Showing papers in "Biological Journal of The Linnean Society in 1985"
TL;DR: In this article, a comparative study of mtDNA and nuclear DNA variability is presented, with emphasis on mtDNA's uniparental and apparently haploid mode of inheritance, which makes mtDNA a superb tool for building trees and time scales relating molecular lineages at and below the species level.
Abstract: This essay reviews comparative studies of animal mitochondrial DNA (mtDNA), with emphasis on findings made and ideas developed at Berkeley. It argues that such studies are bringing together two previous paths of progress in evolutionary biology. One path is that of those who worked far above the species level and were concerned with genealogical trees, time scales and the accumulation of new mutations on surviving molecular lineages. The other path is that of those who worked at and below the species level and were concerned mainly with population structure, migration and the frequencies of alleles that existed in an ancestral population. This fusion of paths is made possible by the high rate at which mutations accumulate on mtDNA lineages and by this molecule's uniparental and apparently haploid mode of inheritance. These properties make mtDNA a superb tool for building trees and time scales relating molecular lineages at and below the species level. In addition, owing to its mode of inheritance, mtDNA is more sensitive to bottlenecks in population size and to population subdivision than are nuclear genes. Joint comparative studies of both mtDNA and nuclear DNA variability give us valuable insights into how effective population size has varied through time. Such studies also give insight into the conditions under which mtDNA from one species can colonize another species.
1,208 citations
TL;DR: Latitude is a better predictor of size in erminea than available measures of climate, seasonality or prey size, and regional differences in the abundance of prey during the growth of young weasels may affect adult size much more in males than in females and contribute to geographic variation in sexual dimorphism.
Abstract: Geographic variation in size (skull length) and sexual dimorphism in Mustela erminea, Mustela frenata and Mustela nivalis in North America is described and analysed in relation to latitude, longitude, climatic variables, and sympatry or allopatry of these species. Only erminea increases in size with latitude; it does so regardless of the presence or absence of frenata or nivalis. Latitude is a better predictor of size in erminea than available measures of climate, seasonality or prey size. There is no evidence for character displacement between any pair of species. The sexes covary in size in frenata and erminea, and probably in nivalis, although geographic variation in sexual dimorphism occurs in frenata and erminea. The principal cause of sexual dimorphism appears to be sexual selection for large size in males rather than the high energetic requirements resulting from an elongate body shape. However, prey size may constrain female size (and possibly also male size). Regional differences in the abundance of prey during the growth of young weasels may affect adult size much more in males than in females and contribute to geographic variation in sexual dimorphism.
168 citations
TL;DR: It is shown that these birds are very little known, in the main, and urged that caution be exercised in the use of what information is available, and an interpretation of parental care and pair-bond patterns in these birds is offered.
Abstract: The breeding behaviour of ratites and tinamous is reviewed. This group includes many of the homeothermic animals which habitually show prominent or exclusive paternal care of eggs and offspring. This unusual parental care pattern is associated with a diverse array of mating systems, ranging from monogamy to mixed polygyny/polyandry. This latter system, typical of the rhcas, is unknown among higher vertebrates outside the taxa considered herein. This diversity of mating systems, together with their great geographical and ecological range, makes ratites and tinamous a group of great potential importance in the investigation of the adaptive significance of social organization, mating systems and parental care patterns. Inadequately described features of their reproductive biology have become incorporated into various considerations of the evolution of reproductive behaviour patterns, and are in danger of assuming the status of fact through repetition. We show that these birds are very little known, in the main, and urge that caution be exercised in the use of what information is available. Directions for new research in ratite breeding biology are suggested, and an interpretation of parental care and pair-bond patterns in these birds is offered.
128 citations
TL;DR: Ultrastructural similarities unite Choanoflagellata and Metazoa as the Kingdom Animalia and proposes that Gastroneuralia and Notoneuralia evolved independently from the trochaea, a blastaea with the blastopore surrounded by a ring of compound cilia, which were both locomotory and particle collecting.
