Biological Journal of the Linnean Society

BLAMIRES, SEAN J.; HOCHULI, DIETER F.; THOMPSON, MICHAEL B.

doi: 10.1111/j.1095-8312.2008.00999.xpmid: N/A

AbstractAn effective visual signal elicits a strong receiver response. The visual receptors of most insects are sensitive to ultraviolet (UV), blue and green light. The decorations of certain orb web spiders may be described as a type of visual signal, a sensory trap, as they exploit visual biases in insects. We filtered UV and blue light from the decorations of Argiope keyserlingi, under field conditions, using plastic sheets to test if the UV and blue light reflected affects the type of prey caught. We found that houseflies, blowflies, stingless bees, honeybees and vespid wasps were caught more frequently in webs with decorations than webs without, while ichneumonid wasps were caught less frequently. Blowflies, stingless bees, honeybees and vespid wasps were caught more often in unfiltered decorated webs. These insects also have receptor sensitivities in the blue and UV. We showed that exploiting visual sensory biases plays an integral role in attracting insects to orb web decorations. Whether UV light, blue light, or both, are the most important cue, however, requires further study.

BERGMAN, THORE J.; BEEHNER, JACINTA C.

doi: 10.1111/j.1095-8312.2008.00981.xpmid: N/A

AbstractAdaptive hypotheses about colour variation are widespread in behavioural ecology, and several methods of objective colour assessment have been proposed and validated for use in a wide variety of taxa. However, to date, the most objective and reliable methods of assessing colour are not readily applied to wild animals. In the present study, we present a simple method for assessing colour in unrestrained, wild subjects using digital photography. The method we describe uses a digital camera, a colour standard, and colour analysis software, and can be used to measure any part of the visible colour spectrum. We demonstrate that the method: (1) is accurate and precise across different light conditions; (2) satisfies previous criteria regarding linearity and red, green, and blue equality; and (3) can be independently validated visually. In contrast with previous digital methods, this method can be used under natural light conditions and can be readily applied to subjects in their natural habitat. To illustrate this, we use the method to measure chest colour in wild geladas (Theropithecus gelada). Unique among primates, geladas have a red patch of skin on their chest and neck, which, for males, is thought to be a sexually selected signal. Offering some support to this hypothesis, we found differences in chest ‘redness’ for males across different age groups, with males in their reproductive prime exhibiting the reddest chests.

BRUNA, EMILIO M.; DARRIGO, MARIA ROSA; PACHECO, ANGELA MIDORI FURUYA; VASCONCELOS, HERALDO L.

doi: 10.1111/j.1095-8312.2008.00962.xpmid: N/A

AbstractIn ant–plant mutualist systems, ants patrol their host plants and search for herbivores. Such patrolling can be inefficient, however, because herbivore activity is spatio-temporally unpredictable. It has been proposed that rapid and efficient systems of communication between ants and plants, such as volatile compounds released following herbivory, both elicit defensive responses and direct workers to sites of herbivore activity. We performed bioassays in which we challenged colonies of two Amazonian plant-ants, Azteca sp. and Pheidole minutula, with extracts of leaf tissue from (1) their respective host-plant species (Tococa bullifera and Maieta guianensis, both Melastomataceae), (2) sympatric ant-plants from the Melastomataceae, and (3) two sympatric but non-myrmecophytic Melastomataceae. We found that ants of both species responded dramatically to host-plant extracts, and that these responses are greater than those to sympatric myrmecophytes. Azteca sp. also responded to non-myrmecophytes with an intensity similar to that of sympatric ant-plants. By contrast, the response of P. minutula to any non-myrmecophytic extracts was limited. These differences may be driven in part by interspecific differences in nesting behaviour; although P. minutula only nests in host plants, Azteca sp. will establish carton satellite nests on nearby plants. We hypothesize that Azteca sp. must therefore recognize and defend a wider array of species than P. minutula.

