Showing papers in "Biological Journal of The Linnean Society in 2000"

A comparative analysis of pollen limitation in flowering plants

Abstract: We conducted a comparative analysis to determine life history and ecological correlates of pollen limitation among 224 species of animal-pollinated flowering plants. To test predictions concerning the occurrence of pollen limitation, species were classified categorically for six life-history traits (self-compatible vs. self-incompatible, autogamous vs. non-autogamous, specialized vs. unspecialized floral morphology, nectariferous vs. nectarless, monocarpic vs. polycarpic, herbaceous vs. woody) and two ecological conditions (presence in open vs. forested habitats and temperate vs. tropical biomes). Pollen limitation of species in contrasting categories was compared using non-parametric tests (TIPs analysis) and phylogenetically-independent contrasts (PICs). The results of TIPs and PICs analyses were generally congruent, although fewer significant contrasts were evident with PICs, probably because of low statistical power. Overall the results suggest that the influence of phylogenetic history on the intensity of pollen limitation was not particularly strong. Nonetheless, significant variation in the degree of pollen limitation was demonstrated among seven angiosperm families suggesting some phylogenetic component to the phenomenon. With both TIPs and PICs, pollen limitation was less intense in self-compatible and autogamous species. TIPs analysis demonstrated that herbaceous, nectariferous, and temperate species were less likely to be pollen-limited, but using PICs this could only be corroborated for those that were self-incompatible. None of the traits were singularly unambiguous predictors of pollen limitation, possibly reflecting the stochastic nature of pollinator service.

How many species of arthropods? Erwin's estimate revised

Abstract: Erwin's much debated estimate of 30 million species of arthropods is revised. The original estimate is based on the evaluation of host specificity of guilds in beetle samples, and subsequent hierarchical ratio extrapolations. The growing number of studies including mass sampling of arthropods have provided several data sets suitable for obtaining an empirical basis of this estimate. The structure in this modified version is somewhat changed compared to the original estimate in order to make each hierarchical step more easily testable. Plant species are separated into different growth forms, and host specificity measures are based only on phytophagous species. Effective specialization is applied as a measure of host specificity to correct for the fauna shared between plant species. A between community correction factor is applied to correct for differences in host specificity at different spatial scales. There are still great uncertainties attended with such estimates. The largest problems refer to the between community correction factor and the proportion of canopy species to total species. Further work on host specificity and the least known hyperdiverse groups are also needed. The revised version of the estimate does not support hyperestimates of 30–100 million species. Rather, it compares nicely with estimates derived from other estimation methods, indicating a global arthropod species richness of 5–10 million species.

Evolution of sexual dichromatism: contribution of carotenoid- versus melanin-based coloration

Abstract: In birds, carotenoid-based plumage coloration is more dependent on physical condition and foraging abilities and less constrained developmentally than is melanin-based coloration. Thus, female mate choice for honest signals should result in more intense sexual selection on carotenoid- than on melanin-based plumage coloration. Using variation in sexual dimorphism as an indirect measure of the intensity of sexual selection, we tested the prediction that variation in sexual dimorphism is driven more by change in carotenoid-based coloration between males and females than by change in melanin-based coloration. Examination of historical changes in carotenoid- versus melanin-based pigmentation in 126 extant species of Cardueline finches supported this prediction. We found that carotenoid-derived coloration changed more frequently among congeners than melanin-based coloration. In both sexes, increase in carotenoid-based coloration score, but not in melanin-based coloration score, was strongly associated with increase in sexual dichromatism. In addition, sexual dimorphism in carotenoid-based coloration contributed more to overall dichromatism than dimorphism in melanin-based plumage. Our results supported the hypothesis that melanin-based and carotenoid-based coloration have fundamentally different signal content and suggest that combining melanin-based and carotenoid-based coloration in comparative analyses is not appropriate.

Phylogenetic relationships in the iguanid lizard genus Liolaemus: multiple origins of viviparous reproduction and evidence for recurring Andean vicariance and dispersal

Abstract: Phylogenetic relationships within the iguanid lizard genus Liolaemus are investigated using 1710 aligned base positions (785 phylogenetically informative) of mitochondrial DNA sequences, representing coding regions for eight tRNAs, ND2, and portions of ND1 and COL Sixty new sequences ranging in length from 1736 to 1754 bases are compared with four previously reported sequences. Liolaemus species form two well-supported monophyletic groups of subgeneric status, Liolaemus and Eulaemus. These subgenera appear to have separated at least 12.6 million years ago based on the amount of molecular evolutionary divergence between them. Hypotheses that species occurring in the Andes, west of the Andes, and east of the Andes, each comprise distinct monophyletic groups are independently rejected statistically. The shortest estimate of phylogeny suggests mat Liolaemus originated either in the Andes or the eastern lowlands. Numerous evolutionary shifts have occurred between the Andes, and the eastern and western lowlands, suggesting recurring vicariance and dispersal. Species occurring at high elevations or high latitudes usually have viviparous reproduction. Depending on whether parity mode is considered reversible in Liolaemus, the most parsimonious reconstruction supports at least six independent origins of viviparity or at least three gains followed by three losses of viviparity among die 60 Liolaemus lineages examined.

