The adaptive significance of dorsal spine variation in the fourspine stickleback, Apeltes quadracus. IV. phenotypic covariation with closely related species

Abstract

SUMMARYThe fourspine stickleback (Apeltes quadracus) and ninespine stickleback (Pungitius pungitius) have similar ecologies, they often coexist, and they share parallel polymorphisms for the number of dorsal spines. Spine number is positively correlated between them for 86 sites in eastern Canada. Dorsal spine length is positively correlated with spine number within each species, and spine length is positively correlated between them. Spine length for both species is also positively correlated with the presence of predatory fishes and negatively correlated with vegetation cover. Finally, spine number for both Apeltes and Pungirius is lower where they coexist with a new species of stickleback (Gasterosteus sp.) which is found only in environments where predation risk is low. These patterns of covariation within and between species are evidence for natural selection, and they suggest that predators are a selective agent favouring the higher-spined morphs. We discuss these results with respect to the idea that geographic variation in Pun gidus reflects historical processes of isolation and differentiation during the Pleistocene era.

The adaptive significance of dorsal spine variation in the fourspine stickleback, Apeltes quadracus. III. correlated traits and experimental evidence on predation

“…Thus samples from 45 sites (table 1) were scored for dorsal spine length. Samples were chosen randomly from among our 570 sites with the restrictions that the full range of variation in dorsal spine number be represented, that sample size be 35 or greater, and that Pungitius pungitius be adequately represented in each sample to allow a search for interspecific covariation in spine number (see Blouw and Hagen, 1984c). The longest dorsal spine (nearly always the first) was measured with a dissection microscope and ocular micrometer while the spine was extended perpendicular to the body axis.…”

Evolution of stickleback spines through independent cis-regulatory changes at HOXDB

“…Although Apeltes sticklebacks typically develop four dorsal spines, many "quadracus" populations in Canada have predominantly three or five spines 49,50 . In an extensive comparison of Apeltes spine numbers and environmental variables across 570 locations, Blouw and Hagen [66][67][68] found that increased spine number was correlated with the presence of predatory fish, while decreased spine number was correlated with more and denser vegetation. To study the possible adaptive value of spine number differences, Blouw and Hagan exposed mixed populations of four-and five-spine Apeltes to predatory fish and measured differential survival of spine morphs when half of the sticklebacks had been eaten 67 .…”

Evolution of stickleback spines through independentcis-regulatory changes atHOXDB

“…In an extensive comparison of Apeltes spine numbers and environmental variables over 570 different locations, Blouw and Hagen found that increased spine number was correlated with the presence of predatory fish, while decreased spine number was correlated with both more and denser types of vegetation (Blouw and Hagen, 1984b, 1984c). Spine numbers in both Apeltes and Pungitius (ninespine stickleback) trend in the same direction when both stickleback species are present in the same lake, suggesting that the changes in spine number are selected in response to shared environmental factors, rather than varying randomly (Blouw and Hagen, 1984d). To further study the possible adaptive value of spine number differences, Blouw and Hagan exposed mixed populations of four- and five-spine Apeltes to predatory fish and measured differential survival of spine morphs when half of the sticklebacks had been eaten (Blouw and Hagen, 1984c).…”