BRECKO, JONATHAN; HUYGHE, KATLEEN; VANHOOYDONCK, BIEKE; HERREL, ANTHONY; GRBAC, IRENA; VAN DAMME, RAOUL

doi: 10.1111/j.1095-8312.2008.00953.xpmid: N/A

AbstractWithin populations, individual animals may vary considerably in morphology and ecology. The degree to which variation in morphology is related to ecological variation within a population remains largely unexplored. We investigated whether variation in body size and shape among sexes and age classes of the lizard Podarcis melisellensis translates in differential whole-animal performance (sprint speed, bite force), escape and prey attack behaviour in the field, microhabitat use and diet. Male and female adult lizards differed significantly in body size and head and limb proportions. These morphological differences were reflected in differences in bite strength, but not in sprint speed. Accordingly, field measurements of escape behaviour and prey attack speed did not differ between the sexes, but males ate larger, harder and faster prey than females. In addition to differences in body size, juveniles diverged from adults in relative limb and head dimensions. These shape differences may explain the relatively high sprint and bite capacities of juvenile lizards. Ontogenetic variation in morphology and performance is strongly reflected in the behaviour and ecology in the field, with juveniles differing from adults in aspects of their microhabitat use, escape behaviour and diet.

LIEFTING, MAARTJE; ELLERS, JACINTHA

doi: 10.1111/j.1095-8312.2008.00969.xpmid: N/A

AbstractWhen populations experience substantial variation in environmental conditions, they may evolve phenotypic plasticity in response to these varying selection pressures. Evolutionary theory predicts differentiation in the level of phenotypic plasticity among different habitats. We evaluated temperature-induced phenotypic responses in juvenile growth rate in natural populations of the springtail Orchesella cincta, inhabiting forest and heathland. These habitats typically co-occur but differ strongly with respect to, for example, thermal regime, relative humidity, and structure. Offspring of females from the two habitats were reared at different temperatures in climate rooms and the temperature response of juvenile growth rate and egg size was measured. We found a habitat-specific difference in plasticity of juvenile growth rate. The reaction norms of the forest populations were steeper than the reaction norms for heath populations at two replicated sampling sites. Egg weight itself was demonstrated to be a plastic trait with a higher egg weight at low temperatures, but the thermal response did not differ between habitats. We conclude that these populations have diverged due to strong local natural selection. Our results support the argument that the level of phenotypic plasticity itself can be under selection and that differentiation in reaction norms can occur even in neighbouring habitats with no barrier to gene flow.

BOLNICK, DANIEL I.; CALDERA, ERIC J.; MATTHEWS, BLAKE

doi: 10.1111/j.1095-8312.2008.00978.xpmid: N/A

AbstractGene flow between ecologically divergent populations can prevent local adaptation, resulting in lower mean fitness and directional selection within a population. Such maladaptation should tend to be stronger in populations receiving a relatively larger fraction of immigrants. We test this expectation by comparing the strength of selection in a pair of three-spine stickleback populations in adjoining but unequal-sized lake basins in British Columbia. A larger deeper basin is connected to a smaller shallower basin by a short channel that allows extensive migration between populations. The two basins contain distinct habitats and prey communities, and stickleback stomach contents and isotope ratios differ accordingly. Trophic morphology is correlated with diet, so we would expect these ecological differences to be accompanied by morphological divergence. However, high gene flow appears to constrain adaptive divergence: microsatellites indicate that the two basins represent a single panmictic gene pool, and phenotypic divergence is very subtle. As a result, fish in the smaller lake basin are subject to persistent directional selection towards a more benthic phenotype, whereas the larger population exhibits no significant selection. The results illustrate the potentially asymmetrical effect of migration-selection balance, and its effect on fitness within populations.

SONG, HOJUN; WENZEL, JOHN W.

doi: 10.1111/j.1095-8312.2008.00983.xpmid: N/A

AbstractSexual selection theory predicts that genital structures in isolated populations are likely to diverge, but male genitalia are often species-specific, which led to the idea that male genitalia are relatively invariable within species. Previous allometric studies collectively suggested that male genitalia are intraspecifically invariable in size compared with external body parts. We investigated whether male genitalia are invariable in shape in three populations of a grasshopper Schistocerca lineata Scudder, 1899, using two independent methods of geometric morphometric analyses. Specifically, we focused on the idea that male genitalia are complex structures consisting of many functionally different components, and studied how these individual parts diverge among three populations. Individual components of male genitalia show different population-level divergence, resulting in the mosaic pattern of genital divergence. Individual components diverge independently from each other. Body size is positively correlated with genitalia size, but is significantly correlated with the shape of only one of the three genital structures we measured. Thus, different components of male genitalia may be influenced by different evolutionary processes. This study is the first to show that components of complex genitalia evolve separately within a species.

