Natural selection by predators on the defensive apparatus of the three-spined stickleback, Gasterosteus aculeatus L.

Abstract

Three-spined sticklebacks (Gasterosteus aculeatus L.) can receive considerable protection against predators from characteristic dorsal and pelvic spines. The size and structure of this defensive apparatus were examined in marine and freshwater populations located throughout the European distribution of this species and exposed to differing predatory species and levels of predation pressure. Marine populations appear to experience the greatest predation pressure and have the largest defensive apparatus. Predation in freshwater appears to decline towards both the northern and southern distributional extremes of Gasterosteus, a result attributable to the differential distributions of major piscine predators, especially pike and perch; and this pattern produces arched clines in the morphometrics of defensive structures. Local differences in central latitudes can also be attributed to site-specific differences in predation pressure. Evidence is given for both hereditary and environmental determination of variation in dorsal spine number.

Modular Skeletal Evolution in Sticklebacks Is Controlled by Additive and Clustered Quantitative Trait Loci

“…Chromosomes 3 and 2 had specific effects on dorsal spines 1 and 2, respectively, while chromosome 20 had regional effects on dorsal spine 3 and the anal spine (Figure 4). QTL controlling the number and area of serrations on the second dorsal spine ( Figure 2P) mapped independently of the QTL controlling the length of the second spine, consistent with previous studies showing that presence or absence of serrations varies substantially among stickleback populations, even among populations with prominent second dorsal spines (Gross 1978).…”

“…Additional QTL controlled the number and area of barb-like serrations along the surface of the second dorsal spine, and these QTL mapped to different genomic regions than QTL that control length of the second dorsal spine. Previous studies have shown that natural populations of sticklebacks differ in the number of spines, the length of particular spines, and the degree of barb development along spines, likely reflecting the key roles of dorsal spine morphology in defense against different types of predators, as well as possible functions in display and dorsal pricking interactions during stickleback courtship (Hoogland et al 1957;Gross 1978;Reimchen 1980;Kitano et al 2009). Across larger phylogenetic distances, many other fish groups show striking changes in the length or morphology of individual spines, for example, the specific elongation of the first dorsal spine in trigger fish and angler fish.…”

“…In addition to head skeletal traits, aspects of the median fin and vertebral skeleton are known to vary and be under selection in stickleback populations. These include dorsal spine lengths (Gross 1978;Bell et al 2006;Hunt et al 2008), the number and position of dorsal and anal fin rays and their supporting pterygiophores, and vertebral number and positioning (Swain 1992a,b;.Here we apply genome-wide linkage mapping to investigate the genetic architecture of .100 trophic, armor, and serially repeating skeletal traits in sticklebacks. Using a large set of newly identified QTL, we address several general questions in evolutionary genetics, including the extent to which loci are clustered in the genome, the dominance distribution of evolutionary alleles, and the proportion of loci that have anatomically regional effects.…”

“…In addition to head skeletal traits, aspects of the median fin and vertebral skeleton are known to vary and be under selection in stickleback populations. These include dorsal spine lengths (Gross 1978;Bell et al 2006;Hunt et al 2008), the number and position of dorsal and anal fin rays and their supporting pterygiophores, and vertebral number and positioning (Swain 1992a,b;.…”

How predation shaped fish: the impact of fin spines on body form evolution across teleosts

“…Spines act as a defence against predators [17] by deterring predation attempts [18], reducing capture success or making it difficult for the predator to ingest the fish [19]. In wild fish populations, spine length increases with predator abundance [20,21] and predators have greater success eating individuals with shorter spines [22]. Moreover, a recent experiment found increases in length of the dorsal-fin spine relative to body length are induced in the presence of predators or predation signals [23].…”