Showing papers in "Biological Journal of The Linnean Society in 1984"

Enemy free space and the structure of ecological communities

Abstract: We define ‘enemy free space’ as ways of living that reduce or eliminate a species' vulnerability to one or more species of natural enemies. Many aspects of species' niches, in ecological and evolutionary time have apparently been moulded by interactions with natural enemies for enemy free space. We review a large number of examples. Yet many ecologists continue to think and write as though classical resource based competition for food or space is the primary determinant of species' niches. Often it is not. The recognition that the struggle for enemy free space is an important component of many species' ecologies may have important consequences for studies of community convergence, limits to species packing, and the ratio of predator species to prey species in natural communities.

Progressive background in moths, and a quantitative measure of crypsis

Abstract: A method is presented for quantitative estimation of the degree of crypsis of species seen by visual predators against known backgrounds. It is based upon a comparison between transects taken across animal and background colour patterns. The method was applied to day-resting moths in deciduous forest in New Jersey. Each species is found for two to four weeks at characteristic dates, and there is a constant turnover of species. In both moths and backgrounds there is a regular change in the colour pattern parameters from winter through spring to early summer. Moths are on average more cryptic at their normal dates than they would be if present earlier or later in the year. Species with known resting sites are on average more cryptic on their resting sites than other background habitats. Species that rest on more than one background habitat are less cryptic on their preferred habitats than are specialists. Species that rest under leaves and are not visible from above are not very cryptic. Specific v. general resemblance, disruptive coloration, and factors affecting ‘aspect diversity’ are discussed. The new method of estimating crypsis is useful for studies of crypsis as well as in sexual selection. It is necessary to know much about the resting sites and behaviour of moths, as well as other functions of colour patterns, to understand colour pattern evolution.

Androdioecy and the evolution of dioecy

Abstract: The likelihood that dioecy could evolve via androdioecy is examined. It is concluded that female-sterility mutations are unlikely to be able to invade populations of self-compatible hermaphrodite species, even if the resources that an hermaphrodite devotes to seed production can be diverted to yield increased survival and also to increase male fertility. These findings are in agreement with the great rarity of androdioecy. Claimed cases of androdioecy are reviewed. All of the species in question appear to be functionally dioecious, with females retaining substantial anther vestiges. It is argued that this morphological androdioecy is in no way indicative of a previous functionally androdioecious state. The details of the reproductive biology of many of these species seem rather to be consistent with their having evolved dioecy via gynodioecy. The rarity of androdioecy, as a route to the evolution of dioecy, suggests that re-allocation of reproductive resources is unlikely to be the sole factor of importance, and supports an important role for inbreeding avoidance. The fact that females in some dioecious species retain anthers of substantial size, containing considerable quantities of pollen, gives further support to the view that male-sterility mutations can sometimes be favoured even when little or no resources are re-allocated to male functions. This is impossible without substantial selfing and inbreeding. It is therefore concluded that inbreeding avoidance is generally important in the evolution of dioecy, though reallocation of reproductive resources is also necessary.

The selection of cleistogamy and heteromorphic diaspores

Abstract: Models for the evolution of a mixture of cleistogamous (closed, autogamous) flowers and chasmogamous (open) flowers are described. The ‘basic’ model takes into account features associated with cleistogamous self-pollination, including the greater economy and certainty of cleistogamous fertilization and the inability of cleistogamous flowers to contribute pollen to the outcrossed pollen pool. Complete cleistogamous selfing is favoured when allocation to maternal function, fertilization rate, and viability of progeny are sufficiently greater for the cleistogamous component, and when the resources spent on ancillary structures in cleistogamous flowers, cleistogamous seed costs, and inbreeding depression are low. The result is discussed with respect to the cost of sex argument and relevant ecological data. Suggestions for the apparent rarity of cleistogamy are presented. The ‘complex habitat’ model extends the basic model to situations in which the success of reproduction by cleistogamy or chasmogamy varies according to the environment of the parent. In this situation, reproduction by both cleistogamy and chasomogamy is sometimes selected. A ‘near and far dispersal’ model addresses the question of the evolution of dual modes of dispersal, which occur in some cleistogamous and non-cleistogamous plants. A dual mode of dispersal may evolve if a narrowly dispersed seed type is more successful in establishing at the sites located within its dispersal range compared with a second, more widely dispersed seed type which experiences less sib competition. The prediction is discussed with respect to data from amphicarpic plants.

