A test for rate-coupling of trophic and cranial evolutionary dynamics in New World bats

The hierarchical radiation of phyllostomid bats as revealed by adaptive molar morphology

Adaptive radiations are bursts in biodiversity that generate new evolutionary lineages and phenotypes. However, because they typically occur over millions of years, it is unclear how their macroevolutionary dynamics vary through time and among groups of organisms. Phyllostomid bats radiated extensively for diverse diets-from insects to vertebrates, fruit, nectar, and blood-and we use their molars as a model system to examine the dynamics of adaptive radiations. Three-dimensional shape analyses of lower molars of Noctilionoidea (Phyllostomidae and close relatives) indicate that different diet groups exhibit distinct morphotypes. Comparative analyses further reveal that phyllostomids are a striking example of a hierarchical radiation; phyllostomids' initial, higher-level diversification involved an "early burst" in molar morphological disparity as lineages invaded new diet-affiliated adaptive zones, followed by subsequent lower-level diversifications within adaptive zones involving less dramatic morphological changes. We posit that strong selective pressures related to initial shifts to derived diets may have freed molars from morpho-functional constraints associated with the ancestral molar morphotype. Then, lineages with derived diets (frugivores and nectarivores) diversified within broad adaptive zones, likely reflecting finer-scale niche partitioning. Importantly, the observed early burst pattern is only evident when examining molar traits that are strongly linked to diet, highlighting the value of ecomorphological traits in comparative studies. Our results support the hypothesis that adaptive radiations are commonly hierarchical and involve different tempos and modes at different phylogenetic levels, with early bursts being more common at higher levels.

Evolvability and Macroevolution: Overview and Synthesis

Evolvability is best addressed from a multi-level, macroevolutionary perspective through a comparative approach that tests for among-clade differences in phenotypic diversification in response to an opportunity, such as encountered after a mass extinction, entering a new adaptive zone, or entering a new geographic area. Analyzing the dynamics of clades under similar environmental conditions can (partially) factor out shared external drivers to recognize intrinsic differences in evolvability, aiming for a macroevolutionary analog of a common-garden experiment. Analyses will be most powerful when integrating neontological and paleontological data: determining differences among extant populations that can be hypothesized to generate large-scale, long-term contrasts in evolvability among clades; or observing large-scale differences among clade histories that can by hypothesized to reflect contrasts in genetics and development observed directly in extant populations. However, many comparative analyses can be informative on their own, as explored in this overview. Differences in clade-level evolvability can be visualized in diversity-disparity plots, which can quantify positive and negative departures of phenotypic productivity from stochastic expectations scaled to taxonomic diversification. Factors that evidently can promote evolvability include modularity—when selection aligns with modular structure or with morphological integration patterns; pronounced ontogenetic changes in morphology, as in allometry or multiphase life cycles; genome size; and a variety of evolutionary novelties, which can also be evaluated using macroevolutionary lags between the acquisition of a trait and phenotypic diversification, and dead-clade-walking patterns that may signal a loss of evolvability when extrinsic factors can be excluded. High speciation rates may indirectly foster phenotypic evolvability, and vice versa. Mechanisms are controversial, but clade evolvability may be higher in the Cambrian, and possibly early in the history of clades at other times; in the tropics; and, for marine organisms, in shallow-water disturbed habitats.

Foraging strategies, craniodental traits, and interaction in the bite force of Neotropical frugivorous bats (Phyllostomidae: Stenodermatinae)

Bats in the family Phyllostomidae exhibit great diversity in skull size and morphology that reflects the degree of resource division and ecological overlap in the group. In particular, the subfamily Stenodermatinae has high morphological diversification associated with cranial and mandibular traits that are associated with the ability to consume the full range of available fruits (soft and hard).We analyzed craniodental traits and their relationship to the bite force in 343 specimens distributed in seven species of stenodermatine bats with two foraging strategies: nomadic and sedentary frugivory. We evaluated 19 traits related to feeding and bite force in live animals by correcting bite force with body size.We used a generalized linear model (GLM) and post hoc tests to determine possible relationships and differences between cranial traits, species, and sex. We also used Blomberg's K to measure the phylogenetic signal and phylogenetic generalized least-squares (PGLS) to ensure the phylogenetic independence of the traits.We found that smaller nomadic species, A. anderseni and A. phaeotis , have a similar bite force to the large species A. planirostris and A. lituratus; furthermore, P. helleri registered a bite force similar to that of the sedentary bat, S. giannae. Our study determined that all the features of the mandible and most of the traits of the skull have a low phylogenetic signal. Through the PGLS, we found that the diet and several cranial features (mandibular toothrow length, dentary length, braincase breadth, mastoid breadth, greatest length of skull, condylo-incisive length, and condylo-canine length) determined bite force performance among Stenodermatiane.Our results reinforce that skull size is a determining factor in the bite force, but also emphasize the importance of its relationships with morphology, ecology, and phylogeny of the species, which gives us a better understanding of the evolutionary adaptions of this highly diverse Neotropical bat group.

On the evolution of trophic position

The trophic structure of food webs is primarily determined by the variation in trophic position among species and individuals. Temporal dynamics of food web structure are central to our understanding of energy and nutrient fluxes in changing environments, but little is known about how evolutionary processes shape trophic position variation in natural populations. We propose that trophic position, whose expression depends on both environmental and genetic determinants of the diet variation in individual consumers, is a quantitative trait that can evolve via natural selection. Such evolution can occur either when trophic position is correlated with other heritable morphological and behavioural traits under selection, or when trophic position is a target of selection, which is possible if the fitness effects of prey items are heterogeneously distributed along food chains. Recognising trophic position as an evolving trait, whose expression depends on the food web context, provides an important conceptual link between behavioural foraging theory and food web dynamics, and a useful starting point for the integration of ecological and evolutionary studies of trophic position.