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141 Publications

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    02/01/96 | The evolution of soldiers in aphids.
    Stern DL, Foster WA
    Biol Rev Camb Philos Soc. 1996 Feb;71(1):27-79

    1. Defensive individuals, termed soldiers, have recently been discovered in aphids, Soldiers are typically early instar larvae, and in many species the soldiers are reproductively sterile and morphologically and behaviourally specialized. 2. Since aphids reproduce parthenogenetically, we might expect soldier production to be more widespread in aphids than it is. We suggest that a more useful way to think about these problems is to attempt to understand how a clone (rather than an individual) should invest in defence and reproduction. 3. Known soldiers are currently restricted to two families of aphids, the Pemphigidae and Hormaphididae, although they are distributed widely among genera within these families. We discuss the use of a phylogenetic perspective to aid comparative studies of soldier production and we demonstrate this approach using current estimates of phylogenetic affinities among aphids. We show that the distribution of soldier production requires a minimum of six to nine evolutionary origins plus at least one loss. 4. At least four main types of soldiers exist and we present and discuss this diversity of soldiers. 5. Most soldier-producing species produce soldiers within plant galls and we discuss the importance of galls for the evolution of soldiers. 6. We summarize the evidence on the interactions between soldiers and predators and between soldier-producing aphids and ants. 7. We present an optimality model for soldier investment strategies to help guide investigations of the ecological factors selecting for soldiers. 8. The proximate mechanisms of soldier production are currently very poorly understood and we suggest several avenues for further research.

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    01/10/96 | A phylogenetic reanalysis of allozyme variation among populations of Galapagos finches
    David L. Stern , Peter R. Grant
    Zoological Journal of the Linnean Society;118(2):119-134. doi: 10.1111/j.1096-3642.1996.tb00222.x

    We reanalysed Yang & Pattern's allozyme data, published in Auk in 1981, of Darwin's finches with a variety of distance and cladistic methods to estimate the phylogeny of the group. Different methods yielded different results, nevertheless there was widespread agreement among the distance methods on several groupings. First, the two species of Camarhynchus grouped near one another, but not always as a monophyletic group. Second, Cactospiza pallida and Platyspiza crassirostris formed a monophyletic group. Finally, all the methods (including parsimony) supported the monophyly of the ground finches. The three distance methods also found close relationships generally between each of two populations of Geospiza scandens, G. difficilis and G. conirostris. There is evidence for inconstancy of evolutionary rates among species. Results from distance methods allowing for rate variation among lineages suggest three conclusions which differ from Yang and Patton's findings. First, the monophyletic ground finches arose from the paraphyletic tree finches. Yang and Patton found that the ground finches and tree finches were sister monophyletic taxa. Second, Geospiza scandens appears to be a recently derived species, and not the most basal ground finch. Third, G. fuliginosa is not a recently derived species of ground finch, but was derived from an older split from the remaining ground finches. Most of these conclusions should be considered tentative both because the parsimony trees disagreed sharply with the distance trees and because no clades were strongly supported by the results of bootstrapping and statistical tests of alternative hypotheses. Absence of strong support for clades was probably due to insufficient data. Future phylogenetic studies, preferably using DNA sequence data from several unlinked loci, should sample several populations of each species, and should attempt to assess the importance of hybridization in species phylogeny.

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    04/22/95 | Phylogenetic evidence that aphids, rather than plants, determine gall morphology
    David L Stern
    Proceedings of the Royal Society of London. Series B: Biological Sciences;260(1357):85-89. doi: 10.1098/rspb.1995.0063

    Many diverse taxa have evolved independently the habit of living in plant galls. For all but some viral galls, it is unknown whether plants produce galls as a specialized plant reaction to certain types of herbivory, or whether herbivores direct gall development. Here I present a phylogenetic analysis of gallforming cerataphidine aphids which demonstrates that gall morphology is extremely conservative with respect to aphid phylogeny, but variable with respect to plant taxonomy. In addition, the phylogeny reveals at least three host plant switches where the aphids produce galls most similar to the galls of their closest relatives, rather than galls similar to the galls of aphids already present on the host plant. These results suggest that aphids determine the details of gall morphology essentially extending their phenotype to include plant material. Based on this and other evidence, I suggest that the aphids and other galling insects manipulate latent plant developmental programmes to produce modified atavistic plant morphologies rather than create new forms de novo.

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    We describe the life cycle and general biology of the tropical cerataphidine aphid Cerataphis fransseni. We demonstrate that this aphid migrates between trees of Styrax benzoin and various species of palms; palm-feeding populations have previously been known as C. variabilis and C. palmae, which now become synonyms of C. fransseni. On S. benzoin the fundatrix induces a relatively simple gall which can contain >6000 aphids at maturity with a large number of reproductively sterile soldiers that protect the gall from predators. These galls are apparently produced throughout the year. Colonies on the secondary host plants, palms, are apparently obligately tended by ants whereas colonies within galls on Styrax are never tended by ants. We discuss the life cycle of this tropical aphid with respect to hypotheses for the evolution and maintenance of host alternation.