Abstract: Ultrastructural similarities unite Choanoflagellata and Metazoa as the Kingdom Animalia. Mctazoa (Porifera + Placozoa + Gastraeozoa) are characterized by the presence of collagen, septate/tight junctions and spermatozoa. Porifera and Placozoa lack basal lamina, nerve cells and synapses, which characterize Gastraeozoa (Cnidaria + Trochaeozoa). Gnidaria have cnidoblasts and lack the multiciliate cells found in almost all Trochaeozoa (Gastroneuralia + Protornaeozoa). Gastroneuralia (Spiralia + Aschelminthes) have an apical brain and a pair of ventral nerves, a blastopore which becomes mouth and anus, a mouth surrounded by a downstream collecting system of compound cilia, and a mesoderm formed from the blastopore lips. Spiralia (Articulata + Parenchymia + Bryozoa) have spiral cleavage and 4d-cell mesoderm, whereas these characters are lacking in Aschelminthes, which all lack primary larvae. Protornaeozoa (Ctenophora + Notoneuralia) have mesoderm from vegetal cells. Ctenophores have colloblasts. Notoneuralia have a dorsal nervous system behind the apical area and form a new mouth surrounded by an upstream collecting system of single cilia on monociliate cells; the blastopore becomes the anus surrounded by a ring of compound cilia.
These features fit the trochaea theory, which proposes that Gastroneuralia and Notoneuralia evolved independently from the trochaea, a blastaea with the blastopore surrounded by a ring of compound cilia, which were both locomotory and particle collecting.
115 citations
TL;DR: Anthecological relations between a long-spurred angraecoid orchid and pollinating Sphingidae are documented for the first time and the monophily in A. arachnites is interpreted as a result of a refined long-term specialization developed within an archaic evolutionary relationship in a relatively stable environment.
Abstract: Anthecological relations between a long-spurred angraecoid orchid and pollinating Sphingidae are documented for the first time. In a primary forest on the Central Plateau of Madagascar Angraecum arachnites Schltr. was found to be pollinated by and adapted to a single species of hawk-moth, Panogena lingens (Butler), despite abundance of many concurrent Sphingidae of which several were also long-tongued. Furthermore, P. lingens was dimorphic in the length and breadth of its proboscis and only the morph with the longest and most slender proboscis was recorded to pollinate A. arachnites. Exclusive and precise adaptation to the latter morph of P. lingens existed in floral morphology and probably in other characteristics such as flowering phenology and chemical signalling. Several concurrently flowering orchid species were sharing P. lingens as a pollinator resource. The monophily in A. arachnites is interpreted as a result of a refined long-term specialization developed within an archaic evolutionary relationship in a relatively stable environment. The extraordinary number and diversity of long-spurred Orchidaceae in Madagascar appears to be a direct coevolutionary consequence of an Old-World-unique diversity of long-tongued archaic Sphingidae that has persisted in this isolated land.
113 citations
TL;DR: It is argued that groups of similarly coloured species of coccinellids are Mullerian mimicry rings, based on a synthesis of the literature about the nature of their biology and aposematic colour patterns, their highly developed chemical defence and the responses of bird predators to them.
Abstract: It is argued that groups of similarly coloured species of coccinellids are Mullerian mimicry rings. This is based on a synthesis of the literature about the nature of their biology and aposematic colour patterns, their highly developed chemical defence and the responses of bird predators to them. The system of multiple mimicry ‘rings’ is illustrated for the Dutch coccinellid fauna. Some polymorphic species, including Adalia, exhibit red forms and black melanic forms which are apparently components of different putative mimicry rings. A similar reasoning is put forward with regard to the orange and the black forms of the soldier beetle Cuntharis livida. Hypotheses involving spatial variation in comimics, as have been developed to account for some other cases of polymorphic Miillerian mimicry, predict that sympatric polymorphic species exhibiting similar sets of phenotypes will show parallels in their geographical variation. This is tested for A. bipunctata and A. decempunctata in The Netherlands. On this local scale there is no parallel variation; A. bipunctata exhibits marked geographical differentiation whereas A. decempunctata shows a general uniformity in morph frequency. Observations on their population biology show that only in A. bipunctata is there a major spring period of adult reproduction on shrubs exposed to direct sunshine. Previous work has demonstrated an influence of thermal melanism in this period of the life cycle. It is suggested that local responses in species such as A. bipunctata may reflect a partial ‘escape’ from stabilizing aposematic selection. The basis of a steep cline found in C. livida, which opposes one in A. bipunctata, is unknown and unlikely to be related to mimicry. There is some evidence that the polymorphism is influenced by non-random mating. When species and communities of coccinellids are considered on a wide geographical scale many observations about their colour patterns and spatial variation, especially those of Dobzhansky, support an interaction between selection favouring mimetic resemblance and forms of climatic selection, especially thermal melanism. The polymorphism in Adalia is discussed in relation to a system of multiple mimicry rings and to Thompson's recent theoretical treatment of the maintenance of some polymorphisms for warning coloration by a balance between aposematic and apostatic selection. This becomes more tenable in coccinellids because of evidence that bird predators show a variable response to them. Frequency-independent selection arising from thermal melanism can provide the basis of spatial variation in equilibrium points. An alternative to such a hypothesis is one in which differences in unpalatability between species of coccinellids are emphasized (after experiments of Pasteels and colleagues). Some less unpalatable species such as Adalia may have responded to periods of prolonged disruptive selection acting in a frequency-dependent way to promote polymorphic mimicry associated with different modal colour patterns and intermediate in nature between classical Batesian and Mullerian mimicry. The likely occurrence of a supergene controlling polymorphism in some coccinellids is consistent with such an explanation.