A review of colour and pattern polymorphisms in anurans

Abstract: Species that exhibit polymorphism, the simultaneous occurrence of two or more discrete, genetically-based phenotypes in a population, are ideal for studying the microevolutionary forces that maintain genetic variation in nature. Many anuran species exhibit striking colour or dorsal pattern polymorphisms, and so provide an excellent system in which to study questions pertaining to the evolution and maintenance of polymorphisms. Despite the wide occurrence of pattern or colour polymorphisms in anurans (current records cite at least 225 species representing 35 genera and 11 families) surprisingly little conclusive work has been done on the inheritance and selective maintenance of this variation. The mode of inheritance has been investigated in 26 species, but conclusively demonstrated in only two. Forty-six species have been described as undergoing ontogenetic change, and 32 species have been described as sexually dimorphic. That anuran polymorphisms are under some sort of selection has been inferred from the large number of polymorphic species, from putative cases of apparent convergent evolution and the existence of identical polymorphisms in closely related species, from cyclical fluctuations in morph frequencies, and from a few observations of non-random survival during bouts of stress. The selective mechanisms maintaining these polymorphisms have been investigated in only 19 species. Most studies looked for physiological traits correlated with the polymorphism, rather than studying the most obvious mechanism, selective predation on colour/pattern itself. Thus, anuran polymorphisms remain a rich but largely unexploited system for studying the evolution of phenotypic variation in nature.

Body size, egg size, and their interspecific relationships with ecological and life history traits in butterflies (Lepidoptera: Papilionoidea, Hesperioidea).

Abstract: The interspecific relationships between egg size and body size in butterflies (Papilionoidea and Hesperiidae), and between size and egg and larval development time, larval trophic specificity, foodplant structure, climate, and phenology were investigated based on a sample of more than 1180 species. The independent contrasts method was used to avoid taxonomy-dependent results. Egg size is allometrically related to adult wing length by a slope of 0.43. Based on a subset of species, fecundity is correlated to adult body size, and there is evidence for a compromise between egg number and egg size (relative to adult size) across species. Butterfly size increases in correlation to the mean annual temperature of the species geographic range, but decreases in relation to increased aridity (or the length of the dry season). Larger butterflies tend to have longer larval development times, use large or structurally complex host plants, and are more likely to lay their eggs in batches, irrespective of climate. Larger eggs tend to develop more slowly, and give rise to larvae with longer developmental periods that will result in larger adults. No evidence was found to support a relationship between butterfly body size and polyphagy. A complex pattern of interrelationships links body size (and egg size) to other traits, although correlations other than that between egg size and body size are generally low. The results suggest the necessity of separating climate and seasonality into components that are relevant to insect life histories in comparative studies.

Molecular data support a rapid radiation of aphids in the Cretaceous and multiple origins of host alternation

Abstract: Many aphids display a remarkably complex life cycle of host alternation, in which cyclical parthenogenesis is combined with the obligate use of two unrelated host plants. We used mitochondrial ribosomal DNA (partial 12S and 16S) sequences to reconstruct the phylogeny of aphids, to determine how many origins of host alternation and correlated major host-plant shifts have occurred. Our results agreed with previous morphological studies in that species clustered with good support at the level of tribes. There was little well-supported phylogenetic structure at levels deeper than tribes, however, except for the monophyly of two subfamilies, Aphidinae and Lachninae. We argue that aphids experienced a rapid radiation at the tribal level, after host shifting from gymnosperms to angiosperms. A rapid radiation is consistent with aphid fossils, which record the presence of few subfamilies in the late Cretaceous, but most extant tribes by the early Tertiary. Plant fossils also record host plants of aphid tribes diversifying during this time. A hypothesized mechanism by which host alternation has evolved (fundatrix specialization), coupled with the rapid radiation, implies that this life cycle may have originated as often as in the ancestor of each tribe that displays it. We also consider, however, an alternative hypothesis of fewer origins. The basal radiation of Aphididae was dated from molecular sequences to have occurred at approximately 80–150 Mya.

Why are there good and poor mimics

Abstract: Among the many Batesian mimetic hoverflies (Diptera: Syrphidae) some have a very precise resemblance to the presumed model («good» or «specific» mimics) while others have a much less precise resemblance («poor» or «general» mimics). Intuitively one might expect that the specific mimics would be commoner and more successful than the general mimics. However, many specific mimics (e.g. Sericomyia silentis , Volucella bombylans ) are quite rare, while general mimics are common (e.g. Syrphus ribesii , Episyrphus balteatus and Eristalis intricarius ). Similarly, some ant-mimicking spiders from several different families are very good morphological and behavioural mimics of just one species of ant while others have a less detailed resemblance to ants in general. Six hypotheses are presented to explain the occurrence of so many poor mimics, and a theoretical model is outlined (the multi-model hypothesis) which shows how a poor general mimic can have a larger population than a good, specific mimic. This hypothesis may apply to some species of hoverfly and to some ant-mimicking spiders.

