Dietary Partitioning in Two Co-occurring Caecilian Species (Geotrypetes seraphini and Herpele squalostoma) in Central Africa

Among burrowing vertebrates, the ecology of caecilians—limbless and tropical amphibians—remains poorly studied (Wells 2007). Adults of most of the 213 species of caecilians are terrestrial, occupying leaf litter and soils in the tropics of Africa, Central, and South America, and southern Asia, and even oceanic islands such as Sao Tome, the Seychelles, and the Philippines (Gower and Wilkinson 2008; AmphibiaWeb 2019). In addition, the free-living and feeding larvae of many caecilians are aquatic as are both larvae and adults of the South American Typhlonectidae. Many caecilians exhibit derived life histories and reproductive modes, including viviparity, direct development, extended parental care, and, perhaps most famously, dermatophagy, in which neonates are attended by the mother and feed on her skin (Wake and Dickie 1998; Wells 2007; Kupfer et al. 2008). Relative to salamanders and frogs, little is known of the diets of juvenile and adult caecilians. Most published accounts have limited sampling of intraspecific variation, including studies with just one or several individuals with no information on variation among individuals, sexes, or ontogenetic stages (e.g., Barbour and Loveridge 1928; Moll and Smith 1967; Presswell et al. 2002). Studies of caecilian diets that incorporate intraspecific variation are relatively recent, beginning largely with a series of quantitative studies on Boulengerula taitana (Gaborieau and Measey 2004), Gegeneophis ramaswamii (Measey et al. 2004), and Schistometopum thomense (Deletre and Measey 2004). These works provide insights into the trophic niche breadth in caecilians and also demonstrate that these poorly known vertebrates are generalist predators of soil and terrestrial invertebrates (Gaborieau and Measey 2004). While there are fewer than a dozen caecilian species for which intraspecific variation in diet has been studied, the dietary breadths of these species are fairly similar. Most studies reveal that caecilian diets are dominated by earthworms and aquatic or terrestrial soil insects such as termites and ants (e.g., Barbour and Loveridge 1928; Wake 1980; Verdade et al. 2000; Measey et al. 2004; Kupfer et al. 2005). Some species are known to consume hard-bodied invertebrate prey, including snails (Ngo et al. 2014) and crabs (Gudynas et al. 1988), and occasionally vertebrates such as scolecophidian snakes (Presswell et al. 2002), lizards (Moll and Smith 1967), and frogs (Gudynas et al. 1988; Kupfer et al. 2005). Hebrard et al. (1992) suggested that caecilians may be at least partially detritivorous, though later authors have rejected this (Deletre and Measey 2004; Gaborieau and Measey 2004). Most caecilians are thought to be dietary generalists with life history, ecology (i.e., aquatic vs. terrestrial), and seasonal changes in local prey abundance all driving variation within and among species (Kupfer et al. 2005; Ngo et al. 2014). Some caecilian species may specialize on particular prey types, including Caecilia gracilis (Maciel et al. 2012) and Schistometopum thomense (Deletre and Measey 2004) which are both thought to specialize on earthworms. Because most studies sampled few individuals and neither prey abundance nor variation across sites or seasons is typically investigated, it is difficult to disentangle whether a species is a specialist or is instead an opportunist feeding on locally abundant prey types. In addition, almost nothing is known of the diets of caecilian species in sympatry, including whether co-occurring species might eat different prey. In the only study to address this issue, Jones et al. (2006) found differences in the diets of sympatric Scolecomorphus vittatus and Boulengerula boulengeri in Tanzania. While these species are found at the same sites, this study suggested that the two species feed on different types of earthworms related to foraging in different soil layers. We extend dietary knowledge of caecilians by providing the second dietary study of co-occurring caecilians and the first studies of intraspecific variation between sexes and ontogenetic stages for two Cameroonian caecilian species, Geotrypetes seraphini (family Dermophiidae) and Herpele squalostoma (family Herpelidae). The caecilian fauna of Cameroon is the most phylogenetically diverse in Africa, comprising seven species in four families, including five endemic species (Wilkinson et al. 2011). In general, the diets of African caecilian species appear similar to that of species from other regions of the world, largely feeding on soil invertebrates (Table 1), but the diets of the diverse Cameroonian fauna have not yet been investigated. We focused our study on the two most common species, G. seraphini and H. squalostoma, in Cameroon. These species are widely distributed across West and Central Africa and can be especially abundant in cultivated areas such as gardens and plantations. In addition, these species are known to be sympatric in at least some parts of their respective ranges, including in Cameroon (Gower et al. 2015). While sometimes sympatric, the biology of each species is distinct, including in reproductive mode. Herpele squalostoma is oviparous with females attending eggs and juveniles, including provisioning young via skin feeding (Kouete et al. 2012, 2013). In contrast, G. seraphini is viviparous but also with altricial young provisioned by the attending mother by skin feeding (Parker 1956; O’Reilly et al. 1998). We conducted field surveys at three sites in Cameroon and examined gut contents of juveniles and adults of both species to (1) characterize the diversity of prey consumed (Deletre and Measey 2004; Gaborieau and Measey 2004; Measey et al. 2004), (2) analyze patterns of intraspecific variation, both between sexes and ontogenetic stages (Kupfer et al. 2005; Jones et al. 2006; Kouete et al. 2012), and (3) test whether the dietary breadth and diversity of prey categories differ for these. Table 1 Summary of prey categories in the diets of the nine African caecilian species studied to date, including members of the Dermophiidae (Geotrypetes, Schistometopum), Herpelidae (Boulengerula, Herpele), Indotyphlidae (Sylvacaecilia), and Scolecomorphidae (Scolecomorphus)