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ABSTRACT: Invasive species may carry with them parasites from their native range, differing from parasite taxa found in the invaded range. Host switching by parasites (either from the invader to native fauna or from native fauna to the invader) may have important consequences for the viability of either type of host (e.g., their survivorship, fecundity, dispersal ability, or geographic distribution). Rhabdias pseudosphaerocephala (Nematoda) is a common parasite of cane toads (Rhinella marina) in the toad's native range (South and Central America) and also in its introduced Australian range. This lungworm can depress host viability and is capable of infecting Australian frogs in laboratory trials. Despite syntopy between toads and frogs for up to 75 yr, our analyses, based on DNA sequence data of lungworms from 80 frogs and 56 toads, collected from 2008 to 2011, did not reveal any cases of host switching in nature: toads and native frogs retain entirely different lungworm faunas. All lungworms in cane toads were the South and Central American species Rhabdias pseudosphaerocephala, whereas Australian frogs contained at least four taxa (mostly undescribed and currently lumped under the name Rhabdias cf. hylae). General patterns of prevalence and intensity, based on the dissection of 1,315 frogs collected between 1989 and 2011 across the toads' Australian range, show that these Australian endemic Rhabdias spp. are widely distributed geographically and across host taxa but are more common in some frog species (especially, large-bodied species) than they are in others.
Journal of wildlife diseases 10/2012; 48(4):951-61. · 1.08 Impact Factor
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ABSTRACT: Laboratory studies show that predatory cane toads (Bufo marinus) exhibit specialized toe-luring behavior that attracts smaller conspecifics, but field surveys of toad diet rarely record
cannibalism. Our data resolve this paradox, showing that cannibalism is common under specific ecological conditions. In the
wet–dry tropics of Australia, desiccation risk constrains recently metamorphosed toads to the edges of the natal pond. Juvenile
toads large enough to consume their smaller conspecifics switch to a primarily cannibalistic diet (67% of prey biomass in
stomachs of larger toads). Cannibalistic attack was triggered by prey movement, and (perhaps as an adaptive response to this
threat) small (edible-sized) toads were virtually immobile at night (when cannibals were active). Smaller metamorphs were
consumed more frequently than were larger conspecifics. The switch from insectivory to cannibalism reflects the high dry season
densities of small conspecifics (in turn, due to desiccation-imposed constraints to dispersal) and the scarcity of alternative
(insect) prey during dry weather. Our study pond (102m in circumference) supported >400 juvenile toads, which consumed many
metamorphs over the course of our study. Toads appear to be low-quality food items for other toads; in laboratory trials,
juvenile toads that fed only on conspecifics grew less rapidly than those that ate an equivalent mass of insects. This effect
was not due to parotoid gland toxins per se. Thus, cane toads switch to intensive cannibalism only when seasonal precipitation
regimes increase encounter rates between large and small toads, while simultaneously reducing the availability of alternative
prey.
Behavioral Ecology and Sociobiology 04/2012; 63(1):123-133. · 3.18 Impact Factor
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ABSTRACT: Invasive species may transmit novel pathogens to native taxa, and lacking a history of coevolutionary interactions with the pathogen, the new hosts may be severely affected. Cane toads (Rhinella marina) were introduced to Australia in 1935, bringing with them a lungworm (Rhabdias pseudosphaerocephala) not found in Australian frogs. Previous studies suggest that most frog species are unaffected by this parasite, but one tree-frog (Litoria caerulea) can harbour high numbers of lungworm. More detailed laboratory studies confirm and extend the earlier results on L. caerulea and show that Rhabdias infection severely depresses the viability of metamorphs of an allied tree-frog species, Litoria splendida. Parasitic larvae infected both of these two closely related tree-frog species, but the two anurans differed in the consequences of infection. Parasitism reduced the survivorship of L. splendida and the stamina of both species. Lungworms did not consistently reduce growth rates or affect heart rates in either tree-frog species. Although L. splendida is potentially vulnerable to the arrival of toad-transported lungworms, rates of host-switching may be reduced by low levels of habitat overlap between the frogs (which are rock-dwelling and arboreal) and the toads (which are terrestrial and most abundant in disturbed habitats).
International journal for parasitology 05/2011; 41(9):943-9. · 3.39 Impact Factor
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ABSTRACT: Parasite transfer to native fauna is a potentially catastrophic impact of invasive species. Introduced cane toads in Australia frequently host the nematode lungworm Rhabdias pseudosphaerocephala, which reduces viability of metamorph toads. If native frogs are vulnerable to this South American parasite, cane toad invasion may affect native species via this route; but if the native taxa are not vulnerable, we may be able to exploit the parasites for managing toads. Our laboratory experiments show that infective larvae can penetrate the body of all seven species of Australian frogs (five hylids: Cyclorana longipes, Litoria caerulea, Litoria dahlii, Litoria nasuta, Litoria rothii, one myobatrachid: Opisthodon ornatus, and one limnodynastid: Limnodynastes convexiusculus) we tested, but most did not host the adult worms at the end of the trials, and none showed major impairment of growth, survival or locomotor performance. One native tree-frog (L. caerulea) retained high infection levels with few ill effects, suggesting that we might be able to use this taxon as a reservoir species to build up local parasite densities for toad management. However, the interspecific variation in lungworm retention suggests that generalizations about parasite effects on native frogs will be elusive.
