A chromosomal inversion polymorphism in Scandinavian populations of the seaweed fly, Coelopa frigida

Abstract

1983. A chromosomal inversion polymorphism in Scandinavian populations of the seaweed fly, Coelopa frigida. -Hereditas 99: 135-145. Lund, Sweden. ISSN 0018-0661. Received November 29, 1982 British populations of the seaweed fly Coelopa frigida are polymorphic for the large a@ inversion on chromosome I (BUTLIN et al., Heredity48: 45-55). Flies from Norway, Swedenand Denmark are shown to possess the same inversion polymorphism, and to exhibit similar though not identical polymorphisms at two enzyme-determining loci associated with this inversion. There is a cline in inversion frequencies from the North Sea, through the Skagerrak and Kattegat, into the Raltic Sea. This cline correlates with salinities, the algal composition of seaweed beds in which Coelopa breeds: and with the presence of the sibling species C. pilipes.It is suggested that heterokaryotypic advantage is the major selective force maintaining this polymorphism, and that genotype-related differences in generation times, and the longevity of seaweed beds, may constitute lesser forces acting on the inversion frequencies.

Balancing selection via life-history trade-offs maintains an inversion polymorphism in a seaweed fly

“…This prediction is supported by field observations reporting temporal variation in genotypic proportions, with the α allele increasing in frequency in summer when the wrackbed was less frequently disturbed by storms (38). Geographic variation in genotypic proportions are also observed in natural populations of C. frigida and have been associated with environmental variations, such as air temperature, depth and temperature of the wrackbed and substrate composition (30,31). Although those factors may correlate with the duration of the wrackbed stability, they are also known to modulate the genotype-phenotype relationships and therefore the associated fitness.…”

“…Here, we focused on the seaweed fly Coelopa frigida, whose natural populations are all polymorphic at a large chromosomal inversion on chromosome I (30)(31)(32). Recombination within large inversions is supressed between the different rearrangements.…”

“…Consequently, inversions typically behave as a single locus, with alleles corresponding to the different haplotypic rearrangements (33)(34)(35). In C. frigida, the two alleles, referred to as α and β, differ by more than 2.5% sequence divergence in coding regions and are observed at intermediate frequencies in both European and North American C. frigida populations, suggesting that the haplotypic rearrangements diverged a long time ago and were maintained ever since by balancing selection (30)(31)(32). The widespread excess of αβ heterozygotes and the higher egg-to-adult survival of heterozygotes compared to αα and ββ homozygotes implicates that this polymorphism is partly maintained by overdominance, possibly due to deleterious alleles captured by the inversion (36,37).…”

“…The widespread excess of αβ heterozygotes and the higher egg-to-adult survival of heterozygotes compared to αα and ββ homozygotes implicates that this polymorphism is partly maintained by overdominance, possibly due to deleterious alleles captured by the inversion (36,37). Moreover, inversion frequencies correlate with environmental factors such as temperature and local substrate characteristics, suggesting that spatially-varying selection combined with migration also contributes to maintain this polymorphism (30,31,38). Furthermore, antagonistic pleiotropy on different fitness components may also favour polymorphism given that the inversion affects adult size ( Fig.…”

Genetic divergence and phenotypic plasticity contribute to variation in cuticular hydrocarbons in the seaweed fly Coelopa frigida

“…We also detected plasticity in CHC composition due to the environment; the wrackbed itself had a strong influence on the CHC composition (Figure c). Wrackbed composition and microbiome (i.e., the food source for C. frigida larvae) vary across C. frigida populations in Europe (E. L. Berdan, M. Wellenreuther, & K. Johannesson, unpublished data, Butlin & Day, ; Day et al, ; Wellenreuther et al, ). Consequently, the CHC composition of C. frigida is likely to differ between natural populations in accordance with other research showing that larval diet impacts CHC composition (Etges & de Oliveira, ; Liang & Silverman, ; Rundle, Chenoweth, Doughty, & Blows, ; Stojkovic et al, ).…”