Impact of larval Dorosoma predation on Daphnia parvula dynamics

• 1 In reservoirs of the south-eastern United States, Daphnia typically decline in abundance during the summer months. Current understanding suggests that adult shad (Dorosoma spp.), the dominant planktivore in these reservoirs, plays a limited role in Daphnia midsummer declines. The impact of shad larvae is beginning to be documented.
• 2 To examine the impact of larval shad on Daphnia seasonal dynamics, larval dynamics were studied over two seasons and stomach contents were analysed during one season.
• 3 Initial Daphnia panwla declines correlated with abundance of shad larvae. During the decline, shad stomach contents consisted of 97—100%D. parvula. After D. parvula declined, Bosmina and Diaphanosoma accounted for up to 97% of larval diets. When shad diets included other cladocerans, D. parvula abundance increased in the reservoir.
• 4 When this predation pattern was incorporated into a predictive model, larval shad predation accounted for an initial, temporary decline in D. parvula abundance. However, when other crustaceans were incorporated into the shad diet, D. parvula populations increased.
• 5 These results suggest that larval shad have a temporary, strong influence on the structure and abundance of D. parvula populations in south-eastern reservoirs of the United States.

     

A review of the bloodsucking midges of Trinidad and Tobago,West Indies (Diptera:Ceratopogonidae)*

Data are presented recording the presence of 49 species of bloodsucking cerato-pogonids in Trinidad, West Indies. Of these, 45 are Culicoides, one is a Leptoconops, and three belong to Forcipomyia (Lasiohelea). Five species are reported from Tobago: three Culicoides, one Leptoconops, and one Lasiohelea. The males of Culicoides benarrochi and C. fluviatilis are described for the first time, and the female of C. debilipalpis is redescribed. Culicoides filariferus and C. pseudodiabolicus are resurrected from synonymy, and characters are presented distinguishing them from C. diabolicus and C. guttatus. Biological data and keys to genera and species are included.     

Does bill size polymorphism affect courtship song characteristics in the African finch Pyrenestes ostrinus?

Vocal characteristics of bill morphs of the African finch Pyrenestes ostrinus were investigated to see whether there were differences between the morphs that could potentially lead to assortative mating. Morphological differences between bill morphs are of a scale that could change resonance characteristics, with as a physical consequence, a change in acoustic characteristics. Song and variation in acoustic characteristics are very likely to be an important factor in mate choice. We analysed recordings of large and small-billed birds, and measured 11 acoustic characteristics focusing on frequency use and possibly correlated temporal features. In addition, we investigated in more detail the energy distribution within the frequency limits. We found no differences between bill morphs in acoustic characteristics of courtship song. Our findings contrast with other empirical studies which show an impact of the suprasyringeal vocal tract on song output. One possible explanation could be that the morphological changes affect resonance characteristics in multiple ways which do not operate in concert. Beside proximate aspects, we discuss the role of song and the bill polymorphism in the context of sympatric speciation.     

To mark the host or the patch: Decisions of a parasitoid searching for concealed host larvae

We found evidence for patch marking in the parasitic wasp Halticoptera laevigata (Hymenoptera: Pteromalidae) foraging for concealed hosts. Wasps attack larvae of the fruit fly Myoleja lucida (Diptera: Tephritidae) in fruits of honeysuckle. A special feature of this host-parasitoid system is the limited food supply of a patch (i.e. a fruit of honeysuckle), which allows the successful development of only a single host fly larva. Females of the parasitoid H. laevigata were found to mark the host patch with a pheromone and to abandon the patch following oviposition into a single host larva. Field data revealed that eggs of the parasitoid were spread out evenly among infested patches, with several larvae of the host fly left unparasitized in those patches that contained more than one host. Since many parasitic insects mark the parasitized host after oviposition, we assumed host marking to be the ancestral character state and studied the patch-marking behaviour of H. laevigata as a derived character state as an alternative foraging strategy. We used stochastic dynamic modelling to investigate under what conditions mutant (patch) markers would be able to invade a population of normal (larval) markers. The models suggested that, under a variety of conditions, wasps marking the patch obtained higher fitness than wasps only marking the larva. Consequently, the results from our model predict the evolution of the patch-marking behaviour found in the empirical investigation. Finally, we discuss alternative pathways to the evolution of patch marking and point out under what circumstances the evolution of a patch-marking behaviour can generally be expected.     

Adaptation of Drosophila to a novel laboratory environment reveals temporally heterogeneous trajectories of selected alleles

The genomic basis of adaptation to novel environments is a fundamental problem in evolutionary biology that has gained additional importance in the light of the recent global change discussion. Here, we combined laboratory natural selection (experimental evolution) in Drosophila melanogaster with genome‐wide next generation sequencing of DNA pools (Pool‐Seq) to identify alleles that are favourable in a novel laboratory environment and traced their trajectories during the adaptive process. Already after 15 generations, we identified a pronounced genomic response to selection, with almost 5000 single nucleotide polymorphisms (SNP; genome‐wide false discovery rates < 0.005%) deviating from neutral expectation. Importantly, the evolutionary trajectories of the selected alleles were heterogeneous, with the alleles falling into two distinct classes: (i) alleles that continuously rise in frequency; and (ii) alleles that at first increase rapidly but whose frequencies then reach a plateau. Our data thus suggest that the genomic response to selection can involve a large number of selected SNPs that show unexpectedly complex evolutionary trajectories, possibly due to nonadditive effects.