LADA, HANIA; MAC NALLY, RALPH; TAYLOR, ANDREA C.

doi: 10.1111/j.1095-8312.2008.00970.xpmid: N/A

AbstractEcological factors are important drivers of phenotypic divergence, which may lead to incipient speciation. A variety of habitats should be preserved to maintain evolutionary potential. We used the marsupial, the yellow-footed antechinus (Antechinus flavipes) as a model species for investigating phenotypic differentiation between animals inhabiting two habitat types in south-eastern Australia: flood-plain river red gum and box–ironbark forests. All tested phenotypic characteristics varied between years at the same sites and therefore were not useful for investigating morphological specialization that may lead to speciation. Males generally were significantly heavier when antechinus densities were lower, but exceptions were found, possibly related to food availability. Teat-number variation recently has been shown to be associated with habitat specialization and incipient speciation within Antechinus agilis. We investigated genetic differentiation associated with this trait in A. flavipes. Population genetic analyses of microsatellite genotypes and mitochondrial DNA haplotypes revealed that sympatric 12-, 13- and 14-teat females in Chiltern forest were part of one freely interbreeding population. Our parentage analyses found two cases where 13-teat mothers produced 12-teat daughters. This suggests either plasticity or paternal genetic influence on the offspring's teat-number phenotype. Laboratory matings may be required to resolve the extent to which teat number is heritable in A. flavipes.

PAMPOULIE, CHRISTOPHE; STEFÁNSSON, MAGNÚS ÖRN; JÖRUNDSDÓTTIR, THÓRA DÖGG; DANILOWICZ, BRET S.; DANÍELSDÓTTIR, ANNA KRISTÍN

doi: 10.1111/j.1095-8312.2008.00995.xpmid: N/A

AbstractMost studies of the genetic structure of Atlantic cod have focused on small geographical scales. In the present study, the genetic structure of cod sampled on spawning grounds in the North Atlantic was examined using eight microsatellite loci and the Pan I locus. A total of 954 cod was collected from nine different regions: the Baltic Sea, the North Sea, the Celtic Sea, the Irish Sea and Icelandic waters during spring 2002 and spring 2003, from Norwegian waters and the Faroe Islands (North and West spawning grounds) in spring 2003, and from Canadian waters in 1998. Temporal stability among spawning grounds was observed in Icelandic waters and the Celtic Sea, and no significant difference was observed between the samples from the Baltic Sea and between the samples from Faroese waters. F-statistics showed significant differences between most populations and a pattern of isolation-by-distance was described with microsatellite loci. The Pan I locus revealed the presence of two genetically distinguishable basins, the North-west Atlantic composed of the Icelandic and Canadian samples and the North-east Atlantic composed of all other samples. Permutation of allele sizes at each microsatellite locus among allelic states supported a mutational component to the genetic differentiation, indicating a historical origin of the observed variation. Estimation of the time of divergence was approximately 3000 generations, which places the origin of current genetic pattern of cod in the North Atlantic in the late Weichselian (Wisconsinian period), at last glacial maximum.

AVTZIS, DIMITRIOS N.; ARTHOFER, WOLFGANG; STAUFFER, CHRISTIAN

doi: 10.1111/j.1095-8312.2008.01004.xpmid: N/A

AbstractDifferentiation among the European populations of the six-toothed spruce bark beetle Pityogenes chalcographus was observed for the first time in the 1970s as mating males from Northern Europe with females from Central Europe led to a significant decline in fecundity. Morphological examination revealed that P. chalcographus can be separated into two European races. Here, we investigated the genetic background of this separation by analysing 39 populations (n = 695), sequencing almost the complete cytochrome oxidase I gene (1543 bp) and applying single-strand conformation polymorphism. Phylogenetic analysis of 58 haplotypes yielded three major clades with a maximum sequence divergence of 2.33%, indicating that the demographic events took place in the late Pleistocene. These results support the hypothesis of allopatric divergence of the mtDNA lineages, which postglacially came into sympatric existence in Europe. However, as a result of partial crossing incompatibility the diverged lineages retained their genetic identity during postglacial times.