Color polymorphism in spiny spiders (gasteracantha fornicata): Testing the adaptive significance of a geographically clinal lure

Darrell J. Kemp, Claire Holmes, Bradley C. Congdon, Will Edwards

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Many sit-and-wait predators use conspicuous displays of color to attract prey. These displays sometimes express discrete polymorphisms; however, the adaptive drivers of such variation are not well understood. Here, we explore a previously unknown color polymorphism in the orb-web spider Gasteracantha fornicata. We discovered that in North Queensland, Australia, female spiders exhibit dorsal bands appearing (to the human observer) either white or yellow and characterized by sigmoidal spectral curves centered on approx. 447 and 496 nm, respectively. Based on sensory drive theory, we hypothesized that morphs may be alternatively favored by the switch in ambient viewing conditions engendered by sunny vs. cloudy skies. We addressed this hypothesis indirectly by studying morph frequencies across a approx. 200 km geographic gradient of solar exposure (a surrogate for cloudiness), and by investigating the phenotypic signature of catch success via a resource stress experiment and in wild spiders. Our data indicate substantial geographic variation in morph frequency, with white morphs dominating at more cloudy northern locations. Rather than a gradual cline, morph frequency inverted mid-way along this range and was closely fit by a logistic relationship with latitude. Experimentally restricted access to larger prey caused spiders to lose more mass than size and to exhibit less bright dorsal markings. Wild-sampled spiders from two localities of divergent morph frequency indicated no differences in residual mass, but intriguingly, the white morph was larger and heavier (than the yellow morph) where it was relatively rare. Our data hint at negative frequency dependence, but remain broadly consistent with a sensory drive explanation based on cloudiness, and we suggest these as worthy avenues for closer investigation.

LanguageEnglish
Pages1126-1137
Number of pages12
JournalEthology
Volume119
Issue number12
DOIs
Publication statusPublished - Dec 2013

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Gasteracantha
polymorphism
spider
Araneae
color
cloud cover
morphs
testing
spider web
cline
frequency dependence
geographical variation
logistics
Queensland
predator
predators
resource
experiment

Cite this

Kemp, Darrell J. ; Holmes, Claire ; Congdon, Bradley C. ; Edwards, Will. / Color polymorphism in spiny spiders (gasteracantha fornicata) : Testing the adaptive significance of a geographically clinal lure. In: Ethology. 2013 ; Vol. 119, No. 12. pp. 1126-1137.
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abstract = "Many sit-and-wait predators use conspicuous displays of color to attract prey. These displays sometimes express discrete polymorphisms; however, the adaptive drivers of such variation are not well understood. Here, we explore a previously unknown color polymorphism in the orb-web spider Gasteracantha fornicata. We discovered that in North Queensland, Australia, female spiders exhibit dorsal bands appearing (to the human observer) either white or yellow and characterized by sigmoidal spectral curves centered on approx. 447 and 496 nm, respectively. Based on sensory drive theory, we hypothesized that morphs may be alternatively favored by the switch in ambient viewing conditions engendered by sunny vs. cloudy skies. We addressed this hypothesis indirectly by studying morph frequencies across a approx. 200 km geographic gradient of solar exposure (a surrogate for cloudiness), and by investigating the phenotypic signature of catch success via a resource stress experiment and in wild spiders. Our data indicate substantial geographic variation in morph frequency, with white morphs dominating at more cloudy northern locations. Rather than a gradual cline, morph frequency inverted mid-way along this range and was closely fit by a logistic relationship with latitude. Experimentally restricted access to larger prey caused spiders to lose more mass than size and to exhibit less bright dorsal markings. Wild-sampled spiders from two localities of divergent morph frequency indicated no differences in residual mass, but intriguingly, the white morph was larger and heavier (than the yellow morph) where it was relatively rare. Our data hint at negative frequency dependence, but remain broadly consistent with a sensory drive explanation based on cloudiness, and we suggest these as worthy avenues for closer investigation.",
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Color polymorphism in spiny spiders (gasteracantha fornicata) : Testing the adaptive significance of a geographically clinal lure. / Kemp, Darrell J.; Holmes, Claire; Congdon, Bradley C.; Edwards, Will.

In: Ethology, Vol. 119, No. 12, 12.2013, p. 1126-1137.

Research output: Contribution to journalArticleResearchpeer-review

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