Adolfo Marco

Shifts in Life History as a Response to Predation in Western Toads (Bufo boreas)

Larval western toads (Bufo boreas) are known to exhibit antipredator behavior in response to both chemical alarm cues released from injured conspecifics and chemical cues of predatory invertebrates. In this study, we tested whether long-term exposure to predator and alarm cues resulted in an adaptive shift in life history characteristics of the toads. We raised groups of tadpoles in the presence of: (1) predatory backswimmers (Notonecta spp.) that were fed toad tadpoles, (2) nonpredatory water boatman (Corixidae), and (3) chemical alarm cues of injured conspecifics. Tadpoles raised in the presence of both chemical alarm cues and cues of predators fed tadpoles metamorphosed in significantly shorter time than those raised in the presence of the nonpredator control. Reducing time taken to reach metamorphosis would reduce exposure to aquatic predators. There was no difference among treatments in the size at metamorphosis. Our results suggest that this shift in metamorphic characteristics may represent a facultative alteration in life history.

Identification of a disturbance signal in larval red-legged frogs, Rana aurora

Animals that are warned about the presence of a predator are more likely to avoid and/or survive an encounter with a predator. Chemical signals released by disturbed or injured conspecifics may provide prey animals with an early warning. In this study we conducted experiments to determine whether larval red-legged frogs respond to chemical stimuli produced by disturbed conspecifics and to examine the chemical compounds that may act as the alarm signal. In laboratory tests, groups of tadpoles responded with antipredator behaviours when exposed to chemical cues of disturbed conspecifics but not when exposed to chemical cues of control (undisturbed) conspecifics. In subsequent tests, disturbed animals increased ammonium (the main metabolic waste of tadpoles) excretion relative to undisturbed individuals. When tadpoles were exposed to low-level ammonium concentrations (1 mg NH4+/litre), they responded by increasing antipredator behaviours. Our results suggest that red-legged frog tadpoles release a chemical that provides conspecifics with an early warning of predator presence, and that ammonium (NH4+) may be a component of the disturbance signal. Copyright 1999 The Association for the Study of Animal Behaviour.

Influence of developmental stage on sensitivity to ammonium nitrate of aquatic stages of amphibians

In static renewal experiments, we studied how developmental stage influences the effect of ammonium nitrate on embryonic and larval stages of anuran amphibians. The observed lethal effects caused by ammonium nitrate increased with both concentration and duration of exposure. Significant differences were observed in sensitivity to ammonium nitrate as a function of developmental stage in Discoglossus galganoi, Pelobates cultripes, and Bufo calamita. In D. galganoi and P. cultripes, younger individuals displayed greater acute effects from the chemical fertilizer compared with older individuals. For example, 100% of P. cultripes hatchlings died after 4 d of exposure to a nominal concentration of 225.8 mg N-NO3NH4/L, whereas less than 40% of individuals from older larval stages died when exposed to this concentration. A delay of 4 d in the beginning of the exposure to the chemical was enough to cause significant differences in sensitivity. Bufo calamita showed a higher sensitivity in later larval stages after 12 d of exposure. Hyla meridionalis and B. calamita were less sensitive than the other two species. Peak ammonium nitrate concentrations usually occur when amphibians are breeding and, thus, when the most sensitive aquatic stage is in the water. The developmental stage of the test animals should be considered when evaluating the risk of ammonium nitrate to amphibians.

Fusarium solani is responsible for mass mortalities in nests of loggerhead sea turtle, Caretta caretta, in Boavista, Cape Verde

The fungus Fusarium solani (Mart.) Saccardo (1881) was found to be the cause of infections in the eggs of the sea turtle species Caretta caretta in Boavista Island, Cape Verde. Egg shells with early and severe symptoms of infection, as well as diseased embryos were sampled from infected nests. Twenty-five isolates with similar morphological characteristics were obtained. Their ITS rRNA gene sequences were similar to the GenBank sequences corresponding to F. solani and their maximum identity ranged from 95% to 100%. Phylogenetic parsimony and Bayesian analyses of these isolates showed that they belong to a single F. solani clade and that they are distributed in two subclades named A and C (the latter containing 23 out of 25). A representative isolate of subclade C was used in challenge inoculation experiments to test Koch postulates. Mortality rates were c. 83.3% in challenged eggs and 8.3% in the control. Inoculated challenged eggs exhibited the same symptoms as infected eggs found in the field. Thus, this work demonstrates that a group of strains of F. solani are responsible for the symptoms observed on turtle-nesting beaches, and that they represent a risk for the survival of this endangered species.

The absence of species and sex recognition during mate search by male common toads, Bufo bufo

During mate search male Bufo bufo do not discriminate between green frogs and conspecifics, between sexes or between gravid females that differ in body size. We studied mate recognition and the mating behaviour of male European common toads, B. bufo using field-based choice experiments. When given a simultaneous choice between R. perezi and B. bufo both matched in size, male toads did not discriminate between species and amplected a frog or a toad with equal frequency. When a male toad amplected a frog, the frog uttered a release call but the toad did not release the frog and the amplexus lasted from several seconds to a few minutes. Usually frogs fought to release the male toad but test toads were tenacious and usually attempted several times to clasp the frog when the frog slipped away from toad. When given a simultaneous choice between a male and a female of equal size, males did not discriminate between the sexes and attempted to amplex a male or a female with equal frequency. When a test male clasped a stimulus male, the stimulus male uttered a specific release call that caused the test male to release the stimulus male. Male-male amplexus never lasted more than 3 sec, and consequently, the search cost associated with mating with the wrong sex was relatively low. Males did not discriminate between gravid females that differed in body size. Moreover, there was no assortative mating by size. Male-female amplexus was tenacious and prolonged in the three experiments.

