Biology subjects

Hardy, N. B.

Publications and source records attributed to Hardy, N. B..

5 recordsLinked to original sources

bioRxiv2026

Cyclic parthenogenesis helps populations cross fitness valleys

Cyclic parthenogenesis is a form of occasional sexual reproduction. Here, we compare the evolvability of cyclic parthenogens and obligate sexuals in adaptive scenarios that entail the crossing of a fitness valley. We divide the valley crossing process into two phases. In the escape phase, a population produces genotypes that lie on the other side of the fitness valley. In the establishment phase, such genotypes are refined and promoted to high frequency. With individual-based models, we find that although cyclic parthenogens are slower to produce escape genotypes, they more efficiently establish such genotypes, and therefore more rapidly complete fitness-valley crossings. In obligate sexuals, genetic and mutational variance and covariances, G and M, are readily shaped by selection. In cyclic parthenogens, the shapes of G and M are less responsive to selection but have relatively little effect on the rate of fitness-valley crossing. In our model, the more adaptive evolution of G and M in obligate sexuals is not enough to overcome the establishment advantage of cyclic parthenogens. Nevertheless, the relative recalcitrance against selection on G and M in cyclic parthenogens could be an evolutionary cost that helps explain its paradoxical rarity.

evolutionary biology↗

bioRxiv2024

Unifying (simple) models of genetic robustness and evolvability

Here, I consolidate and extend simple models of how genetic robustness affects the evolvability of phenotypes with discrete states. I share three main insights. (1) What we already know about the effects of mutational robustness on evolvability can be readily transferred to environmental robustness. (2) Even without a hard genotype-level trade-off between robustness and evolvability, the optimal level of phenotypic robustness depends on the rate of environmental change. But counter-intuitively, when adaptive landscapes are complex, an increase in environmental stability can increase the frequency of environmentally-robust but mutationally-sensitive genotypes. (3) Even with a fixed probability that a mutation is neutral, populations can evolve along the spectrum of robustness and evolvability by evolving the genotype-determined neighborhood of mutationally-accessible phenotypes. Indeed, because it allows for the evolution of increased evolvability without a concomitant increase in genetic load, selection should favor changes in the phenotypic neighborhood over changes in mutational sensitivity. Teaser TextModels of the evolution of discrete phenotypes show that their evolvability is highest when environments fluctuate at intermediate rates, and with intermediate levels of mutational robustness. By merging previous models and relaxing previous assumptions, I show that previous insights are robust. I also show that the same models tell us very different things about the evolvability of discrete traits, namely, that what applies to robustness against mutation is readily transferable to robustness against environmental perturbation, and that selection for evolvability will preferentially work on the neighborhood of mutationally-accessible phenotypes rather than the probability of non-neutral mutation.

evolutionary biology↗

bioRxiv2022

Delaying quantitative resistance to pesticides and antibiotics

How can we best vary the application of pesticides and antibiotics to delay resistance evolution? Previous theoretical studies have focused on qualitative resistance traits, and have mostly assumed that resistance alleles are already present in a population. But many real resistance traits are quantitative, and the evolution of resistant genotypes in the field may depend on de novo mutation and recombination. Here, I use an individual-based, forward-time, quantitative-genetic simulation model to investigate the evolution of quantitative resistance. I evaluate the performance of four application strategies for delaying resistance evolution, to wit, the (1) sequential, (2) mosaic, (3) periodic, and (4) combined strategies. I find that which strategy is best depends on initial efficacy. When at the onset, xenobiotics completely prevent reproduction in treated demes, a combined strategy is best. On the other hand, when populations are partially resistant, the combined strategy is inferior to mosaic and periodic strategies, especially when resistance alleles are antagonistically pleiotropic. Thus, the optimal application strategy for managing against the rise of quantitative resistance depends on pleiotropy and whether or not partial resistance is already present in a population. This result appears robust to variation in pest reproductive mode and migration rate, direct fitness costs for resistant phenotypes, and the extend of refugial habitats.

evolutionary biology↗

bioRxiv2022

Evolution and diversification dynamics of butterflies

Butterflies are a diverse and charismatic insect group that are thought to have diversified via coevolution with plants and in response to dispersals following key geological events. These hypotheses have been poorly tested at the macroevolutionary scale because a comprehensive phylogenetic framework and datasets on global distributions and larval hosts of butterflies are lacking. We sequenced 391 genes from nearly 2,000 butterfly species to construct a new, phylogenomic tree of butterflies representing 92% of all genera and aggregated global distribution records and larval host datasets. We found that butterflies likely originated in what is now the Americas, [~]100 Ma, shortly before the Cretaceous Thermal Maximum, then crossed Beringia and diversified in the Paleotropics. The ancestor of modern butterflies likely fed on Fabaceae, and most extant families were present before the K/Pg extinction. The majority of butterfly dispersals occurred from the tropics (especially the Neotropics) to temperate zones, largely supporting a "cradle" pattern of diversification. Surprisingly, host breadth changes and shifts to novel host plants had only modest impacts.

evolutionary biology↗

bioRxiv2021

Niche specificity, polygeny, and pleiotropy in herbivorous insects

What causes host-use specificity in herbivorous insects? Population genetic models predict specialization when habitat preference can evolve and there is antagonistic pleiotropy at a performance-affecting locus. But empirically for herbivorous insects, host-use performance is governed by many genetic loci, and antagonistic pleiotropy seems to be rare. Here, we use individual-based quantitative genetic simulation models to investigate the role of pleiotropy in the evolution of sympatric host-use specialization when performance and preference are quantitative traits. We look first at pleiotropies affecting only host-use performance. We find that when the host environment changes slowly the evolution of host-use specialization requires levels of antagonistic pleiotropy much higher than what has been observed in nature. On the other hand, with rapid environmental change or pronounced asymmetries in productivity across host species, the evolution of host-use specialization readily occurs without pleiotropy. When pleiotropies affect preference as well as performance, even with slow environmental change and host species of equal productivity, we observe fluctuations in host-use breadth, with mean specificity increasing with the pervasiveness of antagonistic pleiotropy. So, our simulations show that pleiotropy is not necessary for specialization, although it can be sufficient, provided it is extensive or multifarious.

evolutionary biology↗