About Physalaemus nattereri (Steindachner, 1863)
This species, Physalaemus nattereri, is a frog with a dorsal coloration that ranges from light brown to dark brown or reddish, patterned with a mosaic of darker spots and stripes. A key distinctive feature is the presence of two large black ocelli positioned over glands in the inguinal region. The inner thigh is white with black vermiform spots, and the abdomen is light brown with darker spots of the same tone. Males have an average body length of 4.7 centimeters (1.9 in), while females average 4.9 centimeters (1.9 in). The species has a robust trunk, with trunk width ranging from 29.8 to 50.6 millimeters (1.17 to 1.99 in). Its head is wider than its body; the diameter of the eye equals the distance between the two orbits. It has large inguinal glands, but lacks both sacral glands and parotoid glands. Its snout and canthus are rounded, the loreal region is concave, and males have a well-developed vocal sac.
A rare characteristic of this species is that males have brightly colored testicles, often marked with spots of other colors. This trait is only known in five other amphibian species, including Physalaemus cuvieri. This pigmentation is also present in other organs, such as the kidneys, peritoneum, and spleen, and is caused by a high concentration of melanocytes, possibly due to an interaction between these cells and the vascular system of these tissues. Physalaemus nattereri can be easily distinguished from other regional anurans by its unique, easily observable traits, most notably the pair of dorsal ocelli. This ocellus trait is only shared with Physalaemus deimaticus, which is smaller, has a different dorsal mosaic pattern, and is restricted to Serra do Cipó, Minas Gerais.
In terms of distribution and conservation, Physalaemus nattereri occurs in the Central-West, Southeast, and Northeast regions of Brazil, as well as eastern Paraguay and Bolivia, across altitudes from sea level up to 1,500 meters (4,900 ft). It is a fossorial, seasonal species highly adapted to the continental semi-arid climate. It inhabits savannas and low-vegetation areas of the Cerrado, typically near permanent or temporary water bodies such as ponds and swamps, where it nests. It cannot survive in areas degraded by human activity. The International Union for Conservation of Nature (IUCN) classifies this species as Least Concern due to its common occurrence, but its population is declining, threatened by the expansion of intensive agriculture across its range. Parts of its distribution fall within protected environmental parks, which reduces overall risk to the species. The genus Physalaemus holds a total of 47 species including P. nattereri.
For reproduction, a study conducted in Bodoquena, Mato Grosso do Sul, Brazil, found that Physalaemus nattereri is an explosive breeder: all individuals gather synchronously to breed over a few days, typically between October and January. Males form choruses to attract females, and vocalize after heavy daily rainfall exceeding 50 millimeters (2.0 in). The species' vocalization ranges between 530 and 1620 hertz, with a dominant frequency of 710 Hz, and consists of simple, multi-pulsed, harmonic notes. During axillary amplexus, the breeding pair moves to the edge of a pond, and lays approximately 3500 eggs in a foam nest. The nest is built from mucus secreted by the female; the male increases the nest's volume by whipping the mucus with his hind legs, in a process similar to whisking egg whites. This species may produce communal egg masses. Following the anuran reproductive mode classification of Célio Haddad and Cynthia Prado, this species uses Mode 11. Ovaries make up approximately 22% of a female's total body mass, and fecundity increases with female body size.
The tadpoles of Physalaemus nattereri are exotrophic, feeding in the water column. They have a grayish-brown dorsum and a lighter venter, a globular body, and are benthic. Their labial tooth row formula (LTRF) is 2(2)/3(1). Tadpoles feed primarily on microalgae, have low resistance to moisture stress, and complete metamorphosis in an average of 20 to 30 days.
