Ecological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell

Abstract.  1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.
2.  Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed.
3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next.
4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources.
5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches.     

Isolation and characterization of polymorphic microsatellite loci in Acanthoscelides obvelatus Bridwell (Coleoptera: Bruchidae)

Five microsatellite loci were isolated from the bruchid Acanthoscelides obvelatus Bridwell (Coleoptera: Bruchidae). Each locus was polymorphic, with the number of alleles ranging from two to 15. We found high levels of within‐population variation at most loci, with heterozygosity ranging from 0.182 to 0.900. Cross‐species amplification of these loci was tested in two other species of the genus Acanthoscelides, A. obtectus Say and A. argillaceus Sharp.     

Isolation and characterization of polymorphic microsatellite loci in Acanthoscelides obtectus Say (Coleoptera: Bruchidae)

Six microsatellite loci were isolated from the bruchid Acanthoscelides obtectus Say (Coleoptera: Bruchidae). Each locus was polymorphic, with the number of alleles ranging from 3 to 18. We found high levels of within‐population variation at most loci, with heterozygosities ranging from 0 to 0.75. Cross‐species amplification of these loci was tested in two other species of the genus Acanthoscelides, A. obvelatus Bridwell and A. argillaceus Sharp.     

Ancient and recent evolutionary history of the bruchid beetle, Acanthoscelides obtectus Say, a cosmopolitan pest of beans

Acanthoscelides obtectus Say is a bruchid species of Neotropical origin, and is specialized on beans of the Phaseolus vulgaris L. group. Since the domestication and diffusion of beans, A. obtectus has become cosmopolitan through human-mediated migrations and is now a major pest in bean granaries. Using phylogeographic methods applied to mitochondrial DNA (mtDNA) and nuclear microsatellite molecular markers, we show that the origin of this species is probably further south than Mesoamerica, as commonly thought. Our results also indicate that A. obtectus and its Mesoamerican sister species Acanthoscelides obvelatus, two morphologically close species differing principally in voltinism, speciated in allopatry: A. obtectus (multivoltine) arising in Andean America and A. obvelatus (univoltine) in Mesoamerica. In contrast to Mesoamerica where beans fruit once yearly, wild beans in Andean America fruit year-round, especially in regions showing little or no seasonality. In such habitats where resources are continuously present, multivoltinism is adaptive. According to existing hypotheses, multivoltinism in A. obtectus is a new adaptation that evolved after bean domestication. Our data suggest the alternative hypothesis that multivoltinism is an older trait, adapted to exploit the year-round fruiting of wild beans in relatively aseasonal habitats, and allowed A. obtectus to become a pest in bean granaries. This trait also permitted this species to disperse through human-mediated migrations associated with diffusion of domesticated beans. We also show that diversity of Old World A. obtectus populations can be quite well explained by a single colonization event about 500 bp. Human-mediated migrations appear not to be rare, as our results indicate a second more recent migration event from Andean America to Mexico.     

Relative toxicity of phosphine against the bean bruchid Acanthoscelides obtectus (Say) (Col., Bruchidae)

Abstract:  The toxicity of phosphine against adult Acanthoscelides obtectus (Say) was studied over a range of concentrations, viz. 0.01, 0.0125, 0.015, 0.02, 0.04, 0.08, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 mg/l and exposure periods, viz. 0.25, 0.50, 1, 2, 6, 12, 24 and 48 h at 25°C and 65% relative humidity . Results show that both the parameters exhibited significant effects on the mortality of A. obtectus . Data indicate that 100% mortality only occurred in A. obtectus when 1-, 2- and 12-h exposure times were involved in the respective highest individual ct product. The ct products decreased as the exposure times increased for both the mortality levels of 50 and 99%. The minimum ct products for 50 and 99% kill were 0.19 and 0.29 mg h/l, respectively, at an exposure of 12 h. The influence of thresholds on regression equations of the form c ⁿ t  =  k were 0.59 and 13.80 (mg/l) ⁿ h for the fixed concentration for 50 and 99% mortality levels, respectively while they were 0.45 and 12.45 (mg/l) ⁿ h for the six exposure periods for the same mortality levels.     