Variation strategies of plants in heterogeneous environments

Abstract: Plant structures exhibit five principal classes of variation in heterogeneous environments, namely uniformity, continuous lability, genetic specialization (polymorphism), environmentally- or statuscued alternatives (conditional choices) and multiple strategies—the simultaneous operation by one plant of distinct types of structures that perform the same function. Multiple strategies are a diverse but neglected class that includes simultaneous cosexuality (hermaphroditism and other monomorphic sex conditions), facultative cleistogamy, heteromorphic diaspores, and reproduction by both seeds and ramets. An analysis of seven functions in the angiosperm flora of New Zealand shows that uniform and labile strategies considered jointly are most common, and multiple strategies are more common than either polymorphisms or conditional choices. Phenotypic models of the natural selection of structural variation are presented. They predict the general conditions under which multiple, conditional and uniform strategies are selected when the environment is spatially heterogeneous for either parents or their offspring. The models can explain many features of variation strategies, including why multiple strategies are a plant speciality, why conditional strategies such as sex choosing are rare and random choices are even more rare (unknown?), and why some self-fertilizing plants have distinct cleistogamous flowers. The models also suggest further avenues of research.

The evolutionary significance of dry and wet season forms in some tropical butterflies

Abstract: An explanation is developed for the adaptive significance of the forms characteristic of the dry season and wet season adult generations of some tropical butterflies. The divergent phenotypes are accounted for as adaptive responses to a shift in the optimum balance between dependence on the alternative (but interdependent) strategies of active anti-predator devices and of crypsis. The seasonal polyphenisms exhibited by the satyrines Melanitis leda (Fabricius) and Orsotrioena medus (Fabricius) and the nymphalid Junonia almana (Linne) are examined in detail. The wet season forms show prominent marginal eyespot patterns which are displayed at rest and function principally in the deflection of attacks by vertebrate predators. In contrast, the dry season forms show very small or no spots and are wholly cryptic. Wet season butterflies are more active in general than those in the dry season when aestivation behaviour is often observed. The alternative phenotypes represent responses to the differences in behaviour, environment and nature of predation. Reproductive success is optimized in each season by an interaction of phenotype and behaviour. The hypothesis must be tested in detail by an investigation of the behavioural ecology and population biology of particular species. It is argued that these seasonal polyphenisms provide examples of adaptations to a repeating pattern of changing environments where the mode of selection is, in broad terms, understood.

Changes in the native fauna of the Galapagos Islands following invasion by the little red fire ant, Wasmannia auropunctata

Abstract: SUMMARY The little fire ant, Wasmannia auropunctata, occurs on five islands in the Galapagos archipelago. It is still in the process of expanding its range on at least two of these islands (Santa Cruz and San Salvador). At least 17 of the remaining 28 ant taxa currently known from the Galapagos are affected by the presence of Wasmannia. On Santa Cruz and San Salvador few other species of ants co-occurred with Wasmannia, except at the edges of its distribution or in areas which it had only recently invaded. Wasmannia was also found to reduce population densities, or eliminate altogether, three species of arachnids (a scorpion and two theridiid spiders) as well as reducing the overall abundance and species diversity of flying and arboricolous insects at two sites on San Salvador. The mechanisms by which these species are displaced are currently being investigated. Certain arthropods may escape the detrimental influences of Wasmannia through non-overlap of habitat and food requirements (as documented in the case of certain hypogeic ants), while others may actually benefit from the presence of Wasmannia, as appears to be the case for some coccids.

Evolution of nesting strategies of ants: genetic evidence from different population types of Formica ants

Abstract: Genetic population structure was studied in two types of populations in the ants Formica exsecta and F. pressilabris: populations consisting of single-nest colonies (monodomy) and populations consisting of multi-nest colonies (polydomy). These characteristics seem to be associated with the number of egg-laying females (gynes) in a nest, mating structure of the population, sex ratio and male size variation. The monodomous populations are characterized by single-gyne nests, the population sex ratio is either I:1 or female-biased, males are mainly large-sized, and there is slight inbreeding in the population. The polydomous populations have multi-gyne nests with gynes related to each other, sex ratio is strongly male-biased, most males are small-sized, and there is slight genetic microdifferentiation within the populations. Diploid males found in a polydomous F. pressilabris population suggest that the population is inbred and isolated. Habitat localization is presented as a plausible explanation for the evolution of the polygynous and polydomous population structure.