Toward the phylogeny of the family Lacertidae - Why 4708 base pairs of mtDNA sequences cannot draw the picture

Abstract: A phylogeny of the family Lacertidae was derived from DNA sequences of six mitochondrial genes. Only a few nodes were confidently resolved using maximum parsimony, although the data yielded a total of 1664 phylogenetically informative characters. The lacertids grouped into two subfamilies, the Gallotiinae which includes genera Gallotia andPsammodromus , and the Lacertinae which includes the remaining lacertids. The Lacertinae split into two additional groups. The African group included all African and Arabian lacertids and two Eurasian genera, Eremias and Ophisops; the remaining Eurasian lacertids were included in the Eurasian group. Most of the relationships within the African and Eurasian groups cannot be confidently resolved. A permutation tail probability test suggested that there is very little character covariance in the data to support these unresolved relationships. A recent explosive speciation hypothesis was invoked to explain the lack of structure of the data. The common ancestor of the Eurasian group, as well as the ancestor of the African group, experienced simultaneous, or almost simultaneous, multiple speciation events, which left none or very few characters fixed on the internodes. The phylogenetic reconstruction at the family level will be very difficult, if not impossible. Future phylogenetic research should focus on lower levels.

Infraspecific mitochondrial sequence diversity in Hydrobia ulvae and Hydrobia ventrosa (Hydrobiidae: Rissooidea: Gastropoda): Do their different life histories affect biogeographic patterns and gene flow?

Abstract: Infraspecific relationships and population parameters are largely unknown in the ecologically significant mud snail genus Hydrobia s.I. We therefore studied infraspecific variation, population structure and gene flow in two Hydrobia species with different life history strategies: the marine, planktonic H. ulvae and the brackish-water, directly developing H. ventrosa. Based on sequencing data of a 638 bp fragment of the mtDNA gene for cytochrome oxidase 1, we found considerable differences between the two species. H. ulvae shows high average pairwisc nucleotide diversity, low population level differentiation (Fst). AND high average gene flow (Nm) between populations. Dispersal appears to accord with Wright's island model. In contrast, many populations of H. ventrosa have high population level differentiation and low gene flow. The average pairwise nucleotide diversity is relatively low; this species disperses according to Wright's isolation by distance model. Differences in dispersal modes and gene flow could be partly due to differences in type of early ontogeny and quantitative differences in passive dispersal. However, the fact that H. ulvae is a marine species with high tolerance to environmental stress and therefore less sensitive to migration barriers than H. ventrosa may better explain these differences. The extant lineages of H. ulvae and H. ventrosa most likely evolved in the northeastern Atlantic during the Pleistocene.

Evolutionary relationships between morphology, performance and habitat openness in the lizard genus Niveoscincus (Scincidae: Lygosominae)

Abstract: Correlations between an animal's morphology and ecological parameters such as habitat characteristics emphasize the intimate link between phenotype and the environment, but are often difficult to interpret because the functional consequences of morphological variation are frequently unknown. We provide one of the few studies relating limb morphology, functional capabilities, and habitat in reptiles. We tested the hypothesis that species occupying open microhabitats would possess relatively longer limbs and faster sprint speeds than those occurring in more closed microhabitats. A number of morphological characteristics relevant to locomotion were quantified, including the length of the bones of the fore- and hindlimbs and body size. A phylogenetic analysis was then used to examine the evolutionary relationships between morphology, locomotor performance and microhabitat openness in seven species of Niveoscincus and one species of the closely related genus Pseudemoia . A significant evolutionary relationship was established between sprinting ability, morphology, and the openness of the microhabitat occupied by a species. The phylogenetic analysis demonstrated an evolutionary trend in Niveoscincus of species occupying open microhabitats (e.g. N. greeni , N. ocellatus ) being large with long limbs and high sprinting ability, while those occupying closed microhabitats (e.g. N. coventryi , P. entrecasteauxii ) are smaller with short limbs and much slower maximum sprint speeds.

Biogeographic area relationships of lowland Neotropical rainforest based on raw distributions of vertebrate groups

Abstract: Hypotheses of the historic biogeography of Neotropical anurans inhabiting lowland forests were generated using Parsimony Analysis of Endemicity. In order to establish comparisons with the biogeographical patterns of other vertebrates, previous cladistic analyses reported in the literature (for lizards and primates) were extended and reanalysed to match the geographical scope of the anuran analysis. Cladistic analysis of the distribution of 335 anuran species at 14 localities showed two regions that form a basal dichotomy: (1) Central America + Choco and (2) Amazon Basin + Brazilian Atlantic Forest. This result is interpreted as the first vicariance event that separated lowland Neotropical rainforests into Cis-Andean (east from the Andes) and Trans-Andean (west from the Andes) areas. Within the Cis-Andean localities, the earliest separation occurred between the Amazon Basin and the Brazilian Atlantic Forest. Within the Amazon Basin, three distinctive clusters are defined: (1) Belem, (2) Guianan Region, and (3) Upper Amazon Basin. Data sets on the distribution of anurans, lizards, and mammals have strong cladistic signal. Strong congruence exists among the area cladograms of anurans, lizards, and primates. All of them have, or at least did not conflict with: (1) a basal separation between Cis- and Trans-Andean regions, (2) a Central American clade, (3) the Choco Region is sister to the Central American clade, (4) an Amazon Basin clade, (5) an Upper Amazon Basin clade, and (6) a Guianan clade. The area cladograms are dichotomous and therefore do not support biogeographic theories that hypothesize simultaneous isolations of biotas in the Neotropics.