Austral Ecology 02/2011; 36(8):954 - 963. · 1.82 Impact Factor
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Journal of Tropical Ecology 02/2009; 25(02):181 - 191. · 1.40 Impact Factor
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ABSTRACT: Invasive species can affect the ecosystems they colonize by modifying the behaviour of native taxa; for example, avoidance of chemical cues from the invader may modify habitat use (shelter site selection) by native species. In laboratory trials, we show that metamorphs of most (but not all) native frog species on a tropical Australian floodplain avoid the scent of invasive cane toads (Bufo marinus Linnaeus 1758). Cane toads also avoid conspecific scent. This response might reduce vulnerability of metamorph frogs and toads to larger predatory toads. However, similar avoidance of one type of pungency control (garlic), and the presence of this avoidance behaviour in frogs at the toad invasion front (and hence, with no prior exposure to toads), suggest that this may not be an evolved toad-specific response. Instead, our data support the simpler hypothesis that the metamorph anurans tend to avoid shelter sites that contain strong and unfamiliar scents. Temporal and spatial differences in activity of frogs versus toads, plus the abundance of suitable retreat sites during the wet season (the primary time of frog activity), suggest that avoiding toad scent will have only a minor impact on the behaviour of native frogs. However, this behavioural impact may be important when environmental conditions bring toads and frogs into closer contact.
Austral Ecology 01/2009; 34(1):77 - 82. · 1.82 Impact Factor
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ABSTRACT: Survival rates of juvenile reptiles are critical population parameters but are difficult to obtain through mark-recapture programs because these small, secretive animals are rarely caught. This scarcity has encouraged speculation that survival rates of juveniles are very low, and we test this prediction by estimating juvenile survival rates indirectly. A simple mathematical model calculates the annual juvenile survival rate needed to maintain a stable population size, using published data on adult survival rates, reproductive output, and ages at maturity in 109 reptile populations encompassing 57 species. Counter to prediction, estimated juvenile survival rates were relatively high (on average, only about 13% less than those of conspecific adults) and highly correlated with adult survival rates. Overall, survival rates during both juvenile and adult life were higher in turtles than in snakes, and higher in snakes than in lizards. As predicted from life history theory, rates of juvenile survival were higher in species that produce large offspring, and higher in viviparous squamates than in oviparous species. Our analyses challenge the widely held belief that juvenile reptiles have low rates of annual survival and suggest instead that sampling problems and the elusive biology of juvenile reptiles have misled researchers in this respect.
Ecology 04/2008; 89(3):607-11. · 4.85 Impact Factor
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ABSTRACT: If selective forces on locomotor ability and reproductive biology differ among habitats, we expect to see relationships between habitat, morphology, and life-history traits. Comparative (phylogenetically based) analysis of data from 12 pythonid and 12 boid snake species reveals multiple evolutionary shifts in habitat use, notably in the evolution of arboreal habits. Compared to terrestrial and aquatic taxa of the same overall body size, arboreal species have narrower and more laterally compressed bodies and relatively longer tails. Offspring sizes are not affected by arboreality, but presumably reflecting space constraints within their narrow bodies, arboreal species (1) produce smaller clutch sizes relative to maternal body length and (2) have left and right ovaries that overlap little if at all along the length of the body (i.e., the right ovary is positioned anterior to the left ovary) whereas in terrestrial snakes the two ovaries overlap along much of their length. This modification of ovarian morphology in arboreal snakes presumably reduces the degree of bodily distension during vitellogenesis and pregnancy, thus enhancing climbing ability and camouflage among the branches.
Ecology 03/2007; 88(2):359-66. · 4.85 Impact Factor
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ABSTRACT: This study reports on aspects of reproduction in the water snake Liophis miliaris from four regions in Brazil: (1) northern coastal Atlantic forest, (2) southern coastal Atlantic forest, (3) northern inland Atlantic forest; and (4) southern inland Atlantic forest. In the northern coastal Atlantic forest, where there is little climate variation, the reproductive cycle of this species is continuous, with vitellogenesis and oviposition occurring throughout the year. Newly hatched snakes are found mainly in January. In other regions the cycle is seasonal and related to warmer and rainy periods, with vitellogenesis and oviposition occurring mainly from September to February. Hatchlings are more abundant from February to April, at the end of the rainy season. In the northern Atlantic forest newly hatched snakes have smaller body sizes than in the other regions. Sperm production seems to occur throughout the year in all regions, and where reproduction is seasonal, mating seems to be disassociated from vitellogenesis, suggesting that sperm may be stored by females over the winter. Females with oviductal eggs did not feed, whereas those ones with secondary vitellogenic follicles fed more frequently than non-reproductive females. In all regions, the activity pattern of adult Liophis miliaris seems to be related to reproductive cycles and climate variation.
Herpetological Journal 09/2006; 16(4):353-362. · 0.81 Impact Factor
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ABSTRACT: Dissection of preserved Atlantic coral snakes Micrurus corallinus, plus field data and histological analysis, provided information on male reproductive cycles. Testes are larger during autumn, when sperm production occurs, and smaller in spring, when spermatogenesis stops. The diameter of the distal deferent ducts is small in summer–autumn, when sperm are hardly found in the lumen, and it increases in winter–spring, when sperm is abundant, just prior to the mating season. Thus, the male cycle of M. corallinus is post-nuptial, whereas the female cycle is pre-nuptial. Although gametogenesis is not simultaneous in both sexes, the coordination of their cycles is guaranteed by sperm storage by males. Our data indicate that the diameter of the deferent duct is a good indication of the mating season, mainly when reproductive cycles are post-nuptial. Mate searching and aggregation occurs in the spring, and activity in both sexes may be highly related to their reproductive cycles.
HERPETOLOGICAL JOURNAL. 01/2006; 16:371-376.
