Abstract
Presence or absence of predators selects for different kind of morphologies. Hence, we expect variation in traits that protect against predators to vary over geographical areas where predators vary in past and present abundance. Abdominal larval spines in dragonfly larvae provide protection against fish predators. We studied geographical variation in larval spine length of the dragonfly Leucorrhinia dubia across Western Europe using a phylogenetic approach. Larvae were raised in a common garden laboratory experiment in the absence of fish predators. Results show that larvae from northern Europe (Sweden and Finland) had significantly longer larval spines compared to larvae from western and central Europe. A phylogeny based on SNP data suggests that short larval spines is the ancestral stage in the localities sampled in this study, and that long spines have evolved in the Fenno-Scandian clade. The role of predators in shaping the morphological differences among the sampled localities is discussed.
Highlights
Spatial environmental variation act as a major source of divergent natural selection resulting in phenotypic diversification within species and given enough time, might result in speciation [1]
Large parts of the variation in abdominal spine length is associated with the presence/absence of fish predators within and among species of Leucorrhinia, such that populations and species that co-occur with fish on average are having longer spines [17, 18, 30]
We suggest that the difference in spine length among populations is driven by natural selection by predatory fish, and fish abundance in our study area is discussed below
Summary
Spatial environmental variation act as a major source of divergent natural selection resulting in phenotypic diversification within species and given enough time, might result in speciation [1]. Prey species have evolved a richness of highly effective morphological anti-predators traits to avoid and repel predators [3, 4]. Differences in predator abundance and occurrence are predicted to result in variation in anti-predator morphological expression among and within prey species [6]. Such variation could occur at larger geographical scales [7], and a good understanding of the geographical variation in morphological traits that defends against predators will contribute to a thorough understanding on how trait diversification evolves [6]
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