103 citations
TL;DR: The otic features described here reinforce the concept of the amphibian tympanic ear as a prior “invention” with no genealogical relationship to amniote tympic ears.
Abstract: Recent anurans plus all but the most primitive temnospondyl labyrinthodont amphibians are proposed as a monophyletic taxon, based on shared stapedial characters which are derived with respect to all other tetrapods. Within temnospondyls, the mostly Lower Permian dissorophoids are proposed as most closely related to Recent anurans, based on interpretation of the dissorophoid dorsal quadrate process and the anuran tympanic annulus as sequential steps in a character transformation series. The otic features described here reinforce the concept of the amphibian tympanic ear as a prior “invention” with no genealogical relationship to amniote tympanic ears.
102 citations
TL;DR: It is proposed that self-pollinating populations of E. paniculata are evolutionarily derived from tristylous ancestors and that the shift in breeding system is favoured at low density, following population bottlenecks, where pollinator service is unreliable.
Abstract: Eichhornia paniculata (Spreng.) Solms. (Pontederiaceae) is a short-lived perennial or annual of marshes, seasonal pools and ditches of lowland tropical South America, primarily NE Brazil, and the Caribbean islands of Cuba and Jamaica. Comparisons, made under uniform glasshouse conditions, of populations originating from seed collected in the two regions revealed striking differences in their floral biology and breeding systems. The majority of populations sampled in NE Brazil are tristylous. Floral trimorphism is associated with pollen trimorphism and minor differences in anther size and pollen production among the three stamen levels. Unlike the majority of heterostylous plants the floral morphs of E. paniculata are highly self-fertile. Populations sampled on the island of Jamaica are composed exclusively of self-pollinating, semi-homostylous, mid-styled forms. Flowers from these populations are smaller and less showy, with reduced pollen heteromorphism and significantly fewer pollen grains and ovules per flower, in comparison with trimorphic populations from Brazil. Individual genotypes from Jamaican populations display considerable developmental instability in floral expression, particularly with respect to filament elongation of the lower stamen level. It is proposed that self-pollinating populations of E. paniculata are evolutionarily derived from tristylous ancestors and that the shift in breeding system is favoured at low density, following population bottlenecks, where pollinator service is unreliable.
97 citations
TL;DR: It is shown that the tree finches have relatively long legs (tarsi), and that these finches as well as the ground finches which spend most time scratching on the ground or climbing in cacti also have a relatively long hallux (hind toe).
Abstract: Six bill dimensions, and wing, tarsus and hallux lengths were measured on almost all museum specimens of Geospiza species available, and up to 20 specimens from each population of the remaining species of Darwin's finches. The data were subjected to univariate and multivariate analyses in order to provide a quantitative description of size and shape differences among populations and between species.
Each species of Geospiza varies among islands in size, and most of the remaining species do so as well. There is more variation in shape among species than among populations of the same species, especially in bill proportions. Allometric relations differ among species. Approximate morphological counterparts to the ground finch species, Geospiza, can be identified among the tree finches. There is a small amount of overlap in multivariate space between a ground finch species and a tree finch species (two cases), but no overlap between any two species within each group. Size variation among populations is not generally correlated with geographical variables such as latitude, longitude, island area or its degree of isolation. Nor do coefficients of variation show strong geographical trends. Several of the results confirm the findings of other workers from simpler and non-statistical comparisons. In addition we have shown that the tree finches have relatively long legs (tarsi), and that these finches as well as the ground finches which spend most time scratching on the ground or climbing in cacti also have a relatively long hallux (hind toe). To interpret the various morphological patterns a knowledge is required of inter-island variation in food supply, feeding habits and the incidence of genetic exchange between populations. Recent field studies have provided some of this needed information, which helps to explain, among other things, why several populations of Darwin's finches are so unusually variable.