Why are there so few evolutionary transitions between aquatic and terrestrial ecosystems

Abstract: Insects and flowering plants have rarely invaded the sea. Explanations for this have traditionally centered on the unique shortcomings of these groups in the marine environment. We show, however, that transitions among terrestrial, freshwater, and marine environments are infrequent in all major plant and animal clades except tetrapod vertebrates. In general, well-adapted incumbents are at a competitive advantage over would-be invaders from a physically different habitat. Data on the times and places of transition are consistent with our contention that evolutionary transitions among physically different environments are most likely when incumbents in the recipient environment exist in a regime of low-intensity competition and predation, as in terrestrial communities of the middle Paleozoic or the land biotas of oceanic islands. Freshwater environments, in which inferred intensities of predation are lower than in most marine and terrestrial environments, offer less biotic resistance to invaders than do communities in the sea or on land. Most invaders respond to novel physical circumstances by shutting down their metabolic machinery, and therefore add to their subordinate status as competitors with active incumbents. Only active tetrapods, particularly those with high and endothermically driven rates of metabolism, have successfully overcome this limitation.

Analysing spectral data: comparison and application of two techniques

Abstract: This study compares two different methods of condensing complex spectral data into interpretable indices or metrics of colour. Colour spectra were measured on standardized Munsell colour paint chips and estimates of the three fundamental components of colour (brightness, chroma and hue) were generated using principal component analysis (PCA) and segment classification (SC). We tested the accuracy of these techniques for generating colour component estimates from spectral data in four different «colour classes» (red/orange, yellow/green, green/blue, and blue/purple) and in an aggregate data set containing all measured spectra. We conclude that both analysis techniques will generally provide more information than more conventional colour assessment techniques. Neither technique was superior under all conditions; appropriateness of each technique depends on the system under study. Efficacy of both techniques depends on the variability present in the data set; greater variance in colour tends to reduce overall resolution. An application of these techniques is also presented in which we characterize sex-specific differences in colour between different populations of the poecilliid fish, Limia perugia.

Habitat type as a determinant of species range sizes: the example of lotic–lentic differences in aquatic Coleoptera

Abstract: Species differ in the size of their geographical ranges, but it is unclear how this is affected by the intrinsic properties of various habitat types. Using data on range sizes for 490 species of aquatic Coleoptera from the Iberian Peninsula we show that running-water (lotic) species have much smaller distributional ranges than those occurring in standing water (lentic). This robust association of habitat type and range size has independently arisen in at least four monophyletic coleopteran lineages, in Hydradephaga, Hydrophiloidea, Hydraenidae and Byrrhoidea, and several more times within these main groups. We propose that this pattern is due to different evolutionary dynamics of both habitat types: stagnant water bodies are more likely to completely disappear, requiring frequent migration of resident populations. Rivers and streams, on the contrary, have more temporal and spatial continuity, and therefore permit the long-term persistence of local populations. In less permanent habitats species will require a greater geographical mobility, which indirectly results in a larger size range. The less dispersive populations of running water should also have reduced gene flow, increasing the probability of allopatric speciation, and thus reducing the average range of more widespread ancestral species. These differences in population parameters, and the frequency of transitions between the two habitat types, may have strong macroevolutionary consequences, in particular regarding speciation rates and possible morphological specializations.

Morphological phylogenetics of termites (Isoptera)

Abstract: Isoptera (termites) are an ecologically important order, with both a high abundance and biomass in tropical ecosystems. However, there have been few phylogenetic hypotheses for termites, and we present here the first comprehensive cladistic analysis for the group. We analysed relationships between all seven termite families, including representatives of all known feeding group, plus a number of systematically critical taxa. Termite species richness is biased towards the higher termites (Termitidae), and our taxon sampling reflects this. Our analysis was based essentially on morphological characters (96 workers, 93 soldiers) plus seven biological characters. The cladistic analysis gave four equally parsimonious trees, representing two islands of topologies. The strict consensus tree is fully resolved for the higher termites, but less so for the lower termites. Overall there is low statistical support for the suggested topology, and this can be explained by the high incongruence between the data sets (worker, soldier and biological). This study highlights the particular problems of coding morphological characters in social insects with multiple castes. Without the input of additional data sets, e.g. alates, biological, behavioural and molecular, it will not be possible to obtain a well-supported termite phylogeny.

