Anuran tadpoles inhabiting a fluoride-rich stream: diets and morphological indicators

Abstract

We in situ assessed the influence of natural fluoride concentrations in lotic freshwater ecosystems on diet and morphology of Boana cordobae tadpoles. Two streams were sampled in Argentina: Los Vallecitos stream (LF-LV) and Los Cerros Negros stream (HF-CN) with low and high fluoride levels, respectively. We captured tadpoles of B. cordobae in each stream using nets. Body weight (BW), total length (TL) and body condition (BC) of tadpoles was registered. Food items were identified to genus level and assigned to functional traits. Tadpoles showed significant differences in TL between streams, with smaller individuals in HF-CN, while did not show differences in BW and BC. The diet of tadpoles consisted mostly of microalgae. In tadpoles from HF-CN stream the proportion of cyanobacteria was lower than tadpoles from LF-LV. In relation to functional traits, small algae, high profile and colonial algae were more abundant in HF-CN. Algae attached by pads showed a higher proportion in HF-CN diets and stalked algae were more abundant in LF-LV. The differences in TL and diet of tadpoles can be attributed to differences in algal community composition, with genera that are affected by high concentrations of natural fluoride; for example cyanobacteria. The low algal richness registered in HF-CN stream does not affect the physiological state of the tadpoles, possibly because of a higher algal density in HF-CN diets. However, in further studies it would be important to evaluate the population status of B. cordobae from the HF-CN, because a small body length of tadpoles could have consequences at the population level.

Keywords: Boana cordobae; Body condition; Environmental science; Fluoride; Functional traits; Periphyton; Trophic ecology.

Fig. 1

Total length and body weight of tadpoles of Boana cordobae per site. Values are mean ± SE.

Fig. 2

NMDS of the diet of tadpoles of Boana cordobae from high and low fluoride streams and environmental variables with significant association to each vector.

Fig. 3

Rank-abundance curves of abundant taxa (P_i > 1%) in the diet of tadpoles of Boana cordobae from high and low fluoride streams. References: Ach: Achnanthidium sp., Navi: Navicula sp., Cymb: Cymbella sp., Osc: Oscillatoria sp., Encs: Encyonopsis sp., Ulna: Ulnaria sp., Frag: Fragilaria sp., Nitz: Nitzschia sp., Ency: Encyonema sp., Gomp: Gomphonema sp., Dent: Denticula sp., Phor: Phormidium sp., Cocco: Cocconeis sp., Melo: Melosira sp., Euno: Eunotia sp.

Fig. 4

Structural attributes of the algal community in the diet of tadpoles of Boana cordobae from high (HF-CN: Los Cerros Negros stream, black) and low (LF-LV: Los Vallecitos stream, white) fluoride streams. Means and standard errors are shown.

Fig. 5

Relative abundance (P_i) of taxa corresponding to selected functional traits in the diet of tadpoles of Boana cordobae from high and low fluoride streams. Mean and standard error are shown. For size classes, four of the five categories are shown (c1 comprises the smaller organisms and c5 the larger ones), for attachment mechanisms, three of the five and for life-forms, three of the four categories.