Diet of the Bannan Caecilian Ichthyophis bannanicus (Amphibia: Gymnophiona: Ichthyophiidae) in the Mekong Delta, Vietnam
Ichthyophis bannanicus is a terrestrial caecilian, and little is known about many aspects of the ecology of this species. We investigated the correlation between diet and body size, spatiotemporal variation in dietary composition, diversity index of prey, and size dimorphism among populations for this species. Specimens (N = 135) were collected from May 2010 to April 2011 in the Mekong Delta, Vietnam. We found 178 prey items representing 11 unique families and discovered that the diet of I. bannanicus is composed mainly of small prey; the most important were Achatinidae, Lumbricidae, and Formicidae, with a combined importance index of 77%. Diet composition, prey size, and total prey volume in I. bannanicus changed between dry and rainy seasons and among regions (P < 0.001). Mean prey volume increased with body size and showed positive correlations (P < 0.001) between total length and mouth width and prey size consumed. The total dietary breadth of I. bannanicus was 4.52, and all six populations of the Bannan Caecilian were found to consume snails, earthworms, ants, and termites. Results indicated that precipitation, but not temperature, was associated positively with prey volume. All collected I. bannanicus were adult females; we did not find male individuals of this species in the study area.Abstract
Map of Dong Thap and An Giang Provinces showing the geographic location of the six localities where specimens (white circles) of Ichthyophis bannanicus were obtained: (1) Lap Vo, (2) Tam Nong, and (3) Hong Ngu Districts in Dong Thap Province; (4) Thoai Son, (5) Tri Ton, and (6) Tinh Bien Districts in An Giang Province in the Mekong Delta, Vietnam.
Monthly mean precipitation (solid lines, in millimeters) and temperature (broken lines, in °C) in An Giang (filled circles) and Dong Thap (open circles) Provinces in the Mekong Delta, Vietnam, over the last 10 years. Data are presented as the mean ± SE, referred from weather stations in An Giang and Dong Thap Provinces (unpubl. data).
Adult female of Ichthyophis bannanicus Yang, 1985, in life, from the plain region of Lap Vo District in Dong Thap Province, the Mekong Delta, Vietnam (10°22′36″N, 105°42′48″E, at 7 m a.s.l. elevation; total length of 30.1 cm; body mass of 18.2 g). Photo by Nghiep T. Hoang.
Adult female of Ichthyophis bannanicus Yang, 1985, in life, from a hilly region in Tinh Bien District, An Giang Province, the Mekong Delta, Vietnam (10°29′58″N, 104°59′26″E, at 476 m a.s.l. elevation; total length of 24.8 cm; body mass of 12.3 g). Photo by Binh V. Ngo.
Diet of Ichthyophis bannanicus based on total stomach contents (N = 135) in the Mekong Delta, Vietnam. (A) Mean percent volume of the most important prey categories (Ach, Achatinidae; Lum, Lumbricidae; For, Formicidae) and (B) frequency of occurrence and percent volume of each prey category identified in stomachs of the Bannan caecilians. Iso, Isoptera; Ran, Ranidae; Ort, Orthoptera; Sco, Scolopendromorpha; Dip, Diplopoda; Ara, Araneae; Inl, Insect Larvae; and Col, Coleoptera. Data are presented as mean ± SD, for each important prey category on shape A; the asterisks show where a significant among-site or -season difference occurred using the two-factor MANOVA analysis.
Dispersion diagrams from Pearson's correlations between total length and mouth width (A), mouth width and body mass (B), and total length and body mass (C) of adult female Ichthyophis bannanicus in the Mekong Delta, Vietnam.
Relationship between prey size (prey length [L, mm], prey width [W, mm], and prey volume [V, mm3]) and body size (total length [TL, cm], open circles; mouth width [MW, mm], solid circles; and body mass [BM, g], solid triangles) of adult females of Ichthyophis bannanicus in the Mekong Delta, Vietnam. Linear regression equations are (A) prey length, L = 2.73MW + 0.168BM − 0.536TL − 3.89; (B) prey width, W = 0.049MW − 0.015BM + 0.145TL − 0.28; and (C) prey volume, V = 25.2MW + 1.52BM + 0.145TL − 125.
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