Summary1. Measuring the degree of skin-swelling induced by intradermal injection of phytohemagglutinin (PHA) is simple, quick and inexpensive, does not require specialized equipment and is easily conducted under field conditions. 2. PHA is perhaps the most frequently used assay of immunocompetence in field studies of birds. However, the method has rarely been used, and never validated, for studies on ectothermic vertebrates. 3. Here, we document its use in an amphibian. In response to PHA injected into a toe web, cane toads exhibited a 35% increase in web thickness 24 h postinjection. 4. Histologically, PHA injection initiated a rapid (<12 h) infiltration of neutrophils, eosinophils and macrophages at the injection site, followed by an influx of lymphocytes by 24 h postinjection. A second exposure to PHA stimulated a faster, more intense swelling response. 5. In cane toads, PHA injection elicits a rapid innate immune response, followed by a secondary response that may reflect cell-mediated immune activity. Both components are easily quantifiable by the degree of skin-swelling. 6. Hence, PHA injection offers a convenient assay to quantify immune function in anurans and could usefully be incorporated into studies on the reasons for global amphibian declines.

The impact of invasive species on biodiversity has attracted considerable study, but impacts of the invasion process on the invaders themselves remain less clear. Invading species encounter conditions different from those in their ancestral habitats and are subject to intense selection for rapid dispersal. The end result may be significant stress on individual organisms, with consequent health problems. Our studies on invasive cane toads in Australia reveal severe spinal arthritis in Ϸ10% of large adult toads, associated with the same factors (large body size, frequent movement, and relatively long legs) that have enabled toads to invade so rapidly across the Australian tropics.anuran ͉ invasive species ͉ locomotion ͉ spondylitis ͉ colonization

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At an invasion front, energetic and physiological trade‐offs may differ from those at the range‐core as a result of selection for enhanced dispersal, combined with a low density of conspecifics (which reduces pathogen transmission and competition for food). We measured traits related to energy stores and immunity in wild cane toads (Rhinella marina) across a 750‐km transect from their invasion front in tropical Australia, back into sites colonized 21 years earlier. Several traits were found to vary with population age; some linearly and others in a curvilinear manner. The relative size of spleens and fat bodies was highest in the oldest and newest populations, where rates of lungworm infection were lowest. Toads from older populations produced more corticosterone in response to a standardized stressor, and had higher lymphocyte counts (but lower basophil counts). The amount of skin swelling elicited by phytohaemagglutinin injection did not vary geographically, although recruitment of leukocytes to the injected tissue was higher in toads from long‐colonized areas. Because this was a field‐based study, we cannot differentiate the effects of population age, toad density or pathogen pressure on our measures of stress and immune responses, nor can we distinguish whether the causation involves hard‐wired adaptive processes or phenotypically plastic responses. Nonetheless, our data demonstrate substantial variation in immune systems among toads at varying distances from an invasion front, showing that a biological invasion imposes strong pressures on physiological systems of the invader.

We observed an outbreak of necrotizing fasciitis associated with Streptococcus agalactiae infection in a group of juvenile saltwater crocodiles (Crocodylus porosus). We undertook screening of crocodiles and the environment to clarify the source of the outbreak and evaluated the isolates cultured from post-mortem specimens with molecular methods to assess clonality and the presence of known group B streptococcal virulence determinants. The isolates were indistinguishable by pulsed-field gel electrophoresis. They were a typical serotype Ia strain with the Calpha-like protein gene, epsilon (or alp1), the mobile genetic elements IS381 ISSag1 and ISSag2, and belonged to multi-locus sequence type (ST) 23. All of these characteristics suggest they were probably of human origin. We review the medical and veterinary literature relating to S. agalactiae necrotizing fasciitis, epidemiology and virulence determinants.