Insights on the connectivity, genetic diversity, and population structure of Arctodiaptomus dorsalis (Marsh, 1907) (Copepoda: Calanoida: Diaptomidae) in the Philippines

The freshwater calanoid copepod Arctodiaptomus dorsalis (Marsh, 1907) was first recorded from the Philippines in 2001 in Laguna de BayThe copepod gained the status of “invasive species” in 2021 due to its presence in 23 of 32 surveyed Philippine lakes and rivers. Genomic DNA was extracted from 107 individuals of A. dorsalis, representing seven populations on the island of Luzon to gather information on the population structure, genetic connectivity, and range expansion of the species.. A 720-bp fragment of the nuclear ITS1 and ITS2 spacers was used to analyze the genetic structure of the populations. High haplotype diversity (Hd = 0.7951), low nucleotide diversity (π = 0.0024), and low genetic distance between populations indicate high levels of gene flow and low levels of isolation. Six of the 12 haplotypes were unique to particular sites, but the three shared haplotypes suggest panmixia among populations. Tajima’s D (D = 0.4945) and Fu’s F (F = -2.8950) suggest a recent increase in population size following a bottleneck. This may have occurred as the result of the copepod’s suspected initial introduction into the Philippines after 1905 via the trade in ornamental aquarium fish, eventually followed by its expansion into nearby inland waters through one or more aquaculture-mediated introduction events. Laguna de Bay’s role since 1972 as the main source of tilapia fingerlings (Oreochromis niloticus (Linnaeus, 1758)) for release into various Philippine lakes provides circumstantial support for this scenario.