Batesian mimicry in the non-rewarding orchid Disa pulchra, and its consequences for pollinator behaviour

Abstract: The non-rewarding flowers of the South African orchid Disa pulchra are remarkably similar in morphology and spectral reflectance to the flowers of a sympatric nectar-producing iris, Watsonia lepida. Field observations indicated that both D. pulchra and W. lepida are pollinated by the long-tongued fly, Philoliche aethiopica (Tabanidae). The hypothesis that D. pulchra is a floral mimic of W. lepida was supported by choice experiments, which showed that, in terms of visits to inflorescences, flies do not discriminate between the two species. However, flies probed fewer flowers and spent less time on D. pulchra inflorescences than on Watsonia inflorescences. Thus the absence of nectar in the flowers of D. pulchra may reduce the risk of geitonogamy and pollen discounting. A breeding system experiment showed that fruits of D. pulchra that arise from self-pollination contain relatively few viable seeds compared with outcrossed fruits. These findings support the hypothesis that deception in orchids evolved under selection for more efficient mating systems.

Chastity belts in gartersnakes: the functional significance of mating plugs

Abstract: Male red-sided gartersnakes (Thamnophis sirtalis parietalis) deposit a thick gelatinous plug that occludes the female cloaca after copulation. Previous workers have interpreted the plug as a sexually-selected adaptation to (1) physically prevent re-mating by the female, and/or (2) provide pheromonal cues to discourage courtship by rival males or to decrease receptivity by females. Our data support the former hypothesis, but not the latter. Plugs serve as effective physical barriers to additional copulation for <72 h, but this is long enough for most females to become unreceptive, and/or disperse from the mating aggregation. Experimental removal of plugs immediately after copulation results in some re-mating by females, but plug removal several hours later does not rekindle sexual receptivity. Contrary to previous work, our experiments show that fluids associated with copulation (rather than the plug per se) are responsible for the rapid decline of male interest in mated females. Thus, the plug's primary function is to physically prevent matings rather than as a source of pheromonal cues to manipulate the behaviour of females or rival males. Plug mass is determined not only by a male's body size, but by his prior mating history (plug mass decreases with repeated mating) and by the size of his partner (males allocate larger plugs to larger females). Gartersnakes are unusual not only in their production of mating plugs, but also in their brief duration of copulation compared to other snakes. Mating plugs may have evolved in gartersnakes to reduce mating times, because of the extremely high «opportunity cost» of prolonged mating to a male gartersnake in a mating aggregation.

Speciation of Phlebotomus sandflies of the subgenus Larroussius coincided with the late Miocene-Pliocene aridification of the Mediterranean subregion

Abstract: The phylogeny and mode of speciation of Mediterranean Phlebotomus of the subgenusLarroussius were inferred by comparative sequence analyses of a fragment of mitochondrial DNA (Cytochrome b) and of a nuclear gene (Elongation factor alpha). The molecular phylogenies were congruent basally, where their clades matched the species complexes defined by a few genitalic characters of each sex. Reticulate evolution was suggested for the most derived species complex (Phlebotomus perniciosus): the molecular phylogenies were incongruent, and mitochondrial-marker distribution was consistent with introgressive hybridizations not between sister species but between species whose ranges now overlap or abut. By considering the molecular phylogenies, the mitochondrial molecular clock and the ecological niches of the species, as well as the historical biogeography and palaeoecology of the Mediterranean subregion, we propose that the derived lineages arose from a sequential series of speciation events associated with habitat shifts promoted by progressive aridification. This «taxon pulse»-like speciation occurred in the Pliocene, later than previously proposed in a vicariance hypothesis that invoked only tectonic events, but too early for Pleistocene Ice-age refugia to have played any role other than the isolation of geographical races. Speciation occurred before the proposed divergence of members of the Leishmania donovani complex and this helped to rule out any vector-parasite co-speciation or co-cladogenesis.

Patterns and consequences of behavioural responses to predators and parasites in Rana tadpoles

Abstract: We examined the interactive effects of predators and trematodes on Rana sylvatica and Rana clamitans larvae. We hypothesized that exposure to predators would increase tadpole susceptibility to trematode infection, by reducing tadpole activity and thereby increasing time spent on the bottom. We further hypothesized that the tadpoles would experience reduced rates of growth and development in the presence of either predators or parasites, and that predator presence would stimulate both species to develop larger tails and smaller bodies. Rana clamitans and R. sylvatica reduced their activity in the presence of both predators and trematode cercariae. In the longer running R. clamitans experiment, predator-exposed tadpoles developed significantly shallower tails and wider bodies, while trematode infection had no effect on growth, development, or shape. Most significantly, we found that extended exposure to caged fish predators made R. clamitans tadpoles more susceptible to trematode infection. A possible mechanism for this increased vulnerability is that reduced activity in the presence of predators increases tadpoles» proximity to cercariae. Our study suggests that various factors that decrease tadpole activity—predator presence, trematode cercariae and certain pesticides—may act synergistically to negatively impact tadpole populations.

