Gonad examination reveals diandry and baseline DNA methylation in the three sexual phenotypes of the New Zealand spotty wrasse, Notolabrus celidotus
Robertson, H. (2020). Gonad examination reveals diandry and baseline DNA methylation in the three sexual phenotypes of the New Zealand spotty wrasse, Notolabrus celidotus (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/13916
Permanent Research Commons link: https://hdl.handle.net/10289/13916
Understanding reproductive plasticity and how sexual phenotypes arise is of great interest to biology, particularly the form and function of sex changing fish. However, there are gaps regarding detailed descriptions of gonad morphology and structure of the different sexual phenotypes. Furthermore, the role of epigenetic regulation has yet to be applied to these studies. Sexually mature terminal phase (TP) males were significantly larger in length, and weight (214 ± 7.74 mm standard length (SL), 146 ± 16.6 g), than the similar sized sexually mature initial phase (IP) males (169 ± 6.24 mm SL, 67 ± 9.52 g) and sexually mature females (167 ± 3.54 mm SL, 61 ± 4.07 g). There was a large overlap in size distributions with a vast size range in sexually mature males (147 – 240 mm SL, 42 – 221 g) and small sexually mature females (146 – 183 mm, 41 – 82 g). These results suggest small males use female mimicry and overlapping size ranges suggest diandry. Three gonad types were identified, one ovary and two types of testis. Solid testes were more common in IP males than in TP males. It is proposed that the unique and complex shape of the solid testis arises through an evagination process in juvenile males. Hollow testes arise through sex change from female and are more common in TP males. Colour phase not always corresponding to testis type suggests the ability to transition between body colour phenotype according to environmental influences, and two testis types suggest two different developmental pathways to become a male (diandry). Females and one male were identified as juveniles. All sexually mature males had similar testis lobular structure and somatic and germ cell arrangement. The structural arrangement of the solid testis was consistent with primary male testes, and the hollow testis was consistent with secondary male testes. Juvenile males and the existence of primary and secondary testes are associated with diandry in protogynous species. Whole-genome percentage methylation analysis revealed no significant difference in global brain DNA methylation between females (71.4 ± 1.06 %), TP males (72.2 ± 0.5 %) or IP males (75.1 %). Global ovarian methylation (53.7 ± 1.16 %) was significantly lower than both the similarly high global methylation in the IP male testis (82.2 ± 1.39 %) and TP male testis (86.8 ± 0.21 %). Ovaries during spawning season (67.3 ± 1.27 %) had significantly higher global methylation than ovaries outside of spawning season (51.4 ± 0.96 %). Global gonad DNA methylation variations suggest sex-specific differences and seasonal effects on reproduction are under epigenetic control. The results of this study clearly support diandry in N. celidotus and provide insight into the fundamental differences in gonad morphology. Also, the results warrant further investigation into male developmental pathways and the role of epigenetic regulation. These findings provide critical knowledge towards developing the spotty as a model species for sex change research in temperate species.
The University of Waikato
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