Pyrazines as warning odour components in the Monarch butterfly, Danaus plexippus, and in moths of the genera Zygaena and Amata (Lepidoptera)

Abstract: 2-Methoxy-3-alkylpyrazines have been identified as odour components in Danaus plexippus, Zygaena lonicerae and an Australian Amata species, by means of coupled gas chromatography/mass spectrometry, with selected ion monitoring. Wide variability in pyrazine content was observed with D. plexippus and this was correlated with similar variability in the larval food-plants, Asclepias spp., which are presumed to be the odour sources for this butterfly. The importance of pyrazines in the biology of aposematic insects and their role as ingredients of a generalized warning system are discussed.

Miniaturization and its effects on cranial morphology in plethodontid salamanders, genus Thorius (Amphibia: Plethodontidae). I. Osteological variation

Abstract: Cranial skeletal morphology, ontogeny and variation are examined in five species of Thorius, a genus of diminutive plethodontid salamanders that are among the smallest, extant, tailed tetrapods The skull of adull Thorius is characterized by: (1) limited development or absence of several ossified elements and dentition; (2) increased inter-and intraspecific variability; (3) novel morphological configurations of the braincase and jaw suspensorium Posthatching cranial mineralization in all species of Thorius is truncated precociously with respect to that typical of larger and more generalized plethodontid genera, such as Pseudoeurycea These features implicate paedomorphosis as a predominant mechanism responsible for the evolution of decreased size in Thorius from larger plethodontid ancestors Interspecific differences in cranial morphology are evident; species may be characterized by greater or lesser degrees of truncated development However, there is no consistent relationship between degree of paedomorphosis and mean adult body size in interspecific comparisons Adult morphology of several individual elements represent potentially useful taxonomic characters for distinguishing species Reduction, increased variability, and morphological novelty are common to many lineages of dwarfed taxa They represent a null hypothesis for examination of the developmental mechanisms and morphological consequences of miniaturization in other groups

Functional cranial analysis of large animalivorous bats (Microchiroptera)

Abstract: Large animalivorous bats include carnivorous, piscivorous and insectivorous microchiropterans. Skull proportions and tooth morphology are examined and interpreted functionally. Four wide- faced bats from four families are convergent in having wide skulls, large masseter muscle volumes and stout jaws, indicating a powerful bite. Three of the four also have long canine teeth relative to their maxillary toothrows. Carnivorous bats have more elongate skulls, larger brain volumes and larger pinnae. The wide-faced bats are all oral emitters and have heads positively tilted relative to the basicranial axis. The carnivorous species are nasalemitting bats and have negatively tilted heads. The orientation of the head relative to the basicranial axis affects several characters of the skull and jaws and is not correlated with size. The speculation that the type of echolocation may be more of a determinant of evolutionary change than the feeding mechanism is addressed. Wide-faced bats are thought to be capable of eating hard prey items (durophagus) and are probably non- discriminating, aurally less sophisticated insect generalists while the carnivorous and non-durophagus insectivorous bats may be more discriminating and aurally more sophisticated in what they eat.

The mating systems of pinnipeds and marine iguanas : convergent evolution of polygyny

Abstract: The convergent polygynous mating systems of marine iguanas and otariid pinnipeds depend on the existence of large female aggregations. These can build up where abundant marine food resources occur around oceanic islands which harbour fewer predators than continental areas. For marine iguanas distribution of food resources appears to determine the location of colonies, while for pinnipeds habitat choice is more decisive. In marine iguanas females benefit from gregariousness through reduced predation risk and social thermoregulation. In pinnipeds, sea lions may derive thermoregulatory benefits from gregariousness, while fur seals appear to be largely non-gregarious. In both groups males defend territories in areas of high female density. Large sexual size dimorphism presumably evolved in response to strong selection for high fighting potential of males. The capability to fast for prolonged periods of territory tenure is considered a secondary benefit of large male size, but not the driving force behind its evolution. We hypothesize that marginal males, through continuous sexual harassment of females that stay outside territories, have exerted pressure towards the evolution of female gregariousness.