93 citations
TL;DR: The Clean Air Acts and the consequent decline in air pollution levels are probably responsible but there are many ill–understood problems, not the least being how, and the extent to which, non-visual selection operates.
Abstract: Between 1848 and 1895 the melanic form f carbonaria of the peppered moth increased in Manchester from 0 to 98%. The reverse process is now occurring in one locality in Memyside where a year-to-year survey has shown that the pale form f. typica has increased from 6 to 30% between 1959 and 1984. Supporting information also comes from two studies in N Wales. The Clean Air Acts and the consequent decline in air pollution levels are probably responsible but there are many ill–understood problems, not the least being how, and the extent to which, non-visual selection operates.
79 citations
TL;DR: Divergence in mate recognition signals has apparently evolved in advance of general genetic incompatibilities (post-mating isolating mechanisms) in this species.
Abstract: Populations of Nilaparvata lugens from 18 geographically defined and widely distributed regions in Asia and Australasia were maintained in the laboratory on growing rice plants. Crosses between some of these showed varying degrees of success in hybridization. Those between insects from Australia and the Solomon Islands had the lowest success rates, but in successful individual crosses there was little evidence of hybrid inviability. Behavioural barriers in the form of substrate transmitted courtship signals appeared to be primarily responsible for low success in hybridization. Pulse repetition frequencies of male calls were distinctive for different populations: those from Australia and the Solomon Islands showed the greatest difference. Divergence in mate recognition signals (pre-mating ethological isolating mechanisms) has apparently evolved in advance of general genetic incompatibilities (post-mating isolating mechanisms) in this species.
TL;DR: Two subspecies of the grasshopper Chorthippus parallelus have ranges that abut in the Pyrenees and at least one character may be relevant to mate choice but none of the characters show evidence of reinforcement.
Abstract: Two subspecies of the grasshopper Chorthippus parallelus have ranges that abut in the Pyrenees. Males produce two types of song—calling song and courtship song. We have examined the use and structure of these songs in males from nine sites near Mont-Louis, Pyrenees-Onentales, France. These sites were previously used to identify the position of the hybrid zone on morphological characters. The subspecies differ in the use and structure of both types of song. Clines in these characters correspond in position with the morphological cline. At least one character may be relevant to mate choice but none of the characters show evidence of reinforcement.
TL;DR: Examination of museum specimens suggests that this hybrid zone of the grasshopper Chorthippus parullelus extends for most of the length of the Pyrenees, possibly breaking down in the extreme west.
Abstract: Two subspecies of the grasshopper Chorthippus parullelus have distributions that abut in the Pyrenees. We have studied morphological and electrophoretic variation in II populations near Mont Louis, Pyrenees-Orientales, France. The two subspecies differ in several morphological characters and at one enzyme locus, esterase-2, and in this area they hybridize forming a cline in morphology less than 5 km wide. Examination of museum specimens suggests that this hybrid zone extends for most of the length of the Pyrenees, possibly breaking down in the extreme west. As the two subspecies are known to differ in mating behaviour this hybrid zone is well suited to the study of reinforcement.
TL;DR: It is argued first that this pattern of abortion will be selected during a sustained period of heavy wasp infestation because seeds will then become scarce relative to pollen-carrying wasps, and increased expenditure by the fig on seed production would therefore be favoured by natural selection.
Abstract: Figs and their pollinating fig wasps are dependent on one another for propagation of their own kinds. The wasps reproduce by ovipositing through the styles of female flowers within the closed fig receptacles (syconia). About half of the female flowers within the syconia of monoecious figs have styles which are longer than the ovipositors of the wasp, and they will therefore produce seeds rather than wasp larvae. Since a longer ovipositor would enable a wasp to reach more ovules and deposit more eggs, the question arises at to why longer ovipositors have not evolved.
In an attempt to answer this question, four seemingly plausible hypotheses are examined but each is shown to be problematical in some way. Consideration is then given to a fifth hypothesis which proposes that ovipositor length is constrained by abortion of syconia with relatively few seed embryos and many agaonid larvae. It is argued first that this pattern of abortion will be selected during a sustained period of heavy wasp infestation because seeds will then become scarce relative to pollen-carrying wasps. Increased expenditure by the fig on seed production would therefore be favoured by natural selection. A greater expenditure on seeds would occur if young syconia with exceptionally heavy wasp infestations were dropped and the saved nutrients invested in syconia of a subsequent crop containing average levels of wasp larvae and seeds. Provided that the energy and nutrient cost of dropping young syconia is small, the selective advantage to the wasp of longer ovipositors is eliminated in this way. A stable coexistence of figs and wasps is therefore possible. The paper concludes by discussing two general predictions of the abortion hypothesis, and how these may be tested.
