Showing papers in "Biological Journal of The Linnean Society in 1996"
TL;DR: The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences.
Abstract: The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a rapid expansion would be leptokurtic and lead to homozygosity and spatial assortment of genomes. In Europe and North America, ice age contractions were into southern refugia, which would promote genome reorganization. (2) The present day genetic structure of species shows frequent geographic subdivision, with parapatric genomes, hybrid zones and suture zones. A survey of recent DNA phylogeographic information supports and extends earlier work. (3) The grasshopperChorthippus parallelusis used to illustrate such data and processes. Its range in Europe is divided on DNA sequences into five parapatric races, with southern genomes showing greater haplotype diversity — probably due to southern mountain blocks acting as refugia and northern expansion reducing diversity. (4) Comparison with other recent studies shows a concordance of such phylogeographic data over pleistocene time scales. (5) The role that ice age range changes may have played in changing adaptations is explored, including the limits of range, rapid change in new invasions and refugial differentiation in a variety of organisms. (6) The effects of these events in causing divergence and speciation are explored usingChorthippusas a paradigm. Repeated contraction and expansion would accumulate genome differences and adaptations, protected from mixing by hybrid zones, and such a composite mode of speciation could apply to many organisms.
3,850 citations
TL;DR: Secondary sexual characters in many species function both in male-male competition and as cues for female choice, and a literature compilation of existing knowledge of traits with this dual role is compiled.
Abstract: Secondary sexual characters in many species function both in male-male competition and as cues for female choice. Based on a literature compilation of existing knowledge of traits with this dual fu ...
734 citations
TL;DR: The results indicate that although pad area is a strong determinant of clinging ability, other factors enable these lizards to maintain functional similarity, and despite the tight correlation between pad area and clingingAbility, pad area scales with body mass by a lower slope than clinging ability.
Abstract: We examined clinging ability, subdigital pad area and body mass in 14 pad-bearing lizard species from three families to test three predictions: (1) clinging ability and pad area should be tightly correlated among species; (2) pad area and clinging ability should scale similarly to body mass among 14 species; and (3) functional similarity in clinging capabilities should exist among species despite differences in body mass. Our results confirm two predictions; clinging ability is tightly correlated with pad area, even when the effects of body size are removed, and the lizards examined are approximately functionally similar in their clinging capabilities. Nevertheless, despite the tight correlation between pad area and clinging ability, pad area scales with body mass by a lower slope than clinging ability. Overall, these results indicate that although pad area is a strong determinant of clinging ability, other factors enable these lizards to maintain functional similarity.
375 citations
TL;DR: Investigation of the effect of carapace width, major cheliped length and burrow ownership on the fighting success of male fiddler crabs found that released males tended to initiate encounters with burrow owners slightly smaller than themselves.
Abstract: We performed a field experiment to investigate the effect of carapace width, major cheliped length and burrow ownership on the fighting success of male fiddler crabs (Uca annulipes). We removed males from their burrows and released them back into the colony (n = 82). Released males tended to initiate encounters with burrow owners slightly smaller than themselves. Several general predictions of Sequential Assessment Game models of contest behaviour were supported: (1) residents won more encounters; (2) intruders were more likely to win when larger than residents. When body size (carapace width) was controlled for, intruders with relatively large claws for their body size were more likely to win contests; (3) the duration of encounters was related to the size difference between males; (4) encounters won by the larger male were of shorter duration than those won by the smaller male; (5) encounters won by the resident tended to be of shorter duration than those won by intruders (P = 0·07); (6) on average, encounter duration was longer when the intruder was larger than the resident. However, the encounters we documented began with seemingly costly behaviour such as pushing and the inter-locking of claws and did not unambiguously escalate from initial low cost behaviours. Sequential assessment of relative fighting ability may therefore not have been occurring. Prior visual assessment of opponents' fighting ability, followed by ‘all-out fights’ during physical encounters may also provide a plausible explanation for our results.
206 citations
TL;DR: Information on phylogeny, allometric growth, and diet composition is used for an integrated analysis of morphological and ecological diversification in the Antarctic fish family Nototheniidae, mainly focusing on the subfamilies Trematominae and Pleuragramminae.
Abstract: The Antarctic fish family Nototheniidae (Perciformes) presumably originated from a benthic ancestor, and several lineages have evolved to live or at least feed in the water column, a trend called pelagization. Here, we use information on phylogeny, allometric growth, and diet composition for an integrated analysis of morphological and ecological diversification in this group, mainly focusing on the subfamilies Trematominae and Pleuragramminae. A phylogenetic analysis of data published in earlier systematic studies produced eight equally parsimonious trees, all indicating that several previously recognized taxa are paraphyletic. These phylogenetic trees all suggest multiple origins of pelagic life styles. Multivariate morphometric analyses including nine species showed that juveniles and adults grow according to a common pattern of ontogenetic allometry. The morphometric differences among species are mostly the result of lateral transpositions of the growth trajectories, indicating that embryonic and larval development is more important as a determinant of morphological variation than allometric growth as juveniles and adults. We studied patterns of interspecific variation with principal components and the covariation between morphometric variables and food composition with a partial least-squares analysis. Both analyses revealed a gradient from benthic to pelagic foragers. Measurements of structures involved in swimming have a prominent role in these analyses, suggesting adaptive evolution of these traits. Tracing morphometric traits on the phylogenetic trees revealed a considerable amount of evolutionary plasticity, showing that species related phylogenetically need not be morphologically similar, but can diverge considerably, perhaps as a response to natural selection and adaptation to different habitats and foraging modes. In accordance, a test of phylogenetically independent contrasts showed that bursts of increased morphological change accompanied habitat shifts.