The functional basis of frequency-dependent food selection

Abstract: Various animals have been observed to select food in a way that changes according to the relative frequency of the different foods available. Sometimes only the strength of selection varies, its direction remaining constant, but sometimes the direction of selection also changes. Selection of a food may be more intense as that food becomes rarer, or vice versa. I discuss here the situations in which animals, particularly predators, may maximize their feeding efficiency by behaving in ways that result in frequency-dependent selection of their food. These include cases in which different types of prey occupy different ecological niches, those in which there are benefits or costs to mixed diets for the predator, those in which rarer types of prey provide easier targets, those in which the different types of prey provide unequal benefits to the animal eating them, those in which direct comparison of the benefits is possible, those in which sampling is necessary because the benefits are unknown, and Batesian and other mimicries. Frequency-dependent selection of food is likely to be common and widespread: to assume frequency independence, without testing, may often be misleading.

Microgeographic variation in allozyme and shell characters in Littorina saxatilis Olivi (Prosobranchia: Littorinidae)

Abstract: Twenty-three enzymes and five shell parameters were screened in 11 subpopulations of Littorina saxatilis Olivi (=L. rudis Maton) occupying different habitats over a 1 km stretch of coastline. Shell morphology varied considerably and consistently with respect to degree of exposure, and since there is evidence that such morphology is at least partly under genetic control, it is likely that natural selection selects particular genotypes at particular locations. There was significant allozyme heterogeneity between neighbouring subpopulations, sometimes only metres apart, but little of the allozyme variability could be related directly to environmental pressures. Thus, with the exception of the Odh locus, the considerable morphological differentiation between snails from exposed and sheltered sites was not reflected in differentiation of those genes coding for electrophoretically assayed enzymes. At the Odh locus, virtually all the genetic differentiation between subpopulations was attributable to differentiation between habitat types. Two loci, Sod-1 and Aat-1, showed highly significant genetic disequilibrium, and possible reasons for this are explored. The population structure as assessed electrophoretically accords well with the stepping-stone model which permits greater differentiation of neighbouring populations than the island model, and which seems realistic in the ovoviviparously reproducing L. saxatilis, where the greater part of gene flow is likely to occur through the occasional migration of adults between contiguous populations.

Kin selection and frequency dependence: a game theoretic approach

Abstract: Game theory models show that the evolution of interactions between relatives is determined by two kinds of fitness effects: Hamilton's inclusive fitness effect, and a frequency-dependent synergistic effect. The latter arises when an individual's behaviour has different effects on the fitness of interactants, depending on whether or not they perform the same behaviour. Knowing the sign of the synergistic effect is sufficient to understand most of the qualitative features of genetic models that show departures from Hamilton's rule. Since this synergistic effect does not depend on the interactants being related, it is best viewed as something distinct from kin selection. In this view, Hamilton's rule is basically correct for describing kin selection, and most deviations from it are due to the distinct process of synergistic selection.

A seasonal census of phenolics, fibre and alkaloids in foliage of forest trees in Costa Rica: some factors influencing their distribution and relation to host selection by Sphingidae and Saturniidae

Abstract: The foliage of 80 species common in the Santa Rosa National Park, Costa Rica, has been analysed for content of total phenolics, condensed tannins, acid detergent fibre and water. Wherever possible analyses were performed at three stages in the life cycle of the leaf: young but fully expanded (coinciding with the beginning of the rainy season); middle-aged (two months later); and old (six months later). A comparison of the three age classes showed no significant change in the levels of phenolics or fibre as leaves aged but water content decreased significantly. A comparison of deciduous and evergreen species in the sample showed that the latter group had leaves with a significantly higher fibre content at all three sampling times, most particularly at the beginning of the rainy season, but other measures were not significantly different. Alkaloids were much more common in the foliage of deciduous species and it was observed that their distribution differed significantly from that of total phenolics and condensed tannins. It is suggested that the interaction that occurs between many tannins and alkaloids would be liable to reduce the defence capability of both classes of compounds if they occurred together. High levels of defoliation occur in the early rainy season (third to tenth weeks) due to larvae of moths of the Sphingidae and Saturniidae. A comparison of investigated tree species that host larvae of these two taxa shows a striking dichotomy. Species that are selected by Sphingidae tend to be relatively deficient in levels of phenolics but are more likely to contain alkaloids, and probably other small toxic molecules. Saturniidae, on the other hand, appear to prefer host-species rich in phenolics but poor in alkaloids.

