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How did this snail get here? Several dispersal vectors inferred for an aquatic invasive species
No full textHow species reach and persist in isolated habitats remains an open
question in many cases, especially for rapidly spreading invasive
species. This is particularly true for temporary freshwater ponds, which
can be remote and may dry out annually, but may still harbour high
biodiversity. Persistence in such habitats depends on recurrent
colonisation or species survival capacity, and ponds therefore provide
an ideal system to investigate dispersal and connectivity. 2. Here, we
test the hypothesis that the wide distributions and invasive potential
of aquatic snails is due to their ability to exploit several dispersal
vectors in different landscapes. We explored the population structure of
Physa acuta (recent synonyms: Haitia acuta, Physella acuta, Pulmonata:
Gastropoda), an invasive aquatic snail originating from North America,
but established in temporary ponds in Donana National Park, southern
Spain. In this area, snails face land barriers when attempting to
colonise other suitable habitat. 3. Genetic analyses using six
microsatellite loci from 271 snails in 21 sites indicated that (i)
geographically and hydrologically isolated snail populations in the park
were genetically similar to a large snail population in rice fields more
than 15 km away; (ii) these isolated ponds showed an
isolation-by-distance pattern. This pattern broke down, however, for
those ponds visited frequently by large mammals such as cattle, deer and
wild boar; (iii) snail populations were panmictic in flooded and
hydrologically connected rice fields. 4. These results support the
notion that aquatic snails disperse readily by direct water connections
in the flooded rice fields, can be carried by waterbirds flying between
the rice fields and the park and may disperse between ponds within the
park by attaching to large mammals. 5. The potential for aquatic snails
such as Physa acuta to exploit several dispersal vectors may contribute
to their wide distribution on various continents and their success as
invasive species. We suggest that the interaction between different
dispersal vectors, their relation to specific habitats and consequences
at different geographic scales should be considered both when attempting
to control invasive freshwater species and when protecting endangered
species.
Effect of belowground herbivory on parasitoid associative learning of plant odours
No full textRoot herbivores can influence both the performance and the behaviour of parasitoids of aboveground insect herbivores through changes in aboveground plant quality and in the composition of the plant's odour blend. Here we show that root herbivory by Delia radicum larvae did not influence the innate preferences for plant odours of the two closely related parasitoid species Cotesia glomerata and C. rubecula, but did affect their learned preferences, and did so in an opposite direction. While C. glomerata learned to prefer the odour of plants with intact roots, C. rubecula learned to prefer the odour of root-infested plants. The learned preference of C. glomerata for the odour of plants with intact roots matches our previously published result of its better performance when developing in P. brassicae hosts feeding on this plant type. In contrast, the relatively stronger learned preference of C. rubecula for the odour of root-infested plants cannot be merely explained by its performance, as the results of our present study indicate that D. radicum root herbivory did not influence the performance of C. rubecula nor of its host P. rapae. Our results stress the importance of assessing the influence of root herbivores on both innate and learned responses of parasitoids to plant odours
Parental care and UV coloration in blue tits: opposite correlations in males and females between provisioning rate and mate’s coloration
No full textParental investment and sexually-selected signals can be intimately related, either because the signals indicate the amount of investment that an individual is prepared to make, and hence its value as a mate (the ‘good parent process’), or because individuals are selected to vary their own investment in relation to their mate’s signals (‘differential allocation’ or ‘reproductive compensation’). Correlations between parental investment and the sexually selected signals of both an individual and its mate are therefore of central interest in sexual selection. Blue tits Cyanistes caeruleus are an ideal study species to investigate such correlations because they provide substantial amounts of biparental care and possess sexually-selected structural UV coloration that seems to signal attractiveness in both sexes. We investigated whether feeding rates of male and female blue tits were correlated with either their own or their mate’s UV coloration, and whether any such correlation was affected by the sex ratio of the brood. We also investigated whether any such correlations were reflected in offspring phenotype. Feeding rates were not correlated with either sex of parent’s own UV coloration. However, they were correlated with the mate’s UV coloration, but in opposite directions in males and females: females had higher feeding rates when mated to bright UV males, implying differential allocation, while males had lower feeding rates when mated to bright UV females, implying reproductive compensation. These relationships were unaffected by the sex ratio of the brood. In addition, fledgling tarsus length, but not mass, was related to male UV coloration, and to female UV coloration in interaction with male age. These results suggest that both male and female attractiveness influence parental investment of the mate, and that this in turn affects offspring phenotype. We found no evidence for differential sex allocation.
Derivations and evaluations
No full textThis chapter departs from the observation that the minimalist framework
and optimality theory adopt the same overall architecture of grammar (see also the
Introduction): they both assume that a generator defines a set S of potentially wellformed
expressions that can be generated on the basis of a given input, and that there
is a filter component that selects the expressions from S that are actually grammatical
in a given language L. This chapter proposes a hybrid model of grammar which
combines the two frameworks: more specifically, it is argued that the computational
system of human language from MP functions as the generator that creates the
set S of potentially well-formed expressions, and that these are subsequently evaluated
in an optimality-theoretic fashion. The properties of this hybrid model will be
illustrated by means a discussion of object shift in Icelandic and Danish.
