IJP - Co-introduction of Dolicirroplectanum lacustre, a monogenean gill parasite of the invasive Nile perch Lates niloticus: Intraspecific diversification and mitonuclear discordance in native versus introduced areas
General: We examined the intra-specific diversification of Dolicirroplectanum lacustre from L. niloticus in Lake Albert (native range) and Lake Victoria (introduced range) by assessing morphological and genetic differentiation, and microhabitat preference. Hypotheses: We hypothesise that: (1) a founder effect had taken place in Lake Victoria. Hence, we expect reduced genetic and morphological diversity within D. lacustre in its introduced range in comparison with its native population in Lake Albert; (2) we expect high phenotypic variation and low genetic differentiation in Lake Albert, as supported by the presence of distinct morphotypes in earlier studies (Kmentová et al., 2020a; Thurston and Paperna, 1969); (3) there has been a niche shift among the populations in Lake Albert that resulted in differential gill microhabitat preferences which led to morphological changes of D. lacustre, producing an (imperfect) reproductive barrier between the morphotypes. Results and interpretation: We found that D. lacustre displays high morphological variability within and between African freshwaters, with two morphotypes identified. The single shared morphotype between Lake Albert and Lake Victoria displayed similar levels of haplotype and nucleotide diversity. Mitonuclear discordance within the morphotypes of D. lacustre indicates an incomplete reproductive barrier between the morphotypes. The diversification in the mitochondrial gene portion is directly linked with the morphotypes, while the nuclear gene portions indicate conspecificity. Based on our results, we reported reduced genetic and morphological diversity, potentially being a result of a founder effect in Lake Victoria. Data collection: The pairs of gills from 12 specimens of Lates niloticus (5 specimens from Lake Albert, 7 specimens from Lake Victoria) were dissected and preserved in ethanol (99% EtOH). The gills were examined using a Leica EZ4 stereomicroscope. Monogenean gill parasites were extracted, individuals were cut in three parts with the posterior and anterior parts mounted on slides (Hoyer’s medium as fixative) for morphological characterisation, the central part was preserved in ethanol (99% EtOH) for genetic analyses. The microhabitat on the gill was recorded by subdivision of each gill arch into nine microhabitats. Data collection protocols explained in the section 'Steps to reproduce'. Data analysis: The R Script describes the workflow for the morphometric analyses, and the microhabitat description (data files provided).
Steps to reproduce
A total of 20 measurements of the hard parts (haptor, MCO), body size and distances between the two pairs of eyespots were obtained from 71 specimens at a magnification of 1000x with differential interference contrast on a Leica DM2500 optical microscope (S1). Whole genomic DNA was successfully extracted from 64 monogenean parasite individuals. Sequences of a portion of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene, and nuclear gene portions from the small and large ribosomal subunit gene (18S rDNA and 28S rDNA) and internal transcriber spacer 1 (ITS-1) were obtained following PCR. Purified PCR products were sent out for Sanger sequencing. The acquired sequences for each marker were visually inspected and trimmed using the software Geneious v2021.1.1. Sequences were aligned with previously published sequences of D. lacustre using MUSCLE under default settings (S2).