Evolutionary radiation of an inbreeding haplodiploid beetle lineage (Curculionidae, Scolytinae)

Abstract: Haplodiploidy is a highly unusual genetic system that has arisen at least 17 times in animals of varying lifestyles, but most of these haplodiploid lineages remain relatively poorly known. In particular, the ecological and genetic circumstances under which haplodiploidy originates have been difficult to resolve. A recent molecular-phylogenetic study has resolved the phylogenetic position of the haplodiploid clade of scolytine beetles as the sister group of the genus Dryocoetes. Haplodiploid bark beetles are remarkable in that the entire clade of over 1300 species are apparently extreme (sib-mating) inbreeders, most of which cultivate fungi for food while some attack phloem, twigs or seeds. Here we present a much more detailed molecular-phylogenetic study of this clade. Using partial sequences of elongation factor 1-alpha and the mitochondrial small ribosomal subunit (12S), we reconstructed the phylogeny for 48 taxa within the haplodiploid clade, as well as two species of the diplodiploid sister genus Dryocoetes. Results indicate that the genus Ozopemon is the basal lineage of the haplodiploid clade. Since Ozopemon, Dryocoetes, and other outgroups are phloem-feeding, this strongly suggest that haplodiploidy and inbreeding evolved in a phloem feeding ancestor. Following the divergence of Ozopemon there is a series of extremely short internodes near the base of the clade, suggesting a very rapid rate of diversification in early Miocene (based on fossil evidence and sequence divergence). Among the many substrates for breeding and food resources utilized within this species-rich clade, the cultivation of yeast-like ambrosia fungi in tunnels deep into the wood predominates (nearly 90% of the species). The number of transitions to feeding on such fungi was few, possibly only one, and is perhaps an irreversible transition. The habit of feeding on fungi cultured in xylem makes it possible for the beetles to use a great variety of plant taxa. This extreme resource generalism, in conjunction with the colonization advantage conferred by haplodiploidy and inbreeding, may have promoted the rapid diversification of this clade.

Habitat preferences and diet in the predatory Coccinellidae (Coleoptera): an evolutionary perspective

Abstract: Coccinellids (ladybird beetles) exhibit considerable diversity in habitat and dietary preference and specificity. This is evident even when comparing species within some coccinellid genera. Resource limitation and competition are suggested as of greatest importance in the evolution of coccinellid habitat preferences. Dietary and habitat specialization has probably occurred in some lineages within broader preferences possessed by generalist ancestors, to avoid the costs associated with migration between habitats and prey switching. Feeding in atypical habitats, on alternative food, when optimal prey are scarce, is likely to have been of great importance in facilitating evolutionary shifts to novel diets and habitats. The broad host ranges of many coccinellid parasitoids and observed interspecific differences in parasitoid prevalence resulting from physiological differences between coccinellid species argue that enemy free space has been of limited importance in habitat and prey shifts in this group. Rapid change may occur in coccinellid foraging patterns, perhaps due to conditioning, and coccinellids may swiftly adapt to new habitats through selection acting on the expression pre-existing traits. Diet, as a determinant of coccinellid migration and gene flow, is likely to affect probable modes of speciation in different coccinellid groups. Parapatric speciation and possibly sympatric speciation are suggested as of possible importance in the genesis of new coccinellid species through prey and habitat shifts.

Factors driving extreme sexual size dimorphism of a sit-and-wait predator under low density

Abstract: Sexual size dimorphism is often a likely outcome of the interplay between natural selection and sexual selection, with female size dictated primarily by natural selection that maximizes fecundity and male size by sexual selection that maximizes reproductive opportunities. Attention to male fitness has focused heavily on direct male–male conflict selecting for superior male size and/or fighting ability, although male reproductive traits vary immensely among animals. An alternative, advanced by Michael Ghiselin, posits highly mobile dwarf males as a strategy for finding relatively immobile females in low-density populations. Adult male crab spiders Misumena vatia, sit-and-wait predators, are strikingly smaller, much more active, and relatively longer-legged than their females. This size difference results largely from males having two fewer instars than females, which simultaneously results in marked protandry. Populations of M. vatia often were small and of low density, with a female-biased sex ratio and an operational sex ratio that changed strikingly over the season. Sexual selection through scramble competition (locating the female first) should favour this suite of characters in males of low-density populations. Although direct male–male contests favoured large males, the low densities of adult males and the dispersed, relatively immobile females led to low levels of direct intrasexual contest. Females exaggerated the problem of males in finding them by providing few cues to their presence, a pattern consistent with indirect mate choice. In addition to favouring high mobility, scramble competition favoured males that selected flowers attracting many prey, the sites most often occupied by females.

