Loı̈c Bollache

Climate change and the ecology and evolution of Arctic vertebrates

Climate change is taking place more rapidly and severely in the Arctic than anywhere on the globe, exposing Arctic vertebrates to a host of impacts. Changes in the cryosphere dominate the physical changes that already affect these animals, but increasing air temperatures, changes in precipitation, and ocean acidification will also affect Arctic ecosystems in the future. Adaptation via natural selection is problematic in such a rapidly changing environment. Adjustment via phenotypic plasticity is therefore likely to dominate Arctic vertebrate responses in the short term, and many such adjustments have already been documented. Changes in phenology and range will occur for most species but will only partly mitigate climate change impacts, which are particularly difficult to forecast due to the many interactions within and between trophic levels. Even though Arctic species richness is increasing via immigration from the South, many Arctic vertebrates are expected to become increasingly threatened during this century.

Differential influence of Pomphorhynchus laevis (Acanthocephala) on the behaviour of native and invader gammarid species

Although various species of acanthocephalan parasites can increase the vulnerability of their amphipod intermediate hosts to predation, particularly by altering their photophobic behaviour, their influence on the structure of amphipod communities and the success of invader species has so far received little attention. We compared the prevalence and behavioural influence of a fish acanthocephalan parasite, Pomphorhynchus laevis, in two species of amphipods, Gammarus pulex and Gammarus roeseli in sympatry in the river Ouche (Burgundy, eastern France). There, G. pulex is a resident species, whereas G. roeseli is a recent coloniser. Both uninfected G. pulex and G. roeseli were strongly photophobic. although less so in the invading species. However, there was no significant difference in reaction to light between infected and uninfected G. roeseli, whereas infected G. pulex were strongly photophilic. We discuss our results in relation to the parasites ability to manipulate invading host species, the possibility that resistant individuals have been selected during the invasion process, and the role that acanthocephalan parasites can play in shaping the structure of amphipod communities.

The shell matrix of the freshwater mussel Unio pictorum (Paleoheterodonta, Unionoida)

Among molluscs, the shell biomineralization process is controlled by a set of extracellular macromolecular components secreted by the calcifying mantle. In spite of several studies, these components are mainly known in bivalves from only few members of pteriomorph groups. In the present case, we investigated the biochemical properties of the aragonitic shell of the freshwater bivalve Unio pictorum (Paleoheterodonta, Unionoida). Analysis of the amino acid composition reveals a high amount of glycine, aspartate and alanine in the acid‐soluble extract, whereas the acid‐insoluble one is rich in alanine and glycine. Monosaccharidic analysis indicates that the insoluble matrix comprises a high amount of glucosamine. Furthermore, a high ratio of the carbohydrates of the soluble matrix is sulfated. Electrophoretic analysis of the acid‐soluble matrix revealed discrete bands. Stains‐All, Alcian Blue, periodic acid/Schiff and autoradiography with 45Ca after electrophoretic separation revealed three major polyanionic calcium‐binding glycoproteins, which exhibit an apparent molecular mass of 95, 50 and 29 kDa, respectively. Two‐dimensional gel electrophoresis shows that these bands, provisionally named P95, P50 and P29, are composed of numerous isoforms, the majority of which have acidic isoelectric points. Chemical deglycosylation of the matrix with trifluoromethanesulfonic acid induces a drastic shift of both the apparent molecular mass and the isoelectric point of these matrix components. This treatment induces also a modification of the shape of CaCO3 crystals grown in vitro and a loss of the calcium‐binding ability of two of the main matrix proteins (P95 and P50). Our findings strongly suggest that post‐translational modifications display important functions in mollusc shell calcification.

Rapid range extension of the Ponto-Caspian amphipod Dikerogammarus villosus in France: potential consequences

Non-indigenous species are increasingly recognized as altering local com- munities in newly colonized areas. In some north European freshwater systems, the Ponto-Caspian invasive crustacean Dikerogammarus villosus (Amphipoda) is im- plicated to have such an effect, with general monitoring of its progress and general im- pact required. The present study contributes to this monitoring. D. villosus was ob- served in 2003 in all the major French rivers prospected (i.e. Rhine, Meuse, Moselle, Sao ne, Rho ne, Seine, and Loire), a European region previously overlooked for its co- lonization. This species was also detected in some tributaries of the rivers Sao ne and Seine, and in Geneva Lake. The dynamics of this colonisation, inferred from samples made at different dates, show a rapid expansion westward, from its first appearance in the Sao ne in 1997. The colonised rivers are connected with the more important French harbours, which may facilitate future invasion of new countries. In two sites, D. villo- sus rapidly became the dominant crustacean species after its appearance.A comparison of the amphipod fauna between 2003 and ancient surveys also shows that some native species tend to disappear in the East of France. These data suggest an ongoing homo- genisation process of amphipod assemblages.

