Snakes from the Pontal do Triângulo Mineiro Region, Cerrado Domain, Southeastern Brazil

Snakes are a highly diverse group, which are currently 392 known species in Brazil (COSTA and BÉRNILS, 2015). The Cerrado biome harbors a large number of these species (COSTA et al 2007; MARQUES et al. 2015), even though herpetofauna is still poorly documented in several localities (COSTA et al. 2007). In five years the number of snake species rose from 107 in 2002 to 145 in 2007 (COLLI et al. 2002; COSTA et al. 2007), which reinforces the high diversity of snakes in this biome.

Agricultural expansion and intensification, together with cattle raising and urban development observed in the last decades in the Cerrado, the diversity of snakes may have been mainly affected by the loss and fragmentation of natural habitats (PONTES et al. 2009; WADE et al. 2003). This group has great ecological significance and the consequences of diversity loss can be severe, because as predators, they contribute to prey population control (ROCHA et al. 2008).

Some species in the Cerrado are considered as dangerous because of their highly toxic venom, which has medical and pharmacological importance, and the epidemiological distribution of accidents involving them is deeply linked with habitat modifications (WEN et al. 2002). Therefore, habitat loss may cause the snakes to invade anthropic environments, increasing the number of accidents (BASTOS et al. 2005) and frequently being killed by local residents.

The Cerrado biome is a recognized global biodiversity hotspot, with at least 87 priority areas for conservation (CAVALCANTI and JOLY, 2002). The Triângulo Mineiro region, in the west of the state of Minas Gerais, is especially under pressure due to the increase in cultivated areas, mainly for sugar cane, which is one of the major threats to biodiversity and can lead to population decline and local extinctions (GIARETTA et al. 2008; MICHELOTTO, 2008).

Species composition in a determined area is important as a framework for future research related to biodiversity and conservation (COLLI et al. 2002), thus, the aim of the present work was to inventory the snake species of the municipality of Ituiutaba, Minas Gerais. In addition, we compare the species list with a previous snake species list for the municipality of Uberlândia.

During the study, 57 specimens were examined. We recorded for the “Pontal do Triângulo Mineiro” region 23 snake species, distributed in 16 genera and five families (Table 1, Figure 2). In field surveys, (FS) we registered 17 species, including all species of the Boidae family with occurrence in the region. In the Zoonosis Control Center (CCZ) collection, 13 species were identified (six species were only sampled at CCZ), two species were recorded at Ezequiel Dias Foundation (FUNED), all previously recognized in our sample (visual surveys an occasional encounters), and one new record at João Moojen Zoological Museum (MZUFV): Xenodon merremii. The snakes were classified in four categories based on the state in which they were found: Preserved (n=33), Alive (n=9), Road-killed (n=13) or Killed by humans (n=2), (Figure 3).

Table 1:
List of snake species recorded in the municipality of Ituiutaba, with the number of individuals (N), and origin: Field Survey (FS), Zoonosis Control Center (CCZ), Ezequiel Dias Foundation (FUNED), and João Moojen Zoological Museum of the Federal University of Viçosa (MZUFV). The (*) represents the species recorded in the municipality of Uberlândia.

Table 1:
List of snake species recorded in the municipality of Ituiutaba, with the number of individuals (N), and origin: Field Survey (FS), Zoonosis Control Center (CCZ), Ezequiel Dias Foundation (FUNED), and João Moojen Zoological Museum of the Federal University of Viçosa (MZUFV). The (*) represents the species recorded in the municipality of Uberlândia.

Figure 2:
Representatives of snake species found during the field study: A) Epicrates cenchria; B) Erythrolamprus poecilogirus; C) Erythrolamprus reginae; D) Phimopis guerini; to be continued….

Figure 2:
continuation...E) Sibynomorphus mikanii; F) Bothrops moojeni; G) Bothrops neuwiedi; H) Crotalus durissus. Photography authors: Siqueira, L. H. C. (B, C and E) and Facure, K. G. (A, D, F, G and H).

Figure 3
- Number of snakes found in each category: Preserved (Pr), Alive (Al), Road-killed (RK), and Killed by Humans (KH)

The Dipsadidae was the most diverse family, corresponding to 56.5% of the total richness and 55% of the total abundance. Considering all individuals analyzed, the most common species was Bothrops moojeni (n=10, 18.5%), followed by Sibynomorphus mikanii (n=8, 14.8%), and Oxyrhopus guibei (n=6, 11%). Four analyzed individuals could not be identified, three because of the poor state of conservation and roadkill in one case.

