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Many animals undergo changes in functional colors during development, requiring the replacement of integument or pigment cells. A classic example of defensive color switching is found in hatchling lizards, which use conspicuous tail colors to deflect predator attacks away from vital organs. These tail colors usually fade to concealing colors during ontogeny. Here, we show that the ontogenetic blue-to-brown tail color change in Acanthodactylus beershebensis lizards results from the changing optical properties of single types of developing chromatophore cells. The blue tail colors of hatchlings are produced by incoherent scattering from premature guanine crystals in underdeveloped iridophore cells. Cryptic tail colors emerge during chromatophore maturation upon reorganization of the guanine crystals into a multilayer reflector concomitantly with pigment deposition in the xanthophores. Ontogenetic changes in adaptive colors can thus arise not via the exchange of different optical systems, but by harnessing the timing of natural chromatophore development. The incoherent scattering blue color here differs from the multilayer interference mechanism used in other blue-tailed lizards, indicating that a similar trait can be generated in at least two ways. This supports a phylogenetic analysis showing that conspicuous tail colors are prevalent in lizards and that they evolved convergently. Our results provide an explanation for why certain lizards lose their defensive colors during ontogeny and yield a hypothesis for the evolution of transiently functional adaptive colors.
Many animals undergo changes in functional colors during development, requiring the replacement of integument or pigment cells. A classic example of defensive color switching is found in hatchling lizards, which use conspicuous tail colors to deflect predator attacks away from vital organs. These tail colors usually fade to concealing colors during ontogeny. Here, we show that the ontogenetic blue-to-brown tail color change in Acanthodactylus beershebensis lizards results from the changing optical properties of single types of developing chromatophore cells. The blue tail colors of hatchlings are produced by incoherent scattering from premature guanine crystals in underdeveloped iridophore cells. Cryptic tail colors emerge during chromatophore maturation upon reorganization of the guanine crystals into a multilayer reflector concomitantly with pigment deposition in the xanthophores. Ontogenetic changes in adaptive colors can thus arise not via the exchange of different optical systems, but by harnessing the timing of natural chromatophore development. The incoherent scattering blue color here differs from the multilayer interference mechanism used in other blue-tailed lizards, indicating that a similar trait can be generated in at least two ways. This supports a phylogenetic analysis showing that conspicuous tail colors are prevalent in lizards and that they evolved convergently. Our results provide an explanation for why certain lizards lose their defensive colors during ontogeny and yield a hypothesis for the evolution of transiently functional adaptive colors.
In the damselfly Calopteryx maculata, territorial males court potential mates and guard ovipositing females near the surface of the water. We conducted a survey and an experiment to determine whether there was a relationship between territoriality (site fidelity and agonistic behavior) and perch height. In the survey, males were captured, numbered, and released, and their perch height and location along a stream was noted for two weeks. Mean perch height was positively correlated with total distance travelled and negatively correlated with the number and percentage of times observed at the same site. Males that travelled less than 4 m had a significantly lower mean perch height than males that travelled more than 4 m. We conclude that males with greater site fidelity perch lower than males that travel widely. To test for a relationship between agonistic behavior and perch height, live male and female decoys, and a stick control, were run along a 20 m zip-line at two heights (25 cm and 75 cm), and the responses of resident males were recorded. Resident males that perched low (< 1 m high) approached decoys more often than resident males that perched high, and low-flying decoys were approached more than high-flying decoys. We conclude that territorial males—identified by greater site fidelity and agonistic behavior—perch lower than other males and are particularly responsive to low flying intruders. The benefits and costs of perching low and responding to low-flying intruders are discussed.
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