Mimicry and the Monte Carlo predator: the palatability spectrum, and the origins of mimicry

Abstract: With a view to clarifying some recent controversies, the behaviour of a predator confronted with a mixture of models and mimics has been simulated by a simple Monte Carlo computer program. When learning and forgetting are described by a stochastic model in which learning depends on experience, and forgetting on the passage of time, then the ‘spectrum of palatability’ (that is, the continuous variation in the desirability of prey to a predator, from the delectable, through the neutral, to the downright revolting), is converted into a spectrum of protection, in which palatable prey are heavily consumed and distasteful prey are largely avoided. In such a system, a palatable (Batesian) mimic is protected, but causes an increase in the rate of predation on its model (compared with an identical but un-mimicked control); but when both model and mimic are distasteful (Muellerian mimics), both species gain in protection. The mimic in a Muellerian system can be regarded as the species which would be the less protected, and which therefore gains the more from the mimicry. When mimicry evolves by a single large mutation, it is this species which will change: the model will not alter in pattern at this stage. It is useful to recognize a further category, effectively neutral mimicry, in which the mimic, because it is rare or nearly neutral in palatability, has virtually no effect on the model. The fitness of mimics is density-dependent: positively for Muellerian mimics (more protection when common) and negatively for Batesian mimics (more protection when rare). The computer model thus gives results which conform with some of the traditionally accepted differences between Batesian and Muellerian mimicry. It is suggested that warning colour will usually evolve in the form of Muellerian mimicry, or perhaps as Batesian mimicry in species whose behaviour makes them conspicuous, and that distastefulness will usually evolve in cryptically-coloured species. The usual evolutionary pathway to full aposematism is predicted to be distastefulness first and warning colour second.

The classical case of character release: Darwin's finches (Geospiza) on Isla Daphne Major, Galápagos

Abstract: The history of how Darwin's medium ground finch (Geospiza fortis) on Isla Daphne Major, Galapagos became a textbook example of character release is reviewed. Four hypotheses for the evolution of the intermediate-sized Daphne fortis are examined, including genetic drift/founder effect, hybridization with the small ground finch (G'. fuliginosa), food supply (or local adaptation hypothesis) and character release in allopatry. Modern data suggest that genetic drift is unlikely to have been important, due to inadequate isolation and over-riding selection and introgression on Daphne. All three remaining hypotheses have probably played a role. Hybridization with G. fuliginosa occurs, although it cannot counteract the selection pressures seen during our study. Local adaptation has also occurred, with natural selection changing the relative frequencies of fortis phenotypes in response to changes in Daphne food supplies. The selection resulted from correlations between the size of seeds available, feeding behaviour and morphology. However, recent phenotypic tracking has resulted in larger, not smaller phenotypes. There is also evidence for character release in the form of diet expansion by G. fortis during periods of food shortage, and indirect evidence for interspecific competition between fortis and the cactus ground finch (G. scandens). The Daphne fortis phenotype probably represents a balance between introgression with fuliginosa, selection for larger body size in dry years and selection for smaller body size in wet years. The simple textbook account of a character shift caused by the accidental absence of competitors should be qualified to reflect the ecological complexity of the situation.

An insect introduction to the maritime Antarctic

Abstract: Although several invertebrates have been introduced by Man into the Antarctic, no holometabolous insects have survived to colonize terrestrial habitats successfully. Data are presented on the survival of populations of a chironomid midge, together with an enchytraeid worm, for 17 years in a maritime Antarctic site at Signy Island, South Orkney Islands. Both species are thought to have been introduced on plant material transplanted from either South Georgia or the Falkland Islands or both in 1967. Population densities average 25718m-2 for the dipteran larvae and 3243 m-2 for the worms. Successful completion of the midge's life cycle was indicated by emergence of brachypterous adults and oviposition (the population is parthenogenetic with only females present). Although both taxa are capable of supercooling to between -13 and -26°C, this capacity may not be sufficient in a severe winter to avoid lethal freezing. Four potential cryoprotectants were found in insect extracts, but in concentrations (< 1 % fresh weight) unlikely to influence cold hardiness. Both invertebrates appear to be pre-adapted for survival in much harsher conditions than they normally experience, by the extension of existing physiological mechanisms. It is concluded that the main limitations to invertebrate colonization of suitable Antarctic land areas by soil-dwelling species are geographical.

