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PhD Defence

Evolutionary Developmental Biology of Bitterling Fish

  • W. Yi
Date
Tuesday 15 March 2022
Time
Location
Academy Building
Rapenburg 73
2311 GJ Leiden

Supervisor(s)

  • Prof. M. K. Richardson

Summary:

We developed the bitterling as a unique, well-studied model organism in the area of the evolutionary ecology of brood parasitism. The bitterling-mussel relationship, interspecific mussel host preference, and mussel gill structure are studied in detail, to help understand the developmental adaptation of bitterling embryos in response to their mussel hosts. Our complete stage series of the bitterling species R. ocellatus is a new, character-based systems that are compatible with the widely-used zebrafish staging system. With time-lapse video, we demonstrated the dynamic processes of hatching moment of the rosy bitterling in real time, which indicates the hatching process is mechanical rather than enzymatic. I also described the neuroanatomy of bitterling for the first time, filling the gaps in the previous embryonic research in various bitterling taxa. Combined with the molecular analysis of brain early development, brain development in the rosy bitterling is compared with that in the zebrafish D. rerio. The comparison indicated evolutionary adaptations related to the bitterling's brood parasitic lifestyle. We identified developmental delays in retinal pigmentation and pectoral fin development in the rosy bitterling compared to the zebrafish. The morphogenesis of the semicircular canals, the separation of the lagena from the sacculolagenar pouch and the formation of the asteriscus otolith are all pre-displaced in bitterling development. This predisplacement may be related to embryonic development in a dark environment where hearing is more useful than vision. This in turn would also explain why visual developent appears to be delayed in the bitterling. We studied the morphogenetic process of blastokinesis in the bitterling embryo, and its possible relation to brood parasitism. We focused on early pre-hatching development and the hatching event of the rosy bitterling. We profiled the expression of developmental regulatory genes fgf8a, msx3, krt8 and ctslb by whole-mount in situ hybridization (WISH). We visualized morphogenetic movements during gastrulation and neurulation, and the process of body elongation during somitogenesis. We concluded that blastokinesis in the rosy bitterling is functional because it provides optimal positioning of the post-hatching embryo in the gill space of the host mussel. More generally, our study provides an example of variation in yolk shape and egg size consistent with the concept of developmental penetrance of adaptations on later stages.

PhD dissertations

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