Genetic diversity and differentiation of Acanthoscelides obtectus Say (Coleoptera: Bruchidae) populations in China

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Morphology and ultrastructure of the abdominal integumentary glands of Acanthoscelides obtectus Say (Coleoptera : Bruchidae)

The morphology of the abdominal integumentary glands of the bean weevil Acanthoscelides obtectus (Coleoptera : Bruchidae) is described. There are 2 types: glands with long secretory ducts and ampullate glands with short ducts. The former are distributed throughout the integument and have 2 secretory cells, one of which is connected to the reservoir in the distal receptor zone, and the other to the duct. The duct, which is 100 μm long, has an epicuticular structure and its evacuation pore is 0.5 μm in diameter. It is surrounded by cytoplasm rich in microtubules. The epicuticular structure of the duct is resolved into fine filaments in the distal region. The ampullate glands exist only on the abdominal tergites and the pygidium. They are composed of an epicuticular receptor ampoule and a short duct connected to one secretory cell. The 2 types of glands can be placed in class 3 according to the nomenclature of Noirot and Quennedey (1974. Annu. Rev. Entomol. 19: 61–80).     

Determinants of oviposition in Acanthoscelides obtectus: a nonconformist bruchid

Abstract. Acanthoscelides obtectus is atypical of bruchids found in stored seeds because females do not attach eggs individually to host seeds but scatter them irregularly among potential hosts. In other respects, its life history resembles that of other species and comparison provides evidence for the adaptive nature of their behaviour. Individual females differ dramatically in the temporal pattern of their oviposition. The hypothesis is proposed that this is an adaptation to life in heterogeneous habitats. Oviposition is not regulated by host availability to the same extent as in other bruchids, providing evidence that regulation of the number of eggs laid by species which stick eggs to host seeds is an adaptation to the abundance of hosts. The continued presence of males and opportunity for multiple matings does not affect fecundity or egg viability. Females preferentially lay on clean seeds when provided with a choice between them and seeds previously exposed to other adult beetles. However, they do not appear to be deterred by, or cannot detect, the presence of larvae infesting seeds. Other bruchid species avoid such seeds that they can identify by the occurrence of egg cases and pheromones. The number of eggs laid is influenced by the host cultivar available for oviposition. Oviposition by A. obtectus appears to be an adaptation to both storage environments and the heterogeneous environment of a growing crop or uncultivated land. Its behaviour suggests an ancestral condition in bruchids and the changes which might have occurred in the ecology of other bruchid species as they have adapted to become pests of human seed stores.     

The effects of selection for early and late reproduction on metabolite pools in Acanthoscelides obtectus Say

Abstract The present study was aimed at revealing the responses of metabolite pools to selection for alternative reproductive schedules in the seed beetle, Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae). The levels of metabolites (free sugars, glycogen, lipids, soluble and hydrophobic proteins) that were determined in virgin females and males at three ages from adult eclosion onwards were compared among the base population (B) and two derived lines that were selected for either early (Y) or late (O) reproduction. The results showed differences in the accumulation of metabolites during pre‐adult development, as well as in the pattern of their changes during adult ageing. Generally, in comparison to the B population, the short‐lived beetles from the Y line showed increased protein content and reduced carbohydrate and lipid content, whereas the opposite was true for the long‐lived beetles from the O line. Females from the O line exhibited slower utilization of energy reserves and a slower increase in protein contents than females from the Y line. Females contained higher levels of free sugars, glycogen and hydrophobic proteins and lower levels of lipids and soluble proteins than males, although the sexual dimorphism was not evenly expressed among lines. Age‐specific changes in metabolite contents were slower in females than males. Our findings suggest that trade‐offs among capital resources are a physiological basis of early/late fitness trade‐offs and point to a conservation of resources that can be used for somatic maintenance.     

