Tadpole ecomorphological guilds and gut contents as a proxy for diatom diversity
Abstract
Tadpole development significantly depends on the availability of water. Metamorphosis will gradually allow tadpoles to inhabit terrestrial environments (Duellman & Trueb, 1986; Duellman & Trueb, 1994; Harvey Pough, 2007). This causes considerable diversity in functional morphology which, in addition to spatial distribution, ecological drivers, and feeding habits are used to establish ecomorphological guilds (Bower & Piller, 2015; Karr, 1975; Sherratt et al., 2018; Williams, 1972). Tadpoles typically feed on algae, of which a large amount is diatoms. Some diatom species are also specific regarding habitat selection (Necchi, 2016; Round et al., 2007). The aim of this study was to assess diatom diversity in the intestinal content of tadpoles from various ecomorphological guilds sampled from different sites in relation to environmental diatom samples. Ecomorphological guilds applied in this study were adapted from Botha (2013). Three study sites were selected from Ukutula Lodge and Conservation Centre, South Africa and eight from Aliwal North, South Africa. Diatoms were isolated from environmental and tadpole samples collected at each study site. For this purpose, tadpoles were euthanized and subsequently identified. Additionally, samples were collected from tadpoles sampled at Ukutula to test for the presence of a parasitic, chytrid fungus referred to as Batrachochytrium dendrobatidis. After the excision of intestinal tracts, the diatom content was isolated by means of exposure to caustic chemicals. Microscope slides were made using cleaned material and examined under a light microscope. Diatoms were counted and identified. An extensive literature review was conducted to study these diatom’s habitat occurrences in relation to the involved tadpole guild’s feeding habits. Ecomorphological tadpole guilds sampled at Ukutula included Rheophilic, Benthic type 2 (Profundal), Suspension feeder, and Lentic Nektonic. Ecomorphological tadpole guilds sampled at Aliwal North also included Rheophilic, Lentic-nektonic, Lentophytophilic, and Lentic-benthic. None of the attempted cultures from Ukutula demonstrated growth that represented Bd. The relative abundances of diatom species counted in environmental and diatom samples were used to construct a Detrended Correspondence Analyses (DCA) and calculate Shannon’s diversity index, Species Evenness, and Species Richness. The practical and statistically significant differences were also calculated for these samples. One hundred thirty-nine and 178 diatom species were identified from examining the gut content of tadpoles from Ukutula and Aliwal North respectively. Some diatoms were ingested as theoretically expected by tadpoles from the guilds according to existing information on guild-associated feeding habits. Although many seemingly unrelated diatom species were found in the digestive tracts of tadpoles. These species were coincidentally ingested due to resuspension or disturbances in the water
column. There was furthermore no statistical or practical significant difference between diatom samples taken from sites, tadpole species, or guilds. No clusters were discernible between samples and sites when DCA’s were analysed as constructed for Ukutula and Aliwal North. The lack of significant differences between tadpoles and environmental diatom samples implies that tadpoles could be used as a method of diatom sampling in the case of insufficient substrata. It additionally gives rise to opportunities to integrate research pertaining to diatoms and zoology.