Resumen: Los amplexos interespecíficos ocurren entre anfibios del mismo género o familia. Se presentan observaciones de amplexos interespecíficos entre Rhinella major y Rhinella marina en una poza temporal en Ilha de Santana, Santana, Amapá, Región Norte de Brasil.

Several anuran species that breed in water bodies form mating aggregations after heavy rains (Pombal Jr. & Haddad, 2007). Interspecific amplexi are especially common in anurans in which numerous adults occur at breeding sites for a short period (Rodrigues et al., 2007, Wells, 1977, 2007). In these species, females are important resources for males, since females are available for a short period and males occur at higher density than females, even from the start of the breeding season (Chandler & Zamudio, 2008).

Herein we present records of interspecific amplexi between Rhinella major (Müller & Hellmich, 1936) and Rhinella marina Linnaeus, 1758. These species have reproduction throughout the year, but with a peak in the wet season. Several males aggregate in temporary ponds for two-three days, where thousands of fertilized eggs are deposited on the water surface in gelatinous strings (Lima et al., 2012).

The records are from the Ilha de Santana, Santana municipality, Amapá state, North Brazil. The area, located in the North of the Amazon River, is characterized by a high diversity of vegetation mosaics, where there are transitional areas between upland forest, flooded forest and savannas (Valente et al., 1998). On June 21th, at night, around 21:38, in a temporary pond (0.073611°S, 51.176389°W, datum: WGS84), 14 males of R. major and two males of R. marina were found calling. We observed interspecific amplexi between a male of R. major (SVL = 46.5 mm) and a male of R. marina (SVL = 78.8 mm) and a male of R. marina (SVL = 134.8 mm) and multiple amplexi of two males of R. major (SVL = 49.4 mm and 56.9 mm) (Fig. 1). The toads maintained their position for at least an additional 15 minutes. During this entire time R. marina did not emit a release call. The males of R. marina use specialized signals, such as "release" calls and body vibrations or inflate the body to discourage erroneous amplexi (Izzo et al., 2012).

Figure 1
Interspecfic amplexi: (A) male of Rhinella major and a male of Rhinella marina attached by axillar amplexus; (B) male of Rhinella marina and two males of Rhinella major.

According to Pombal Jr. & Haddad (2005), males of the genus Rhinella are not very selective, moving toward and forming amplexi with anything that moves nearby. In anurans, interspecific amplexi have been recorded, even between families (Green 1985, Mollov et al., 2010, Machado & Bernarde, 2011, Ribeiro et al., 2014, Yadav & Yankanchi, 2014, Kinderman, 2015, Lombardo et al., 2016) and different amphibian orders (Moldowan et al., 2013, Simović, 2014).

Our observations confirm the occurrence of interspecific amplexi between individuals of two common toad species found in sympatry, R. major and R. marina, and suggest that this behavior is more widespread than previously recognized. Further studies are needed to fully understand the amplexi mechanisms in the amphibians and compare if this behavior is more common in species of Rhinella than in other groups.