202 citations
TL;DR: It is suggested that PAE can be used as a tool to objectively identify areas of endemism at an intra-continental scale as well as to make historical inferences and the value of a PAE cladogram should be always evaluated by congruence with area cladograms built upon cladistic biogeography procedures.
Abstract: The distributions of 51 non-human primate species are used for Parsimony Analysis of Endemicity (PAE) to determine the relationships among 14 interfluvial regions in the Amazon basin, South America. Two most parsimonious cladograms were found. The strict consensus tree of these cladograms suggests an early separation between Lower Amazonia (eastern) and Upper Amazonia (western). The major clusters of interfluvial regions identified in the PAE cladogram are congruent with the areas of endemism delimited for birds. When interfluvial regions are converted into avian areas of endemism, the PAE cladogram is congruent with one of the two general areas cladograms suggested for Amazonia based on phylogenies of several clades of forest birds. Our analysis suggests that PAE can be used as a tool to objectively identify areas of endemism at an intra-continental scale as well as to make historical inferences. However, the value of a PAE cladogram in this latter application should be always evaluated by congruence with area cladograms built upon cladistic biogeography procedures.
191 citations
TL;DR: A data matrix consisting of 61 characters for 32 phyla from this book is extracted and treated in more formal analyses using three different parsimony programs, and one cladogram emerged as the most parsimonious explanation of the data.
Abstract: A recently published book on the phylogeny of the animal kingdom, written by the first author, provided a classification based on a ‘manual’ cladistic analysis at the phylum level. We have extracted a data matrix consisting of 61 characters for 32 phyla from this book and treated it in more formal analyses using three different parsimony programs. Following a posteriori weighting, one cladogram emerged as the most parsimonious explanation of the data. This cladogram is compared to those in recent publications. Congruence is greatest with the phylogeny published by the first author, as the monophyly of 18 of the 21 supraphyletic categories proposed therein are supported in our cladogram. The exceptions are Aschelminthes, Protornaeozoa and Neorenalia, but the latter group does emerge as a monophyletic taxon in a number of equally parsimonious, equally weighted trees. Comparisons with other recent phylogenies show varying degrees of divergence, especially concerning the monophyly of Spiralia and Articulata, both of which are advocated in the present paper. Significant characters of most of the supraphyletic taxa proposed by the first author are discussed.
177 citations
TL;DR: Evidence is presented that the important events in the generation of clades were earlier than the Cambrian ‘explosion’, at which time the groups become manifest in the fossil record.
Abstract: The origin and differentiation of major clades is often assumed to have occurred in tandem with the ‘explosion’ of fossil evidence of diverse morphologies (‘disparity’) at the base of the Cambrian. Evidence is presented that this was not the case. Biogeographical and morphological differentiation among the earliest trilobites reveals incompleteness in the known early Cambrian record; similar evidence can be accrued for other major groups. Phylogenetic analysis proves the likelihood of ‘ghost’ lineages extending into the Precambrian. The important events in the generation of clades were earlier than the Cambrian ‘explosion’, at which time the groups become manifest in the fossil record. It is likely that the important phylogenetic changes happened in animals of small size; sister taxa of major groups are shown to be small animals. Decoupling cladogenesis from the Cambrian ‘explosion’ removes the necessity of invoking unknown evolutionary mechanisms at the base of the Phanerozoic. Genes controlling development may have played a role in generating new morphologies, through heterochrony for example, in the early differentiation of metazoan body plans.
176 citations
TL;DR: A reappraisal of the zoogeography and systematics of Asian colobines demonstrates marked discontinuities in their distribution, and the greater significance of climatic than topographical barriers in delineating the Oriental zoogeographic region, and a rapid speciation rate is implied.
Abstract: A reappraisal of the zoogeography and systematics of Asian colobines demonstrates marked discontinuities in their distribution. The Borean proboscis monkey is separated by Sumatra from its sole congener on the Mentawai Islands.Pygathrixspecies have a discontinuous distribution at the range limit of the Asian Colobinae. The existence in the Himalayas of some disjunct relatives of the south Indian fauna, has obscured a wider disjunction in which for example, the hooded black leaf monkey,Semnopithecus johnii, has one subspecies in southern India and another in north Vietnam. A closely related Vietnamese leaf monkey is a subspecies of the otherwise IndonesianS. auratus. Presbytis comatais disjunct between west Java, northern Sumatra and northern Borneo. The Mentawai IslandsP. potenzianiis closely related. Biogeographic parallels imply a common cause and previous continuity across the intervening areas. The only wholly compatible explanation is that the disjunct areas alone retained adequate moisture and temperature to support their endemic biota during a cool drought. That not only genera, but species are disjunct, indicates such conditions prevailed recently, and are probably attributable to the Pleistocene glaciations. The supposition that its maritime climate shielded Asian rainforest from the glacial drought known to have partially deforested Africa and South America, is inapplicable to the Indian subcontinent, and ignores the climatic effects of the emergence of the Sunda and the Sahul shelves. Such known influences, the distribution of drought indicator plants, fossil plants and fossil mammals, grassland birds and freshwater fish, and the anatomical specializations ofNasalisconfirm the instability of the Asian environment. The absence of endemic representatives of certain primates in north Sumatra implies the occurrence of two cold droughts. Available evidence appears to correlate the deforestations with the abrupt curtailment of glacial Stages 7 and 5, at about 190 000 years BP and about 80 000 years BP. The greater significance of climatic than topographical barriers in delineating the Oriental zoogeographic region, and a rapid speciation rate, is implied. Morphological change is evidently generated by geographic dispersal, rather than geographic isolation.
