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Coevolution How species adapt to each other Species exist in a web of interactions Coevolution: Reciprocal evolutionary change between interacting species, driven by natural selection Interactions Effect on fitness Definition Examples Positive / Positive mutualism A relationship between species that raises each other’s fitness Cleaners Anemone Symbiosis Positive / Neutral commensalism A relationship in which one Remoras on sharks species benefits but the other suffers no loss in fitness Negative / Positive A relationship in which one Predators / Prey species benefits but the Deception Host and parasite other suffers a loss in fitness Coevolution requires genetic variation SS, South to South (green, solid line) SN, South to North (blue, dashed line); NN, North to North (black, solid line) NS, North to South (red, dashed line). May, initial phenotypic values; June, midpoint phenotypic values (45 days); August, final phenotypic values (90 days). Genetic variation can fuel rapid evolution Abundance of Synechococcus cells (red solid line) and infectious viral particles (blue dashed line) over time Host phenotypes detected at six time points labeled by their ability to resist infection The viral phenotypes detected at the same six time points, numbered in their order of infectivity • detected between 4 and 13 newly evolved viral phenotypes (differing in host range) • Detected between 4 and 11 newly evolved Synechococcus phenotypes (differing in viral resistance) The strength of selection varies geographically Response can be affected when traits have other costs Number of mussels consumed by Nucella in foraging experiments Final shell thickness of Nucella raised with waterborne cues from no crab (control), Carcinus, or native Cancer crabs. Geographic mosaic theory of coevolution Coevolutionary alteration can occur in interactions involving many species Coevolutionary arms race • Examples from experimental evolution Coevolutionary arms races • • Cost to coevolution Prochlorococcus resistance to phage results in lower genome size, • • reduced growth, or resistance to infection by other phages Deceleration in arms race Population decline of evolved resistant cultures during phage infection. Growth of the R1 (A), R5 (B), and R8 (C) evolved cultures Evolved(Ev; red) were compared with susceptible wild-type control strains (WT; black) and initial resistant substrains (iR; blue) when infected with the P-TIP38 phage (filled circles). They were also compared with growth of noninfected cultures (open circles). Key Concepts • The intensity and specificity of coevolutionary interactions can vary geographically and over time • Antagonistic interactions may involve frequencydependent selection that maintains genetic variation • Also applies to mutualistic relationships Müllerian mimicry facilitates learned avoidance Hypselodoris fontandraui (a), H. villafranca (b), H. cantabrica (c), H. picta (d), and H. fontandraui everting its buccal bulb in aquarium on a sponge fragment Batesian mimicry creates frequency dependent selection Colour pattern changes in Stegostoma fasciatum d. Newborn Stegostoma fasciatum swimming at the surface in shallow inshore, turbid waters off the Kimberley coastline of north-western Australia e. a sea snake on the swimming on the surface in Shark Bay, north-western Australia Key Concepts • Arms races result when antagonistic interactions lead to directional selection on each species • Strongly antagonistic interactions may evolve to be less antagonistic over time • When mutualistic species exert positive frequencydependent selection rapid coevolution can result • Mutualisms are vulnerable to cheating • Long standing mutualisms often have mechanisms to punish cheaters Diversifying coevolution can accelerate divergence between populations Echinoderms Myzostomida Summers et al. 2014 Extinctions can disrupt mutualisms Global preserved reef volume constructed by corals in the Mesozoic and Cenozoic plotted at a stage-level stratigraphic resolution. Note logarithmic scale. Tr— Triassic, J—Jurassic, K— Cretaceous, Pg—Paleogene, Ng—Neogene. Ecological selectivity of coral extinctions at the K–T boundary. Extinctions rates depend strongly on feeding mode with presumably zooxanthellae bearing corals (z-like) being much more affected than azooxanthellate corals (az-like). Human impacts on species diversity Broadnosed pipefish Trematode Effect of temperature on proportion of lymphocytes (A), proportion of monocytes (B) and activity of lymphocytes (C) for head kidney cells of S. typhle experienced a heat wave (black boxes, 256C) and control treatment (white boxes, 186C). Key Concepts • Highly specialized mutualisms make species dependent on each other • Extinction of one species may drive extinction of the other