Evolutionary change in metabolic rate of Daphnia pulicaria in response to the invasive predator Bythotrephes longimanus

Metabolic rate is a trait that can be hypothesized to evolve in response to a change in predation. In the current study, we address this question by utilising an invasive event by the predatory zooplankton Bythotrephes longimanus in Lake Mendota, Wisconsin, US. This invasion dramatically impacted the prey Daphnia pulicaria, causing a ~60% decline in their biomass. Using a resurrection ecology approach, we compared the metabolic rate of D. pulicaria clones originating from prior to the Bythotrephes invasion with that of clones having evolved in the presence of Bythotrephes. We observed a 7.4% reduction in metabolic rate among post-invasive clones compared to pre-invasive clones. This change is in the opposite direction to what might be expected to evolve in response to increased predation. The evolution of a lower metabolic rate may instead be due to a habitat shift in the prey species into deeper and less productive waters and associated changes in the optimal metabolic rate.

Evolutionary change in the construction of the nursery environment when parents are prevented from caring for their young directly

Parental care can be partitioned into traits that involve direct engagement with offspring and traits that are expressed as an extended phenotype and influence the developmental environment, such as constructing a nursery. Here, we use experimental evolution to test whether parents can evolve modifications in nursery construction when they are experimentally prevented from supplying care directly to offspring. We exposed replicate experimental populations of burying beetles (Nicrophorus vespilloides) to different regimes of posthatching care by allowing larvae to develop in the presence (Full Care) or absence of parents (No Care). After only 13 generations of experimental evolution, we found an adaptive evolutionary increase in the pace at which parents in the No Care populations converted a dead body into a carrion nest for larvae. Cross-fostering experiments further revealed that No Care larvae performed better on a carrion nest prepared by No Care parents than did Full Care larvae. We conclude that parents construct the nursery environment in relation to their effectiveness at supplying care directly, after offspring are born. When direct care is prevented entirely, they evolve to make compensatory adjustments to the nursery in which their young will develop. The rapid evolutionary change observed in our experiments suggests there is considerable standing genetic variation for parental care traits in natural burying beetle populations—for reasons that remain unclear.

Population genetic bottleneck has only marginal effects on fitness evolution and its repeatability in dioecious C. elegans

Evolution is a key process by which populations can adapt to novel conditions, but it is not well understood how predictable this process is. Predictability is expected to depend on the ratio of deterministic and stochastic processes that contribute to evolutionary change and this ratio is modulated by the effective population size. Smaller effective populations harbor less genetic diversity and stochastic processes are generally expected to play a larger role, leading to less repeatable evolutionary trajectories. Empirical insight into the relationship between effective population size and repeatability is limited and biased towards asexual unicellular organisms. Here, we used populations of obligately outcrossing Caenorhabditis elegans to test whether fitness increase and selection response were more heterogeneous after a moderate or strong population bottleneck compared to a scenario without bottleneck. Nematodes were exposed to a novel bacterial prey and lower temperature. Population sizes after one week of growth (as a proxy of fitness) were measured before and after 15 generations of evolution. We found that replicates across all (no/moderate/strong bottleneck) treatments evolved higher fitness and no significant difference in average or maximum fitness was found among treatments. Partitioning fitness variance among effects from selection and effects from chance showed that a strong (but not a moderate) bottleneck reduced the relative contribution of selection effects to fitness variation. However, the reduced contribution from selection did not translate to a significant reduction in the repeatability of fitness evolution. Thus, although a strong bottleneck reduced the contribution of deterministic evolutionary change, we found only marginal effects on quantitative measurements of repeatability in evolution. We conclude that the extent to which evolution is predictable may not universally depend on effective population size.

The extended Price equation: migration and sex

The Price equation provides a general partition of evolutionary change into two components. The first is usually thought to represent natural selection and the second, transmission bias. Here, we provide a new derivation of the generalised equation, which contains a largely ignored third term. Unlike the original Price equation, this extension can account for migration and mixed asexual and sexual reproduction. The derivation here expresses the generalised equation explicitly in terms of fitness, rendering this otherwise difficult third term more open to biological interpretation and use. This re-derivation also permits fundamental results, derived from the Price equation, to be more easily generalised. We take Hamilton's rule as a case study, and provide an exact, total expression that allows for population structures like haplodiploidy. Our analysis, more generally, makes clear the previously hidden assumptions in similar fundamental results, highlighting the caution that must be taken when interpreting them.

Competitive evolution of H1N1 and H3N2 influenza viruses in the United States

Seasonal influenza causes vast public health and economic impact globally. The prevention and control of the annual epidemics remain a challenge due to the antigenic evolution of the viruses. Here, we presented a novel modeling framework based on changes in amino acid sequences and relevant epidemiological data to retrospectively investigate the competitive evolution and transmission of H1N1 and H3N2 influenza viruses in the United States during October 2002 and April 2019. To do so, we estimated the time-varying disease transmission rate from the reported influenza cases and the time-varying evolutionary rate of the viruses from the changes in amino acid sequences. By incorporating these time-varying rates into the transmission models, we found that the models could accurately capture the evolutionary transmission dynamics of influenza viruses in the United States. Our modeling results also showed that models incorporating evolutionary change of the virus could provide better modeling performance suggesting the critical role of the evolutionary change of virus on the disease transmission.

Global topographic uplift has elevated speciation in mammals and birds over the last 3 million years

Topographic change shapes the evolution of biodiversity by influencing both habitat connectivity and habitat diversity as well as abiotic factors like climate. However, its role in creating global biodiversity gradients remains poorly characterized because geology, climate and evolutionary data have rarely been integrated across concordant timescales. Here we show that topographic uplift over the last 3 million years explains more spatial variation in the speciation of all mammals and birds than do the direct effects of palaeoclimate change and both present-day elevation and present-day temperature. By contrast, the effects of topographic changes are much smaller than those of present-day temperatures in eroded areas. Together, our results stress that historical geological processes rather than traditionally studied macroecological gradients may ultimately generate much of the world’s biodiversity. More broadly, as the Earth’s surface continues to rise and fall, topography will remain an important driver of evolutionary change and novelty.

Decomposing phenotypic skew and its effects on the predicted response to strong selection

The major frameworks for predicting evolutionary change assume that a phenotype's underlying genetic and environmental components are normally distributed. However, the predictions of these frameworks may no longer hold if distributions are skewed. Despite this, phenotypic skew has never been decomposed, meaning the fundamental assumptions of quantitative genetics remain untested. Here, we demonstrate that the substantial phenotypic skew in the body size of juvenile blue tits (Cyanistes caeruleus) is driven by environmental factors. Although skew had little impact on our predictions of selection response in this case, our results highlight the impact of skew on the estimation of inheritance and selection. Specifically, the non-linear parent-offspring regressions induced by skew, alongside selective disappearance, can strongly bias estimates of heritability. The ubiquity of skew and strong directional selection on juvenile body size implies that heritability is commonly overestimated, which may in part explain the discrepancy between predicted and observed trait evolution.