145 citations
TL;DR: The finding that very unusual conditions are required to reduce N e below N /10, low estimates of N e / N need to be examined critically: the lowest published ratio, for a natural population of oysters, was found to be questionable because of possible immigration into the population by cultivated oysters.
Abstract: Understanding the relationship between effective population size ( N e ) and the number of adults in a population ( N ) is important for predicting genetic change in small populations. In general, N e is expected to be close to N /2, i.e. in the range N /4–3 N /4, provided that the powerful effect of population bottlenecks on reducing N e is factored out (using the harmonic mean of N). However, some very low published estimates of N e / N ( N e have been underestimated. Here one such factor, variation in female fecundity, is investigated. Its effect on N e depends on the standardized variance in fecundity (per breeding season), a measure that is generally independent of mean fecundity. Empirical estimates of this standardized variance from 16 animal studies yielded an average value of 0·44, and a maximum value less than 1·5. To investigate the effect of such values, three kinds of fecundity variation were modelled: random (seasonal); individual; and age-related. Fixed individual differences among females reduce N e the most. However, to reduce N e to N /10, the resulting standardized variance must usually be 10 or more. Random differences need to be even larger to achieve the same reduction. One possible mechanism, the random loss of whole families, requires very high family mortality (90% or more). The third model, fecundity that increases linearly with age, is ineffective at causing a marked decrease in N e . Given the finding that very unusual conditions are required to reduce N e below N /10, low estimates of N e / N need to be examined critically: the lowest published ratio, for a natural population of oysters, was found to be questionable because of possible immigration into the population by cultivated oysters.
123 citations
TL;DR: It is concluded that it is premature to discard the convergence hypothesis without further tests, because the role of adaptive forces, such as interspecific competition, predation or phenology in shaping the observed differences is largely unexplored.
Abstract: The goal of this study was to investigate the extent of convergence in four basic life history and socio-ecological traits among the primates of Africa, Asia, South America and Madagascar. The convergence hypothesis predicts that similar abiotic conditions should result in similar adaptations in independent taxa. Because primates offer a unique opportunity among mammals to examine adaptations of independent groups to tropical environments, we collected information on body mass, activity pattern, diet and group size from all genera for quantitative tests of this hypothesis. We revealed a number of qualitative and quantitative differences among the four primate groups, indicating a lack of convergence in these basic aspects of life history and socio-ecology. Our analyses demonstrated that New World primates are on average significantly smaller than primates in other regions and characterized by a lack of species larger than about 10 kg. Madagascar harbours significantly more nocturnal species than the other regions and is home to all but one of the primates with irregular bursts of activity. Asia is the only region with strictly faunivorous primates, but lacks primarily gummivorous ones. The Neotropics are characterized by the absence of primarily folivorous primates. Solitary species are not represented in the New World, whereas solitary and pair-living species make up the majority of Malagasy primates. Lemurs live in significantly smaller groups than other primates, even after controlling for differences in body size. The lack of convergence among the major primate groups is neither primarily due to phylogenetic constraints as a result of founder effects, nor can it be sufficiently explained as a passive consequence of body size differences. However, because the role of adaptive forces, such as interspecific competition, predation or phenology in shaping the observed differences is largely unexplored, we conclude that it is premature to discard the convergence hypothesis without further tests.
TL;DR: Results indicate that the learning process in kingbirds may demand a large mortality in prey populations, even among species generally accepted as unpalatable and aposematic, and support the assertion that escaping ability and unpalatability evolved in butterflies as alternative strategies to avoid predation by birds.
Abstract: The palatability and the ability of neotropical butterflies to escape after being detected, attacked, and captured by wild kingbirds ( Tyrannus melancholicus Vieillot), was investigated by the release of 668 individuals of 98 butterfly species close to the birds, during their usual feeding activities. Most of the butterflies were attacked and eaten. Only the troidine swallowtails ( Parides and Battus ; Papilionidae) were consistently rejected on taste and elicited aversive behaviours in birds. Most other aposematic and/or mimetic species in the genera Danaus and Lycorea (Danainae), Dione, Eueides and Heliconius (Heliconiinae), Hypothyris, Mechanitis and Melinaea (Ithomiinae), Biblis, Callicore and Diaethria (Limenitidinae) were generally eaten. Cryptic and non-mimetic species were always attacked and, if captured, they were also eaten. All Apaturinae, Charaxinae, Nymphalinae, Hesperidae, most Limenitidinae, Heliconiinae ( Agraulis, Dryas, Dryadula and Philaethria ) and Papilionidae ( Eurytides, Heraclides and Protesilaus ) were in this group. Results indicate that the learning process in kingbirds may demand a large mortality in prey populations, even among species generally accepted as unpalatable and aposematic. They also support the assertion that escaping ability and unpalatability evolved in butterflies as alternative strategies to avoid predation by birds. Mimetic relationships among several species are discussed. Evidence for the evolution of aposematism not related to unpalatability, but to escaping ability, was found for two hard-to-catch Morpho species.