Factors affecting the co-existence of the serpentine endemic Mimulus nudatus Curran and its presumed progenitor, Mimulus guttatus Fischer ex DC

Abstract: Population genetics theory suggests that two species which are reproductively isolated only by postzygotic barriers cannot co-exist in sympatry since the rarer population will become extinct Mimulus nudatus andMimulus guttatus are two closely related species that are isolated by a postzygotic barrier operating at the seed provisioning stage On several sites on the serpentine soils of Lake and Napa counties, California, M nudatus and M guttatus live in sympatry and flowering times of the species overlap, so the species are sometimes flowering next to each other We investigated whether there was any reduction in fertility of M nudatus and M guttatus caused by interspecific crosses when growing in sympatry The pollinators of M nudatus and M guttatus were identified Small sweat bees, Dialictus sppreferentially visited the smaller flowered M nudatus species and honey bees,Apis mellifera , preferred the larger flowered M guttatus In spite of most pollinator visits being intra-specific, individuals of both bee species made transitions between the Mimulus species This will result in greater pollen transfer from M guttatus to M nudatus than vice versa because firstly, M guttatus produces more pollen and secondly, the sweat bees were too small to touch the stigma of a M guttatus flower This asymmetry in gene flow was detected by a greater reduction in viable seed produced by M nudatus plants when surrounded by M guttatus plants than vice versa Only when M nudatus was the maternal parent could any hybrids be detected in field produced seed To enable M nudatus and M guttatus to co-exist in sympatry, the two species may thus need to be sufficiently ecologically different Such ecological differentiation was attributed to the greater drought tolerance of M nudatus In addition, greenhouse experiments suggested that M nudatus may have evolved greater tolerance to calcium deficient soils

Phylogenetic systematics and biogeography of the poison frogs: evidence from mitochondrial DNA sequences

Abstract: Regions of the mitochondrial genome were sequenced and analysed in representative species of poison frogs, in order to investigate phylogenetic relationships within the family Dendrobatidae. Mitochondrial DNA (mtDNA) fragments from three gene regions; cytochrome b, 16S ribosomal RNA (rRNA), and 12S rRNA, provided 1198 base pairs of DNA sequence and 589 informative sites. Phylogenetic analysis using parsimony was used to infer the evolutionary relationships among the species in the survey. Our analysis supported previous partitions of species into the genera Epipedobates, Phyllobates andDendrobates , with two exceptions Epipedobates (Allobates) femoralis was placed outside the clade containing the other toxic dendrobatids, and Minyobates minutus was placed within the genus Dendrobates. Genetic distances estimated between all pairs of taxa using the Kimura 2-parameter model indicated substantial genetic divergence between species, particularly those found in Amazonia. Time of divergence estimates were highly variable depending on gene region, but even the lowest estimates were inconsistent with the Pleistocene Refugia hypothesis.

The allopatric phase of speciation: the sharp-beaked ground finch (Geospiza difficilis) on the Galápagos islands

Abstract: Using microsatellite DNA variation, morphological measurements and sonagrams made from tape-recordings in the field, we examine the allopatric differentiation of six populations of the sharp-beaked ground finch, Geospiza difficilis , in the Galapagos archipelago. We ask how and why the populations became differentiated, and consider what the differences imply about speciation. An important factor is time G. difficilis is one of the phylogenetically oldest species. Populations became differentiated by adapting in beak morphology to different food supplies. Since beak size and shape also function in conspecific mate recognition and choice, the potential for reproductive isolation from sister and parental taxa arose as a correlated effect of natural selection on resource-exploiting traits. This conforms to a standard explanation for the origin of pre-mating isolation as a byproduct of adaptive changes in allopatry without being adaptive itself. However, this explanation is incomplete. Vocal characteristics also differentiated, partly as a result of natural and sexual selection independent of beak size change in environments with different sound transmitting properties. An additional element of chance is indicated by a comparison of closely-related populations on two islands, Wolf and Darwin, that are geographically close, and topographically and floristically similar. The populations have markedly different vocalizations. Morphological characters, vocalizations and genetic traits do not vary concordantly among the six populations. One population (Genovesa) is genetically more similar to other congeneric species. Phenotypic similarities with G. difficilis are the result of a uniquely long retention of shared ancestral traits. Arguments under the phylogenetic species concept justify recognizing this population as a separate species, Geospiza acutirostris. Under the biological species concept it should remain as currently classified, G. difficilis .

Functional morphology and palaeobiology of the pliocene rodent Actenomys (Caviomorpha: Octodontidae): the evolution to a subterranean mode of life

Abstract: The Pliocene caviomorph rodent Actenomys has long been recognized as an early fossorial representative of the subfamily Ctenomyinae (Octodontidae), which includes one living genus, Ctenomys (tuco-tucos), and several species widely distributed in South America. To assess the degree of specialization for digging in Actenomys , we performed morphological comparisons with other octodontid genera ( Octodon , Spalacopus , and Ctenomys ) of known mode of life and behaviour. As a whole, our results indicate that, in terms of morphological specializations for digging, Actenomys occupies an intermediate position between Octodon , a generalized semi-fossorial rodent which forages above ground, and Ctenomys-Spalacopus , two highly specialized subterranean forms. The position of the deltoid process (humerus) and the length of the olecranon process (ulna)—two traits which affect the out-forces exerted by several forelimb muscles—were in Actenomys intermediate between non-subterranean and subterranean taxa. The skull, particularly the rostrum, appears to be strong, and sagittal and nuchal crests are well marked. The zygomatic arches are as flared as those of the generalized Octodon . Notably, the upper and lower incisors of Actenomys were extremely procumbent, as in many highly specialized chisel-tooth digging species. Based upon the stratigraphic and sedimentological analysis of the palaeosoils containing its fossil remains, we suggest that Actenomys lived in an environment of moderate to hig primary productivity. The texture of the palaeosoils indicate that theywere hard and highly cohesive. This situation, which contrasts with that observed in living Ctenomyinae, has relevant implications for burrowing cost. The integration of morphological and palaeoenvironmental data allowed testing of hypotheses about the palaeobiological attributes of this ancestral ctenomyine.

