Lungworm infection modifies cardiac response to exercise in cane toads

Immunoendocrinology and Ecoimmunology in Brazilian Anurans

This paper reviews several aspects of immunoendocrinology and ecoimmunology in Brazilian species of anurans under investigation for more than a decade, including (1) patterns of annual covariation of circulating steroids, calling behavior and innate immunity, (2) endocrine and immune correlates of calling performance, (3) behavioral and physiological correlates of parasite load, (4) thermal sensitivity of immune function, and (5) endocrine and immunomodulation by experimental exposure to acute and chronic stressors, as well as to endocrine manipulations and simulated infections. Integrated results have shown an immunoprotective role of increased steroid plasma levels during reproductive activity in calling males. Moreover, a higher helminth parasite load is associated with changes in several behavioral and physiological traits under field conditions. We also found anuran innate immunity is generally characterized by eurythermy, with maximal performance observed in temperatures close to normal and fever thermal preferendum. Moreover, the aerobic scope of innate immune response is decreased at fever thermal preferendum. Experimental exposure to stressors results in increased corticosterone plasma levels and immune redistribution, with an impact on immune function depending on the duration of the stress exposure. Interestingly, the fate of immunomodulation by chronic stressors also depends in part on individual body condition. Acute treatment with corticosterone generally enhances immune function, while prolonged exposure results in immunosuppression. Still, the results of hormonal treatment are complex and depend on the dose, duration of treatment, and the immune variable considered. Finally, simulated infection results in complex modulation of the expression of cytokines, increased immune function, activation of the Hypothalamus-Pituitary-Interrenal axis, and decreased activity of the Hypothalamus-Pituitary-Gonadal axis, as well as reduced melatonin plasma levels, suggesting that anurans have a functional Immune-Pineal axis, homologous to that previously described for mammals. These integrated and complementary approaches have contributed to a better understanding of physiological mechanisms and processes, as well as ecological and evolutionary implications of anuran immunoendocrinology.

New host record, Sclerophrys regularis (Bufonidae), for Rhabdias africanus (Rhabdiasidae, ) based on molecular and morphological evidence

With diversity of hosts range, most identified nematode species still lack the crucial connection between morphological and molecular make-up, which is important for precisely classifying the specimens. The present study provides the complete description of Rhabdias africanus in the new host record, Sclerophrys regularis. Fifty toad specimens were collected, and a high prevalence of R. africanus infection (74%) was observed. Morphology and ultrastructure were observed using light and scanning electron microscopes. Morphological characteristics, including peculiarities of the head, the shape and position of the lips, and the number of labial papillae, were described. The length of the body, the esophageal length, the distance from an anterior end to the nerve ring, and the tail length were reduced in the studied samples relative to previously described specimens. Furthermore, some variable matrices that have not previously been described, e.g., ovarian part widening, the nerve ring and its location, and eggs with different stages of larvae, were included in the present study. Genus and species identification was confirmed by comparing partial 12S (619 bp) and ITS (878 bp) gene sequences to those of Rhabdias species deposited in GenBank. The studied species showed a 99.34% resemblance to R. africanus from South Africa. We assume our findings will aid in the molecular identification of adult and larval stages of this genus in amphibians. We strongly recommend further studies on the environmental factors that promote Rhabdias infection and transmission.

Molecular Diversity of Nematode Parasites in Afrotropical Reed Frogs (Hyperolius spp.)

The diversity of nematodes infecting amphibians is understudied in tropical Africa and unknown in Rwanda. Diversity assessment is hampered by the fact that species descriptions refer mostly to morphological features that are unlinked to DNA sequences of marker genes available in public databases. In this paper, we explore the abundance and diversity of parasitic nematodes in reed frogs Hyperolius kivuensis (n = 115), H. parallelus (n = 45) and H. viridiflavus (n = 100) collected in Rwanda. Five nematode species were identified morphologically as Orneoascaris chrysanthemoides, O. schoutedeni, Gendria leberrei, Aplectana chamaeleonis and Rhabdias collaris. Corresponding DNA sequences of 18S and COI genes were determined and subsequently deposited in GenBank. Aplectana chamaeleonis showed the highest prevalence (8.7%), but O. chrysanthemoides the highest mean intensity of infection (6.0) and largest number (24) of individuals in H. kivuensis. To the best of our knowledge, all amphibian hosts are new records for these nematode species, which are known to infect a wide range of amphibian and reptile species. Our findings suggest that nematode diversity is probably lower than previously assumed due to low host specificity. As morphological species identification is often challenging, our data facilitate molecular identification of adult and specifically larval nematodes found in amphibians of Sub-Saharan Africa.