TL;DR: Evidence from related Heliconius supports a hypothesis that ecological adaptation is the driving force for speciation in the group and suggests that similar genetic processes are involved in the morphological divergence of species and races.
Abstract: To understand speciation we need to study the genetics and ecology of intermediate cases where interspecific hybridization still occurs. Two closely related species of Heliconius butterflies meet this criterion: Heliconius himera is endemic to dry forest and thorn scrub in southern Ecuador and northern Peru, while its sister species, H. erato, is ubiquitous in wet forest throughout south and central America. In three known zones of contact, the two species remain distinct, while hybrids are found at low frequency. Collections in southern Ecuador show that the contact zone is about 5 km wide, half the width of the narrowest clines between colour pattern races of H. erato. The narrowness of this cline argues that very strong selection (s 1) is maintaining the parapatric distributions of these two species. The zone is closely related with a habitat transition from wet to dry forest, which suggests that the narrow zone of parapatry is maintained primarily by ecological adaptation. Selection on colour pattern loci, assortative mating and hybrid inviability may also be important. The genetics of hybrids between the two species shows that the major gene control of pattern elements is similar to that found in previous studies of H. erato races, and some of the loci are homologous. This suggests that similar genetic processes are involved in the morphological divergence of species and races. Evidence from related Heliconius supports a hypothesis that ecological adaptation is the driving force for speciation in the group.
TL;DR: It is suggested that it occurs widely in eggs of Plecoptera and in the mayfly Rhithrogena loyolaea , cold-adapted species that may use diapause to survive periods of high temperature.
Abstract: Average reaction norms relating number of day-degrees required to complete egg development to temperature are described for 95 species (115 populations) of Plecoptera, Odonata, Ephemeroptera, and Diptera (mainly Culicidae, with some Tipulidae and Sciomyzidae). The slope of the average reaction norm is used as an index of adaptation, with positive slopes indicating cold-adapted species, negative slopes indicating warm-adapted species, and slopes around zero indicating generalist species; 57% of the between-taxon variation in slope is associated with differences between orders, 14% among families, 7% among genera, 14% among species, and 8% among populations. Significant differences between congeneric species are found in only 4 of 92 possible comparisons. Only Plecoptera show much cold-adaptation, with 40% of the species having significantly positive slope. However, 26% of the species (mainly in the Systellognatha) have significantly negative slope, suggesting adaptation to warmer waters than those in which the order is believed to have originated. The other orders probably originated in warm water and have generally maintained this adaptation. All Odonata, 71% of the Diptera and 81% of the Ephemeroptera have significantly negative slopes. Diapause is a common alternative to metabolic adaptation to deal with unfavourable thermal environments. We suggest that it occurs widely in eggs of Plecoptera and in the mayfly Rhithrogena loyolaea , cold-adapted species that may use diapause to survive periods of high temperature.
TL;DR: The effect of infection with cytoplasmically inherited male-lethal symbionts on mitochondrial genome evolution is discussed and the possibility that estimation of gene flow between populations may also be confounded by symbiont presence is discussed.
Abstract: Variation in mitochondrial DNA is often used to trace the evolutionary history of populations and species. We here discuss the effect of infection with cytoplasmically inherited male-lethal symbionts on mitochondrial genome evolution. Male-lethal symbionts spread when killing male hosts increases the lifetime reproductive success of sibling female hosts. This increase in the survivorship of daughters from individuals bearing a male-killer will produce a concomitant increase in the frequency of mitotypes associated with the male-killer. If horizontal transmission of the microoorganism is rare and population sizes not very small, then linkage disequilibrium between microorganism and particular mitotypes will result in a reproduction of within-population mitochondrial variability both because of a selective sweep during the spread of such a micro-organism, and also at equilibrium. Male-killing symbionts may thus confound the use of mtDNA variability in estimation of population parameters. We discuss the differences between the effects of male-killers and the cytoplasmic incompatibility-inducing symbiont Wolbachia , and the possibility that estimation of gene flow between populations may also be confounded by symbiont presence.
TL;DR: Diversity of Synalpheus, which is already among the most species-rich crustacean genera, is probably several times higher than currently recognized, and species of sponge-dwellingsynalpheus are highly host-specific, with related species distinctly segregated among hosts.