Effects of two acanthocephalan parasites on the fecundity and pairing status of female Gammarus pulex (Crustacea: Amphipoda).

Acanthocephalan parasites are known to alter the reproductive biology and physiology of their hosts in various ways. In this study we investigated the influence of two acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, on the fecundity and pairing success of female Gammarus pulex. The results show that P. laevis and P. minutus affect female intermediate host reproduction in different ways. Females infected with P. minutus were totally castrated, whereas those infected with P. laevis only showed reduced fecundity. The oocytes of P. laevis-infected females showed a similar structure to those of uninfected females, although infected females had a higher proportion of oocytes that had failed to reach complete maturity. In comparison, the oocytes of P. minutus-infected females demonstrate a clearly altered structure that suggests a major disruption to the process of vitellogenesis. In the field, males paired more frequently with uninfected females than with infected ones, and is a stronger effect for P. minutus-infected females than P. laevis-infected females. We suggest that the difference in pairing success of P. minutus-infected and P. laevis-infected females is a direct result of the different effects that the two parasites have on female fecundity.

The effects of parasite age and intensity on variability in acanthocephalan-induced behavioural manipulation

Numerous parasites with complex life cycles are able to manipulate the behaviour of their intermediate host in a way that increases their trophic transmission to the definitive host. Pomphorhynchus laevis, an acanthocephalan parasite, is known to reverse the phototactic behaviour of its amphipod intermediate host, Gammarus pulex, leading to an increased predation by fish hosts. However, levels of behavioural manipulation exhibited by naturally-infected gammarids are extremely variable, with some individuals being strongly manipulated whilst others are almost not affected by infection. To investigate parasite age and parasite intensity as potential sources of this variation, we carried out controlled experimental infections on gammarids using parasites from two different populations. We first determined that parasite intensity increased with exposure dose, but found no relationship between infection and host mortality. Repeated measures confirmed that the parasite alters host behaviour only when it reaches the cystacanth stage which is infective for the definitive host. They also revealed, we believe for the first time, that the older the cystacanth, the more it manipulates its host. The age of the parasite is therefore a major source of variation in parasite manipulation. The number of parasites within a host was also a source of variation. Manipulation was higher in hosts infected by two parasites than in singly infected ones, but above this intensity, manipulation did not increase. Since the development time of the parasite was also different according to parasite intensity (it was longer in doubly infected hosts than in singly infected ones, but did not increase more in multi-infected hosts), individual parasite fitness could depend on the compromise between development time and manipulation efficiency. Finally, the two parasite populations tested induced slightly different degrees of behavioural manipulation.

Trans-Equatorial Migration Routes, Staging Sites and Wintering Areas of a High-Arctic Avian Predator: The Long-tailed Skua ( Stercorarius longicaudus )

The Long-tailed Skua, a small (<300 g) Arctic-breeding predator and seabird, is a functionally very important component of the Arctic vertebrate communities in summer, but little is known about its migration and winter distribution. We used light-level geolocators to track the annual movements of eight adult birds breeding in north-east Greenland (n = 3) and Svalbard (n = 5). All birds wintered in the Southern Hemisphere (mean arrival-departure dates on wintering grounds: 24 October-21 March): five along the south-west coast of Africa (0–40°S, 0–15°E), in the productive Benguela upwelling, and three further south (30–40°S, 0–50°E), in an area extending into the south-west Indian Ocean. Different migratory routes and rates of travel were documented during post-breeding (345 km d−1 in late August-early September) and spring migrations (235 km d−1 in late April) when most birds used a more westerly flyway. Among the different staging areas, a large region off the Grand Banks of Newfoundland appears to be the most important. It was used in autumn by all but one of the tracked birds (from a few days to three weeks) and in spring by five out of eight birds (from one to more than six weeks). Two other staging sites, off the Iberian coast and near the Azores, were used by two birds in spring for five to six weeks. Over one year, individuals travelled between 43,900 and 54,200 km (36,600–45,700 when excluding staging periods) and went as far as 10,500–13,700 km (mean 12,800 km) from their breeding sites. This study has revealed important marine areas in both the south and north Atlantic Ocean. Sustainable management of these ocean basins will benefit Long-tailed Skuas as well as other trans-equatorial migrants from the Arctic.

