Ignacio M. Soto

A study of wing morphology and fluctuating asymmetry in interspecific hybrids between Drosophila buzzatii and D. koepferae.

In this work we investigate the effect of interspecific hybridization on wing morphology using geometric morphometrics in the cactophilic sibling species D. buzzatii and D. koepferae. Wing morphology in F1 hybrids exhibited an important degree of phenotypic plasticity and differs significantly from both parental species. However, the pattern of morphological variation between hybrids and the parental strains varied between wing size and wing shape, across rearing media, sexes, and crosses, suggesting a complex genetic architecture underlying divergence in wing morphology. Even though there was significant fluctuating asymmetry for both, wing size and shape in F1 hybrids and both parental species, there was no evidence of an increased degree of fluctuating asymmetry in hybrids as compared to parental species. These results are interpreted in terms of developmental stability as a function of a balance between levels of heterozygosity and the disruption of coadaptation as an indirect consequence of genomic divergence.

Host alkaloids differentially affect developmental stability and wing vein canalization in cactophilic Drosophila buzzatii

Host shifts cause drastic consequences on fitness in cactophilic species of Drosophila. It has been argued that changes in the nutritional values accompanying host shifts may elicit these fitness responses, but they may also reflect the presence of potentially toxic secondary compounds that affect resource quality. Recent studies reported that alkaloids extracted from the columnar cactus Trichocereus terscheckii are toxic for the developing larvae of Drosophila buzzatii. In this study, we tested the effect of artificial diets including increasing doses of host alkaloids on developmental stability and wing morphology in D. buzzatii. We found that alkaloids disrupt normal wing venation patterning and affect viability, wing size and fluctuating asymmetry, suggesting the involvement of stress–response mechanisms. Theoretical implications are discussed in the context of developmental stability, stress, fitness and their relationship with robustness, canalization and phenotypic plasticity.

Nutritional Composition of Opuntia sulphurea G. Don Cladodes

Abstract: Several studies have shown the interesting properties of Opuntia spp. (“prickly pears”), although most of this knowledge is based on O. ficus-indica. O. sulphurea is a species that is largely distributed in the Monte region of Argentina, where it has been used as an edible resource, especially in periods of food shortage. This is the first report evaluating the chemical composition of O. sulphurea cladodes. Our results show that cladodes are composed primarily of water, as with most other prickly pears that have been studied, which is consistent with their expected role as water reservoir in desert communities. Ash and protein content in O. sulphurea are consistent with values found for other species of the genus, whereas carbohydrates are well below levels of other Opuntia spp. Finally, the percentage of lipids in O. sulphurea cladodes is larger than in other studied species and fatty acid composition is quite different from observations made in similar studies. These earlier studies showed that linoleic acid is the major constituent of fatty acid fractions, followed by palmitic and oleic acids. Our analyses showed that these fatty acids are also principal constituents of O. sulphurea cladodes, although linolenic acid proved to be the most abundant. Curiously, the previous works found relatively low quantities of this fatty acid. Other minor fatty acids were also detected in cladodes of O. sulphurea, although the percentages are larger than in other studies of prickly pears. We discuss our results in the context of the potential nutraceutical and economic utility of O. sulphurea cladodes as a new source of essential fatty acids, especially in semi-arid areas as the Monte region where this species represents an abundant edible resource which is available even in periods of scarcity.

Rapid Divergent Evolution of Male Genitalia Among Populations of Drosophila buzzatii

Increasing evidence from multiple animal systems suggests that genital evolution and diversification are driven by rapid and strong evolutionary forces. Particularly, the morphology of male genital structures is considered to be among the fastest evolving traits in animal groups with internal fertilization. In this study, we investigated patterns of male genital variation within and between natural populations of the cactophilic fly Drosophila buzzatii in its original geographic distribution range in the Neotropics. We detected significant morphological differences among populations and distinguished five differentiated groups. Moreover, among population differentiation in genital morphology was associated with the degree of geographic isolation among populations and clearly contrasted with the general homogeneity detected for the putatively neutral mitochondrial gene COI. Integrating our present data with previous molecular population genetic surveys, our results suggest that male genital morphology has rapidly diverged after the recent demographic expansion that D. buzzatii has undergone in the arid zones of South America. Because the “lock and key” hypothesis failed to explain the present pattern, we explored alternative explanations for the observed pattern of genital diversification including drift-facilitated sexual selection.

Oviposition site preferences and performance in natural resources in the human commensals Drosophila melanogaster and D. simulans.

The choice of egg laying site and progeny’s performance in a rearing site are important components of habitat selection. Despite the huge amount of genetic, morphological, behavioral and physiological data regarding Drosophila melanogaster Meigen and D. simulans Sturtevant, oviposition site preferences remain poorly known. We investigated resource preference (acceptance and choice) and performance (measured as larval viability, developmental time and wing size) in Vitis vinifera Linneo (grape) and Cydonia oblonga Miller (quince), two fruit plants that D. melanogaster and D. simulans use as breeding substrates in Western Argentina. Females of both species preferred V. vinifera over C. oblonga when offered to lay eggs on grape and/or quince, with D. melanogaster showing a more biased preference for V. vinifera than its sibling. Concerning performance, flies reared in C. oblonga developed faster than in V. vinifera, regardless of the species and D. simulans had a shorter developmental time than D. melanogaster. We also observed inter and intraspecific (between flies reared in different resources) differences in wing size and shape. Our study provides novel data concerning ecological aspects scarcely addressed in these species, and suggest that the use of different resource may be a relevant factor in their recent evolutionary history.

