Inference of evolutionary pattern: diversionary displays of three-spined sticklebacks

In three lakes and one marine lagoon in British Columbia, Canada,groups of three-spined sticklebacks (Gasterosteus aculeatus)cannibalize embryos and fry guarded by conspecific parentalmales. At the approach of these groups, males perform displaysthat divert the groups, often causing them to bypass the male'sterritory. Similar large groups failed to elicit such displaysfrom males in three noncannibalistic populations. The diversionarydisplays in two lakes are similar, apparently attracting conspecificsthrough foraging deception, but sticklebacks in a third lakeand in a marine lagoon perform a more complex array of displaytypes, some of which appear to incorporate ritualized elementsof other behavioral repertoires. Because the freshwater populationsare derived from marine populations of Gasterosteus, the complexdisplay repertoire is apparently ancestral relative to thefreshwater radiation. This inference is strengthened by comparisonwith the diversionary display repertoire in an Atlantic marinepopulation (primitive outgroup). Thus, the absence of the displayin some populations and the relatively limited display formsin others appear to represent a loss of all or part of theancestral display. Loss of the display in noncannibalistic populations may be adaptive because it enhances mating success.The significance of partial loss in some cannibalistic populationsis less clear. Interpretations of these patterns demonstratethe value of accounting for past historical relationships amongpopulations when inferring historical patterns of behavior evolution.     

Facilitated predation through interaction between life stages in the stinkbug predatorperillus bioculatus (Hemiptera: Pentatomidae)

Competitive interactions in arthropod predators are well-known, but positive interactions have received less attention. The two-spotted stinkbugPerillus bioculatus often feeds gregariously on leaf beetle larvae and caterpillar prey. Consequences of prey sharing amongP. bioculatus conspecifics of dissimilar size (instar) was studied using Colorado potato beetle (CPB) prey. Rearing second-instar (N2) nymphs ofP. bioculatus with an N5 conspecific facilitated early feeding on L4 CPB larvae (a difficult prey to handle by N2 nymphs but not by N5’s), thus increasing survival and accelerating development. One in every 20 cases ofP. bioculatus foraging in the field was accounted for by pairs or small groups of mostly feeding individuals. CPB egg masses and L4’s represented a disproportionate number of cases of aggregated feeding byP. bioculatus, compared to feeding singly. Small CPB larvae decreased in the diet of aggregated stinkbugs compared to L4 larvae and egg masses, suggesting that sharing these prey may be favorable or unavoidable. In a field test measuring residence/survival of N2’s limited to L4 prey, the N2’s rate of residence/survival increased significantly when large nymphs acting as food providers were also present. The function of communal feeding inP. bioculatus is discussed, as well as the potential for greater impact on prey density that may be expected from tolerance to opportunistic feeding by conspecifics in slightly gregarious predators.     

Spacing behaviour in resting Culex pipiens (Diptera, Culicidae): a computer modelling approach

Abstract. We compared two models based on Monte Carlo simulations with the spacing patterns of resting adults of the mosquito Cx pipiens L. (form molestus ) (Diptera, Culicidae). The comparison with the first model which assumed a distribution of complete spatial randomness showed that there was a tendency for mosquitoes to repel other mosquitoes which were too close, resulting in high local regularity. The second model took this repulsion into account. A final test of global patchiness using Model 2 indicated that the spacing behaviour of Cx pipiens was not sufficiently described by local regularity only, but also required a gregarious element. This supports the hypothesis that the molestus form of Cx pipiens shows spaced-out gregariousness in the sense of Kennedy & Crawley (1967).     

THE EFFECT OF BIASED INCLUSION OF TAXA ON THE CORRELATION BETWEEN DISCRETE CHARACTERS IN PHYLOGENETIC TREES

In a published paper, a method for testing the correlation between two discrete characters was presented and applied to test whether in butterfly larvae origins of gregariousness are concentrated to lineages with aposematic coloration. The relationship was found to be nonsignificant. However, the butterfly data on which the test was applied had been compiled in another study to investigate evolutionary sequences and was biased, because there was an overrepresentation of aposematic, as compared to cryptic, branches in the sample. In the paper presented here, aposematic and cryptic clades of the original phylogeny were resolved to the same degree, and the resulting set of branches may be regarded as unbiased with respect to the hypothesis being tested. A method for testing the contingency of states in two characters was then applied to the new data set, resulting in a highly significant relationship between origins of gregariousness and aposematic coloration. I argue that when using statistical methods on phylogenetic data, it is crucial to resolve various parts of the phylogeny to the same comparable systematic unit in order not to get a distorted sample of taxa/branches.