Twenty-eight species were recorded in the municipality of Uberlândia, being that nineteen species of that list were found in this study (Table 1). Nine species (Liotyphlops ternetzii, Clelia clelia, Erythrolamprus aesculapi, Oxyrhopus rhombifer, Pseudoboa nigra, Sibynomorphus turgidus, Thamnodynastes strigilis, Micrurus lemniscatus, and Bothrops alternatus) were not registered in our study. On the other hand, four species were recorded only in the municipality of Ituiutaba (Epicrates cenchria, Eunectes murinus, Philodryas nattereri, and Trilepida koppesi).

The snakes we found have already been reported in the Cerrado and correspond to about 15.6% of the richness of this biome and none endemic species were recorded (COLLI et al. 2002; COSTA, 2007). The number of species found was smaller than those found in well-preserved and protected natural areas in this biome (richness ranged from 29 to 47; ARAUJO et al. 2010; FREITAS et al. 2016; RODRIGUES et al. 2015; SAWAYA et al. 2008; VALDUJO et al. 2009; VAZ-SILVA et al. 2007). However, considering the highly disturbed areas in the region of Ituiutaba, the snake assemblage presented here is relatively diverse. Besides, the visual surveys were conducted during the dry season (April, May and June), whereas snakes tend to have their activity peak during the wet/rainy season (BROWN et al. 2002; BROWN and SHYNE, 2002; MARQUES et al. 2000).

Five species (27.7%) from our sample are considered potentially dangerous (Philodryas olfersii, Micrurus frontalis, Bothrops moojeni, Bothrops neuwiedi and Crotalus durissus), including the most abundant species, Bothrops moojeni. This number represents almost one third of the species sampled in this region, which draws attention to the need of studies of these species mostly for the medical area (BERNARDE, 2011). Still, considering the proximity to the urban environment, several snakes can feed on animals that possibly are illness vectors, such as rodents, bats and snails (ZANOTTI-MAGALHÃES et al. 1991).

Several taxonomic groups have their historical classification marked by confusion, and the Bothrops complex is a very good example of it. During the data collection of the present study, the genus Bothrops was divided into “Rhinocerophis, Bothrops and Bothropoides (Bothrops pauloensis was included in this list” (FENWICK et al. 2009). Carrasco et al. (2012) proposed the synonimization of the three genera under Bothrops a few years later. This instability in nomenclature is a complicating factor to taxonomy and future surveys and can be especially dangerous for medical and pharmacological issues (CARRASCO et al. 2016).

There were a huge number of snakes found dead either roadkill or killed by humans (Figure 3). This number must be due to the length of the snakes and their slow speed when crossing roads, besides they have the habit of using these sites, which provides considerable heat for thermoregulation (KUNZ and GHIZONI Jr., 2009).

Comparing our results with those shown by Brites and Bauab (1988) for the municipality of Uberlândia, it is possible to observe that the number of sampled species is approximately the same. This fact can be explained by the proximity of the study sites, despite the divergence in time expended in data collection (13 months in this work and 39 months in BRITES and BAUAB, 1988) and methodology (field surveys and material examined in collections in this work, while snakes were brought to the university by citizens in BRITES and BAUAB, 1988). Combining both lists, the total number of snake species known to the Triângulo Mineiro region is thirty-two. In both studies, S. mikanii was one of the most abundant, indicating that this species is very common in that region.

The species richness in the municipality of Ituiutaba is probably higher, and this subsample might be associated partly with the fossorial or cryptic habits of some snakes, such as Apostolepis assimilis (LEMA, 2001), which makes it difficult to find those species. Such habits can explain the absence of snakes of the Anomalepididae family, recorded previously in Uberlândia (BRITES and BAUAB, 1988).

The snake assemblage of the municipality of Ituiutaba has a large diversity of habitat use, and many are widely distributed, including other biomes, e.g. the Atlantic Forest (MARQUES et al. 2004). Hence, it is necessary to consider that due to strong anthropic pressure, since there are different ways the species may be impacted, mainly by population decline and community homogenization (MCKINNEY, 2006). It is important to stress that the majority of snakes recorded were identified from preserved animals in collections; such fact is an evidence of the great importance of zoological collections for biodiversity studies.

For the species discussed here, many have ecological and medical importance (ROCHA et al. 2008), which evidences the necessity to know the local fauna. The present study contributes to the knowledge about the snake assemblage in the west of Minas Gerais (Ituiutaba region), and sheds light on the need of future studies on diversity and distribution of this vertebrate group in the Cerrado under an unfavorable scenario with respect to conservation of natural areas.

We are grateful to the Zoonosis Control Center of Ituiutaba for specimen loans for this study, and to MZUFV and FUNED for the access to specimens. We thank all the people who contributed to the data collection, especially Ariovaldo A. Giaretta and Thaís de Cássia Rodrigues. To Paulo Sérgio Bernarde for helping with species identification, to all friends and staff from FACIP - UFU that collaborated on this work. We thank Thiago R. de Carvalho for critically reading an earlier version and providing valuable insight into this manuscript, and for linguistic help.