TL;DR: The paradoxical occurrence of a large adaptive radiation on a small (40 km2), isolated, oceanic island is analysed in its evolutionary and ecological aspects: how did so many species of weevils evolve, and how is such a diversity of weevil species maintained?
Abstract: Rapa Island in SE Polynesia hosts a remarkable adaptive radiation of small, flightless weevils in the genus Miocalles Sixty-seven species are known at present, of which 26 are described as new One new name, two new combinations, and two new synonyms are established The paradoxical occurrence of a large adaptive radiation on a small (40 km2), isolated, oceanic island is analysed in its evolutionary and ecological aspects: how did so many species of weevils evolve, and how is such a diversity of weevils maintained? Most of the speciation has taken place on Rapa itself Two principal methods of intra-island isolation of weevil populations have led to speciation: between high mountain ranges, and between Rapa and its satellite islets Glacial sea level fluctuations aided in speciation by connecting the satellite islets to Rapa at times, and by the downward extension, and connection of high-altitude cloud forests Some speciational events may have taken place in 15000–150 000 years Close relatives of Rapan weevils are known from nearby Marotiri, an almost sunken island, and from the neighbouring Austral archipelago, with which some inter-island speciation has taken place The weevil species are almost all host-plant specific There are often several species occupying the same host plant, in which case they may inhabit different parts of it Some plants with a longer history on Rapa host more weevil species than newer arrivals
TL;DR: The evidence supports the contention that these heliozoa have a common ancestry with the heterokont algae and have evolved along a line involving the pedinellids and some colourless helioflagellates, and a substantial reclassification of these organisms is required.
Abstract: The fine structure of Pteridomonas danica, a new species of helioflagellate (protozoa), is described The organism has a single apical flagellum which bears two rows of tripartite tubular hairs There are two kinetosomes which are bound to each other and to the surface of the single nucleus by amorphous electron-dense material The flagellum is surrounded by a wreath of fine arms, which are supported internally by triads of microtubules The triads terminate on the nucleus The mitochondria have tubular cristae which contain wisps of intracristal material The dictyosomes are located in the posterior part of the cell, being clustered around the internal element of the contractile stalk Extrusomes are present Pteridomonas has substantial similarities with the colourless flagellate Ciliophrys and with the pedinellid algal flagellates As Ciliophrys resembles the actinophryid heliozoa in several important respects, the evidence supports the contention that these heliozoa have a common ancestry with the heterokont algae and have evolved along a line involving the pedinellids and some colourless helioflagellates If the perceived relationships are to be reflected in their taxonomy, then a substantial reclassification of these organisms is required
TL;DR: Variants on this technique, which may have advantages, include novel means of generating genetic loads in populations of Lepidioptera and sheep blowflies and the introduction into mosquito populations of genes making them unable to transmit malaria.
Abstract: Genetic control is a form of biological control of pest species which exploits the insect's mate-seeking expertise to introduce genetic abnormalities (typically, but not necessarily, dominant lethal mutations) into the eggs of the wild population. The effectiveness of radiation-sterilized males depends on the mating competitiveness of released males being adequate in relation to the recovery potential of and rate of immigration into the target population. This technique is now being applied on a very large scale against agricultural pests especially in Mexico, Egypt and Japan. Variants on this technique, which may have advantages, include novel means of generating genetic loads in populations of Lepidioptera and sheep blowflies and the introduction into mosquito populations of genes making them unable to transmit malaria.
TL;DR: The larval stage is early because mature leaves of many host trees are unsuitable as food, because parasitism against later larvae is more intense, and because summer temperatures may be injurious to larvae.
Abstract: Adult winter moths (Operophtera brumata (L.)) are active in late autumn or early winter. The eggs overwinter in the canopy of trees and hatch simultaneously with the bursting of host tree buds. Many young larvae disperse on the wind on silk strands. Larvae are polyphagus and feed until late spring when they pupate in soil or leaf litter. The duration of the egg and pupal stages is genetically determined and varies with latitude. The egg stage is long in the north and short in the south, while the pupal stage is short in the north and long in the south.
