THE RELATIVE IMPORTANCE OF SHORT- AND LONG-RANGE MOVEMENT OF FLYING APHIDS

1. Aphids are notorious pests of world agriculture. Even so, uncertainty persists as to their capacity for successful aerial dispersal. Evidence exists that, under some conditions, aphids can be wind-borne over long distances, i.e. hundreds of kilometers over desert or sea. It has been argued, in the recent past, that this phenomenon may be part of a strategy to locate fresh host plants in new distant areas. However, the proportion of these insects successfully colonizing new hosts is unknown. 2. Other work using meteorological backtracking has also indicated long-distance movement, but the accuracy of such predictions is dubious unless the altitude of transport is known. Mark-releaseecapture experiments with such small insects have limited potential due to large dilution effects. Static ‘snap-shots’ of demographic population densities, using suction traps, cannot accurately distinguish local aerial density fluxes and population movements from a distance. However, genetic and physiological markers may provide more direct information on population mixing; for example, some allozyme studies have shown a limited level of inter-population gene flow. 3. Under suitable conditions, aphids take off, maintain flight and alight in response to the appropriate visual and olfactory cues. Undoubtedly successful long-distance movement occurs from time to time, but its ecological relevance may have been overstated in the past. It may be selectively disadvantageous for aphids to move from areas containing their host plants. In contrast, it is advantageous for aphids to maximise their chances of survival and reproductive success by landing on suitable plant hosts at the earliest opportunity. 4. The clonal nature of aphids (a single genotype may comprise vast numbers of individuals) means that there may be advantages to phenotypic variation between individuals in the readiness to move. Recent evidence indicates that such a variation exists in the duration of the behavioural migratory phase, the initial period of maiden flight when host-plant cues are ignored and when landing is inhibited. 5. The relative biological importance of short- us. long-distance movements is reassessed with reference to plant virus epidemiology and the spread of new genotypes, e.g. insecticide resistance. It is concluded that the biological relevance of short-distance movements have a much greater impact on population and genotype distribution than long-distance movements, which may be comparatively infrequent.     

POLYPHYLY OF THE BLACKBIRD GENUS AGELAIUS AND THE IMPORTANCE OF ASSUMPTIONS OF MONOPHYLY IN COMPARATIVE STUDIES

A phylogeny for Agelaius blackbirds was constructed using sequence data from an 890 base-pair (bp) region of the mitochondrial cytochrome-b gene in nine species of Agelaius and a single species from all but 1 of the 28 described blackbird genera and subgenera. The genus was found to be polyphyletic with the South American members of Agelaius more closely related to other South American blackbird genera. Application of bootstrap and jackknife manipulations supports this conclusion. That this relatively well-known genus is polyphyletic represents a warning to those attempting to construct phylogenies without first demonstrating monophyly of the ingroup. The conclusion that Agelaius is polyphyletic necessitates (1) the reinterpretation of previous studies that assumed monophyly and (2) the initiation of a variety of new comparative behavioral and ecological studies suggested by this finding.     

THE INFLUENCE OF ENVIRONMENTAL VARIATION ON GROUP AND INDIVIDUAL SELECTION IN A CRESS

An experimental study of group and individual selection for leaf area under different patterns of environmental variation is presented. This study, which uses the cress Arabidopsis thaliana, demonstrates that group selection can occur in plants. The response to group selection was always in the expected direction, but surprisingly, the response to individual selection was not. Furthermore the interaction between group and individual selection was significant. Individual selection interfered with the response to group selection whether the two forces were acting in concert or were opposed. The effects of the environmental variation treatments were detected mainly as three-way interactions with group and individual selection. Group selection was more effective in environments that interfered with individual selection, as well as in environments that did not interfere with group selection. These results suggest that the ability of a character to respond to group selection, individual selection, or both will depend on a great many factors and that the relative importance of the different levels of selection can only be determined empirically.     

OF MICE AND KIN: THE FUNCTIONAL SIGNIFICANCE OF KIN BIAS IN SOCIAL BEHAVIOUR

1. Sharing recent ancestry (kinship) increases the degree of genetic similarity between individuals, where genetic similarity could mean anything from sharing a particular allele to sharing an entire genome. 2. Genetic similarity can influence behavioural and other responses between individuals in a number of ways, discriminatory and non-discriminatory. All are likely to result in kin bias, because of the correlation between genetic similarity and kinship, but only some should be regarded as involving kin discrimination. 3. Non-discriminatory kin bias could arise through close relatives sharing, for instance, physical characteristics (such as those influencing competitive ability), thresholds of behavioural response or requirements for particular resources. 4. Discriminatory kin bias could arise through the direct perception of genetic similarity between individuals (direct similarity discrimination) or the use of cues likely to correlate with genetic similarity (indirect similarity discrimination--of which kin discrimination is one form). Alternatively, it could arise incidentally through mistaken identity or discrimination at some other level, such as species identification. 5. Experiments with laboratory and wild house mice have revealed kin bias in a number of contexts, including (a) parental and infanticidal behaviour, (b) sexual development and behaviour and (c) investigatory behaviour and passive body contact among juveniles and adults. 6. While kin bias in mice has been interpreted as evidence for kin discrimination, there are several problems with such an interpretation. These include (a) pronounced and complex effects of familiarity on discrimination, (b) a high risk of error-proneness in the indirect cues used in apparent kin discrimination and (c) weak and easily disrupted kin bias effects in certain contexts. 7. Consideration of social structure and discriminatory responses within populations of wild house mice leads to an alternative explanation for some kin bias in terms of incidental discrimination based on social group membership. 8. Several results from laboratory experiments suggest incidental discrimination is a more parsimonious explanation than kin discrimination for some intrasexual kin bias in behaviour. However, kin or direct similarity discrimination appears to be the most likely explanation for other aspects of intrasexual kin bias and for intersexual kin bias.     

