Effect of larval density and substrate quality on the wing geometry of Stomoxys calcitrans L. (Diptera: Muscidae)

Abstract

Background: In insects, oviposition decisions may lead to egg deposition in substrates with different larval density and nutritional levels. Individuals developing in such substrates may present plasticity in their phenotype. Here, we investigated the effect of two factors related to oviposition decisions, namely larval density and substrate quality, on the wing size and wing shape of the stable fly, Stomoxys calcitrans L. (Diptera: Muscidae).

Methods: We reared S. calcitrans larvae at different densities (5, 15 and 25) and on different substrates (camel, cow, donkey and sheep dung). For each fly that emerged, we recorded body weight, and detached, slide-mounted and photographed the right wing. Next, we collected 15 landmarks on each photographed wing, and applied geometric morphometric analysis to assess variation in wing size and wing shape of S. calcitrans across the different larval densities and substrate types.

Results: We observed that wing size and wing shape of S. calcitrans were affected by larval density and the nature of the developmental substrate. Flies reared in a group of 5 had larger wing centroid size, wing length, wing width, wing area and wing loading compared with those reared in a group of 25. Also, flies developed in donkey and sheep dung had larger wing centroid size, wing length, wing width, wing area and wing loading in comparison with those grown in camel and cow dung. Canonical variate analysis followed by discriminant analysis revealed significant wing shape variation in S. calcitrans across the different densities and substrates. Wing size had a significant but weak positive effect on wing shape.

Conclusions: This study demonstrates the high sensitivity of S. calcitrans wings to variation in larval density and developmental substrate, and that use of landmark-based geometric morphometric analysis could improve our understanding of how flies of veterinary importance respond to environmental variability.

Keywords: Developmental substrate; Geometric morphometrics; Larval density; Phenotypic plasticity; Stomoxys calcitrans; Wing morphology.

Fig. 1

Dorsal view of the right wing of S. calcitrans. Numbers indicate the location of 15 selected landmarks (described in Table 1)

Fig. 2

Wing size and adult weight of S. calcitrans is significantly affected by larval density. a Boxplots depicting variation in wing centroid size (i), wing length (ii), wing width (iii), wing area (iv), adult weight (v), and wing loading (vi) across the different larval densities. Boxplot whiskers indicate ± 1.5 interquartile range limits. Boxplots with different letters show significant differences as grouped by ANOVA tests followed by SNK post-hoc tests (P < 0.05, n = 30). b Principal components biplot showing the similarities (or dissimilarities) existing among flies reared at different densities (5, 15 and 25)

Fig. 3

Wing shape of S. calcitrans is significantly affected by larval density. a Thin plate spline deformation grids modelling the difference of S. calcitrans wing shape across the different larval densities. The number displayed on each grid represents the landmark positions. Yellow to orange-red colours indicate landmark expansions, light to dark-blue indicates landmark contraction. b Scatter plot showing the difference in wing shapes of S. calcitrans individuals reared at different larval densities along the first two canonical variate axes [CV1 (82.56%) and CV2 (17.44%)] with 90% confidence ellipses. c Discrimination histograms comparing the S. calcitrans wing shape between pairs of larval densities

Fig. 4

Wing size and adult weight of S. calcitrans significantly varies across different developmental substrates. a Boxplots depicting variation in wing centroid size (i), wing length (ii), wing width (iii), wing area (iv), adult weight (v), and wing loading (vi) across the different dung substrates. The limit of each boxplot whiskers represents the minimum and maximum of all the data. Boxplots with different letters depict significant differences as grouped by ANOVA tests followed by SNK post-hoc tests (P < 0.05, n = 30). b Principal components biplot showing the similarities (or dissimilarities) existing among flies reared from different dung types

Fig. 5

Wing shape in S. calcitrans is significantly affected by developmental substrate. a Thin plate spline (TPS) deformation grids modelling the difference of S. calcitrans wing shape across the different larval densities. The number displayed on each grid represents the landmark positions. Yellow to orange-red colours indicate landmark expansions, light to dark-blue indicates landmark contraction. b Scatter plot showing the difference in wing shapes of S. calcitrans individuals reared from different developmental substrates along the first two canonical variate axes [CV1 (66.06%) and CV2 (19)] with 90% confidence ellipses. c Discrimination histograms comparing S. calcitrans wing shape between developmental substrate pairs