Abstract: The survival of marine predators depends on
behavioural plasticity to cope with changes in prey distribution.
Variability in behaviour might predict plasticity
and is easier to assess than plasticity. Using miniaturized
GPS loggers over several breeding seasons in two Norwegian
Northern gannet (Morus bassanus) colonies, we
investigated if and how the variability within and between
individuals, but also between colonies and years, affected
foraging strategies. Results revealed strong individual
variability (foraging trip durations, foraging effort and
different foraging areas). Individuals from both colonies
showed preferred commuting routes, flight bearings and
feeding hotspots. Individuals from the largest colony used
larger and more foraging areas than individuals from
the small colony. Feeding hotspots and foraging ranges
varied amongst years in the largest colony only. Our study
demonstrated that gannets show flexibility by changing
prey fields that are driven by shifting oceanographic
conditions.
Abstract: Seabirds, as other marine top predators, are often assumed to forage in an unpredictable environment. We challenge this concept and test the hypothesis that breeding Northern gannets (Morus bassanus) anticipate the spatio-temporal occurrence of their prey in the English Channel. We analyzed 23 foraging tracks of Northern gannets breeding on Rouzic Island (Brittany) that were recorded using GPS loggers during 2 consecutive years. All birds commuted between the breeding colony and foraging areas located at a mean distance of 85 km and 72 km (in 2005 and 2006, respectively) from the colony. Mean linearity indices of the outbound and inbound trips were between 0.83 and 0.87, approaching a beeline path to and from the foraging area. Additional parameters (flight speed, and number and duration of stopovers at sea) for the outbound and inbound trip were not statistically different, indicating that birds are capable of locating these feeding areas in the absence of visual clues, and to pin-point their breeding site when returning from the sea. Our bearing choice analysis also revealed that gannets anticipate the general direction of their foraging area during the first 30 min and the first 10 km of the trip. These results strongly suggest that birds anticipate prey location, rather than head into a random direction until encountering a profitable area. Further investigations are necessary to identify the mechanisms involved in seabird resource localization, such as sensorial abilities, memory effects, public information or a combination of these factors.
Abstract: Phylogenetic relationships among the Chiastocheta species (Diptera, Anthomyiidae) were investigated using a 1320-bp mitochondrial DNA fragment including parts of cytochrome oxidase subunits I and II. Larvae of the Chiastocheta genus feed exclusively on Trollius (Ranunculaceae) seeds. Six Chiastocheta species (and two vicariant taxa) coexist on Trollius europaeus in Europe, where they were shown to be the sole pollinator of their host plant. In Asia, several Trollius species are parasitized by Chiastocheta spp., and several other Trollius species are free of Chiastocheta. The plant-insect association is thus obligate in Europe but facultative in Asia. This system therefore provides a unique opportunity to study the evolution of an obligate mutualism between a plant and its seed parasite pollinators and its consequences on insect diversification. Most parsimonious, distance, and maximum likelihood analyses of 16 haplotypes from Europe and 14 from Asia show that European species do not form a monophyletic group. The species relationship indicated by egg morphology is only partly supported by molecular data. Moreover, a strong discrepancy between nucleotide variation and male genitalia morphology variation was found, particularly within and among European species coexisting on a single host plant. Molecular divergence across species ranges from 0 to 4.6%, suggesting a recent origin of the genus and several events of diversification, involving both host shifts and within-host-plant radiation. We discuss alternative evolutionary scenarios that are consistent with molecular data.
