Perchlorate exposure does not modulate temporal variation of whole-body thyroid and androgen hormone content in threespine stickleback

Abstract

Previously we showed that exposure of threespine stickleback (Gasterosteus aculeatus) to the endocrine disruptor perchlorate results in pronounced structural changes in thyroid and gonad, while surprisingly, whole-body thyroid hormone concentrations remain unaffected. To test for hormone titer variations on a finer scale, we evaluated the interactive effects of time (diel and reproductive season) and perchlorate exposure on whole-body contents of triiodothyronine (T3), thyroxine (T4), and 11-ketotestosterone (11-KT) in captive stickleback. Adult stickleback were exposed to 100ppm perchlorate or control water and sampled at 4-h intervals across the 24-hday and at one time-point (1100h) weekly across the reproductive season (May-July). Neither whole-body T3 nor T4 concentration significantly differed across the day in control or perchlorate treated stickleback. Across the reproductive season, whole-body T3 concentration remained stable while T4 significantly increased. However, neither hormone concentration was significantly affected by perchlorate, verifying our previous studies. The concentration of whole-body 11-KT, a major fish androgen, displayed significant diel variation and also steadily declined across the reproductive season in untreated males; perchlorate exposure did not influence the concentration of 11-KT in either diel or reproductive season schedules. Diel and reproductive season variations in 11-KT content in male stickleback are likely related to reproductive physiology and behavior. The observed increase in T4 content across the reproductive season may be reflective of increased energy investment in reproduction near the end of the life cycle.

Keywords: 11-Ketotestosterone; Diel; Gasterosteus aculeatus; Reproductive season; Thyroid hormone.

Figure 1

Experimental sampling schedule with diel and reproductive season components. Clock icons indicate days with continuous sampling at four hour intervals.

Figure 2

(A-D). Means ± SE for whole-body T₃ concentration in stickleback following chronic exposure to 100 ppm perchlorate or control conditions on Day 1 (A), Day 15 (B), Day 29 (C), and Day 43 (D).

Figure 3

(A-D). Means ± SE for whole-body T₄ concentration in stickleback following chronic exposure to 100 ppm perchlorate or control conditions on Day 1 (A), Day 15 (B), Day 29 (C), and Day 43 (D).

Figure 4

(A-B). Means ± SE for whole-body T₃ (A) and T₄ (B) in stickleback that were chronically exposed to 100 ppm perchlorate or control conditions and sampled at 1100 h across the reproductive season (May-July). Different letters indicate significant differences between groups evaluated by post-hoc Tukey HSD test (p<0.05) following ANOVA.

Figure 5

(A-B). Means ± SE for whole-body 11-KT in male stickleback that were chronically exposed to 100 ppm perchlorate or control conditions at 4 hour intervals throughout Day 29 of the exposure (A) and across the reproductive season (B). Different letters indicate significant differences between groups evaluated by post-hoc Tukey HSD test (p<0.05) following ANOVA.