Prevalence of Fox Tapeworm in Invasive Muskrats in Flanders (North Belgium).

One way in which invasive alien species affect their environment is by acting as pathogen hosts. Pathogens limited by the availability of the native host species can profit from the presence of additional hosts. The muskrat (Ondatra zibethicus) is known to act as an intermediate host for the fox tapeworm (Echinococcus multilocularis). From 2009 to 2017, 15,402 muskrats caught in Flanders and across the border with Wallonia and France were collected and dissected with the aim of understanding the prevalence of this parasite in muskrats. Visual examination of the livers revealed 202 infected animals (1.31%). Out of the 9421 animals caught in Flanders, we found 82 individuals (0.87%) infected with E. multilocularis. No increase in prevalence was observed during this study. All of the infected animals in Flanders were found in municipalities along the Walloon border. We did not observe a northward spread of E. multilocularis infection from Wallonia to Flanders. We hypothesise that the low prevalence is the result of the reduced availability of intermediate hosts and the successful control programme which is keeping muskrat densities in the centre of the region at low levels and is preventing influx from other areas. Our results illustrate that muskrats are good sentinels for E. multilocularis and regular screening can gain valuable insight into the spread of this zoonosis.

Using structured eradication feasibility assessment to prioritize the management of new and emerging invasive alien species in Europe.

Prioritizing the management of invasive alien species (IAS) is of global importance and within Europe integral to the EU IAS regulation. To prioritize management effectively, the risks posed by IAS need to be assessed, but so too does the feasibility of their management. While the risk of IAS to the EU has been assessed, the feasibility of management has not. We assessed the feasibility of eradicating 60 new (not yet established) and 35 emerging (established with limited distribution) species that pose a threat to the EU, as identified by horizon scanning. The assessment was carried out by 34 experts in invasion management from across Europe, applying the Non-Native Risk Management scheme to defined invasion scenarios and eradication strategies for each species, assessing the feasibility of eradication using seven key risk management criteria. Management priorities were identified by combining scores for risk (derived from horizon scanning) and feasibility of eradication. The results show eradication feasibility score and risk score were not correlated, indicating that risk management criteria evaluate different information than risk assessment. In all, 17 new species were identified as particularly high priorities for eradication should they establish in the future, whereas 14 emerging species were identified as priorities for eradication now. A number of species considered highest priority for eradication were terrestrial vertebrates, a group that has been the focus of a number of eradication attempts in Europe. However, eradication priorities also included a diverse range of other taxa (plants, invertebrates and fish) suggesting there is scope to broaden the taxonomic range of attempted eradication in Europe. We demonstrate that broad scale structured assessments of management feasibility can help prioritize IAS for management. Such frameworks are needed to support evidence-based decision-making.

Cost-benefit analysis for invasive species control: the case of greater Canada goose Branta canadensis in Flanders (northern Belgium).

BACKGROUND: Sound decisions on control actions for established invasive alien species (IAS) require information on ecological as well as socio-economic impact of the species and of its management. Cost-benefit analysis provides part of this information, yet has received relatively little attention in the scientific literature on IAS. METHODS: We apply a bio-economic model in a cost-benefit analysis framework to greater Canada goose Branta canadensis, an IAS with documented social, economic and ecological impacts in Flanders (northern Belgium). We compared a business as usual (BAU) scenario which involved non-coordinated hunting and egg destruction with an enhanced scenario based on a continuation of these activities but supplemented with coordinated capture of moulting birds. To assess population growth under the BAU scenario we fitted a logistic growth model to the observed pre-moult capture population. Projected damage costs included water eutrophication and damage to cultivated grasslands and were calculated for all scenarios. Management costs of the moult captures were based on a representative average of the actual cost of planning and executing moult captures. RESULTS: Comparing the scenarios with different capture rates, different costs for eutrophication and various discount rates, showed avoided damage costs were in the range of 21.15 M€ to 45.82 M€ under the moult capture scenario. The lowest value for the avoided costs applied to the scenario where we lowered the capture rate by 10%. The highest value occurred in the scenario where we lowered the real discount rate from 4% to 2.5%. DISCUSSION: The reduction in damage costs always outweighed the additional management costs of moult captures. Therefore, additional coordinated moult captures could be applied to limit the negative economic impact of greater Canada goose at a regional scale. We further discuss the strengths and weaknesses of our approach and its potential application to other IAS.

