The Prawn <i>Macrobrachium vollenhovenii</i> in the Senegal River Basin: Towards Sustainable Restocking of All-Male Populations for Biological Control of Schistosomiasis

<div><p>Early malacological literature suggests that the outbreak of schistosomiasis, a parasitic disease transmitted by aquatic snails, in the Senegal River basin occurred due to ecological changes resulting from the construction of the Diama dam. The common treatment, the drug praziquantel, does not protect from the high risk of re-infection due to human contact with infested water on a daily basis. The construction of the dam interfered with the life cycle of the prawn <i>Macrobrachium vollenhovenii</i> by blocking its access to breeding grounds in the estuary. These prawns were demonstrated to be potential biological control agents, being effective predators of <i>Schistosoma</i>-susceptible snails. Here, we propose a responsible restocking strategy using all-male prawn populations which could provide sustainable disease control. Male prawns reach a larger size and have a lower tendency to migrate than females. We, therefore, expect that periodic restocking of all-male juveniles will decrease the prevalence of schistosomiasis and increase villagers' welfare. In this interdisciplinary study, we examined current prawn abundance along the river basin, complemented with a retrospective questionnaire completed by local fishermen. We revealed the current absence of prawns upriver and thus demonstrated the need for restocking. Since male prawns are suggested to be preferable for bio-control, we laid the molecular foundation for production of all-male <i>M. vollenhovenii</i> through a complete sequencing of the insulin-like androgenic gland-encoding gene (IAG), which is responsible for sexual differentiation in crustaceans. We also conducted bioinformatics and immunohistochemistry analyses to demonstrate the similarity of this sequence to the IAG of another <i>Macrobrachium</i> species in which neo-females are produced and their progeny are 100% males. At least 100 million people at risk of schistosomiasis are residents of areas that experienced water management manipulations. Our suggested non-breeding sustainable model of control—if proven successful—could prevent re-infections and thus prove useful throughout the world.</p></div

Phylogenetic tree of the IAGs.

<p>The tree is based on the CLUSTAL W algorithm of all known IAGs from decapod crustacean species, calculated and presented by MEGA4 <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003060#pntd.0003060-Tamura1" target="_blank">[48]</a>. A <i>C. elegans</i> insulin-like protein serves as an out-group. The numbers on the junctions represent the percentage of attempts, reflecting the specific divergence within 5,000 replicates, while the bar represents the number of amino acid substitutions per site.</p

The quantity of prawns (in kg) caught at different locations in the Senegal River upstream of the Diama Dam during one week of fishing, as compared to numbers before construction of the dam, according to fishermen interviews.

<p>The quantity of prawns (in kg) caught at different locations in the Senegal River upstream of the Diama Dam during one week of fishing, as compared to numbers before construction of the dam, according to fishermen interviews.</p

Demonstration of <i>Mv-IAG</i> transcription in the AG of a sexually mature <i>M. vollenhovenii</i> male.

<p>RT-PCR showed no amplification of this transcript in the ovary (Ov) of a female or in the hepatopancreas (Hepa) of a male. Transcription of <i>M. rosenbergii</i> β-actin (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003060#pntd-0003060-t001" target="_blank">table 1</a>) served as a positive control. A negative control (NC) contained no cDNA template.</p

The <i>M. vollenhovenii IAG</i> gene and its deduced amino acid sequence.

<p>(A) <i>Mv-IAG</i> cDNA sequence and deduced Mv-IAG protein. The amino acids of the signal peptide (encoded by nucleotides 231 to 315) are shown in bold. The putative B and A chains are <u>underlined</u> and putative C peptide is <i>italicized</i>. The predicted arginine C-proteinase cleavage sites are boxed. The stop codon is mark with an asterisk. (B) Linear model of Mv-IAG. The model describes the deduced sequence of the components of prepro-Mv-IAG, the signal peptide, B chain, C peptide and A chain. The mature hormone consists of the B and A chains interlinked by two disulfide bridges; a third disulfide bridge, an intra-chain bridge, is formed within the A chain.</p

Monthly distribution of <i>M. vollenhovenii</i> catches in the Senegal River.

<p>(A) Total catch of 631 prawns around Diama Dam during 10 months between September, 2012 and August, 2013. (B) Comparisons between male and female average sizes and an average of the largest three specimens in each group. Bars represent SEM.</p

Project locations.

<p>Map of the Diama Dam area. (A) The Diama Dam (marked with a black arrow). The area in which the prawns were caught is marked “Fisherman's location”. Map of the Senegal River basin. (B). The areas of the survey are marked with stars; black stars represent interview locations while white stars represent trapping locations. Grey stars denote sites where both a trap was placed and an interview was conducted. (C) Map of Africa. The natural distribution area of <i>M. vollenhovenii</i> along the west coast of Africa is marked in gray.</p

Multiple-sequence alignment of Mv-IAG with four IAGs of representative decapods from different groups (prawn, shrimp, crayfish and crab).

<p>Shown are Mr-IAG from <i>M. rosenbergii</i> (freshwater prawn), Pp-IAG from <i>Portunu spelagicus</i> (crab), Cq-IAG from <i>Cherax quadricarinatus</i> (crayfish) and Fc-IAG from <i>Fenneropenaeus chinensis</i> (marine shrimp). The sequences were aligned using the CLUSTAL W algorithm. The degree of conservation is presented by the dots under the columns. One dot represents less conserved than two dots, while an asterisk indicates identity. The most conserved feature is the backbone consisting of six cysteine residues (boxed) which gives rise to disulfide bridges (lines connecting the boxes).</p

Immunohistochemical localization of Mv-IAG.

<p>The top pictures (A, B) show sections incubated with anti-<i>Mr-IAG</i> anti-serum, while the bottom pictures (C, D) portray controls incubated only with normal rabbit serum. The AG nuclei are stained blue with DAPI (B, D). A specific signal (stained red with Cy³) appears only in the cytoplasm of the treated AG cells (A, top left). No specific signal appears in the negative control sections incubated only with normal rabbit serum (C).</p

Gene Bank accession numbers.

<p>Gene Bank accession numbers.</p