The literature on the ecology and physiology of winter moth is reviewed. The factors maintaining the unusual phenology are discussed. It is concluded that the larval stage is early because mature leaves of many host trees are unsuitable as food, because parasitism against later larvae is more intense, and because summer temperatures may be injurious to larvae. The adult period is late in the year so that the final stages of pupal development occur in cool conditions and so that adults emerge after most insect predators have ceased activity. Throughout most of the range retarding the adult emergence period would cause activity to be impeded by severe winter weather; in the south this is not so and it is suggested that eggs must be on the trees for a minimum period to ensure synchronization of egg hatch with bud burst. The protracted adult emergence period may be an adaptation reducing predation by birds.
TL;DR: Two largely independent studies of chromosomes from natural populations of anopheles maculatus provide evidence for several genetic species within the taxon, including two allopatric populations and heterochromatic variation occurs in both X and Y chromosomes.
Abstract: : Two largely independent studies of chromosomes from natural populations of anopheles maculatus provide evidence for several genetic species within the taxon. (1) Polytene chromosome variation shows four different rearrangements of arm 2 and three rearrangements of the X chromosome. There is strong evidence for three species. Two allopatric populations represent either dramatic geographic variation for two independent inversion systems within one of the genetic species, or represent two additional species. Their species status remains unresolved by this work. (2) Heterochromatic variation occurs in both X and Y chromosomes as revealed by Giemsa-banding of mitotic chromosomes from larval brains. The distribution and association of these various sex chromosomes give further evidence of a species complex. A preliminary correlation of these two kinds of chromosomal variation is given.
TL;DR: The zonation of 15 species of Littoraria in the scabra group is described, using a transect method, at 13 mangrove localities in Australia, Thailand, Malaysia and Hawaii, and it is suggested that vertical distribution is determined mainly by behavioural responses, while the landward limits of horizontal distribution may be set by physiological tolerance.
Abstract: The zonation of 15 species of Littoraria in the scabra group is described, using a transect method, at 13 mangrove localities in Australia, Thailand, Malaysia and Hawaii. At these localities the littorinids occurred only on trees, and showed both vertical and horizontal patterns of zonation, with broad overlaps between co-occurring species. It is suggested that vertical distribution is determined mainly by behavioural responses, while the landward limits of horizontal distribution may be set by physiological tolerance. Several species occurred predominantly on either leaf or bark substrates, but no consistent associations with tree species were found. On the basis of local distribution patterns, Littoraria species can be classified as continental or oceanic in character. Oceanic species may be less tolerant of sediment in the water or on the substrate.
TL;DR: The species displays many features typical of dioecious tropical plants with the unusual feature of pollen being the main food reward for pollinators, and was pollinated effectively in Sulawesi.
Abstract: Decaspermum parviflorum is a common shrub or treelet in clearings in eastern Sulawesi, Indonesia. It is widely distributed in SE Asia. It produces numerous white flowers and small blue-black fruits. Individual shrubs were of two types in 1:1 ratio, one bearing staminate flowers, the other bearing flowers with both stamens and carpels. The ‘hermaphrodite’ flowers were shown to have sterile pollen so the species is functionally dioecious. The flowers and floral sprays of the two sexes differed in several measurements: the male flowers had more anthers and were larger and more numerous, making the corporate visual image of male sprays more than twice as large as that for sprays of female flowers. Flowers, individuals of which last only one day, opened only every second day, when all bushes flower synchronously. When the anthers burst in the morning, pollen and sterile pollen was collected vigorously by a variety of bees, mostly Apis dorsata and Nomia spp. Most of the pollen was collected within 1 h of anthesis. Anthesis in males takes place about 20 min earlier than in females; insect visitation follows this pattern. The minute quantity of nectar was collected by only few insects and mostly after the pollen had gone, if at all. Fruits were eaten by birds. The species displays many features typical of dioecious tropical plants with the unusual feature of pollen being the main food reward for pollinators. It was pollinated effectively in Sulawesi.
TL;DR: It is concluded that this zone resulted from secondary contact, and that the zone is maintained either by selection against hybrids (less likely) or by hybrid superiority (more likely).
