Morphological measurements of two host specialists of the dipteran Tephritis conura, both in sympatry and allopatry
Nilsson, Kalle; Ortega, Jesús; Friberg, Magne; Runemark, Anna (2022), Morphological measurements of two host specialists of the dipteran Tephritis conura, both in sympatry and allopatry, Dryad, Dataset, https://doi.org/10.5061/dryad.s4mw6m98j
Adaptation to new ecological niches is known to spur population diversification and may lead to speciation if gene flow is ceased. While adaptation to the same ecological niche is expected to be parallel, it is more difficult to predict whether selection against maladaptive hybridization in secondary sympatry results in parallel divergence also in traits that are not directly related to the ecological niches. Such parallelisms in response to selection for reproductive isolation can be identified through estimating parallelism in reproductive character displacement across different zones of secondary contact. Here, we use a host shift in the phytophagous peacock fly Tephritis conura, with both host races represented in two geographically separate areas East and West of the Baltic Sea to investigate convergence in morphological adaptations. We asked i) if there are consistent morphological adaptations to a host plant shift and ii) if the response to secondary sympatry with the alternate host race is parallel across contact zones. We found surprisingly low and variable, albeit significant, divergence between host races. Only one trait, the length of the female ovipositor, which serves an important function in the interaction with the hosts, was consistently different between host races. Instead, co-existence with the other host race significantly affected the degree of morphological divergence, but the divergence was largely driven by different traits in different contact zones. Thus, local stochastic fixation or reinforcement could generate trait divergence, and additional evidence is needed to conclude whether divergence is locally adaptive.
The dataset describes morphological measurements of the dipteran Tephritis conura. This species has specialised to utilise two different host plants (Cirsium heterophyllum and C. oleraceum), and thereby formed stable host races. Individuals of both host races, both collected in sympatry and allopatry from eight different populations in northern Europe was measured, after having been hatched in a common lab environment. One female and one male from each bud was measured. We took magnified photographs of each individual, and of the wings of each individual.
Measured traits include wing length, wing width, wing area, melanised area, melanised ratio and a Procrustes fit of landmark data for wing shape (included in the data are the six most variable relative warps produced by a PCA of wing shape data). Body length and ovipositor length were measured digitally from lateral photographs. Wing melanisation was measured using an automated script, which quantified how many pixels of the wing was melanised. Wing shape data was produced from 15 landmarks on each wing. After a Procrustes fit, six relative warps were extracted from the loadings of a principal component analysis. Each wing shape principal component in the dataset represents a wing shape phenotype.