Nutritional constraints on brain evolution: Sodium and nitrogen limit brain size.

Nutrition has been hypothesized as an important constraint on brain evolution. However, it is unclear whether the availability of specific nutrients or the difficulty of locating high-quality diets limits brain evolution, especially over long periods of time. We found that dietary nutrient content predicted brain size across 42 species of butterflies.

Does Hormonal Pleiotropy Shape the Evolution of Performance and Life History Traits?

Hormonal pleiotropy occurs when a part of the endocrine system (e.g., hormone concentrations) influences the expression of two or more phenotypes.

Nutrition shapes life-history evolution across species.

Nutrition is a key component of life-history theory, yet we know little about how diet quality shapes life-history evolution across species. Here, we test whether quantitative measures of nutrition are linked to life-history evolution across 96 species of butterflies representing over 50 independent diet shifts. We find that butterflies feeding on high nitrogen host plants as larvae are more fecund, but their eggs are smaller relative to their body size.

Cryptic individual scaling relationships and the evolution of morphological scaling.

Morphological scaling relationships between organ and body size-also known as allometries-describe the shape of a species, and the evolution of such scaling relationships is central to the generation of morphological diversity. Despite extensive modeling and empirical tests, however, the modes of selection that generate changes in scaling remain largely unknown. Here, we mathematically model the evolution of the group-level scaling as an emergent property of individual-level variation in the developmental mechanisms that regulate trait and body size.

Brain size predicts problem-solving ability in mammalian carnivores.

Despite considerable interest in the forces shaping the relationship between brain size and cognitive abilities, it remains controversial whether larger-brained animals are, indeed, better problem-solvers. Recently, several comparative studies have revealed correlations between brain size and traits thought to require advanced cognitive abilities, such as innovation, behavioral flexibility, invasion success, and self-control. However, the general assumption that animals with larger brains have superior cognitive abilities has been heavily criticized, primarily because of the lack of experimental support for it.

A molecular signaling approach to linking intraspecific variation and macro-evolutionary patterns.

Macro-evolutionary comparisons are a valued tool in evolutionary biology. Nevertheless, our understanding of how systems involved in molecular signaling change in concert with phenotypic diversification has lagged. We argue that integrating our understanding of the evolution of molecular signaling systems with phylogenetic comparative methods is an important step toward understanding the processes linking variation among individuals with variation among species.

Insulin-like growth factor-1 is associated with life-history variation across Mammalia.

Despite the diversity of mammalian life histories, persistent patterns of covariation have been identified, such as the 'fast-slow' axis of life-history covariation. Smaller species generally exhibit 'faster' life histories, developing and reproducing rapidly, but dying young. Hormonal mechanisms with pleiotropic effects may mediate such broad patterns of life-history variation.

Developmental constraints on behavioural flexibility.

We suggest that variation in mammalian behavioural flexibility not accounted for by current socioecological models may be explained in part by developmental constraints. From our own work, we provide examples of constraints affecting variation in behavioural flexibility, not only among individuals, but also among species and higher taxonomic units. We first implicate organizational maternal effects of androgens in shaping individual differences in aggressive behaviour emitted by female spotted hyaenas throughout the lifespan.

Multiple determinants of whole and regional brain volume among terrestrial carnivorans.

Mammalian brain volumes vary considerably, even after controlling for body size. Although several hypotheses have been proposed to explain this variation, most research in mammals on the evolution of encephalization has focused on primates, leaving the generality of these explanations uncertain. Furthermore, much research still addresses only one hypothesis at a time, despite the demonstrated importance of considering multiple factors simultaneously.

Mediation of vertebrate life histories via insulin-like growth factor-1.

Life-history traits describe parameters associated with growth, size, survival, and reproduction. Life-history variation is a hallmark of biological diversity, yet researchers commonly observe that one of the major axes of life-history variation after controlling for body size involves trade-offs among growth, reproduction, and longevity. This persistent pattern of covariation among these specific traits has engendered a search for shared mechanisms that could constrain or facilitate production of variation in life-history strategies.

Lifetime selection on a hypoallometric size trait in the spotted hyena.

Size-related traits are common targets of natural selection, yet there is a relative paucity of data on selection among mammals, particularly from studies measuring lifetime reproductive success (LRS). We present the first phenotypic selection analysis using LRS on size-related traits in a large terrestrial carnivore, the spotted hyena, which displays a rare pattern of female-biased sexual size dimorphism (SSD). Using path analysis, we investigate the operation of selection to address hypotheses proposed to explain SSD in spotted hyenas.