Negative effects of parasitic lung nematodes on the fitness of a Neotropical toad (Rhinella horribilis)

Pathogens are increasingly implicated in amphibian declines but less is known about parasites and the role they play. We focused on a genus of nematodes (Rhabdias) that is widespread in amphibians and examined their genetic diversity, abundance (prevalence and intensity), and impact in a common toad (Rhinella horribilis) in Panama. Our molecular data show that toads were infected by at least four lineages of Rhabdias, most likely Rhabdias pseudosphaerocephala, and multiple lineages were present in the same geographic locality, the same host and even the same lung. Mean prevalence of infection per site was 63% and mean intensity of infection was 31 worms. There was a significant effect of host size on infection status in the wild: larger toads were more likely to be infected than were smaller conspecifics. Our experimental infections showed that toadlets that were penetrated by many infective Rhabdias larvae grew less than those who were penetrated by few larvae. Exposure to Rhabdias reduced toadlet locomotor performance (both sustained speed and endurance) but did not influence toadlet survival. The effects of Rhabdias infection on their host appear to be primarily sublethal, however, dose-dependent reduction in growth and an overall impaired locomotor performance still represents a significant reduction in host fitness.

Behavioral, physiological and morphological correlates of parasite intensity in the wild Cururu toad (Rhinella icterica)

Large numbers of parasites are found in various organs of anuran amphibians, with parasite intensities thought to modulate the host's Darwinian fitness traits. Interaction between the anuran hosts and their multiple parasites should modulate the host's phenotypic characteristic, such as those associated with high energetic demand (such as calling effort and locomotor performance), energy balance (standard metabolic rate), and morphological plasticity (as indicated by organ masses). The present study investigated the impact of parasite intensities on the behavioral, physiological, and morphological traits of wild adult male Rhinella icterica (Anura: Bufonidae). We tested as to whether individuals with higher parasite intensities would present: 1) lower vocal calling effort in the field, as well as poorer locomotor performance and body-condition index; and 2) higher standard metabolic rates and internal organ masses. Measurements included: calling effort in the field; standard metabolic rate; locomotor performance; parasite intensity; internal organ masses (heart, liver, kidneys, intestines, stomach, lungs, hind limb muscle, and spleen); and the body-condition index. Results showed a negative association of parasite intensities with locomotor performance, and standard metabolic rate of R. icterica. A positive association between parasite intensities and relative organ masses (heart, intestines and kidneys) was also evident. Toads with higher pulmonary and intestinal parasites intensities also showed higher total parasite intensities.

The things they carried: The pathogenic effects of old and new parasites following the intercontinental invasion of the Australian cane toad (Rhinella marina)

Brought to Australia in 1935 to control agricultural pests (from French Guiana, via Martinique, Barbados, Jamaica, Puerto Rico and Hawai'i), repeated stepwise translocations of small numbers of founders enabled the cane toad (Rhinella marina) to escape many parasites and pathogens from its native range. However, the infective organisms that survived the journey continue to affect the dynamics of the toad in its new environment. In Australia, the native-range lungworm Rhabdias pseudosphaerocephala decreases its host's cardiac capacity, as well as growth and survival, but not rate of dispersal. The lungworm is most prevalent in long-colonised areas within the toads' Australian range, and absent from the invasion front. Several parasites and pathogens of Australian taxa have host-shifted to cane toads in Australia; for example, invasion-front toads are susceptible to spinal arthritis caused by the soil bacterium, Ochrobactrum anthropi. The pentastome Raillietiella frenata has host-shifted to toads and may thereby expand its Australian range due to the continued range expansion of the invasive toads. Spill-over and spill-back of parasites may be detrimental to other host species; however, toads may also reduce parasite loads in native taxa by acting as terminal hosts. We review the impact of the toad's parasites and pathogens on the invasive anuran's biology in Australia, as well as collateral effects of toad-borne parasites and pathogens on other host species in Australia. Both novel and co-evolved pathogens and parasites may have played significant roles in shaping the rapid evolution of immune system responses in cane toads within their invaded range.

•

Invasive cane toads have lost many parasites due to serial translocations.

•

One native lungworm (Rhabdias pseudosphaerocephala) has been retained.

•

Toads have also acquired novel parasites and pathogens from Australian hosts.

•

Toads either amplify parasite numbers or act as a parasite sink.

•

Differences in immune function exist between toad populations within Australia.