Abstract: Microevolutionary studies and natural history suggest that host-specialization has promoted the high diversity of tropical sponge-dwelling snapping shrimps (Decapoda, Alpheidae, Synalpheus). Yet the taxonomic difficulty of this genus has precluded rigorous tests of this hypothesis. S. rathbunae Coutiere is among the most abundant invertebrates inhabiting the framework of sponges and dead coral that forms the floor of Caribbean coral reefs. Even within a small area S. rathbunae exhibits the apparently wide variation in size, color, and morphology that has long frustrated efforts to identify and define species boundaries within this large ( > 100 described species) genus. Here I show that sympatric populations of this nominal species occupying different sponge hosts display clear, concordant differences in allozyme genotypes and in multivariate morphometrics, confirming that the populations represent three distinct biological species. Moreover, careful field sampling revealed that the three S. rathbunae taxa and the closely related S. filidigitus Armstrong showed almost no overlap in the species of hosts occupied. Interestingly, while there was significant differentiation between Belizean and Panamanian populations of the one taxon that occurred at both sites ( ~ 1500 km apart), these populations were recognizable as conspecific using both genetic and morphological characters. These results show that (1) diversity of Synalpheus, which is already among the most species-rich crustacean genera, is probably several times higher than currently recognized, and (2) species of sponge-dwelling Synalpheus are highly host-specific, with related species distinctly segregated among hosts. Together with previous evidence of host race differentiation within shrimp species, these results suggest a primary role for resource specialization in the origin and/or maintenance of this group's characteristically high diversity.
TL;DR: It is concluded that studies reporting the proportion of specialist insect herbivores associated with particular tropical tree species will yield only a portion of the information needed to estimate global arthropod species richness, but may be useful for elucidating certain aspects of food-web ecology in tropical rain forests.
Abstract: The assumptions on the host specificity of beetles that led Terry Erwin to suggest that there may be over 30 million arthropod species were tested for 10 species of trees and their insect associates at a rainforest site in Papua New Guinea. The data included 391 species and 4696 individuals of herbivorous beetles collected during a one year period using hand collecting, beating, branch clipping, intercept flight traps and pyrethrum knockdown. Insect host specificity was assessed by feeding trials in captivity. The data suggest that between 23 and 37 monophagous leaf-feeding species are most likely to be present in this system, whereas Erwin's method yields an estimate of 138 monophagous species. The major factors responsible for the discrepancy between our observations and Erwin's assumptions appears to be (a) the importance of transient species; (b) the insect fauna that is shared among tree species; (c) some generalist wood-eating species may inflate the apparent species richness of leaf-feeding beetles; and (d) the proportion of specialist species varies significantly among tree species. We conclude that studies reporting the proportion of specialist insect herbivores associated with particular tropical tree species will yield only a portion of the information needed to estimate global arthropod species richness, but may be useful for elucidating certain aspects of food-web ecology in tropical rain forests.
TL;DR: It is proposed that the genetic structuring and subsequent speciation of this group has been promoted by the absence of the marine juvenile phase that is found in five other members of the genus native to New Zealand.
Abstract: We examined genetic differentiation among 23 samples of non-migratory river galaxias from 17 streams in the Taieri River system, South Island, New Zealand. Four major genetic types were found, two of which occur in narrow sympatry in one location. These were compared with topotypical material representing Galaxias anomalus from the Clutha system (Otago) and G. vulgaris from the Waimakariri system (Canterbury) in order to establish identity. Morphological examination of these four major genetic types revealed consistent concomitant differences. The results suggest that there are at least three species of river galaxias in the Taieri system: G. anomalus, G. vulgaris and at least one previously undescribed species. We propose that the genetic structuring and subsequent speciation of this group has been promoted by the absence of the marine juvenile phase that is found in five other members of the genus native to New Zealand. This structuring may be exacerbated by population fragmentation over the last century owing to the negative influence of introduced trout. The phylogenetic diversity within the river system mirrors the diverse flora and invertebrate fauna of the region, and has conservation implications that parallel those resulting from our improved knowledge of the New Zealand herpetofauna through the application of genetic analysis.
TL;DR: It is concluded that, since these traits are strongly intercorrelated, it is very difficult to distinguish between their separate effects on the evolution of gregariousness, but potentially, the presence of repellent defence may be sufficient for the Evolution of gRegariousness.
Abstract: Gregariousness in insects is often associated with aposematism, which has two distinct properties, repellent defence and warning coloration Theoretically, both repellent defence and warning coloration are expected to facilitate the evolution of gregariousness This paper investigates whether the likelihood for gregariousness to evolve is higher (1) in the presence of chemical/physical defence and (2) in the presence of warning coloration, in a sample of over 800 tree-living macrolepidopteran species A new phylogenetic technique for investigating the correlation between two discrete characters, based on independent contrasts, is used For each of nine contrasts, based on presence/absence of repellent defence that included transitions to gregariousness, the frequency of such transitions was highest in the lineage with repellent defence present Similarly, out of 12 contrasts based on presence/absence of warning coloration 10 had the highest frequency of transitions to gregariousness in the lineage with warning coloration Thus, gregariousness is more likely to evolve in lineages with repellent defence and in lineages with warning coloration, but it is concluded that, since these traits are strongly intercorrelated, it is very difficult to distinguish between their separate effects on the evolution of gregariousness Our findings indicate, however, that potentially, the presence of repellent defence may be sufficient for the evolution of gregariousness
TL;DR: This work compares the success of the Workshop-90 method in representing these plant species with the results of using a simple quantitative method for seeking complementary areas, and shows species representation is shown to be increased within the 90 top-priority areas when using the complementary areas method.