A dipteran from south of the Antarctic Circle: Belgica antarctica (Chironomidae) with a description of its larva

Abstract: Belgica antarctica Jacobs is recorded for the first time from two localities south of the Antarctic circle: Orford Cliff (66°55'S) on the Continental mainland and the Refuge Islands (68°21'S) The larva is described, and measurements of head capsule lengths indicate four instars The larvae south of the Antarctic circle appear to be slightly smaller than those from within the main distributional range Belgica antarctica is certainly the earth's southernmost free-living holometabolous insect, but the flea Glaciopsyllus antarcticus has been recorded 14 minutes of latitude farther south than the southernmost records of B antarctica

The adaptive bases of ant-mimicry in a neotropical aphantochilid spider (Araneae: Aphantochilidae)

Abstract: The aphantochilid spider Aphanlochilus rogersi accurately mimics black ants of tribe Cephalotini, and is commonly found in the neighbourhood of its models’ nests. The mimic seems to be a specialized predator of this type of ant, rejecting any insect offered as prey other than cephalotines. In the field, A. rogersi was observed preying on the model species Zac7yptocerus pusillus. In captivity, the spider preyed on the models Z. pusillus and Z. depressus, as well as on the yellow non-model z, cbpealus. Recognition of correct prey by A. rogersi appears to he based primarily on visual and tactile stimuli. Capturing ant prey from behind was the most common attack tactic observed in A. rogersi, and is probably safer than frontal attacks, as in this case the spider can be bitten on the legs before the ant is immobilized. Aphanlochilus rogersi, when feeding on the hard-bodied ant models, uses the ant corpses as a ‘protective shield’ against patrolling ants of the victim’s colony and resembles an ant carrying a dead companion. Certain types of mimetic traits in A. rogersi (close similarity to ant models in integument texture and pilosity of body and legs), together with ‘shielding behaviour’, are thought to function as ant-deceivers, facilitating the obligatory intimate contact the mimic must make with cephalotines in order to capture a prey among other ants. The close similarity in the arrangement of dorsal spines, body shape, integument brightness and locomotion, together with antenna1 illusion, is regarded as a strategy of A. rogersz for deceiving visually-hunting predators that avoid its sharp spined ant models. It is proposed that ant-mimicry in A. rogersi has both an aggressive and a Batesian adaptive component, and evolved as a result of combined selective pressures exerted both by Cephalotini ant models (through defensive behaviour towards the mimics which attack them) and predators that avoid cephalotines (through predatory hehaviour toward imperfect mimics). This suggestion is schematized and discussed in terms of two tripartite mimicry

Geology of Galapagos

Abstract: This paper reviews the origins and geological history of the Galapagos Islands. The islands arose from a ‘hot-spot’. The oceanic crust on which the islands are built can be no more than 10 million years old, and the islands themselves have been in existence at least 3.3 million years. The Galapagos are among the most active volcanic groups in the world, and the physical nature of the islands is dominated by lava structures of various ages, including lava tubes or tunnels, which have been of particular interest to biologists. Weathering of the rock to produce soil has generally been slow, particularly in the drier parts.

Variation among populations of Galapagos land iguanas (Conolophus): contrasts of phylogeny and ecology

Abstract: A phylogenetic scheme derived via multivariate analyses of adaptively neutral scale characteristics is compared to patterns of ecological adaptation in body size and shape, hatchling size, clutch size, and reproductive seasonality, in extant populations of Galapagos land iguanas (genus Conolophus). Three groups of land iguana populations are identified, the oldest being the population of Isla Santa Fe, followed by the populations of the central islands (Santa Cruz, Plaza Sur and Baltra), the youngest populations are those of the western islands (Fernandina and Isabela). Patterns of ecological similarity among these populations are not concordant with phylogenetic lineage. Populations most similar in ecological characteristics are often phylogenetically divergent. Adaptation to local conditions by iguana populations is apparently more important than phylogenetic constraint in explaining variation in ecological characteristics. The assumption that phylogenetically closely-related organisms are also ecologically more similar than less closely-related organisms is not supported by this evidence. Some previous studies may have been misled by using ecological characteristics to derive phylogenetic lineages, resulting in circular support of the assumption.

