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

Testing repeatability, measurement error and species differentiation when using geometric morphometrics on complex shapes: a case study of Patagonian lizards of the genus Liolaemus (Squamata: Liolaemini)

The repeatability of findings is the key factor behind scientific reliability, and the failure to reproduce scientific findings has been termed the ‘replication crisis’. Geometric morphometrics is an established tool in evolutionary biology. However, different operators (and/or different methods) could act as large sources of variation in the data obtained. Here, we investigated inter-operator error in geometric morphometric protocols on complex shapes of Liolaemus lizards, as well as measurement error in three taxa varying in their difficulty of digitalization. We also examined the potential for these protocols to discriminate among complex shapes in closely related species. We found a wide range of inter-operator error, contributing between 19.5% and 60% to the total variation. Moreover, measurement error increased with the complexity of the quantified shape. All protocols were able to discriminate between species, but the use of more landmarks did not imply better performance. We present evidence that complex shapes reduce repeatability, highlighting the need to explore different sources of variation that could lead to such low repeatability. Lastly, we suggest some recommendations to improve the repeatability and reliability of geometric morphometrics results.

Interspecific hybridization does not affect the level of fluctuating asymmetry (FA) in the Drosophila bipectinata species complex

The Drosophila bipectinata species complex comprises of four very closely related species namely D. bipectinata, D. parabipectinata, D. malerkotliana and D. pseudoananassae. It was found that irrespective of the evolutionary divergence among the species, FA which is reflective of the developmental precision remains nearly same in four species. During the present study, the level of FA in different morphological traits was studied in interspecific hybrids and compared with that of parental species with the view that it would throw light on the degree of divergence between the parental species. If they have not diverged much, the interspecific hybrids may have a similar FA level, incompatibilities between their genomes being negligible. On the other hand, if there is substantial divergence, the level of FA may be higher due to incompatibility between the genomes of the parental species. The morphological traits taken were sternopleural bristle number and wing length in both males and females and ovariole number and sex-comb tooth number in females and males respectively. However, except in a few cases, we could not detect any significant differences in the level of FA in hybrids as compared to pure species. On the other hand, a number of abnormalities like poor viability, dystrophied ovaries, asymmetrical eyes etc., could be detected in hybrids from crosses involving D. pseudoananassae as one of the parents. Therefore, we conclude that specific developmental pathways are more susceptible to developmental disturbances due to genomic incompatibilities than the large complex system bringing about developmental stability.

Contrasting patterns of within-species morphological variation in two cactophilic Drosophila species (Diptera: Drosophilidae)

In this work, we investigated the morphological variation of the intromittent male copulatory organ (aedeagus) of specimens from natural populations of two cactophilic Drosophila species distributed in the southeast region of Brazil, Drosophila gouveai Tidon-Sklorz & Sene and Drosophila antonietae Tidon-Sklorz & Sene. It was explored how the within-species variability is arranged for both species, considering their historical and ecological features. Our results showed two distinct aedeagal morphologies for these species, and differences within species were observed only in D. gouveai as specimens could be distinguished by their population origin. In contrast, after size discrepancies correction, this feature was not detected in D. antonietae. The contrasting patterns of intraspecific variation, together with the other features exhibited by these two species, are most likely to be explained by differences in the historical host plant association and distribution and in demographic events, which determined the evolutionary history of these two South American cactophilic Drosophila species.

Effects of genetic factors and infection status on wing morphology of Triatoma dimidiata species complex in the Yucatán peninsula, Mexico

Triatoma dimidiata is one of the main vectors of Chagas disease, and it has been shown to be a species complex. In the Yucatán peninsula, Mexico, vector populations are non-domiciliated, and the transmission of Trypanosoma cruzi thus critically relies on vector dispersal. This leads us to study the morphologic variations in T. dimidiata wings with respect to genetic factors (sex and genotype at the ITS-2 locus), geographic location, and T. cruzi-infection status. Females were found to have larger and more symmetrical wings than males. Wing shape was influenced by ITS-2 genotypes, although differences are unlikely sufficient to allow taxonomic discrimination of the sibling species. Hybrids were shown to have similar fluctuating asymmetries in wing size and shape as parental species, but the level of asymmetry in shape varied slightly between villages. The two later findings are consistent with a high level of gene flow between parental species, and the high dispersal potential of these non-domiciliated vectors. More surprisingly, individuals infected with T. cruzi were found to have larger wings than non-infected ones. This effect, which was consistently observed across sexes, genotypes and villages, is likely to be due to a direct impact of T. cruzi on insect development. Sex and infection status are thus likely to be key factors influencing vector dispersal with important impacts on disease transmission, since dispersal directly controls the domestic abundance of these vectors. These aspects should be investigated further to fully capture the ecology and evolution of Chagas disease transmission by non-domiciliated vectors.

