Michelle Anne Bernabe Diano’s research while affiliated with Mindanao State University – Iligan Institute of Technology and other places

Dalan L, Tañan V, Diano MA, Demayo C, Tabelin M, Sumaya NH. 2024. Life history traits of the gastropod-associated bacterivorous nematode Caenorhabditis brenneri (Nematoda: Rhabditida). Biodiversitas 25: 3106-3113. Caenorhabditis species are associated with decaying plant materials and invertebrates such as terrestrial gastropods. Few Caenorhabditis species have been studied regarding their ecology, genetics, development, and essential life history traits (LHT). In this study, we describe the life cycle of a free-living, wild-type, bacterivorous nematode, Caenorhabditis brenneri Sudhaus and Kiontke 2007, associated with the terrestrial slug Philippinella moellendorffi Collinge 1899 and account for the effects of food density and temperature on its population dynamics by employing the hanging drop technique. The bacterial food supply was sourced from the slug cadaver and identified as Alcaligenes faecalis (MT012081). C. brenneri was fed with varying bacterial densities (109 and 5×109 cells mL-1) and incubated at 20 and 25°C. The bacterial food density-temperature interaction was found to have no significant influence on the offspring production of C. brenneri. Moreover, the total fertility rate (TFR) and net reproductive rate (Ro) are higher in 109 cells mL-1 in both temperatures (TFR at 20°C: 139; 25°C: 169 and Ro at 20°C: 134; 25°C: 156). Whereas the alternative generation time (To, T1, T) and population doubling time (PDT) are faster at 25°C in both bacterial densities, the intrinsic rate of natural increase (rm) is faster at lower temperatures (20°C) in both bacterial densities. The average lifespan of C. brenneri is seven days when fed with A. faecalis. Offspring somatic growth (body length and width) was influenced by bacterial food density-temperature interaction with increased length and girth observed in higher bacterial density and temperature in our knowledge. This study is the first attempt to use A. faecalis, a wild-type bacterium from the terrestrial slug P. moellendorffi cadaver, as the bacterial food source for a Caenorhabditis LHT analysis.

Herein, we first report the comprehensive description of the terrestrial slug, Sarasinula plebeia (Gastropoda: Veronicellidae) by employing morphology, morpho-taxometrics and molecular analysis. A rapid survey on terrestrial slug invasive alien species (IAS) was conducted in La Dicha, Malangas, Zamboanga Sibugay, the Philippines. Obtained COI gene sequences shared 100% similarities to S. plebeia from Brazil (JX532107, KM489378), Dominica (KM489500) and Vietnam (KM489367) and further supported using Bayesian analysis thus designated as S. plebeia isolate LDZS. Notably, the first reported S. plebeia in 2013 from Batan island, Batanes, northern Philippines, characterized through COI gene markers (JQ582277, JQ582278, JQ582279) showed 100% sequence similarities to a closely related veronicellid slug, Laevecaulis alte isolates (LC636101, LC636102, LC636103, and LC636104) from Japan. Taken this into account, our S. plebeia LDZS isolated from an agricultural field is the first report in the Philippines with combined diagnostic tools for the taxon.

Gastropod-associated nematodes have been previously studied and documented worldwide, with some species forming host-specific association as obligate parasites of molluscs while others form intermediate and temporary association. Philippinella moellendorffi from Imelda, Zamboanga Sibugay, Philippines, were collected, washed and maintained in the laboratory until death. Cadavers were placed on nutrient agar to allow nematode proliferation. Nematode pure culture was obtained using one gravid female for propagation. Morphology and molecular analyses (18S ribosomal DNA (rDNA) and D2–D3 expansion segments of 28S rDNA) were employed as diagnostic tools in identifying the nematode species isolated from P. moellendorffi. The newly isolated nematode was identified as Caenorhabditis brenneri , thus designated as C. brenneri strain IZSP from the Philippines. This is the first record of C. brenneri isolated from the terrestrial slug P. moellendorffi .

Gastropods are extremely diverse taxa comprising nearly 60,000 species, of which, the giant African land snail, Achatina fulica is a well-known member. It is an invasive species, and it serves as vector and host for several free-living and parasitic nematodes. This makes studies on the diversity of nematodes isolated from gastropods be more emphasized. Studies have been conducted on other Caenorhabditis-gastropod associations such as in the model organism C. elegans, however, less attention is given to other Caenorhabditis species. Through morphological and morpho-taxometrical data, and analysis of the D2-D3 of 28S rDNA and 18S rDNA regions, nematodes found inside a dissected A. fulica cadaver from Kabacan, North Cotabato (7°6’3.076” N, 124°51’68.33” E) in Mindanao, Philippines were identified as Caenorhabditis brenneri. We herein report for the first time C. brenneri from A. fulica. Moreover, to our knowledge, this is also the first report of C. brenneri-gastropod association.