Selection by passerine birds is anti‐apostatic at high prey density

Abstract: Most of the results from past experiments with wild birds and green and brown pastry ‘baits’ have suggested that disproportionately more of the rare forms are eaten when bait density is high (i.e. selection is anti-apostatic). In two separate series of experiments we presented birds with dishes containing 270 baits of one colour and 30 of another. In series I, five different pairs of colours were presented simultaneously to wild birds at two sites. One colour of each pair was common at one site and the same colour was rare at the other site. After 35 days the ratios of the colours were reversed and the dishes were presented for another 35 days. There was a statistically significant tendency for the colours to be at a higher risk when rare. In series II, three caged blackbirds were offered green and brown baits in two dishes simultaneously; in one dish green was rare and in the other brown was rare. Selection over 6 days was anti-apostatic for all three birds combined but the data proved heterogeneous both between and within individuals. At any one time, each bird tended to concentrate on one colour, irrespective of whether that colour was rare or common. We believe that this behaviour leads to anti-apostatic selection, as has been observed in these and other experiments with pastry prey.

Olfactory response and resource utilization in Drosophila: interspecific comparisons

Abstract: Olfactory response and resource utilization in Drosophila were compared among three domestic (D. melanogaster, D. simulans, D. immigrans) and one Australian endemic (D. lativittata) species. Olfactory response was measured in a choice type olfactometer (Fuyama, 1976). The following chemicals common in Drosophila resources were used as odourants: acetaldehyde, acetic acid, propionic acid, methanol, ethanol, n-propanol, isopropanol, n-butanol. Resource status of these chemicals was determined either from the literature or by adult longevity tests. All species were attracted by acetaldehyde, while methanol, isopropanol and n-butanol were unattractive. Ethanol attracted all species except D. immigrans, while only D. lativittata and D. melanogaster were attracted to n-propanol, propionic acid and acetic acid Methanol and isopropanol were not utilized as resources by any of the species, while D. melanogaster and D. lativittata showed greater utilization/tolerance of the other chemicals. Some correlation between resource utilization and olfactory response was found at the interspecific level, although not all chemicals utilized as resources are attractants. The adaptive significance of the interspecific variation in olfactory response is discussed, especially in relation to habitats selected. The results provide suggestions for habitat selection studies at the intraspecific level.

Evolutionary divergence of giant tortoises in Galapagos

Abstract: The giant tortoises in the Galapagos Archipelago diverge considerably in size, and in shape and other carapace characteristics. The saddleback morphotype is known only from insular faunas lacking large terrestrial predators (i.e. Galapagos and Mauritius) and in Galapagos is associated with xeric habitats where vertical feeding range and vertical reach in agonistic encounters are adaptive. The large domed morphotype is associated with relatively cool, mesic habitats where intraspecific competition for food and other resources may be less intense than in xeric habitats. Other external characteristics that differ between tortoise populations are also correlated with ecological variation. Tortoises have radiated into a mosaic of ecological conditions in the Galapagos but critical data are lacking on the role of genetic and environmental controls on phenotypic variation. Morphological divergence in tortoises is potentially a better indicator of present ecological conditions than of evolutionary relationships.

Enzyme polymorphism, morphometric variation and population structure in a restricted endemic, Silene diclinis (Caryophyllaceae)

Abstract: Silene diclinis is a dioecious perennial herb, restricted to a small area of the SE Spanish province of Valencia. Polyacrylamide gel electrophoresis and morphometric analysis were carried out on cultivated material derived from seed collected from the main population of S. diclinis at Jativa. Only two out of 26 inferred enzyme loci showed substantial variation. There was some indication of population subdivision in both. The esterase locus also showed homozygote excess within the population as a whole and within one subpopulation. Morphological characters showed significant differentiation between subpopulations. Low allozyme variability characterizes populations of most endemic species that have been investigated. Isolation and historical events may have been as important as population size or edaphic specialization in causing this low variability. But S. diclinis resembles other outbreeding plants in showing population structure and homozygote excess, suggesting restricted within-population gene flow. Mechanisms that may restrict gene flow in S. diclinis include environmentally-induced differences in flowering time, poor seed dispersal and possibly short pollinator foraging distances. Morphological variability and the incidence of developmental abnormalities are speculatively linked with homozygosity. Storage of genetic diversity in space can occur in restricted as well as widespread species and sampling for gene banking should then be spatially representative. Silene diclinis is threatened by continued habitat loss and consequent genetic erosion; its long-term future may depend on the gene bank and the botanic garden.

