The process of rapid range expansion (as seen in many invasive species, and in taxa responding to climate change) may substantially disrupt host–parasite dynamics. Parasites and pathogens can have strong regulatory effects on their host population and, in doing so, exert selection pressure on host life history. We construct a simple individual‐based model of host–parasite dynamics during range expansion. This model shows that the parasites and pathogens of a range‐expanding host are likely to be absent from the host's invasion front, because stochastic events (serial founder events) in low‐density frontal populations result in local extinctions or transmission failure of the parasite/pathogen and, hence, a preponderance of uninfected hosts in the invasion vanguard. This pattern is true for both density‐dependent and density‐independent transmission rates, although it is exacerbated in the case of density‐dependent transmission because, in this case, transmission rates also decline on the front. Data from field surveys on the prevalence of lungworms (Rhabdias pseudosphaerocephala) in invasive cane toads (Bufo marinus) support these predictions, in showing that toads in newly invaded areas of tropical Australia lack the parasite, which only arrives 1–3 years after the toads themselves. The resultant “honeymoon phase” immediately post‐invasion, when individuals in the invasion‐front population are virtually pathogen‐free, may lead to altered host population dynamics on the invasion front, causing, for example, high densities in invasion‐front populations, followed by a decline in numbers as parasites and pathogens arrive and begin to reduce host viability. The honeymoon phase may ultimately impact the evolution of life‐history investment strategies in both host and parasite on the invasion vanguard, as hosts are released from immune challenges and parasites continuously expand into a favorable and unoccupied niche.

Investigating patterns and processes of parasite diversification over ancient geological periods should involve comparisons of host and parasite phylogenies in a biogeographic context. It has been shown previously that the geographical distribution of host-specific parasites of sarcopterygians was guided, from Palaeozoic to Cainozoic times, mostly by evolution and diversification of their freshwater hosts. Here, we propose phylogenies of neobatrachian frogs and their specific parasites (Platyhelminthes, Monogenea) to investigate coevolutionary processes and historical biogeography of polystomes and further discuss all the possible assumptions that may account for the early evolution of these parasites. Phylogenetic analyses of concatenated rRNA nuclear genes (18S and partial 28S) supplemented by cophylogenetic and biogeographic vicariance analyses reveal four main parasite lineages that can be ascribed to centers of diversity, namely Australia, India, Africa, and South America. In addition, the relationships among these biogeographical monophyletic groups, substantiated by molecular dating, reflect sequential origins during the breakup of Gondwana. The Australian polystome lineage may have been isolated during the first stages of the breakup, whereas the Indian lineage would have arisen after the complete separation of western and eastern Gondwanan components. Next, polystomes would have codiverged with hyloid sensu stricto and ranoid frog lineages before the completion of South American and African plate separation. Ultimately, they would have undergone an extensive diversification in South America when their ancestral host families diversified. Therefore, the presence of polystome parasites in specific anuran host clades and in discrete geographic areas reveals the importance of biogeographic vicariance in diversification processes and supports the occurrence and radiation of amphibians over ancient and recent geological periods.

As pressure on coastal marine resources is increasing globally, the need to quantitatively assess vulnerable fish stocks is crucial in order to avoid the ecological consequences of stock depletions. Species of Sciaenidae (croakers, drums) are important components of tropical and temperate fisheries and are especially vulnerable to exploitation. The black‐spotted croaker, Protonibea diacanthus, is the only large sciaenid in coastal waters of northern Australia where it is targeted by commercial, recreational and indigenous fishers due to its food value and predictable aggregating behaviour. Localized declines in the abundance of this species have been observed, highlighting the urgent requirement by managers for information on fine‐ and broad‐scale population connectivity. This study examined the population structure of P. diacanthus across north‐western Australia using three complementary methods: genetic variation in microsatellite markers, otolith elemental composition and parasite assemblage composition. The genetic analyses demonstrated that there were at least five genetically distinct populations across the study region, with gene flow most likely restricted by inshore biogeographic barriers such as the Dampier Peninsula. The otolith chemistry and parasite analyses also revealed strong spatial variation among locations within broad‐scale regions, suggesting fine‐scale location fidelity within the lifetimes of individual fish. The complementarity of the three techniques elucidated patterns of connectivity over a range of spatial and temporal scales. We conclude that fisheries stock assessments and management are required at fine scales (100 s of km) to account for the restricted exchange among populations (stocks) and to prevent localized extirpations of this species. Realistic management arrangements may involve the successive closure and opening of fishing areas to reduce fishing pressure.

Infrapopulation dynamics of the nematode Rhabdias cf. hylae within naturally-infected Bufo marinus in north Queensland, Australia, were detailed. Over 80% of 580 toads were infected with Rh. cf. hylae with a mean intensity of 16·1. Distribution of Rh. cf. hylae within the toad population was aggregated, with an increase in the variance-to-mean ratio with increasing toad size. Intensity of infection and length of nematode were both correlated with length of toad in the smaller size classes. Length of nematode was not related to intensity of infection at any time. Mean intensity of infection rose significantly in small toads following initial infection after metamorphosis. Over the same period, average length of nematode did not increase implying constant re-infection of the toads. Larger toads were not reinfected to the same extent, and the number of uninfected toads in the larger size class increased which indicated a natural loss of infections. Changes in parameters of Rh. cf. hylae infection within B. marinus were attributed to seasonal rainfall and its subsequent effect on the behaviour of the toad.