Abstract
DNA barcoding was used to investigate dietary habits and prey selection in members of the African-endemic family Distichodontidae noteworthy for displaying highly specialized ectoparasitic fin-eating behaviors (pterygophagy). Fin fragments recovered from the stomachs of representatives of three putatively pterygophagous distichodontid genera (Phago, Eugnathichthys, and Ichthyborus) were sequenced for the mitochondrial gene co1. DNA barcodes (co1 sequences) were then used to identify prey items in order to determine whether pterygophagous distichodontids are opportunistic generalists or strict specialists with regard to prey selection and, whether as previously proposed, aggressive mimicry is used as a strategy for successful pterygophagy. Our findings do not support the hypothesis of aggressive mimicry suggesting instead that, despite the possession of highly specialized trophic anatomies, fin-eating distichodontids are opportunistic generalists, preying on fishes from a wide phylogenetic spectrum and to the extent of engaging in cannibalism. This study demonstrates how DNA barcoding can be used to shed light on evolutionary and ecological aspects of highly specialized ectoparasitic fin-eating behaviors by enabling the identification of prey species from small pieces of fins found in fish stomachs.
Highlights
Fishes of the family Distichodontidae, distributed throughout the freshwaters of much of sub-Saharan Africa and the Nile River basin, are one of the major groups of the African freshwater ichthyofauna (Vari 1979; Arroyave et al 2013)
With the exception of all 19 Ichthyborus ornatus specimens and an individual of Eugnathichthys macroterolepis, all remaining stomachs contained between one and five distinct fin fragments
DNA barcodes confirmed the species identity of all individuals of the pterygophagous distichodontid species investigated in this study (i.e., Phago boulengeri, P. intermedius, Eugnathichthys macroterolepis, Ichthyborus quadrilineatus, and I. ornatus)
Summary
Fishes of the family Distichodontidae, distributed throughout the freshwaters of much of sub-Saharan Africa and the Nile River basin, are one of the major groups of the African freshwater ichthyofauna (Vari 1979; Arroyave et al 2013). Moderate in diversity (~100 spp. arrayed in 15 genera), distichodontids display remarkable variation in oral anatomy and exhibit a wide array of trophic ecologies, including detritivory, herbivory, insectivory, piscivory, and even ectoparasitic fin-eating behaviors ( referred to as “pterygophagy”), facilitated by highly specialized jaw morphologies (Fig. 1). Pterygophagy in distichodontid fishes, has not been investigated beyond the study that first documented this behavior more than 50 years ago (Matthes 1961) and two subsequent studies (Matthes 1964; Roberts 1990). Based on an observed similarity in caudalfin coloration and patterning – as revealed by traditional stomach content analysis – between the ectoparasitic distichodontids Eugnathichthys eetveldii and E. macroterolepis and their putative prey Synodontis decorus and Mesoborus crocodilus, respectively, Roberts (1990) hypothesized that the barred caudal-fin pattern in pterygophagous distichodontids reflects a form of aggressive mimicry, allowing them to avoid detection by their monospecific prey.
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