American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“What determines the distinct morphology of species with a particular ecology? The roles of many-to-one mapping and trade-offs in the evolution of frog ecomorphology and performance”

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Daniel S. Moen (Oct 2019)

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Many-to-one mapping leads to specialized ecomorphs without compromising performance in a shared behavior

This Malagasy arboreal frog, <i>Boophis madagascariensis</i>, was included in this study. It is from a family of frogs that has diversified into many microhabitats on Madagascar.<br />(Credit: Daniel S. Moen)
This Malagasy arboreal frog, Boophis madagascariensis, was included in this study. It is from a family of frogs that has diversified into many microhabitats on Madagascar.
(Credit: Daniel S. Moen)

Ecologists and evolutionary biologists have long recognized that species that share a similar ecology (e.g. habitat use, diet) have similar body forms, or morphology. Yet the reasons why some body forms are related to ecology are often complicated by the fact that some organisms have many different behaviors associated with their ecology. For example, if an animal that lives mostly in the water has large leg muscles, it may have such muscles because those larger muscles help those species swim better than species that do not regularly swim. But such species may also move terrestrially (e.g. running or jumping), and it may be unclear whether the big muscles will aid or inhibit the terrestrial movement. A new article in The American Naturalist by Daniel Moen explores why certain frog body forms are associated with the microhabitats those species use by linking ecology, morphology, and functional performance. He looked at frogs and toads from three different continents and compared microhabitat (e.g. living in trees or water), leg morphology (leg length and muscle mass), and performance in two different behaviors (jumping and swimming). The results showed that frogs in different microhabitats were different in their leg morphology, and some of those differences were mirrored by swimming ability. However, all species – regardless of microhabitat – jumped equally well, as might be expected for organisms like frogs that use jumping as their primary terrestrial locomotion. The similar jumping ability despite differences in swimming ability and body form can be explained by a concept called many-to-one mapping, in which multiple anatomical traits affect functional performance, allowing species to specialize in body form for some behaviors but maintain similar performance in others. More generally, the study emphasizes the use of evolutionary analyses at large scales (temporally and geographically) for understanding the evolution of body form and its fit to ecology.


Organisms inhabiting a specific environment often have distinct morphology, but the factors that affect this fit are unclear when multiple morphological traits affect performance in multiple behaviors. Does the realized morphology of a species reflect a compromise in performance among behaviors (i.e. trade-offs)? Or does many-to-one mapping result in morphological distinctness without compromising performance across behaviors? The importance of these principles in organismal design has rarely been compared at the macroevolutionary scale. Here, I study 191 species of frogs around the world that inhabit different microhabitats, using models of phenotypic evolution to examine how form-function relationships may explain the fit between ecology and morphology. I found three key results. First, despite being distinct in leg morphology, ecomorphs were similar in jumping performance. Second, ecomorphs that regularly swim showed higher swimming performance, which paralleled the higher leg muscle mass in these taxa. Third, many-to-one mapping of form onto function occurred at all but the highest levels of both jumping and swimming performance. The seemingly contradictory first two results were explained by the third: when one behavior occurs in all species while another is restricted to a subset, many-to-one mapping allows species with distinct ecologies to have distinct body forms that reflect their specialized behavior while maintaining similar performance in a more general, shared behavior.