We introduce the concept of many-to-one mapping of form to function and suggest that this emergent property of complex systems promotes the evolution of physiological diversity. Our work has focused on a 4-bar linkage found in labrid fish jaws that transmits muscular force and motion from the lower jaw to skeletal elements in the upper jaws. Many different 4-bar shapes produce the same amount of output rotation in the upper jaw per degree of lower jaw rotation, a mechanical property termed Maxillary KT. We illustrate three consequences of many-to-one mapping of 4-bar shape to Maxillary KT. First, many-to-one mapping can partially decouple morphological and mechanical diversity within clades. We found with simulations of 4-bars evolving on phylogenies of 500 taxa that morphological and mechanical diversity were only loosely correlated (R(2) = 0.25). Second, redundant mapping permits the simultaneous optimization of more than one mechanical property of the 4-bar. Labrid fishes have capitalized on this flexibility, as illustrated by several species that have Maxillary KT = 0.8 but have different values of a second property, Nasal KT. Finally, many-to-one mapping may increase the influence of historical factors in determining the evolution of morphology. Using a genetic model of 4-bar evolution we exerted convergent selection on three different starting 4-bar shapes and found that mechanical convergence only created morphological convergence in simulations where the starting forms were similar. Many-to-one mapping is widespread in physiological systems and operates at levels ranging from the redundant mapping of genotypes to phenotypes, up to the morphological basis of whole-organism performance. This phenomenon may be involved in the uneven distribution of functional diversity seen among animal lineages.

Many physiological traits consist of two hierarchically related levels: physical structures and the emergent functional properties of those structures. Because selection tends to act on the emergent functional traits, the evolution of structural phenotypes will depend on the nature of the form-function relationship. Complex physiological or biomechanical traits are often characterized by many-to-one mapping: numerous structural phenotypes can yield equivalent functions. We suggest that this redundancy can promote the evolution of phenotypic diversity, and we illustrate this effect with a combination of empirical and analytical studies of a complex biomechanical trait, the four-bar linkage found in the jaws of labrid fishes. We show that labrid jaws are subject to many-to-one mapping of form-to-jaw mechanical properties but that some mechanical types have higher levels of morphological redundancy than others. This variation in redundancy has affected the diversity and distribution of labrid jaw shapes: labrid species are disproportionately concentrated around functional traits with higher potential for redundancy. Many-to-one mapping can also mitigate evolutionary constraints imposed by mechanical trade-offs by allowing a species to simultaneously optimize multiple functional properties. Many-to-one mapping may be an important factor in generating the uneven patterns of diversity in physiological traits.

The family Scaridae comprises about 90 species of herbivorous coral reef, rock reef, and seagrass fishes. Parrotfishes are important agents of marine bioerosion who rework the substrate with their beaklike oral jaws. Many scarid populations are characterized by complex social systems including highly differentiated sexual stages, territoriality, and the defense of harems. Here, we test a hypothesis of relationships among parrotfish genera derived from nearly 2 kb of nuclear and mitochondrial DNA sequence. The DNA tree is different than a phylogeny based on comparative morphology and leads to important reinterpretations of scarid evolution. The molecular data suggest a split among seagrass and coral reef associated genera with nearly 80% of all species in the coral reef clade. Our phylogenetic results imply an East Tethyan origin of the family and the recurrent evolution of excavating and scraping feeding modes. It is likely that ecomorphological differences played a significant role in the initial divergence of major scarid lineages, but that variation in color and breeding behavior has triggered subsequent diversification. We present a two-phase model of parrotfish evolution to explain patterns of comparative diversity. Finally, we discuss the application of this model to other adaptively radiating clades.

Aim Capuchin monkey species are widely distributed across Central and South America. Morphological studies consistently divide the clade into robust and gracile forms, which show extensive sympatry in the Amazon Basin. We use genetic data to test whether Miocene or Plio-Pleistocene processes may explain capuchin species' present distributions, and consider three possible scenarios to explain widespread sympatry.Location The Neotropics, including the Amazon and Atlantic Coastal Forest.Methods We sequenced the 12S ribosomal RNA and cytochrome b genes from capuchin monkey specimens. The majority were sampled from US museum collections and were wild-caught individuals of known provenance across their distribution. We applied a Bayesian discrete-states diffusion model, which reconstructed the most probable history of invasion across nine subregions. We used comparative methods to test for phylogeographic association and dispersal rate variation.

Interactions between fungi and plants, including parasitism, mutualism, and saprotrophy, have been invoked as key to their respective macroevolutionary success. Here we evaluate the origins of plant-fungal symbioses and saprotrophy using a time-calibrated phylogenetic framework that reveals linked and drastic shifts in diversification rates of each kingdom. Fungal colonization of land was associated with at least two origins of terrestrial green algae and preceded embryophytes (as evidenced by losses of fungal flagellum, ca. 720 Ma), likely facilitating terrestriality through endomycorrhizal and possibly endophytic symbioses. The largest radiation of fungi (Leotiomyceta), the origin of arbuscular mycorrhizae, and the diversification of extant embryophytes occurred ca. 480 Ma. This was followed by the origin of extant lichens. Saprotrophic mushrooms diversified in the Late Paleozoic as forests of seed plants started to dominate the landscape. The subsequent diversification and explosive radiation of Agaricomycetes, and eventually of ectomycorrhizal mushrooms, were associated with the evolution of Pinaceae in the Mesozoic, and establishment of angiosperm-dominated biomes in the Cretaceous.

Abstract. Like many phenotypic traits, biomechanical systems are defined by both an underlying morphology and an emergent functional property. The relationship between these levels may have a profound impact on how selection for functional performance is translated into morphological evolution. In particular, complex mechanical systems are likely to be highly redundant, because many alternative morphologies yield equivalent functions. We suggest that this redundancy weakens the relationship between morphological and functional diversity, and we illustrate this effect using an evolutionary model of the four-bar lever system of labrid fishes. Our results demonstrate that, when traits are complex, the morphological diversity of a clade may only weakly predict its mechanical diversity. Furthermore, parallel or convergent selection on function does not necessarily produce convergence in morphology. Empirical observations suggest that this weak form-function relationship has contributed to the morphological diversity of labrid fishes, as functionally equivalent species may nevertheless possess morphologically distinct jaws. We suggest that partial decoupling of morphology and mechanics due to redundancy is a major factor in morphological diversification.

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The rich diversity of primate faces has interested naturalists for over a century. Researchers have long proposed that social behaviours have shaped the evolution of primate facial diversity. However, the primate face constitutes a unique structure where the diverse and potentially competing functions of communication, ecology and physiology intersect, and the major determinants of facial diversity remain poorly understood. Here, we provide the first evidence for an adaptive role of facial colour patterns and pigmentation within Neotropical primates. Consistent with the hypothesis that facial patterns function in communication and species recognition, we find that species living in smaller groups and in sympatry with a higher number of congener species have evolved more complex patterns of facial colour. The evolution of facial pigmentation and hair length is linked to ecological factors, and ecogeographical rules related to UV radiation and thermoregulation are met by some facial regions. Our results demonstrate the interaction of behavioural and ecological factors in shaping one of the most outstanding facial diversities of any mammalian lineage.