A massive invasion of the Neotropical calanoid copepod Arctodiaptomus dorsalis (Marsh, 1907) has been taking place in the Philippines since at least 1993. This copepod’s fecundity is known to depend on food concentration, increasing temperature appears to have detrimental effects on its hatching success and survivorship, but parameters that are truly predictive of the successful integration and propagation of this species in particular bodies of water have not yet been identified. We conducted a spatial analysis of morphometric features and reproductive capacity, the latter proxied by clutch size (CS), of different populations of A. dorsalis inhabiting 11 tropical lakes in the Philippines. Correlations between either morphometry or CS and selected water quality parameters were investigated based on collections and measurements made from December 2018 to April 2019. Means of morphometric measurements differed significantly (P < 0.001) among the populations of A. dorsalis in all lakes. Total length (TL) of adult males, TL of non-ovigerous adult females, and CS of ovigerous females all showed significant (P < 0.001) inverse correlations with lake depth, accounting for about 30% of the observed variability among lakes (r = –0.55, –0.55, and –0.58, respectively). Shallow lakes, which are more homogenous in terms of nutrient distribution throughout the water column, thus provide a more suitable habitat than deep lakes for A. dorsalis and provides a partial explanation of the widespread occurrence and abundance of the species in the shallower, more eutrophic lakes in the Philippines.
Arctodiaptomus dorsalis has been reported in the Philippines as an invasive species, which originated from Central America. Apart from its wide distribution in the United States and Central America, it is now widely distributed in many lakes in the Philippine islands, such as Luzon Island and southwestern Mindanao, making it an ideal specimen for studies on population dynamics and population genetics. Recently, new techniques have been emerging as important zooplankton monitoring tools, such as metabarcoding and the use of environmental DNA/environmental RNA. However, these would only be useful if good-quality reference DNA sequences are available before utilizing these techniques. This study sequenced the nearly complete nuclear ribosomal DNA (nrDNA) of A. dorsalis from 202 individuals from Lake Taal, Batangas. The total length was 5887 bp, which includes the partial 18S sequences, and the complete 5.8S, ITS and 28S sequences with an organization that is typical for any eukaryotic organism. This is the first record of a nearly complete nrDNA sequence for freshwater calanoid copepods and is considered an important stepping stone for further molecular studies in freshwater Copepoda.
The genus Pseudodiaptomus is represented by 19 species in Philippine coastal waters. Of all these species found in the Philippines, P. brehmi Kiefer, 1938 is the only known truly freshwater pseudodiaptomid endemic to this country, which was originally described from Lake Naujan, Mindoro Island. After numerous attempts to find it in its type locality, we concluded that the former is no longer extant in this lake and has now been displaced by the invasive Neotropical calanoid Arctodiaptomus dorsalis (Marsh, 1907). Sampling in Lake Taal, on the nearby island of Luzon, resulted in the surprise discovery of P. brehmi populations coexisting with A. dorsalis. This rediscovery of P. brehmi in Lake Taal and its absence from its type locality, necessitate this report as well as the species’ morphological redescription.
The original description of Diaptomus vexillifer Brehm, 1933,
endemic to Lake Danao (Leyte Island), was elementary and lacking taxonomically
satisfactory characters. In this paper, we redescribe the Philippine-endemic
genus Filipinodiaptomus Lai, Mamaril Sr. & Fernando, 1979
and the species D. vexillifer collected from its type locality,
using light and scanning electron microscopy and an analysis of the mtCOI gene
and the ITS of the nuclear 18S operon. We found that D.
vexillifer is the second species under this endemic genus. A
neotype and paraneotypes are hereby designated. Also a detailed morphological
comparison is made between Filipinodiaptomus vexillifer (Brehm,
1933) comb. nov. and Filipinodiaptomus insulanus (Wright,
1928). Their taxonomic characters, interspecies relationship, and biogeography
are likewise discussed.
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