Reproductive isolation and phylogenetic divergence in Neurospora: comparing methods of species recognition in a model eukaryote

We critically examined methods for recognizing species in the model filamentous fungal genus Neurospora by comparing traditional biological species recognition (BSR) with more comprehensive applications of both BSR and phylogenetic species recognition (PSR). Comprehensive BSR was applied to a set of 73 individuals by performing extensive crossing experiments and delineating biological species based on patterns of reproductive success. Within what were originally considered two species, N. crassa and N. intermedia, we recognized four reproductively isolated biological species. In a concurrent study (Dettman et al. 2003), we used genealogical concordance of four independent nuclear loci to recognize phylogenetic species in Neurospora. Overall, the groups of individuals identified as species were similar whether recognized by reproductive success or by phylogenetic criteria, and increased genetic distance between parents was associated with decreased reproductive success of crosses, suggesting that PSR using genealogical concordance can be used to reliably recognize species in organisms that are not candidates for BSR. In one case, two phylogenetic species were recognized as a single biological species, indicating that significant phylogenetic divergence preceded the development of reproductive isolation. However, multiple biological species were never recognized as a single phylogenetic species. Each of the putative N. crassa x N. intermedia hybrids included in this study was confidently assigned to a single species, using both PSR and BSR. As such, no evidence for a history of hybridization in nature among Neurospora species was observed. By performing reciprocal mating tests, we found that mating type, parental role, and species identity of parental individuals could all influence the reproductive success of matings. We also observed sympatry-associated sexual dysfunction in interspecific crosses, which was consistent with the existence of reinforcement mechanisms.     

The Labeninae (Hymenoptera: Ichneumonidae): a study in phylogenetic reconstruction and evolutionary biology

The internal phylogenetic relationships of the ichneumonid subfamily Labeninae (Hymenoptera) are re‐assessed using 136 characters for 54 species representing all currently known species‐groups. New character sets are used. These include a new form of seta (named the grossulariform setae) which are present on the inner surface of the hind coxa of some females, and the extensive structural modifications of the terminal segments of the female metasoma, which are described and structural homologies established. The monophyly of the Labeninae and of the four component tribes, Groteini, Poecilocryptini, Xenothyrini and Labenini, is demonstrated. The Groteini is shown to be the sister‐group to the Poecilocryptini + (Xenothyrini + Labenini). Monophyletic genera are established, including three new genera: Ozlabium gen. nov. Gauld & Wahl (type‐species 0. arcadium sp. nov.) in the Groteini from Australia; Torquinsha gen. nov. Gauld & Wahl (type‐species Certonotus invictus Porter) in the Labenini from Chile, and Gauldianus gen. nov. Lanfranco (type‐species Gauldianus chilensis sp. nov. Lanfranco) in the Labenini from Chile. Apechoneura is removed from synonymy and re‐instated as a valid genus for a complex of tropical American species. The biogeographic patterns shown by the Labeninae are discussed. Evidence suggests that the group radiated on Gondwanaland after the separation of Africa/India/Madagascar, but prior to the separation of Australia. Species occurring off the southern continental fragments, in North America, are shown to be members of highly derived lineages, a result consistent with the hypothesis that labenines colonized North America recently through Mesoamerica. Patterns of host utilization and mating behaviour are examined for the group. Members of the more derived lineages show progressively more female specializations for attacking hosts deeply concealed in woody substrates. Males in the more specialized lineages are shown to have a wider array of secondary sexual characteristics and genitalic ornamentations than more plesiomorphic taxa.     

Plant species delimitation: A comparison of morphological and molecular markers

Abstract

Species delimitation is fundamental in many areas of biology. Despite its importance, there is no agreement on criteria for species delimitation mostly due to divergence on the point of view adopted by the different biological disciplines. Two main groups of diagnostic characters are commonly used to distinguish species: the traditional morphological ones and the molecular ones. Field species recognition and sampling are generally based on morphological characters, but they can either fail to discriminate species and mask the presence of cryptic species or discriminate different species while in reality there is only one. To overcome this problem it is common to compare clusters obtained on the basis of the observed polymorphism of both characters, and to analyse their agreement. Here we compile a set of studies that have examined species delimitation with both markers. This provides a review of the different morphological and molecular markers, and of the sampling strategy and clustering methodology generally employed to delimitate species. Some conclusions are drawn with regard to species delimitation, when comparing diagnostic morphological and molecular markers.     

