Comparative testis morphology of Neotropical anurans

Anuran testes have generally similar germinative and somatic anatomical components, but their morphology varies among species groups. However, little is known about how environmental and evolutionary factors influence testis shape and sperm quantity. Here, we tested the hypothesis that the arrangement of both germinal compartment (seminiferous locules containing germ cells) and somatical compartment (interstitial fibers and somatic cells) differ between species with distinct reproductive modes and breeding activities. We compared the testes of eight species from two families of Neobatrachian anurans: Physalaemus centralis, Physalaemus cuvieri, Physalaemus marmoratus, Physalaemus olfersii, Pseudopaludicola sp. (aff. murundu) (Leptodactylidae: Leiuperinae), Crossodactylus caramaschii, Hylodes cardosoi, and Hylodes sazimai (Hylodidae). We built a 3D model of the testis to visualize the morphology and arrangement of seminiferous locules. We measured locular diameter and area, thickness of reticular fiber bundles, and area of both collagen fibers and sperm bundles. Hylodids had the highest values for most characters, except for sperm and reticular fiber bundles. For example, their locular diameter was 50%, and locular area 20% larger than leiuperines, which usually had thicker reticular fibers bundles. These fibers provide greater stability to the large quantity of small, spherical seminiferous locules found in leiuperines. Conversely, hylodids had larger area of collagen fibers, which provides greater flexibility and resistance to a few large and flattened seminiferous loci. Our results can shed light on how testicular morphology is influenced by evolutionary processes and ecological strategies, such as breeding seasonality and reproductive modes in anurans.