Living Together but Remaining Apart: Atlantic and Mediterranean Loggerhead Sea Turtles (Caretta caretta) in Shared Feeding Grounds

Juvenile loggerhead sea turtles (Caretta caretta) from Atlantic nesting populations migrate into the western Mediterranean, where they share feeding grounds with turtles originating in the Mediterranean. In this scenario, male-mediated gene flow may lead to the homogenization of these distant populations. To test this hypothesis, we genotyped 7 microsatellites from 56 Atlantic individuals sampled from feeding grounds in the western Mediterranean and then compared the observed allele frequencies with published data of 112 individuals from Mediterranean nesting beaches. Mediterranean populations were found to be genetically differentiated from the Atlantic stock reaching the western Mediterranean (F(st) = 0.029, P < 0.001); therefore, the possible mating events between Atlantic and Mediterranean individuals are not sufficient to homogenize these 2 areas. The differentiation observed between these 2 areas demonstrates that microsatellites are sufficiently powerful for mixed stock analysis and that individual assignment (IA) tests can be performed in combination with mitochondrial DNA (mtDNA) analysis. In a set of 197 individuals sampled in western Mediterranean feeding grounds, 87% were robustly assigned to Atlantic or Mediterranean groups with the combined marker, as compared with only 52% with mtDNA alone. These findings provide a new approach for tracking the movements of these oceanic migrants and have strong implications for the conservation of the species.

DNA REPAIR AND RESISTANCE TO UV-B RADIATION IN WESTERN SPOTTED FROGS

We assessed DNA repair and resistance to solar radiation in eggs of members of the western spotted frog complex (Rana pretiosa and R. luteiventris), species whose populations are suffering severe range reductions and declines. Specifically, we measured the activity of photoreactivating enzyme (photolyase) in oocytes of spotted frogs. In some species, photoreactivation is the most important mechanism for repair of UV-damaged DNA. Using field experiments, we also compared the hatching success of spotted frog embryos at natural oviposition sites at three elevations, where some embryos were subjected to ambient levels of UV-B radiation and others were shielded from UV-B radiation. Compared with other amphibians, photolyase activities in spotted frogs were relatively high. At all sites, hatching success was unaffected by UV-B. Our data support the interpretation that amphibian embryos with relatively high levels of photolyase are more resistant to UV-B radiation than those with lower levels of photolyase. At the embryonic stage, UV-B radiation does not presently seem to be contributing to the population declines of spotted frogs.

Lost at sea: genetic, oceanographic and meteorological evidence for storm-forced dispersal

For many species, there is broad-scale dispersal of juvenile stages and/or long-distance migration of individuals and hence the processes that drive these various wide-ranging movements have important life-history consequences. Sea turtles are one of these paradigmatic long-distance travellers, with hatchlings thought to be dispersed by ocean currents and adults often shuttling between distant breeding and foraging grounds. Here, we use multi-disciplinary oceanographic, atmospheric and genetic mixed stock analyses to show that juvenile turtles are encountered ‘downstream’ at sites predicted by currents. However, in some cases, unusual occurrences of juveniles are more readily explained by storm events and we show that juvenile turtles may be displaced thousands of kilometres from their expected dispersal based on prevailing ocean currents. As such, storms may be a route by which unexpected areas are encountered by juveniles which may in turn shape adult migrations. Increased stormy weather predicted under climate change scenarios suggests an increasing role of storms in dispersal of sea turtles and other marine groups with life-stages near the ocean surface.

Ultraviolet Radiation and Amphibians

Environmental changes, including those associated with the atmosphere, may significantly affect individual animals, populations, and ultimately communities. Ultraviolet-B (UV-B) radiation, increasing because of stratospheric ozone depletion, has been suggested as causing mortality and a variety of sublethal effects in a number of organisms, including amphibians. At the terrestrial surface, UV-B (280–315 nm) radiation is extremely important biologically. Critical biomolecules absorb light of higher wavelength less efficiently, and stratospheric ozone absorbs most light of lower wavelength (Blaustein et al. 1994a).

Global distribution of two fungal pathogens threatening endangered sea turtles.

Nascent fungal infections are currently considered as one of the main threats for biodiversity and ecosystem health, and have driven several animal species into critical risk of extinction. Sea turtles are one of the most endangered groups of animals and only seven species have survived to date. Here, we described two pathogenic species, i.e., Fusarium falciforme and Fusarium keratoplasticum, that are globally distributed in major turtle nesting areas for six sea turtle species and that are implicated in low hatch success. These two fungi possess key biological features that are similar to emerging pathogens leading to host extinction, e.g., high virulence, and a broad host range style of life. Their optimal growth temperature overlap with the optimal incubation temperature for eggs, and they are able to kill up to 90% of the embryos. Environmental forcing, e.g., tidal inundation and clay/silt content of nests, were correlated to disease development. Thus, these Fusarium species constitute a major threat to sea turtle nests, especially to those experiencing environmental stressors. These findings have serious implications for the survival of endangered sea turtle populations and the success of conservation programs worldwide.