The function of zebra stripes

Abstract

Despite over a century of interest, the function of zebra stripes has never been examined systematically. Here we match variation in striping of equid species and subspecies to geographic range overlap of environmental variables in multifactor models controlling for phylogeny to simultaneously test the five major explanations for this infamous colouration. For subspecies, there are significant associations between our proxy for tabanid biting fly annoyance and most striping measures (facial and neck stripe number, flank and rump striping, leg stripe intensity and shadow striping), and between belly stripe number and tsetse fly distribution, several of which are replicated at the species level. Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses. Susceptibility to ectoparasite attack is discussed in relation to short coat hair, disease transmission and blood loss. A solution to the riddle of zebra stripes, discussed by Wallace and Darwin, is at hand.

Toll ligand Spätzle3 controls melanization in the stripe pattern formation in caterpillars

“…The molecular mechanism underlying spot formation in adult and larval insects has become more apparent via many studies in Drosophila (4,5), Bombyx mori (6, 7), and several butterflies (8)(9)(10). Although stripe pattern formation is well-studied in vertebrates, such as the zebra (11), rodents (12), and zebrafish (13), the molecular backgrounds of this pattern in insects are largely unknown. Because the stripe pattern is often observed in lepidopteran larva and its biological roles are more evident than in other animals (14,15), it is intriguing to study the mechanism and evolutionary origin of caterpillar stripe formation.…”

Why the Donkey Did Not Go South: Disease as a Constraint on the Spread of Equus asinus into Southern Africa

“…These regions experienced rainfall that was too low to support populations of Glossina spp., and animals living there cannot therefore have been exposed to trypanosomiasis. That E. africanus only has thin stripes on its lower legs is fully consistent with this since the distribution of zebras shows an almost perfect correlation with that of biting flies, especially Glossina spp., and the width of zebra stripes appears to deter tsetse and tabanid flies from biting them (Caro et al 2014;Fig. 2).…”

A Generalized Selected Effects Theory of Function

“…Specifically, in some contexts, when a biologist attributes a function to a trait, he or she purports to explain why the trait exists. When Tim Caro and his colleagues (Caro et al 2014) argued that a function of zebra stripes is to deter biting flies, they purported to explain, in some causalhistorical sense, why zebras are striped, rather than, say, mono-colored. Biologists do not always use function in this explanatory, "why-it-is-there" sense.…”

“…For example (if certain biologists are correct), a function of zebra stripes is to ward off biting flies, because that is why they evolved by natural selection (Caro et al 2014). Of course, SE allows a trait to have more than one function, since a trait can be selected for more than one feature.…”