Patterns of feeding behaviour in adult male riodinid butterflies and their relationship to morphology and ecology

Abstract: Adult butterflies are known to visit a wide variety of food substrates, but, with the exception of flower visitation, little is known about what substances are being sought or what determines substrate choice. This is especially true for the Riodinidae, a large family ( c. 1300 spp.) of almost exclusively Neotropical butterflies. We present adult male feeding records for 124 species in 41 genera of Riodinidae (out of a total of 441 species in 85 genera collected in the study), based on ten months sampling in Ecuador. Records of food substrates visited in this study include flowers, damp sand or mud («puddling») and rotting carrion. Rotting carrion placed in traps was the most frequently recorded food source in terms of numbers of individuals and taxa, attracting 89 species from 32 genera. A correlation is found between food substrate choice and morphology, specifically wing area to thoracic volume ratio (WA:TV ratio). Our data suggest the possible existence of two adaptive syndromes whose species have significantly different mean WA:TV ratios and differing suites of accompanying ecological traits, with lower ratios being significantly correlated with species that were recorded feeding. Among species recorded feeding, carrion feeders and puddlers have significantly lower mean WA:TV ratios than flower nectarers, and carrion feeders have a lower mean WA:TV ratio than species not recorded on this food source, a correlation that is significant across all tribes and within some tribes (Riodinini and Saratoni). We reanalyse previously published data on flight and morphology for species in other butterfly and moth families and show that the ratio of wing area to thoracic mass is significantly negatively correlated with flight speed and oxygen consumption (a direct indicator of metabolic rate). We suggest that adult male riodinids may puddle and feed at rotting carrion to supplement nutrient stores from larval feeding, not only to increase reproductive success, but also to provide the necessary nutrients to maintain high metabolic rates during rapid flight.

Microsatellite analysis of natterjack toad Bufo calamita Laurenti populations: consequences of dispersal from a Pleistocene refugium

Abstract: Populations of the amphibian Bufo calamita were sampled for genetic analysis in eleven areas distributed across its biogeographical range in Europe. Genetic diversity estimates across eight microsatellite loci showed a decline in polymorphism, numbers of alleles and heterozygosity as a function of distance from the presumed ice-age refugium in Iberia. Trials with a selection of tree-building algorithms indicated that UPGMA of Cavalli-Sforza chord distances ( D c ) generated the tree topology most easily reconciled with other biogeographical information. Genetic distance measures were also calibrated against a postglacial event from which the separation of extant populations could be estimated in real time. D c again outperformed two other measures (Nei's standard distance, D s , and δμ 2 ) in producing realistic correlations with minimal variance. The genetic analysis was consistent with the hypothesis that B. calamita survived in a single refugium (Iberia) during the Pleistocene glaciation and indicated that it spread north and east from there during the last interstadial which commenced about 14 000 years before present (BP). Microsatellites should provide useful tools for biogeographical investigations of other species, especially with respect to patterns of population dispersal.

Assessing the heritability of body condition in birds: a challenge exemplified by the great tit Parus major L. (Aves)

Abstract: The definition and measurement of body condition are central to many ecological and evolutionary studies, yet the fundamental issue of whether variation in condition is inherited genetically remains unresolved. Furthermore, confusion has been caused through diverse uses of the word 'condition' itself In this paper, we introduce the terms 'broad-sense condition' and 'narrow-sense condition' in an attempt to reduce this confusion. Because of the difficulty of measuring condition, field biologists use the mass relative to body size as a convenient index of condition. Such indices have also been used to estimate the heritability of condition. Using data from a wild great tit Pants major population, we demonstrate that a condition index may still contain residual variance that is due to body size. Hence, using a condition index to study the heritability of condition can give misleading results because that residual variance may itself be heritable. To avoid this problem, direct measures of condition, such as reserve tissues, should be used. We provide the first heritability estimates of direct measures of condition of full-grown birds in a wild population by the regression of mean offspring (both in winter, and when breeding) on mean parent (when breeding) values of two reserve tissues, fat and pectoral muscle, which are independent of body-size. A great tit's fat and muscle reserves in winter were significantly correlated with their respective values when the birds bred. However there was no evidence that the level of fat reserves in winter resembled those of the parents (when breeding), more than expected by chance. Slight resemblances between parents and offspring were detected for muscle in winter and for fat reserves when breeding. Muscle size in the breeding season provided stronger evidence for the inheritance of condition.