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Title: Multivariate sexual selection on performance-related traits in scrambling and territorial damselflies ,,
Other Titles: Multivariate seksuele selectie op kenmerken gerelateerd met performantie in niet-territoriale en territoriale waterjuffers ,,
Authors: Gyulav√°ri, Hajnalka Anna
Issue Date: 23-Jun-2016
Abstract: Sexual selection is a powerful force directing evolution which can vary in strength (strong or weak), direction (positive or negative) and form (linear or nonlinear). Despite the many studies on sexual selection, three aspects remain understudied, yet very relevant to fully understand sexual selection on the traits of a given species. (1) While most of the studies on sexual selection focused on a single or few phenotypic traits, a minority of studies followed a multivariate approach. This is important to disentangle direct selection versus indirect sexual selection on a trait. (2) Most studies focused on morphological traits (mainly body size) and ignored physiological traits, for example related to energy reserves, and locomotor performance. (3) Finally, recent studies suggest that sexual selection may vary both among populations and among time periods within a given population. Paying attention to such spatiotemporal variation in sexual selection will learn whether the same traits are preferred across populations and seasons which is directly relevant to understand the evolutionary dynamics of these traits.
To study these aspects in-depth we used damselflies, upcoming model systems in ecology and evolution. In this thesis we combined field and laboratory studies to obtain a multivariate picture of sexual selection on whole-organism performance and the underlying morphological and physiological traits in the scrambling damselfly Coenagrion puella and the territorial damselfly Chalcolestes viridis. In addition, we performed a detailed morphometric analysis and reconstructed phylogenetic trees to resolve the position of C. viridis and its eastern form, C. parvidens.
1. The taxonomic position of C. viridis and C. parvidens
Our genetic data supported the genus status of Chalcolestes. We found that the two Chalcolestes taxa formed a monophyletic group separated from other investigated European Lestes species based on both the mitochondrial COI gene and the nuclear ribosomal ITS region. The morphometric study showed that C. viridis and C. parvidens were differentiated in morphometric space, even though there were no single morphometric characters that could conclusively distinguish the two taxa. Our genetic analysis further supported the species status of C. parvidens. The two Chalcolestes taxa do not share haplotypes, suggesting that lineage sorting was complete. Although we find the data supportive of recognizing C. parvidens as a distinct species, further detailed morphologic and genetic analyses are needed to shed further light on how both species are separated reproductively.
2. Spatial and temporal variation of sexual selection on whole-organism performance and the underlying morphological and physiological traits
Although the two study species have a contrasting mating system, we found that flight endurance had a key role determining mating success in both species. In contrast, we could not detect selection on flight speed in neither of the species. This indicates that flight speed is not as relevant as flight endurance neither for territorial defence nor for scrambling in the study species. This is intriguing as speed is likely to play a role in capturing the female, especially in scrambling species. More likely, speed is already maximized due to strong selection by other agents such as predators leaving less variation to detect selection on this performance trait, while endurance is less relevant for damselflies to escape predators. From the six key phenotypic traits, four were found to be under sexual selection. The detected selection patterns that could not be explained via their effect on flight performance are generating novel testable hypotheses about how the covariation between these traits and mating success was generated. This urges caution when using different traits as proxies for the two studied aspects of flight performance. We provided support that not only spatial but also temporal variation occurs within a single reproductive season for sexual selection on phenotypic traits. Furthermore, we provided the first test for spatially and temporally varying sexual selection on performance traits, which confirmed our novel hypothesis that selection on performance (here flight endurance) is more stable through space and time than the observed selection on the underlying traits. We hypothesize this to be a general pattern given that, compared to morphological and physiological traits, performance is the direct target of selection. In contrast, selection on phenotypic traits may be more variable as the contribution of phenotypic traits to performance may depend on environmental conditions. Additionally, different combinations of underlying morphological and physiological traits may result in similar performance.
The here reported studies are the first investigating sexual selection on flight performance and the underlying physiological and morphological traits in an aerial scrambling and territorial species. The PhD thesis adds to the increasing number of studies finding that the strength, direction, and form of selection are often spatially and temporally dynamic. This thesis helps to refine our knowledge of the spatial and temporal dynamics of selection patterns in nature, which is of paramount importance to arrive at a better understanding of adaptive evolutionary dynamics of traits in natural populations.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Ecology, Evolution and Biodiversity Conservation Section

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