The exchangeability of shape

<p>Abstract</p> <p>Background</p> <p>Landmark based geometric morphometrics (GM) allows the quantitative comparison of organismal shapes. When applied to systematics, it is able to score shape changes which often are undetectable by traditional morphological studies and even by classical morphometric approaches. It has thus become a fast and low cost candidate to identify cryptic species. Due to inherent mathematical properties, shape variables derived from one set of coordinates cannot be compared with shape variables derived from another set. Raw coordinates which produce these shape variables could be used for data exchange, however they contain measurement error. The latter may represent a significant obstacle when the objective is to distinguish very similar species.</p> <p>Results</p> <p>We show here that a single user derived dataset produces much less classification error than a multiple one. The question then becomes how to circumvent the lack of exchangeability of shape variables while preserving a single user dataset. A solution to this question could lead to the creation of a relatively fast and inexpensive systematic tool adapted for the recognition of cryptic species.</p> <p>Conclusions</p> <p>To preserve both exchangeability of shape and a single user derived dataset, our suggestion is to create a free access bank of reference images from which one can produce raw coordinates and use them for comparison with external specimens. Thus, we propose an alternative geometric descriptive system that separates 2-D data gathering and analyzes.</p

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>The final article in a series of three publications examining the global distribution of 41 dominant vector species (DVS) of malaria is presented here. The first publication examined the DVS from the Americas, with the second covering those species present in Africa, Europe and the Middle East. Here we discuss the 19 DVS of the Asian-Pacific region. This region experiences a high diversity of vector species, many occurring sympatrically, which, combined with the occurrence of a high number of species complexes and suspected species complexes, and behavioural plasticity of many of these major vectors, adds a level of entomological complexity not comparable elsewhere globally. To try and untangle the intricacy of the vectors of this region and to increase the effectiveness of vector control interventions, an understanding of the contemporary distribution of each species, combined with a synthesis of the current knowledge of their behaviour and ecology is needed.</p> <p>Results</p> <p>Expert opinion (EO) range maps, created with the most up-to-date expert knowledge of each DVS distribution, were combined with a contemporary database of occurrence data and a suite of open access, environmental and climatic variables. Using the Boosted Regression Tree (BRT) modelling method, distribution maps of each DVS were produced. The occurrence data were abstracted from the formal, published literature, plus other relevant sources, resulting in the collation of DVS occurrence at 10116 locations across 31 countries, of which 8853 were successfully geo-referenced and 7430 were resolved to spatial areas that could be included in the BRT model. A detailed summary of the information on the bionomics of each species and species complex is also presented.</p> <p>Conclusions</p> <p>This article concludes a project aimed to establish the contemporary global distribution of the DVS of malaria. The three articles produced are intended as a detailed reference for scientists continuing research into the aspects of taxonomy, biology and ecology relevant to species-specific vector control. This research is particularly relevant to help unravel the complicated taxonomic status, ecology and epidemiology of the vectors of the Asia-Pacific region. All the occurrence data, predictive maps and EO-shape files generated during the production of these publications will be made available in the public domain. We hope that this will encourage data sharing to improve future iterations of the distribution maps.</p

The Diachasmimorpha longicaudata complex : reproductive isolation and geometric patterns of the wing

Diachasmimorpha longicaudata is an endoparasitoid of Tephritid fruit fly larvae and is regarded as an important biocontrol agent. However, it is likely that under this specific name several biological species may be contained, the correct identification of which is essential for effective use in control programs. In this paper, three populations (DLA, DLB and DLBB) of D. longicaudata designated according to geography and/or natural hosts were reared in the same laboratory. They were tested for reproductive compatibility and characterized by morphometric analyzes. Forced-contact mating technique showed either complete lack of inter-population reproductive compatibility or the production of rare, sterile female offspring. The three populations, indistinguishable on the basis of morphological characters alone, were readily identified by the geometry of the wing. Results strongly suggest that the DLA, DLB and DLBB are distinct biological species, and highlight the usefulness of wing geometry to distinguish them

Phenetic structure of two Bactrocera tau cryptic species (Diptera : Tephritidae) infesting Momordica cochinchinensis (Cucurbitaceae) in Thailand and Laos

Morphometric variation with respect to wing venation patterns was explored for 777 specimens of the Bactrocera tau complex collected in Thailand (nine provinces) and Laos (one locality). Cryptic species B. tau A and C were identified based on their wing shape similarity to published reference images. In Thailand, the B. tau A species was identified in four provinces and the B. tau C species in seven provinces, and both species in one locality of Laos. The objective of the study was to explain the geographic variation of size and shape in two cryptic species collected from the same host (Momordica cochinchinensis). Although collected from the same host, the two species did not show the same morphological variance: it was higher in the B. tau A species, which currently infests a wide range of different fruit species, than in the B. tau C species, which is specific to only one fruit (M. cochinchinensis). Moreover, the two species showed a different population structure. An isolation by distance model was apparent in both sexes of species C, while it was not detected in species A. Thus, the metric differences were in apparent accordance with the known behavior of these species, either as a generalist (species A) or as a specialist (species C), and for each species our data suggested different sources of shape diversity: genetic drift for species C, variety of host plants (and probably also pest-host-relationship) for species A. In addition to these distinctions, the larger species, B. tau C, showed less sexual size and shape dimorphism. The data presented here confirm the previously established wing shape differences between the two cryptic species. Character displacement has been discussed as a possible origin of this interspecific variation. The addition of previously published data on species A from other hosts allowed the testing of the character displacement hypothesis. The hypothesis was rejected for interspecific shape differences, but was maintained for size differences

The geometric approach to explore the Bactrocera tau complex (Diptera: Tephritidae) in Thailand

Specimens of the genus Bactrocera were collected from several host plants in northern and western Thailand. They were morphologically recognized as Bactrocera tau and were subdivided into eleven samples according to host plant, geographic origin and time of collection. Twelve landmarks of the right wing were described in a total of 264 males and 276 females. An exploratory analysis using kernel density estimates was performed on the multivariate morphometric space. Non-parametric classification highlighted the existence of two non-overlapping clusters within both males and females. The clusters were not congruent with geography. One cluster (cluster I) contained only one plant, Momordica cochinchinensis, the other one (cluster II) contained five different plants including M. cochinchinensis. Further morphometric analyses on selected samples indicated that the influence of the plants on the shape of the wing could not explain satisfactorily the presence of two clusters. Genetic techniques identified the presence of B. tau cryptic species C in M. cochinchinensis from cluster I. and of B. tau cryptic species A in Coccinia grandis from cluster II. Our working hypothesis is that the two clusters identified by geometric morphometrics were species A and C, respectively