太行山猕猴下颌骨变量相关性研究

本研究测量了１８例（雄４,雌１４）成年太行山猕猴下颌骨的１２项变量。通过对下颌骨变量的性别判别分析和相关分析。结果显示：太行山猕猴下颌骨变量有其自身特征,与其它猕猴下颌骨资料比较表现出一定差异;用Ｏｔｔｅｓｔａｔ方法对有关变量建立性别判别函数式,其判别率达８６．８６％,下颌骨变量相关性研究表明,各变量之间有正相关,也有负相关,大多数变量之间相互程度较差,不同变量之间其相关程度存在一定差异。     

POPULATION STRUCTURE AND COMPETITION AMONG KIN IN THE CHORUS FROG (PSEUDACRIS TRISERIATA)

In natural populations on Isle Royale, tadpoles of the chorus frog live in small pools on the shore of Lake Superior. Hatchling densities are high and sufficient to cause competitive impact on survivorship, growth, and development. The temporal and spatial pattern of egg laying indicates that tadpoles in many of the pools belong to single sibships. I calculated average coefficients of relationship among tadpoles under the assumption that eggs laid together are the products of the same breeding pair; the coefficients indicate that relationship among competing larvae averages approximately 0.35, and varies widely among larval subpopulations, from less than 0.1 to about 0.5. Two growth experiments were carried out in pens to test whether growth trajectories and larval characteristics at metamorphosis are influenced by relationship among competing tadpoles. In both experiments, initial density was crossed with average relationship; relationship was controlled by varying the number of sibships per pen from one to four. The same sibships were used in both experiments, but one experiment had lower initial densities and less water volume per pen than the other. In both experiments, density reduced growth, developmental rate, size at metamorphosis, survivorship to the onset of metamorphosis, and the proportion of survivors which actually attained metamorphosis by the end of the experiment. Kin effects occurred only in the experiment carried out in small pens at high initial densities: in this experiment, pure sib populations grew faster, and a higher proportion attained metamorphosis. However, there were no kin effects on larval period or body size at metamorphosis. The chorus frog appears to have a population structure conducive to kin-group selection. Furthermore, high variance in the average coefficient of relationship among pools should favor kin recognition and kin-specific interference behavior. The growth experiments suggest that the tadpoles respond to the genetic relationship of competitors, with significant effects on the distribution of fitness at metamorphosis among members of the group.     

RELATIVE IMPORTANCE OF CHOLINE TRANSPORT TO SPONTANEOUS AND POTASSIUM DEPOLARIZED RELEASE OF ACh

—The importance of extracellular choline transport to spontaneous and K⁺ depolarized release of ACh was studied using mouse brain cortex minces. The results suggest that extracellular choline transport is not essential to spontaneously released ACh but is essential to K⁺ depolarized ACh release. Similar cumulative amounts of choline and ACh were found in the incubation media following incubation of minces in either Krebs or 35 mm -K⁺ Krebs suggesting the same production of free choline during both conditions. Double reciprocal plots of choline accumulation by non-depolarized cortex minces yield high and low affinity components. Conversely, similar analysis of choline accumulation by depolarized minces yields a single Michaelis constant (68 μm ) similar to the low affinity (50 μm ) Michaelis constant determined for choline accumulation by non-depolarized minces. Kinetic analysis of ACh release as a function of extracellular choline concentration during K⁺ depolarization also yields a Michaelis constant of 68 μm These data suggest a link between choline transport and ACh release during K⁺ depolarization.     

THE RELATIVE IMPORTANCE OF pH AND CARBON DIOXIDE TENSION IN DETERMINING THE CESSATION OF CILIARY MOVEMENT IN ACIDIFIED SEA WATER

The length of time that cilia from the gills of Mylilus continue to beat in acidified sea water depends to some extent on the pH of the solution but to a greater extent on its carbon dioxide tension.     

THE RELATIVE IMPORTANCE OF MOLLUSCS AND INSECTS AS SELECTIVE GRAZERS OF ACYANOGENIC WHITE CLOVER (TRIFOLIUM REPENS)

Selective grazing of acyanogenic and cyanogenic white cloverwas investigated by a field experiment using biocides to maintain(a) mollusc only, (b) insect only, (c) both mollusc and insect,and (d) neither mollusc nor insect, grazing regimes. Molluscsfed more on acyanogenic clover throughout the year, whereasinsects damaged more acyanogenic plants in late summer, butmore cyanogenic plants in spring. When both molluscs and insectswere present, the net effect was greater damage to acyanogenicplants. However, in situations where insects are more abundantthan molluscs there might be a net selection against cyanogenicclover. (Received 16 December 1988; accepted 22 February 1989)