An electrophoretic study of the systematic relationships of some closely related goby species (Pisces, Gobiidae)

Abstract: An electrophoretic study of genetic variation at 31 loci in each of nine closely related gobiid species was carried out in order to assess their systematic relationships. The species used were: Pomatoschistus canestrinii, P. lozanoi, P. marmoratus, P. microps, P. minutus, P. norvegkus, P. pictus, Knipowitschia caucasica, Neogobius melanostomus. Genetic distances (D) and identities (I) were calculated by Nei's method for all 36 pairwise comparisons and dendrograms were constructed. The results show that the very similar and cross-fertile species pair, P. lozanoi and P. minutus, have the highest I value; P. norvegkus has high I values with both species. Pomatoschistus marmoratus and P. microps also display high genetic similarity with each other. The remaining Pomatoschistus species and Knipowitschia caucasica are broadly and moderately equidistant from each other and from the five species refferred to above, while Neogobius melanostomus is considerably more distant from all other species. These findings essentially agree with the pattern of relationships established using classical taxonomic approaches. However, the observation that Knipowitschia caucasica is as similar to Pomatoschistus spp. as the latter are to each other suggests that the generic distinction of Knipowitschia could usefully be reconsidered.

Darwin and the Galapagos

Abstract: Charles Darwin's historic visit to the Galapagos Islands in 1835 represents a landmark in the annals of science. But contrary to the legend long surrounding Darwin's famous Galapagos visit, he continued to believe that species were immutable for nearly a year and a half after leaving these islands. This delay in Darwin's evolutionary appreciation of the Galapagos evidence is largely owing to numerous misconceptions that he entertained about the islands, and their unique organic inhabitants, during the Beagle voyage. For example, Darwin mistakenly thought that the Galapagos tortoise–adult specimens of which he did not collect for scientific purposes–was not native to these islands. Hence he apparently interpreted reports of island-to-island differences among the tortoises as analogous to changes that are commonly undergone by species removed from their natural habitats. As for Darwin's finches, Darwin initially failed to recognize the closely related nature of the group, mistaking certain species for the forms that they appear, through adaptive radiation, to mimic. Moreover, what locality information he later published for his Galapagos finch specimens was derived almost entirely from the collections of three other Beagle shipmates, following his return to England. Even after he became an evolutionist, in March of 1837 (when he discussed his Galapagos birds with the eminent ornithologist John Gould), Darwin's theoretical understanding of evolution in the Galapagos continued to undergo significant developments for almost as many years as it took him to publish the Origin of Species (1859). The Darwin-Galapagos legend, with its romantic portrait of Darwin's ‘eureka-like’ insight into the Galapagos as a microcosmic ‘laboratory of evolution’, masks the complex nature of scientific discovery, and, thereby, the real nature of Darwin's genius.

Apostatic selection on prey that match the background

Abstract: There is good experimental evidence that predators often remove disproportionately more of the common prey types. This ‘apostatic selection’ could maintain colour polymorphisms within prey species. In nature, morphs of many species appear to match components in the background, but most of the experiments that have tested apostatic selection have used prey that were conspicuous. In work described in this paper, wild birds at one site were presented a random order of 51 experiments. Seventeen frequencies of orange and grey pastry prey were presented on each of three types of background: a hessian sheet scattered with either orange and grey stones (the ‘matching’ background), or lilac and yellow stones, or green stones (two sorts of ‘control’ background). Each experiment consisted of four trials in succession and the numbers of the two colours eaten in each trial were recorded when about half the total prey had been eaten. Two methods of graphical analysis revealed that apostatic selection occurred on the prey on all three backgrounds, but was strongest in the grey/orange one. This last result must have been caused by some effect of the match between prey and background colour, and behavioural explanations are suggested. It is unclear whether the prey were exhibiting ‘crypsis’ or ‘masquerade’.