Development of the osteocranium in Corydoras aeneus (Gill, 1858) Callichthyidae, Siluriformes.

Development in the osteocranium of Corydoras aeneus was studied based on 48 cleared and stained specimens and 10 series of serial sections. Development overall follows the general trends observed in siluriform development, with ossifications appearing as a response to functional demands. Early development of the skull occurs in two distinct phases. In a first phase, several new bony elements, all of dermal origin and related to feeding, appear shortly after yolk depletion (4.4 mm SL). Between 5 and 8 mm SL, developmental priorities seem to shift to size increase of the cartilaginous skull and no new bony elements appear. Finally, a second phase of osteogenesis occurs from 8 to 18 mm SL, in which all remaining dermal and perichondral bones appear.

Kinematics of benthic suction feeding in Callichthyidae and Mochokidae, with functional implications for the evolution of food scraping in catfishes.

Food scraping has independently evolved twice from suction feeding in the evolution of catfishes: within neotropical Loricarioidea and paleotropical Mochokidae. To gain insight in the evolutionary transitions associated with the evolution towards scraping, we analyzed prey capture kinematics in two species of benthic suction feeders which belong to taxa that are closely related to the scraper lineages (respectively, Corydoras splendens and Synodontis multipunctatus), and compared it to prey capture in a more distantly related, generalist suction feeder (Clarias gariepinus). Simultaneous ventral and lateral view high-speed videos were recorded to quantify the movements of the lower jaw, hyoid, pectoral girdle and neurocranium. Additionally, ellipse modeling was applied to relate head shape differences to buccal expansion kinematics. Similarly to what has been observed in scrapers, rotations of the neurocranium are minimal in the benthic suction feeders, and may consequently have facilitated the evolution of a scraping feeding mechanism. The hypothesis that fish with a more laterally compressed head rely more heavily on lateral expansion of the buccal cavity to generate suction, was confirmed in our sample of catfish species. Since an important contribution of lateral expansion of the head to suction may avoid the need for a strong, ventral depression of the mouth floor during feeding, we hypothesized that this may have allowed a closer association with the substrate in the ancestors of scrapers. However, our hypothesis was not supported by an ancestral state reconstruction, which suggests that scraping probably evolved from sub-terminal mouthed ancestors with dorsoventrally flattened heads.

Ontogeny of the chondrocranium in Corydoras aeneus (Gill, 1858) (Callichthyidae, Siluriformes).

Callichthyids take a basal position in the loricarioid evolutionary lineage leading up to an algae scraping feeding mechanism in the loricariid family. Therefore, the study of the morphology and development of a callichthyid representative would contribute to a better knowledge on the differences in cranial morphology and their impact on feeding ecology within this superfamily. Therefore, development in the chondrocranium of Corydoras aeneus was studied based on 22 cleared and stained specimens and 6 series of serial sections. The latter sections were also digitized and used for 3D reconstructions. Development overall follows the typical siluriform trends in chondrocranial development. Even the low complexity of the chondrocranium at hatching fits the trend observed in other siluriforms, although other studies showed loricarioid hatchlings to generally show more complex chondrocrania. In contrast to other catfish, in C. aeneus, the notochord was never found to protrude into the hypophyseal fenestra. In addition, also differing from other siluriforms, a commissura lateralis is present, a state also reported for Ancistrus cf. triradiatus (Geerinckx et al., [2005] J Morphol 266:331-355). The splanchnocranium again has the typical siluriform shape during its ontogeny, with the presence of a compound hyosymplectic-pterygoquadrate plate, although not fused to the neurocranium or interhyal at any time during ontogeny, a state described earlier for Callichthys callichthys (Hoedeman, [1960a] Bull Aquat Biol 1:73-84; Howes and Teugels, [1989] J Zool Lond 219:441-456). The most striking difference found in comparison to other catfishes, however, involves thebranchial basket, which arises as a single element with a further differentiation from the middle arches on in both a rostral and caudal direction.

Evolution: a catfish that can strike its prey on land.

An important step towards understanding the evolution of terrestriality in vertebrates is to identify how the aquatic ancestors of tetrapods were able to access ground-based prey. We have discovered that the 'eel catfish' Channallabes apus, an inhabitant of the muddy swamps of tropical Africa, has a remarkable ability to forage and capture prey on land. The animal's capacity to bend its head down towards the ground while feeding seems to be an essential feature that may have enabled fish to make the transition from an aquatic to a terrestrial mode.