An investigation of sexual reproduction and development in the giant tiger prawn, Penaeus monodon
Creators: name: Ryan, Luke
Publisher: name: University of the Sunshine Coast, Queensland
Year: 2019
Subjects: vitellogenesis
biogenic amines
dopamine
neuropeptides
gene silencing
insulin-like androgenic gland hormone
giant tiger prawn
monosex
decapods
eyestalk ablation
RNA-Seq

description: Penaeid prawn aquaculture is the largest decapod crustacean industry worldwide, with a production of ~2.5 million tonnes/year, of which the tiger prawn Penaeus monodon accounts for 29%. To improve the overall production and therefore revenue in penaeid aquaculture, Research and Development focuses on improving growth rates and the total tonnage produced. The first two result chapters in this thesis focus on improving growth rates in penaeid aquaculture by targeting the fact penaeid female growth is superior to that of males and therefore attempting to develop a commercially viable biotechnology to produce all-female monosex populations. Advancement in our understanding of the androgenic gland (AG), a male-specific endocrine gland in crustaceans, and its secreted insulin-like AG hormone (IAG), has enabled the development of monosex populations in the paleomonid freshwater prawn Macrobrachium rosenbergii. However, despite recent attempts, no successful monosex culture has been reported in any commercially significant marine penaeids. We produced a P. monodon recombinant IAG (rPm-IAG) and tested it in vivo to induce masculinisation, but to no avail. To determine if additional factors were needed together with IAG in inducing masculinisation, we investigated AG specific transcripts using RNA-Seq analysis. We identified several highly expressed AG specific transcripts related to sexual development, previously shown to play a role in testis development and maintenance, and insulin binding. We propose that these AG specific transcripts may be required in addition to IAG in order to induce masculinisation in P. monodon. Following on from this hypothesis, the second results chapter describes the use of AG cells in an attempt to induce masculinisation. After exhaustive attempts in P. monodon we found that injected AG cells did not induce sex change in sexually undifferentiated post larvae. We performed a retrospective comparative analysis that attempts to reconcile these contrasting results, aided by RNA-Seq analysis. We identified penaeid-specific duplication in IAG, as well as duplication in the IAG receptor, unique to P. monodon. These duplications do not occur in paleomonids, suggesting neo-functionalization of IAG and its receptor in penaeids, perhaps hinting that a stricter regulation over sexual differentiation occurs in penaeids which is governed upstream of the AG, at the sex determination cascade. Evidently, other studies indicate that doublesex and mab-3 related transcription factors (Dmrts), the single most conserved factors in the sex determination pathway across animals, infer tighter regulation of IAG expression in a penaeid as compared with M. rosenbergii. Taken together, we conclude that sexual manipulations in penaeids should focus on the sex determination cascade factors, upstream IAG.