Abstract: A population of hybrid pocket gophers (Geomys bursarius × G. lutescens) exists 1–2 km west of Oakdale, Antelope County, Nebraska, U.S.A. The hybrids occur in soil that has characteristics intermediate between that occupied by G. lutescens (sand) and by G. bursarius (silt loam); the vegetation associations on the different soils are Sandhills Prairie and Tall-grass Prairie, respectively, with mixed prairie on the intermediate soils. Hybrids are identifiable on the basis of both qualitative and quantitative morphological characteristics, allozymes and karyology. Concordance between morphological, allozymic, karyotypic and ecological data sets is very high. Hybrids appear to reproduce normally and survive well; i.e. they suffer no obvious loss of fitness. Backcrossing to either parental type is apparently rare. The parental species each support obligate parasitic lice (Geomydoecus: Trichodectidae) of different species; these species are not sister species. We suggest that hybrid zones resulting from primary and secondary contact may be distinguished by (1) concordance of clines in different character sets, (2) fossil and biogeographic data, and (3) parasite data. We conclude that this zone resulted from secondary contact, and that the zone is maintained either by selection against hybrids (less likely) or by hybrid superiority (more likely).
TL;DR: The consequences of the particulate nature of matter and of light, the wave nature of light and sound, and the mechanical properties of materials are explored, as well as limits to aerodynamic and hydrodynamic performance and the behaviour of electricity.
Abstract: The laws of physics and the properties of the physical environment impose constraints on evolution Structures and processes that may be imagined cannot in some cases be evolved, because they are physically impossible This paper explores the consequences of the particulate nature of matter and of light; of the wave nature of light and sound; of the laws of diffusion and heat exchange; of the mechanical properties of materials; of limits to aerodynamic and hydrodynamic performance; and of the behaviour of electricity
TL;DR: The biological simplicity of the exceptionally uniform tussac ecosystem offers ideal conditions for testing ecological hypotheses, especially those related to trophodynamics and predator-prey interrelationships, and its potential for research is emphasized.
Abstract: Beauchene Island is the most isolated of the Falkland Islands archipelago and until the authors' visit there in 1980 little was known or published about the island and its biota apart from its avifauna. The first collections and identifications of various plant and invertebrate groups were made and a brief account of their ecology and interrelationships is given; many of the arthropods are first records for the Falkland Islands and some are new to science. More detailed information is presented for tussock grass (or tussac), Poa flabellata, which reaches a height of 3.5 m and covers two-thirds of the island with a unique monospecific grassland. The underlying deep peat, in places reaching 13 m depth, was investigated and radiocarbon dates obtained at various levels through the profile, indicating that the grassland has existed virtually unchanged for 12 500 years. The status of the avifauna was assessed. The black browed albatross and rockhopper penguin colonies were counted reasonably accurately and calculated to contain up to 170000 and 300000 pairs, respectively. A population of about 250 striated caracaras was counted, together with 67 nests, possibly the largest concentration of these rare raptors anywhere. The recently discovered population of fairy prions was estimated at several thousand birds. Sea lions were not abundant and fur seals, once said to occur in large numbers on the island, were absent. The biological simplicity of the exceptionally uniform tussac ecosystem offers ideal conditions for testing ecological hypotheses, especially those related to trophodynamics and predator-prey interrelationships, and its potential for research is emphasized. The importance of applying strict conservation measures to protect this unique island is stressed in view of the possible future economic development of the Falkland Islands.
TL;DR: The results suggest that the major role of cyanogenesis may be as a feeding inhibitor, not as a toxin, in insects and molluscs exposed to cyanide.
Abstract: In laboratory feeding choice experiments several species of insects and molluscs eat acyanogenic Lotus corniculatus leaves or petals in preference to cyanogenic alternatives. These species can be characterized as generalist feeders for which L. corniculatus forms only an occasional dietary item for any particular individual. Some of the insects that were found to display selective eating were maintained on exclusive diets of either cyanogenic or acyanogenic L. corniculatus. Survival times varied considerably between species, but there was no evidence that mortalities were higher amongst the groups exposed to cyanide. These results suggest that the major role of cyanogenesis may be as a feeding inhibitor, not as a toxin.
TL;DR: A series of morphometric and meristic analyses conducted on specimens of sand smelt, Atherina, from populations around the British Isles, and including classic A. boyeri and A. presbyter forms, has shown that the characteristics variously used in the past to distinguish these two species are invalid as discussed by the authors.
Abstract: A series of morphometric and meristic analyses conducted on specimens of sand smelt, Atherina, from populations around the British Isles, and including classic A. boyeri and A. presbyter forms, has shown that the characteristics variously used in the past to distinguish these two species are invalid. Multivariate analyses showed no significant splitting of the material into two groups which might correlate to these two species; classic A. boyeri and the very large Atlantic coast A. presbyter individuals represent the tails of a continuum of form. From these and published data, it is concluded that the A. boyeri morphology varies under the influence of conditions of temperature and salinity during embryo development, and the isolation of populations maintains comparative morphological distinctions resulting from local selection and random genetic drift.
