Sex-specific behavioral syndromes allow the independent evolution of behavioral dimorphism

When selection differs by sex, the capacity for sexes to reach optimal phenotypes can be constrained by the shared genome of males and females. Because phenotypic traits are often correlated, this difference extends across multiple traits and underlying genetic correlations can further constrain evolutionary responses. Behaviors are frequently correlated as behavioral syndromes, and these correlations often have a genetic basis. However, whether cross-sex and across behavior correlations lead constrained evolution remains unknown. Here, we show that a boldness-activity syndrome is strongly sex-specific at the genetic level in the western field cricket (Gryllus integer) and that emergence from a shelter is genetically independent between males and females. However, male activity is strongly related to female shelter emergence, creating the potential for biased responses to selection. Our results show that the sex-specific genetic architecture of behavioral syndromes can shape the evolution of behavioral phenotypes.

Ancestral neural computations constrain the evolution of novel computations in simulated color vision networks

Efficient coding has been a successful organizational principle in neuroscience, but a more general theoretical framework needs to include the capacity for biological constraints to impede the realization of optimal circuit design. Here, we explore how evolution shapes the computational organization of a circuit using color vision as a model system. Taking a theoretical, machine learning approach allowed us to simulate the evolution of tetrachromatic color vision from a trichromatic ancestor both within and across distinct phylogenetic lineages. Analyzing network performance showed that trichromatic starting weights impose a significant constraint on learning rate, although the incremental increase in input layer complexity leads to better overall performance. Analyzing hidden layer computations showed that ancestry severely constrained evolution into a restricted and predictable portion of the theoretically available computational state space. Overall, our simulations of color vision evolution suggest that phylogenetic history is an important aspect of the functional organization of neural circuits.

Genomic Signals of Adaptation towards Mutualism and Sociality in Two Ambrosia Beetle Complexes

Mutualistic symbiosis and eusociality have developed through gradual evolutionary processes at different times in specific lineages. Like some species of termites and ants, ambrosia beetles have independently evolved a mutualistic nutritional symbiosis with fungi, which has been associated with the evolution of complex social behaviors in some members of this group. We sequenced the transcriptomes of two ambrosia complexes (Euwallacea sp. near fornicatus–Fusarium euwallaceae and Xyleborus glabratus–Raffaelea lauricola) to find evolutionary signatures associated with mutualism and behavior evolution. We identified signatures of positive selection in genes related to nutrient homeostasis; regulation of gene expression; development and function of the nervous system, which may be involved in diet specialization; behavioral changes; and social evolution in this lineage. Finally, we found convergent changes in evolutionary rates of proteins across lineages with phylogenetically independent origins of sociality and mutualism, suggesting a constrained evolution of conserved genes in social species, and an evolutionary rate acceleration related to changes in selective pressures in mutualistic lineages.

Early bursts of disparity and the reorganization of character integration

‘Early bursts' of morphological disparity (i.e. diversity of anatomical types) are common in the fossil record. We typically model such bursts as elevated early rates of independent character change. Developmental theory predicts that modules of linked characters can change together, which would mimic the effects of elevated independent rates on disparity. However, correlated change introducing suboptimal states should encourage breakup (parcellation) of character suites allowing new (or primitive) states to evolve until new suites arise (relinkage). Thus, correlated change–breakup–relinkage presents mechanisms for early bursts followed by constrained evolution. Here, I analyse disparity in 257 published character matrices of fossil taxa. For each clade, I use inverse-modelling to infer most probably rates of independent change given both time-homogeneous and separate ‘early versus late' rates. These rates are used to estimate expected disparity given both independent change models. The correlated change–breakup–relinkage model also predicts elevated frequencies of compatible character state-pairs appearing out of order in the fossil record (e.g. 01 appearing after 00 and 11; = low stratigraphic compatibility), as one solution to suboptimal states induced by correlated change is a return to states held before that change. As predicted by the correlated change–breakup–relinkage model, early disparity in the majority of clades both exceeds the expectations of either independent change model and excess early disparity correlates with low stratigraphic compatibility among character-pairs. Although it is possible that other mechanisms for linking characters contribute to these patterns, these results corroborate the idea that reorganization of developmental linkages is often associated with the origin of groups that biologists recognize as new higher taxa and that such reorganization offers a source of new disparity throughout the Phanerozoic.

On the minimizing movement with the 1-Wasserstein distance

We consider a class of doubly nonlinear constrained evolution equations which may be viewed as a nonlinear extension of the growing sandpile model of [L. Prigozhin, Eur. J. Appl. Math. 7 (1996) 225–235.]. We prove existence of weak solutions for quite irregular sources by a semi-implicit scheme in the spirit of the seminal works of [R. Jordan et al., SIAM J. Math. Anal. 29 (1998) 1–17, D. Kinderlehrer and N.J. Walkington, Math. Model. Numer. Anal. 33 (1999) 837–852.] but with the 1-Wasserstein distance instead of the quadratic one. We also prove an L1-contraction result when the source is L1 and deduce uniqueness and stability in this case.