Abstract: Priority areas forin situconservation are an unavoidable consequence of competition with other land uses, although they are certainly not to be seen as the only areas of value for conservation. In 1990 an international workshop was convened in Manaus, Brazil, to identify priority areas within Amazonia by committee (Workshop-90). A substantial part of the data for this assessment came from five plant families recorded for theFlora Neotropica. We compare the success of the Workshop-90 method in representing these plant species with the results of using a simple quantitative method for seeking complementary areas. The promises of quantitative methods are twofold. First, they force people to make their values explicit, which is important because priorities are dependent on the values and goals of individuals and are not universal. Second, quantitative methods can achieve representation of more of what is valued. For example, within the 90 top-priority areas (an arbitrary but convenient figure taken from Workshop-90), species representation is shown to be increased when using the complementary areas method by 83%. Simple computer implementations of this method can provide the means for fast inter-active exploration of flexibility in the many alternative area choices. This permits monitoring and review with minimum effort as new data on species and threats are acquired. On the other hand, the problem for all methods is the need for very large numbers of data, whether based on species or on any other surrogates for biodiversity, if well-informed decisions are to be made. This is not a particular problem of quantitative methods, but their explicit nature does highlight the shortcomings of data. For example, patterns in theFlora Neotropicadata show effects from small samples even though these data are among the best available for any large tropical wet-forest region. Furthermore, in order to assess the longer-term consequences of area choices, quantitative methods will require many explicit local data on factors affecting viability, threat and cost.
TL;DR: The raised position of the anthers in nototribic flowers as a possible means to reduce excessive pollen losses caused by pollen-collecting hymenopterans is discussed.
Abstract: In the Central European apoid and masarid fauna, 13 bee species belonging to seven different taxonomic groups and one honey wasp species were found to be equipped with a specialized pollen-collecting apparatus on the face which is used to harvest pollen from nototribic flowers, viz. representatives of the Lamiaceae and the Scrophulariaceae. Pollen from these two plant families plays an important part in the larval nourishment of these hymenopteran species. The pollen-collecting apparatus consists of a peculiar facial pilosity composed of transformed hairs which are thickened at their base and either knobbed apically (Celonites abbreviatus) or extended into a thin tail which is either straight and bent at right angles (Rophitesspp.,Anthophora borealis,A. furcata) or wavy (Anthidiumspp.,Anthocopa andrenoides,Osmia aurulenta,O. caerulescens). Nototribic flowers are worked by pollen-collecting females by rubbing the facial area covered with the transformed hairs over the anthers (Celonites,Anthidium,Anthocopa,Osmia), by puzzling the pollen amongst the transformed hairs (Anthophora furcata) or by a combination of rubbing movements and buzzing (Rophites). Bee species lacking special morphological devices were observed to perform specialized behaviours when collecting pollen at nototribic flowers. Nototribic flowers, therefore, appear to be difficult to exploit for pollen. The raised position of the anthers in nototribic flowers as a possible means to reduce excessive pollen losses caused by pollen-collecting hymenopterans is discussed.
TL;DR: Bioassays with wild caught and freshly emerged adults suggest that protection against predation by the orb weaving spiderNephila clavipes may be dependent on PA concentration and maybe some spider idiosyncrasies, but freshly emerged Aeria olenawithout PAs are also liberated by Nephila, suggesting other protective compounds.
Abstract: Pyrrolizidine alkaloids (PAs) often serve as chemical mediators of plant-herbivore-predator interactions. Butterflies (Danainae and Ithomiinae) and moths (Arctiidae) usually acquire PAs from plant sources (larval host plants, flowers or withered leaves visited by adults — pharmacophagy) and thereby become chemically protected against predators; they also use PAs as pheromone precursors. Study by GC-MS of PAs in three species of Ithomiinae butterflies, their larval host plants and adult alkaloid sources showed three different acquisition patterns: (1) larvae of the primitiveTithorea harmoniasequester PAs from their food plantPrestonia acutifolia(Apocynaceae: Echitoideae), and adults may also acquire these alkaloids from plant sources; (2) larvae of the more derivedAeria olenafeed onPrestonia coalita, in whose leaves no PAs were detected, but freshly emerged adults sometimes contain PAs and males intensively seek and sequester these alkaloids in plant sources; and (3) larvae of the still more advancedMechanitis polymniafeed on several PA-freeSolanumspecies, and adult males sequester the alkaloids from various plant sources. Males and females of all three species contain mostly two PAs, the diastereoisomeric retronecine monoesters lycopsamine and intermedine, stored in the N-oxide form. Larval host plants and adult plant sources showed a large array of PA structures, the most abundant and frequent being lycopsamine and its diastereoisomers intermedine, echinatine, rinderine and indicine, and the deoxy-analogues supinine and amabiline. Bioassays with wild caught and freshly emerged adults suggest that protection against predation by the orb weaving spiderNephila clavipesmay be dependent on PA concentration and maybe some spider idiosyncrasies, but freshly emergedAeria olenawithout PAs are also liberated byNephila, suggesting other protective compounds. The role of this spider as a selective pressure for PA acquisition by ithomiines is not clear.
TL;DR: A multivariate model to analyse population genetics data based on the properties of ‘joint scaling’ of populations and loci is developed and the relevance of the CRT-MCA model is illustrated by the analysis of population structure of 15 dogwhelk populations in south-west England.