TL;DR: The results suggest that population histories affect variation in Cepaea even in areas of relative habitat stability, and a clear colonization effect is seen in the inverse relationship between age of habitat and frequency of yellow in woodland populations.
Abstract: Populations of Cepaea nemoralis in Warwickshire occupy habitats of considerable temporal stability, most being at least 250 years old, and some much older. As expected from earlier work, shell pattern polymorphisms in these populations show variation with habitat of a kind suggesting the operation of visual selection for crypsis. They also show patterns of microgeographical variation unrelated to habitat. Although of a less extreme character, this variation resembles the ‘area effects’ seen in downland populations of Cepaea, in the lack of coincidence of variation at different loci, and in the existence of stronger and larger scale patterns in banding than in colour morphs. A similar explanation is advanced for their occurrence: previous bottlenecks and colonization from small relicts with founder effects. The less marked character of the variation is expected from the greater habitat stability and continuity in Warwickshire compared with downland. A clear colonization effect is seen in the inverse relationship between age of habitat and frequency of yellow in woodland populations. The results suggest that population histories affect variation in Cepaea even in areas of relative habitat stability.
TL;DR: For non-cervid ungulate females, there appear to be no overriding or unifying aptive factors governing the evolutionary development of horns or hornlike organs, although the trait may be aptive in some cases.
Abstract: The evolutionary bases for horns, antlers, and tusks in male ungulate mammals have been extensively investigated, but the reasons for the presence or absence of hornlike organs in female ungulates have not been thoroughly reviewed. Here I examine (1) the taxonomic distribution of horns and hornlike organs in females and evidence on the evolutionary history of the trait; (2) behavioural evidence on the uses of horns and hornlike organs by females and socio-ecological correlations with female hornedness or hornlessness; and (3) evidence on the role of genes and hormones in controlling the expression of female horns. In cervids, antlered females may be rare because of a constraint to regrow antlers yearly, if at all, small social group sizes, and a direct linkage between androgen production and the initiation of antler growth. For non-cervid ungulate females, there appear to be no overriding or unifying aptive factors governing the evolutionary development of horns or hornlike organs, although the trait may be aptive in some cases.
TL;DR: It seems from the botanical side that the evolution of Ficus into subgenera and sections preceded that of its insects into genera, and there are no grounds for reclassification of Ficua, but leaf structure indicates that some rearrangement of the species of subgen.
Abstract: Attempts are made to meet discrepancies between the botanical classification of Ficus and the zoological classification of its pollinators. They are discussed as Ficus elastica, subgen. Pharmacosycea, subsect. Palaeomorphe, dioecism in Ficus, the Ceratosolen complex, and sect. Conosycea. It seems from the botanical side that the evolution of Ficus into subgenera and sections preceded that of its insects into genera. On the whole there are no grounds for reclassification of Ficua, but leaf structure indicates that some rearrangement of the species of subgen. Urostigma sect. Conosycea may be needed to fit the entomology. Ficus asperiuscula poses a problem in sect. Sycidium.
TL;DR: Evidence for the orthodox view of rhipidistian-tetrapod relationships is not as strong as generally believed and Tetrapod-fish relationships need to be re-examined by means of a properly conducted cladistic analysis.
Abstract: It is generally accepted that rhipaidistian crossopterygians are the closest relatives of tetrapods Rosen, Forey, Gardiner & Patterson (1981) challenge this view and contend that lungfishes are the sister group of tetrapods They present a detailed cladistic analysis and claim to identify a large number of synapomorphies shared by lungfishes and tetrapods but not by rhipidistians Their analysis is faulty Although Rosen et al (1981) correctly emphasize that cladistic relationships must be based on shared derived characters, they often fail to take intragroup variation into account in postulating synapomorphies They also use evidence inconsistently by attributing greater significance to similarities between lungfishes and tetrapods than to even more detailed similarities between rhipidistians and tetrapods They misinterpret the skeletal pattern of the paired appendages The many synapomorphies that they claim to have identified are either invalid, irrelevant, or are characters involving reduction or loss (which have a high probability of convergence) Consequently, they make an unconvincing case for a sister-group relationship between lungfishes and tetrapods On the other hand, Rosen et al (1981) do show that evidence for the orthodox view of rhipidistian-tetrapod relationships is not as strong as generally believed The uncertain interrelationships among rhipidistians is a major problem Tetrapod-fish relationships need to be re-examined by means of a properly conducted cladistic analysis