![\"Bulgy+Typical+tadpoles\"](\"http:\/\/ok.fsc.hokudai.ac.jp\/en\/wp-content\/uploads\/sites\/2\/2015\/02\/Bulgy-Typical-tadpoles.jpg\")
A Tadpole with the non-defensive phenotype (left), and one with the defensive bulgy phenotype (Right)<\/p><\/div>\n
![\"tadpole+swallowed+by+salamander2\"](\"http:\/\/ok.fsc.hokudai.ac.jp\/en\/wp-content\/uploads\/sites\/2\/2015\/02\/tadpole-swallowed-by-salamander2.jpg\")
<\/a>A salamander larva swallowing a tadpole whole<\/p><\/div>\n
Reference:\u00a0Kishida, O. & Nishimura, K. (2004) Bulgy tadpoles: inducible defense morph.\u00a0Oecologia<\/em>\u00a0141:414-421.<\/p>\n Prey organisms need to use different defensive tactics against predators that employ different hunting methods. We think that Rana pirica <\/em>tadpoles use phenotypic plasticity in just this way, because they can not only acquire a bulgy phenotype as a defense against the larval salamanders, they can also acquire a “high-tail” phenotype in response to predation risk from dragon\ufb02y (Aeshna nigro\ufb02ava<\/em>) larvae, which bite their prey instead of swallowing it whole.\u00a0 We interpret these predator-specific phenotypes as predator-specific defenses (Kishida & Nishimura 2005).<\/p>\n Expression of these predator-specific defensive phenotypes by the tadpoles is highly flexible (Kishida & Nishimura 2006). Even a tadpole that has already expressed one predator-speci\ufb01c phenotype can modify its morphology if the predator is removed or exchanged for the other predator species. When the predator species is removed, a tadpole with either predator-speci\ufb01c phenotype reverts its phenotype to the non-defensive one. If one predator species is exchanged for the other, then the tadpole changes its phenotype to the one specific for the new predator. Thus, a tadpole can \ufb02exibly shift its phenotype from the bulgy morph to the high-tail morph, or vice versa, depending on whether it must defend itself against salamander or dragonfly larvae\u00a0 (Kishida & Nishimura 2006).<\/p>\n Three tadpole morphs: (top) Non-defensive, (middle) dragonfly-induced high-tail, and (bottom) salamander-induced bulgy morphs<\/p><\/div>\n References:<\/p>\n Salamander larvae with displaying the offensive (above) and the non-offensive phenotype (bottom)<\/p><\/div>\n Just as\u00a0R. pirica<\/em>\u00a0frog tadpoles can acquire a defensive phenotype to protect themselves from predation, H. retardatus<\/em> salamander larvae can exhibit an offensive phenotype that makes them more effective predators.\u00a0When salamander hatchlings are raised among R. pirica<\/em> tadpoles or conspecifi hatchlings, some of them acquire an enlarged gape during their early development (Michimae & Wakahara 2002).\u00a0They are especially likely to enlarge their gape in the\u00a0presence of small tadpoles (Michimae & Wakahara 2002). This broadened gape, which\u00a0allows the salamander larvae to swallow large prey items more easily, is a good example of \u2018inducible offense\u2019 (Takatsu & Kishida 2013). Interestingly, Rana pirica<\/em> tadpoles that are exposed to predation pressure from salamander larvae with this offensive morph\u00a0develop an even bulgier phenotype (relative to body length), compared with tadpoles exposed to\u00a0predation pressure from salamander larvae with the non-offensive phenotype (Kishida et al. 2006). This variable\u00a0response of the tadpoles to this gape-limited predator may be adaptive, because its hard for salamander larvae that don’t have the offensive phenotype to swallow the bulgy tadpoles (Takatsu\u00a0& Kishida 2013). In fact, R. pirica<\/em> tadpoles may have evolved the inducible bulgy defense morph as a response\u00a0to the variable expression of the offensive morph by salamander larvae.<\/p>\n References:<\/p>\n To deepen our\u00a0understanding of the evolution of inducible defenses, we examined genetic variation and geographic differentiation in the inducible bulgy defense of R. pirica<\/em>\u00a0tadpoles (Kishida et al. 2007). We crossed frogs from a mainland population where there were predaceous salamanders with other mainland frogs or with frogs from a population from an island without predaceous salamanders, and we also crossed frogs from the island population with other island frogs. Then we raised the\u00a0resulting offspring\u00a0in the presence\u00a0or absence of H. retardatus<\/em>\u00a0salamander larvae. We found that tadpole offspring of mainland frogs\u00a0were better able to express the inducible morphology (i.e., they acquired a more bulgy body) than the offspring of frogs from\u00a0the predator-free island. In addition, expression of the bulgy morph by mainland-island hybrids\u00a0and expression of the bulgy morph in mainland\u2013island hybrids was intermediate between the phenotypes produced by the pure crosses. In this experiment, the expression of the bulgy morph was the same whether the mother or the father came from the mainland population. These experimental results support our hypothesis that geographic variation in the inducible defenses of\u00a0R. pirica<\/em>\u00a0reflects the additive effects of autosomal alleles that differ depending on a population’s historical exposure to\u00a0H. retardatus<\/em>\u00a0salamanders.<\/p>\n Left: Mainland\u00a0x\u00a0mainland tadpole not exposed to predation. Middle: Island x Island tadpole exposed to predation risk for three weeks.\u00a0Right: Mainland x mainland tadpole\u00a0exposed to predation risk for three weeks.<\/p><\/div>\n <\/p>\n Size-adjusted body depth of Rana pirica<\/em>\u00a0tadpoles produced by four different genetic crosses and exposed (solid circles) or not exposed (control; oplen circles) to predation by larval salamanders. A larger body depth means a more bulgy morph. Significantly different means are labeled with different letters (from\u00a0Kishida et al. 2007).<\/p><\/div>\n Reference: Kishida O.,\u00a0Trussell GC. & Nishimura K. (2007) Geographic variation in a predator-induced defense and its genetic basis.\u00a0Ecology<\/em>\u00a088:1948-1954<\/p>\n An adaptive phenotypic response to predation can impose a new challenge on a prey species. \u00a0How do organisms cope with the new challenge? The dragonfly, A. nigro\ufb02ava<\/em>, preys on H. retardatus<\/em> salamander larvae as well as on frog tadpoles.\u00a0 These larvae sometimes exhibit a surfacing behavior in order to take in oxygen from the air, but they surface less frequently in the presence of a dragonfly predation risk, because surfacing makes them conspicuous to this visual predator. To compensate for the unavoidable cost (hypoxia) associated with this induced behavioral defense, the salamander larvae develop enlarged gills (Iwami et al. 2007). Interestingly, gill enlargement is induced in response to not only hypoxic conditions but also chemical cues from the dragonfly. This finding suggests that organisms may evolve functional interactions among multiple inducible traits that allow them to cope with the variable nature of the selective environment.<\/p>\nPredator-specific inducible morphological defenses.<\/h1>\n
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Antagonistic phenotypic plasticity<\/h1>\n
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Geographic variation of inducible defenses and its genetic basis<\/h1>\n
<\/a><\/a>Phenotypic plasticity\u00a0of multiple traits<\/h1>\n