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    12/01/94 | A test of geometric hypotheses for soldier investment patterns in the gall producing tropical aphidCerataphis fransseni (Homoptera, Hormaphididae)
    D. L. Stern , S. Aoki , U. Kurosu
    Insectes sociaux;41(4):457-460. doi: 10.1007/BF01240648

    The gall-forming aphidCerataphis fransseni produces soldiers that defend against predators. Soldiers are produced soon after colony foundation and the number of soldiers increases nonlinearly during colony growth. The number of soldiers scales to the square-root of the number of non-soldiers and linearly to the surface area of the gall. This suggests that soldiers are produced to defend an area, for example the perimeter of the colony or the surface of the gall, rather than individual aphids.

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    05/23/94 | A phylogenetic analysis of soldier evolution in the aphid family Hormaphididae.
    Stern DL
    Proc Biol Sci. 1994 May 23;256(1346):203-9. doi: 10.1098/rspb.1994.0071

    Aphid soldiers, altruistic larvae that protect the colony from predators, are an example of highly social behaviour in an insect group with a natural history different from the eusocial Hymenoptera and Isoptera. Aphids therefore allow independent tests of theory developed to explain the evolution of eusociality. Although soldiers have been discovered in five tribes from two families, the number and pattern of origins and losses of soldiers is unknown due to a lack of phylogenetic data. Here I present a mtDNA based phylogeny for the Hormaphididae, and test the hypothesis that soldiers in the tribe Cerataphidini produced during two points in the life cycle represent independent origins. The results support this hypothesis. In addition, a minimum of five evolutionary events, either four origins and one loss or five origins, are required to explain the distribution of soldiers in the family. The positions of the origins and losses are well resolved, and this phylogeny provides an historical framework for studies on the causes of soldier aphid evolution.

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    12/01/93 | Nonfloral sources of chemicals that attract male euglossine bees (Apidae: Euglossini).
    Whitten WM, Young AM, Stern DL
    J Chem Ecol. 1993 Dec;19(12):3017-27. doi: 10.1007/BF00980599

    We present chemical analysis of four rotten or fungus-infected logs that attracted fragrance-collecting male euglossine bees. Eight of the 10 volatile compounds detected have never been found in the fragrances of orchids pollinated by male euglossine bees. Nonfloral sources of chemicals such as rotting wood may constitute an important fragrance resource for male bees. Since rotten logs produce large quantities of chemicals over long periods of time, such nonfloral sources might be more important than flowers as a source of certain fragrances for some euglossine bee species. Fragrance collecting in euglossine bees might have evolved originally in relation with rotting wood rather than flowers.

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    11/30/91 | Aphid soldiers discriminate between soldiers and non-soldiers, rather than between kin and non-kin, in Ceratoglyphina bambusae
    Shigeyuki Aoki , Utako Kurosu , David L Stern
    Animal behaviour;42(5):865-866. doi: 10.1016/S0003-3472(05)80135-6

    Examined kin discrimination and colony defense in soldier-producing aphids from the surface of 3 galls. Soldiers always attacked conspecific nonsoldiers, regardless of origin, and never attacked conspecific soldiers. Soldier attacks of nonsoldiers may exclude unrelated nonsoldier aphids from the gall where they would propagate and compete with resident aphids. (PsycINFO Database Record (c) 2012 APA, all rights reserved)

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    During a four month study of male territoriality males of the euglossine bee Eulaema meriana exhibited the two alternative behavior patterns of territoriality and transiency. Territorial males patrolled an area adjacent to a tree upon which they perched. Territorial males utilized the same territory for up to 49 days, though often not on consecutive days, and appeared to non-violently relinquish territories to new males. Transients did not defend territories but flew from one territory to another and flew with the territorial male around the territory, rarely bumping, and never grappling. Transient males left the territory soon after the territorial male flew back and forth in front of the perch tree in a zig-zag flight. The alternative behaviors were correlated with wing wear such that males with little wing wear defended territories and males with considerable wing wear pursued a transient strategy. Behavior patterns were not correlated with head width. Comparison of territory trees with the territory trees of a closely related species indicate that each species utilized trees of a certain diameter class for perching. In addition, analysis of hemispherical canopy photographs indicates that males appeared to prefer territories that received a maximum of diffuse sunlight but a minimum of direct sunlight. Both territorial and transient males consistently returned to specific territories over their lifetime but appeared to travel long distances to forage for fragrances. Territorial and transient males visited fragrance baits with equal frequency suggesting that non-territorial, as well as territorial, males required fragrances.

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    01/01/91 | Wing buzzing by male orchid bees, Eulaema meriana (Hymenoptera: Apidae)
    David L Stern , Robert Dudley
    Journal of the Kansas Entomological Society;64(1):88-94

    Male orchid bees of the species Eulaema meriana buzz their wings while stationary at territory perches. During buzzing, wings are first positioned laterally and then moved in a plane parallel to the ground, which probably generates a substantial airflow past the body. Within a perching episode, the ratio of buzz to pause duration decreases nonlinearly. The incidence of wing buzzing increases with ambient temperature and with duration of activity. Bees never defended territories when ambient temperatures exceeded 28.5°C. Wing buzzing may be a visual or acoustic display to conspecifics, although the brightly colored abdomen is never obscured by the wings during buzzing, and the sounds of wing buzzing are low in amplitude. The increase in buzzing frequency with increased ambient temperature and the nonlinear decrease in buzz to pause duration during perching suggest that wing buzzing may be a thermoregulatory mechanism.

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