Estrogen contamination increases vulnerability of amphibians to the deadly chytrid fungus

Aquatic contaminants and infectious diseases are among the major drivers of global amphibian declines. However, the interaction of these factors is poorly explored and could better explain the amphibian crisis. We exposed males and females of the Brazilian Cururu Toad, Rhinella icterica, to an environmentally relevant concentration of the estrogen 17-alpha-ethinylestradiol (an emerging contaminant) and to the chytrid infection (Batrachochytrium dendrobatidis), in their combined and isolated forms, and the ecotoxicity was determined by multiple biomarkers: cutaneous, hematological, cardiac, hepatic, and gonadal analysis. Our results showed that Cururu toads had many physiological alterations in response to the chytrid infection, including the appearance of cutaneous Langerhans's cells, increased blood leukocytes, increased heart contraction force and tachycardia, increased hepatic melanomacrophage cells, which in turn led to gonadal atrophy. The estrogen, in turn, increased the susceptibility of the toads to the chytrid infection (higher Bd loads) and maximized the deleterious effects of the pathogen: reducing leukocytes, decreasing the contraction force, and causing greater tachycardia, increasing hepatic melanomacrophage cells, and leading to greater gonadal atrophy, which were more extreme in females. The exposure to estrogen also revealed important toxicodynamic pathways of this toxicant, as shown by the immunosuppression of exposed animals, and the induction of the first stages of feminization in males, which corroborates that the synthetic estrogen acts as an endocrine disruptor. Such an intricate relationship is unprecedented and reinforces the importance of studying the serious consequences that multiple environmental stressors can cause to aquatic populations.

The cardiorespiratory system of miniature frogs

Anurans of the genus Brachycephalus are among the smallest vertebrates in the world, due to an extreme process of miniaturization. As an example of this process, Brachycephalus species show loss of fingers, loss of the eardrum and middle ear, bone fusions, and the presence of paravertebral plates and parotic plaque. However, no studies addressing the consequences of miniaturization on internal organs, such as the lungs and heart, are currently available. Thus, this study aimed to investigate if overall small body size has affected the cardiorespiratory system. We investigated, via dissections, individuals of four Brachycephaloidea species: Brachycephalus rotenbergae, B. pitanga, Eleutherodactylus johnstonei, and Ischnocnema parva. We observed that B. rotenbergae and B. pitanga present a reduction of the atrial septum and absence of the carotid body. On the other hand, despite being a member of the sister genus to Brachycephalus (both genera belong to the Brachycephalidae), individuals of Ischnocnema present a heart with a complete septum and carotid body; this is also observed in E. johnstonei (Eleutherodactylidae). We observed that B. rotenbergae and B. pitanga have thin skin with a one to two cell thick germ layer, and their lungs likely exhibit lower blood supply when compared to individuals of the E. johnstonei and I. parva species. Based on the observed structures, we suggest that in species of Brachycephalus, respiration is performed mainly through the skin, and their lungs may have a reduced respiratory function.

Hidden shifts in allometry scaling between sound production and perception in anurans

Background

Animal communication consists of signal production and perception, which are crucial for social interactions. The main form used by anurans is auditory communication, in most cases produced as advertisement calls. Furthermore, sound perception happens mainly through an external tympanic membrane, and plays an important role in social behavior. In this study, we evaluated the influence of body and tympanic membrane sizes on call frequency across the phylogeny of anurans.

Methods

We use data on snout-vent length, tympanic membrane diameter, and dominant frequency of the advertisement call from the literature and from natural history museum collections. We mapped these traits across the anuran phylogeny and tested different models of diversification. Our final dataset includes data on body size, tympanic membrane size, and call dominant frequency of 735 anuran species.

Results

The best explanatory model includes body and tympanum size with no interaction term. Although our results show that call frequency is strongly constrained by body and tympanum size, we identify five evolutionary shifts in allometry from that ancestral constraint. We relate these evolutionary shifts to the background noise experienced by populations. Body size is important for myriad ecological interactions and tympanum size is strongly associated with female call frequency preferences. Thus, allometric escape in frog calls might arise through environmental selection such as breeding in fast flowing or soundscape competition, as well as sexual selection linked to tympanum size.

White-edged cowards: high-pitched treefrogs will be attacked by those with orange legs

Anurans are one of the most diverse groups of animals, with single and multi-modal communication forms commonly used to settle disputes over territory and to attract females. Thus, I aimed to evaluate if male white-edged treefrogs tend to attack smaller individuals and which morphometric factor is related to it. Advertisement calls of this species were recorded and used in a four-choice experiment with the emission of artificially designed calls. I evaluated which speaker individuals approached and if morphometric variables could predict it. I observed that individuals approached significantly more often towards the high-pitched call than other treatments, and the frequency to do so was predicted by the extension of orange colour in their legs. These results indicate that smaller individuals are actively excluded from calling sites.

Presence of invasive American bullfrogs may reduce infectious disease in a native frog species

Amphibians breeding in aquatic environments may encounter a myriad of threats during their life cycle. One species known to prey on native amphibians in aquatic habitats is the invasive North American bullfrog Lithobates catesbeianus, which, besides being a voracious predator and competitor, often acts as a pathogen carrier and disease superspreader because it tolerates high infection loads of the frog-killing fungus Batrachochytrium dendrobatidis (Bd). Here, we hypothesized that the presence of the bullfrogs in microcosms should either (1) decrease Bd disease severity in native frog species by discouraging them from using the aquatic environment, or (2) increase the mortality of the native species. We tested these 2 mutually exclusive hypotheses by co-housing the snouted treefrog Scinax x-signatus (native to our study area) with L. catesbeianus in the laboratory, exposing them to Bd, and using qPCR analysis to quantify the resulting Bd infection loads in the native frogs. Our experiment had the following replicated treatments: (1) native-only treatment (3 individuals of S. x-signatus), (2) native-predominant treatment (2 S. x-signatus + 1 L. catesbeianus), and (3) exotic-predominant treatment (1 S. x-signatus + 2 L. catesbeianus). We found that Bd infection loads in the native S. x-signatus were highest in the native-only treatment, and lowest in the exotic-predominant treatment, indicating that bullfrogs may discourage native frogs from occupying the aquatic habitat, thus reducing encounter rates between native frogs and the waterborne pathogen. This effect could be driven by the bullfrogs' predatory behavior and their high philopatry to aquatic habitats. Our results highlight that predation risk adds to the complexity of host-species interactions in Bd epidemiology.

Release call of Bokermannohyla ibitipoca Caramaschi amp; Feio, 1990 (Anura, Hylidae)

Bokermannohyla ibitipoca is a small-sized hylid frog (males reaching up to 43 mm in snout-vent length) of the B. circumdata group (Faivovich et al. 2005). This species was described from the Ibitipoca State Park (Municipality of Lima Duarte) in southern Minas Gerais, at the elevation of 1200 m. Bokermannohyla ibitipoca is restricted to the Mantiqueira Complex area (Caramaschi Feio, 1990), where it occurs in primary and secondary gallery forests. This species is found on the ground or on the leaf-litter near water and uses permanent streams for calling and reproduction. Here, we quantitatively describe the release call of B. ibitipoca, with comments on similarity to its advertisement call. Although used less frequently than advertisement calls, release calls have been used to diagnose species and infer phylogenetic relationships (Sullivan Malmos, 1994; Stöck et al. 2000; di Tada et al. 2001; Wogel et al. 2004; Márquez Eekhout 2006; Oliveira et al. 2012; Sanabria Quiroga 2012; Grenat Martino 2013).