Evolutionary disequilibrium and activity period in primates: a bayesian phylogenetic approach

Activity period plays a central role in studies of primate origins and adaptations, yet fundamental questions remain concerning the evolutionary history of primate activity period. Lemurs are of particular interest because they display marked variation in activity period, with some species exhibiting completely nocturnal or diurnal lifestyles, and others distributing activity throughout the 24-h cycle (i.e., cathemerality). Some lines of evidence suggest that cathemerality in lemurs is a recent and transient evolutionary state (i.e., the evolutionary disequilibrium hypothesis), while other studies indicate that cathemerality is a stable evolutionary strategy with a more ancient history. Debate also surrounds activity period in early primate evolution, with some recent studies casting doubt on the traditional hypothesis that basal primates were nocturnal. Here, we used Bayesian phylogenetic methods to reconstruct activity period at key points in primate evolution. Counter to the evolutionary disequilibrium hypothesis, the most recent common ancestor of Eulemur was reconstructed as cathemeral at ～9-13 million years ago, indicating that cathemerality in lemurs is a stable evolutionary strategy. We found strong evidence favoring a nocturnal ancestor for all primates, strepsirrhines and lemurs, which adds to previous findings based on parsimony by providing quantitative support for these reconstructions. Reconstructions for the haplorrhine ancestor were more equivocal, but diurnality was favored for simian primates. We discuss the implications of our models for the evolutionary disequilibrium hypothesis, and we identify avenues for future research that would provide new insights into the evolution of cathemerality in lemurs.     

Rule-breaking mimics: palatability of the butterflies Hypolimnas bolina and Hypolimnas misippus,a sister species pair

Sibling species are, by definition, closely related and Hypolimnas bolina and Hypolimnas misippus are good examples. It has been known for some years that H. misippus often breaks the rules of mimicry, being polymorphic in the female and retaining the mimetic patterns even where no models are present. Hypolimnas bolina is here shown to follow a similar course, with no models present in Madagascar. The toxicity of both butterflies seems usually to be largely dependent on the foodplant but this is irrelevant to mimicry in the absence of models. The evidence suggests that in both species mimicry at the present time is of little or no importance to the survival of these butterflies.     

How species longevity, intraspecific morphological variation, and geographic range size are related: a comparison using late Cambrian trilobites

Phenotypic variation is fundamental to evolutionary change. Variation not only evinces the connectivity of populations but it is also associated with the adaptability and evolvability of taxa. Despite the potential importance of morphological variation in structuring evolutionary patterns, little is known about how relative differences in intraspecific morphological variation and its geographic structure are linked to differences in species longevity. This study offers a novel combination of analyses that reveal the quantitative relationships among intraspecific variation, geographic range size and duration in the fossil record using late Cambrian trilobites. Results show that geographic range size and duration are positively correlated. Surprisingly, longer lived species tend to have less intraspecific variation. Phylogenetic effects were also explored and found not to determine the association between these variables. However, the distribution of geographic range sizes shows strong phylogenetic signal. In light of previous work, one possible explanation for these results is that species with shorter durations have comparatively higher rates of morphological evolution, reflected in higher phenotypic variation overall.     

Pheromone-like substances affecting host-related behaviour of larvae and adults in the dry bean weevil, Acanthoscelides obtectus

Males and females of the dry bean weevil, Acanthoscelides obtectus deposit chemically unknown substance(s) on beans during various activities (most probably during defecation), under laboratory conditions. The marking results in avoidance of these beans by other females for oviposition. Also, first-instar larvae are influenced to disperse more by the deposited substance(s), so that they are more likely to find unmarked beans to enter. No specific marking behaviour by adults was noted. That the deterring substance(s) might originate from microorganismic activity after deposition has occurred, is improbable. Possible explanations for sources of marking substance(s) and the significance of the corresponding behaviour in this species are discussed.

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Résumé Les mâles et les femelles d'A. obtectus déposent des substance(s) encore non-identifiées sur les grains du haricot au cours de leurs diverses activités. Ce comportement de marquage fait que les autres femelles hésitent à pondre des ufs sur ces grains. De plus, les substance(s) déposée(s) poussent les larves du 1^er stade à se disperser plus vigoureusement, par conséquent, elles sont enclines positivement à entrer dans les grains sans marque. On n'a observé aucun comportement marqueur spécifique chez les adultes. La possibilité d'une origine microbiologique des substance(s) répulsive(s) a été eliminée. Les origines possibles des substance(s) de marquage et la signification de ce comportement sont discutés.

