries of freshly captured females in June (N=4, non-breeding season), October (N=4), and December (N=4, breeding season). White, previtellogenic oocytes; cross-hatched pattern, lipid yolk oocytes; hatched pattern, protein yolk oocytes; black, fully grown oocytes. Previtellogenic oocytes are present throughout the year. ch, chorion; fg, fully grown oocyte; fc, follicular cells; l, lipid yolk; lo, lipid yolk oocyte; n, nucleolus; og, oogonia; p, protein yolk; po, protein yolk oocyte; pv, previtellogenic oocyte.

View larger version (114K): [in a new window]   Fig. 2. Germ cell features (A,C,E) and panoramic views of testes (B,D,F). (A) Two very early spermatogonia which have peripherical condensed chromatin in their nucleus, a single nucleolus and lightly colored and scarce cytoplasm. On the left hand side of the picture it is possible to observe a cluster of spermatogonias that have probably undergone further mitosis, given their smaller size. Scale bar, 10 µm. (B) Resting testis from a fish captured in July. The tubules are filled with spermatogonia. Scale bar, 20 µm. (C) Cyst of early spermatocytes. Note that the chromatin is in the initial phase of condensation. Scale bar, 10 µm. (D) Recovering testis from a fish captured in October. The tubules are mainly filled with cysts of spermatocytes. It is also possible to observe cysts of spermatids. Scale bar, 20 µm. (E) Spermatids oriented inside the cysts, with their heads towards the periphery and their tails towards the center. On the right hand side there is free sperm in the lumen Scale bar, 10 µm. (F) Mature testis from a fish captured in December. The germinal epithelium has become thinner, cysts of spermatocytes remain but testis is dominated by pools of free sperm in the lumen. Scale bar, 20 µm. The maturing testis, present in October and November is not shown. (G) Relative distribution of three different groups of germ cells in testis of freshly captured males in June (N=4, non-breeding season), October (N=4), and December (N=4, breeding season). White, spermatogonia; hatched pattern, spermatocytes; black, spermatids and sperm. sc, spermatocyte; sd, spermatid; sg, spermatogonia; sp, sperm.

View larger version (19K): [in a new window]   Fig. 3. Annual cycle of physicochemical water parameters and electrical characteristics of Brachyhypopomus pinnicaudatus in the wild. (A) water conductivity, (B) sunlight, (C) water temperature, (D) male electric dimorphism (DP2/DP1), (E) EOD temperature sensitivity index (TS). In A and C, solid and open symbols represent values taken during 1999 and 2000, respectively.

View larger version (11K): [in a new window]   Fig. 4. Temperature sensitivity of EOD waveform. (A) Recordings of EOD waveform at 20°C (black) and after 30 min at 30°C (red) in males with high (left) and low (right) temperature sensitivity. Fish with high temperature sensitivity lose their negative component (P2) at 30°C whereas the amplitude of the negative component is not different at 20° and 30°C in fish with low temperature sensitivity. (B,C) Temperature sensitivity is inversely correlated to gonadal stages of maturity. Stage 1, regressing/resting; stage 2, recovering; stage 3, maturing; stage 4, mature. TS index is high in males and females that present resting gonads and low in fish with mature gonads (Mann–Whitney test, P<0.05; n1=4, n2=4).

View larger version (16K): [in a new window]   Fig. 5. Acclimation induces electrophysiological dimorphism in males of Brachyhypopomus pinnicaudatus. (A) Normalized EOD recordings of a male captured in July before (grey line) and after (black line) acclimation (30 days at 28°C, constant photoperiod and water conductivity). (B) Electrophysiological dimorphism of the male, measured by the duration of P2/duration P1 (DP2/DP1) ratio, of males captured from the natural habitat in August/September and October (grey bars) and males captured in August/September and acclimated for 30 days at 28°C (black bar). The DP2/DP1 ratio was significantly higher after acclimation than those obtained in freshly captured fish (Mann–Whitney test, P<0.05).

View larger version (30K): [in a new window]   Fig. 6. Acclimation induces gonadal maturity in males. The relative number of spermatogonia, spermatocytes and spermatids/sperm present in the testis were assessed in five experimental groups. Jul, fish captured in July; Accl.1, fish captured in July and acclimated for 30 days at 28°C (constant photoperiod and water conductivity); Sept, fish captured in September; Accl.2, Fish captured in September and acclimated for 30 days at 28°C (constant photoperiod and water conductivity); Nov, fish captured in November. Testes of males freshly captured in July have spermatogonia and spermatocytes. After acclimation (grey) the cell profile changed and resembled a mature male, presenting almost 40% of advanced germ cells (spermatids and sperm). The experiment was repeated with a group of fish collected in September, with similar results. White bars, spermatogonia; hatched bars, spermatocytes; black bars, spermatids and sperm.