Song in oscine birds is a culturally inherited mating signal and sexually dimorphic. From differences in song production learning, sex differences in song recognition learning have been inferred but rarely put to a stringent test. In zebra finches, Taeniopygia guttata, females never sing and the species has one of the greatest neuroanatomical differences in song-related brain nuclei reported for songbirds. Preference tests with sibling groups for which exposure to song had been identical during the sensitive phase for song learning in males, revealed equally strong influence of the tutor's song (here the father) on males' and females' adult song preferences. Both sexes significantly preferred the father's over unfamiliar song when having free control over exposure to playbacks via an operant task. The sibling comparisons suggest that this preference developed independently of the song's absolute quality: variation between siblings was as great as between nests. The results show that early exposure has an equally strong influence on males' and females' song preferences despite the sexual asymmetry in song production learning. This suggests that the trajectory for song recognition learning is independent of the one for song production learning.

Understanding the evolution and maintenance of within-sex reproductive morphs, or alternative reproductive phenotypes (ARPs), requires in depth understanding of the proximate mechanisms that determine ARP expression. Most species express ARPs in complex ecological environments, yet little is know about how different environmental variables collectively affect ARP expression. Here, I investigated the influence of maternal and developmental nutrition and sire phenotype on ARP expression in bulb mites (Rhizoglyphus robini), where males are either fighters, able to kill other mites, or benign scramblers. In a factorial experiment, females were raised on a rich or a poor diet, and after maturation they were paired to a fighter or a scrambler. Their offspring were put on the rich or poor diet. Females on the rich diet increased investment into eggs when mated to a fighter, but suffered reduced longevity. Females indirectly affected offspring ARP expression as larger eggs developed into larger final instars, which were more likely to develop into a fighter. Final instar size, which also strongly depended on offspring nutrition, was the main cue for morph development: a switch point, or size threshold, existed where development switched from one phenotype to the other. Sire phenotype affected offspring phenotype, but only if offspring were on the poor diet, indicating a gene by environment interaction. Overall, the results revealed that complex environmental effects can underlie ARP expression, with differential maternal investment potentially amplifying genetic effects on offspring morphology. These effects can therefore play an important role in understanding how selection affects ARP expression and, like quantitative genetics models for continuous traits, should be incorporated into models of threshold traits.Keywords Differential allocation hypothesis Á Environmentally cued threshold model Á Liability Á Life-history trade-offs Á Male attractiveness Á Reaction norm between age and size at maturity Electronic supplementary material The online version of this article (

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Summary1. Integral projection models (IPMs) provide a powerful approach to investigate ecological and rapid evolutionary change in quantitative life-history characteristics and population dynamics. IPMs are constructed from functions that describe the demographic rates -survival, growth and reproduction -in relation to the characteristics of individuals and their environment. Currently, however, demographic rates are estimated using phenomenological regression models that lack a mechanistic representation of the biological processes that give rise to observed demographic variation. This lack of mechanistic underpinning limits the ability of the model to predict future dynamics under novel environmental conditions because the model ingredients pertain to current environmental conditions only. 2. Here, we use dynamic energy budget (DEB) theory to construct DEB-IPMs based on a mechanistic representation of individual life-history trajectories. We derive the demographic functions describing growth and reproduction from a simple DEB growth model. The functions describing mortality and the association between parent and offspring characteristics do not follow DEB theory and hence are estimated from individual-level observations. 3. We apply the DEB-IPM to two contrasting systems: the small, fast-reproducing bulb mite Rhizoglyphus robini and the large, slow-reproducing reef manta ray Manta alfredi. In both cases, predictions of population growth rate, lifetime reproductive success and generation time agree with empirical observations. In case of the bulb mite, predictions and observations even agree across different feeding conditions. 4. If the DEB energetics model is accepted as describing growth and reproduction, DEB-IPMs can be parameterised using easy-to-collect life cycle information (growth rate, length at birth, maturation and old age) making them suitable for data-deficient species. Because species differ only in these DEB parameters, comparative studies of character and population dynamics between species are straightforward, particularly since DEB-IPMs can be extended to include population feedback on resources, of which we give an example. Most crucially, because DEB theory specifies growth and reproduction rates as explicitly dependent on environmental conditions such as food availability or temperature, DEB-IPMs provide a mechanistic platform to investigate the biological processes that determine joint change in phenotypic characters, life-history traits, population size and community structure.

Smallegange, I. M., van der Meer, J. and Kurvers, R. H. J. M. 2006. Disentangling interference competition from exploitative competition in a crab Á/bivalve system using a novel experimental approach. Á/ Oikos 113: 157 Á/167.In predator Á/prey relationships such as those between crabs and their bivalve prey, interference competition is a topic of intense investigation as it can have profound consequences on the dynamics of both predator and prey populations. However in laboratory experiments Á/ also those on crab Á/bivalve systems Á/ workers never adequately disentangled interference competition from exploitative competition, as prey depletion was never compensated. Hitherto, experimental studies on crab Á/bivalve systems lack direct behavioural observations and have provided only indirect and thus inconclusive evidence of interference competition. We studied interference competition in adult male shore crabs Carcinus maenas that foraged on blue mussels Mytilus edulis. We developed a novel type of experimental tank to replenish each consumed mussel, and thus to keep prey levels constant. We conducted two experiments in which we varied number of crabs (1, 2, 4) and number of mussels (first experiment: 4, 8, 16, 32; second experiment: 8, 32, 128) and directly observed the foraging behaviour of crabs (foraging area 0/0.25 m 2 ). In the first experiment, feeding rates decreased with increasing crab density only at mussel density 16 because both search time and time spent in agonistic interactions increased. At other mussel densities, variation in crab density did not affect feeding rates, possibly because of low statistical power and the narrow range of mussel densities offered. In the second experiment feeding rates decreased with increasing crab density because crabs spent more time in agonistic interactions and handling their prey. Feeding rates increased with increasing mussel density. Overall, crabs spent on average 14 Á/18% of their foraging time in agonistic behaviours, while on three out of 64 occasions feeding rates decreased because mussels were stolen (kleptoparasitism). Concluding, we have shown that interference competition occurs in absence of prey depletion, while conducting direct behavioural observations aid to identify the behavioural processes that underlie interference competition.