     

Birding and DNA: species for the new millennium

Capsule Based on the 1999 Witherby Memorial Lecture – reviews how developments in molecular and population genetics have led to a reappraisal of species limits in birds.

The taxonomy of birds of the West Palearctic has moved from the comparative stability of the ‘Voous List’ into a period of serious activity, with new data emerging in almost every issue of every evolutionary and avian journal! This activity comes from two directions. Firstly, developments in population genetics, molecular biology, acoustics, behaviour and distributional studies have opened new avenues to measuring differentiation among groups of birds. This, in turn, has led to the recognition that earlier views of what constitutes a ‘species’ are in need of modification (‘improvement’), and the emergence of the ‘lineage concept’ of species. I review some of the species concepts most relevant to avian studies, and attempt to show how and why this change has happened, and its consequences for taxonomy and species limits. Examples are given in the form of ‘case studies’, and include Carrion/Hooded Crows Corvus corone/cornix, Green-winged/Eurasian Teals Anas carolinensis/crecca and Phylloscopus warblers.     

物种多度和径级尺度对于评价群落系统发育结构的影响: 以尖峰岭热带山地雨林为例

研究不同径级尺度群落系统发育多样性有助于了解不同年龄模式下物种的亲缘关系及其群落系统发育结构; 但是关于物种多度对群落系统发育结构影响的研究较少。以海南尖峰岭热带山地雨林群落为例, 首先在不同径级尺度比较物种多度加权与否分别对4个广泛采用的系统发育指数的影响, 继而利用其中2个经过标准化处理的系统发育多样性指数: 净种间亲缘关系指数(net relatedness index, NRI)和净最近种间亲缘关系指数(nearest taxon index, NTI), 结合群落的生境类型来量度不同局域生境条件下不同径级尺度木本植物系统发育关系。结果发现: (1)未考虑物种多度加权的系统发育平均成对距离(mean pairwise distance, MPD)指数比考虑物种多度加权的MPD指数显著地高估了群落整体系统发育多样性, 且这种现象在小径级尺度(1 cm≤DBH<5 cm)最为明显。因此, 在森林监测样地中对于中、小径级群落系统发育结构研究中建议考虑物种多度信息。(2) 从群落组成整体系统发育结构来看, 尖峰岭热带山地雨林在几乎所有径级尺度和生境下均倾向于系统发育发散, 且随着径级的递增发散程度趋于明显(NRI<0)。(3)从群落组成局部系统发育结构来看, 尖峰岭热带山地雨林在中、小径级倾向于系统发育聚集(NTI>0), 而在大径级(DBH≥15 cm)则倾向于系统发育发散(NTI<0)。总之, 研究群落系统发育结构时应考虑物种多度的影响以及径级尺度效应。     

Mesoamerican Origin and Pre- and Post-Columbian Expansions of the Ranges of Acanthoscelides obtectus Say,a Cosmopolitan Insect Pest of the Common Bean

An unprecedented global transfer of agricultural resources followed the discovery of the New World; one consequence of this process was that staple food plants of Neotropical origin, such as the common bean (Phaseolus vulgaris), soon expanded their ranges overseas. Yet many pests and diseases were also transported. Acanthoscelides obtectus is a cosmopolitan seed predator associated with P. vulgaris. Codispersal within the host seed seems to be an important determinant of the ability of A. obtectus to expand its range over long distances. We examined the phylogeographic structure of A. obtectus by (a) sampling three mitochondrial gene sequences (12s rRNA, 16s rRNA, and the gene that encodes cytochrome c oxidase subunit I (COI)) throughout most of the species’ range and (b) exploring its late evolutionary history. Our findings indicate a Mesoamerican origin for the current genealogical lineages of A. obtectus. Each of the two major centers of genetic diversity of P. vulgaris (the Andes and Mesoamerica) contains a highly differentiated lineage of the bean beetle. Brazil has two additional, closely related lineages, both of which predate the Andean lineage and have the Mesoamerican lineage as their ancestor. The cosmopolitan distribution of A. obtectus has resulted from recent expansions of the two Brazilian lineages. We present additional evidence for both pre-Columbian and post-Columbian range expansions as likely events that shaped the current distribution of A. obtectus worldwide.