Abstract: Very few studies have attempted to relate the properties of some ordination techniques to classical tools of population genetics as F -statistics. A multivariate model to analyse population genetics data based on the properties of ‘joint scaling’ of populations and loci is developed. The design of population genetics data means that this model deals with a modified version of the classical Multiple Correspondence Analysis which is called Constant Row Total-Multiple Correspondence Analysis (CRT-MCA) and is an original tool in population genetics. Such a model allows estimates of the degree of population differentiation by studying the variability of the distribution of allele frequencies in different samples. Some clear relationships exist between some model parameters and the classical F st statistics. The CRT-MCA also allows all the studied loci to be considered simultaneously and the role of each locus in patterns of population differentiation to be expressed. Such a multivariate approach prevents the use of any pooling strategy as is classically used in studies of hierarchical F -statistics. The relevance of the CRT-MCA model is illustrated by the analysis of population structure of 15 dogwhelk ( Nucella lapillus ) populations in south-west England. The advantages and limitations of CRT-MCA are presented.
TL;DR: It is suggested that a correlation should exist between mating system and ploidy level, with outcrossing favouring diploid life cycles and inbreeding or asexual reproduction favouring haploids life cycles.
Abstract: According to the ‘masking hypothesis’, diploids gain an immediate fitness advantage over haploids because diploids, with two copies of every gene, are better able to survive the effects of deleterious recessive mutations. Masking in diploids is, however, a double-edged sword: it allows mutations to persist over time. In contrast, deleterious mutations are revealed in haploid individuals and are more rapidly eliminated by selection, creating genetic associations that are favourable to haploidy. We model various mating schemes and show that assortative mating, selfing, and apomixis maintain the genetic associations that favour haploidy. These results suggest that a correlation should exist between mating system and ploidy level, with outcrossing favouring diploid life cycles and inbreeding or asexual reproduction favouring haploid life cycles. This prediction can be tested in groups, such as the Chlorophyta, with extensive variation both in life cycle and in reproductive system. Confirming or rejecting this prediction in natural populations would constitute the first empirical test of the masking hypothesis as a force shaping the evolution of life cycles.
TL;DR: The results support the notion that ecological conditions like predation pressure are important in shaping wader parental care systems, with implications for mating systems.
Abstract: Data on 12 factors presumed to influence the distribution of aggressive nest defence in 111 species of waders (incubation-sharing by the parents, number of parents present near the nest, incubation time, nest habitat, breeding latitude, body mass, wing loading, wing structure, detectability on the nest, predator regime, coloniality and alternative prey) were collected from literature and field researchers. Body mass and number of parents present on the nest territory (within response range when avian predators appear) explain 50% of the variation in aggressive defence behaviour. The results support the notion that ecological conditions like predation pressure are important in shaping wader parental care systems, with implications for mating systems. Altogether, the investigated factors explain around 70% of the variation in the samples. Future research on the level of individuals is suggested in order to explain the remaining variation.
TL;DR: An example of the spatial relations among several apparatuses in the head of the cichlid fish, Astatoreochromis alluaudi, is presented and the transformations of these appar atuses and their functions due to a change in the pharyngeal jaw apparatus resulting from a functional shift are investigated.
Abstract: Organisms are tightly packed with structures so architectonic interdependency of structures is an obvious aspect of integration. This aspect of functional morphology, however, has received remarkably little attention. The present paper presents an example of the spatial relations among several apparatuses in the head of the cichlid fish, Astatoreochromis alluaudi . It investigates the transformations of these apparatuses and their functions due to a change in the pharyngeal jaw apparatus resulting from a functional shift (insect eating to snail crushing or vice versa ). The volume of the pharyngeal jaw apparatus differs 55% between the insect eating- and the snail eating morph. The increase in volume of the pharyngeal jaw apparatus has an impressive number of spatial effects, both direct and indirect, on other structures. Reallocation of space within the pharyngeal jaw apparatus occurs. Total head volume increases 31% but a reallocation of space is still necessary as the increase of the opercular compartment where the pharyngeal jaw apparatus is situated compensates for only 59% of the volume increase of that. Not all spatial effects do impose constraints. Spatial constraints are avoided when one of the apparatuses can use a topographically different volume of space. The respiratory apparatus shows internal reallocations of space without loss of total volume. The same solution occurs for elements of the expansion apparatus and the buccal cavity. The eyes are not influenced. Finally spatial effects can have positive repercussions. The muscles of the oral jaw apparatus increase in size. This may be an example of an epiphenomenon.
TL;DR: The assumption of a simple vicariant evolution of the shrews was rejected, but several concordant patterns indicate that the phylogeny of these mammals was indeed shaped by these events, consistent with the hypothesis of a relatively recent colonization of the Malay Archipelago by shrews of the genus Crocidura.