Facultative Sex Allocation and Sex-Specific Offspring Survival in Barrow's Goldeneyes
No full textSex allocation theory predicts that females should bias their reproductive investment towards the sex generating the greatest fitness returns. The fitness of male offspring is often more dependent upon maternal investment, and therefore, high-quality mothers should invest in sons. However, the local resource competition hypothesis postulates that when offspring quality is determined by maternal quality or when nest site and maternal quality are related, high-quality females should invest in the philopatric sex. Waterfowl showing male-biased size dimorphism but female-biased philopatry are ideal for differentiating between these alternatives. We utilized molecular sexing methods and high-resolution maternity tests to study the occurrence and fitness consequences of facultative sex allocation in Barrow's goldeneyes (Bucephala islandica). We determined how female structural size, body condition, nest-site safety and timing of reproduction affected sex allocation and offspring survival. We found that the overall sex ratio was unbiased, but in line with the local resource competition hypothesis, larger females produced female-biased broods and their broods survived better than those of smaller females. This bias occurred despite male offspring being larger and tending to have lower post-hatching survival. The species shows strong female breeding territoriality, so the benefit of inheriting maternal quality by philopatric daughters may exceed the potential mating benefit for sons of high-quality females. [KEYWORDS: local resource competition conspecific nest parasitism common goldeneye ratio variation bucephala-islandica natural-selection natal philopatry red deer birds size]
Geographic parthenogenesis and plant-enemy interactions in the common dandelion
No full textBackground: Many species with sexual and asexual variants show a pattern of geographic parthenogenesis where asexuals have broader and higher-latitude distribution than sexuals. Because sexual reproduction is often considered a costly evolutionary strategy that is advantageous in the face of selection by coevolving pests and pathogens, one possible explanation for geographic parthenogenesis is that populations at higher latitudes are exposed to fewer pests and pathogens. We tested this hypothesis in the common dandelion (Taraxacum officinale), a species with well-established geographic parthenogenesis, by screening prevalence and effects of several specialized pests and pathogens in natural dandelion populations. Results: We did a population survey of 18 dandelion populations along a geographic transect that ranged from the area where sexual and asexual dandelions co-occur northward into the area where only asexuals occur. In addition we used four southern and four northern populations in a 8x8 cross-inoculation greenhouse experiment in which plants were exposed experimentally to each other's natural field soil microbial communities. The cross-inoculation experiment indicated a higher pathogenicity of soil microbial communities from the southern, mostly sexual, populations compared to soil microbial communities from the northern asexual populations. Northern dandelion populations also showed reduced infestation by a specialized seed-eating weevil. A similar trend of reduced rust fungus infection in northern populations was observed but this trend was not statistically significant. Conclusions: The prevalence of pests and pathogens decreased along the south-to-north axis of geographic parthenogenesis. This highlights the potential of biotic interactions in shaping patterns of geographic parthenogenesis.
Retourmigratie vanuit Nederland
No full textJaarlijks komen er circa 120.000 migranten naar Nederland. Een aanzienlijk deel daarvan verlaat ons land binnen afzienbare tijd; hoogopgeleide migranten eerder dan laagopgeleide migranten.
Nederland wil juist de hogeropgeleiden vasthouden met het oog op de toekomstige schaarste op de arbeidsmarkt. Dat vraagt om herziening van het kennisimigratiebeleid.
Changes in plant defense chemistry (pyrrolizidine alkaloids) revealed through high-resolution spectroscopy
No full textPlant toxic biochemicals play an important role in defense against natural enemies and often are toxic to humans and livestock. Hyperspectral reflectance is an established method for primary chemical detection and could be further used to determine plant toxicity in the field. In order to make a first step for pyrrolizidine alkaloids detection (toxic defense compound against mammals and many insects) we studied how such spectral data can estimate plant defense chemistry under controlled conditions.
In a greenhouse, we grew three related plant species that defend against generalist herbivores through pyrrolizidine alkaloids: Jacobaea vulgaris, Jacobaea erucifolia and Senecio inaequidens, and analyzed the relation between spectral measurements and chemical concentrations using multivariate statistics.
Nutrient addition enhanced tertiary-amine pyrrolizidine alkaloids contents of J. vulgaris and J. erucifolia and decreased N-oxide contents in S. inaequidens and J. vulgaris. Pyrrolizidine alkaloids could be predicted with a moderate accuracy. Pyrrolizidine alkaloid forms tertiary-amines and epoxides were predicted with 63% and 56% of the variation explained, respectively. The most relevant spectral regions selected for prediction were associated with electron transitions and CH, OH, and NH bonds in the 1530 and 2100 nm regions.
Given the relatively low concentration in pyrrolizidine alkaloids concentration (in the order of mg g−1) and resultant predictions, it is promising that pyrrolizidine alkaloids interact with incident light. Further studies should be considered to determine if such a non-destructive method may predict changes in PA concentration in relation to plant natural enemies. Spectroscopy may be used to study plant defenses in intact plant tissues, and may provide managers of toxic plants, food industry and multitrophic-interaction researchers with faster and larger monitoring possibilities