Patterns of intermediate host use and levels of association between two conflicting manipulative parasites

For many parasites with complex life cycles, manipulation of intermediate host phenotypes is often regarded as an adaptation to increase the probability of successful transmission. This phenomenon creates opportunities for either synergistic or conflicting interests between different parasite species sharing the same intermediate host. When more than one manipulative parasite infect the same intermediate host, but differ in their definitive host, selection should favour the establishment of a negative association between these manipulators. Both Polymorphus minutus and Pomphorhynchus laevis exploit the amphipod Gammarus pulex as intermediate host but differ markedly in their final host, a fish for P. laevis and a bird for P. minutus. The pattern of host use by these two conflicting manipulative parasites was studied. Their incidence and intensity of infection and their distribution among G. pulex were first examined by analysing three large samples of gammarids collected from the river Tille, Eastern France. Both parasites had low prevalence in the host population. However, temporal fluctuation in the level of parasitic infection was observed. Overall, prevalence of both parasite species was higher in male than in female G. pulex. We then assessed the degree of association between the two parasites among their intermediate hosts, using two different methods: a host-centred measure and a parasite-centred measure. Both measures gave similar results; showing random association between the two acanthocephalan species in their intermediate hosts. We discuss our results in relation to the selective forces and ecological constraints that may determine the pattern of association between conflicting manipulative parasites.

Co-variation between the intensity of behavioural manipulation and parasite development time in an acanthocephalan–amphipod system

Pomphorhynchus laevis, a fish acanthocephalan parasite, manipulates the behaviour of its gammarid intermediate host to increase its trophic transmission to the definitive host. However, the intensity of behavioural manipulation is variable between individual gammarids and between parasite populations. To elucidate causes of this variability, we compared the level of phototaxis alteration induced by different parasite sibships from one population, using experimental infections of Gammarus pulex by P. laevis. We used a naive gammarid population, and we carried out our experiments in two steps, during spring and winter. Moreover, we also investigated co‐variation between phototaxis (at different stages of infection, ‘young’ and ‘old cystacanth stage’) and two other fitness‐related traits, infectivity and development time. Three main parameters could explain the parasite intra‐population variation in behavioural manipulation. The genetic variation, suggested by the differences between parasite families, was lower than the variation owing to an (unidentified) environmental factor. Moreover, a correlation was found between development rate and the intensity of behavioural change, the fastest growing parasites being unable to induce rapid phototaxis reversal. This suggests that parasites cannot optimize at the same time these two important parameters of their fitness, and this could explain a part of the variation observed in the wild.

Variation and covariation in infectivity, virulence and immunodepression in the host–parasite association Gammarus pulex–Pomphorhynchus laevis

Parasites often manipulate host immunity for their own benefit, either by exacerbating or suppressing the immune response and this may directly affect the expression of parasite virulence. However, genetic variation in immunodepression, which is a prerequisite to its evolution, and the relationship between immunodepression and virulence, have rarely been studied. Here, we investigated the variation among sibships of the acanthocephalan parasite, Pomphorhynchus laevis, in infecting and in immunodepressing its amphipod host, Gammarus pulex. We also assessed the covariation between infectivity, parasite-induced immune depression and host mortality (parasite virulence). We found that infectivity, the intensity of immunodepression and virulence were variable among parasite sibships. Infectivity and the level of immunodepression were not correlated across parasite sibships. Whereas infectivity was unrelated to host mortality, we found that gammarids that were exposed to the parasite sibships that immunodepressed their hosts the most survived better. This positive covariation between host survival and immunodepression suggests that gammarids exposed to the less immunodepressive parasites could suffer from damage imposed by a higher activity of the phenoloxidase.