Abstract: Genetic variation of 20 species of shrews from the Malay peninsula, Sumatra, Java, Borneo, the Philippines and Sulawesi was assessed by allozyme electrophoresis at 32 loci. According to Mantel's tests, the genetic differentiation of these species of shrews is not a function of the geographic distance separating them (r = 0·09, NS), but is correlated to the water depth surrounding the islands where they live (r = 0·49,P < 0·01). The results are just the reverse if the correlations are computed for the Sunda Shelf taxa only. In this case, the sampled populations show an isolation-by-distance relationship (r = 0·32;P < 0·01), while no significant correlation with water depth was detected (r = 0·20;P = 0·07). Qualitative predictions based on eustatic sea level variation and water depth were formulated as a model of historic connections between the islands. This palaeogeographic model was tested through Brooks Parsimony Analysis. The assumption of a simple vicariant evolution of the shrews was rejected, but several concordant patterns indicate that the phylogeny of these mammals was indeed shaped by these events. Homoplasies demonstrated that the SE Asian species ofCrocidurainclude composite zoogeographic histories. Sulawesi, for example, supports at least six species, five of which are closely related, while the last one,C. nigripes, is more closely related to a Bornean taxon. This pattern was interpreted as the result of a first wave of colonizers which subsequently radiated, followed by a more recent, second colonization event from Borneo. The overall small genetic distance found within the assemblage of the five old endemics (DN = 0·151 ± 0·041) suggests that the radiation was not accompanied by extensive differentiation, although from a karyological point of view, they exhibit unusual variations when compared to other IndomalayanCrocidura. By contrast, the four species found on Sumatra are more differentiated (DN = 0·221 ± 0·063) and never form sister-group relationships in any phylogenetic reconstruction; each one is more closely related to different taxa living outside Sumatra. This suggests that they are probably remnants of an important centre of dispersal for the entire Malay Archipelago. The standard genetic distance averaged among all Southeast Asian species (DN = 0·235 ± 0·094) is about half that measured within Palearctic or African taxa. Such an overall lower mean level of genetic variability is consistent with the hypothesis of a relatively recent colonization of the Malay Archipelago by shrews of the genusCrocidura.
TL;DR: Two comparative approaches demonstrated that male guarding and male-male contest variables are linked to SSD in minnows.
Abstract: Sexual size dimorphism (SSD) is predicted to vary across mating systems. A previous study examined a model of SSD in fishes as it relates to three mating system variables: probability of sperm competition, male territorial guarding, and male-male contest. I tested the ability of these variables to predict SSD in North American freshwater minnows, after controlling for phylogenetic effects by an independent contrasts method. Across 58 species only male territorial guarding was significantly related to SSD in a stepwise multiple regression. When tested for 26 genera and subgenera, both male territorial guarding and male-male contest were significant in the model. The concentrated-changes test revealed that character changes in SSD (from males the same size or smaller than females, to males larger than females) were more concentrated on branches with presence of male guarding (similar results were found for changes in SSD and presence of sperm competition), at the species and genus levels. Both comparative approaches demonstrated that male guarding and male-male contest variables are linked to SSD in minnows.
TL;DR: A polyphyletic concept of arthropod evolution from soft-bodied, segmented, haemocoele-possessing, non-annelid worms is elaborated and the degree of convergence demanded is amply matched by proven examples of the phenomenon.
Abstract: Recent claims that arthropods are monophyletic because all have jaws composed of a five-segmented coxa, that the groundplan of arthropod legs has no less than 11 segments, that crustaceans, chelicerates and insects share a 'polyramous arthropod leg', and that the labrum is formed from a pair of legs, are rejected on factual grounds. It is suggested that the earliest arthropod appendages were unsegmented. Putative homologies among mandibulate arthropods are considered. Striking as some of these are, a good case can be made for their convergent evolution, and the concept of the Mandibulata is rejected. Suggested separate ancestries of crustaceans and tracheates are compared. A realistic explanation of radiation from a common arthropod ancestor remains illusory. A polyphyletic concept of arthropod evolution from soft-bodied, segmented, haemocoele-possessing, non-annelid worms is elaborated. The degree of convergence demanded is amply matched by proven examples of the phenomenon. If the earliest arthropods lacked compound eyes, and these were acquired several times, as they have been at least twice in non-arthropods, several otherwise intractable problems are resolved. Sequence comparisons provide a powerful tool for determining relationships but seem powerless to establish whether arthropods are monophyletic, or polyphyletic in the manner envisaged here.
TL;DR: Genetic divergence in some marginal or isolated natural populations was similar to, or greater than, Kenny's pond guppies (Reynolds' genetic distance,R = 0·496), indicating that chance colonization and founder effects may have contributed to the observed geographic patterns of genetic differentiation in Trinidad.
Abstract: The evolutionary consequences of three artificial introductions of the guppy,Poecilia reticulata, in Trinidad were examined by comparing the allozymic structure (observed heterozygosity (Ho), and mean number of alleles (Na)) of each corresponding source (S) and transplant (T) population. In ‘Haskins’ (H) and ‘Endler's’ (E) introduction, 200 guppies (half female) were transferred to guppy-free habitats in 1957 and 1976 respectively. ‘Kenny's’ (K) introduction in 1981 involved the release of a single pregnant female into an isolated ornamental pond. Analysis of allozyme frequencies at 25 enzyme-coding loci revealed reductions in observed heterozygosity at some loci in all three transplant samples, and a marked decline in the mean number of alleles in Kenny's pond sample. Significant genetic differentiation occurred between (S) and (T) samples at some loci in all introductions, but was most marked in H(T) and K(T). Despite previous studies on rapid evolutionary changes in the life histories and morphology of Endler's transplant guppies, there was little support for any major effects of stochastic forces on allozymic diversity arising from the introduction. Selection arising from changes in predation pressure appeared to be the predominant factor causing the remarkably rapid adaptation of guppies to their new environments. Genetic divergence in some marginal or isolated natural populations was similar to, or greater than, Kenny's pond guppies (Reynolds' genetic distance,R = 0·496), indicating that chance colonization and founder effects may have contributed to the observed geographic patterns of genetic differentiation in Trinidad.