Male genital and wing morphology in the cactophilic sibling species Drosophila gouveai and Drosophila antonietae and their hybrids reared in different host plants

Cactophilic Drosophila flies are excellent models to study adaptation to a relatively narrow spectrum of potential host plants and host-driven evolutionary diversification. Previous studies suggested a complex genetic architecture of wing and male genital morphology in phylogenetically basal species of the D. buzzatii cluster. In this work, we investigate the effect of experimental hybridization and host plant shifts on male genital and wing morphology in D. gouveai Tidon-Sklorz and Sene and D. antonietae Tidon-Sklorz and Sene, a pair of more recently derived species. We explicitly tested the hypotheses that wing and male genital morphology in interspecific hybrids depend on the host plant in which flies were grown. Our study shows that cactus hosts exert a strong effect on genital and wing morphology and that hybrids can be clearly differentiated on the basis of wing and genital morphology from both parental species. However, the extent of morphological differentiation between hybrids and pure species as well as plasticity patterns varied across organs, suggesting a complex genetic architecture for the studied traits.

Genome-wide QTL mapping for three traits related to teat number in a White Duroc x Erhualian pig resource population

BACKGROUND

Teat number is an important fertility trait for pig production, reflecting the mothering ability of sows. It is also a discrete and often canalized trait presenting bilateral symmetry with minor differences between the two sides, providing a potential power to evaluate fluctuating asymmetry and developmental instability. The knowledge of its genetic control is still limited. In this study, a genome-wide scan was performed with 183 microsatellites covering the pig genome to identify quantitative trait loci (QTL) for three traits related to teat number including the total teat number (TTN), the teat number at the left (LTN) and right (RTN) sides in a large scale White Duroc x Erhualian resource population.

RESULTS

A sex-average linkage map with a total length of 2350.3 cM and an average marker interval of 12.84 cM was constructed. Eleven genome-wide significant QTL for TTN were detected on 8 autosomes including pig chromosomes (SSC) 1, 3, 4, 5, 6, 7, 8 and 12. Six suggestive QTL for this trait were detected on SSC6, 9, 13, 14 and 16. Eight chromosomal regions each on SSC1, 3, 4, 5, 6, 7, 8 and 12 showed significant associations with LTN. These regions were also evidenced as significant QTL for RTN except for those on SSC6 and SSC8. The most significant QTL for the 3 traits were all located on SSC7. Erhualian alleles at most of the identified QTL had positive additive effects except for three QTL on SSC1 and SSC7, at which White Duroc alleles increased teat numbers. On SSC1, 6, 9, 13 and 16, significant dominance effects were observed on TTN, and predominant imprinting effect on TTN was only detected on SSC12.

CONCLUSION

The results not only confirmed the QTL regions from previous experiments, but also identified five new QTL for the total teat number in swine. Minor differences between the QTL regions responsible for LTN and RTN were validated. Further fine mapping should be focused on consistently identified regions with small confidence intervals, such as those on SSC1, SSC7 and SSC12.

Wing morphology and fluctuating asymmetry depend on the host plant in cactophilic Drosophila

As in most insect groups, host plant shifts in cactophilic Drosophila represent environmental challenges as flies must adjust their developmental programme to the presence of different chemical compounds and/or to a microflora that may differ in the diversity and abundance of yeasts and bacteria. In this context, wing morphology provides an excellent opportunity to investigate the factors that may induce changes during development. In this work, we investigated phenotypic plasticity and developmental instability of wing morphology in flies on the cactophilic Drosophila buzzatii and Drosophila koepferae raised on alternative breeding substrates. We detected significant differences in wing size between and within species, and between flies reared on different cactus hosts. However, differences in wing shape between flies emerged from different cactus hosts were not significant either in D. buzzatii or in D. koepferae. Our results also showed that morphological responses involved the entire organ, as variation in size and shape correlated between different portions of the wing. Finally, we studied the effect of the rearing cactus host on developmental instability as measured by the degree of fluctuating asymmetry (FA). Levels of FA in wing size were significantly greater in flies of both species reared in non-preferred when compared with those reared in preferred host cacti. Our results are discussed in the framework of an integrative view aimed at investigating the relevance of host plant shifts in the evolution of the guild of cactophilic Drosophila species that diversified in South America.