First phylogenetic analysis of the family Neriidae (Diptera), with a study on the issue of scaling continuous characters

Neriidae are a small family of acalyptratae flies, mostly distributed in the tropics. Very little is known about their biology, and the evolutionary relationships among species have never been evaluated. We perform the first comprehensive phylogenetic analysis of the family, including 48 species from all biogeographic regions inhabited, as well as five species of Micropezidae and one Cypselosomatidae as outgroups. We build a morphological data matrix of 194 characters, including 72 continuous characters. We first explore ways to deal with the issue of scaling continuous characters, including rescaling ranges to unity and using implied weighting. We find that both strategies result in very different phylogenetic hypotheses, and that implied weighting reduces the problem of scaling, but only partially. Furthermore, using implied weighting after rescaling characters improves the congruence between partitions and results in higher values of group support. With respect to the Neriidae, we confirm the monophyly of the family and of most its genera, although we do not obtain any of the currently accepted suprageneric groups. We propose to restrict the Eoneria and Nerius groups exclusively to the Neotropical fauna, and synonymize Glyphidops subgenus Oncopsia Enderlein with Glyphidops subgenus Glyphidops Enderlein, eliminating the subgeneric divisions. This revised phylogeny presents a striking biogeographic consistency, and shows that previous main divisions of the family were based on events of convergence.

Phenotypic variation of the Aedeagus of Drosophila serido vilela & sene (Diptera: Drosophilidae)

Drosophila serido Vilela & Sene is a polytypic and cactophilic species with broad geographic distribution in Brazil. The morphology of the aedeagi of eight natural populations of D. serido was analyzed. Based on features of their aedeagi, populations of D. serido were discriminated with an efficiency of nearly 75%. The analysis using the Mantel test suggests that the morphological divergence of D. serido is correlated with the geographic distance among populations. There is no single cause to explain the observed pattern; therefore, the results were discussed considering the three main hypotheses to explain the aedeagus evolution: lock and key, pleiotropy and sexual selection. Alternatively, the aedeagus variability of D. serido might be related to environmental causes, such as temperature and/or host cacti.

Aedeagal Divergence in Sympatric Populations of Two Sibling Species of Cactophilic Drosophila (Diptera: Drosophilidae): Evidence of Character Displacement?

Aedeagal morphology of two sibling cactophilic species, Drosophila buzzatii Patterson & Wheeler and Drosophila koepferae Fontdevila & Wasserman, was analyzed in nine allopatric and three sympatric locations throughout South America. Morphological differences were detected for both aedeagus size and shape between sympatric and allopatric populations of D. buzzatii, despite the significant variability within both groups. Populations of D. buzzatii sympatric with D. koepferae displayed smaller aedeagus than the allopatric ones as well as more differentiated aedeagus shape. The shape differences were non-allometric and mainly consisted in a change of curvature of the dorsal margin of the aedeagus being more pronounced in males from populations sympatric with D. koepferae. It is concluded that aedeagal morphology presented some degree of character displacement in both size and shape in populations of D. buzzatii in sympatry with D. koepferae. These results might suggest the existence of mechanisms of interspecific recognition and hybridization prevention between these species that include the morphology of the male genitalia.

Walk before you jump: new insights on early frog locomotion from the oldest known salientian

Abstract. Understanding the evolution of a Bauplan starts with discriminating phylogenetic signal from adaptation and the latter from exaptation in the observed biodiversity. Whether traits have predated, accompanied, or followed evolution of particular functions is the basic inference to establish the type of explanations required to determine morphological evolution. To accomplish this, we focus in a particular group of vertebrates, the anurans. Frogs and toads have a unique Bauplan among vertebrates, with a set of postcranial features that have been considered adaptations to jumping locomotion since their evolutionary origin. This interpretation is frequently stated but rarely tested in scientific literature. We test this assumption reconstructing the locomotor capabilities of the earliest known salientian, Triadobatrachus massinoti. This extinct taxon exhibits a mosaic of features that have traditionally been considered as representing an intermediate stage in the evolution of the anuran Bauplan, some of which were also linked to jumping skills. We considered T. massinoti in an explicit evolutionary framework by means of multivariate analyses and comparative phylogenetic methods. We used length measurements of major limb bones of 188 extant limbed amphibians (frogs and salamanders) and lizards as a morphological proxy of observed locomotor behavior. Our findings show that limb data correlate with locomotion, regardless of phylogenetic relatedness, and indicate that salamander-like lateral undulatory movements were the main mode of locomotion of T. massinoti. These results contrast with recent hypotheses and indicate that derived postcranial features that T. massinoti shared with anurans might have been later co-opted as exaptations in jumping frogs.

First Record of Drosophila buzzatii (Patterson & Wheeler) (Diptera: Drosophilidae) Emerging from a Non-Cactus Host.

Drosophila buzzatii (Patterson & Wheeler), a typical cactophilic species of the repleta group, is registered for the first time emerging from Melon (Cucumis melo) in western Argentina. The analysis of inversion polymorphism and genetic diversity of mitochondrial cytochrome oxidase subunit I gene (mtCOI) provided additional evidence that corroborated the presence of a high proportion of D. buzzatii among the flies emerged from melon. This finding set the scenario for a broader range of possible hosts and host-related distribution and dispersion for this widespread species.